Hierarchical Branched Mesoporous TiO₂-SnO₂ Nanocomposites with Well-Defined n-n Heterojunctions for Highly Efficient Ethanol Sensing

The direct assembly of functional nanoparticles into a highly crystalline mesoporous semiconductor with oriented configurations is challenging but of significance. Herein, an evaporation induced oriented co-assembly strategy is reported to incorporate SnO₂ nanocrystals (NCs) into a 3D branched mesoporous TiO₂ framework by using poly(ethylene oxide)-block-polystyrene (PEO-b-PS) as the template, SnO₂ NCs as the direct tin source, and titanium butoxide (TBOT) as the titania precursor. Owing to the combined properties of ultrasmall particle size (3-5 nm), excellent dispersibility and presence of abundant hydroxyl groups, SnO₂ NCs can easily interact with PEO block of the template through hydrogen bonding and co-assemble with hydrolyzed TBOT to form a novel hierarchical branched mesoporous structure (SHMT). After calcination, the obtained composites exhibit a unique 3D flower-like structure, which consists of numerous mesoporous rutile TiO₂ branches with uniform cylindrical mesopores (≈9 nm). More importantly, the SnO₂ NCs are homogeneously distributed in the mesoporous TiO₂ matrix, forming numerous n-n heterojunctions. Due to the unique textual structures, the SHMT-based gas sensors show excellent gas sensing performance with fast response/recovery dynamics, high sensitivity, and selectivity toward ethanol.