Abstract:
The invention disclosed relates to intrinsically bacteriostatic synthetic polymer membranes, and to process for the manufacture thereof. In one embodiment, bacteriostatic metal ions are attached to a surface of a preformed synthetic polymer membrane by static adsorption/adsorption and reduced to the metal in situ. In another embodiment, the instrinsically bacteriostatic membranes are formed by providing a casting solution of a membrane forming synthetic polymer and bacteriostatic metal ions, and casting into a bath containing a reducing agent for the metal ions to form the membrane containing the metal ions incorporated therein.

Description:
This application claims the benefit of Provisional application Ser. No. 60/131,140, filed Apr. 27, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     In potable water membrane purification systems, there are many surfaces that are normally contaminated by bacteria, causing rapid flux decline because of the bacteria themselves, or the slime they produce to attach themselves on surfaces. 
     It is well known that bacterostatic metal and metal ions can be used to address this problem. The metal and metal ions are chemically or non-chemically bonded to the membrane surface. The action of a bacteriostatic metal, which often includes toxic metals, needs to be on the active high pressure side of the membrane. It is mainly in this region that bacteria can colonize and cause pore blockage. 
     It is also known that it takes 2-30 ppb of dissolved silver to disinfect 20,000 gallons of water. However, a surface with a bacteriostatic metal e.g. silver and copper, will prevent microbial colonization. The mechanism is not known, but it is possible that even the lowest metal ion concentration (parts per billion) can be detected or “felt” by microorganisms and prevent their attachment and/or growth. It is believed by some that many forms of bacteria, fungus, and virus utilize a specific enzyme for their metabolism. Silver acts as a catalyst, effectively disabling the enzyme. It is toxic to all species tested of bacteria, protazoa, parasites, and many viruses, while copper is specific to fungi. To primitive life forms, silver is as toxic as the most powerful chemical disinfectants. However, this toxicity does not apply to higher life forms, which actually use some heavy metals in their metabolic pathways. 
     In U.S. Pat. No. 3,953,545, Stoy discloses the use of copper and silver ions as complexes with nitrile groups to be used in the formation of polymers and co-polymers. DuPont discloses in WO 94/15463 the use of barium particles successively coated with silver, copper oxide, silicon, hydrous alumina and droctyl azelate as powders for delustering fibers and providing anti-bacterial properties. A Japanese patent, JP 5,245,349, uses silver on zeolite particles that are added to a membrane formulation. There are many uses of various metals as antibacterial preparations in DuPont U.S. Pat. No. 5,180,585. Nitro, in JP 57084703 and Courtney, Gilehrist, and Park, in GB 1,521,171, disclose a silver “salt” or complex similar to U.S. Pat. No. 3,953,545. 
     Also, U.S. Pat. No. 5,102,547 discloses a synthetic polymer membrane incorporating fine particles of dispersed water-insoluble bioactive material e.g. metal and metal alloys linked to the polymer without chemical binding. Anti-bacterial activity is supposedly provided by the dissolving out of the metal. High metal concentrations of 0.05 to 15%/w, on a dry weight basis, are disclosed. It is noted that the application to water purification is not disclosed, and that in view of the disclosure of the use of several toxic metals antimony, bismuth and mercury, it is apparent that there is no contemplation of water treatment. It is also noted that the loose binding of the metals inside the porous matrix of the membrane instead of the active surface permits dissolution of the metals to the permeate without affecting the concentrate side of the membrane would result in the wastefull washing away of the metal in a water treatment system. This patent could be useful in supplying a source of metal ions to already treated water rather than preventing the fouling of treatment equipment (thus would not prevent fouling and flux decline of the membrane). The present invention, using a reductive technique, places only minute quantities (compared to the whole volume of the membrane) of porous metals such as silver copper and/or nickel at the very point of potential fouling by bacteria. It can also place metal or metal alloys, not only on the membrane surface, but on all surfaces in contact with the water that is being treated. In this way the system can be shut down having to add toxic bacteriostatic chemicals, and without the possibility of bacterial bloom. 
     To the best of the inventors&#39; knowledge, there are presently no membranes or systems on the market that are intrinsically bacteriostatic, at the active separation surface layer. 
     SUMMARY OF THE INVENTION 
     It is an object of our invention to prevent the colorization of membrane surfaces by mircoorganisms when processing water. 
     The invention relates to a method and apparatus for rendering both systems and individual membranes toxic or otherwise incompatible to pathogens but harmless to animals, including humans. The invention provides a permanent solution to the deleterious effects of bacterial colonization and sliming of membrane systems. The membranes themselves separate all bacteria, viruses and cysts from drinking water in a cost-effective manner. In case adverse conditions affect or deteriorate the bacteriostatic properties of membranes and system, a simple reapplication of the treatment will be able to restore the bacteriostatic properties. 
     Due to their bacteriorstatic or other desirable properties, silver, copper, tin, nickel and other metals and/or mixtures and alloys are incorporated into a polymer membrane. Several methods can be employed to achieve the desired metal content: (1) adding a metal salt or mixture of compatible salts to the membrane polymer casting solution before formation of the film and gelling it into a bath containing sufficient reducing agent to deposit the metals; (2) once a membrane has been cast in the normal phase-inversion method, performing a static adsorption of soluble metal salts on the polymer membrane followed by exposure to a reducing agent, (3) incorporating the reducing agent into the membrane either as an additive before casting, (4) contacting the cast membrane with reducing agent and then contacting the membrane with the desired salt or mixture of compatible salts that deposit as metals, or (5) contacting the preformed membrane and/or water purification apparatus simultaneously with the metal salts and a reducing agent therefor. 
     Methods (2), (4) and (5) are preferred, since less metal is used. In Methods (1) and (3), the metal is incorporated in the matrix of the polymer. However, it takes considerably more metal incorporated into the polymer to have the same effect at the surface, as compared to the other methods. 
     The invention includes the choice of materials that are used and in the method of application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a graph, showing the effect of various reducing agents on membranes containing silver salts; 
     FIG. 2 is a graph illustrating the effect of the adsorption of various concentrations of copper metal into the membrane; 
     FIG. 3 is a graph illustrating the effect of absorption of silver metal on the membrane; 
     FIG. 4 is a graph illustrating the effect of the addition of metal alloys to the membrane, and reduced in situ by the single step method; 
     FIG. 5 is a graph illustrating the effect of the sequential addition of metals, by the multi-step method; and 
     FIG. 6 is a graph illustrating the effect of the addition of the reducing agent before the metal alloys. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     To achieve desired properties, metal or metal alloys are either incorporated into the membrane at the time of casting, as in the case of ultrafiltration and microfiltration membranes, and further enhanced by post treatment, or in the case of pre-formed membranes such as thin film composite reverse osmosis membranes or other preformed commercial membranes and systems, where the incorporation may not be possible or practical, the alloys are deposited and bound to all surfaces including the components of the module, pumps and plumbing. The procedures and methodology used for developing and evaluating the products in the inventions are described/summarized below: 
