The Experimental Research On The Degradation Of Indoor Formaldehyde By Absorption-Photocatalytic Of Co-doped TiO₂/ACF Composite Material

"Indoor air pollution" marked the third pollution period has come. Nowadays, the indoor air pollution brought public attention significantly, especially the pollution of formaldehyde. Photocatalytic oxidation technology could be considered as a great potential method for indoor air purification. However, there were two important problems: The high recombination rate of photo-induced carriers and the low rate of sunlight utilization. The researchers had combined photocatalytic technology with activated carbon adsorption technology, they discoverded that the degradation efficiency was increased, but the united technology remained limited adsorption capacity, lowcatalytic activity and so on. In order to make breakthrough in the two fields, this theme mainly researched on modified TiO₂/ACF, then adopted in formaldehyde pollution control. Here were the main research contents.This theme firstly discussed the influence factors of ACF adsorption properties, such as thickness, adsorption time, temperature, humidity and so on, then modified ACF by oxidant, groups including N, NaOH, the adsorption properties were evaluated by formaldehyde removing rate; pure nanometer TiO₂ powder, transition metal and rare earth nanometer co-doped TiO₂ powder and rare earth co-doped TiO₂ powder were respectively prepared by sol-gel method, modified TiO₂/ACF by coupling method, discussed the influence factors such as calcination temperature, light and so on, according to the degradation rate of formaldehyde, selected the best TiO₂/ACF composite photocatalyst, and then characterized it by X-ray diffraction (XRD); the best TiO₂ and ACF were modified by oxidant, groups including N, NaOH, the modified co-doped TiO₂/ACF composite photocatalyst was prepared by coupling method, and the adsorption-photocatalytic property was evaluated by the degradation rate of formaldehyde, meanwhile, the formaldehyde removing rate of ACF and the formaldehyde degradation rate of the modified co-doped TiO₂/ACF composite photocatalyst were compared.The results indicated that:①The adsorption ability of 4mm ACF was the best; ACF absorbed formaldehyde very soon, the adsorption ability was very strong in the first 30 minutes and then it reached adsorption equilibrium in the later 60 minutes. While the temperature was 23±1℃and the humidity was 50±2%, the adsorption removal rate of formaldehyde reached the upper limit, was 13.11%.②The absorption efficiency made by ACF, which was modified by NaOH, was better than both the ACF modified by groups including N and the ACF modified by oxidant. The removal rate to formaldehyde of the ACF modified by 1.0mol/L sulfuric acid, the 1.0mol/L nitric acid, the 25% ammonium carbonate and the 0.5mol/L NaOH were 16.67%, 17.78%, 19%, 20%.③The photocatalytic activity of the co-doped TiO₂ was mainly affected by factors such as doping content,doping ratio and calcinate temperature.1)When the co-doping amount (in molar ratio) for Fe and Ce was n(Fe):n(Ce):n(TiO₂)=0.1%:1%:1 and the temperature of heat treatment was 500℃. Under UV light and 2 hours, Fe-Ce-TiO₂/ACF's degradation efficiency to formaldehyde was 58.67%, higher than Fe-TiO₂/ACF's 51.11%,Ce- TiO₂/ACF's 49.78% and much higher than pure TiO₂/ACF's 39% and ACF0(the pretreatment ACF)'s 13.11%. When under the visible light, the Fe-Ce-TiO₂/ACF's degradation efficiency to formaldehyde was 32.33%, higher than Fe-TiO₂/ACF's 23.33%,Ce-TiO₂/ACF's 25.56% and much higher than pure TiO₂/ACF's 17.78% and ACF0's 13.11%.2)When the co-doping amount for Fe-La was n(Fe):n(La):n(TiO₂)=0.1%:0.2%:1 and the temperature of heat treatment was 500℃. Under UV light and 2 hours, Fe-La-TiO₂/ACF's degradation efficiency to formaldehyde was 59.56%, higher than Fe-TiO₂/ACF's 51.11%,La-TiO₂/ACF's 50% and much higher than pure TiO₂/ACF's 39% and ACF0's 13.11%. When under the visible light, the Fe-La-TiO₂/ACF's degradation efficiency to formaldehyde was 32.67%, higher than Fe-TiO₂/ACF's 23.33%,La-TiO₂/ACF's 26.67% and much higher than pure TiO₂/ACF's 17.78% and ACF0's 13.11%.3)When the co-doping amount for La-Ce was n(La):n(Ce):n(TiO₂)=0.2%:0.1%:1 and the temperature of heat treatment was 600℃. Under UV light and 2 hours, La-Ce-TiO₂/ACF's degradation efficiency to formaldehyde was 62.22%, higher than La-TiO₂/ACF's 50%,Ce-TiO₂/ACF's 49% and much higher than pure TiO₂/ACF's 39% and ACF0's 13.11%. When under the visible light, the La-Ce-TiO₂/ACF's degradation efficiency to formaldehyde was 33.33%, higher than La-TiO₂/ACF's 26.67%,Ce-TiO₂/ACF's 25.56% and much higher than pure TiO₂/ACF's 17.78% and ACF0's 13.11%.④Modified by sulfuric acid, nitric acid, 25% ammonia waters, hydrochloric acid hydrogen amine, ammonium carbonate and NaOH, the La and Ce co-doped TiO₂/ACF had the varying degree enhancement to the formaldehyde degeneration rate, respectively wais 65%, 65.5%, 66%, 66.3%, 66.67% and 63%, higher than the unmodified TiO₂/ACF's 60%. The modified rare-earth element compound altogether doped TiO₂/ACF, the co-doping La and Ce rare-earth elements, the adsorption and the photochemical catalysis showed synergistic effect, the modifications were advantageous to adsorption, and also advantageous to photocatalytic.⑤The XRD test showed that the prepared La and Ce co-doped TiO₂ was mostly presented to be anatase. The diameter of particals were pretty small and well-distributed, the diameter of particals was about 18.1nm.⑥The co-doped TiO₂ showed stronger activities than single metal doped TiO₂ and undoped TiO₂. And the La and Ce co-doped TiO₂ showed the strongest activities. Co-doping of La and Ce restrained the growth of the grains, caused the smaller particle size, increased the surface area, caused the distortion and expansion of TiO₂ lattice, The co-doping of La and Ce did not showed a inhibition effect, and showed synergistic effect for photocatalytic activity of TiO₂, reduceed the composite chance of electronic and cavitation, and the co-doped TiO₂ showed higher photocatalytic activity.