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

As traditional-scale or single-component nanomaterials cannot meet the increasing demand for advanced materials,it is urgent to extend the library of current nanostructures.Ultrathin nanostructures(UNs)with at least one dimension in the range of sub-5 nm,possess high ratio of surface atoms 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 performance.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.Thus,chalcogenide-based ultrathin-/hetero-nanostructures appear 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 synthetic strategy and application investigation 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 synthesis of doped transition metal chalcogenide ultrathin nanostructures(UNs).We described a soft template mediated colloidal synthesis of Fe-doped NiSe2 ultrathin nanowires(UNWs)with diameter down to 1.7 nm.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 oxygen evolution electrocatalysis.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 CdS ultrathin nanoplates(UNPs)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 UNPs 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.2.A precursor triggering chemical transformation route of metastable chalcogenides was developed for the synthesis of a family of HNs.We described a facile one-pot chemical transformation route to the synthesis of self-coupled Cu1.94S-CuS HNs,which were the intermediate products of the phase transition and shape evolution process from monoclinic egg-like Cu1.94S nanocrystals to hexagonal CuS nanoplates mediated by a manganous precursor Mn(S2CNEt2)2.Moreover,this type of HNs exhibits good absorption in visible light and near-infrared wave band,demonstrating enhanced photoelectric conversion properties compared with the individual CI 94S nanocrystals and CuS nanoplates.According to DFT calculations,the work function difference at the heterointerface results in electrons flow from Cu1.94S to CuS.The charge distribution and band alignment analysis at the interface indicate an emerging type ? 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 to Bi nanocrystals,accompanied by self-limited lateral growth of single-layer MoS2/WS2 nanosheets.The obtained Bi?MoS2/WS2 core-shell HNs enable efficient hydrogen evolution electrocatalysis in alkaline medium.3.Based on the interaction between ligands and metastable chalcogenides,we designed a strategy for the synthesis of HNs with controllable component and phase.According to the electronic theory of acid and alkali,trialkylphosphine(TAP)can not only bind strongly to Ag+ and Bi3+cations,but also form complex with elemental S/Se.This would break the solubility equilibrium of Ag+-and Bi3+-based chalcogenide nanocrystals 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-ZnS,Ag-AgInS2,Ag-Bi,and Bi-Cu7S4 nanostructures were synthesized.TAP could target phase-selective synthesis of Au@NiS(millerite)/Ni3S4(polydymite)/Ni3S2(heazlewoodite)core-shell HNs by extracting elemental S from NixSy.These HNs could bring different activities towards electrocatalysis induced by the heterointerfaces between Au and NixSy.Moreover,introducing 532 nm laser could regulate the catalytic performance based on the effects between localized surface plasmon resonance(LSPR)of Au nanoparticles and band structures of NixSy.(3)TAP and Mo(CO)6 could trigger phase transition and shape evolution process from Ni3S4 nanorods to high-order hybrid nano-architectures Ni3S4-Ni@MoS2 with multiple heterointerfaces and active sites,which endow these HNs with superior hydrogen evolution electrocatalysis performance.