     Different Methods of Reducing Metals and Alloys in the Matrix of the Membrane 
     The inventors have identified a variety of suitable reducing agents for incorporating the metal into the membranes. For example: A membrane composed of 20% polyphenylsulfone, 20% polyvinylpyrrolidinone and 2% silver nitrate in 1-methyl-2-pyrrolidinone is cast onto polyester backing and gelled into 1% hydroquinone mixed with 1% formaldehyde. This membrane gives a flux rate of 446 Liters/square meters/hour (LMH) with a polyethylene glycol (PEG) separation of 78% at 35,000 Daltons (35K). The same polymer membrane gelled into 1% formaldehye gives a flux rate of 346 LMH and a PEG 35K separation of 75%. 
     The inventors have performed experiments with other reducing agents including sodium azide, potassium chloride, sodium iodide, sucrose, potassium sodium tartrate and mixtures and various concentrations of these (0.5 to 5% w/w). Although lower concentrations were effective, a standard value of 1% of reducing agent was used for most tests. Additionally, work with commercial plating solutions with a lower concentration was completed. Detailed examples of the method of reducing silver and/or copper and nickel into the matrix of the membrane by addition into the polymer solution are described. 
     Different Metals Fixated onto the Surface of the Membrane 
     Various concentrations of metals have been tested in the concentrations of 0.25 to 15% (w/w). For example: A membrane composed of 20% polyphenylsulfone and 20% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone is cast onto polyester backing is gelled into water and a static adsorption is performed followed by a reduction. A static adsorption in 13% silver nitrate followed by 1% hydroquinonone produces a membrane that has a flux rate of 110 LMH and 87% separation of PEG 6K. A similar membrane after static adsorption in 6% silver nitrate followed by 1% hydroquinonone generates a membrane with a flux rate of 148 LMH and 93% separation of PEG 6K. Both of these membranes were negative for  E. coli  growth. 
     Work was completed on setting the limits of metal and reducer concentrations. Although lower concentrations were effective, a standard value of 6% metal salt and 1% reducing agent was used for most tests. 
     Tests were performed on various commercial and NRC-fabricated membranes of different materials and porosities. The change in pure water permeability rate after the treatment ranged from 0.422 for the polyvinylidene fluoride membrane, and 1.336 for the polyvinyl alcohol membrane. All membranes were viable after treatment. Tests performed with polyethersulfone-polyetherethersulfone co-polymer and polyphenylsulfone indicated that both polymers are suitable for silver treatment and therefore both were used for the majority of testing. According to visual methods, most of the other polymers tested had a metallic surface after static adsorption with 6% silver nitrate. These included both commercial and NRC membranes on a variety of backing materials. 
     Tests indicate certain conditions give better coating such as a very clean system (after a degreasing or caustic wash and pure water rinse) and higher temperature. Also, the system and membrane may be treated separately to obtain the best membrane porosity versus the requirements of the system coating. Components of the spiral wound module may be treated separately before winding (i.e. vexar and permeate carrier) to ensure an even coating. A membrane composed of 25% polyethersulfone-polyetherethersulfone co-polymer and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone is cast onto polyester backing and gelled into water and spiral wound into a module. The membrane was treated with 3% silver nitrate, drained and 1% hydroquinone was added. After treatment the module was dismantled and examined for coverage. Bacteria testing was negative for  E. coli.    
     Different Alloys Fixated onto the Surface of the Membranes 
     The inventors have analyzed both a single reduction step and a multi-reduction step. In the first, the metals are introduced to the membrane and then the membrane is reduced in a second step. In a multi-reduction step, each metal salt is added separately and reduced before the next metal salt is introduced. 
     A membrane composed of 25% polyethersulfone-polyetherethersulfone co-polymer and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone is cast onto polyester backing, gelled into water and a single step static adsorption/reduction performed. Membranes treated in a 6% total 1:1:1 ratio of silver nitrate:cupric nitrate:tin sulfate, a 6% total 1:1:1 ratio of silver nitrate:nickelous nitrate:tin sulfate, and a 3% total 1:1:1 ratio of silver nickelous:nickel nitrate:cupric sulfate all tested negative for  E. coli  presence. 
     A membrane composed of 25% polyethersulfone-polyetherethersulfone co-polymer and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone is cast onto polyester backing is gelled into water and the multi-step method of reduction is used. A static adsorption in 6% silver nitrate and then reduction in 1% hydroquinonone followed by a static adsorption in 6% cupric nitrate and reduction in 1% hydroquinone is performed. This produces a membrane with a flux rate of 121 LMH and 96% separation of PEG 6K. The untreated membrane gives a flux rate of 167 LMH and 95% separation of PEG 6K giving a change in pure water permeability of 0.725. 
     The effects of relative ratios of incorporated metals in the range of 1 to 10% were evaluated. Although lower concentrations are effective, a standard value of 6% was chosen for the small scale. 
     Preferred Methods of Reducing Metals and Alloys in the Matrix of the Membrane 
     In this methods, the reducing agent is first introduced into the membrane, by incorporation as an additive before casting, as in the case of the use of hydroquinone, or by soaking of the formed or commercial membrane in a reducing agent solution chosen from hydroquinone, hydrazine, an aldehyde, sucrose, reducing salts as in a previous example. The reducing agent laden membrane is then sprayed, wiped or otherwise contacted with a metal salt or mixture of desired salts, to reduce them on the surface and in the porous matrix of any separation membrane. For example an 18% polyethersulfone-polyetherthersulfone co-polymer and 18% polyvinypyrrolidinone with 5% hydroquinone in 1-methyl-2-pyrrolidinone is cast onto polyolefin backing and gelled into 0.5% hydroquinone. A 6% silver nitrate solution is sponged on the surface of the membrane. The final membrane gives a pure water permeability of 659 LMH and 72% separation with PEG 35,000. An unmodified membrane gives a pure water flux rate of 512 LMH and 60% separation with PEG 35,000. 
     In all tests, at least three membranes of each type of treatment were tested for pure water permeability (PWP) and the molecular weight cut off determined by sieving methods with 200 ppm polyethylene glycols (PEG) and polyethylene oxide (PEO). Flux rates and separation data are determined at 345 kPa and 3.1 L/m, unless otherwise indicated. Percentage separations were determined by total carbon using a Shimadzu Total Organic Carbon Analyzer. In all examples given, the percentage of solutions used is based on weight/weight calculations. 
     The bacteria analysis was performed by Accu Test Laboratories Inc. in Nepean using standard  E. coli  determination and counting methods. 
     Metals in the Matrix of the Membrane 
     A 20% polyphenylsulfone (PPS), 20% polyvinylpyrrolidinone (PVP), and 2% silver nitrate in 1-methyl-2-pyrrolidinone solution is cast onto polyester backing and gelled into: 
     1% and 2% formaldehyde 
     1% sodium azide 
     0.5% and 1% hydroquinone 
     1% sodium chloride exposed to light and then into 1% sodium hypophosphite hydrate and then into 0.5% hydroquinone 
     1% sodium iodide and then 1% hydroquinone 
     1% hydrochloric acid and then 1% hydroquinone 
     1% silver nitrate and then 1% hydroquinone 
     1% hydroquinone mixed with 1% formaldehyde 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Observations of Membranes with Silver Nitrate Gelled in Reducing Agents 
               
             
          
           
               
                 Gellation 
                 Membranes 
               
               
                   
               
               
                 1% sodium chloride left in the light and 
                 The membrane was a pinkish 
               
               
                 then into 1% sodium hypophosphite 
                 beige colour. 
               
