Patent Publication Number: US-2011070138-A1

Title: Use of photocatalytically coated particles for decomposition of air pollutants

Description:
FIELD OF THE INVENTION 
     The invention relates to use of iron oxide particles coated with titanium dioxide, and in particular to their use for decomposing air pollutants photocatalytically. 
     BACKGROUND OF THE INVENTION 
     In recent years, pollution of air, water and soil has become a key issue especially in urban areas. Air pollutants are mainly emitted into the environment by production processes such as industrial activities or combustion processes such as heating, power generation and motor vehicles. These pollutants can contribute to urban air quality problems, for example photochemical smog, as well as adversely affect human health and the health of other living things. 
     Two of the major environmental polluting substances include nitrogen oxides (NO x ) and volatile organic compounds (VOCs). In particular, these compounds are dangerous as they initiate formation of secondary polluting substances. NO and VOCs are also referred to as ozone precursors as the majority of tropospheric ozone formation occurs when NO x  and VOCs react in the atmosphere in the presence of sunlight and carbon monoxide. Moreover, reaction of NO x  and VOCs in the presence of sunlight causes photochemical smog containing inter alia peroxyacetyl nitrate (PAN) which is a significant form of air pollution, especially in the summer. Children, people with lung diseases such as asthma, and people who work or exercise outside are susceptible to adverse effects of photochemical smog such as damage to lung tissue and reduction in lung function. 
     Various solutions have been proposed to reduce the concentration of air polluting substances in the environment. 
     WO 02/38272 discloses a photocatalytic coating film having oxidizing properties on toluene and which is suitable for deodorization of indoor ambient and purification of gaseous streams contaminated by VOCs. 
     A building material with photocatalytic activity towards air pollutants such as NO is described in WO 2006/000565, wherein the photocatalytic activity arises from the presence of TiO 2  nanoparticles physically mixed with cement. 
     A photocatalytic reactor for oxidation of organic contaminants from gases or water is described in U.S. Pat. No. 6,136,186, wherein the photocatalyst is a porous layer or surface of TiO 2  or a binary TiO 2  oxide, eventually doped with another metal catalyst, formed on a porous surface. 
     WO 2006/008434 describes a titanium dioxide coating having VOC degrading as well as self-cleaning and antimicrobial properties. 
     EP1559753 relates to a photocatalytic potassium silicate paint that contains TiO 2  in the anatase form. The paint is designed for use in residential and public buildings to give anti-pollutant, self cleaning properties. 
     There remains a need for materials with improved capability to decompose polluting substances such as nitrogen oxides (NO x ) and volatile organic compounds (VOC) in the environment. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is the provision of a photocatalytically active material for effectively decomposing air pollutants. The present invention is the provision of and use of a suitable material for photocatalytically decomposing air pollutants selected from nitrogen oxides (NO x ) and volatile organic compounds (VOC). Still another object of the present invention is the use of such materials for decomposing air pollutants, selected from NO x  and VOCs, in building materials. Still another object of the present invention is the use of such materials for decomposing air pollutants, selected from NO x  and VOCs, in paint. 
     A further object of the present invention is the provision of and use of a suitable material for reducing photo-corrosion during photocatalytically decomposing air pollutants selected from nitrogen oxides (NO x ) and volatile organic compounds (VOC). 
     Furthermore, the invention is directed to the use of iron oxide particles being at least partially coated with titanium dioxide for photocatalytically decomposing NO at reduced NO 2  production. 
     Furthermore, the invention is directed to the use of iron oxide particles being at least partially coated with titanium dioxide for photocatalytic decomposition of air pollutants selected from nitrogen oxides (NO x ) and volatile organic compounds (VOC). 
     Furthermore, the invention is directed to the use of iron oxide particles being at least partially coated with titanium dioxide for photocatalytically decomposing NO under UV and/or visible light. 
     Furthermore, the invention is directed to the use of iron oxide particles being at least partially coated with titanium dioxide for photocatalytically decomposing VOC under UV and/or visible light. 
