Effects of Silver on the Photocatalytic Degradation of Gaseous Isopropanol

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1 See discussions, stats, and author profiles for this publication at: Effects of Silver on the Photocatalytic Degradation of Gaseous Isopropanol Article in Water Air and Soil Pollution January 2009 Impact Factor: 1.55 DOI: /s x CITATIONS 11 READS 51 5 authors, including: Chih-Ming Ma St. Mary's Junior College of Medicine, N 56 PUBLICATIONS 256 CITATIONS Young Ku National Taiwan University of Science 158 PUBLICATIONS 3,037 CITATIONS SEE PROFILE SEE PROFILE Yu-Lin Kuo National Taiwan University of Science 85 PUBLICATIONS 660 CITATIONS Yiang-Chen Chou Industrial Technology Research Institute 17 PUBLICATIONS 143 CITATIONS SEE PROFILE SEE PROFILE Available from: Yu-Lin Kuo Retrieved on: 12 May 2016

2 Water Air Soil Pollut (2009) 197: DOI /s x Effects of Silver on the Photocatalytic Degradation of Gaseous Isopropanol Chih-Ming Ma & Young Ku & Yu-Lin Kuo & Yiang-Chen Chou & Fu-Tien Jeng Received: 1 April 2008 / Accepted: 20 July 2008 / Published online: 23 August 2008 # Springer Science + Business Media B.V Abstract The decomposition of gaseous isopropanol (IPA) by UV/TiO 2 process in an annular photoreactor was studied under various conditions such as UV light intensity and inlet IPA concentrations. In order to impede the rapid electron/hole recombination during photoreaction, the Ag deposited on TiO 2 photocatalysts were prepared by a photodeposition process. This study was aimed at applying the photocatalytic oxidation using the Ag/TiO 2 and pure TiO 2 catalysts to remove gaseous IPA. The PL analyses indicated that the silver C.-M. Ma Department of Cosmetic Application & Management, St. Mary s Medicine Nursing and Management College, 100, Lane 265, San-shing Road, Section 2, San-shing Shiang, Yi-lan 266, Taiwan Y. Ku (*) : Y.-C. Chou Department of Chemical Engineering, National Taiwan University of Science and Technology, 43, Keelung Road, Section 4, Taipei 106, Taiwan ku508@mail.ntust.edu.tw Y.-L. Kuo Department of Materials Engineering, Tatung University, 40, Zhongshan North Road, Section 3, Taipei 104, Taiwan F.-T. Jeng The Graduate Institute of Environmental Engineering, National Taiwan University, 71, Chou-Shan Road, Taipei 106, Taiwan on the surface of TiO 2 could inhibit the electron/holes recombination. For experiments conducted with gaseous IPA under UV light irradiation, the photocatalytic activity of Ag deposited TiO 2 surface was significantly superior to that of TiO 2 only ones. Keywords Photocatalysis. Silver. Titanium dioxide. Isopropanol 1 Introduction Volatile organic compounds (VOCs) are typical gaseous emissions from numerous industries and pose various hazards for human health and environment (Chin et al. 2006). Many technologies currently used for the treatment of VOCs, such as carbon adsorption or wet scrubber, merely transfer VOCs from the gas phase to another phase. In recent years, photocatalytic technologies are studied and reported to be effective on oxidizing several VOCs at mild conditions. (Chin et al. 2006; Mohseni and David 2003; Doucet et al. 2006; Xu and Raftery 2001; Einaga et al. 2004; Strini et al. 2005). However, the practical application of photocatalytic processes for the treatment of volatile organic pollutants in gaseous streams is hindered by the development of effective photocatalysts. Anatase form of titanium dioxide (TiO 2 ) is the most frequent studied photocatalyst for environmental applications because it is stable, non-toxic and is capable of degrading a wide range of organic pollutants. Al-