               
                 hydrate and then to 0.5% 
               
               
                 hydroquinone 
               
               
                 formaldehyde 
                 The membrane was dark brown 
               
               
                   
                 with lighter streaks. 
               
               
                 Sodium azide 
                 The membrane was dark brown 
               
               
                   
                 with lighter streaks. 
               
               
                 hydroquinone 
                 The membrane was dark upon 
               
               
                   
                 initial gellation and then turned 
               
               
                   
                 an orangey-brown. A lighter 
               
               
                   
                 surface could be wiped off. 
               
               
                 Sodium iodide then hydroquinone 
                 The membrane was a pinkish 
               
               
                   
                 beige colour. 
               
               
                 hydroquinone mixed with formaldehyde 
                 The membrane was light beige 
               
               
                   
                 with a darker surface that could 
               
               
                   
                 be wiped off. 
               
               
                 hydrochloric acid then hydroquinone 
                 The membrane was orange and 
               
               
                   
                 then turned a marbley 
               
               
                   
                 brown/beige. 
               
               
                 Silver nitrate then hydroquinone 
                 The membrane immediately 
               
               
                   
                 turned black and then slowly 
               
               
                   
                 lightened. 
               
               
                 Distilled water then hydroquinone 
                 Nothing on surface of 
               
               
                   
                 membrane. 
               
               
                 hydroquinone mixed with formaldehyde 
                 Membrane was grey in colour. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Flux and Separation Data of Membranes containing Silver Nitrate Gelled 
               
               
                 in Reducing Agents 
               
             
          
           
               
                 20% PPS - 20% PVP 2% AgNO3 
                 PWP 
                 200 ppm PEG 35K 
               
             
          
           
               
                 Reduced into: 
                 (LMH) 
                 (LMH) 
                 % sep 
               
               
                   
               
               
                 1% formaldehyde 
                 346 
                 247 
                 75% 
               
               
                 1% sodium azide 
                 554 
                 368 
                 42% 
               
               
                 1% hydroquinone 
                 665 
                 358 
                 44% 
               
               
                 2% formaldehyde 
                 516 
                 315 
                 45% 
               
               
                 1% sodium chloride exposed to light then 
                 365 
                 229 
                 72% 
               
               
                 into 1% sodium hypophosphite hydrate 
               
               
                 and then 0.5% hydroquinone 
               
               
                 1% sodium iodide then 1% hydroquinone 
                 539 
                 289 
                 55% 
               
               
                 1% hydrochloric acid then 1% 
                 470 
                 270 
                 67% 
               
               
                 hydroquinone 
               
               
                 1% silver nitrate then 1% hydroquinone 
                 514 
                 271 
                 62% 
               
               
                 1% hydroquinone mixed with 1% 
                 446 
                 259 
                 78% 
               
               
                 formaldehyde 
               
               
                 Standard 
                 292 
                 205 
                 99% 
               
               
                   
               
             
          
         
       
     
     A 20% polyphenylsulfone and 2% silver nitrate in 1-methyl-2-pyrrolidinone solution is cast onto polyester backing and gelled into 1% hydroquinone mixed with 1% formaldehyde. This was to determine the effects of polyvinylpyrrolidone (PVP) additive on metal deposition. The membrane with PVP gave a pure water flux rate of 446 LMH and flux rate with PEG 35K of 259 LMH (78% separation). The membrane with no PVP additive gave a pure water flux rate of 436 LMH and flux rate with PEG 35K of 307 LMH (70% separation). 
     FIG. 1 shows that the addition of metal salts to the polymer solution does change the original porosity of the membrane, but also that a feasible membrane is produced. To obtain a membrane with smaller pore sixes, an original membrane polymer solution producing smaller pores would be used for the addition of the metal salts. 
     A 18% polyethersulfone-polyetherethersulfone co-polymer (PES-PEES), 18% polyvinylpyrrolidinone (PVP), and 5% cupric choride in 1-methyl-2-pyrrolidinone solution is cast onto polyester backing and gelled into: 
     1. 0.5% formaldehyde 
     2. 0.5% formaldehyde then 6% silver nitrate 
     3. 0.5% hydroquinone 
     4. 0.5% hydroquinone then 6% silver nitrate 
     5. 0.5% silver nitrate 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes containing Cupric Chloride in 
               
               
                 Reducing Agents 
               
             
          
           
               
                 18% PES-PEES - 18% 
                   
                   
                   
               
               
                 PVP - 5% CuCl 2   
                 PWP 
                 200 ppm PEG 6K 
                 200 ppm PEG 35K 
               
             
          
           
               
                 Reduced into: 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 % sep 
               
               
                   
               
               
                 0.5% formaldehyde 
                 751 
                 666 
                  7% 
                 369 
                 44% 
               
               
                 0.5% formaldehyde 
                 582 
                 525 
                 22% 
                 355 
                 76% 
               
               
                 then 6% silver nitrate 
               
               
                 0.5% hydroquinone 
                 210 
                 208 
                 73% 
                 185 
                 97% 
               
               
                 0.5% hydroquinone 
                 255 
                 251 
                 70% 
                 214 
                 99% 
               
               
                 then 6% silver nitrate 
               
               
                 0.5% silver nitrate 
                 499 
                 470 
                 26% 
                 311 
                 68% 
               
               
                 Standard 
                 512 
                 378 
                 48% 
                 345 
                 60% 
               
               
                   
               
             
          
         
       
     
     The membrane gelled in formaldehyde produced a white membrane. The membrane gelled in hydroquinone had a pink/beige coloured membrane. When these membranes were put into silver nitrate, the membranes became a dark brown colour indicating the presence of silver. The membrane gelled in silver nitrate produced a brown coloured membrane, there were silver/grey particles in the solution indicating self reduction. 
     A 18% polyethersulfone-polyetherethersulfone co-polymer (PES-PEES), 18% polyvinylpyrrolidinone (PVP), and 5% nickelous nitrate in 1-methyl-2-pyrrolidinone solution is cast onto polyester backing and gelled into: 
     1. 0.5% hydroquinone 
     2. 0.5% hydroquinone then 6% silver nitrate 
     3. 0.5% hydroquinone then 6% cupric nitrate 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes containing Nickelous Nitrate 
               