     These and other objects of the present invention can be solved by the use described in the claims. Preferred embodiments arise from a combination of the features of the dependent claims with those of the independent claims. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a scheme of an experimental setup ( 10 ) suitable for nitrogen conversion tests. The sample ( 40 ) is placed inside a 3.6 l cell ( 50 ) through which the test gas obtained from a gas cylinder ( 20 ) is passed at a flow rate of 1.5 l/min. The sample is illuminated through a glass cover ( 60 ) by the selected light source ( 30 ) mounted above the cell ( 50 ). The NO concentration in the outlet gas is analyzed continuously using a gas chromatograph ( 70 ). 
         FIG. 2  shows the NO, NO 2 , NO x  and O 3  conversion versus time of irradiation for sample a of Example 1 which is a concrete block containing 6% photocatalytic iron oxide and standard cement. 
         FIG. 3  and  FIG. 4  show the photocatalytic conversion of NO and NO 2 , respectively, measured before aging, after 96 h and after 192 h for the 4 samples described in example 3. Sample 1 is a photocatalytic cement containing no pigment; sample 2 is a photocatalytic cement containing standard iron oxide yellow (3.8 wt.-% based on total cement weight); sample 3 is a standard cement containing photocatalytic iron oxide 1 (45 wt.-% TiO 2  based on total pigment weight) in an amount of 6.8 wt.-% based on total cement weight; and sample 4 is a standard cement containing photocatalytic iron oxide 2 (45 wt.-% TiO 2  based on total pigment weight) in an amount of 6.8 wt.-% based on total cement weight). 
         FIG. 5  and  FIG. 6  show the NO, NO 2 , NO and O 3  conversion versus time of UV irradiation for sample 2 and sample 3 of Example 2, respectively. Sample 2 is a coloured block made with photocatalytic cement and standard iron oxide and sample 3 is a coloured block made with photocatalytic pigment and standard cement. 
         FIG. 7  shows the photodissolution data of Fe(II) for three different samples of Example 3. The plot shows the Fe(II) concentration in the water extract obtained from concrete samples exposed to NO and UV light for different lengths of time as described in example 3. Sample a is Ferroxide 48(3 wt.-%) on cement; sample b is a photocatalytic iron oxide (TiO 2  21 wt.-% based on total pigment weight) in an amount of 5 wt.-% based on total cement weight; and sample c is Ferroxide 48 (3%) on photocatalytic cement. 
         FIG. 8  and  FIG. 9  illustrate the conversion and the average conversion, respectively, of VOCs under UV light for four different samples of Example 4.  FIG. 8  shows conversion of VOCs under UV light as described in example 4. Sample a is a photocatalytic cement containing no pigment; sample b is a photocatalytic cement containing standard iron oxide yellow (3.8 wt.-% based on total cement weight); sample c is a standard cement containing photocatalytic iron oxide yellow A (TiO 2  45 wt.-% based on total pigment weight) in an amount of 6.8 wt.-% based on total cement weight; and sample d is a standard cement containing photocatalytic iron oxide yellow B (TiO 2  45 wt.-% based on total pigment weight) in an amount of 6.8 wt.-% based on total cement weight.  FIG. 9  shows the total conversion of a mixture of Benzene, Ethylbenzene, Toluene and o-styrene, under UV light as described in example 4. Sample a is a photocatalytic cement containing no pigment; sample b is a photocatalytic cement containing standard iron oxide yellow (3.8 wt.-% based on total cement weight); sample c is a standard cement containing photocatalytic iron oxide yellow A (TiO 2  45 wt.-% based on total pigment weight) in an amount of 6.8 wt.-% based on total cement weight; and sample d is a standard cement containing photocatalytic iron oxide yellow B ((TiO 2  45 wt.-% based on total pigment weight) in an amount of 6.8 wt.-% based on total cement weight. 
         FIG. 10  show the NO, NO 2 , NO x  and O 3  conversion versus time of irradiation for a silicate paint coloured with 5% of a photocatalytic iron oxide (23 wt.-% TiO 2  based on total pigment weight) as described in Example 6. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Surprisingly, it has been found that a specific type of photocatalytic material, titanium dioxide coated iron oxide particles, are especially suitable for highly effective photocatalytic decomposition of air pollutants, specifically NO x  and VOCs. 
     The use of iron oxide particles coated with titanium dioxide for photocatalytically decomposing NO x  and/or VOC is highly advantageous, since it allows the provision of conventionally used pigments for colouring applications with photocatalytic properties, e.g. for colouring of building materials, in the paint and coating field or in the paper manufacturing industry. 
