Study On Electrocatalytic Oxidation Of Dye Wastewater By Rare Earth Element Modified Lead Dioxide Anode

Electrocatalytic oxidation technology is a clean,effective and environmentally friendly advanced oxidation technology and has been favored by many researchers.Existing researches indicated that electrode material is the leading factor to directly affect the degradation efficiency of organic pollutants.Lead dioxide electrode is considered to be one of the most promising anodes.However,lead dioxide electrode is easily corroded when exposed to electrolyte,resulting in poor stability.The main content of this work focused on the modification of lead dioxide anode and the anode morphology,crystal structure and electrocatalytic oxidation degradation performance were systematically investigated.The main research content consists of three parts:?1?Novel Ti/Sb₂O₃-SnO₂/Er-PbO₂ anodes were fabricated based on doping Er ions into the PbO₂ crystal and enhanced electrocatalytic degradation efficiency for organic pollutants was achieved successfully.The doping principle,possible degradation pathway of MB and electrocatalytic mechanism have been discussed in depth.Based on the comprehensive analysis of crystal parameters by X-ray diffraction?XRD?results and typical formulas,the Pb ions in PbO₂ nanocrystal might be partially substituted by Er ions and form point defects.Additionally,cyclic voltammetry and electrochemical impedance spectroscopy?EIS?investigation indicated that the Ti/Sb₂O₃-SnO₂/Er-PbO₂ anodes possessed higher oxygen overpotential and better conductivity than undoped electrodes.The optimum conditions for the degradation of MB were obtained via studying the effects of different parameters,such as electrolyte concentration?0.01 to 0.4 M Na₂SO₄?,current density(20 to 60 mA·cm^-2),initial MB concentration(10 to 70 mg·L^-1)and initial pH?3 to 11?.At the optimum conditions,the total organic carbon?TOC?,the decolorization rate constant(k_dec)and the energy consumption?EC?reached up to 65.34%,0.036 min^-1 and 0.08?kWh?gTOC??^-1,respectively.Moreover,the electrocatalytic degradation mechanism of the Ti/Sb₂O₃-SnO₂/Er-PbO₂ anodes to MB was proposed to be that,the presence of point defects induced an increase of electron transport tunnels,and promoted the production of more hydroxyl radicals?^·OH?and SO₄^·-.Finally,the path of two electrocatalytic mineralization of MB was speculated according to the different ways of bond breaking.?2?Co and Ce co-doped PbO₂ electrodes were obtained and the co-doping mechanism,possible mineralization pathways and the electrocatalytic mechanism were systematically investigated.The micromorphology and element composition were obtained by scanning electron microscopy?SEM?.XRD confirmed that Co and Ce were successfully doped into the crystal lattice of PbO₂.The crystal parameters obtained by the typical formula indicated that the crystal size of Ti/Sb₂O₃-SnO₂/Co-Ce-PbO₂?1:2?was smaller.Moreover,the linear sweep voltammetry and cyclic voltammetry analysis showed that the Ti/Sb₂O₃-SnO₂/Co-Ce-PbO₂?1:2?electrode has higher oxygen evolution overpotential.Different electrolytes,initial CV concentration and current density were analyzed to optimize the electrocatalytic degradation performance of crystal violet?CV?.The electrocatalytic degradation of CV on the Ti/Sb₂O₃-SnO₂/Co-Ce-PbO₂?1:2?electrode was confirmed to be significantly effective,and the degradation process obviously followed a pseudo-first-order kinetic model.When the proposed Ti/Sb₂O₃-SnO₂/Co-Ce-PbO₂?1:2?electrode as the anode,99.4%of CV could be degraded after treated for 150 minutes.Compared with the pure PbO₂ electrode,it had higher removal rate,higher mineralization current efficiency?MCE?and lower energy consumption?EC?.Finally,the electrocatalytic mechanism of Ti/Sb₂O₃-SnO₂/Co-Ce-PbO₂?1:2?anode was proposed.?3?A novel Ti/Sb₂O₃-SnO₂/PbO₂/Y₂O₃ nano-composite anode was successfully prepared by co-electrodeposition method.The electrocatalytic activity,electrocatalytic oxidation performance to malachite green?MG?and the electrocatalytic mechanism were deeply investigated.Based on a series of typical formulas,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?results confirmed that the partial incorporation of Y₂O₃nanoparticles reduced the crystal size and facilitate the adsorption of hydroxyl oxygen(O_ads).The detailed calculations of the bipotential step chronoamperometry curve suggested that Ti/Sb₂O₃-SnO₂/PbO₂/Y₂O₃?1:0.18?anodes possessed larger diffusion coefficients(D,3.419×10^-15 cm²·s^-1)and catalytic rate constants(K_cat,17.327 cm³·M^-1·s^-1).Moreover,the electrolyte(Cl^-,SO₄^2-and NO₃^-),current density(10 to 50 mA·cm^-2)and initial MG concentration(20 to 60 mg·L^-1)were optimized and the total organic carbon?TOC?removal,decolorization rate constant(k_dec)and energy consumption?EC?were obtained.Finally,the electrocatalytic mechanism of Ti/Sb₂O₃-SnO₂/PbO₂/Y₂O₃ anode to MG was proposed:The partial incorporation of Y₂O₃ nanoparticles promoted the electrocatalytic activity at the anode interface and enhanced the electron transfer to generate more reactive oxygen species?ROS?.The possible mineralization pathways of electrocatalytic degradation to MG were deduced based on UV-vis absorption spectrum and gas chromatography combined with mass spectrometry?GC-MS?.