               
                 Gelled in Reducing Agents 
               
             
          
           
               
                 18% PES-PEES - 18% 
                   
                   
                   
               
               
                 PVP - 5% NiNO 3   
                 PWP 
                 200 ppm PEG 6K 
                 200 ppm PEG 35K 
               
             
          
           
               
                 Reduced into: 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 % sep 
               
               
                   
               
               
                 0.5% hydroquinone 
                 603 
                 564 
                 21% 
                 358 
                 78% 
               
               
                 Standard 
                 512 
                 378 
                 48% 
                 345 
                 60% 
               
               
                   
               
             
          
         
       
     
     The nickel membrane was originally white. When it was put into a cupric nitrate solution, the membrane colour changed to a slightly beige/pink colour. Then the membrane was put into a 6% silver nitrate solution and the membrane immediately became dark brown. This indicated the original presence of nickel on the surface and pores of the membrane. 
     A 20% polyphenylsulfone, 20% polyvinylpyrrolidinone, and 2% silver nitrate in 1-methyl-2-pyrrolidinone solution is cast onto polyolefin backing and gelled into a bath of 156.6 g/L commercial developer solution (hydroquinone, p-methylaminophenol sulfate, sodium carbonate). This membrane gave pure water flux rates of 529 LMH and flux rates of 676 LMH (11% separation) with PEG 6K and 426 LMH (38% separation) with PEG 35K. This membrane has changed from a standard membrane which gives a pure after flux rate of 339 LMH and flux rate of 310 LMH (54% separation) with PEG 6K. 
     Metals Reduced on the Membrane with Static Adsorption 
     Method 1—Static Adsorption with One Metal Reduced with Hydroquinone 
     A membrane comprised of 25% polyphenylsulfone (PPS) and 21% polyvinylpyrrolidinone (PVP) in 1-methyl-2-pyrrolidinone solution cast onto polyester backing and gelled into reverse osmosis water is contacted with solutions of the following before reducing in 1% hydroquinone: 
     1%, 6%, 13% cupric sulfate 
     1%, 6%, 13% nickelous nitrate 
     6% nickel sulfate 1%, 6%, 13% silver nitrate 
     6% silver sulfate 
     1%, 6%, 13% tin sulfate 
     1%, 6%, 13% zinc nitrate 
     6% zinc sulfate 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Flux and Separation Data of Membranes with Adsorbed Metals 
               
             
          
           
               
                 25% PPS - 21% PVP 
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                 all membranes reduced into 1% 
                   
                 200 ppm 
                   
                 200 ppm 
                   
               
               
                 hydroquinone 
                 PWP 
                 PEG 6K 
                 PWP 
                 PEG 6K 
                 change in 
               
             
          
           
               
                 Adsorption of: 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 PWP 
               
               
                   
               
               
                 1% cupric sulfate 
                  67 
                 36 
                 87% 
                  70 
                  72 
                 88% 
                 1.043 
               
               
                 6% cupric sulfate 
                 101 
                 77 
                 89% 
                 111 
                 109 
                 90% 
                 1.099 
               
               
                 13% cupric sulfate 
                 120 
                   
                   
                 105 
                 109 
                 89% 
                 0.872 
               
               
                 1% nickelous nitrate 
                  90 
                 63 
                 86% 
                  82 
                  95 
                 90% 
                 0.912 
               
               
                 6% nickelous nitrate 
                  94 
                 64 
                 74% 
                 162 
                 154 
                 83% 
                 1.723 
               
               
                 13% nickelous nitrate 
                  77 
                 52 
                 85% 
                  70 
                  80 
                 87% 
                 0.905 
               
               
                 6% nickel sulfate 
                   
                   
                   
                 199 
                 189 
                 88% 
               
               
                 1% silver nitrate 
                   
                   
                   
                 117 
                 102 
                 93% 
               
               
                 3% silver nitrate 
                 147 
                 228  
                 78% 
                 112 
                 139 
                 94% 
                 0.762 
               
               
                 6% silver nitrate 
                 206 
                 219  
                 89% 
                 148 
                 163 
                 93% 
                 0.718 
               
               
                 13% silver nitrate 
                   
                   
                   
                 110 
                 107 
                 87% 
               
               
                 6% silver sulfate 
                   
                   
                   
                 190 
                 171 
                 90% 
               
               
                 1% tin sulfate 
                 128 
                 77 
                 89% 
                  94 
                  97 
                 95% 
                 0.735 
               
               
                 6% tin sulfate 
                 109 
                 83 
                 80% 
                 133 
                 121 
                 78% 
                 1.220 
               
               
                 13% tin sulfate 
                 112 
                   
                   
                  82 
                  86 
                 95% 
                 0.736 
               
               
                 1% zinc nitrate 
                  98 
                 96 
                 87% 
                  91 
                 103 
                 90% 
                 0.927 
               
               
                 6% zinc nitrate 
                  87 
                 63 
                 89% 
                 154 
                 152 
                 90% 
                 1.770 
               
               
                 13% zinc nitrate 
                  46 
                 37 
                 82% 
                  48 
                  54 
                 91% 
                 1.039 
               
               
                 6% zinc sulfate 
                   
                   
                   
                 215 
                 196 
                 93% 
               
               
                 Standard (no metal salt additive, 
                 202 
                 219 
                 64% 
                 181 
                 185 
                 91% 
                 0.896 
               
               
                 no treatment) 
               
               
                   
               
             
          
         
       
     
     FIG. 2 shows that the adsorption of metals on the surface of the membrane does not drastically change the porosity of the membranes. Similar curves were obtained for the other metals. 
     Membranes were black after silver reduction. A whitish film could be wiped off but darker colour remained. The silver treated membranes were sent for bacteria testing and the control was positive for  E. coli  growth but all others were negative. There was a slight change in the cupric sulfate treated membranes, and the membrane became darker a few days later. All the others showed no initial change. One percent sodium hypophosphite was added to tin sulfate, zinc sulfate, nickel sulfate, zinc nitrate and nickelous nitrate. Still no change but a few days later there was more colour on the nickel membranes and a white precipitate in the tin sulfate solution. 
     Higher percentages of metal gave darker surface coatings. Higher amounts of hydroquinone accelerated the reaction. The tests were performed with 1% hydroquinone as a standard. 
     Other polymers were examined for silver adsorption with 6% silver nitrate then reduced into 1% hydroquinone. Polymers tried were polyethersulfone-polyetherethersulfone co-polymer, polyphenylsulfone, polyacrylonitrile, polyvinylidenefluoride, polyether-imide, cellulose acetate, polyamide-imide, acrylic, polysulfone, modified polysulfone, regenerated cellulose, thin-film composite, cellulose triacetate, and polyamide. A range of molecular weight cut offs were treated with 6% silver nitrate and then 1% hydroquinone. All membranes showed colour change which remained after testing. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Pore Size Ranges for Three Polymers Treated 
               
