Development Of Chiral Mesoporous TiO₂ Composite Photocatalyst With Visible-light Response And Research On Its Degradation Performance

The increasingly strict policies of environmental discharge and treatment such as the zero-discharge policy advocated by coal and chemical industries put forward higher requirements for the treatment of industrial wastewater containing organic pollutants.In view of the refractory and highly toxic organic pollutants,effective advanced treatment is the crux to the treatment of industrial wastewater.For refractory and highly toxic organic pollutants,effective advanced treatment is a key problem to be solved urgently in industrial wastewater treatment.With the advantages of complete mineralization and no secondary pollution,the heterogeneous photocatalysis technology represented by TiO₂ is one of the most potential technologies for advanced treatment of organic pollutants.However,it is difficult for traditional TiO₂ photocatalyst to effectively carry out photodegradation reaction under the excitation of visible light.In this paper,a novel chiral mesoporous TiO₂ photocatalyst with asymmetric spiral structure was synthesized by self-assembly method with chiral surfactant as template,butyl titanate as inorganic precursor and 3-aminopropyltriethoxysilane as co-structure directing agent.The asymmetric microstructure introduced Ti³⁺、a large number of oxygen vacancies and Ti-N bonds into TiO₂ catalyst,which significantly promoted its visible light response and visible light photocatalytic performance.Then,the effects of different preparation conditions on the structure and visible light photocatalytic performance of chiral photocatalyst were studied.Furthermore,the visible light photocatalytic performance of chiral mesoporous TiO₂ was improved by doping,and the specific conclusions are as follows:（1）Mesoporous TiO₂ photocatalyst with spiral stacked chiral structure was successfully obtained by soft template method using chiral surfactant C₁₄-L-Ala A.Ti³⁺ and oxygen vacancies were formed in TiO₂ photocatalyst due to asymmetric structure,which improved the catalytic degradation effect of rhodamine B and phenol under visible light response and visible light excitation.By contrast,the photocatalyst synthesized with achiral surfactants cetyltrimethylammonium bromide（CTAB）and sodium dodecyl sulfate（SDS）as templates has no chiral stacking structure,no visible light response,and cannot degrade rhodamine B and phenol under the excitation of visible light.（2）The asymmetric chiral structure of mesoporous TiO₂ determines its visible light catalytic activity.It is found that the formation mechanism of mesoporous TiO₂ chiral structure is that C₁₄-L-Ala A firstly forms a chiral frame through self-assembly,and then the positively charged amino group on the co-structure directing agent APES interacts electrostatically with the negatively charged carboxyl group on the head of chiral surfactant.Due to the pairing effect,the amino group will form a spiral arrangement with the spiral micelle,forming a Si O₂ chiral frame.Butyl titanate is hydrolyzed slowly at low temperature and the sol particles can be combined with silica chiral framework by condensation with APES.Then,the bonded small TiO₂ particles grow up to form spiral spherical deposits,forming spiral spherical chiral structures.（3）The synthesis conditions affect the structure of chiral mesoporous TiO₂ photocatalyst and then affect the generation of Ti³⁺and oxygen vacancy,resulting in the difference of visible light response of chiral mesoporous TiO₂ photocatalyst and the catalytic degradation effect of rhodamine B and phenol under visible light excitation.Chiral mesoporous TiO₂ photocatalyst has the best visible light photocatalytic degradation performance when the amount of butyl titanate is 2.92 m L,the reaction temperature is 0℃,the calcination temperature is 600℃,the rotation speed is 400 rpm and the value of p H is 6.The effect of synthesis conditions on the structure and visible light photocatalytic degradation performance of D-type chiral mesoporous TiO₂ photocatalyst is consistent with that of L-type chiral mesoporous TiO₂ photocatalyst,indicating that the influence of synthesis conditions on the structure and performance of chiral mesoporous TiO₂ photocatalyst is independent of chiral direction.（4）Chiral mesoporous TiO₂ can catalyze the degradation of tetracycline under the excitation of visible light.The visible light photocatalytic performance of chiral mesoporous TiO₂ photocatalyst is further improved when La³⁺and Fe³⁺are doped with chiral mesoporous TiO₂ photocatalyst.La³⁺affects the energy band and electronic structure of TiO₂photocatalyst,causing electronic transition.Fe³⁺doping makes the band gap generate impurity energy level.Both methods increase the content of hydroxyl oxygen,adsorbed oxygen and Ti³⁺on the material surface,improve the visible light photocatalytic degradation efficiency of chiral mesoporous TiO₂ photocatalyst for pollutants.