Preparation And Catalytic Performance Of Mxene-based Composite Catalysts

As a novel two-dimensional（2D）material with abundant oxygen-containing functional groups on the surface of the sheet,MXene has certain advantages such as a large specific surface area,lots of active sites,reduction and adsorption.Ti₃C₂ is one of the typical MXene materials with abundant sources,stable mechanical properties,corrosion resistance,and acid&alkali resistance.Therefore,Ti₃C₂ can be used as an excellent carrier for the precious metal nanoparticles.The precious metal nanoparticles can be obtained by in-situ self-reduction from the precious metal salt solutions through the reducibility of Ti₃C₂,so the precious metal nanoparticles can be evenly loaded on the surface of Ti₃C₂ to avoid the agglomeration.However,Ti₃C₂ is prone to oxidative inactivation when stored in a conventional environment.Therefore,two excellent modifiers,polydopamine（PDA）and tannic acid（TA）,are grafted on the surface of Ti₃C₂,which can effectively inhibit the oxidation of Ti₃C₂ in air.Both PDA and TA have certain adhesion,which can promote the loading of the precious metal nanoparticles.In this paper,a series of PDA and TA modified MXene-based precious metal nanoparticles catalysts were prepared,and their catalytic degradation performance toward various dyes and catalytic reduction performance for nitrophenol were explored.The details were as follows:（1）Preparation of silver-loaded MXene-based catalysts and their catalytic degradation performance toward dyesTi₃C₂-TA@Ag NPs and Ti₃C₂-PDA@Ag NPs were prepared by the reduction of Ti₃C₂ to reduce Ag NO₃ with TA and PDA as modifiers,respectively.The micromorphology and chemical composition of composite nanomaterials had been analyzed by a series of characterization methods.The catalytic degradation performance of the resulting catalysts toward rhodamine B（RB）and methyl orange（MO）had been explored.The results show that the degradation rate of the two catalysts[Ti₃C₂-TA_X@Ag NPs and Ti₃C₂-PDA_X@Ag NPs（X=0.6,0.8 and 1.0）]toward RB and MO can reach 100%.With the increasing content of TA and PDA in the catalyst,the catalytic degradation performance toward RB and MO is also improved accordingly.The pseudo-first-order kinetic model can be used to simulate the catalytic reaction process.The catalytic degradation rate of Ti₃C₂-TA_1.0@Ag NPs toward RB and MO decreases to 80%after 10cycles of catalysis,while the catalytic degradation rate of Ti₃C₂-PDA_1.0@Ag NPs toward RB and MO remains above 90%.（2）Preparation of gold-loaded MXene-based catalysts and their catalytic performance for dye degradationTi₃C₂-PDA@Au NPs catalyst was synthesized by the reduction of Ti₃C₂ to reduce HAu Cl₄ with PDA as the modifier.The micromorphology and chemical composition of the composite catalyst had been analyzed by a series of characterization methods.The catalytic degradation performance,catalytic kinetics and recycling performance of the catalysts toward amaranth（AR）,methylene blue（MB）,chrome black T（EBT）and Congo red（CR）had been investigated.The effect of gold content in the composite catalyst on the catalytic degradation performance toward these dyes had also been explored.The results indicate that the catalytic degradation rate of the Ti₃C₂-PDA_1.0@Au NPs（X）（X=3,4,5）toward AR,MB,EBT and CR can achieve 100%.The catalytic performance of Ti₃C₂-PDA_1.0@Au NPs（4）is the best,and the pseudo-first-order kinetic model is very consistent with the catalytic reaction process.The rate constants of catalytic reaction of Ti₃C₂-PDA_1.0@Au NPs（4）toward AR,MB,EBT and CR are 0.0721 s^-1,0.0411 s^-1,0.0273 s^-1 and 0.0105 s^-1,respectively.Even after 10 cycles,the catalytic degradation rate toward these four dyes still maintains above 89%.（3）Preparation of palladium-loaded MXene-based catalysts and their catalytic performance toward nitrophenol and dyesTi₃C₂-PDA@Pd NPs catalysts were prepared by the reduction of Ti₃C₂to reduce Pd Cl₂ with PDA as the modifier.The microstructure and chemical composition of the composites had been analyzed by a series of characterizations.The catalytic reduction performance of the composite catalysts toward o-nitrophenol（2-NP）,p-nitrophenol（4-NP）,MO,and MB had been explored.The influence of PDA content in the composite catalysts on the catalytic performance had also been studied.Finally,the catalytic reduction mechanism toward o-nitrophenol had been discussed.The results show that the conversion rate of these four pollutants by the resulting catalysts all reach 100%.The pseudo-first-order kinetic model can be used to simulate the catalytic reaction process well.The rate constants of catalytic reaction of Ti₃C₂-PDA_1.0@Pd NPs toward 2-NP,4-NP,MO and MB are 0.1536 s^-1,0.1245 s^-1,0.2014 s^-1 and 0.0732 s^-1,respectively.After 10 cycles,the catalytic conversion rate of the Ti₃C₂-PDA_1.0@Pd NPs toward these four pollutants still remains above 92%.In this thesis,a variety of composite catalysts for the treatment of various dyes and nitrophenol wastewater were prepared.The catalytic performance of Ti₃C₂-PDA@Ag NPs,Ti₃C₂-PDA@Au NPs and Ti₃C₂-PDA@Pd NPs toward these pollutants is gradually improved.Compared with other previously reported catalysts,the composite catalysts prepared in this thesis have more excellent catalytic performance,better recycling performance and stabler property.In conclusion,this thesis may provide considerable prospects for expanding the application of MXene-based precious metal nanocomposite catalysts in the field of wastewater treatment.56 Figures,10 Tables and 125 References...