Amphiphilic Block Copolymer Templated Synthesis of Mesoporous Indium Oxides with Nanosheet-Assembled Pore Walls

Abstract

A solvent evaporation induced coassembly approach combined with a comburent CaO₂-assisted calcination strategy was employed for the synthesis of ordered mesoporous indium oxides by using lab-made high-molcular weight amphiphilic diblock copolymer poly­(ethylene oxide)-<i>b</i>-polystyrene (PEO-<i>b</i>-PS) as a template, indium chloride as an indium source, and THF/ethanol as the solvent. The obtained mesoporous indium oxide materials exhibit a large pore size of ∼14.5 nm, a surface area of 48 m² g^–1, and a highly crystalline In₂O₃ nanosheets framework, which can facilitate the diffusion and transport of gas molecules. By using an integrated microheater as the chemresistance sensing platform, the obtained mesoporous indium oxides were used as sensing materials and showed an excellent performance toward NO₂ at a low working temperature (150 °C) due to their high porosity and unique crystalline framework. The limit of detection (LOD) of the microsensor based on mesoporous indium oxides can reach a concentration as low as 50 ppb of NO₂. Moreover, the microsensor shows a fast response-recovery dynamics upon contacting NO₂ gas and fresh air due to the highly open mesoporous structure and the large mesopores of the crystalline mesoporous In₂O₃