3 314 Water Air Soil Pollut (2009) 197: though the quantum yields of several applications of UV/TiO 2 process were demonstrated to be higher than most other photocatalysts (Diebold 2003), the quantum efficiency of TiO 2 catalyst is still hindered primarily by the electrons/hole recombination effects. Lately, several researchers (Li and Li 2002; Sano et al. 2004; Qi et al. 2005; Zhang et al. 2005) reported that modifications of the TiO 2 surface with noble metal, such as Pt (Li and Li 2002; Sano et al. 2004), Fe (Qi et al. 2005), Ag (Zhang et al. 2005; Rengaraj and Li 2006; Coleman et al. 2005; Liu et al. 2004; Kato et al. 2005), Au and Pd (Sakthivel et al. 2004), are the successful ways to enhance the photocatalytic activity of TiO 2 and increase the quantum yield. Silver is particularly suitable for industrial applications due to its relatively low cost and ease of preparation rather than other rare metals. Several theories have been presented in the literature to explain that the metallic particles on the TiO 2 surface could accumulate the electrons resulting in a better charge separation (Li and Li 2002; Qi et al. 2005, Rengaraj and Li 2006; Coleman et al. 2005; Liu et al. 2004). However, metal deposition usually causes some new problems which result in the decreased photocatalytic activity such like that metal deposits might occupy the active sites to reduce surface activity (Coleman et al. 2005). Another problem is that metallic particles on the TiO 2 surface are large enough to become new recombination centers of electrons/hole due to the decrease of electron transfer rate to the oxidant (Zhang et al. 2005; Rengaraj and Li 2006; Sakthivel et al. 2004). The formations of byproducts during the reaction were often observed due to low degradation ratio of intermediate compounds formed by the partial oxidation of original VOCs. Therefore, enhancement of the degradation of intermediates is required for ultimate mineralization of VOCs, but few literatures were mentioned. This study was aimed at applying the photocatalytic oxidation using the Ag/TiO 2 and pure TiO 2 catalysts to decompose gaseous isopropanol (IPA); IPA is a major contaminant in indoor air and industrial air streams (Xu and Raftery 2001). The kinetics of photocatalytic processes for the treatment of volatile organic pollutants in gaseous streams was investigated in detail with changing various experimental parameters and the related reaction mechanisms are discussed. 2 Experimental The photoreactor system employed in this research consisted of a 20 cm long plug flow annular photoreactor was made exclusively of Pyrex glass with an effective volume of 1.13 L. The photoreactor consisted of one 1.5-cm diameter quartz tube housing a GTE F15T8/BLB lamp (365 nm) used in this study flow meter 2. gas mixer 3. valve 4. filter and dryer 5. valve 6. flow controller 7. VOC vaporizer 8. H 2 O vaporizer 9. mass flow meter 10. thermometer 11. sampling valve 12. photoreactor 13. GC/FID 14. cooling system 15.water bath Fig. 1 Schematic diagram of an annular photoreactor

4 Water Air Soil Pollut (2009) 197: was adjusted by a variable voltage transformer and was detected by a Spectroline model DRC-100X digital radiometer with a DIX-365 radiation sensor. The schematic diagram of the photoreactor system employed in this research is shown in Fig. 1. Chemicals used in this study were of analytical grade without further purification. The isopropanol-laden air stream was prepared by extracting isopropanol vapor by dry air from an isothermal isopropanol solventcontaining bottle. The isopropanol-laden air stream was mixed with a humidity-containing air stream and oxygen gas in a gas mixer to maintain the level of humidity and oxygen concentration. The mixed air stream was then directed into the pre-warmed tubular photocatalytic reactor for the study of isopropanol decomposition. Gas samples were taken for further analyses after the flow rate, pressure, and humidity of the reactor system were steady. The operating time required to reach the steady state was usually about 45 min. The temperature of the photoreactor system was maintained constant at 