Preparation And Performance Study Of Fe And WO₃ Modified TiO₂ Nanopowders

Photocatalysis is a kind of friendly technology with broad prospects and no environmental pollution.It can be used in the fields of solar catalytic degradation of toxic and harmful pollutants and hydrogen production from water cracking.TiO₂ material is the most widely used photocatalyst due to its easy availability of raw materials,non-toxicity,stable structure and reusable characteristics.However,due to the large band gap of TiO₂（3.0-3.2 e V）and the easy recombination of photogenerated electron hole pairs,the photocatalytic efficiency of visible light of pure TiO₂ is extremely low.The research on the modification of TiO₂ and the photocatalytic performance under visible light irradiation has aroused great interest.This paper aims to develop a novel preparation method of TiO₂ based photocatalyst and greatly improve the photocatalytic activity of TiO₂ by using metal doping and semiconductor recombination.Fe-TiO₂ nanopowders were prepared by coprecipitation method and hydrothermal method respectively,and then TiO₂ was co-modified by WO₃ recombination and Fe doping.The internal relationship between the structure,morphology,composition and photocatalytic performance of nanopowders was studied as follows:（1）Fe-TiO₂ nanoparticles with single anatase crystal structure were prepared by coprecipitation method.The factors affecting the crystallization,morphology and composition of Fe-TiO₂ nanopowders of TiO₂ nanoparticles were investigated.In the experiment,the Fe doping concentration was controlled to be 0-1.8 at.%,and the calcination temperature was between 200℃and 400℃to explore the influence of doping amount and calcination temperature on the photocatalytic performance of TiO₂ nanopowders.The results show that the photocatalytic efficiency of TiO₂ nanopowders increases first and then decreases with the increase of calcination temperature.The increase of Fe doping concentration will lead to the increase of light absorption range and decrease of band gap width.It is found that a small amount of Fe doping content can significantly reduce the recombination probability of carriers and greatly improve the visible photocatalytic performance of TiO₂ nanopowders,while the excessive Fe doping will inhibit the photocatalytic efficiency.When Fe doping concentration is0.3 at.%and calcination temperature is 300℃,the photocatalytic efficiency of Fe-TiO₂ reaches the highest,and the degradation efficiency of methyl orange reaches 46%after 15 W fluorescent lamp illumination for 2 hours.（2）On the basis of coprecipitation method study,the influence of hydrothermal temperature,calcination temperature and reaction condition on the structure and properties of Fe-TiO₂ nanopowders was studied by hydrothermal method with the constant Fe doping concentration of 0.3 at.%.The results show that the hydrothermal method favors the formation of well-crystallized nanopowders at lower temperature,and the average grain size（8-12nm）is finer than that of samples prepared by the precipitation method（10-20nm）.With the increase of hydrothermal temperature,the grain size of nanopowders increases continuously.The photocatalytic performance of Fe-TiO₂ prepared by hydrothermal method was further improved compared with that prepared by coprecipitation method.In addition,the effects of acid and organic additives on the structure and properties of Fe-TiO₂ nanoparticles were studied in the hydrothermal preparation method.The results showed that hydrochloric acid could reduce the agglomeration of Fe-TiO₂ nanopowders compared with acetic acid,and the ability of photocatalytic degradation of organic pollutants was significantly enhanced under acidic conditions.Polyethylene imine（PEI）and methylene cellulose（CMC）as additives can significantly promote the crystallization of Fe-TiO₂,and their photocatalytic degradation efficiency of methyl orange is higher than that of the samples without additives（3）In order to study the effect of WO₃ composite on the structure and properties of Fe-TiO₂ nanopowders,WO₃ was prepared by hydrothermal method firstly using sodium tungstate,hydrochloric acid and oxalic acid as raw materials,and the effects of hydrothermal temperature,calcination temperature and p H value on the structure of WO₃ were studied.The results show that tungstic acid precipitation can only occur under the environment of p H value less than 1.5,and the increase of hydrothermal temperature will lead to the enhancement of crystallinity.With the increase of calcination temperature,the crystal structure of WO₃ will change from monocline to hexagonal phase.（4）WO₃/Fe-TiO₂ composite nanopowders with different WO₃ content（0.5-25 at.%）were prepared using sodium tungstate,tetrabutyl titanate,hydrochloric acid and oxalic acid as raw materials.The doping concentration of Fe was 0.3 at.%in all samples.The results show that TiO₂ can inhibit the crystallization of WO₃ phase,and there is obvious WO₃ monoclinic phase when WO₃ content is 5 at.%.When the calcination temperature exceeds 700℃,WO₃/Fe-TiO₂phase changes from anatase to plate titanium,and the introduction of WO₃ improves the photocatalytic performance.When the molar ratio of WO₃ content is 0.5 at.%,the photocatalytic performance of the composite powder is the best.