Anatase TiO2 has attracted a lot of attention due to its applications as a photocatalyst in water and air treatment technologies. However, its large band gap energy (⁓3.2 eV) limits its application only to UV light. Also, anatase TiO2 suffers from high electron/hole recombination, which diminishes its photocatalytic activity. Therefore, different methods have been employed to decrease its band gap energy and reduce the recombination of the charge carriers. One of the methods is to incorporate impurities as dopants in its crystal lattice. Different metal and non-metal dopants have been studied for this aim. Among the different choices, Fe3+ has showed a great potential to improve the photocatalytic activity of TiO2 under visible light irradiation. Firstly, the d orbitals of Fe3+ interact with the 3d orbitals of Ti4+ generating intermediate band gap energy levels to facilitate excitation of electrons under visible light by a red shift in the absorption of light. Secondly, Fe3+ can interact with both electrons and holes to produce Fe2+ and Fe4+ trapping the charge carriers and reducing their recombination rate. Fe2+ and Fe4+ can release the electron and hole and revert back to the Fe3+. The released charge carriers migrate to the surface of the nanoparticles to initiate the photocatalytic reactions. However, it was found that the photocatalytic activity of Fe-TiO2 is not as high as expected. Therefore, in this research study I investigated the cause for its low photocatalytic activity and found methods to improve it. The Fe-TiO2 was synthesized using a facile sol-gel method and its structure and properties were characterized by different instrumental techniques. Using TEM and HRTEM an amorphous layer was seen on the surface of the nanoparticles. This layer characterized using XPS and EDX was composed of iron oxide layers. This layer was contaminating the surface of the nanoparticles where the photocatalytic reactions take place. Moreover, the contamination layer was acting as a recombination center for the electrons and holes. To the best of our knowledge, no previous study was conducted to investigate the effect of an iron oxide contamination layer on the photocatalytic activity of Fe-TiO2 nanoparticles. This layer was removed using a concentrated HCl solution confirmed using HRTEM and XPS. Also, using DRS it was shown that its removal does not effect the optical properties of the Fe-TiO2 confirming that the acid treatment process did not influence the doped Fe3+ in the TiO2 crystal lattice. The degradation of methelyne orange (MO), a representative pollutant, was increased from 25% to 98% under visible light irradiation. Also, in order to achieve the highest performance of the photocatalyst, it was necessary to study the parameters of the photocatalytic activity and the degradation efficiency. Therefore, experiments using a phenol solution, another representative pollutant, were conducted to investigate and optimize the effects of the catalyst load, reaction time, initial concentrating of the pollutant and pH. The degradation efficiency of the phenol solution was found to increase from 31% to 57% by the removal of the contamination layer and by controlling the pH of the solution. / Graduate