37NC. A China Chromatography model 8700F GC equipped with a flame ionization detector (FID) was used for analyzing the inlet and effluent isopropanol concentrationsin the air streams. The concentrations of CO 2 in the effluent streams were determined with an O.I.C. nondispersed infrared (NDIR) detector. P-25(Degussa) and TPX-85(Kon Corporation) were commercial samples, P-25 TiO 2 powder was employed in this study as received without further treatment. Half liter of aqueous solution containing 160 g of TiO 2 and 0.02 g of dioctyl sulfosuccinate (used as dispersing agent) was held in a 1-L beaker and was then sonicated for 8 h. A quartz tube was then impregnated in the solution for about 1 min before it was took out and air-dried. The impregnation process could be repeated for several times to increase the amount of TiO 2 coated on the surface of the quartz tube. The quartz tube was then contained in a photoreactor to house an UV lamp. TPX-85 TiO 2 solution also was employed in this study as received without further treatment. A quartz tube was then impregnated in the solution in the same impregnation process. The Ag deposited on TiO 2 catalysts have been prepared by photoimpregnation according to the following technique. Half liter of aqueous solution containing 160 g P-25 of TiO 2 particles was held in a 1-liter beaker, and was then purged with nitrogen to remove dissolved oxygen while stirred by a magnetic stirrer. Predetermined amount of AgNO 3 were dissolved in 20 ml methanol, the methanol solution was then mixed with the aqueous solution containing TiO 2. After the mixed solution was irradiated with a UV light using a GTE F15T8/BLB lamp at energy intensity of 13.3 W cm 2 for 8 h, about 0.02 g L 1 dioctyl sulfosuccinate used as dispersing agent was subsequently put into the mixed solution and was stirred by a sonicator for more than 8 h. A quartz tube was then impregnated in the mixed solution for about 1 min before it was took out and air-dried. The coated quartz tube was then put in an oven isothermally at 300 C for 2 h. The amount of catalyst coated was determined by measuring the weight difference of the quartz tube before and after coating. The morphology and the specific BET surface area of the TiO 2 was determined by a Rigaku RTP 300 X-ray diffractometer (XRD) and a Micromeritics ASAP 2000 analyzer, respectively. The light absorbance of the coatings was determined by a Cray-300 UV/VIS spectrophotometer. The impregnation process could be repeated for several times to increase the amount of catalyst coated. To study the recombination of electrons/holes in the photocatalysts, the photoluminescence (Fluorscence lifetime system TAU-3, PL) emission spectra of the samples were measured. 3 Results and Discussion Peaks marked A and R showns in Fig. 2 indicated the X-ray diffraction patterns of P-25 TiO 2 and Ag- Intensity A(101) R(110) Ag 2 O A R A R Ag 2 O Fig. 2 X-ray diffraction patterns of Ag/TiO2 catalyst at different Ag loadings: a TiO 2 (P25), b 0.04% Ag/TiO 2, c 0.5% Ag/TiO 2, d 1.0% Ag/TiO 2 2θ Ag A A (d) (c) (b) (a)

5 316 Water Air Soil Pollut (2009) 197: Table 1 Surface area and crystal size of TiO 2 (P25) and Ag deposited on TiO 2 Material Actual loading of Ag (wt.%) Crystal size of anatase (nm) Crystal size of rutile (nm) Surface area (m 2 g 1 ) TiO wt.% Ag/TiO wt.% Ag/TiO wt.