Functionalization of Mesoporous Semiconductor Metal Oxides for Gas Sensing: Recent Advances and Emerging Challenges

Abstract

With the emerging of the Internet of Things, chemiresistive gas sensors have been extensively applied in industrial production, food safety, medical diagnosis, and environment detection, etc. Considerable efforts have been devoted to improving the gas-sensing performance through tailoring the structure, functions, defects and electrical conductivity of sensitive materials. Among the numerous sensitive materials, mesoporous semiconductor metal oxides possess unparalleled properties, including tunable pore size, high specific surface area, abundant metal-oxygen bonds, and rapid mass transfer/diffusion behavior (Knudsen diffusion), which have been regarded as the most potential sensitive materials. Herein, the synthesis strategies for mesoporous metal oxides are overviewed, the classical functionalization techniques of sensitive materials are also systemically summarized as a highlight, including construction of mesoporous structure, regulation of micro-nano structure (i.e., heterojunctions), noble metal sensitization (e.g., Au, Pt, Ag, Pd) and heteroatomic doping (e.g., C, N, Si, S). In addition, the structure-function relationship of sensitive materials has been discussed at molecular-atomic level, especially for the chemical sensitization effect, elucidating the interface adsorption/catalytic mechanism. Moreover, the challenges and perspectives are proposed, which will open a new door for the development of intelligent gas sensor in various applications.

Polymerization-Induced Aggregation Approach toward Uniform Pd Nanoparticle-Decorated Mesoporous SiO2/WO3 Microspheres for Hydrogen Sensing

“…The electron depletion layer is formed by the electron transfer between WO 3 surface defects and surface-adsorbed oxygen. Based on the “adsorption–catalyst–desorption” principle, ,, the oxidation reaction between H 2 and O 2 induces electron transfer on the surface of the sensing materials, which leads to a rapid change in the resistance of the Pd/Si-mWO 3 - x . The sensing behavior of hydrogen can be generally divided into three stages.…”

“…The working principle of SMOs gas sensors is based on their chemiresistance features, that is, the resistance of SMOs can change rapidly upon contact with guest molecules followed by gas adsorption and catalytic reaction. − In the last decade, various SMOs such as ZnO, − SnO 2 , − MoO 3 , − In 2 O 3 , − and WO 3 , have been extensively explored as sensitive materials for gas sensors toward hydrogen. Among various SMOs, WO 3 -based composites have been considered an ideal sensing material with great potential for applications because they have the advantages of a wide band gap (2.6–3.0 eV), , tunable redox property, and good stability .…”

Metal and Metal Oxide Supported on Ordered Mesoporous Carbon as Heterogeneous Catalysts

“…Configurational diffusion is controlled by the micropore structure and sorbate–sorbent interactions . While for mesoporous and macroporous materials, the mass transfer behavior can be significantly improved, and the collision between reactants and the active sites located on pore walls is determined by the pore size . When the relative size of pore diameter is much larger than the mean free path of the guest molecule (λ), the collision occurs among reactant molecules during the molecular movement.…”

Heterojunctions of ZnO-Nanorod-Decorated WO3 Nanosheets Coated with ZIF-71 for Humidity-Independent NO2 Sensing

“…Nanoscale WO 3 as a famous metal-oxide semiconductor (MOS) gas sensing material is widely used in various applications, , such as gas sensors, , catalysis, photochromic, and electrochromic, due to their wide band gap, excellent sensing properties, thermal stability, and ease of synthesis. , As one of the widely used gas sensing materials, the low sensitivity, high operating temperature, and weak moisture resistance of single tungsten oxide materials still remain critical limitations for the application of WO 3 -based gas sensors. The performance of gas sensors can typically be improved by surface morphology tuning, noble metal decoration, and the construction of heterojunctions.…”