Preparation, Micro-structure And Photocatalysis Of Nano-TiO₂Doped With Ion Additives

With the booming of the world’s population and the rapid development of theeconomy, it had been causing a series of problems, and water pollution incidentsoccured frequently. Statistic data from the Ministry of Supervision of China showedthat the numbers of water pollution accidents were over1700each year recently. Thepopulation involved in unsafe sources of drinking water had been up to140millionpeople in cities and towns. Because of a lot of organic matter existing in sewage andwaste water, furthermore, many organic pollutants were difficult to be degradedcompletely, which has become a problem of environmental governance. Due to itssimple and easy-to-operate processing method, photocatalysis especially suits fortreatments of toxic organic compounds that hardly or even cannot be biodegradable.As a photocatalyst, it is the most promising photocatalyst currently. In order toimprove the photocatalytic performance of nano-TiO2, this paper attempted to prepareTiO2-doped photocatalysts for wastewater treatment. In this study, metallic elementsIn3+, non-metallic elements B doped powder, rare earth elements Nd3+andnon-metallic elements N co-doped powder, metallic elements V and non-metallicelement N co-doped nano-TiO2photocatalyst powder were prepared by sol-gelmethod. XRD, UV-Vis, TEM, UV-Vis spectrophotometer and other testing methodswere used for characterization of microstructures and performances of the samples.The influence of semiconductor doped nano-TiO2on performance of grain structure,morphology and photo catalytic were studied.As In3+content increased, photocatalytic activity(MB degradation rate) ofIn3+/TiO2samples first increased and then declined slightly. The D3sample of12mol%In3+content showed the best photocatalytic degradation performance withhighest kinetic constants of8.7×10-3min-1, degradation rate of4h reached90.48%. The In3+/TiO2doped samples are anatase structure, and the lattice distortionis larger. The D3sample has the highest absorption wavelength of537.45nm, with11nm redshift compared with the pure sample. The stripe width of D3samplebetween parallel crystal surface is0.3524nm, corresponding to the (101) plane. The fourier transform of the electron diffraction spots is polycrystalline diffraction ringsbelonging to thetetragonal system, and grain size is about20~30nm. So In2O3caninhibit the growth of TiO2nanoparticles. Mechanism of improving the photocatalyticactivity is that the adding In3+forms O-Ti-Cl structure on the surface of TiO2,producea lot of vacancy that capture photoproduction electronic; lowband gap of In2O3cantrap electron, electrons located in the conduction band of In2O3transfer to theconduction band of TiO2, come into being the capture traps of electron and holes,hinder the recombination of electron and holes, improve the photocatalytic activity ofsamples.As H3BO3content increased, photocatalytic activity of nano-TiO2first increasedand then declined slightly. The G3sample of0.8mol/L H3BO3content showed thebest photocatalytic degradation performance, degradation rate of4h with methyleneblue reached89.74%, which is higher than pure phase TiO2sample which degradationrate was82.75%.The first kinetic constants of G5reaches8.5×10-3min-1. The H3BO3doped nano-TiO2samples are hexagonal wurtzite structure with high crystallinity,which states that the addition of H3BO3inhibits TiO2grain growing up. The averagecrystallite size of G5sample is the minimum (23.68nm), but lattice deformationreached maximum. The G5sample has the absorption wavelength of448.42nm,corresponding to the forbidden band width which is2.77eV, with22nm redshiftcompared with the nano-TiO2sample. The stripe width of G5sample between parallelcrystal surface is0.3517nm, corresponding to the interplanar spacing of strongdiffraction peak (101).The mechanism of photocatalytic efficiency is during thedoping reaction process, B ion enter into the TiO2clearance, exists as B-O-Ti bond inthe TiO2crystal lattice is most possible. The2p of the B ion and2p of O orbitaloverlap, which narrows the band gap and broaden its absorption spectrum.As Nd3+content increased, the MB photocatalytic activity of N-Nd3+/TiO2firstincreased and then declined slightly. The M3sample content of15mol%N and0.5mol%N3+showed the best photocatalytic degradation performance with highestkinetic constants of9.2×10-3min-1, degradation rate of4h reached89.52%. TheN-Nd3+doped nano TiO2samples are anatase structure with high crystallinity, lots ofcrystal lattice distortion and the unit cell volume expansion. The M3sample has463.29nm redshift and the width of band gap narrowed0.23eV, with37nm redshift compared with the pure sample. The stripe width of M3sample between parallelcrystal surface is0.3513nm, corresponding to the strong diffraction peak (101) crystalplane spacing. The diffraction spots are quadrilateral. Mechanism of improving thephotocatalytic activity is that N atoms partly replace O atoms and a small amount ofN3-enter into the TiO2crystal lattice which result in lattice distortion in the dopingreaction process, leading to imbalance of charge and increase of Ti3+in the dopedsamples. Doping Nd3+leads to lattice defects which affecs the electron transferprocess, excites the separation of electrons and holes, narrows the TiO2band gap,results in redshift, extends corresponding range of light and absorbs visible light.As V content increased, photocatalytic activity of nano-TiO2first increased andthen declined slightly. The M3sample of0.9mol%V content showed the bestphotocatalytic degradation performance with degradation rate of4h reached89.13%. Kinetic analysis indicated that the photocatalytic degradation process ofsamplesT1~T5are in line with the first order kinetics equation, the optimal samplingT2reaches highest kinetic constants of8.08×10-3min-1. N-V doped nano TiO2samples are anatase structure with high crystallinity. The redshift of sample T2reached a maximum of71nm, corresponding to the band gap of2.49eV,0.42eVnarrower than the undoped sample. There are a lot of aggregations between N-Vco-doped TiO2nanoparticles, which accumulate in serious condition, and the stripewidth of T2sample between parallel crystal surface is0.3514nm, corresponding tothe main diffraction peak of TiO2(101) crystal plane spacing. The Fourier transformof the electron diffraction spots are quadrilateral. Mechanism of improving thephotocatalytic efficiency is that V ions can be used as photoproduction electroniccapturecenter to hinder the recombination of electron and holes in the doping reactionprocess.V ion-doping can form TiO2into Ti1-xVxO2solid solution, which decrease theforbidden band width and can absorb energy in the visible region. As N3-contentincreased, N3-form the impurity level or N atoms replace the O atoms of TiO2semiconductor, which could make the valence band position of TiO2higher, narrowthe forbidden band width, and broaden its absorption spectrum.The study on single metal doped, single nonmetal doped, nonmetal-rare earthco-doped and nonmetal-nonmetal co-doped nano-TiO2found that the doped withfours methods benefited photocatalytic activity improvement greatly of nano-TiO2, comparing with the pure phase TiO2, the redshift of nonmetal-nonmetal co-dopednano-TiO2was the largest, which was up to71nm, followed by metal doped, theredshift was68nm, nano-TiO2with N-V co-doped have the best performance, whichindicated that nonmetal-nonmetal co-doped nano-TiO2had better prospects in sewagetreatment.