Preparation Of N-doped TiO₂ Molecular Imprinted Of Rhodamine B Photocatalyst And Study Of Its Selective Photocatalytic Activity Under Visible-light

It is one of the hot spots to improve the photocatalytic activity of TiO₂ in combination with molecular imprinting technique to improve the photocatalytic activity of low concentration and high toxic organic pollutants under visible light.In this paper,two kinds of molecular imprinting techniquewere used to preparenitrogen-doped TiO₂ imprinted photocatalyst with rhodamine as template.The preparation conditions were explored,and samples were characterized by XRD,TEM,BET,UV-Vis,DRS,FT-IR,XPS characterization.The visible-light activity and mechanism were discussed by the comparison with the degradation and kinetics of rhodamine B,rhodamine 6G,methyl violet,and methyl green,which werewith similar structure belonged to triphenylmethane dyes.Rhodamine B molecularly imprinted nitrogen-doped TiO₂（N-TiO₂-RhB）powder was prepared by sol-gel method,with urea as nitrogen source and RhB as template molecule under acidic conditions.The results showed that the samples were 10-15 nm anatase,and the edge of TiO₂ absorption red shifted by N2 P and O2 P mixed to narrowing the band gap with nitrogen-doping,by which induced visible-light activity.Both doping and molecular-imprinting were improved pore structure.The pore structure of N-TiO₂-RhB was complex,including the typical "ink bottle" hole,pipe hole and particle pores.The pore size distribution mainly concentrated in the 0-10 nm,the most probable aperture was at 2.1nm,another at 6.0nm,which increased the specific surface area of N-TiO₂-Rh B effectively.Under visible light,the characteristics of three-dimensional hole generation special adsorption behaviorof nitrogen doped with rhodamine B molecularly imprinted TiO₂ of target pollutant rhodamine B exhibited good selectivity,the degradation was 92.7%.The mixture degradation systemof RhB,Rh6 G,MV and MG,even if the same concentration,the degradation rate of rhodamine B template molecules under N-TiO₂-RhB was larger than the other pollutants,with as Rh6 G,MV,MG 21.3,3.9,3.6 times respectively,which proved that N-TiO₂-RhB showed good selectivity behavior.The rhodamine B surface molecularly imprinted nitrogen-doped TiO₂（N-TiO₂-MIP）prepared with surface molecular imprinting technique,with N-TiO₂ as stroma,rhodamine B as the template molecule to the adjacent benzene two amine as crosslinking agent and functional monomerandpolymerized under UV light.On the basis of single factor experiment,theoptimumcondition selected by response surface analysis for the four factors and three levels of analysis such as: the mass ratio of RhB/N-TiO₂ with 1.9,polymerization time with 31 min under UV light irradiation,pH value at 2.0 and calcination temperature at 420℃.The characterization of optimized sample showed that nano-grade anatase;the sample edge red shifted both by the band gap narrowing induced by N2 P and O2 P mixed with nitrogen doped,and by two amine from domain conjugate structureπ-π* transition.TheN-TiO₂-MIP was showed improved pass and pore structure by surface coating and doping.The pore size distribution of N-TiO₂-MIP peak was significantly higher than that of other catalysts,in addition to have more holes at 2.2nm,5.2nm also has a number of holes,and the circular cylindrical openings at both ends of the diameter of uniform holes increase the surface area.By comparing the four kinds of pollutants degradation under visible light,due to the discovery of specific recognition sites for molecular imprinting,N-TiO₂-MIP degradation for target pollutant rhodamine B was 93.2%,the selective coefficient between 2.3-3.0,and good selectivity was even showed in the mixed system.N-TiO₂-RhB and N-TiO₂-MIP catalysts were all anatase.The specific surface area were all increased,even with differenthole pattern and pore distribution,but they all possed three-dimensional hole generation special adsorption behavior for rhodamine B to displayed the good selectivity of target pollutants.A layer of poly-o-phenylenediamine surface-coating of N-TiO₂-RhB was not only shifted red more,but also hindered pollutant touch to TiO₂,which induced the similar degradation of rhodamine B for N-TiO₂-RhB and N-TiO₂-MIP.