Preparation And Photocatalytic Properties Of TiO₂ Composite Films By Anodic Oxidation

With the development of industrial modernization,human beings are confronted with the crises of energy shortage and environmental pollution,photocatalyst represented by TiO2 is attracting more attention gradually.However,photocatalytic performance of TiO2 is restricted due to the wide bandgap(3.0-3.2eV)and high recombination rate of electron-hole pairs.Many methods have been studied to increase photocatalytic activity of TiO2,narrow bandgap semiconductor compounding and noble metal deposition are considered to be superior in modification of TiO2.For the doping of narrow bandgap semiconductor and noble metal into TiO2,the methods of anodizing in the electrolyte contained doping ions,photo-reduction,electrodeposition and impregnation after anodizing are widely used.However,the method of anodic oxidation synchronized with electrolytic deposition is rarely reported.Thus,it is important in scientific significance and valuable in practical application of preparing narrow bandgap semiconductor and noble metal co-doped TiO2 by one-step achieving anodic oxidation and electrodeposition.In this paper,Cu2O/TiO2 nanotube array composite films(Cu2O-TNTs)and Cu2O/Ag/TiO2 nanotube array composite films(Cu2O-Ag-TNTs)were prepared by pulse reversing voltage power supply in the fundamental electrolyte of NH4F,ethylene glycol and the additive electrolyte of Cu(NO3)2·3H2O or Cu(NO3)2·3H2O and AgNO3 complex solution.The morphologies,phases,chemical composition,photocatalytic properties and mechanism of the nanotube forming and photocatalysis were studied by the means of SEM,EDS,XRD,XPS,TEM,UV-vis absorption spectra,PL and photocatalytic degradation.The experimental results are as follows:In the electrolyte of 0.3wt%NH4F,95vol%ethylene glycol and 5vol%Cu(NO3)2·3H2O with the concentration of 4-20mM,Cu2O-TNTs were prepared and annealed.Cu in nanotubes was Cu2O and existed in the forms of few sedimentary particles and dispersion;the bandgap of Cu2O-TNTs decreased to 3.12eV from 3.22eV,and the recombination of electron-hole pairs reduced;under the irradiation of UV light,the degradation rate of MB reached 58.7%with the Cu2O-TNTs catalyst concentration of 0.25cm2/mL;the degradation rate reached 77.6%with the catalyst concentration of 0.5cm2/mL under visible light.In the electrolyte of 0.3wt%NH4F,95vol%ethylene glycol and 5vol%addtive complex solution of Cu(NO3)2·3H2O with the concentrate of 8mM and AgNO3 with the concentraion of 2-10mM,Cu2O-Ag-TNTs were prepared under the reverse voltage of 4V-9V and annealed.Most Ag in nanotubes was metallic Ag and a little on the surface of films was AgO,also existed in the forms of sedimentary particles and dispersion;The bandgap decreased to 2.71 eV and recombination of electron-hole pairs reduced significantly;under the irradiation of UV light,the degradation rate of MB reached 81.6%with the Cu2O-Ag-TNTs catalyst concentration of 0.25cm2/mL;the degradation rate reached 98%with the catalyst concentration of 0.5cm2/mL under visible light;Conducting recycle experiments under visible light,the degradation rate reached 78.5%and 80.8%respectively in the second run and the third run,demonstrating the good durability and recyclability.