Construction Of Pd@MXene Based Electrodes And Its Electrocatalytic Dehalogenation Performance Study

Due to the existence of carbon-halogen bonds,the emerging Halogenated Organic Pollutants（HOPs）have high biological toxicity,environmental persistence and bioaccumulation.Conventional biological,physical and chemical treatment technologies have certain limitations.Electrocatalytic hydrodehalogenation（ECH）selectively attacks C-X bonds of emerging HOPs by active atomic hydrogen（H^*）,reducing their biotoxicity and achieving green and efficient removal.Palladium（Pd）based catalyst is a commonly used catalyst in ECH,which has high performance in H^*production and storage.However,its low abundance in the environment,high price,and problems such as aggregation and toxicity in the process of use lead to low catalytic efficiency.Generally,the carrier can improve the dispersion of Pd catalyst and improve the electrochemical performance of the electrode,thus enhancing the ECH performance.Therefore,a new two-dimensional material MXene was used as the carrier of Pd to prepare Pd@MX/CC electrode in this thesis,and the ECH performance of the electrode was investigated using DCF as a model contaminant.Metallic and non-metallic modifications are thought to be effective in tuning the electronic structure of Pd,improving Pd poisoning,thereby reducing the amount of Pd and improving electrode ECH performance.Subsequently,the Pd-M@MX/CC and P-Pd@MX/CC electrodes were further prepared based on Pd@MX/CC electrodes using transition metal doping and phosphor modification,and the ECH performance of these electrodes was investigated,eventually the low-cost and efficient ECH was achieved.The main conclusions are as follows:（1）MXene could effectively decrease the average particle size（3.62±0.34 nm）of Pd nanoparticles（NPs）,improve the dispersion of Pd,increase the crystallinity of Pd.MXene promoted the electron transfer of Pd,which in turn improves the electrochemical performance of the Pd@MX/CC electrode.Under the conditions of-0.8 V（vs.SCE）cathodic potential,Pd to MXene mass ratio of 1,and the Pd loading of 4 mg/cm²,the best removal rate of DCF was achieved at 97.09±0.71%,and the reaction rate constant(k_obs)was 0.36 h^-1.The initial p H of the cathode electrolyte（3-11）and the initial concentration of diclofenac（5-100 mg/L）were demonstrated neglectable on the ECH performance,and the DCF remove rate was higher than93%in all conditions.The mechanisms analysis suggested that the increase dispersion and the adjust of crystal and electronic structure of Pd improved the H^*-producing performance and the adsorption performance of H^*,reaction substrates and products,which in turn led to an efficient H^*-mediated indirect dehalogenation reaction of DCF.In addition,the Pd@MX/CC electrode exhibited high stability and high anti-interference performance to Cl^-and NO₃^-,and was applicable to the removals of levofloxacin,tetrabromobisphenol A,and diatrizoate.（2）Cu doped electrode had the best ECH performance.Cu doping improved the dispersion of Pd,adjusted the crystal and electronic structure of Pd.Further optimization of electrochemical performance of Pd-Cu@MX/CC electrodes with suppressed hydrogen precipitation side reactions.Under the conditions of-0.8 V of cathodic potential and a molar ratio of Pd to Cu of 1,the highest DCF removal rate was achieved at 93.29±0.10%,and the k_obswas 0.34 h^-1.The ECH performance showed an overall decreasing trend with the initial p H of the electrolyte and the initial concentration of pollutants.The mechanisms analysis suggested that the high dispersion and the optimized electronic and crystal structure of the Cu-doped Pd catalyst enhance the H^*production and storage performances,thus enabling an efficient H^*-mediated indirect dehalogenation reaction.The Pd-Cu@MX/CC electrode has a high stability of the removal of DCF in ten batches（>93%）and was applicable to the remove the tetrabromobisphenol A（77.61±0.89%）and diatrizoate（100%）.（3）The phosphating modification could reduce the amount of Pd by 80%while maintaining a DCF removal rate of about 95%.Phosphating modification improved the dispersion of Pd and made Pd exist in a partial amorphous structure.There is more electron transfer between Pd and P.P-Pd@MX/CC electrode had higher catalytic activity and lower charge transfer resistance than Pd@MX/CC electrode.Under the conditions of-0.8 V（vs.SCE）of cathodic potential,the highest DCF removal rate was achieved,and the removal of DCF decreased with the increase of the initial concentration of pollutants,but was almost independent of the initial p H of the electrolyte.The mechanistic analysis showed that the high dispersion and optimized electronic and crystal structure of the catalyst enhanced the H^*production and storage performance of the P-Pd@MX/CC electrode,thus enabling an efficient H^*-mediated indirect dehalogenation reaction.The P-Pd@MX/CC electrode had high stability and was applicable to the removals of the tetrabromobisphenol A（82.26±2.42%）and diatrizoate（97.13±0.23%）.In addition,the P-Pd@MX/CC electrode exhibited high resistance to sulphur poisoning.In addition,the P-Pd@MX/CC electrode had a somewhat improved resistance to sulphur poisoning compared to the Pd@MX/CC and Pd-Cu@MX/CC electrodes.