Preparation And Modification Of Bi₂WO₆ And Its Photocatalytic Properties

Environmental pollution is an issue of common concern in today's society?The photocatalytic technology has become a very important research hot spot,which is regarded as a new,effcient and clean water treatment technology.As a conventional photocatalysts,due to band gap of TiO2 which results in low utilization of light energy,there is a limit of TiO2 application.BiZWO6,whichThe BiZWO6 catalyst which proved favourable photocatalytic activity in visible light,has attracted more and more interest.It is well known that the morphologies and grain size of photocatalytic materials has important effect for its photocatalytic properties,so it is of great significance to study the controllable morphology and grain size of Bi2WO6 and improve its photocatalytic properties.In this thesis,the different morphologies Bi2WO6 samples were synthesized by hydrothermal method.The photoactivities under visible light of the as-prepared samples for the rhodamine-B(RhB)were investigated systematically.The samples which we obtained were characterized by X-ray diffraction(XRD),Inductively Couple Plasma(ICP),X-ray fluorescence(XRF),FT-IR spectroscopy,field emission scanning electron microscopy(FESEM),and ultraviolet-visible diffuse reflectance spectroscopy(UV-Vis DRS)in detail.The main contents of this thesis are as follows:The influence of synthesis conditions such as temperature,the molar ratio of n(Bi)/n(W),pH value of reaction solution,reaction time on morphology have been investigated.As a result,five different morphology samples have been obtained.The effects of different hydrothermal process conditions on phase structure,morphologies of the Bi2WO6 samples were discussed,and the special morphologies formation mechanism of Bi2WO6 samples were explored.The result shows that the optimum reaction temperature and time for the complete morphologies of Bi2WO6 samples are 160? and 48 h.When n(Bi)/n(W)is 1:1,pH value at 2,5,and 7,the morphologies of Bi2WO6 samples are multilayer round sheet,flower-like spheres and thick disk-shaped.When pH is 7,and the molar ratios of n(Bi)/n(W)are 2:1 and 1:1,the morphologies of Bi2WO6 samples are square sheet and scattered pieces sheet.The Bi2WO6 samples with flower-like spheres exhibit the best photocatalytic activity because of the largest BET surface area,the minimum grain size and narrower band gap.H2O2 as cocatalyst,after visible light irradiation for 100 min,the degradation rate of Rh-B(10 mg·L-1)reaches 98.8%.Bi2WO6 was modified by doping rare earth ions,in order to extend the visible light absorption region and improve solar efficiency.Firstly,different types of earth ions were doped.It is found that various doping can change the catalytic activities,moreover,among them,Tb3+ is the best active.Additionally,different concentrations of Tb3+ were investigated in order to determine the optimal concentration.The results reveal that the certain amount Th3+ doping on Bi2WO6 does not destroy the sample spherical morphology and crystal structure,but produce the lattice distortion,reduce grain size,and improve the catalytic activities.0.5%Tb3+,doping sample displays the highest photochemical activity under visible-light irradiation.