Application Study Of Niobium Oxide/Metal Sulfide Composite Adsorption-Photoreduction For Removal U(Ⅵ) From Water

The rapid industrial development and population growth have increased global energy demands.Driven by the need for alternative energy sources that generate less carbon-emission than fossil fuels,there has been an increasing development in the industry of renewable energy resources nuclear energy.In addition,other anthropogenic causes such as mining and processing of mineral ores,military activities and nuclear weapons production have also introduced uranium wastes into the environment.Owing to the toxicity and radioactivity of uranium,it can be easily lead to serious environmental pollution problems and ultimately extend throughout the food chain,posing a threat to the health of animals and humans.Adsorption is a widely used method of removing uranium-containing wastewater.However,this method only adsorbs uranyl ions on the surface of the adsorbent and its toxicity remains almost unchanged.Photocatalytic reduction of U（Ⅵ）to U（IV）to immobilize the high valent U（Ⅵ）is an important way for the efficient remediation of U-contaminated water.While the low utilization of light absorption and few active sites of conventional photocatalysts limits its application in the treatment of practical wastewater.Therefore,the bifunctional catalysts adsorption and photocatalysis is produced by modifying metal sulfides Cd S and Zn In₂S₄（ZIS）with niobium oxides Nb₂O₅ and NaNbO₃,respectively,for the treatment of uranium-containing wastewater.The materials were characterized by XRD,FTIR,SEM,BET and XPS to analyze the morphological structure,elemental composition and specific surface area,and UV-vis DRS and PL spectroscopy to analyze the optical properties of the materials.The materials were applied to the adsorption and photocatalytic reduction treatment of uranium-containing wastewater,and their photocatalytic reduction mechanism was analyzed.The main conclusions were obtained as follows.（1）The Nb₂O₅ nanorods/Cd S nanoparticles（NC）heterojunction materials were successfully synthesized by a one-step solvothermal method.It was demonstrated by the characterization that Cd S nanoparticles attached to the surface of Nb₂O₅ nanorods to form a heterojunction structure with increased specific surface area.Compared with pure Nb₂O₅ and Cd S,the adsorption-photoreduction removal rates of Nb₂O₅ nanorods/Cd S nanoparticle heterojunction materials for U（Ⅵ）were increased.The optimum NC catalyst with the Nb/Cd molar ratio of 1/3（NC-3）,with the total removal rate for U（Ⅵ）wastewater（100 m L,50 mg/L）was up to 97%after 90 min of dark adsorption and 150 min of photoreduction.The adsorption kinetic process of NC-3 for U（Ⅵ）was consistent with pseudo-secondary kinetics,and the adsorption isotherm The maximum Langmuir adsorption capacity was 126.43 mg/g.The catalysts had good regeneration performance and catalytic stability,and the removal rates of both catalysts for U（Ⅵ）could still reach more than 85%after five consecutive cycles.（2）The adsorption photocatalytic bifunctional catalysts NaNbO₃/ZIS（NZIS）heterojunction were synthesized by a two-step hydrothermal method,which exhibited both high adsorption and photocatalytic performance for U（Ⅵ）.Among them,the NZIS-2（NaNbO₃ content 15 wt.%）showed the best effect of total adsorption photocatalytic removal.The adsorption of U（Ⅵ）by NZIS-2 catalyst was chemisorbed and monolayer adsorption,which can be described by the secondary kinetic process model and Langmuir model,and its maximum adsorption capacity was 151.91 mg/g.After 60 min of dark adsorption and 120 min of photoreduction,the total removal rate of NZIS-2 catalyst for U（Ⅵ）wastewater（100 m L,50mg/L）was up to 97%.NZIS-2 catalyst still had a good catalytic stability rate for U（Ⅵ）after five consecutive cycles,and the removal rate reached more than 90%.The above conclusions indicate the successful synthesis of two adsorption-based photocatalysts modified by niobium oxides and can be of research significance for the treatment of uranium-containing wastewater.