The Study On Synthetic Strategy And Applications Of Several Chalcogenide Ultrathin-/Hetero-Nanostructures

Chalcogenide nanomaterials,due to their versatile chemistry and unique electronic structures,are attractive for applications in catalysis,optoelectronic devices and energy conversion and storage fields,etc.As traditional material systems（e.g.,relatively larger size or single composition）cannot meet the increasing demand for advanced materials,it is urgent to extend the spectrum of new chalcogenide-based nanostructures.Surface/interface is the main structural and functional region of nanomaterials.Ultrathin nanostructures（UNs）with at least one dimension in the range of sub-5 nm,possess high specific surface-to-volume area and highly-controllable interplay between surface and ligands,which results in unusual reactivity or stability.Heteronanostructures（HNs）containing two or more chemically distinct components,can integrate advantages of different domains and the special physical and chemical properties of the heterointerfaces,achieving multifunctionalities or enhanced performances.Thus,the study on surface/interface of chalcogenide-based ultrathin-/hetero-nanostructures appears to be particularly important.However,fabricating nanostructures beyond conventional synthetic approaches and further investigating the formation and function mechanisms of surface/interfacial structures are rather challenging.This thesis will focus on the controllable synthesis and applications of chalcogenide ultrathin-/hetero-nanostructures.We designed new strategies for the fabrication of a series of chalcogenide ultrathin-/hetero-nanostructures and fully studied the intrinsic nucleation and growth mechanisms.Furthermore,we investigated the effects of surface/interfacial electronic structures on electrocatalysis and photoelectric conversion through synchrotron radiation techniques,ultrafast spectroscopic characterizations and density function theory（DFT）calculation methods.The main results are summarized as follows:1.A soft template approach was developed for the controllable synthesis of doped transition metal chalcogenide UNs.We described a soft template mediated colloidal synthesis of Fe-doped Ni Se2 ultrathin nanowires（UNWs）with diameter down to 1.7nm.The synergistic interplay between oleylamine and 1-dodecanethiol is crucial to yield these UNWs.These UNWs exhibit unsaturated local coordination environment and favorable electronic structures for catalysis.Furthermore,the in-situ formed amorphous hydroxide layer that is confined to the surface of the ultrathin scaffolds enable efficient electrocatalytic oxygen evolution reaction（OER）.According to DFT calculations,Fe doping favors the formation of*OOH intermediates,which results in the reduction of Gibbs free energy changes of the rate-determining step and improves the catalytic performance.We reported a unique ternary soft template route to synthesize single-layer Mn-doped Cd S ultrathin nanoplates（UNPls）with 1.1 nm thickness through the combined effects of short-chain butylamine,long-chain hexylamine and rigid-chain oleylamine.The ultrathin nature of the UNPls enhances the intrinsic ultrafast electron transfer compared to the bulks,while Mn doping can reconstruct the band alignment by introducing new energy levels,further regulating the photoelectric conversion properties.This multinary soft template synthetic strategy not only enriches the library of UNs,but also indicates promising potential for the design of high-performance catalysts.2.A precursor triggering chemical transformation route of metastable chalcogenides was developed for the synthesis of morphology controlled HNs.We described a facile one-pot chemical transformation route to the synthesis of self-coupled Cu1.94S-Cu S HNs,which were the intermediate products of the phase transition and shape evolution process from egg-like Cu1.94S nanocrystals（NCs）to hexagonal Cu S NPls mediated by a manganous precursor Mn（S2CNEt2）2.Moreover,this type of HNs exhibits good absorption in visible light and infrared wavelengths,demonstrating enhanced photoelectric conversion properties compared to the individual Cu1.94S NCs and Cu S NPls.According to DFT calculations,the work function difference at the heterointerface results in electrons flow from Cu1.94S to Cu S.The charge distribution and band alignment analysis at the interface indicates an emerging type II structure,which can realize efficient photogenerated electron-hole separation and transfer.We reported a Mo（CO）6/W（CO）5 precursor triggering phase transition and shape evolution process from Bi2S3 nanorods（NRs）to Bi NCs,accompanied by self-limited lateral growth of single-layer Mo S2/WS2 nanosheets.The obtained Bi@Mo S2/WS2 core-shell HNs enable efficient electrocatalytic hydrogen evolution reaction（HER）in alkaline medium.This precursor triggering synthetic method contributes to the rigorous control of nanostructures and provides new insights for photoelectric conversion with noble-metal-free conventional HNs.3.Based on the interaction between ligands and metastable chalcogenides,we designed a strategy for the synthesis of HNs with controllable composition and phase.Trialkylphosphine（TAP）can form complex with elemental S^2-/Se^2-,which would break the solubility equilibrium of Ag⁺-and Bi³⁺-based chalcogenide NCs in solution,promoting their reduction into Ag-and Bi-based nanostructures.Thus,a TAP-driving chemical reduction route has been developed for the synthesis of Ag-and Bi-based chalcogenide nanostructures.Based on this transformation law,a series of Ag,Bi,Ag-Ni3S2,Ag-Zn S,Ag-Ag In S2,Ag-Bi,and Bi-Cu7S4 nanostructures were synthesized.TAP can target phase-selective synthesis of Au@Ni S（millerite）/Ni3S4（polydymite）/Ni3S2（heazlewoodite）core-shell HNs by extracting elemental S^2-from Nix Sy.These HNs could bring different activities towards electrocatalysis induced by the heterointerfaces between Au and Nix Sy.Moreover,introducing 532 nm laser could regulate the catalytic performance based on the effects between localized surface plasmon resonance（LSPR）of Au nanoparticles（NPs）and band structures of Nix Sy.Moreover,multiple heterointerfaces and active sites endow these HNs with superior photo/electrocatalytic HER and OER performances.This ligand-mediated transformation route is a great supplement to the synthetic methodologies for colloidal NCs,realizing the precise phase and composition tuning and in-depth understanding between ligand and NCs.