# Presentation: 161394

## Membrane-Based Nanostructured Metals for Reductive Degradation of Hazardous Organics at Room Temperature

- _D. Bhattacharyya_ (PI)*, D. Meyer, J. Xu, L. Bachas (Co-PI),
- Dept. of Chemical and Materials Engineering and Dept. of
- Chemistry, University of Kentucky, and S. Ritchie (Co-PI), L. Wu,
-  Dept. of Chemical Engineering, Univ. of Alabama
- * email: db@engr.uky.edu
- * phone: 859-257-2794

- Project Officer: Dr. Nora Savage, US EPA

- EPA Nanotechnology Grantees Workshop
- August 17-20, 2004

## Functionalized Materials and

- Membranes
- (Nano-domain Interactions)

- Ultra-High
- Capacity Metal
- Sorption (Hg, Pb etc)

- Reactions and Catalysis
- (_nanosized metals_,
-  Vitamin B12, Enzymes)

- Tunable
-  Separations
- (with Polypeptides)
- Hollman and Bhattacharyya, LANGMUIR
- (2002,2004); JMS (2004)
- Smuleac, Butterfield, Bhattacharyya,
- Chem. of Materials (2004)

**Bhattacharyya, Hestekin, et al, J. Memb. Sci. (1998)**
**Ritchie, Bachas, Sikdar, and Bhattacharyya, LANGMUIR (1999)**
**Ritchie, Bachas,Sikdar,  and Bhattacharyya, ES&T (2001)**

- *Ahuja, Bachas, and Bhattacharyya, I&EC (2004)

**Notes:**
Membranes provide an excellent platform for the attachment of macromolecules (high capacity ion exchange and tunable separations) and for in-situ generation of nanoparticles.

## Why Nanoparticles?

-  High Surface Area
-  Significant reduction in materials usage
-  Reactivity (role of surface defects, role of dopants such as, Ni/Pd)
-  Polymer surface coating to alter pollutant partitioning
-  Alteration of reaction pathway (ex, TCE -- ethane)
-  Bimetallic (role of catalysis and hydrogenation,
- 		minimizing surface passivation)
-  Enhanced particle transport in groundwater

## Synthesis of Metal Nanoparticles in Membranes and Polymers

**Chelation (use of polypeptides,poly(acids), and polyethyleneimine)**
- Capture and borohydride reduction of metal ions using polymer films containing **polyfunctional **ligands.
- Mixed Matrix Cellulose Acetate Membranes
- Incorporation of metallic salts in membrane casting solutions for dense film preparation.  Formation of particles within the membrane occurs after film formation.
- External Nanoparticle synthesis followed by membrane casting
**Thermolysis and Sonication**
- Controlled growth of metal particles in polymeric matrices by decomposition of metal carbonyl compounds  thermally or by sonication.
**Di-Block Copolymers**
- The use of block copolymers containing metal-interacting hydrophilic and hydrophobic segments provide a novel approach for in-situ creation of nanostructured metals (4-5 nm) in the lamellar space of self-assembled thin films.

## Preparation of supported iron nanoparticles

**Preparation of supported iron nanoparticles**

** ****The weight content of iron is 6.6% by AA (Atomic Absorption).**

- Water in oil micelle

- 5 ml NaBH4 (5.4M) solution drop-wisely

- N2 in

- N2 out

- Washed using methanol

- CA acetone solution

- Iron nanopartilces

- Mixing

**Iron naoparticles**** ****in Cellulose acetone solution**

- Ethanol bath

- Casting

**Synthesis reaction:**

## TEM Characterization of pre-produced iron particles

- TEM bright field image of pre-produced iron particles

- TEM bright field image of CA membrane-supported iron nanoparticles

## Change of chloride ions in aqueous phase (TCE degradation to Cl-)

## Mixed-Matrix Membrane Preparation

**Cellulose Acetate/Fe****2+****/Ni****2+**** Mixed-Matrix Membrane**

**Reduction**

- Phase Inversion

- Dry Process

- Wet Process (nonsolvent gelation bath)
- Water or ethanol

- Meyer, Bachas, and Bhattacharyya, Env. Prog (2004)

## Mo + PAA

- Mo        M2+ + 2e-

- R-Cl + H+ + 2e-        R-H + Cl-

- Chlorinated organics in water R-Cl

- Selective Sorption

- In Membrane

- Metal Reduction
- (Borohydride or  electrochemical)

- M2+ Recapture with membrane-bound PAA Carboxylic Groups
- (loss of metals and metal hydroxide pptn. On Mo surface prevented)

- M2+ + PAA-Na+          M2+-PAA + Na+

- PAA:Poly-amino acid
- Or Poly-acrylic acid

**Notes:**
We have already demonstrated that metals can be captured at high capacity using poly-ligands (such as, PLGA). The membranes can be inexpensive cellulose or cellulose acetate-based. This Figure shows an example of an overall reductive dechlorination reaction scheme and the role of simultaneous dissolved metal ion capture/reuse for the case of functionalized membrane-based nanoparticle systems.  Metal interactions reactions with PLGA are not shown in balanced form. 

