Two-step Gas/liquid Strategy For Production Of N-doped Defect-rich Transition Metal Dichalcogenides Nanosheets And Their Antibacterial Applications

Transition metal disulfide,as a graphene-like two-dimensional material such as molybdenum disulfide?MoS₂?,tungsten disulfide?WS₂?,etc.Due to its unique physical and chemical properties,it has aroused great interest in catalysts,sensors,energy storage,biomedicine,etc.In particular,single-layer/multi-layer transition metal disulfide?TMDs?nanosheets have great advantages in biomedical applications such as antibacterial,tumor treatment,and biomolecule detection.However,efficient and high-yield synthesis methods for single-layer or multi-layer TMDs nanosheets are still lacking,and most applications require a large number of TMDs nanosheets,thus limiting their applications in catalysts,sensors,energy storage,biomedicine,etc.In order to further promote its application,it is necessary to develop a simple,versatile and high-yield method for synthesizing TMDs nanosheets.At present,among the various synthesis methods,the most commonly used methods are:ion intercalation,protein intercalation,organic solvent intercalation,ultrasonic-assisted gas intercalation,and hydrothermal synthesis.Unfortunately,the ion intercalation method will introduce some impurities into the synthesized TMDs nanosheets,which will cause the structural deformation of the TMDs nanosheets.In the work of this paper,a simple,fast,green,universal intercalation method was explored,which can efficiently and high-yield synthesize the N doped TMDs nanosheets rich in defect structures and explore its antibacterial applications.The research results are as follows:?1?We have designed a simple and universal ultrasonic-assisted liquid phase exfoliation strategy that can perform nitrogen doping while increasing the yield of N-MoS₂/N-WS₂ nanosheets.In the intercalation peeling process of N-MoS₂/N-WS₂nanosheets,we first dry-milled it for 8 hours using a ball mill,and then selected urea as the intercalating agent.Through simple hydrothermal process at 160?,nitrogen intercalation was performed while the intercalation layer was peeled off.In addition,through a series of characterization analyses such as SEM,AFM,TEM,and XPS,we proposed a possible synthesis mechanism:after urea is dissolved in water,urea molecules are inserted the layers of bulk MoS₂ or WS₂.During the hydrothermal reaction at 160?,it will decompose to produce gas NH₃.Therefore,the van der Waals force between layers of bulk MoS₂ or WS₂ is expanded and broken by the NH₃generated after hydrothermal treatment.The reaction equation is as follows:???.At the same time,The N atom from NH₃ replaced the sulfur atom in MoS₂ or WS₂ for nitrogen doping.Subsequently,the expanded N-MoS₂ and N-WS₂ aqueous solutions were exfoliated by tip-sonication,and the acoustic cavitation effect produced by the tip-sonication formed defect structure.The yield of N-MoS₂ and N-WS₂ NSs increased with the extension of the sonication time.After sonicating for 6 h and allowing it to stand overnight,then centrifuge at 1000,3000,5000,8000,12000 rpm for 1 minute,the yield of N-MoS₂ and N-WS₂ NSs can reach?80 wt%and?75 wt%.?2?The morphology of N-MoS₂ and N-WS₂ nanosheets were measured by transmission electron microscopy?TEM?,high resolution transmission electron microscopy?HRTEM?,and field emission scanning electron microscopy?FE-SEM?.The TEM images show that the N-MoS₂ and N-WS₂ NSs have sheet-like structures with diameters of 70?90 nm and 20?40 nm,respectively.In contrast,a similar hydrothermal experiment was performed without adding urea at 160?,and then the MoS₂ or WS₂ aqueous solution was sonicated for 6 hours.It was found that the yields of MoS₂ and WS₂ NSs were only 6.7 wt%and 5.5 wt%,respectively,which indicated that urea played an important role in the process of gas expansion and intercalation.In the HRTEM images of N-MoS₂ and N-WS₂ NSs,some dislocations and deformations can be observed,indicating that the formation of defect structures significantly increases the exposure of active edge sites to improve catalytic activity.The interplanar spacing of N-MoS₂ and N-WS₂ NSs are 0.272 nm and 0.273 nm,respectively,corresponding to the?100?plane of 2H-MoS₂?JCPDS no.37-1492?and 2H-WS₂?JCPDS no.84-1398??100?plane.Atomic force microscopy?AFM?images show that the height of the defect-rich N-MoS₂ and N-WS₂ NSs are?1.0 nm and?0.8 nm,respectively,which also means that the N-MoS₂ and N-WS₂ NSs have a single-layer structure.The size distribution of N-MoS₂ and N-WS₂ NSs measured by dynamic light scattering?DLS?was?70 nm and?40 nm.It was found that the hydrated ion radius of these two nanosheets was close to the value obtained from the TEM image.It was further proved that the bulk material was successfully exfoliated into nanosheets.In addition,the zeta potential values of the bulk MoS₂ and WS₂ are-71 m V and-63 m V,respectively,while the N-MoS₂ and N-WS₂ nanosheets rich in defect structures are-40.81 m V and-19.64 m V,respectively.?3?Using disodium terephthalate?TA?probes,it was found that defected N-MoS₂ and N-WS₂ NSs can catalyze H₂O₂ to generate more hydroxyl radicals??OH?than non-nitrogen-doped MoS₂ and WS₂ NSs synthesized by concentrated sulfuric acid.And N-MoS₂ and N-WS₂ nanosheets have good biocompatibility.After incubating 100?g/m L N-MoS₂ and N-WS₂ NSs with human umbilical vein endothelial cells?HUVEC?cells for 24,48,and 72 hours,the survival rate of HUVEC cells is still above 81.5%.We also evaluated the antibacterial effect of N-MoS₂ and N-WS₂ NSs using plate counting method and in vivo experiments.The experimental results show that the inactivation rates of defect-rich N-MoS₂ and N-WS₂ NSs?100?g/m L?on Gram-negative ampicillin resistant Escherichia coli?Amp^r E.coli?reached94.8%and 85.28%,respectively,and the inactivation rates on Gram-positive endospore-forming Bacillus subtilis?B.subtilis?86.04%and 80.96%.N-MoS₂ and N-WS₂ NSs can more effectively kill infected bacteria on the wound to promote wound healing,and have no effect on the main organs such as heart,liver,spleen,lung,and kidney.