     Furthermore, it has been observed that with conventionally used photocatalysts that are solely titanium dioxide based, the photocatalytic activity degrades over time. With the use of titanium dioxide coated iron particles, the photocatalytic titanium dioxide as well as the pigment are significantly more stable under UV and visible radiation, allowing for extended lifetime of the pigment as well as the photocatalyst. Also, with the use of titanium dioxide coated iron oxide particles as photocatalysts for degrading NO x  and/or VOC, a broader spectrum of radiation can be used, ranging from UV to visible light. It is believed that this is due to a synergistic effect between iron oxide and titanium dioxide. 
     Also, with the use of titanium dioxide coated iron oxide particles as photocatalysts for degrading NO x  and/or VOC, the NO 2  production regularly occurring during the degradation of NO is significantly reduced. Ozone production, that may occur during irradiation with 1N and visible light in the presence of NO x , has been measured and observed to be limited with these photo-catalytic materials. 
     In one embodiment of the present invention iron oxide particles used for photocatalytically decomposing air pollutants selected from nitrogen oxides (NO x ) and volatile organic compounds (VOC) are at least partially coated with titanium dioxide. In another embodiment of the present invention the iron oxide particles used for photocatalytically decomposing air pollutants selected from nitrogen oxides (NO x ) and volatile organic compounds (VOC) are completely coated with titanium dioxide. 
     The titanium dioxide can be randomly distributed on the surface of the inorganic particulate material, e.g. in the form of more or less densely distributed crystalline spots, preferably nano-sized crystallites of titanium dioxide. Alternatively, at higher loadings, the titanium dioxide may also form larger areas of crystalline material on the carrier particle&#39;s surface, up to substantially complete coverage. 
     In an exemplary embodiment of the uses of the present invention the iron oxide particles being at least partially coated with titanium dioxide are incorporated into a building material. For example, the particles can be mixed with the building material. In another exemplary embodiment of the uses of the present invention the iron oxide particles being at least partially coated with titanium dioxide are applied on a building material. For example, the particles can be applied on a building material in form of a water-based coating or paint. The building material of the present invention can comprise an inorganic material such as concrete, cement, mortar, limestone or gypsum. 
     In another exemplary embodiment of the uses of the present invention the iron oxide particles being at least partially coated with titanium dioxide are incorporated into a paint. For example, the particles can be mixed with the paint or dispersed in the paint. The paint can comprise, e.g., a silicate based paint, an acrylic paint, oil paint or water-based paint. 
     The particles for the use described in the present invention can be manufactured by a process as described in applicant&#39;s co-pending patent application no. PCT/EP2006/068245, wherein, for example, an inorganic iron oxide dispersion is mixed with an aqueous solution of at least one titanyl salt, e.g., titanyl sulfate, titanium chloride or titanyl oxalate, and precipitating titanium dioxide on said iron oxide particle by adding an alkali, wherein the titanium oxide is precipitated at least partially. Finally, the iron oxide particle coated with the photocatalytically active compound is isolated from the reaction mixture by, for example, filtration and subsequent washing and drying at low temperatures. The particles suitable for the uses of the present invention may have a particle size ranging from 0.01 to 100 μm and may have a surface area ranging from about 5 to 200 m 2 /g. For the uses of the present invention the particles can be provided in shaped form, e.g. granulates, pellets or tablets. 
     Without wishing to be bound to any theory, it is believed that upon exposure to sunlight, the polluting substances nitrogen oxides (NO x ) and volatile organic compounds (VOC) can be disintegrated in the presence of titanium dioxide coated iron oxide particles, which produces radicals and/or other active species which interact with the pollutants. This results in degradation or decomposition reactions of these molecules, e.g., nitrogen oxide gases can be oxidized to nitrates, and can substantially reduce concentrations of such pollutants. Thus, the concentration of these substances, e.g. on building materials, is reduced, resulting in a maintained brilliance of the colour for an extended period of time and, furthermore, to a reduced concentration of environmental polluting substances in the environment. In addition, the quality of the air can be improved, resulting in an anti-smog-effect. 
