Study On Photocatalysis To Decompose The Formaldehyde Of Indoor Pollution

As the economic development and the life standard improvement, indoor pollution has been paid more attention. Formaldehyde which is called the first "killer" is one of the most serious and familiar pollutants in indoor pollution, so it should be paid more attention and studied especially.TiO₂ is a kind of n-type semiconductor material, with strong oxidizing property and reducing property. It uses the O₂ in the air as oxidant directly and the reaction condition is warm (normal temperature and press). Because of its high activity, it can oxidize the most of organic and inorganic contaminant, and decompose them into harmless material, such as CO₂, H₂O etc..In this study, the method of TiCl₄ hydrolyze was used to prepare the nanopowder TiO₂. In the reaction system, the concentration of TiCl₄ was 1.1mol/L, Ti⁴⁺/H⁺= 5, Ti⁴⁺/SO₄^2-= 1/2, heating-up to 95℃and heat preservation for one hour, regulating PH with stronger ammonia water, ageing and filtering when the thin and small precipitate existed, drying and calcining.In order to make full use of the photochemical catalysis activity of TiO₂, the TiO₂ was loaded on the glass tube. In order to improve the photochemical catalysis activity of TiO₂, the TiO₂ was complexed with activated carbon so as to combine the photochemical catalysis and adsorption. The common glass tube was used as supporter of photocatalyst. The photocatalyst was loaded in 3 forms using dipping-swinging means: the load of TiO₂ photocatalyst, the load of TiO₂ and activated carbon mixture and the load using new method of TiO₂ and activated carbon.The TiO₂ photocatalyst was characterized by TGA -DTA,XRD and SEM. From the XRD chart, the nanopowder TiO₂ had the anatase without any heat processing. After calcination at 500℃and 600℃, the nanometer TiO₂ powder was the anatase totally. When it was calcined, the particle size of TiO₂ photocatalyst was 9.4nm at 500℃and 10.4nm at 600℃. From the SEM chart, the surface of film was homogeneous and flat, and the nanometer grain size was uniform. For the film thickness, one layer was about 28μm and two layers were about 45μm, after two layers the increased film thickness was about 5μm every time.Designed the photocatalysis action device independently and imitated the indoor pollution of formaldehyde. By the action device made some researches about three types of photocatalyst of the purifying character of the formaldehyde. Studied the formaldehyde concentration, the calcine temperature of catalyst, the film number of catalyst and lighting Respectively, find out the real influence factor about the purifying efficiency of the TiO₂ photocatalyst photocatalysis. Experiment condition: pressure 0.1 MP, air flux 0.15 L·min^-1, formaldehyde start consistence 20×10^-4mg·L^-1, calcine temperature 500℃, the glass tube of TiO₂ with 2 layers is 21, the decomposition rate of the formaldehyde can raise to 100%.With the above-mentioned experiment condition, after continuously reaction for 100 hours, this catalyst still kept a good catalysis activity. When the TiO₂ photocatalyst and the activated carbon were mixed with a simple physical mix, the best quantity proportion of the TiO₂ and activated carbon is:m(TiO₂): reactivated carbon)=1:0.5, the photocatalysis purifies formaldehyde with best efficiency. No matter the TiO₂ photocatalyst more or less all disadvantageous to cooperate the adsorption function with the photocatalysis functions. When the TiO₂ photocatalyst and activated carbon were mixed with new method: first glue one well-proportioned adsorption layer of activated carbon in the glass with gooey, the photocatalyst TiO₂ was loaded on the adsorption layer of activated carbon as an outside photocatalyst layer. At the adsorption layer of activated carbon loaded one layer TiO₂ catalyst had the best catalysis effect. Compared these three load types of photocatalyst purifying effect, we can prove that the new mixed load method with the best efficiency to purify the indoor formaldehyde pollution, under the experiment condition: pressure 0.1 MP, air flux 0.15 L·min^-1, three different types of formaldehydes decomposed quantity respectively is: 128.5 mg·g-1, 153.4 mg·g^-1, 187.9 mg·g^-1.Preliminary kineticstudies of photocatalytic oxidation of formaldehyde suggests that 1/r hasx linear relation with 1/C₀, the equation is y=0.81217+0.94009x, and the coefficient of association R=0.98317, so the the reaction can be best described using the Langmuir-Hinshelwood kinetic equation. The result shows that formaldehyde photocatalytic degradation reaction obeys the rule of first-order kinetic reaction.