Application Of Enzyme Immobilization And Sodium Ion Batteries Based On Two-dimensional Material MXene

As a new type of two-dimensional nanomaterial,MXene possesses good physicochemical properties,thus having broad application prospects.There are many functional groups on the surface of MXene,making it easy to be chemically modified and applied into enzyme immobilization.What's more,the excellent electrical conductivity and flexibility of MXene enable it a promising candidate in energy storage like lithium ion batteries(LIBs)or sodium ion batteries(SIBs).In the first study,MXene(Ti₃C₂T_x)nanosheets was first obtained by selectively etching Al layers from Ti₃Al C₂ phase with LiF/HCl mixture.Then the hydroxyl groups on the surface of MXene(Ti₃C₂T_x)nanosheets was used to realize the amination modification of Ti₃C₂T_x by silanization reaction,followed by the lipase molecules covalently immobilized on the surface of Ti₃C₂T_x nanosheets.In addition,combined with the excellent photothermal properties of Ti₃C₂T_x,the catalytic performance of the immobilized enzyme was studied by catalyzing the reaction of p-nitrophenylpalmitate(p NPP).It can be found that the immobilized lipase shows an enhanced catalytic activity for the hydrolysis of p NPP after near-infrared(NIR)irradiation,and the immobilized enzyme exhibits better thermal stability than the free enzyme.After 180 min of incubation,the residual activity of free lipase is only 39%,while the immobilized lipase could retain about 74%of its original activities after the same time period.The lipase immobilized on functionalized Ti₃C₂T_x nanosheets exhibits better p H and temperature sensitivity.In addition,the immobilized lipase can retain approximately 55%of its initial activity after five consecutive cycles under NIR light irradiation.Another research work in this thesis was to prepare MXene(d-Ti₃C₂T_x)nanosheets by HF treatment and TMAOH delamination,establish a hydrothermal preparation method for Ti₃C₂T_x/Co S_x composite,and systematically study its application in SIBs.It was found that the pristine Co S_x nanoparticles are easy to agglomerate,and the introduction of d-Ti₃C₂T_x nanosheets can effectively improve the agglomeration phenomenon,enabling Co S_x nanoparticles to grow uniformly on the surface of MXene nanosheets.Electrochemical test shows that at a current density of 1000 m A g^–1,the pure Co S_x electrode only has a discharge specific capacity of34.7 m Ah g^–1 after 150 cycles,while the d-Ti₃C₂T_x/Co S_x-0.045 composite can retain a 479.2 m Ah g^–1 discharge capacity after 200 cycles.In addition,the composite exhibits excellent rate performance.The significant improvement of the electrochemical performance of the composite may be due to the following two aspects:first,d-Ti₃C₂T_x nanosheets can act as a buffer layer during charge and discharge,effectively alleviating the large volume expansion of Co S_x during sodium entrapment;on the other hand,the introduction of d-Ti₃C₂T_x nanosheets effectively enhances the conductivity of the electrodes.