Synthesis And Properties Of BiVO₄ And SnC₂O₄ Novel Photocatalyst Materials

Semiconductor photocatalytic technology has the advantages of mild reaction conditions,no secondary pollution,simple operation and significant degradation effect.However,there are still some problems such as narrow spectral response range,low visible light utilization,low photo-generated electron-hole separation efficiency,and difficulty for recycle.Therefore,it is of great significance to develop new and efficient photocatalytic materials and improve the photocatalytic efficiency for semiconductor photocatalytic technology in the treatment of organic pollutants.Visible-light responsive BiVO₄ with high activity,novel magnetically separable BiVO₄/Fe₃O₄ and novel buttfly-like SnC₂O₄ photocatalytic materials were synthesized by simple precipitation method and hydrothermal method.The structure,morphology,optical absorption properties and photocatalytic proterties of the as-synthesized samples were characterized and analyzed by X-ray powder diffractometer,scanning electron microscope,specific surface area and pore structure analyzer,UV-Vis spectrophotometer,FTIR spectrometer,fluorescence spectrophotometer,X-ray photoelectron spectroscopy,respectively.Moreover,photocatalytic activities of the as-prepared samples were evaluated by the degradation of simulated dye wastewater,and the influence of photocatalytic reaction time,dosage,the pH and initial concentration of dye wastewater on degradation percentage were explored in detail.The main research contents and results are as follows:?1?Visible-light responsive photocatalytic materials BiVO₄ with high active were synthesized by simple precipitation method using Bi?NO₃?₃·5H₂O and NH₄VO₃ as raw materials,following by calcination process.Acid Black 10 B was used as simulated dye wastewater to investigate the photocatalytic activity of BiVO₄.The results indicate that the samples obtained under different calcination temperature are all monoclinic phase BiVO₄ with cell parameters a = 0.5195 nm,b = 1.1701 nm,c = 0.5092 nm,? = 90.38°.The band gap energy of BiVO₄ calcined at 500 oC,600 oC,700 oC are 2.50 eV,2.45 eV and 2.37 eV,respectively.BiVO₄ calcined at 600 oC shows excellent photocatalytic activity,and the particles are nearly spherical-like in shape.When the concerntration of Acid Black 10 B is 20 mg/L,the dosage of BiVO₄ photocatalyst is 200 mg/50 m L,visible light is used as irradiation source and reaction time is 60 min,the degradation rate of the dye can reach to about 100 %.The degradation process can be considered as the first-order reaction kinetics.?2?Novel magnetically separable BiVO₄/Fe₃O₄ visible-light-driven photocatalysts were successfully fabricated by simple precipitation method and hydrothermal method.The results show that the BiVO₄ in the composite are all in monoclinic phase,and exhibits stalactite-like shape with the length of about 9.8 ?m.The Fe₃O₄ are all in the cubic phase,and present spherical-like shape with an average particle diameter of 300 nm.The photocatalytic activity of BiVO₄/Fe₃O₄ photocatalysts under visible-light illumination is higher than that of pure BiVO₄ owing to the narrow band gap energy and delayed electron-hole recombination.Among them,BiVO₄/30% Fe₃O₄ composite exhibits superior activity,which makes the degradation rate of Acid Red B reach to 97.6 % after 40 min visible-light illumination.The degradation reaction accords with first-order reaction kinetics equation.The rate constant of dye degradation reaction using BiVO₄/30% Fe₃O₄ as photocatalyst is about 2.19 times of pure BiVO₄.Furthermore,a photocatalytic degradation mechanism was proposed and ·O₂^-was confirmed as the main active radical in photocatalytic reaction on the basis of IR,XRD and PL analysis,and the introduction of the scavengers for the reactive species.More importantly,the magnetic properties of BiVO₄/Fe₃O₄ composite were measured and the result shows that the composite has superparamagnetic behavior.The degradation rate of the dye under the existence of composite photocatalyst was also kept 81.7 % after five successive runs applying an external magnetic field,suggesting that the as-synthesized Bi VO4/Fe₃O₄ composites not only have good stability,but also can keep high photocatalytic activity.?3?Semiconductor SnC₂O₄ powders with novel butterfly-like shape were synthesized by the one-step precipitation method.The results indicate that the samples obtained at different reaction time are all pure monoclinic phase SnC₂O₄ with space group C2/c?15?,and displays butterfly-like shape.The formation mechanism was proposed on the basis of intrinsic crystal structure and synthesis time.The average band gap is estimated to be 3.33 eV.The PL spectrum suggests that the SnC₂O₄ samples might have a large number of oxygen vacancies and some other defects.The photocatalytic activity of SnC₂O₄ was investigated using Acid Red B and Methyl Orange as simulated dye wastewater.For 40 mg/L Acid Red B and MO,the degradation rate can reach to 96.5 % and 96.4 % under ultraviolet light,respectively.The corresponding reaction kinetics was explored.Furthermore,the degradation mechanism of the dye was explored by introducing the scavengers of active species and comparing with active carbon.The results show that the decolorization of dye Acid Red B is caused by the degradation reaction under the existence of SnC₂O₄,and ·OH as well as ·O₂^-play a dominant role in the degradation of the dye.Recycling test indicates that as-synthesized SnC₂O₄ powders have good stability and recyclability.