Preparation Of Molybdenum Disulfide Nanosheets And Their Application In Supercapacitors

Molybdenum disulfide(MoS2)is a typical representative of transition metal dichalcogenides.MoS2 nanosheet has large specific surface area,large and easy modification energy band,strong adsorption capacity,low friction coefficient,and high reactivity,so it has attracted much attention and has been applied to supercapacitors,catalytic hydrogen evolution,biosensors and many other aspects.However,it is still a difficult problem to prepare high-quality molybdenum disulfide nanosheets on a large scale.Generally,MoS2 nanosheets were prepared by hydrothermal,lithium-intercalation and micromechanical,etc.However,these methods need harsh conditions or experimental equipment complexit,and all of these were difficult to meet the requirements within both the high quality and the high yield simultaneously.The appearance of the liquid phase exfoliation method provides a means for large-scale preparation of high-quality molybdenum disulfide nanosheets.However,the yield of MoS2 nanosheets prepared by direct liquid phase exfoliation with pure solvent is not high enough.In this paper,the direct liquid exfoliation method was improved to increase the exfoliation yield.The MoS2 nanosheets(prepared by direct liquid phase exfoliation)were combined with aniline monomer to prepare MoS2/PANI composites,which were used as the supercapacitor electrode materials.And then,this paper was first tried to prepare a composites of MoS2 nanosheets and graphene obtained by directly exfoliating the graphite and MoS2 powder mixture,and then the aniline monomers were polymerized on the MoS2 nanosheets and graphene composites to prepare MoS2/PANI composites used as electrode materials for supercapacitors.This paper mainly includes the following three parts:(1)We added some common salts(potassium ferrocyanide(K4Fe(CN)6),sodium tartrate(C4H4O6Na2)or sodium potassium tartrate(C4H4O6KNa))in isopropyl alcohol(IPA,a low-boiling organic solvent)as the exfoliation assistant.After simple sonication,we could obtain high quality MoS2 nanosheets.The concentration of MoS2 nanosheets dispersion could be up to 0.240 mg mL-1 after 2 h sonication,which is 73 times compared with pure IPA.Through characterization,it can be known that the MoS2 nanosheets are mostly monolayers,have no defects,and can stably at least for 30 days without significant aggregation.It is indicated that salt-assisted exfoliation in IPA has a very good effect.(2)We could obtain MoS2/PANI composites by in-situ polymerization of aniline monomers on the MoS2 nanosheets(obtained by salt-assisted exfoliation in IPA),which were used as the electrode material of the supercapacitors.We investigated the effects of in-situ polymerization temperature(T),initial concentration of MoS2 nanosheets(C),aniline monomer usage(P)on the electrochemical performance of MoS2/PANI composites to find the best conditions for preparation.The results of electrochemical measurements showed that the MoS2/PANI composites prepared under the optimal conditions have a specific capacitance of 263.7 F g-1 at a scan rate of 5 mV s-1and a specific capacitance of 180.5 F g-1 at a current of 0.5 A g-1.Compared with pure MoS2 nanosheets as supercapacitor electrode materials,the capacitance increases by dozens times.(3)We first one-step direct preparation MoS2 nanosheets and graphene composites dispersion by salt-assisted exfoliation of MoS2 powder and graphite powder in IPA simultaneously.Then the MoS2 nanosheets and graphene composites were mixed with aniline monomers to prepare MoS2/graphene/PANI composites through in-situ polymerization.We investigated the temperature of polymerization(T),the initial concentration of MoS2 nanosheets and graphene composites dispersion(C),aniline monomer usage(P)to find the best conditions for preparation.The results of electrochemical measurements showed that the MoS2/graphene/PANI composites prepared under optimal conditions have a specific capacitance of 381.4 F g-1 at a scan rate of 5 mV s-1,and a specific capacitance of 267 F g-1 at a current density of 0.5 A g-1.The capacitance increases by nearly 50%compared to the MoS2/PANI composites.