## Nanoparticle Synthesis in Membrane (use of PAA)

**Nanoparticle Synthesis in Membrane (use of PAA)**

- Polyether sulfone
- (PES)

- Polyacrylic acid (PAA)

- Polyvinylidene
- fluoride (PVDF)

- Dip Coating

- Membrane support

- PAA+Fe2++EG

- NaBH4 solution

- Crosslinked PAA-Fe2+

- 110 °C 3 hour

- Uncrosslinked PAA-Fe2+

- Nano Fe/Ni or Fe/Pd particles immobilized in membrane

- Cross-section

- Ethylene glycol
- (EG)

- Post coating with Ni or Pd

**Notes:**
Here is the typical procedure for nanoparticles synthesis based on membrane domain. Basically, there are two steps involved in this procedure. First is the preparation of membrane containing metal ions as the precursor for nanoparticles. Second is the reduction of metal ions to form nanoparticles in membrane matrix. In membrane preparation part, polyacrylic acid (PAA) was used to entrap metal ions in aqueous phase, and then added to polyether sulfone (PES) support membrane by a dip-coating process. After heated at 110C for three hours, crosslinked PAA/PES composite membrane containing metal ions was obtained. Immersing the membrane into NaBH4 solution cause the formation of nanoscale metal particles.  The PES support membrane is microfiltration membrane. It has open structure and large porosity which is ideal to attain high efficient utilization of available sites and the easy access to particles immobilized inside the membrane matrix. Besides, PES is a highly hydrophobic polymer, which has a strong interaction with chlorinated organics like TCE. Using PES as support platform will enhance the TCE transport from aqueous phase to membrane phase, and thus increase the overall dechlorination rate. PAA is a well known polymer for metal ions interaction because of the carboxylic group. It was largely used in ion exchange and heavy metal removal as a chelating agent.

## B

**B**

- (A) SEM surface image of nanoscale Fe/M particles immobilized in PAA/MF composite membrane (reducing Fe followed by metal deposition) (100,000); (B) Histogram from the left SEM image of 150 nanoparticles. The average particle size is 28 nm, with the size distribution standard deviation of 7 nm.

## Image of Fe/Ni particles Prepared in a TEM Grid

-  (Ni post-Coated)

- 50.8 nm

**Notes:**
Because of the limitation of SEM, TEM was used to study the particle size and composition in nano domain. This is a typical bright field TEM image of Fe/Ni particles inside PAA matrix. From the right figure, we know that the particle has average size 5nm, with standard deviation of 0.8nm, which is much smaller than the size in SEM image. We think this is because 30nm may be the limit of SEM. Small and individual particle less than 30nm can not be resolved in SEM. Only cluster of particles or lager one can be identified in SEM. 

## STEM-EDS Mapping (using JOEL 2010)

**Notes:**
EDS Mapping was also performed to confirm the Fe/Ni distribution we obtained in the line profile. The EDS mapping was also done in the STEM mode. The top one is reducing Fe followed by  Ni, Fe and Ni appears always together, suggesting Fe are well coated by Ni. the bottom one is simultaneous reduction of Fe and Ni, some region Fe and Ni are together, but some region Fe and Ni are separated. Therefore, both EDS line profile and mapping prove that simultaneous reduction of Fe and Ni can cause the separation of Fe and Ni.

## TCE Dechlorination by Fe/Ni and Fe/Pd 

- TCE Dechlorination by Fe/Ni and Fe/Pd
- Nanoparticles in Membrane

**Notes:**
This is the TCE dechlorination with different Fe/Ni particles. We have three Fe/Ni particles. First is reducing Fe followed by Ni, second is simultaneous reduction of Fe and Ni, third is solution phase reduction of Fe and Ni. The reaction rate by solution phase Fe and Ni is the slowest, compared to the results by membrane phase particles. For dechlorination by membrane particles, reducing Fe followed by Ni give faster reaction rate. This is because Fe is well coated by Ni. We know that in bimetallic system, the second metal should be in close contact with first metal. Separation of two metals can’t promote the reaction rate.  