The study combined photoelectrocatalytic technology (PEC) with electrical glassfiber filter (EGF) to decompose volatile organic compounds (VOCs). External electrical voltage was applied to retard the recombination of electron-electron hole pairs and increase the surface temperature of the photocatalysts coated on the electrical glassfiber filter, which could further decompose VOCs more effectively via photoelectrocatalytic technology. Acetone was selected as the gasous pollutant for this particular study. A commercial TiO2 photocatalyst (AG-160) was coated on GFF via impregnation to decompose acetone in a batch PEC reactor. Operation parameters investigated in this study included acetone concentration (50~400 ppm), electrical voltage (0~6,500V), water content (0~20,000 ppm), reaction temperature (40¢J~80¢J).The incident UV light of 365 nm wavelength was irradiated by three 15-wat low pressure mercury lamps (£f=365 nm) placing above the batch PEC reactor. The TiO2-coated EGF was placed at the center of the batch PEC reactor. Acetone was injected into the reactor by a gasket syringe to conduct the PEC decomposition test. Acetone was analyzed quantitatively by a gas chromatography with a flame ionization detector (GC/FID). Finally, a Langmuir-Hinshelwood kinetic (L-H) model was proposed to simulate the PEC reaction rate of acetone. Experimental results showed that the size range of the self-produced nano-sized photocatalyst prepared by sol-gel was 35~50 nm. Three duplicate tests of PC and PEC degradation of acetone indicated that TiO2 was not deactivated during the PC and PCE reactions, hence TiO2 can be reused in the experiments. Results obtained from the PC and PEC degradation experiments indicated that the PEC reaction rate was higher than the PC reaction rate.The PEC reaction rate increased with applied electrical voltage, and the highest decomposition efficiency occurred at 6,500 V. Electrical field generated by the differences of electrical voltage can effectively enhance the oxidation capability of TiO2 since electron (e-) can be conducted to retard the recombination of electron and electron hole pairs. Both PC and PEC technologies could be used to decompose acetone. Among them, PEC had highter decomposition efficiency of acetone than PC up to 34%. Rsults obtained from the operation parameter tests reaveled that raising electrical voltage could enhance the decomposition efficiency of acetone only for electrical voltages above 2,000 V. However, the decomposition efficiency of acetone tended to level off as electrical voltage became higher. Zero-order reaction rate of the PEC reaction was observed for initial acetone concentration of 100~400 ppm, while the PEC reaction decreased gradually for initial acetone concentration reaction below 100 ppm. It revealed that the PEC reaction was pseudo ozero-order for initial acetone concentration of 100~400 ppm, and pseudo first-order reaction for acetone concentration below 100 ppm. Additionally, the PC reaction rate increased with temperature at 45-80¢J. However the PEC reaction rate increased with temperature at 45-60¢J, and decreased with temperature at 60-80¢J. An adsorptive competition between acetone and water molecules at the active sites over TiO2 surface caused either promotion or inhibition of TiO2 decomposition depending on moisture content . For the PC and PEC reactions, the optimum operating condition of water vapor concentration was 10,000 ppm, but inhibition occurred when the water vapor concentration increased up to 20,000 ppm. Finally, the Langmuir-Hinshelwood kinetic model was applied to investiage the influences of reaction temperature, initial concentration of acetone, and water content on the photoelectrocatalytic reaction rate of acetone. Model simulation results showed that photoelectrocatalytic reaction rate constant of acetone(kLH) and adsorptive equilibrium constant(KA) increased with electrical voltage and acetone initial concentration. This study sevealed that experimental and simulated results were in good agreement. Thus, PEC reaction rate of acetone on the surface of TiO2 can be also succesfully simulated by the L-H kinetic model.

This study combined photocatalytic technology with activated carbon cellulose-paper filter (ACCF) adsorption to decompose gaseous pollutants. Gaseous pollutants were initially adsorbed by activated carbon and could be further decomposed by photocatalytic technology. This study selected acetone (CH3COCH3) as gaseous pollutants. Two market available photocatalysts (photocatalysts¢¹and¢º) were coated on ACCF by impregnation to decompose acetone in a batch photocatlytic reactor. Operating parameters investigated in this study included initial acetone concentration (4.1~10.2 £gM), reaction temperature (40~70¢J), and water vapor (0~20 %). The incident UV light of 365 nm was irradiated by a 20-watt low-pressure mercury lamp placing above the batch photocatalytic reactor. The ACCF coated with TiO2 was placed at the center of the photocatalytic reactor. Acetone was injected into the reactor by a gasket syringe to conduct the photocatalytic tests. Reactants and products were analyzed quantitatively by a gas chromatography with an electron capture detector (GC/DCD) and a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer). Finally, a Langmiur-Hinshewood (L-H) kinetic model was proposed to describe the rate of photocatalytic reaction. Results obtained from the photocatalytic tests indicated that photocatalyst¢º was better than photocatalyst¢¹ for the decomposition of acetone. Experimental results indicated that the size range of self-produced TiO2 photocatalyst by sol-gel was 20~70 nm. The end products were mainly CO and CO2, which resulted in the mineralization ratio up to 98%. Results obtained from the operating parameter tests revealed that the increase of initial acetone concentration enhanced the amount of acetone adsorbed on ACCF, which however did not increase the reaction rate of acetone. Although the increase of reaction temperature could reduce the amount of acetone adsorbed on ACCF, the decomposition rate of acetone could be promoted, so as the yield rate and mineralization ratio of products (CO and CO2). The increase of water vapor could slightly decrease the amount of acetone adsorbed on ACCF. The competitive adsorption phenomenon between acetone and water molecules on active sites could decelerate the decomposion of acetone. Moreover, the ACCF would not be saturated since the adsorbed acetone could be further decomposed quickly by the photocatalysts, which made the TiO2/ACCF more effective on removing acetone and lasted longer than the conventional ACCF. Finally, a modified bimolecular Langmuir-Hinshelwood kinetic model was developed to investigate the influences of initial acetone concentration reaction, temperature, and relative humidity on the promotion and inhibition for the photocatalytic oxidation of acetone. The modified L-H kinetic model could successfully simulate the photocatalytic reaction rate of acetone. Thus, the reaction rate of acetone over TiO2/ACCF could be described by the modified L-H kinetic model.

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