Study On ?-FeOOH And Loading TiO₂ Photocatalytic Reduction Of Cr??? Effect And The Mechanism Of Action

Chromium widely exists in the nature mainly in the forms of Cr???or Cr?III?.Cr???is of high toxicity and mobility,which poses a seriously threat to human health and the environment.Chromium and its compounds are the basic raw material used in the industries of metallurgy,metal processing,plating,leather,pigments and organic synthesis.If chromium generated in the production process of these industries cannot be effectively controlled or is unreasonably discharged,it will result in serious chromium pollution problems.Therefore,to seek effective and rapid methods to solve chromium pollution problem is of important theoretical and practical significances.Photocatalysis technology involving in TiO₂ has provided an effective and promising means for remediation of environmental pollutants in air and water.However,their applications for industrial wastewater treatment are mainly reported at bench study scale due to low efficiency in photoenergy utilization.In recent years,iron-containing materials have become a kind of photocatalytic materials with great application prospect due to their excellent physical and chemical properties.This paper selected Cr???as a target pollutant and mainly studies schwertmannite,jarosite,akaganeite and its composites as photocatalysts for the reduction of Cr???and the catalytic reaction mechanism.Research contents include:?the photocatalytic reduction efficiency of Cr???over schwertmannite,jarosite and akaganeite by different low-molecular-weight organic acids?tartaric acid,citric acid,oxalic acid?.?comparing the photocatalytic reduction of Cr???over ?-FeOOH prepared by biological and chemical methods,the effects of various factors such as pH,concentration of catalyst and the initial concentrations of SOAs on the potoreduction of Cr???and its mechanism were also discussed.?complexes ?-FeOOH/TiO₂ were synthesized by chemical and biological method,the synthesis products were analyzed and characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and specfic surface area?BET?.The effects of the changes of the experimental conditions on the photocatalytic reduction of Cr???were investigated.?The factorial design methodology was employed to evaluate the statistically important operating conditions?pH of solution,loading of catalyst,Cr???concentration and reaction time?and their interactions on the photocatalytic reduction efficiency of Cr???over chemical synthesized ?-FeOOH/TiO₂,and get the best reaction conditions.After a series of experiments,the obtained main results were as follows:1.Of the tested three biosynthesized iron containing materials,the efficiency for photocatalytic reduction of Cr???was in the order of akaganeite>schwertmannite>jarosite.In the three kinds of low-molecular-weight organic acid,tartaric acid facilitated by akaganeite or schwertmannite or jarosite has the highest Cr???reduction efficiency of 92.8%,99.2%and 67.8%,respectively.2.The results showed that the photocatalytic reduction efficiency of Cr???by tartaric acid in the presence of biosynthesized P-FeOOH was 4.35 times higher than that of the control without the addition of biosynthesized ?-FeOOH.The photocatalytic reduction efficiency of Cr???was obviously affected by many factors such as pH,catalyst amount,and tartaric acid concentrations.But the photocatalytic reduction efficiency of Cr???by tartaric acid in the presence of chemical synthesized P-FeOOH has not been significatly improved and wasn't sensitive to the change of experimental conditions.Biosynthesized?-FeOOH has good reusability.After using four times,the reduction efficiency of Cr???can reach 60%.3.The photocatalytic properties of biosynthesized P-FeOOH can be improved greatly by using TiO₂ as a template.The photocatalytic ability of 60?-FeOOH/TiO₂?Fe3+/TiO₂ mole ratio of 60:40 in the initial suspensions?was best.The reduction efficiency of Cr???could reach 100%within 40 min in the presence of 100 ?mol/L of tartaric acid and pH 2,which is 2 times higher than the reduction efficiency of Cr???faciliated by biosynthesized?-FeOOH at the same condition.4.?-FeOOH/TiO₂ composites were prepared by chemical method and show superior photocatalytic property.The photocatalytic ability of 75?-FeOOH/TiO₂?Fe3+/TiO₂ mole ratio of 75:25 in the initial suspensions?was best.When there is no tartaric acid,the reduction efficiency of Cr???could reach 100%within 30 min and at pH 4.Factorial design methodology was used and the experimental results showed that pH of the solution exhibited the highest contribution?47.76%?followed by reaction time?30.03%?,Cr???concentration?10.43%?,and loading of catalyst?7.80%?,whereas the interaction effects only accounted for 3.98%of the total contribution.ANOVA shows that the developed model in this study for predicting Cr???photocatalytic reduction efficiency has a high coefficient of determination value?R2 = 97.84%?.