%ag/tio Ag loading was determined by AA. deposited TiO 2 catalysts corresponding to anatase and rutile phases, respectively. As shown in the curve (b) of Fig. 2 for 0.04% Ag/TiO 2, the presence of TiO 2 in the anatase and rutile forms was detected. However, peaks of Ag 2 O found in the curves (c) and (d) indicate that increasing the Ag amount deposited on TiO 2 enhanced the peak intensity of Ag 2 O. The surface area of Ag/TiO 2 from the Brunauer Emmett Teller surface area measurements (BET) only slightly increases as shown in Table 1. On the basis of the XRD results (Table 1), the crystal sizes (D) of Ag/ TiO 2 powder can also be estimated using the Scherrer equation (Warren 1990): D ¼ Kl B cos q ð1þ where D is the crystal size, l is the X-ray wavelength corresponding to Cu K α radiation, is the diffraction angle, and B is full width half maximum (FWHM) of diffraction peak at 2. K is the Scherrer constant as The crystal sizes (D) of all samples indicate that the anatase crystal size slightly decreased from 19.2 to 15.8 nm and the rutile crystal size slightly decreased from 28.6 to 26.2 nm. The photoactivity of Ag coated TiO 2 surface was apparently affected via the covalently anchored property such as of lattice parameters and the unit cell volume of Ag/TiO 2. The photodecomposition of gaseous IPA by UV/ TiO 2 process for experiments conducted in reactors coated with various catalysts under various inlet IPA concentrations between 140 and 520 ppmv at a residence time of s, light intensity of 3.09 mw cm 2, gas flow rate of 400 ml min 1, relative humidity 10% are presented in Figs. 3 and 4. It was found that increasing the inlet IPA concentration slightly decreased the decomposition and mineralization of IPA. The decomposition efficiencies of IPA in reactor coated with P-25 TiO 2 decreased from 71% (for experiments conducted at 140 ppmv IPA) to 48% (for experiments conducted at 520 ppmv IPA), and the mineralization rates of IPA decreased from 56% to 21%. Similar experimental results were observed by other researcher (Obee 1996) and our previous study (Ku et al. 2001) for the decomposition of gaseous toluene and trichloroethylene by UV/TiO 2 process, the observed experimental results were possibly owing to the limited active sites on the TiO 2 surface available for the adsorption of IPA. Light intensity was also an important parameter that influenced the decomposition of pollutants by photocatalytic processes (Chin et al. 2006). An increase of light intensity may increase the number of photons striking on the surface of photocatalyst to form more electrons and holes. Figs. 5 and 6 depict C/C P-25 TiO % Ag/TiO2 0.5% Ag/TiO2 1.0% Ag/TiO IPA conc. (ppmv) Fig. 3 Effect of initial concentration on the IPA decomposition by photocatalytic oxidation at various photocatalysts: 3.09 light intensity mw cm 2, 400 ml min 1 flow rate, 10% humidity

6 Water Air Soil Pollut (2009) 197: mineralization rates P-25 TiO % Ag/TiO 2 0.5% Ag/TiO 2 1.0% Ag/TiO IPA conc. (ppmv) Fig. 4 Effect of initial concentration on the mineralization rates of IPA by photocatalytic oxidation at various photocatalysts: 3.09 light intensity mw cm 2, 400 ml min 1 flow rate, 10% humidity the effect of light intensity on the IPA decomposition and mineralization by UV/TiO 2 process coated with various catalysts. The decomposition rates of IPA were increased almost linearly with light intensity in the range of 1.43 to 4.08 mw cm 2 with various catalysts loadings. But for light intensity higher than 3.09 mw cm 2, the effect of light intensity on the decomposition rate of IPA was retarded. This phenomenon implies that the more photons are generated to excite the electron-hole pair with the increase of light intensity and then further improve the decomposition rate. However, the limited amount of activity site on the surface of photocatalyst restrains the enhancement of decomposition rate even through the more photons are generated under the light intensity higher than 3.09 mw cm 2. Furthermore, the mineralization rate of IPA was increased while enhancing the UV light intensity as show on Fig. 6. A possible explanation is that the higher light intensity applied was excessive in comparison with the amount of various catalysts and therefore could not generate more photons on the surface of TiO 2 particles to initiate the decomposition of IPA. Furthermore, Figs. 3, 4, 5 and 6 shown the photocatalytic performance