## Surface-Area-Normalized Dechlorination Rate (wide variation of kSA showing the importance of surface – active sites and role of hydrogenation)

- Surface-Area-Normalized Dechlorination Rate (wide variation of kSA showing the importance of surface – active sites and role of hydrogenation)

| Material | KSA (L·h-1·m2) |
| --- | --- |
| Nano Fe | 2.010-3 |
| Nano Fe/Ni (3:1) | 0.098 |

**Other source *****k******SA************ **

- * From B. Schrick, J.L. Blough, A.D. Jones, T.E. Mallouk, Hydrodechlorination of Trichloroethylene to Hydrocarbons Using Bimetallic Nickel-Iron Nanoparticles. Chem.Mater. 2002, 14, 5140-5147.

- Fe/Pd

- Fe/Ni

## Effect of Ni content in Fe/Ni particles on KSA 

**Effect of Ni content in Fe/Ni particles on *****K*****SA**** **

- Fe

- Ni

**Initial TCE: 20mg/L**
**Reaction volume: 110mL**
**Fe/Ni in PVDF support (Posting coating Ni)**

**All experiments were performed in batch systems using nanosized Fe/Ni particles (Post coating Ni) immobilized in PAA/PVDF membrane.**

**Notes:**
To get a better comparison of all the dechlorination results, the Surface-Area-Normalized Dechlorination Rate was calculated. Assuming first order reaction, As is surface area, p is the metal concentration. These can be consider as constant. The surface area was obtained according to the average particles size which was calculated based on the SEM image. As we saw before, Fe/Pd has the fastest reaction rate because Pd is more reactive than Ni. Ni deposition on Fe can make Fe and Ni in close contact, which give faster reaction rate. Solution phase Fe/Ni got slowest reaction rate. We think there are two reason for it. One is because of the agglomeration of particles which will cause less available surface area. The other is because of the PES membrane matrix. PES is hydrophobic polymer, which has strong interaction with TCE. So it can enhance the transport of TCE from aqueous phase to membrane phase. The reaction rate we are talking about is the overall reaction rate, which includes the intrinsic rate and mass transfer rate. Improving any of them can enhance the overall reaction rate. Here is the reaction rate from other source, these nanoparticles are produced in solution phase. For Fe/Ni, our ksa is close to them. 

## Reactions of 2,3,2’,5’-Tetrachlorobiphenyl (PCB) with Fe/Pd (~30 nm) in PAA/PVDF membrane

**Notes:**
To get a better comparison of all the dechlorination results, the Surface-Area-Normalized Dechlorination Rate was calculated. Assuming first order reaction, As is surface area, p is the metal concentration. These can be consider as constant. The surface area was obtained according to the average particles size which was calculated based on the SEM image. As we saw before, Fe/Pd has the fastest reaction rate because Pd is more reactive than Ni. Ni deposition on Fe can make Fe and Ni in close contact, which give faster reaction rate. Solution phase Fe/Ni got slowest reaction rate. We think there are two reason for it. One is because of the agglomeration of particles which will cause less available surface area. The other is because of the PES membrane matrix. PES is hydrophobic polymer, which has strong interaction with TCE. So it can enhance the transport of TCE from aqueous phase to membrane phase. The reaction rate we are talking about is the overall reaction rate, which includes the intrinsic rate and mass transfer rate. Improving any of them can enhance the overall reaction rate. Here is the reaction rate from other source, these nanoparticles are produced in solution phase. For Fe/Ni, our ksa is close to them. 

## Dechlorination Study under Convective Flow Mode(PVDF-MF membrane & Fe/Pd nanoparticles) 

**Dechlorination Study under Convective Flow Mode(PVDF-MF membrane & Fe/Pd nanoparticles) **

- 2,2’- Chlorobiphenyl Degradation

**Notes:**
To get a better comparison of all the dechlorination results, the Surface-Area-Normalized Dechlorination Rate was calculated. Assuming first order reaction, As is surface area, p is the metal concentration. These can be consider as constant. The surface area was obtained according to the average particles size which was calculated based on the SEM image. As we saw before, Fe/Pd has the fastest reaction rate because Pd is more reactive than Ni. Ni deposition on Fe can make Fe and Ni in close contact, which give faster reaction rate. Solution phase Fe/Ni got slowest reaction rate. We think there are two reason for it. One is because of the agglomeration of particles which will cause less available surface area. The other is because of the PES membrane matrix. PES is hydrophobic polymer, which has strong interaction with TCE. So it can enhance the transport of TCE from aqueous phase to membrane phase. The reaction rate we are talking about is the overall reaction rate, which includes the intrinsic rate and mass transfer rate. Improving any of them can enhance the overall reaction rate. Here is the reaction rate from other source, these nanoparticles are produced in solution phase. For Fe/Ni, our ksa is close to them. 

## Acknowledgements

-  US EPA- STAR Program Grant #  R829621
-  NSF-IGERT Program
-  NIEHS-SBRP Program
-  Dow Chemical Co.
-  Undergrads: UK--Melody Morris, Morgan Campbell, Alabama--Cherqueta Claiborn