     The inventors have found that the use of titanium dioxide coated iron oxide particles instead of conventional pigments in colouring applications results in an improved colour fastness for an extended period of time. Moreover, the inventors have found that titanium dioxide coated iron oxide particles show reduced photo-corrosion in comparison with conventional iron oxide pigments.  FIG. 7  shows that photodissolution of Fe(II) is evident only for the cement block including standard iron oxide pigment but not for the cement block including titanium dioxide coated iron oxide particles. Thus, the present invention also provides for a long term stability of the iron oxide pigments by reducing photo-corrosive effects. 
     Furthermore, the inventors have found that with the use of titanium dioxide coated iron oxide particles a greater stability of nitric oxide conversion over time of exposure compared to the use of conventional photocatalytic compounds can be attained. As shown in  FIGS. 5 and 6  the decrease in nitric oxide conversion during UV exposure is less pronounced for the coloured cement blocks made with titanium dioxide coated iron oxide particles compared to the coloured cement blocks comprising conventional photocatalytic cement and an iron oxide pigment. In addition  FIG. 3  shows the cements blocks made with titanium coated iron oxide particles exhibit greater stability of nitric oxide conversion compared with the cement blocks made with colored photocatalytic cement. 
     Also, it was found that with the use of titanium dioxide coated iron oxide particles the formation of NO 2  regularly occurring during the photocatalytic process is significantly reduced compared the use of conventional photocatalytic compounds. Without wishing to be bound to any theory, the inventors believe that at least some of the aforementioned observations suggest a synergetic effect of iron oxide and titanium oxide when being in intimate contact. 
     EXAMPLES 
     Nitrogen Oxide Conversion Test 
     The experimental apparatus ( 10 ) used for the nitrogen oxide (NO) conversion tests is shown schematically in  FIG. 1 . The sample ( 40 ) is placed inside a 3.6 l cell ( 50 ) through which the test gas obtained from a gas cylinder ( 20 ) is passed at a flow rate of 1.5 l/min. The sample is illuminated through a glass cover ( 60 ) by the selected light source ( 30 ) mounted above the cell ( 50 ). 
     A mixture of synthetic humid air (79% N 2 , 21% O 2 , 50% relative humidity) and 0.5 ppmv of NO at 1.5 l/min was used as inlet gas. For testing under UV illumination the sample was irradiated with a Hg HP125 (radiant power 40 Wm −2  in the range 290-400 nm) lamp emitting in the UV region. The concentration of NO in the outlet gas was continuously analyzed by gas chromatography ( 70 ). 
     For measurement under visible or UV-visible light, the irradiating source was a Philips PAR30S lamp (100 W, radiant power 178 W m 2  in the range 400-700 nm) or a Xenon LOT Oriel lamp (150 W operated at 140 W, 25% power of the Philips lamp and 36% Hg lamp), respectively. 
     The percentages of NO converted into NO 2  are defined as: 
       % NO Conversion=( C   NO inlet   −C   NO outlet )/ C   NO inlet )*100% 
       NO 2  Conversion= C   NO2 outlet   /C   NO inlet *100 
     NO x  is the NO converted in products different from NO 2  and is defined as: 
     % NO x  Conversion=% NO Conversion-% NO 2  Conversion 
     Volatile Organic Compounds Conversion Test The experimental arrangement was similar to the NO conversion test described above, the outlet gas was analyzed in a discontinuous way (every 30-40 min) after trapping in a cryogenic apparatus by gas-mass quadrupole spectroscope. The inlet gas was a BTEX mixture (13.5 ppbv toluene, 23 ppbv ethylbenzene, 20 ppbv o-xylene, 20 ppbv benzene) of 76.5 ppbv total partial pressure flowing at 1.5 l/min. 
     Colorimetric Measurement 
     The colorimetric measurements are performed on the concrete sample using a Minolta Konica DP301 coupled with an illuminating system CR310 with a D65 lamp. Data are expressed using the CieLab scale. 
     For the tinting strength a Gardner-BYK colorimeter (45/0 measurement angle) was used. Tinting strength values are based on the difference between areas under the reflectance curves for the tested samples and the standard sample. 
     Concrete Sample Preparation Methods 
     Method 1: Concrete samples were prepared by mixing the respective pigment with white Portland cement (Aquila Bianca CEM IUB-LL 32, 5R), sand (Sibelco 2, Sibelco 5/RD) and water. The relative quantities are given in the table below: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 weight (g) 
                 wt. - % based on . . . 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Sibelco 2 
                 289 
                 72.3 total sand weight 
               
