Preparation Of Hybrid Crystal Catalytic Electrodes And Electroreduction Removal Mechanism Of Heavy Metals

In recent years,environmental pollution caused by heavy metal wastewater discharge have become more and more serious.As a result,people are trying to find clean,pollution-free sustainable energy and green wastewater treatment technologies.Since bioelectrochemical systems（BES）can produce electricity and degrade pollutants simultaneously,extensive research has been conducted on the electricity production and heavy metal wastewater treatment performance of BES.To solve the problems of high energy consumption and low treatment efficiency of heavy metal wastewater treatment methods such as physical and chemical methods,bioelectrochemical methods were used in this study to treat heavy metal wastewater.The bioelectrochemical method can achieve energy-saving and efficient treatment and recovery of heavy metal ions in heavy metal wastewater due to its self-production of electrical energy and electric reduction characteristics.The performance of bioelectrochemical methods for treating heavy metal wastewater is closely related to the redox properties of the electrode surface catalyst.Compared with precious metal catalysts,conductive-based hybrid crystal catalysts（such as transition metals and lanthanides）have the advantages of low cost and good electrocatalytic performance,which can be used in bioelectrochemical system for heavy metal wastewater treatment to further improve the capacity and treatment efficiency.Based on the conductive-based hybrid crystal catalytic electrode preparation,the following research works were performed in this paper:（1）The Fe/Mg/Zr@NC-CF-H catalytic electrodes are prepared by secondary hydrothermal and calcination methods using carbon felt as the substrate.The first hydrothermal is to achieve the Fe and Mg nanoparticles loading,while the second hydrothermal is to achieve the zirconium MOF construction（Ui O-66）.Four Fe/Mg/Zr polycrystalline catalytic electrodes are prepared by changing the Fe and Mg molar ratio and the sequence of the second hydrothermal and calcination.In electrochemical performance tests,the Fe（1）/Mg（1）/Zr@NC-CF-H catalytic electrode exhibits excellent catalytic oxygen reduction property.The electrode application to BES exhibits superior property in electricity production and radioactive wastewater treatment.After domestication,a steady voltage output of 0.8 V is recorded,and the dual-chamber microbial fuel cell obtains a maximum power density of 1.4 W m^-2 at the catholyte of p H 2,which is superior to Pt/C cathode.Moreover,the BES system removal efficiency for Co²⁺,Sr²⁺,Cs⁺,La³⁺,Ce³⁺exceeds 80%under optimal operating conditions,and the system can achieve high efficiency for La³⁺and Ce³⁺（removal efficiency>98%）at an ion concentration of 5 mg L^-1.（2）The PVDF/La/Sm/CeO₂ catalytic electrode is prepared by co-precipitation method and thermally induced phase separation method using stainless steel mesh as the substrate.Lanthanide metal oxide heterojunction catalytic electrode is served as both MFC cathode and MBR filter to construct a coupled microbial fuel cell and membrane bioreactor system（CMMS）to achieve the pollutants removal from simulated tannery wastewater.The developed electrode exhibits high electrochemically active surface areas(q T^*=3.53×10^-3C cm^-2,q_o^*=2.2×10^-3 C cm^-2),facilitating electron transfer(i₀ 7.624×10^-3 A cm^-2,Tafel slope 1.44 V dec^-1;electron transfer number 3.91-3.94).Self-energy production(maximum power generation 146.2 m W m^-2)and pollutant removal property of the assembled CMMS are evaluated.The Cr（VI）reduction process follows pseudo-second-order model,with the rate constant of 0.01 h^-1 under Al anode coordination（synergistic removal efficiency of organic contaminants 94.7%）.Results of microbial community composition indicate the enhanced performance of CMMS benefits from integrated synergies of denitrifying bacteria,methanogens and electricigens.（3）The PVDF/rGO/TFe/MnO₂ electrode was fabricated by chemical synthesis and phase conversion method based on carbon cloth.This transition metal oxide heterojunction catalytic electrode exhibits low total resistance（Rt 38.1Ω）and high electrochemical active surface area(q_o^*0.03 C cm^-2),facilitating electron transfer(i₀ 1.53 m A cm^-2,Tafel slope0.78 V dec^-1).A seawater electromembrane reactor assisted electrolytic cell（SEMR-EC）system is constructed and evaluated for the self-generated electricity performance(maximum power density 2.24 W m^-2,Coulomb efficiency 38.7%)and pollutant removal performance（CN^-100%,TOC 88.49%,Fe 99.74%）by transferring pollutants from cyanide tailings to seawater through leaching method.Kinetic studies confirm that the Fe（Ⅲ）reduction process conforms to the pseudo first-order kinetic model with the rate constant of0.18 h^-1 at the current density of 5 m A cm^-2 and the electrode area of 1×7 cm^-2.The high flux and antifouling characteristics of the electrode due to its hydrophilicity are revealed by constant pressure filtration test.Based on the analysis results of membrane surface before and after treatment,a feasible mechanistic insight including electrooxidation,electroflocculation,electroreduction and membrane filtration is proposed.