Rational Synthesis and Gas Sensing Performance of Ordered Mesoporous Semiconducting WO₃/NiO Composites

Semiconducting metal oxides have attracted increasing attention in various fields due to their intrinsic properties. In this study, a facile solvent evaporation-induced multicomponent co-assembly approach coupled with a carbon-supported crystallization strategy is employed to controllably synthesize crystalline mesoporous nickel oxide-doped tungsten oxides in an acidic THF/H₂O solution with poly(ethylene oxide)-b-polystyrene diblock copolymers (PEO-b-PS) as the structure-directing agent, tungsten(VI) chlorides as WO₃ precursors, and Ni(AcAc)₂ as the NiO precursor. The obtained materials possess a face-centered cubic mesoporous structure, large pore size (∼30 nm), high surface area (30-50 m² g^-1), large pore volume (0.15-0.19 cm³ g^-1), and ultralarge pore windows (12-16 nm) connecting adjacent mesopores, and the mesoporous WO₃ framework was decorated by ultrafine NiO nanocrystals. Due to their well-connected porous structure and high surface areas with rich WO₃-NiO interfaces, the composite materials exhibit superior gas sensing performance with an ultrafast response (∼4 s), high sensitivity (R_a/R_g = 58 ± 5.1), and selectivity to 50 ppm H₂S at a relatively low working temperature (250 °C). The chemical mechanism study reveals complicated surface reactions of WO₃/NiO-based gas sensors, and SO₂, WS₂, and NiS intermediates were found to be generated during the gas sensing process.