of TiO 2 films can be improved by the addition of Ag and the decomposition rates are larger than TiO 2 -only fims. Similar experimental results were observed by other researchers for the decomposition of aqueous trichlorophenol (Rengaraj and Li 2006), aqueous phenol (Liu et al. 2004), gaseous hydrogen sulfide and methylmercaptan (Kato et al. 2005) by photocatalytic process. In this system, the experimental results indicated that the deposition of 0.04% Ag on TiO 2 film shows the C/C P-25 TiO % Ag/TiO 2 0.5% Ag/TiO 2 1.0% Ag/TiO2 mineralization rates P-25 TiO % Ag/TiO 2 0.5% Ag/TiO 2 1.0% Ag/TiO UV light intensity (mw cm ) UV light intensity (mw cm ) Fig. 5 Effect of UV light intensity on the IPA decomposition by photocatalytic oxidation at various photocatalysts: 280 ppmv IPA, 400 ml min 1 flow rate, 10% humidity Fig. 6 Effect of UV light intensity on the mineralization rates of IPA by photocatalytic oxidation at various photocatalysts: 280 ppmv IPA, 400 ml min 1 flow rate, 10% humidity

7 318 Water Air Soil Pollut (2009) 197: highest photocatalytic activity among all the composition investigated. The decomposition and mineralization rates are 0.04% Ag/TiO 2 >0.5% Ag/TiO 2 >1% Ag/TiO 2 >pure TiO 2. That is because that the silver deposited on TiO 2 film acts the role of scavenger to remove the electrons that are generated by the photocatalytic process; therefore, the probability of recombination of electrons and holes can be decreased. However, the excess silver results in the decrease of photocatalytic activity of TiO 2 because the excess silver occupies the activity site of TiO 2 to reduce its activity. It has been reported that the lower PL intensity indicates the lower recombination rate of electron-holes under irradiation (Li and Li 2002; Jing et al. 2006). In order to investigate the efficiency of charge carrier trapping, immigration and transfer and to realize the behavior of electron-hole pairs in all the coatings, the photoluminescence emission spectra at room temperature was conducted in Fig. 7, which shows the PL emission spectra of TiO 2 and Ag TiO 2 thin films in the wavelength range of ( nm). In Fig. 6a, several peaks appeared at 3.348, 3.042, 2.832, 2.250, and ev and the PL emission peaks of Ag TiO 2 and pure TiO 2 coatings also show similar positions for most peaks. In addition, the PL intensity of the pure TiO 2 coating is apparently greater than those of the Ag TiO 2 coatings. It implies that the Agdoped TiO 2 exhibits the higher activity compared with P-25 TiO 2. Moreover, Figure 8 represents the UV/VIS absorption spectra of the TiO 2 thin films and Ag-modified TiO 2 thin films in the range of nm. Similar patterns of all coatings were observed in the region below 400 nm which also Intensity (a.u.) (a) (b) (c) (d) Visible range Photon Energy (ev) UV range Fig. 7 PL emission spectra of the photocatalyst in the range of nm at 300 K: a TiO 2 (P25), b 0.04 wt.% Ag/TiO 2, c 0.50 wt.% Ag/TiO 2, and d 1.00 wt.% Ag/TiO 2 Absorptiom represent no apparent difference on Ag TiO 2 coatings in comparison to the pure TiO 2 coatings. The Ag and Ag 2 O deposited on the surface of TiO 2 can significantly absorb visible light. The energy band gap values can be estimated by using the Kabelka Munk function (Sreethawong et al. 2005); the calculated band gap values slightly decrease than those of the Ag TiO 2 coatings(3.351 ev at pure TiO 2 coating and ev at 1.0 wt.% Ag TiO 2 coating), which is the other evidence responsible for the Ag-TiO 2 exhibits higher activity than P-25 TiO 2. The decomposition rate of IPA, R A, of the condition at constant relative humidity and oxygen concentration can be expressed by a Langmuir Hinshelwood rate expression as shown below (Mohseni and David 2003; Wang et al. 2005): R A ¼ k 0 I n where R A Wavelength (nm) P-25 TiO % Ag/TiO 2 0.5% Ag/TiO 2 1.0% Ag/TiO 2 Fig. 8 Wavelength distribution of FL15D-T25 fluorescent lamp and absorbance UV-Vis spectra of the photocatalysts in the range of nm K C A 1 þ K C A ð2þ the decomposition rate of isopropyl alcohol (ppmv min 1 ) C A concentration of gaseous IPA in air stream (ppmv) k 0 reaction rate constant (ppmv 1 cm 2 s 1 ) K adsorption equilibrium constant of IPA on TiO 2 particle (ppmv 1 )

