Growth mechanism of Te nanotubes by a direct vapor phase process and their room-temperature CO and NO2 sensing properties

The growth of Te nanotubes by the direct vapor phase process is dominated by the vapor–solid(VS) mechanism, where the intrinsic anisotropic crystal structure of tellurium and axialdislocations contained in the Te nanostructures should play crucial roles. During the growthprocess, Te nanoparticles will nucleate on the growth substrate in the initial stage, and thengrow into nanoflakes and two-faced nanoscreens lying horizontally on the substrate until theyfully cover the substrate. Some of the nanoscreens with certain horizontal angles with respectto the substrate surface will protrude out of the growth substrate and become preferentialabsorption sites for the incoming Te atoms. The two-faced nanoscreens then gradually developinto three-faced nanoscreens, four-faced nanogrooves, and finally perfect hexagonal nanotubesdue to the lateral diffusion of Te atoms. Upon exposure to CO and NO2 at room temperature,Te nanotube sensors showed the same direction of resistance change, adequate sensitivities,and fast response and recovery times, making them promising candidates for use in air-qualitysingle sensors

Vapor–Solid Growth of p-Te/n-SnO2Hierarchical Heterostructures and Their Enhanced Room-Temperature Gas Sensing Properties

We have synthesized brushlike p-Te/n-SnO2 hierarchical heterostructures by a two-step thermal vapor transport process. The morphologies of the branched Te nanostructures can be manipulated by adjusting the source temperature or the argon flow rate. The growth of the branched Te nanotubes on the SnO2 nanowire backbones can be ascribed to the vapor-solid (VS) growth mechanism, in which the inherent anisotropic nature of Te lattice and/or dislocations lying along the Te nanotubes axis should play critical roles. When exposed to CO and NO2 gases at room temperature, Te/SnO2 hierarchical heterostructures changed the resistance in the same trend and exhibited much higher responses and faster response speeds than the Te nanotube counterparts. The enhancement in gas sensing performance can be ascribed to the higher specific surface areas and formations of numerous Te/Te or TeO2/TeO2 bridging point contacts and additional p-Te/n-SnO2 heterojunctions

Vapor–Solid Growth of p‑Te/n-SnO₂ Hierarchical Heterostructures and Their Enhanced Room-Temperature Gas Sensing Properties

We have synthesized brushlike p-Te/n-SnO₂ hierarchical heterostructures by a two-step thermal vapor transport process. The morphologies of the branched Te nanostructures can be manipulated by adjusting the source temperature or the argon flow rate. The growth of the branched Te nanotubes on the SnO₂ nanowire backbones can be ascribed to the vapor–solid (VS) growth mechanism, in which the inherent anisotropic nature of Te lattice and/or dislocations lying along the Te nanotubes axis should play critical roles. When exposed to CO and NO₂ gases at room temperature, Te/SnO₂ hierarchical heterostructures changed the resistance in the same trend and exhibited much higher responses and faster response speeds than the Te nanotube counterparts. The enhancement in gas sensing performance can be ascribed to the higher specific surface areas and formations of numerous Te/Te or TeO₂/TeO₂ bridging point contacts and additional p-Te/n-SnO₂ heterojunctions

Facile Synthesis of Monodispersed In2O3 Hollow Spheres and Application in Photocatalysis and Gas Sensing

Monodispersed, agglomerate-free In2O3 hollow spheres have been prepared via a simple synthetic route involving permeation and anchoring of In3+ ions with carbonyl groups of swollen commercial polymer beads in tetrachloroethylene solvent followed by thermal removal of the template cores in ambient air. The as-synthesized hollow spheres exhibit a narrow size distribution with tunable particle size (0.5–1.2 μm) and shell thickness (62–230 nm) over the process variables examined, i.e., InCl3 precursor concentration (4.5 × 10−3–6.7 × 10−2 M), reaction temperature (55°C–95°C), and reaction time (1–6 h). Kinetics calculation reveals that the formation of permeating In3+-rich shell in the swollen template beads becomes energetically less favorable to proceed as the reaction time increases. This limits the maximum shell thickness attainable at the given process variables. The shell is nanoporous with a Horvath-Kawazoe (HK) pore size of ~3 nm, which remains essentially unchanged as the process variables alter. The In2O3 hollow spheres with an increased Brunauer-Emmett-Teller (BET) surface area (up to 329 m2/g) show an improved capability in photodegradation of aqueous methylene blue (MB) dye under UV exposure as well as an increased sensitivity for CO-gas detection. This metal-implantation scheme is general and can be extended to the synthesis of other hollow materials in various solvent liquids