               
                   
                 Sibelco 5/RD 
                 111 
                 27.7 total sand weight 
               
               
                   
                 Water 
                 46.2 
                   35 total cement weight 
               
               
                   
                 Cement 
                 132 
                   33 total sand weight 
               
               
                   
               
            
           
         
       
     
     Sand, pigment and water were mixed with an electric mixer (Bifinet KH203, 230 W, 5 speed) with one metal beater for 30 s at speed 2, then cement was added and mixed for another 30 s at speed 2. Subsequently, the obtained material is manually mixed with a spatula followed by another 60 s of electric mixing at speed 3. The concrete mixture is poured into a rounded mould having a diameter of 7 cm. The samples were dried in an oven at 110° C. for two hours inside a plastic bag and for another 15 min in contact with the atmosphere. 
     In some tests, instead of Portland cement, a photocatalytic cement was used (TX Aria white). The pigment employed as standard yellow iron oxide was Ferroxide 48 produced by Rockwood Pigment. After drying in a vented oven, the samples were aged at 90° C. and 95% relative humidity for 192 h to accelerate the deactivating effect of ageing. 
     Method 2: Samples were prepared using normalised sand DIN EN 196-1 (Normensand) mixed in the following qu2 ntities 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 weight (g) 
                 wt. - % based on . . . 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Normalised sand 
                 400 
                   77 total mixture weight 
               
               
                   
                 Water 
                 27 
                   30 total cement weight 
               
               
                   
                 Cement 
                 90 
                 22.5 total sand weight 
               
               
                   
               
            
           
         
       
     
     Mixing and drying procedure were as in Method 1. 
     Samples were tested after 3 months outdoor aging. 
     Example 1 
     The NO conversion under UV lamp of a photo-catalytic iron oxide sample (TiO 2  23 wt.-% based on total pigment weight) was measured, under UV illumination, on the pigment itself and when included (6 wt.-% pigment based on cement weight) in a concrete matrix (Sample a). In addition, a concrete sample, (Sample b), was made with photo-catalytic cement (TX Aria white) and 6% Ferroxide 48. All concrete samples were prepared according to Method 2 above and tested after 3 months outdoor aging. 
     Results are reported in the following table: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                 converted % NO 
                 converted % NO 2   
                   
               
               
                   
                 at 180 min 
                 at 180 min 
                 % NO 2  produced 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Pigment 
                 66.4 
                 45.4 
                 68.4 
               
               
                 Sample a 
                 31.5 
                 1 
                 3.2 
               
               
                 Sample b 
                 30 
                 7 
                 23.3 
               
               
                   
               
            
           
         
       
     
     The data show that the cement containing photocatalytic iron oxide produces less NO 2  than the reference photocatalytic cement commercially in use today. 
       FIG. 2  shows the conversion versus time of irradiation for sample a. As can be seen from the plot the conversion starts from 0 and increases in few minutes after switching the light, reaches an equilibrium value, and then remains stable under irradiation. 
     It should be noted that the conversion plot shown in  FIG. 5  and reported in Example 2 for sample 2 (photocatalytic cement/iron oxide) instead shows a different profile, evidencing the different conversion mechanism of the two photocatalytic materials. 
     The photocatalytic material of this invention exhibits greater stability of nitric oxide conversion over time of exposure compared to reference photocatalytic cements. In addition the reaction over photocatalytic iron oxide generates less NO 2 . While the inventors do not wish to be bound by the theory, these two considerations suggest a synergetic effect of the two oxides (iron and titanium) when in intimate contact. 
     Example 2 
     Four concrete samples were prepared as described in Method 1 and left in a humidity chamber at T=95° C. and 90% humidity (accelerated aging) for different length of time. The following samples were prepared:
     Sample 1: Photocatalytic cement, no pigment   Sample 2: Photocatalytic cement, standard iron oxide yellow (3.8 wt.-% based on total cement weight)   Sample 3: Standard cement, photocatalytic iron oxide 1 (45 wt.-% TiO 2  based on total pigment weight), 6.8 wt.-% based on total cement weight   Sample 4: Standard cement, photocatalytic iron oxide 2 (45 wt.-% TiO 2  based on total pigment weight), 6.8 wt.-% based on total cement weight   