               
                 with Silver Nitrate 
               
             
          
           
               
                   
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                   
                   
                 200 ppm PEG 
                   
                 200 ppm PEG 
                   
               
               
                 6% silver nitrate then 1% 
                 PWP 
                 6K 
                 PWP 
                 6K 
                 change in 
               
             
          
           
               
                 hydroquinone 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 PWP 
               
               
                   
               
               
                 polysulfone 1,000 
                  4 
                  5 
                 94% 
                  8 
                  7 
                 93% 
                   
               
               
                 polysulfone 5,000 
                  49 
                  52 
                 56% 
                  64 
                  60 
                 64% 
                 1.309 
               
               
                 polysulfone 10,000 
                 856 
                 845 
                  8% 
                 867 
                 915 
                  5% 
                 1.013 
               
               
                 polysulfone 50,000 
                 1372  
                 1298  
                  9% 
                 1400  
                 1410  
                 13% 
                 1.021 
               
               
                 polysulfone 100,000 
                 1883  
                 1952  
                  6% 
                 2029  
                 1996  
                  7% 
                 1.077 
               
               
                 regenerated cellulose 2,000 
                 402 
                 441 
                  9% 
                 438 
                 574 
                  9% 
                 1.089 
               
               
                 regenerated cellulose 5,000 
                  72 
                  70 
                 95% 
                  74 
                  76 
                 92% 
                 1.022 
               
               
                 regenerated cellulose 10,000 
                  99 
                 104 
                 99% 
                 110 
                 102 
                 100%  
                 1.104 
               
               
                 cellulose acetate 2,000 
                  52 
                  54 
                 54% 
                  24 
                  29 
                 92% 
                 0.466 
               
               
                 cellulose acetate 20,000 
                 153 
                 106 
                 28% 
                  84 
                 140 
                 27% 
                 0.548 
               
               
                 cellulose acetate 50,000 
                 1666  
                   
                   
                 1503  
                 1631  
                  0% 
                 0.902 
               
               
                   
               
             
          
         
       
     
     Two spiral wound modules (4″×20″) made with membrane of 25% polyethersulfone-polyetherethersulfone co-polymer and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone cast onto polyester backing gelled into reverse osmosis water were treated with 3% silver nitrate. To one spiral 1% hydroquinone was added directly. The other spiral was drained and then 1% hydroquinone was added. After testing, the spirals were dismantled to determine adsorption patterns. Most areas of the membrane were coated except for the areas directly underneath, in contact with and shielded by the spacer material. The spiral that was drained prior to reducing did not have reduced particulate matter in solution and caught in areas of the spiral as the spiral that hydroquinone was added directly to the silver nitrate solution. A piece of this membrane was tested for bacteria analysis and came back negative for  E. coli  growth. The flux rate through the membrane was 107 LMH at 345 kPa and 58 Liters/minute flow. The percentage separation of PEG 6K was 91% and PEG 35K was 99%. After initial cleaning with normal amounts of pure water flushed through the permeate lines, the permeate was negligible in desolved silver content. 
     Method 2—Static Adsorption with One Metal Reduced with Other Agents 
     A 25% polyphenylsulfone and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone solution cast onto polyester backing and gelled into reverse osmosis water was treated with solutions of 1% silver nitrate and 1.5% potassium sodium tartrate. This was acidified to pH 3.5 with hydrochloric acid. Once the membranes were added, ammonium hydroxide was added until the silver was reduced. All membranes were orange/brown after the dip. Whitish silver film could be wiped off with some difficulty but darker colour remained. After testing, the colour remained on the surface of the membranes. These membranes gave flux rates of 147 LMH of pure water and 144 LMH with 200 ppm PEG 6K (85% separation) before the treatment and gave flux rates of 131 LMH of pure water and 139 LMH with 200 ppm PEG 6K (84% separation) after the treatment. This demonstrates minimal changes in performance. 
     A 25% polyphenylsulfone (PPS) and 21% polyvinylpyrrolidinone (PVP) in 1-methyl-2-pyrrolidinone solution cast onto polyester backing and gelled into reverse osmosis water. These membranes were subjected to the following process: To 38 mL of a 7% silver nitrate solution, ammonium hydroxide was added drop by drop until the dark brown precipitate dissolved. 13 mL of 14% potassium hydroxide was added and ammonium hydroxide added drop by drop until the solution became clear. 15 mL of a solution of 6.5% dextrose in 17.5% of ethyl alcohol in distilled water was added. The solution was mixed for 1 minute and the membranes added. One series was completed at the previous concentrations, and the second was completed at 50% dilution of the amount of silver. Membranes were left in for 10, 15, 20, and 30 seconds, 5, 10 and 15 minutes. One membrane was contacted with the solutions with no ammonium hydroxide addition. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes with Adsorbed Silver Nitrate 
               
               
                 Reduced with Dextrose 
               
             
          
           
               
                   
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                 25% PPS - 21% PVP 
                   
                 200 ppm 
                   
                 200 ppm 
                   
               
               
                 Reduced into 6.5% dextrose 
                 PWP 
                 PEG 6K 
                 PWP 
                 PEG 6K 
                 change 
               
             
          
           
               
                 Adsorption of: 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 in PWP 
               
               
                   
               
               
                 3.5% silver nitrate with 14% 
                 138 
                 134 
                 87% 
                 113 
                 107 
                 89% 
                 0.774 
               
               
                 potassium hydroxide and 
               
               
                 ammonium hydroxide 
               
               
                 7% silver nitrate with 14% 
                 141 
                 135 
                 84% 
                  62 
                  69 
                 93% 
                 0.491 
               
               
                 potassium hydroxide and 
               
               
                 ammonium hydroxide 
               
               
                 7% silver nitrate with 14% 
                 163 
                 156 
                 85% 
                 154 
                 144 
                 90% 
                 0.886 
               
               
                 potassium hydroxide 
               
               
                 Standard (no treatment) 
                 148 
                 143 
                 86% 
                 142 
                 140 
                 91% 
                 0.948 
               
               
                   
               
             
          
         
       
     
     All membranes were orange/brown after the dip. A whitish silver film could be wiped off but the darker colour remained. After testing, the colour remained on the surface of most of the membranes. 
     FIG. 3 shows the similarities in porosity of the membranes before and after treatment with the silver nitrate. This indicates that although silver has been deposited in the active surface area, the membrane retained its separation ability. 
     Various commercial and NRC membranes were subjected to the following process: To 38 mL of a 7% silver nitrate solution, ammonium hydroxide was added drop by drop until the dark brown precipitate dissolved. 13 mL of 14% potassium hydroxide was added and ammonium hydroxide added drop by drop until the solution became clear. 15 mL of a solution of 6.5% dextrose in 17.5% ethyl alcohol in distilled water was added. The solution was mixed for 1 minute and the membranes added and allowed to absorb for 5 minutes. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Various Membrane Polymer Types with 
               
