Organic/inorganic hybrid nanostructures based on n-doped carbon nanotube assembly and their application

Abstract

The organic and inorganic hybrid nanostructures based on graphitic carbon nanomaterials, such as carbon nanotubes and graphene, have attracted a research attention for environmental and energy applications. Even though organic and inorganic nanostructures are well-known active materials due to their distinctive properties and large active surface area, their applications have a big challenge by the facile aggregation and low electrical conductivity. Thus, graphitic carbon nanomaterials are promising hybridizing structures for individually distribution and increased conductivity due to their superior intrinsic properties. However, the surface of graphitic carbon nanomaterials is chemically inert, which impose chemically surface modification for hybridization. This modification commonly induced intrinsic properties degradation and undesirable electrical resistance in hybrid interface. In this dissertation, I focus on the self-assembly of organic/inorganic hybrid nanostructures based on carbon nanotubes with tailored interface because the interfaces play a role in the synthesis, properties, and performance of hybrid nanostructures. Especially, this dissertation aims to investigate the effects of heteroatom dopant sites as tailored interface for self-assembly, stable immobilization, specific binding site, inorganic molecular conformation, specific interaction mechanism, and performance for catalysis and sensing. First, I presents the linker-free spontaneous binding of inorganic nanomaterials, tetracobalt-based polyoxometalates ($Co_4POMs$), on nitrogen-doped carbon nanotubes (NCNTs) via electrostatic hybridization. Protonated nitrogen-dopant sites at NCNTs enable linker-free immobilization of the Co4POMs and fluent electron transfer in the resultant $Co_4POM/NCNT$ hybrid structures, as demonstrated by the low overpotential of 370 mV for the water oxidation at pH 7. Accordingly, the hybrids exhibit fast reaction kinetics with a turnover frequency of 0.211 $s^{-1}$ at 2.01 V vs. RHE. Density functional theory calculation proposes that POMs vertically align at the NCNT surface exposing the maximal catalytic surfaces. This work suggests a reliable route to highly efficient water oxidation catalysis by employing POMs under neutral conditions and NCNTs as self-binding nanoelectrodes in a synergistic well-oriented hybrid structure. Second, I present the spontaneous and highly specific nucleation of perovskite crystals, that is, methylammonium lead iodide perovskite ($CH_3NH_3PbI_3$, $MAPbI_3$) at NCNT surfaces for the self-assembly of MAPbI3/NCNT hybrids. It is demonstrated that the lone-pair electrons of pyridinic nitrogen-dopant sites at NCNTs mediate specific interactions with the cationic component in the perovskite structure and serve as the nucleation sites via coordinate bonding formation, as supported by X-ray photoelectron spectroscopy and density functional theory calculation. The potential suitability of $MAPbI_3/NCNT$ hybrids is presented for highly sensitive and selective $NO_2$ sensing layer. This work suggests a reliable self-assembly route to the molecular level hybridization of organic-inorganic halide perovskites by employing the substitutional dopant sites at graphene-based nanomaterials. In conclusion, this dissertation present inorganic or organic/inorganic nanostructure on CNT by N-dopant sites and demonstrate the specific binding site and interaction mechanism through experimental chemical analysis and theoretical first-principles calculations. My reliable assembly approach and interfacial engineering expected to provide heterojunction structures with unique functionalities for catalysis and sensing performance and expand various organic and inorganic nanomaterials in conjunction with graphene-based nanomaterials by employing the substitutional dopant sites.