     Photocatalytic iron oxide 1 and 2 are materials prepared as described in patent application no. PCT/EP2006/068245 following two different preparation steps. 
     The photocatalytic conversion under UV light was measured before aging, after 96 h and after 192 h. The data are reported in  FIGS. 3 and 4  and in the following tables: 
     
       
         
           
               
               
               
               
               
            
               
                   
                   
               
               
                   
                 conversion 
                 conversion 
                 conversion 
                   
               
               
                   
                 at 0 h 
                 at 96 h 
                 at 192 h 
                 Δ(converted %) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 % 
                   
                 % 
                 % 
                 % 
                 NO 196 
               
               
                 Sample 
                 % NO 
                 NO 2   
                 % NO 
                 NO 2   
                 NO 
                 NO 2   
                 h-0 h aging00 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 41.7 
                 5.39 
                 26.3 
                 4.02 
                 14.6 
                 2.58 
                 −65% 
               
               
                 2 
                 42.7 
                 4.49 
                 9.56 
                 1.8 
                 6.7 
                 2.23 
                 −84% 
               
               
                 3 
                 21.9 
                 3.3 
                 6.93 
                 1.12 
                 7.5 
                 1.2 
                 −66% 
               
               
                 4 
                 23.6 
                 2.37 
                 8.89 
                 0.92 
                 6.2 
                 1.6 
                 −74% 
               
               
                   
               
            
           
         
       
     
     Furthermore, the NO conversion of the two photocatalytic oxides was comparable to the coloured block produced with photocatalytic cement. 
       FIGS. 5 and 6  show that the decrease in NO conversion with time of UV exposure is less pronounced for the coloured blocks made with photocatalytic pigment compared to the coloured blocks made with photocatalytic cement showing a higher NO conversion stability of these materials. The conversion plots also shows that the conversion under UV light in presence of NO did not produce ozone. 
     For sample 3 and 4 also the colorimetric values were measured as reported in the following table showing good colouring performances of the photocatalytic pigment. 
     Tinting strength was measured against Ferroxide 48 at 3.8 wt.-% based on total cement weight (equal iron oxide contents). 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 L 
                 a 
                 b 
                 TS % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Sample 3 
                 74.76 
                 2.96 
                 36.04 
                 83.9 
               
               
                   
                 Sample 4 
                 73.94 
                 3.77 
                 35.94 
                 81.8 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Two concrete samples were prepared as in Method 1 and irradiated under UV light:
     Sample a: Ferroxide 48.3% on cement   Sample b: Photocatalytic iron oxide (TiO 2  21 wt.-% based on total pigment weight,) 5 wt.-% based on total cement weight   

     As in the NO conversion test the samples were exposed to UV light in presence of NO. Fe(II) was determined on the extraction liquid after different lengths of time, wherein the extraction procedure was performed as follows: The concrete block was percolated with H 2 SO 4  2 mM previously deoxygenated and exposed for 10 min to microwave at 375 W. The solution was filtered and Fe(II) was measured by the Absorbtion at a wavelength of 510 mu after o-phenanthroline addition. Data are plotted in the  FIG. 7  showing that photodissolution of Fe(II) is evident only for the standard iron oxide (Ferroxide 48) under UV-NO condition but not for the photocatalytic iron oxide. 
     