               
                 Adsorbed Silver Nitrate 
               
             
          
           
               
                 3.5% silver nitrate with 
                   
                   
                   
               
               
                 14% potassium hydroxide 
                 Before Treatment 
                 After Treatment 
               
             
          
           
               
                 and ammonium 
                   
                 200 ppm PEG 
                   
                 200 ppm PEG 
                   
               
               
                 hydroxide reduced in 
                 PWP 
                 6K 
                 PWP 
                 6K 
                 % change of 
               
             
          
           
               
                 6.5% dextrose 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 PWP 
               
               
                   
               
               
                 modified polysulfone 
                  55 
                  52 
                 89% 
                 54 
                 50 
                 81% 
                 0.969 
               
               
                 polyacrylonitrile 
                 113 
                 126 
                 10% 
                 98 
                 100  
                 34% 
                 0.862 
               
               
                 polyamide-imide 
                 349 
                 365 
                 31% 
                 409  
                 455  
                  0% 
                 1.174 
               
               
                 polyetherethersulfone 
                 853 
                 891 
                  6% 
                 860  
                 887  
                  2% 
                 1.009 
               
               
                 polyether-imide 
                  32 
                  54 
                 93% 
                 42 
                 40 
                 95% 
                 1.327 
               
               
                 polyethersulfone 
                 179 
                 167 
                 94% 
                 44 
                 39 
                 51% 
                 0.248 
               
               
                 polyphenylsulfone 
                  91 
                  45 
                 82% 
                 99 
                 98 
                 82% 
                 1.089 
               
               
                 polysulfone 
                  23 
                  24 
                 92% 
                 27 
                 27 
                 94% 
                 1.171 
               
               
                 polyvinyl alcohol 
                  43 
                  39 
                  8% 
                 58 
                 54 
                 15% 
                 1.336 
               
               
                 polyvinylidene fluoride 
                  85 
                  85 
                 19% 
                 36 
                 37 
                 57% 
                 0.422 
               
               
                 thin film composite 
                 438 
                 463 
                 34% 
                 402  
                 392  
                 60% 
                 0.917 
               
               
                   
               
             
          
         
       
     
     All membranes were orange/brown after the dip. The polyethersulfone, polyvinylidene fluoride and thin film composite membranes had a shiny surface. After testing, the colour remained on the surface of all of the membranes. 
     A 25% polyphenylsulfone and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone solution is cast polyester backing and gelled into reverse osmosis water. These membranes were subjected to a process using a 2.5% silver nitrate solution treated with ammonium hydroxide, then a 4.5% potassium hydroxide solution was added and both were treated with ammonium hydroxide. This was reduced with a 8% sugar in 1% alcohol with 0.5% nitric acid solution. Membranes were left in the solution for 5 minutes. All membranes were orange/brown after the dip. A whitish film could be wiped off but the darker colour remained. After testing, the colour remained on the surface of most of the membranes. These membranes gave flux rates of 135 LMH of pure water and 131 LMH with 200 ppm PEG 6K (87% separation) before the treatment and gave flux rates of 110 LMH of pure water and 105 LMH with 200 ppm PEG 6K (92% separation) after the treatment. This again demonstrates minimal performance changes. 
     Another process is performed using a heated 6% hydrazine sulfate to which a saturated cupric hydroxide is added and ammonium hydroxide. The membranes were subjected to this solution. A solution of 1% potassium hydroxide is heated and added to the first solution containing the membranes. These membranes gave flux rates of 120 LMH of pure water and 116 LMH with 200 ppm PEG 6K (82% separation) before the treatment and gave flux rates of 124 LMH of pure water and 111 LMH with 200 ppm PEG 6K (90% separation) after the treatment. This shows minimal membrane porosity changes. 
     Alloys Reduced on the Membrane with Static Adsorption 
     Method 1—Alloys Reduced in the Single Step Method with Hydroquinone 
     A 25% polyethersulfone-polyetherethersulfone co-polymer and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone on polyester backing membranes cast into reverse osmosis water and subjected to the following solutions before reduction with 1% hydroquinone. 
     
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 1. 
                 6% total 
                 1:1:1 
                 silver nitrate:cupric nitrate:tin sulfate 
               
               
                 2. 
                 6% total 
                 1:1:1 
                 silver nitrate:nickelous nitrate:tin sulfate 
               
               
                 3. 
                 6% total 
                 1:1:1 
                 silver nitrate:nickelous nitrate:cupric nitrate 
               
               
                 4. 
                 6% total 
                 1:1:1 
                 cupric nitrate:nickelous nitrate:tin sulfate 
               
               
                 5. 
                 3% total 
                 1:1:1 
                 silver nitrate:cupric sulfate:tin sulfate 
               
               
                 6. 
                 3% total 
                 1:1:1 
                 silver nitrate:nickelous nitrate:tin sulfate 
               
               
                 7. 
                 3% total 
                 1:1:1 
                 silver nitrate:nickelous nitrate:cupric sulfate 
               
               
                 8. 
                 3% total 
                 1:2 
                 silver nitrate:nickelous nitrate 
               
               
                 9. 
                 3% total 
                 1:2 
                 silver nitrate:cupric sulfate 
               
               
                 10. 
                 3% total 
                 1:2 
                 silver nitrate:tin sulfate 
               
               
                 11. 
                 1% total 
                 1:1:1 
                 silver nitrate:nickelous nitrate:tin sulfate 
               
               
                   
               
             
          
         
       
     
     The membranes contacted with silver nitrate cupric nitrate:tin sulfate and silver nitrate:nickelous nitrate:tin 
     sulfate were very dark. There was a coppery colour on the surface. The membranes treated with cupric nitrate:nickelous nitrate:tin sulfate solution showed only slight changes in surface colour. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes with Alloys Reduced by the 
               
               
                 Single Step Method 
               
             
          
           
               
                 25% PES-PEES 21% 
                   
                   
                   
               
               
                 PVP 
                   
                   
                 200 ppm PEG 
               
               
                 Gelled 
                 PWP 
                 200 ppm PEG 6K 
                 35K 
               
             
          
           
               
                 into 1% hydroquinone 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 % sep 
               
               
                   
               
               
                 1% total 1:1:1 silver 
                 226 
                 232 
                 65% 
                 243 
                 100% 
               
               
                 nitrate:nickelous nitrate: 
               
               
                 tin sulfate 
               
               
                 3% total 1:2 silver 
                 217 
                 221 
                 79% 
                 226 
                 100% 
               
               
                 nitrate:nickelous nitrate 
               
               
                 3% total 1:2 silver 
                 208 
                 207 
                 72% 
                 219 
                 100% 
               
