Preparation Of Bismuth Catalyst And Photoreduction Of Cr(â…¥) Ions Under Visible Light Irradiation

Hexavalent chromium Cr(VI) is well known for highly toxic and mutagenic andcarcinogenic when assimilated, stored and accumulated by living organisms. However,trivalent chromium Cr(III) will be slightly toxic，just about one hundredth of Cr(VI),so many countries strictly limit its emissions. Methods dealing withchromium-containing waste water discharged from industry such as chemicalreduction, ion exchange, electrochemical treatment, have been intensively studied.Among them, photocatalytic reduction as a potential environmental-benign method,with the advantages of low consume, easy operation and no secondary pollutions,attracts extensive attention.Recent years, semiconductor photocatalytic technology developed rapidly, andhas broken the limitation of studies on materials only with UV response. Amounts ofnarrow bandgap photocatalysts could response under visible light attract researcherssight. Bismuth-based photocatalysts as a sort of narrow bandgap materials, have anexcellent photocatalytic abilities under visible light, for effectively avoid therecombination of photo-generated electrons and holes.The text starts with the synthesis of different morphologies of Bi2WO6andBiVO4, by characterizing Bi2WO6and BiVO4samples with XRD, SEM, TEM, andBET, and evaluating the abilities of photoreduction of Cr(VI) ions, and first-kineticfitting, to analyze the performance of each photocatalyst, which can ecaluate withkinetics of per unit surface area. Experimental results show that: whether Bi2WO6orBiVO4with different morphology, their kinetics of per unit surface area are varied.We can initially infer the reasons caused different photocatalytic performances by thecharacterized data and activity curve of photoreduction of Cr(VI) ions. For bismuthtungstate, the activity of Bi2WO6nanosheet is two times as the lower nanoparticles. It is found that high exposure of {100} facets and good crystallinity are benefit for theenhancement of photocatalytic performance. And for BiVO4, the effects ofmorphology are even more obvious. As the experimental data shows, the bestphotocatalytic performance of BiVO4octahedral is8.6times of the less active ofnanosheet, and154times of the worst active of needlelike BiVO4. It was found thatthe intensity ratio of BiVO4octahedral is16.0%, obviously higher than that ofneedlelike BiVO4, which is5.0%, in the case of similar degrees of crystallization.The priority growth of crystal facet tremendous affects the photoreduction ability ofBiVO4. Comparing nanosheet with octahedral BiVO4, though they share similar peakintensity ratios, the ability of the latter is still higher than the former, for thecrystallinity of the latter is higher with the crystalline size of34.3nm, which is1.26times of nanosheet. So it can be conclude, it is the prior growth along {040} facetsand crystallinty degree that affect the photoreduction of BiVO4, especially the prioranisotropy growth along {040} facet.