The Preparation Of Phosphorus-doped Tungsten Trioxide Nanomaterials And Their Photocatalytic Performances

Photocatalytic technology,among the existing water treatment technologies,has attracted extensive attention due to its advantages such as using only light energy without secondary treatment,simple facilities,low cost,and high performance in treating refractory organic matters.The primary task is to find a perfect photocatalyst in the photocatalysis processes.Tungsten trioxide（WO3）,being an indirect n-type semiconductor,has been widely used as a visible-light-driven photocatalyst due to its relative narrow band-gap（2.4eV to 2.8eV）and strong absorption（about 12%）in the visible region.Nonetheless,the wide application of WO3 is limited by some intrinsic factors.Thus,the phosphorus doping modification was conducted to improve the photocatalytic performance of tungsten trioxide photocatalyst in this paper.The main obtained conclusions are as follows:（1）The photocatalytic performance of P-WO₃ is affected by a variety of factors.Some characteristics of photocatalyst such as crystal phase composition,crystal lattice defects,crystallinity and stability can be controlled under appropriate conditions in preparing photocatalyst,which are contribute to improve the photocatalytic performance.The preparation of P-WO3 were optimized by controlling the mole ratio of P/W,the roasting temperature and time,solvent,dispersant and inhibitor dosage in this paper.The results showed that P-WO₃ with the best photocatalytic performance can be obtained under the conditions of a P/W mole ratio of 6%,a roasting of 500℃for 4h,and the amount of deionized water,ethanol and glacial acetic acid is 30mL,20mL and 10mL,respectively.The degradation rate of the methylene blue by the obtained optimum P-WO₃ can reach 97%（120 min）in solution.（2）The microstructure,morphology,surface and optical properties of WO₃ and P-WO₃were characterized by using the FESEM,TEM,XRD,XPS,UV-Vis DRS and BET technologies.The results showed that the WO₃ prepared by hydrothermal method is monoclinic nanocrystalline particles with good crystallinity,fixed shape and a size range of50nm to 100nm.Phosphorus was successfully dopped into the WO₃ lattice in form of P⁵⁺,stable W-O-P bonds being formed on the surface of WO₃,resulting in a crystal form change from monoclinic to orthorhombic.The doping of phosphorus has no obvious effect on the microstructure and particle size of the photocatalyst.The absorption edge of WO₃ has a slight red shift,and the absorption of light in the visible region enhanced.The band gap decreased from 2.4ev to 2.33ev,which is helpful in enhancing the photocatalytic performance of WO₃.（3）The controllability of the preparation and the stability of the catalyst are key factors in the practical applications of photocatalytic technology.The stability and practical application of P-WO₃ were investigated in this study.Reproducibility experiments indicated that the P-WO₃ presents high physical stability,and the preparation process can be well controlled.The results of recycling experiments showed that the photocatalytic efficiency of P-WO₃ for degrading methylene blue can still reach up to 86%of the initial catalyst after three cycles of applications,suggesting a high photocatalytic stability of P-WO3.In addition,P-WO3 also exihibited high photodegradation performance for treating low concentration organic matters from actual wastewater.After 1h of photodegradation reaction,the degradation rate of organic compounds in the inlet and outlet sewage of a biological wastewater treatment plant can reach40%and 55%,respectively.（4）In addition,the photocatalytic mechanism of P-WO₃ was discussed by analyzing the active species of P-WO₃.Experimental results showed that the contribution of active species for oxidative capacity of the P-WO₃ is in a decreasing order of·OH>h⁺>·O₂^-.In sum,orthorhombic P-WO₃ with fixed morphology,prepared by a two-step method in this paper,presented high photocatalytic performance and stability.The prepared P-WO₃ also exhibited excellent performance in practical application.These results demonstrated that P-dopping can effectively improve the photocatalytic performance of WO₃.