               
                 nitrate:cupric sulfate 
               
               
                 3% total 1:1:1 silver 
                 225 
                 227 
                 70% 
                 231 
                 100% 
               
               
                 nitrate:nickelous nitrate: 
               
               
                 tin sulfate 
               
               
                 6% total 1:1:1 cupric 
                 156 
                 149 
                 84% 
                 156 
                 100% 
               
               
                 nitrate:nickelous nitrate: 
               
               
                 tin sulfate 
               
               
                 6% total 1:1:1 silver 
                 118 
                 105 
                 92% 
               
               
                 nitrate:nickelous nitrate: 
               
               
                 cupric nitrate 
               
               
                   
               
             
          
         
       
     
     The 6% total 1:1:1 silver nitrate:cupric sulfate:tin sulfate membrane, the 6% total 1:1:1 silver nitrate:nickelous nitrate:tin sulfate membrane, and the 3% total 1:1:1 silver nitrate:nickelous nitrate:cupric sulfate were negative for  E. coli  testing. 
     FIG. 4 shows the effect of the alloys in and on the active surface layer of the treated membranes. It is shown that the treated membranes gave PEG separation performance very similar to the original, untreated membranes. This indicates that although the metals are being deposited, as determined by the colour changes and negative  E. coli  testing, the membranes have retained their original porosity and minimal pore blockage has occurred. 
     The following were contacted in the listed sequence by draining the original solution, and added the next metal salt solution. Once completed, the membranes were reduced with 1% hydroquinone: 
     1. 6% nickelous nitrate then 6% cupric nitrate 
     2. 6% nickelous nitrate then 6% silver nitrate 
     3. 6% cupric nitrate then 6% silver nitrate 
     4. 6% cupric nitrate then 6% nickelous nitrate 
     5. 6% nickelous nitrate then 6% cupric nitrate then 6% silver nitrate 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes with Alloys Reduced in the 
               
               
                 Single Step Method 
               
             
          
           
               
                 25% PES-PEES - 21% 
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                 PVP 
                   
                 200 ppm PEG 
                   
                 200 ppm PEG 
                   
               
               
                 Reduced into 1% 
                 PWP 
                 6K 
                 PWP 
                 6K 
                 change in 
               
             
          
           
               
                 hydroquinone: 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 PWP 
               
               
                   
               
               
                 6% nickelous nitrate 
                 165 
                 148 
                 89% 
                 129 
                 111 
                 88% 
                 0.778 
               
               
                 then 6% cupric nitrate 
               
               
                 6% nickelous nitrate 
                 175 
                 165 
                 91% 
                 131 
                 118 
                 85% 
                 0.749 
               
               
                 then 6% silver nitrate 
               
               
                 6% cupric nitrate then 
                 180 
                 165 
                 92% 
                 133 
                 122 
                 91% 
                 0.738 
               
               
                 6% silver nitrate 
               
               
                 6% cupric nitrate then 
                 189 
                 172 
                 85% 
                 138 
                 124 
                 90% 
                 0.730 
               
               
                 6% nickelous nitrate 
               
               
                 6% nickelous nitrate 
                 190 
                 136 
                 85% 
                 139 
                 125 
                 85% 
                 0.732 
               
               
                 then 6% cupric nitrate 
               
               
                 then 6% silver nitrate 
               
               
                   
               
             
          
         
       
     
     All the membranes were dark in colour except for the nickelous nitrate with cupric nitrate which only had a slight grey colour change. The membranes containing the three metal salts together resulted in a shiny metallic surface. 
     Method 2—Alloys Reduced in the Multi-Step Method 
     A 25% polyethersulfone-polyetherethersulfone co-polymer and 21% polyvinylpyrrolidinone in 1-methyl-2-pyrrolidinone on polyester backing membranes gelled into reverse osmosis water and treated with: 
     1. 100 ppm tin sulfate then 1% silver nitrate and 1% cupric sulfate 
     2. 100 ppm tin sulfate then 50 ppm palladium nitrate/50 ppm tin sulfate then 1% silver nitrate, 1% cupric sulfate and 1% nickelous nitrate 
     3. 100 ppm palladium nitrate for then 50 ppm palladium nitrate/50 ppm tin sulfate for then 1% silver nitrate, 1% cupric sulfate and 1% nickelous nitrate 
     4. 100 ppm palladium nitrate for then 1% nickelous nitrate 
     The membrane contacted with 100 ppm tin sulfate then 1% silver nitrate and 1% cupric sulfate gave flux rates of 222 LMH with pure water and 221 LMH (76% separation) with PEG 6K. The membrane contacted with 100 ppm palladium nitrate then 1% nickelous nitrate gave pure water flux rates of 159 LMH and 157 LMH (82% separation) with PEG 6K. The tin sulfate and palladium nitrate were added as accelerators or initiators for the reduction of copper and nickel. 
     The following were contacted in the sequence listed. After each addition of metal salt, the metal on the membrane was reduced with 1% hydroquinone before the addition of the next metal salt. 
     1. 6% cupric nitrate then 6% silver nitrate 
     2. 6% nickelous nitrate then 6% cupric nitrate then 6% silver nitrate 
     3. 6% silver nitrate then 6% cupric nitrate 
     4. 6% silver nitrate then 6% cupric nitrate then 6% nickelous nitrate 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes with Alloys Reducing in the 
               
               
                 Multi-Step Method 
               
             
          
           
               
                   
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                   
                   
                 200 ppm PEG 
                   
                 200 ppm PEG 
                   
               
               
                 25% PES-PEES - 21% 
                 PWP 
                 6K 
                 PWP 
                 6K 
                 change in 
               
             
          
           
               
                 PVP 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 PWP 
               
               
                   
               
               
                 6% cupric nitrate then 6% 
                 200 
                 176 
                 87% 
                  93 
                  86 
                 95% 
                 0.468 
               
               
                 silver nitrate 
               
               
                 6% nickelous nitrate then 
                 196 
                 173 
                 84% 
                  99 
                  85 
                 89% 
                 0.507 
               
               
                 6% cupric nitrate then 6% 
               
               
                 silver nitrate 
               
               
                 6% silver nitrate then 6% 
                 167 
                 155 
                 95% 
                 121 
                 106 
                 96% 
                 0.725 
               
               
                 cupric nitrate 
               
               
                 6% silver nitrate then 6% 
                 162 
                 117 
                 92% 
                 117 
                 100 
                 91% 
                 0.719 
               
               
                 cupric nitrate then 6% 
               
               
                 nickelous nitrate 
               
               
                   
               
             
          
         
       
     
