Construction Of Ti₃C₂T_x MXene-based Electrocatalysts And Their Applications In Removal Of Contaminates In Water

Electrocatalysis is regarded as the key to clean energy conversion technologies in the future,and thus has attracted much attention in the fields of energy and environment.As the core component and active centers of electrocatalysis,electrocatalysts,especially nano-electrocatalysts,have always been the focus of related research due to their low dosage and high catalytic efficiency.However,nano-electrocatalysts are facing with problems such as easy agglomeration,limited activity and short lifespan,which seriously hinder their practical application.Therefore,it is urgent to introduce suitable conductive carrier materials to improve the dispersibility,reactivity and stability of nano-catalysts.In recent years,two-dimensional transition metal carbides(nitrides or carbonitrides)named MXene have been widely studied because of their excellent electrical conductivity,hydrophilicity,large specific surface area and abundant surface active sites.Using MXene as a carrier to disperse nano-electrocatalysts to prepare more stable and active MXene-based composite electrocatalysts is one of the most promising strategies.Herein,taking the relatively stable Ti3C2Tx MXene as the electrocatalysts carrier,a series of MXene-based electrocatalyst materials were designed and synthesized,and were applied in the electrochemical reduction of water pollutants.The main research results obtained are summarized as follows.(1)Few-layer/single-layer Ti3C2Tx MXene nanosheets were prepared by LiF/HCl etching.Taking the nanosheets as carriers,a composite catalyst(CuPc@MXene)was synthesized.CuPc@MXene combines the advantages of CuPc which can inhibit hydrogen evolution reaction with Ti3C2Tx MXene which has excellent electrical conductivity,together increases the number of active sites,and significantly improves the electrocatalytic performance of CuPc for ammonia production from nitrate.CuPc@MXene achieved higher ammonia selectivity(94.0%)and higher nitrate conversion(90.5%)compared with those of pure CuPc.And remained high ammonia selectivity(～80%)and stable ammonia yield rate after seven recycling tests.The reaction pathway of nitrate on CuPc@MXene was deduced by on-line differential electrochemical mass spectrometry(DEMS)and density functional theory(DFT)calculations.Finally,it is verified by experiments that MXene can be used to support a variety of metal phthalocyanines(MPcs,M=Fe,Co,Ni),and the obtained catalysts are all exhibit the activity in the reduction of nitrate.(2)To further improve the performance of MXene-based electrocatalyst and expand its application in electro-reduction of water pollutants,on the basis of system(1),the same method was used to disperse and anchor ultrafine platinum nanoparticles(Pt NPs)on Ti3C2Tx MXene nanosheets(Pt@MXene).The experimental results exhibited that Ti3C2Tx MXene can promote the electron transfer and has good electrical conductivity,together with the good dispersivity of Pt NPs,the agglomeration of Pt NPs is greatly improved,thus reducing the amount of platinum and the cost.Meawhile,due to the strong synergistic effect of electron transfer and atomic H*,Pt@MXene could efficiently degrade 50 ppm of chloramphenicol(CAP)by electrochemical reduction within 90 minutes,with a rate constant per metal mass(k/ratio)contribution of 75 times that of the commercial Pt/C catalyst.It also exhibited good stability,with a removal rate of 86.5%after 25 cycles.The intermediates were identified by liquid chromatography-mass spectrometry(LC-MS),and then the hydrodechlorination pathway of CAP was proposed.Furthermore,Pt@MXene can degrade most of the CAP in synthetic urine,showing its potential in practical treatment of medical wastewater.(3)On the basis of the above systems and previous work,nano-copper was grown in situ on amino-modified Ti3C2Tx MXene nanosheets to form Cu@Ti3C2NH2.The effect of amino modification on the morphology and composition of nano-copper and the performance of electroreduction of CAP were explored.Through a series of characterization,it is found that the nano-copper supported by amino-modified Ti3C2Tx MXene is quite different from that supported by pure Ti3C2Tx MXene in terms of morphology,chemical composition and state.After modification on the surface of MXene,the conductivity of the catalysts increased.Among them,Cu@Ti3C2NH2-2 has the lowest charge transfer resistance of 4.76 Ω and the highest normalized current density of 2.65 mA/cm2ECSA,thus showing a faster electron transfer rate and higher catalytic activity.Cu@Ti3C2NH2-2 could rapidly degrade CAP(98.6%)within 90 min and maintained a high degradation rate of 91.5%after 10 stable cycle tests.The performance of Cu@Ti3C2NH2 synthesized by the composite/surface modification coupling strategy is comparable to that of Pt@MXene,but the cost is greatly saved,which provides a feasible idea and method for developing MXene-based electrocatalysts with better performance and lower cost.