Researches On Preparation Of N,Fe, H₃PW₁₂O₄₀ And CdS Dopping TiO₂ Composite Catalysts And Photocatalytic Elimination Of Gas Organic Pollutants

Toxic volatile organic pollutants in the living and working environment have serious impact on people's health and work efficiency. It is very meaningful job that toxic volatile organic pollutants are photocatalytic eliminated in the lower cost, lower energy consumption.(1) N-Fe doped TiO₂ catalysts are synthesized by sol-gel method. To activation temperature, activation time, iron and nitrogen doped quantity as influence factors design the orthogonal experiment plan. The ultraviolet catalytic elimination n-butanol is used as the probes experiment, screening high catalytic activity catalyst. The spectral properties and the morphology of the catalyst is systematically studied by FT-IR, TG-DTA, XPS, SEM, PL, nitrogen adsorption-desorption. The relationship between the intrinsic properties of the catalyst and its photocatalytic activity has been discussed. The results show that: under UV-irradiation , the composite catalysts doped with Fe3+ (0.15%), N (10%) and activated at 400℃for 3h demonstrate the highest activity. The main products are carbon dioxide and water, but when concentration of n-butanol is higher than 12.1g·m^-3, the organic by-product acetaldehyde is found in the process of photocatalytic eliminating n-butanol.The kinetic behaviors of the photocatalytical elimination of methanol, ethanol and acetone over the N-Fe doped TiO₂ catalysts have been studied. The results show that in the tested temperature range, the photocatalytical elimination reaction of methanol, ethanol, acetone are all conform to first order reaction. The apparent activation energy of methanol, ethanol, acetone are 50.817 kJ·mol^-1, 24.331 kJ·mol^-1 and 18.17kJ·mol^-1 respectively. Moreover, the methanol, ethanol, acetone can be completely mineralized without by-products. The research show that nitrogen and ferric expand the wavelength range of light response of titanium dioxide and increase its absorption intensity of visible light, which make it has photocatalytical activity under visible light. When the temperature is 66℃, acetone with initial concentration of 0.76g·m^-3 and flow rate of 10.0 mL·min^-1 can be completely eliminated over 0.15g catalysts under the visible light, but only about sustainable 10h. With the increase of acetone concentration in the process of photocatalytic reaction, the instantaneous eliminated amount of the photocatalytic elimination reaction will has a maximum value, which shows that the photocatalytic activity of catalysis is influenced by the substrate concentration in a certain degree. (2) The N-Fe-H3PW12O40 doped TiO₂ catalysts are prepared on the basis of the N-Fe co-doped TiO₂ catalysts. The visible photocatalytical activity of the catalyst are observed using acetone as the substrate. The results show that visible light photocatalytical activity of the catalysts (H3PW12O40 0.05%) are the best. The catalyst has no photocatalytic activity under UV as the introduction of H3PW12O40, but the photocatalytic activity visible light has increased. Phosphotungstic acid decreases the required photocatalytic reaction temperature. Under the same other conditions, 1.10 g·m^-3 acetone can be mineralized completely at the reaction temperature 40℃, but the catalysts activity can only maintain about 7h. Results of the characterization of intrinsic properties of the catalyst indicate that by introduction of phosphorus acid, the surface characteristics of the catalyst is changed, the catalyst surface area is significantly increased and the adsorption performance is enhanced. The experimental results show that the dominant mechanism of the photocatalytic elimination acetone over this catalyst is the indirect oxidation mechanism.(3) CdS doped TiO₂ mesoporous catalysts were prepared by hydrothermal. The influence factors of photocatalytic activity in the process of catalysts preparation are investigated by orthogonal experiments. The impact factor order is: CTAB amount > the intermingled quantity of CdS > calcination temperature > hydrothermal temperature > hydrothermal time. Various characterization results show that the catalysts have small particle size (only 6⁷nm), the large surface area and strong adsorption capacity. Photocatalysis activity of acetone and methanol are tested, the results show that the elimination activity of acetone increase significantly under the UV light, and the catalyst can keep it's its activity even at large substrates concentration. But compare with the pure TiO₂, the methanol photocatalytic eliminated activity of the CdS doped TiO₂ catalyst is not significantly increaseed. This phenomenon shows that the interaction force between acetone and catalyst surface is different from which between methanol and catalyst surface. As the existence of this difference, the maximum eliminated concentration of methanol is far less than that of acetone. The tests show that the the catalytic activity of TiO₂ haven't been improved by CdS dopping, under the visible light.