Surface Modification Of Two-dimensional Nanomaterials And Regulation Of Their Electronic Structure

Owing to the ultrathin characteristic and quantum confinement effect,two-dimensional nanomaterials exhibit distinguished electronic structure and spin structure compared to that of the three-dimensional counterparts,bringing about brand new platform of nanomaterials to develop and design novel electronic devices,magnetic materials, highly-efficient catalysis materials and energy storage devices.With the progress achieved in synthesis of two-dimensional nanomaterials,researchers have turned to probe and regulate the intrinsic property of two-dimensional nanomaterials. Compared to the three-dimensional counterparts,two-dimensional nanomaterials with abundant exposed atoms on the surface of the nanosheets entail their high chemical reactivity, providing the ideal platform to manipulate the surface modification of the ultrathin structure; furthermore, the quantum confinement effect enables the stronger electron-electron correlation, as well as the coupling of the spin, charge and orbital in the two-dimensional materials,endowing a sensitive response to the surface modification of the two-dimensional nanomaterials, which shows great promise for the regulation of their electronic and spintronic structure.In this dissertation, by means of surface chemical modification of the well-defined two-dimensional nanomaterials, we aim to regulate the electronic and spin structure, aiming to unveil the relationship between electronic & spin structure and intrinsic physical properties. In our case, the surface modification of two-dimensional nanomaterials taking advantage of the high chemical reactivity of the abundant exposed atoms on the surface layer, such as surface molecular adsorption, and surface heteroatoms modification, has demonstrated great advance in regulating the intrinsic physical properties of two-dimensional nanomaterials,delivering novel magnetic response, electron transport property and optimized electrocatalytic performance. Details are in the following:1. In this chapter, we demonstrate the surface molecular adsorption of polar reductive hydrazine molecules to induce structural distortion in two-dimensional NbSe2nanosheets, which led to the successful expression of the magnetic moment of the Nb ions with ordered spin behavior, thus representing freestanding case of the coexistence of superconductivity and ferromagnetism in one two-dimensional nanomaterial. The surface distortion triggered by this molecular adsorption resulted in an elongated Nb-Se covalent bond, which weakened the covalent Nb-Se interaction and reduced the hybridization of Nb with Se atoms, thereby augmenting the unpaired electrons around the Nb ions and thus resulting in ferromagnetism. Within this two-dimensional superconducting framework, the induced ferromagnetic momentum coupled with conduction electrons to generate unique correlated effects of intrinsic negative magneto resistance and the Kondo effect. We anticipate that this strategy for surface-structural modification via polar molecular adsorption will provide versatile paths for the preparation of correlated systems with coexisting electronic phases.2. In this chapter, we successfully obtained new hydric titanium disulfide graphene-likeultrathin nanosheets, with less than five atomic layers, by an efficiently chemical exfoliation method, of which the electrical conductivity can be greatly enhanced by hydrogen incorporation. The hydric titanium disulfide realized an unprecedentedly high electrical conductivity in the assembled thin films behaving the conductivity as high as 6.76×104 S/m at 298 K. Together with synergic advantages of the excellent mechanical flexibility, remarkably great stability, and ready stamp-transfer to any substrates, our hybric titanium disulfidethin films show promising capability for being the next generation electrode material in the nanodevice fields. We anticipate that regulating the electron-electron correlations will be a powerful tool for engineering the electrical properties in the 2D material systems.3. In this work, we demonstrate the surface sulfur modification way to successfully regulate electronic structure in Ni(OH)2 nanosheets, realizing the first metallic case of 2D transitional metal hydroxide. The sulfur incorporation successfully accomplishes dual regulation of active sites and electrical behavior in metallic Ni(OH)2 nanosheets.Metallic nanosheets deliver ultrahigh conductivity of 3.19×103 S/m at room temperature, ensuring effective electron transport; Modulated Ni chemical state in metallic nanosheets resulted in accelerated CO2 desorption rate from surface of catalytic center and the consequent more exposed active sites. Benefiting from synergistic effects of more exposed active sites, good wetting behaviors and effective electron transport,metallic Ni(OH)2 nanosheets deliver much enhanced UOR performance than pristine Ni(OH)2 nanosheets. Metallic nanosheets have a much higher current density, smaller onset potential and the stronger stability than pristine Ni(OH)2 nanosheets. This work provides effective strategy to regulate the electrocatalytic performance of Ni-based structure.