Oxidation/adsorption Performance And Mechanism Of Highly Toxic Antimony(Ⅲ) On Modified Carbon Nanotube Filters Based On Auxiliary Electric Field

In recent years,a series of water environmental pollution and ecological safety problems caused by the new pollutants（Sb）exceeding the standard have attracted the attention of scholars at home and abroad.In the natural water environment,the occurrence of antimony is significantly affected by the redox state of the water environment,mainly in the form of antimonite（antimony（Ⅲ））and antimonate（antimony（V））.Among them,antimony（Ⅲ）is the most common form of existence,and its toxicity is 10 times higher than that of antimony（V）.Therefore,the development of new technologies that are efficient,rapid,and economically effective in solving antimony pollution,especially for highly toxic antimony（Ⅲ）compounds,is a powerful guarantee for the sustainable use of national water resources and has important practical significance for alleviating the increasingly severe environmental pressure.Due to the low concentration of antimony in the environmental water（usually from ng/L to g/L）,the current mainly treatment technologies tend to be constrained by kinetic limitations.Although the coagulation sedimentation method has relatively high treatment efficiency,it has problems such as large sludge production,high cost,complicated process and secondary pollution.The adsorption method has the characteristics of low energy consumption and recyclability,and is considered to be a more promising antimony pollution treatment technology.In this study,an electroactive filtration system based on titanium dioxide-carbon nanotube（TiO₂-CNT）filters were designed to simultaneously achieve high toxicity antimony（Ⅲ）oxidation and low toxicity antimony（V）adsorption.The adsorption behavior,properties and mechanism of antimony（Ⅲ）were studied in depth by various advanced spectroscopy and imaging characterization techniques.The main research contents are as follows:（1）Antimony（Ⅲ）removal performance study.The removal performance of antimony（Ⅲ）in the continuous-flow system and the traditional hybrid system of this study was compared.The effects of TiO₂ loading,CNT acidification,flow rate,voltage,pH and coexisting ions on the removal kinetics of antimony（Ⅲ）were investigated.The experimental results show that the adsorption kinetics and adsorption capacity of antimony（Ⅲ）increase with the increase of applied voltage and flow rate.Compared with the traditional hybrid reactor,the internal convection mass transfer performance unique to the continuous flow system significantly improves the mass transfer and adsorption performance of the reaction system.Upon application of the auxiliary electric field,in-situ transformation of highly toxic antimony（Ⅲ）to low toxicity antimony（V）can be achieved,and antimony（V）can be further removed by nano-TiO₂ adsorption.The system maintains high adsorption properties in the pH range of 3 to 11.In addition,the presence of sulfate,chloride and bicarbonate ions has no significant effect on the removal performance of antimony（Ⅲ）,while phosphate reduces the adsorption of antimony（Ⅲ）to a certain extent.（2）Study on the mechanism of antimony（Ⅲ）removal.In this study,the removal mechanism of antimony（Ⅲ）by TiO₂-CNT filters under the action of auxiliary electric field was studied by means of spherical aberration correction scanning transmission electron microscope（STEM）,X-ray photoelectron spectroscopy（XPS）,and X-ray absorption fine structure spectroscopy（XAFS）,atomic fluorescence spectroscopy,density function theoretical calculation（DFT）.The results show that antimony is mainly adsorbed by nano-TiO₂.XPS,XAFS and AFS show that the removal of antimony is mainly due to the auxiliary electric field accelerating the oxidation of antimony（Ⅲ）to antimony（V）,which is then adsorbed by nano-TiO₂.DFT calculation results show that the adsorption energy of antimony（Ⅲ）on nano-TiO₂ increases（from-3.81 eV to-4.18eV）,and the auxiliary electric field can accelerate the oxidation process of antimony（Ⅲ）.（3）Evaluation of the application prospect of the adsorption system.To further evaluate the application prospects of the adsorption system,evaluation was carried out by regeneration experiments,normalized adsorption performance analysis,and actual wastewater removal experiments.The results showed that the TiO₂-CNT filters still showed good antimony（Ⅲ）removal performance after repeated regeneration.The TiO₂-CNT composite prepared in this study also showed a significantly improved normalized adsorption capacity compared with the literature:1.2 mg/m².Under the action of a limited auxiliary electric field（such as 2 V）,the TiO₂-CNT composite film also exhibits high removal performance for antimony（Ⅲ）-containing tap water.In summary,this study provides new ideas and means for the effective removal of antimony（Ⅲ）and similar variable heavy metal pollutants in water.