Rapid Synthesis Of Sub-5 Nm Sized Inorganic Nonmetallic Nanocrystals Via Electrochemical Shock For The Study On Photoelectric Properties

Compared to the bulk materials,the corresponding nanocrystals due to quantum confinement and edge effects show unique electrical/optical behaviors.Developing more interesting properties in sub-5 nm sized nanocrystals via mechanical exfoliation has been the research frontier in the fabrication of nanocrystals.The conventional methods for nanocrystal preparation are either based on liquid exfoliation with the help of organic such as dimethylformamide?DMF?,N-Methyl pyrrolidone?NMP?,isopropanol?IAP?and so forth to reduce the surface energy,or based on electrochemical exfoliation with alkali metal ions insertion.However,long-time high-power sonication,complicate battery assembly process and the use of extremely reactive Li/K may greatly limit its practical application.In our three-electrode fabrication system,Al³⁺can be driven to insert and extracte in the bulk materials.Compared with traditional monovalent alkali metal ions,Al³⁺has thrice the charge of Li⁺/K⁺but a smaller radius and much stronger electrostatic forces.Meanwhile three-electrode system is more conducive to operate under ambient conditions when comparedwithconventionalbuttoncell,thusthenewlydevelopedAl³⁺intercalation/extraction method?electrochemical shock?under three-electrode system might have paved a facile route for inorganic nanocrystals fabrication.Since the advent of graphene,owing to its excellent electrical,mechanical and thermal properties,it has a wide range of appliccation in the field of energy storage and conversion.However,the inherent zero band gap characteristic may limit its further application for high quality optoelectronic devices.Thus its family materials,transition-metal dichalcogenide?TMD?and“white graphene”BN has become the hot spot of scientific research.This paper has mainly discussed the fabrication of TMD nanocrystals,BN NCs and discover their perfect behaviors in the electro-optic field.Transition-metal dichalcogenide?TMD?nanomaterials including WS₂,MoS₂,WSe₂,MoSe₂ are connected in the[001]crystal through van der Waals force.The special space in z axis can sufficiently accommodate proper amount of ions.Herein,we used a hybrid fabrication method combining electrochemistry and liquid exfoliation with propylene carbonate/Al?ClO₄?₃?9H₂O as the electrolyte and ethanol/oleic acid as the dispersion agent to prepare for the inorganic nanocrystals.In the discharging process aluminum ions with large charge and high impact power can cause the distortion and charge redistribution of the intraplane covalent bonds and ready to break down the crystalline lattice of bulk materials.Further in the sonication process oleic acid has good affinity towards Al³⁺and helps to extract Al³⁺from bulk material,which may be favorable to facilitate the efficient formation of monolayer nanocrystals with an average size of 3 nm.Meanwhile,there exists a strong resonance energy transfer?RET?mechanism between nanocrystals and 2,4,6-trinitrophenol?TNP?.As a result the fast prepared WS₂ nanocrystals are successfully applied to detect the highly explosive molecules with a low detection limit of 10^-6 M.Eelectrochemical shock for ultrasmall nanocrystals preparation is also applied to prepare for BN nanocrystals including c-BN and h-BN.As a new type of piezoelectric material,the as prepared ultrafine c-BN and h-BN nanocrystals exhibit a remarkably strong piezoresponse compared to the bulk materials,and the piezoelectric coeffient(d₃₃)of the nanocrystals is up to 25.7 pC/N,which is almost 6 times larger than that from bulk c-BN and even competitive to conventional piezoelectric materials.Meanwhile,the piezoelectric behavor of c-BN is more excellent than that of h-BN,which may be ascribed to the difference of these two kinds of BN nanocrystals on nanostructure.This work paves an interesting route for exploring new properties of superhard NCs.In summary,our electrochemical shock method might have built a bridge between 0D nanocrystals and bulk materials,as well as their fascinating properties and important applications.