       
         
           
               
               
               
            
               
                   
               
               
                   
                 Soluble iron(II) μM/cm2 
                   
               
            
           
           
               
               
               
            
               
                 Time min 
                 Sample a 
                 Sample b 
               
               
                   
               
            
           
           
               
               
               
            
               
                 0 
                 1.5 · 10 −03   
                 7.0 · 10 −04   
               
               
                 190 
                 2.3 · 10 −03   
                 7.0 · 10 −04   
               
               
                 370 
                 7.7 · 10 −03   
                 6.0 · 10 −04   
               
               
                 530 
                 5.5 · 10 −03   
                 7.0 · 10 −04   
               
               
                 720 
                 6.0 · 10 −03   
                 8.0 · 10 −04   
               
               
                   
               
            
           
         
       
     
     Those data may be compared with the value for a concrete block made of photocatalytic cement and 3% Ferroxide (Sample c) which is also shown in  FIG. 7 . After 250 min the Fe(II) present in the extract was 4.23·10 −3 , higher than for the photocatalytic oxide used according to the invention. 
     Example 4 
     Four concrete samples were prepared as described in Example 1 and left in a humidity chamber at T=95° C. and 90% humidity (accelerated aging) for 192 hours. The following samples were prepared:
     Sample a: Photocatalytic cement, no pigment   Sample b: Photocatalytic cement, standard iron oxide yellow 3.8 wt.-% based on total cement weight   Sample c: Standard cement, photocatalytic iron oxide yellow A (TiO 2  45 wt.-% based on total pigment weight), 6.8 wt.-% based on total cement weight   Sample d: Standard cement, photocatalytic iron oxide yellow B ((TiO 2  45 wt.-% based on total pigment weight), 6.8 wt.-% based on total cement weight   

     Photocatalytic iron oxide yellows A and B were both prepared according to PCT/EP2006/068245 with 45 wt.-% TiO 2  loading based on total pigment weight. 
     Conversion of VOCs under UV light were measured as described above. Percentages of conversion are reported in the following table: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                 conversion 
                   
                   
                   
                 o- 
                 average BTEX 
               
               
                 in % 
                 benzene 
                 toluene 
                 ethylbenzene 
                 xylene 
                 conversion in % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 a 
                 0 
                 3.6 
                 1.1 
                 1 
                 1.4 
               
               
                 b 
                 1.5 
                 3.3 
                 4.6 
                 4 
                 3.4 
               
               
                 c 
                 2.7 
                 5.1 
                 4.3 
                 4.5 
                 4.2 
               
               
                 d 
                 4.3 
                 5.9 
                 5.9 
                 6.2 
                 5.6 
               
               
                   
               
            
           
         
       
     
     The results plotted in  FIGS. 8 and 9  demonstrate that the photocatalytic iron oxides of the present invention show a greater capacity to remove VOC&#39;s than the conventional photocatalytic materials in use today. 
     Example 5 
     Two concrete samples were prepared as described in Example 1 and left in a humidity chamber at T=95° C. and 90% humidity (accelerated aging) for 192 hours. The following samples were prepared:
     Sample 1: Standard cement, photocatalytic iron oxide yellow (Sample A) (TiO 2  45 wt.-% based on total pigment weight, Sample a) 6.8 wt.-% based on total cement weight   Sample 2: Standard cement, photocatalytic iron oxide yellow (Sample B) (TiO 2  45 wt.-% based on total pigment weight, Sample b) 6.8 wt.-% based on total cement weight   

     Both photocatalytic oxides convert NO when irradiated with light in the visible spectra region as can be seen from the data shown in the following table. As in Example 4 with UV irradiation, ozone is not produced during the reaction. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Sample 
                 % converted NO 
                 % converted NO 2   
                 % converted O 3   
               
               
                   
               
             
            
               
                 A 
                 7.9 
                 2.2 
                 0 
               
               
                 B 
                 6.2 
                 3.1 
                 0 
               
               
                   
               
            
           
         
       
     
     Example 6 
     5% of a photocatalytic iron oxide (23 wt.-% TiO 2  based on total pigment weight) has been incorporated into a silicate based paint (based on 28.25% water, 23% Consolref K, 38% inerts, 9% styrene acrylate) and applied on a concrete surface. Conversion of NO was measured in the standard method, and conversion plot is shown in  FIG. 10 .