8 Water Air Soil Pollut (2009) 197: Table 2 Reaction rate constant of decomposition of IPA, adsorption equilibrium constant of IPA under UV light irradiation, and the order of UV light intensity Material I UV light intensity (mw cm 2 ) n reaction order with respect to applied UV light intensity The mass conservation of reacting species was concerned base on the equation of continuity for isopropyl alcohol in cylindrical coordinate, that where D A þ v þ v q ¼ D AB 1 r A þ v þ 2 C A r 2 C 2 þ R A the binary diffusivity of isopropyl alcohol in air, L 2 min 1 ð3þ According to the author s previous study (Ku et al. 2001), the following assumptions are used for simplicity: the reactor used is an ideal plug-flow reactor and operated at steady state, the results discussed in the previous sections for experiments can be correlated by a dual-site, and the isopropyl alcohol properties, such as density (ρ) and diffusivity (D AB ), in the photoreactor system can be seen as constant values. Since this system is assumed to be operated under steady state and the diffusion term in Eq. 3 is considered to be negligible, the Eq. 3 can be further simplified as follow: v ¼ R A ð4þ where t k 0 (ppmv 1 cm 2 s 1 ) K (ppmv 1 ) TiO wt.% Ag/P-25 TiO wt.% Ag/ P-25 TiO wt.%ag/ P-25 TiO the retention time of photoreactor (min) n The Langmuir Hinshelwood type rate equation can be expresses as follow by connecting the Eqs. 2 and 4 to taking into consideration the effects of IPA and light ¼ R A ¼ k 0 I n KC A ð5þ 1 þ KC A The parameters, such as k 0, K and n can be obtained by regression after inserting the experimental results under various initial concentrations of IPA and light intensities. The above rate equation was solved to describe the decomposition behavior of IPA in the annular photoreactor and summarized in Table 2. Fairly good agreement was found between the experimental results conducted with different photocatalysts and the calculated values as shown in Fig. 9. The major role of silver or silver oxide incorporated on TiO 2 could be treated as a scavenger to decrease the probability of electron-hole recombination because the electrons that exist in conduction band can be captured by silver or silver oxide easily. However, silver or silver oxide coating usually causes some new C/C Retention time, sec Fig. 9 Effect of retention times (τ) on the IPA decomposition by photocatalytic oxidation at various photocatalysts: 280 ppmv IPA, 400 ml min 1 flow rate, 10% humidity: a, c, e, and g were simulation values at TiO 2 (P25), 0.04 wt.% Ag/ TiO 2, 0.50 wt.% Ag/TiO 2, and 1.00 wt.% Ag/TiO2: b, d, f and h were experimental result at TiO 2 (P25), 0.04 wt.% Ag/TiO 2, 0.50 wt.% Ag/TiO 2, and 1.00 wt.% Ag/TiO 2 (a) (b) (c) (d) (e) (f) (g) (h)

9 320 Water Air Soil Pollut (2009) 197: problems which result in the decreased photocatalytic activity of TiO 2 such as competition occupancy of silver or silver oxide deposits on TiO 2 surface to reduce its activity. Another problem is that silver or silver oxide on the TiO 2 surface is large enough to become new recombination centers of electrons and holes due to the decrease of electron transfer rate to the oxidant. The order of UV light intensity, adsorption equilibrium constant (Table 2) helps to define the reasons. The comparison of the order of UV light intensity shows that 1% Ag TiO 2 is slight increase than 0.5% Ag TiO 2. In addition, Figure 7 shows that the PL spectrum of the 0.04% Ag thin films is more intense than that of 0.5% and 1%Ag-doped TiO 2 thin films, 1%Ag-doped TiO 