Large-Scale Fabrication of High-Performing Single-Crystal SiC Nanowire Sponges Using Natural Loofah

Abstract

This study presents large-scale fabrication of singlecrystal SiC nanowire (SiC nw ) sponges through a carbothermal reduction approach using agricultural residue loofah, which is believed to be a perfect alternative to traditional petrochemical materials as the carbon source in industrial fabrication of SiC nanowires, without additional chemical C sources or catalysts. The single-crystal ultralong SiC nw are observed to have diverse morphologies with diameters of 50−400 nm, which possess a significant anisotropic and hierarchical microstructure with planaraligned bamboo joints. A roughly 2 nm thick amorphous SiO 2 layer is identified wrapping the crystalline 3C-SiC. The underlying vapor−solid mechanism is systematically investigated via thermodynamic calculations on the formation and interactions of SiO, CO, and SiC. Noteworthily, the fabricated loofah-based SiC nw sponge exhibits prominent high-temperature performance after thermal insulation tests of alcohol lamp flame and butane blowtorch flame, which is attributed to the stacking faults, SiO 2 layer, SiC/ SiO 2 interface of the nanowires, and the overlength pathway in the porous aerogel−sponge domain synergetically acting as a phonon barrier to enhance phonon scattering, prolong phonon diffusion, and eventually reduce solid thermal conductivity in the sponge architecture. Our current work has great potential to be applied in the eco-friendly industrial preparation of high-performing SiC nw as thermal protection materials in harsh environments.

Synthesis of 3C/2H/6H heterojunction SiC nanowires with high-performance supercapacitors by thermal evaporation

“…The formation of SiC NWs can be divided into four processes: SiO gas formation, CO gas formation, nucleation of SiC, and growth of SiC. 72,73 The SiO gas is generated as per the following reactions expressed in eqn (5) and (6):SiO 2 (solid) + C(solid) = SiO(vapor) + CO(vapor)SiO 2 (solid) + Si(solid) = 2SiO(vapor)…”

High-Yield Synthesis of SiC@SiO2 Core–Shell Nanowires on Graphite Substrates for Energy Applications

“…The formation of solid SiC@SiO 2 NWs occurs via gas–gas reactions between the intermediate gases of SiO and CO (as shown in Table S1). – The unavoidable presence of trace amounts of O 2 in the equipment, so in the Si–C–O systems, SiO gas should first be formed through possible solid–solid reactions or solid–gas reactions as follows: , 2 S i false( normals false) + O 2 ( g ) = 2 S i O false( normalg false) normalS normali normalO 2 ( s ) + normalC ( s ) = normalS normali normalO ( g ) + normalC normalO ( g ) normalS normali normalO 2 ( s ) + normalC normalO ( g ) = normalS normali normalO ( g ) + normalC normalO 2 ( g ) normalS normali normalO 2 ...…”

“…However, Hao et al suggested that reactions and have positive feedback characteristics to each other, so that reaction occurs and leads to stable growth of NWs . The Δ G of reaction is much less than zero in the range of 500–1600 °C, which means that reaction can occur at the synthesis temperature, thus generating a mixture of products that produce SiC crystals and SiO 2 amorphous crystals . As the melting point of SiC is much higher than that of SiO 2 , SiC crystals precipitate and separate out to form SiC@SiO 2 core–shells. , According to the principle of minimum energy, SiC NWs grow along the direction of [111]. , …”

“…Due to the unsaturated chemical bonding and the presence of gas flow, the SiO gas could be easily adsorbed on the graphite surface . The SiO gas will react with the active carbon atoms to form SiC nuclei . Under continuous supplementation of SiO gas, it will react with CO to form SiC nuclei, which are deposited on the SiC(111) plane due to the least-energy principle, leading to SiC@SiO 2 NWs along the SiC [111] direction.…”

“…It can be seen that the ΔG values of reactions 3−6 in the standard state show a linear decrease with increasing temperature (Figure S4a), where ΔG for reaction 3 is negative in the range of 500−1600 °C while those for reactions 4−6 are positive, implying that the thermodynamically relevant chemical reaction 3 can occur spontaneously. 64 Theoretically, reactions 4−6 would not occur, but due to the high activity of amorphous SiO 2 , which reduces ΔG and make them possible. 40,68 Chen et al indicated that amorphous SiO 2 could react with graphene to form SiO gas at 1000 °C.…”