Self-template synthesis of spherical mesoporous tin dioxide from tin-polyphenol-formaldehyde polymers for conductometric ethanol gas sensing

Spherical mesoporous tin dioxides are emerging sensing materials for fabrication of gas sensor applied in various fields. However, the synthesis of spherical mesoporous SnO₂ with uniform shape and small diameter (i.e., <100 nm) is still challenging. Herein, spherical mesoporous SnO₂ materials with tunable diameter (55−110 nm), large pore size (∼5.8 nm) and high specific surface area (80.9-185.6 m²/g) are synthesized via a self-template strategy by direct thermal decomposition of tin-polyphenol-formaldehyde polymers (TPFPs). Spherical TPFPs are synthesized via a sol-gel process using a low-cost, nontoxic and renewable natural polyphenol (i.e., tannic acid) as a ligand, formaldehyde as a cross-linking agent, tin ions as a metal source in alkaline conditions. Block copolymers can regulate the polymerization process and promote the formation of uniform spheres. The diameter of TPFPs and their derived spherical mesoporous SnO₂ can be adjusted by changing the amount of block copolymers. The gas sensors fabricated from spherical mesoporous SnO₂ exhibit excellent sensitivity to ethanol (18.9@50 ppm), fast response and recovery time (4 s / 44 s), good repeatability and long-term stability. This work demonstrates a reliable method for synthesis of spherical mesoporous SnO₂, which could be potentially applied in catalysis, sensing and energy storage.