Controllable Producing Two-dimensional Titanium Carbide Nanosheets With Optical Behavior And Chemical Stability

The ultrathin two dimension nanosheet as a novel nanomaterial has a rapid development as the graphene was discovered.MXene as a new member of two dimension nanomaterial is utilized in energy storage,catalysis and photoelectricity because of its high conductivity and hydrophilicity.However,the synthesis process focuses on the acid environment and F^-ion limit the utilization of this material with decreased thickness.Facing with these two problems,the organic base is used to etch,intercalate and delaminate the MXene sheet.On the other hand,the TMAOH is also used for simultaneous intralayer cutting and interlayer delamination to generate the ultrasmall MXene sheet.This study not only finds out two novel kinds of MXene sheet but also discovers a new way to expand the path of MXene synthesis.?1?The article reports that the reaction of gallery Al with an organic base?TMAOH?after Ti₃AlC₂ crystal is treated by low concentration HF produces monolayer or bilayer Ti₃C₂ sheets?size:0.5-1?m;thickness:1.6-2.0 nm?with surface-functionalized by hydrolyzed Al?OH?₄^-that possesses an unusually enhanced light absorption ability in the NIR region.The mass extinction coefficient is as high as 29.1 L g^-1 cm^-1 at 808 nm,which is comparable to,or even higher than those of state-of-the-art NIR-absorption materials,which works as a very efficient photothermal agent for applications.?2?This article demonstrates an approach for creating ultrasmall Ti₃C₂ sheet by etching selectively from the high concentration HF and TMAOH simultaneous used for intralayer cutting and interlayer delamination followed by sonication.Interestingly,the resulting product possesses monolayer thickness with a lateral dimension of 2-8 nm that exhibited bright and tunable fluorescence.The optical behavior displays some special properties such as excitation-dependent strong emission.Importantly,although the strong covalent M-C bond is to some extent broken,all of the characterizations of our method suggest that the chemical structure is composed of well-maintained host layers without observing of any serious damages,demonstrating the superior reaction efficiencies and safeties.Comparing with other Ti₃C₂ sheet,the ultrasmall Ti₃C₂ sheet shows good chemical stability against the oxidizong agent.This method is attempted to expand to the other MAX phases for producing ultrasmall Nb₂C and Ti₂C sheet successfully,although the lateral dimensions of final products seemed to be highly related with the chemical stability of MAX phases.?3?This article was focus on three kinds of Ti₃C₂ sheets?terminated with Al?OH?₄^-,terminated with OH/F/O,and ultrasmall sheets?and systematically compare the Ti₃C₂products with chemical stability in oxidation environment which are affected by the functional groups and sizes.Al?OH?₄^-groups can resist against oxidation for longer time as compare with OH/F/O.And the monolayer ultrasmall Ti₃C₂ sheets manifest an unusual high stability against the oxidation reaction from Ti₃C₂O₂ to TiO₂ and involve a structural recrystallization,atomic diffusion in thinner sheets is supposed to be more difficult.?4?The optical behavior of newly two kinds of Ti₃C₂ sheets is characterized in this article.The surface functional groups and sizes of Ti₃C₂ sheets have a huge influence on their optical behavior.The Ti₃C₂ sheet terminated with Al?OH?₄^-show a strong absorbance in the NIR region when its mass extinction coefficient is as high as 29.1 Lg^-1cm^-1 at 808nm.Meanwhile,this special Ti₃C₂ sheet has a huge potential in photothermal therapeutic.The ultrasmall Ti₃C₂ sheet displays a strong ultraviolet absorption and excitation-dependent emission behavior due to the size effect.