Hierarchical Branched Mesoporous TiO(2)–SnO(2) 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 SnO(2) nanocrystals (NCs) into a 3D branched mesoporous TiO(2) framework by using poly(ethylene oxide)‐block‐polystyrene (PEO‐b‐PS) as the template, SnO(2) 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, SnO(2) 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 TiO(2) branches with uniform cylindrical mesopores (≈9 nm). More importantly, the SnO(2) NCs are homogeneously distributed in the mesoporous TiO(2) 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.