2 is slight decsrease than 0.5% Ag-doped TiO 2. It could be concluded that the Ag particles deposited on the TiO 2 surface might become new recombination centers of photogenerated electrons and holes, resulting in a decrease in photocatalytic ability. Furthermore, It is very clear that the adsorption equilibrium constant of IPA on photocatalyst is pure P-25 TiO 2 >0.04% Ag/TiO 2 > 0.5% Ag/TiO 2 > 1% Ag/TiO 2. It can be explained that Ag is the coverage and occupation of some semiconductor surfaces, causing the decrease the adsorption equilibrium constant, decreasing the photocatalytic ability. 4 Conclusions In the present work, enhancements of the photocatalytic activity of TiO 2 materials by deposition of silver have been achieved. The experimental results indicated that the deposition of 0.04% Ag on TiO 2 film shows the highest photocatalytic activity among all the composition investigated; specifically, the reaction rate constant of IPA photodegradation using the 0.04% Ag/TiO 2 was 2.0 times than that of using the pure TiO 2. Furthermore, the experimental results demonstrated that the TiO 2 doped with Ag has a significant absorption of visible light and a lower intensity of PL emission than pure P-25 TiO 2. According to these observations, we could conclude that silver particles on the surface of TiO 2 promote the better charge separation and less recombination, the optical absorption enhanced significantly in the visible light region owing to the presence of Ag in comparison to pure TiO 2. Above the 0.04% Ag loading, the experimental results approved that silver particles can also act as recombination centre, coverage and occupation of catalysts surfaces, resulting in a decrease the photocatalytic ability. In addition, experimental results obtained in this study can be satisfactorily described by the developed dual-site Langmuir Hinshelwood kinetic model. Acknowledgements This research was supported by Grant NSC E from the National Science Council, Taiwan, Republic of China References Chin, P., Yang, L. P., & Ollis, D. F. (2006). Formaldehyde removal from air via a rotating adsorbent combined with a photocatalyst reactor: Kinetic modeling. Journal of Catalysis, 237, doi: /j.jcat Coleman, H. M., Chiang, K., & Amal, R. (2005). Bactericidal effects of titanium dioxide-based photocatalysts. Chemical Engineering Journal, 113, Diebold, U. (2003). The surface science of titanium dioxide. Surface Science Reports, 48, doi: /s (02) Doucet, N., Bocquillon, F., Zahraa, O., & Bouchy, M. (2006). Kinetics of photocatalytic VOCs abatement in a standardized reactor. Chemosphere, 65, doi: /j. chemosphere Einaga, H., Ibusuki, T., & Futamura, S. (2004). Improvement of Catalyst Durability by Deposition of Rh on TiO 2 in Photooxidation of Aromatic Compounds. Environmental Science & Technology, 38, doi: / es034336v. Jing, L. Q., Qu, Y. C., Wang, B. Q., Li, S. D., Jiang, B. J., Yang, L. B., et al. (2006). Review of photoluminescence performance of nano-sized semiconductor materials and its relationships with photocatalytic activity. Solar Energy Materials and Solar Cells, 90, doi: /j. solmat Kato, S., Hirano, Y., Iwata, M., Sano, T., Takeuchi, K., & Matsuzawa, S. (2005). Photocatalytic degradation of gaseous sulfur compounds by silver-deposited titanium dioxide. Applied Catalysis. B, Environmental, 57, Ku, Y., Ma, C. M., & Shen, Y. S. (2001). Decomposition of gaseous trichloroethylene in a photoreactor with TiO 2 - coated nonwoven fiber textile. Applied Catalysis. B, Environmental, 34, Li, F. B., & Li, X. Z. (2002). The Enhancement of Photodegradation Efficiency using Pt-TiO 2 Catalyst. Chemosphere, 48, doi: /s (02) Liu, S. X., Qu, Z. P., Han, X. W., & Suna, C. L. (2004). A mechanism for enhanced photocatalytic activity of silverloaded titanium dioxide. Catalysis Today, 95, doi: /j.cattod

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