     All membranes were dark in colour. The membranes with silver nitrate as their last step had a metallic sheen. It was found during longer term permeation tests that when the membranes are reduced to the metal after each addition, the metals remain on the surface of the membrane for a longer time that if two or three metals are reduced all in one step. 
     FIG. 5 shows the effect of the alloys reduced using the multi-step method on membrane performance. It is shown once again that the treated membranes gave PEG separation performance very similar to the original, untreated membranes. 
     Method 3—Alloys Reduced using Other Reducing Agents 
     A 25% polyethersulfone-polyetherethersulfone co-polymer (PES-PEES) and 21% polyvinylpyrrolidinone (PVP) in 1-methyl-2-pyrrolidinone solution cast onto polyester backing gelled into reverse osmosis water. These membranes were subjected to a silver nitrate deposit by the following method: To 38 mL of a 7% silver nitrate solution, ammonium hydroxide was added drop by drop until the dark brown precipitate dissolved. 13 mL of 14% potassium hydroxide was added and ammonium hydroxide added drop by drop until the solution became clear. 15 mL of a solution of 6.5% dextrose in 17.5% ethyl alcohol in distilled water was added. The solution was mixed for 1 minute and the membranes added and allowed to adsorb. This was followed by a static adsorption of 3.5% cupric sulfate, followed by a static adsorption of 3.5% zinc nitrate. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes Reduced with Dextrose 
               
             
          
           
               
                   
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                 25% PES-PEES - 21% PVP 
                   
                 200 ppm PEG 
                   
                 200 ppm PEG 
                   
               
               
                 Silver deposited membranes 
                 PWP 
                 6K 
                 PWP 
                 6K 
                 change in 
               
             
          
           
               
                 absorption of: 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 PWP 
               
               
                   
               
               
                 3.5% cupric sulfate 
                 139 
                 135 
                 85% 
                 117 
                 125 
                 88% 
                 0.837 
               
               
                 3.5% cupric sulfate then 
                 128 
                 125 
                 91% 
                 118 
                 115 
                 92% 
                 0.928 
               
               
                 3.5% zinc nitrate 
               
               
                 Standard (no treatment) 
                 148 
                 143 
                 86% 
               
               
                   
               
             
          
         
       
     
     The membranes contacted with zinc nitrate were yellowish in colour. After testing, the colour remained on the surface. 
     Metal and Alloys Reduced on the Membrane using Reduction Step First 
     A 20% polyphenylsulfone, 20% polyvinylpyrrolidinone, 2% silver nitrate, and 2% hydroquinone in 1-methyl-2-pyrrolidinone solution was cast onto polyester backing and gelled into reverse osmosis water. This membrane gave a pure water flux rate of 609 LMH and PEG 35K flux rate of 463 LMH (27% separation). This has changed from the standard membrane of this type which gives pure water flux rates of 292 LMH and PEG 35K flux rates of 205 LMH (99% separation). 
     An 18% polyethersulfone-polyetherethersulfone co-polymer (PES-PEES), 18% polyvinylpyrrolidinone (PVP), and 5% hydroquinone in 1-methyl-2-pyrrolidinone solution was a cast onto polyolefin backing and gelled into 0.5% hydroquinone. Silver nitrate (6%) was sponged onto the surface of the membrane. By this method, as little or as much silver can be added. Cupric nitrate (6%) was also added in this method, but was slower to react. The concentration and the temperature of the solution was increased to shorten the time required for reaction. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes with Hydroquinone in the 
               
               
                 Casting Solution 
               
             
          
           
               
                 18% PES-PEES - 18% 
                   
                   
                   
               
               
                 PVP - 5% hydroquinone 
                   
                   
                 200 ppm PEG 
               
               
                 Gelled 
                 PWP 
                 200 ppm PEG 6K 
                 35K 
               
             
          
           
               
                 into 0.5% hydroquinone 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 % sep 
               
               
                   
               
               
                 6% silver nitrate sponged 
                 659 
                 624 
                 16% 
                 405 
                 72% 
               
               
                 on surface 
               
               
                 6% cupric nitrate 
                 619 
                 601 
                 22% 
                 411 
                 73% 
               
               
                 sponged on surface 
               
               
                 Standard (no treatment) 
                 512 
                 378 
                 48% 
                 345 
                 60% 
               
               
                   
               
             
          
         
       
     
     A 25% polyethersulfone-polyetherethersulfone co-polymer (PES-PEES) and 21% polyvinylpyrrolidinone (PVP) in 1-methyl-2-pyrrolidinone solution cast onto polyester backing and gelled into reverse osmosis water. These membranes were subjected to: 
     1. 1% hydroquinone then 6% total 1:1:1 nickelous nitrate:cupric nitrate:silver nitrate 
     2. A sequential treatment of 1% hydroquinone then 6% silver nitrate then 1% hydroquinone then 6% cupric nitrate then 1% hydroquinone then 6% nickelous nitrate 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 14 
               
             
             
               
                   
               
               
                 Flux and Separation Data for Membranes Treated with Reducing Agent 
               
               
                 Before Metal Salts 
               
             
          
           
               
                   
                 Before Treatment 
                 After Treatment 
                   
               
             
          
           
               
                   
                   
                 200 ppm 
                   
                 200 ppm 
                   
               
               
                   
                 PWP 
                 PEG 6K 
                 PWP 
                 PEG 6K 
                 change 
               
             
          
           
               
                 25% PES-PEES - 21% PVP 
                 (LMH) 
                 (LMH) 
                 % sep 
                 (LMH) 
                 (LMH) 
                 % sep 
                 in PWP 
               
               
                   
               
               
                 1% hydroquinone then 6% 
                 169 
                 120 
                 89% 
                 117 
                 103 
                 82% 
                 0.690 
               
               
                 total 1:1:1 nickelous 
               
               
                 nitrate:cupric nitrate:silver 
               
               
                 nitrate 
               
               
                 1% hydroquinone then 6% 
                 132 
                 124 
                 94% 
                  94 
                  82 
                 95% 
                 0.711 
               
               
                 silver nitrate then 6% cupric 
               
               
                 nitrate then 6% nickelous 
               
               
                 nitrate 
               
               
                   
               
             
          
         
       
     
     The membranes were very dark in colour with a white surface and metallic sheen. By this method, the membranes retained their quality of metallic content better than those membranes contacted with the metal salt first. 
     FIG. 6 shows the effects of the reducing agent addition before the metal salts. As shown, the treated membranes give a slightly lower molecular weight cut off value than the untreated membranes. This would be due to the incorporation of metals into the surface pores of the membrane. As discussed previously, a more open initial membrane could be chosen in order to obtain a tighter final, metal-treated membrane. 
     In the formation of hollow fibers, a casting solution was made with 25% polyethersulfone-polyetherethersulfone co-polymer (PES-PEES), 21% polyvinylpyrrolidinone (PVP), and 5% hydroquinone in 1-methyl-2-pyrrolidinone solution. The fiber was cast through a spinerette with 2% cupric nitrate, 2% nickelous nitrate and 2% silver nitrate solutions in the bore liquid to produce predominantly inside metalized fibers. With the same casting solution, but by using metal salts on the outside of the fiber, a predominantly outside metallization was obtained.