Synthesis, Modification And Photocatalytic Properties Of Nano-stucture TiO₂/SiO₂ Composite

The physical and chemical properties of titania has been the subject of much science and technological attention.This material is extensively used as a white pigment in making paints and cosmetics,an enamel,a catalyst,an antimicrobial.Titania is the most effective photocatalyst and widely applied in purification of air and water because of its unique properties.Power-suspended system and coated-photocatalysis system is the mainly phototcatalysis system.However,TiO₂ as a high surface area powder is easily to lose its surface area and difficultly to be reclaimed.Therefore,several groups have investigated titania coating on supports.In particular,applying of TiO₂ onto silica offers a way to obtaining a titania withdraw the shortcomings.Nowadays,the necessitates of ultraviolet irradiation confine the practical applications of titania.So the modification of titania to advance its photocatalytic activity and extensive its photo-absorption property in visible light wavelength range is very necessary.The aim of this thesis is to obtain nano-structure TiO₂/SiO₂ composite by combining the sol-gel technology and layer-by-layer self-assembly method;using low-cost TiCl₄ as the raw material;Modifying the composite with transition metal and PEG2000 and studying the photocatalytic properties of it.The major work includes the following aspects:1.Utilizing the sol-gel technology and layer-by-layer self-assembly method with low-cost TiCl₄ as the raw material and as SiO₂ supports,successfully obtained nano-structure TiO₂/SiO₂ composite.The influence of calcining temperature,experimental conditions, hydrolyzing temperature and addition of anions on the preparation and the influence of the surface condition,the content of TiO₂ in the composite on the times of self-assembly are studied;2.Photocatalytic activity of nano-structure TiO₂/SiO₂ composite has been studied by decomposing the solution of phenol irradiated by ultraviolet and the solution of methyl orange irradiated by sunlight.The experiments showed that there have not linear relations between the anantase contents and the photocatalytic properties.The composite have the best photocatalytic activity with 95%contents of anatase;the composite have better photocatalytic activity with twice assembly;3.Photocatalytic activity of nano-structure TiO₂/SiO₂ composite modified by transition metals has been studied by decomposing the solution of methyl orange irradiated by sunlight. With the adequate addition of transition metal,the photocatalytic activity can be enhanced and the reaction time be shortened.The results showed the photocatalytic activity of the modified composite is relation to the kind and amount of the transition metal,the assembled times and the calcined temperature.Whereas samples prepared from Fe(NO)₃·9H₂O containing low amounts of iron(0.02wt.%)and from Zn(NO₃)₂·6H₂O containing 0.1wt.%of Zn²⁺were more efficient for methyl orange decomposition than pure TiO₂.It can regard the rule of the transition metal modified composites to the rule of the ratio between charge amount and radius of the cation(Z/r).The photocatalytic activity will be enhanced with several assemble times.4.Photocatalytic activity and surface conditions of nano-structure TiO₂/SiO₂ composite modified by PEG2000 has been studied by decomposing the solution of methyl orange irradiated by sunlight.There are some honeycomb-like configurations on the surface of the samples modified by PEG2000 after calcining.With the increasing addition of PEG2000,the honeycomb-like configurations are becoming more distinctive.After several assembled times, the honeycomb-like configurations become more perfect.There are not only some honeycomb-like configurations on the surface,we also obtained some needle-shaped comfugerations on it.The photocatalytic properties of the composites modified by PEG2000 are better than unmodified samples.The assemble times of the samples can also influence the photocatalytic properties,when assemble one time(with H₂SO₄),assemble two time(with NaH₂PO₄),the samples can always have better activities,the reason should be discussed.