The Electrocaalytic Reduction Of Carbon Dioxide At A Nd(?)-containing Cyano-bridged Heterometallic Coordination Polymer Composite Modified Electrode And The Evaluation Of Its Liquid Organic Matter Yield By Measuring The COD Index

At present,the selective conversion of greenhouse gas carbon dioxide(CO₂)for the valuable chemicals or organic fuels is the frontier field of catalytic chemistry.Some important progress has been made in the study of catalytic reduction of CO₂ to organic fuel containing C₁ or C₂ molecules by electrochemical pathway.In this paper,a novel composite modified electrode coated with aminoacid copolymer/neodymium-containing heterometallic cyano-bridged coordination polymers/silver phosphate@silver ferrocyanide materials(Aminoacid copolymer/Nd(III)-Cy HMCPs/Ag₃PO₄@Ag₄Fe(CN)₆/GCE)was prepared on the glassy carbon substrate by combining electrochemical deposition and continuous chemical bath deposition technology.Using this electrode as the working electrode,we has mainly studied the electrocatalytic reduction behavior of CO₂,while the experimental results also show that there is an good synergistic effect among the modified materials,with which the CO₂ can be efficiently reduced to liquid phase organic products.In addition,based on the improvement of measure method for the chemical oxygen demand(COD)of the water samples containing trace organic matter by using the two-step wet-chemical microwave-assisted digestion technique,we have proposed for the first time that COD index can be applied to estimate the total amount of liquid-phase organic products in the electrocatalytic reduction reaction of CO₂.Therefore,a convenient and fast experimental test scheme will be exploited in order to develop the new catalyst materials for the selective electrocatalytic reduction of CO₂ to liquid-phase organic fuel.This thesis mainly consists of four parts:Part one:Literature reviewThis section mainly includes five aspects:(1)The research background of effective utilization of carbon dioxide;(2)Overview of main methods and ways of catalytic reduction of carbon dioxide;(3)Main types of catalysts for electrochemical reduction of carbon dioxide;(4)New detection methods and related research progress of COD index of trace organic matter;(5)The significance and innovation of my studies.Part two:Electrocatalytic reduction behavior of carbon dioxide on an aminoacid copolymer/cyano-bridged heterometallic coordination polymers/silver salts composite modified electrodesIn this section,A new type of composite modified electrode with Aminoacid copolymer/Nd(III)-Cy HMCPs/Ag₃PO₄@Ag₄Fe(CN)₆/GCE was prepared on glassy carbon electrode substrate by combining electrochemical deposition and continuous chemical bath deposition technology,and its surface morphology was characterized by scanning electron microscopy(SEM).Using this new composite electrode as a working electrode,the electrocatalytic voltammetric behavior of CO₂ was studied by CV method.Thus,the experimental conditions for the preparation of the new composite modified electrode were carefully optimized by observing the change of current density at a specific potential,after CO₂ and Ar gas were alternately introduced into the same electrolytic cell.Furthermore,through the evaluation of experimental data,we could confirm that there was a synergistic catalytic effect among modified materials of the composite electrode.The effective faraday current density of CO₂ electroreduction at-1.50V electrolytic potential reached 0.64m A·cm^-2,and its electrocatalytic performance still remained steady after tens of hours of repeated use.Thus,it was true that the composite modified electrode held a relatively stable electrocatalytic activity for CO₂ electroreduction.Part three:Determination of COD value in water samples by potentiometric titration with the microwave-assisted digestion in sealed tankIn this section,with the mode of microwave-assisted digestion in a sealed tank,we have greatly improved the two-step wet-chemical digestion potentiometric titration method for the determination of COD value of trace organic matter.Using methanol as the probe,a new method has established for the determination of COD value of volatile organic matter at the micromoles concentration level(?mol/L).In the process of optimizing the experimental conditions,the effects of experimental parameters such as microwave digestion time,oxidant dosage and catalyst ratio on the total digestion rate of methanol have been studied.The results show that when the ratio of oxidants to catalysts in the two-step wet-chemical digestion solution are adjusted to n(KMn O₄):n(Mn SO₄)=6:1,n(KMn O₄):n(K₂Cr₂O₇)=3:2,n(K₂Cr₂O₇):n(Cu²⁺+Ag⁺)=2.5:1,meanwhile added by four drops of the turbid liquid consisting of apatite/tungsten trioxide/zirconia ternary nano-powder as auxiliary digestion additive,the total degradation rate of methanol in simulated water sample can be increased to98.7%and the linear range of methanol concentration was of 0-400?mol/L.Moreover,several kinds of organic compounds(oxalic acid,formic acid,acetic acid)are used to prepare simulated water samples for COD value determination,and the working curve equation between their concentrations and the measured COD index are obtained.Hence,it is also shown that this method can be used to estimate the total amount of trace organic matter in water samples by accurately measuring the low-level COD value.Part four:Study on a novel COD index method for estimating the total amount of liquid-phase organic products in the electroreduction reaction of carbon dioxideIn this section,when a novel composite modified electrode(Aminoacid copolymer/Nd(III)-Cy HMCPs/Ag₃PO₄@Ag₄Fe(CN)₆/GCE)was used as the working electrode,the constant potential electrolysis was carried out under the condition of bubbling in CO₂ gas and stirring electrolyte.Then,the liquid-phase products due to the electroreduction of CO₂ in the electrolyte were be collected and analyzed by water-phase infrared absorption spectrum and COD index measurement.There were the four results:the measured COD value increased with the increase of electrolysis time at constant potential mode;the total amount of organic products in liquid-phase electrolyte could not always be increased by applying more negative electrolysis potential;the experimental evidence of water-phase infrared spectrum showed that the conversion efficiency of CO₂ electroreduction to formate was higher at-1.3 V(vs.saturated calomel electrode).In conclusion,the improved COD index method would be more than sufficient to estimate the total amount of liquid-phase organic products in CO₂ electroreduction reaction.