A Heterogeneous Reaction Strategy Towards The General Synthesis Of 2D Non-layered Metal Sulfides/Oxides Nanomaterials

Ultrathin atomic structure endows two-dimensional（2D）non-layered materials with extremely high specific surface area,and the 2D non-layered materials have a large number of unsaturated suspended bonds and high active sites,which are widely used in catalysis and energy storage fields.However,due to the inherent isotropic chemical bonds in two-dimensional non-layered materials,it is difficult to break all the chemical bonds on a given plane to get its two-dimensional structure by traditional top-to-down methods（mechanical exfoliation,ion intercalation,etc.）.Therefore,there is still a formidable challenge for the preparation of 2D non-layered materials.In this work,a diffusion-controlled heterogeneous interface reaction strategy is proposed to drive the two-dimensional anisotropic growth of non-layered crystals.In heterogeneous reaction,such as the solid-solid reaction,mass diffusion process is always severely suppressed and the chemical conversion primarily occurs at the interface of the involved reactants.Only the very top surface of the reactants can convert into the products at the initial stage and this atomically thin interfacial product is considered as a naturally formed 2D structure,which would in principle provide a universal and robust strategy for the synthesis of 2D non-layered materials.The results are as follows:（1）Hexagonal Cd S nanosheets with a thickness of 2-3 nm were prepared by a simple gas-liquid reaction.The gas-liquid interphase boundary set a natural diffusion barrier for the reactants,thus the encounter of the involved precursors was mainly limited near the interface region,driving the 2D anisotropic growth of the products.To observe the crystal growth,the products of different reaction time were collected,and the whole process from crystal nucleus formation to crystal growth into stacked hexagonals nanosheet was observed by SEM.In order to verify the universality of heterogeneous reaction system,bismuth sulfide nanosheets were prepared by designing an appropriate solid-solid heterogeneous reaction.The ultrathin two-dimensional nanosheets obtained have regular morphology and well crystallization.（2）In order to expand the species of nanosheets that can be prepared by heterogeneous reaction system,monoclinic Cu O nanosheets were successfully prepared by a solid-liquid-solid heterogeneous reaction.Tetragonal Ti O₂ and cubic Al₂O₃ nanosheets were prepared by a solid-solid reaction.The as-prepared two-dimensional nanosheets have smooth surface,pure phase and highly crystalline structure.The preparation of two-dimensional non-layered metal oxides not only verifies the feasibility of heterogeneous reaction system,but also confirms the variety of materials applicable to this method.This principle can provide a fresh avenue for the preparation of two-dimensional non-layered materials.Taking Ti O₂ as the research object,the application of Ti O₂ in catalytic degradation of dyes was explored.Compared with the degradation rate and stability of bulk Ti O₂,the advantages of two-dimensional materials in practical applications were demonstrated.