Preparation And Photocatalytic Application Research Of Nonmetallic Modified Titanium Dioxide

The growing environmental crisis is forcing people to look for clean energy sources that can replace fossil energy and effective technologies that can control environmental pollution.Photocatalytic technology can realize the photocatalytic degradation of pollutants and the photocatalytic hydrogen evolution by splitting water.It is a technical means with broad application prospects for treating environmental pollution and developing clean energy.Titanium dioxide is the first photocatalyst discovered and has the advantages of non-toxicity,low cost and high stability.However,titanium dioxide has a large band gap and cannot absorb visible light,resulting in its poor utilization of sunlight and a high photogenerated electron-hole recombination rate,which greatly limits its wide application.In this paper,titanium dioxide is modified by introducing non-metal elements and constructing heterojunctions to improve its photocatalytic activity,which is applied to photocatalytic organic degradation,hydrogen evolution and organic synthesis.The main research work is as follows:（1）A kind of phosphorus-doped TiO₂（P-TiO₂）is fabricated by boric acid-induced hydrolysis of tetrabutyl titanate in ethanol solution of triphenylphosphine,then calcination and washing.Under the irradiation of blue light-emitting diode（LED）,P-TiO₂ can successfully realize the oxidative coupling of benzylamine（conversion>95%,selectivity>99%）with air as oxidant.Besides the photodegradation of phenol can also be conducted smoothly under the irradiation of Xenon lamp.Control experiments demonstrate that boric acid-induced hydrolysis and calcination temperature determine the size-distribution and surface area of TiO₂nanoparticles,which further impact the photocatalytic performance.Density Functional Theory（DFT）calculations demonstrate that the orthophosphate species covalently bonding to the titania surface facilitates the adsorption of oxygen molecule on the surface of P-TiO₂ by forming P-O bond,thereby exhibiting excellent photocatalytic oxidation activity.（2）A straightforward hydrolysis-carbonization strategy for synthesizing carbon-coated TiO₂ photocatalyst is developed.During the calcination process,boric acid functions as a template to maintain the size of TiO₂ nanoparticles,exposing more active surfaces.And butanol generated from the hydrolysis of butyl titanate is carbonized and covered on the surface of TiO₂nanoparticles,in-situ forming carbon-coated TiO₂ photocatalyst.Under the irradiation of Xenon lamp,the catalyst TiO₂-500-W shows excellent photocatalytic hydrogen evolution ability(434.91μmol h^-1 g^-1)and recycling stability.The band gap of carbon-coated TiO₂-500-W is2.82 e V so that it can even promote the hydrogen evolution under visible-light irradiation.Experiments and DFT calculations reveal that the presence of carbon sheet on TiO₂ can reduce the band gap,generate valence band tail,and decrease the work-function,which facilitate the improvement of photocatalytic activity for hydrogen evolution.（3）With tetrabutyl titanate as raw material,rutile@anatase heterojunction photocatalyst was prepared by boric acid-induced hydrolysis and following calcination in the presence of urea.During this process,boric acid functions as hydrolytic reagent and template,and urea serves as crystal phase regulator.The calcination temperatures and the dosages of urea are screened to determine the optimal photocatalyst CN（0.5）-TiO₂-600 through evaluating the photocatalytic performance in hydrogen evolution reaction.Characterizations confirm that the formation of rutile@anatase heterojunction in CN（0.5）-TiO₂-600.It was analyzed that the synergistic effect of rutile and anatase can reduce the recombination of photogenerated electrons and hole pairs,and further improve the activity and stability of photocatalytic hydrogen evolution.