Mesoporous SnO₂@Co₃O₄ Core–Shell Nanospheres for High-Performance Toluene Gas Sensors

Toluene is a toxic gas harmful to human health, and accurate detection of trace toluene is of great significance for life safety. This paper first prepared SnO 2 mesoporous nanospheres via a hydrothermal method and then composited different ratios of Co 3 O 4 on the surface and interior of nanospheres through hydrothermal-high temperature calcination. The toluene gas-sensing properties of the six resultant samples were tested. The results show that SnO 2 @Co 3 O 4 -20% exhibits extremely high response ( R g / R a = 10.2) to 100 ppm toluene under 300 °C conditions, approximately 2.2 times that of pristine SnO 2 nanospheres, with a detection limit reaching an 831 ppb level, along with excellent repeatability and stability. The enhanced performance is primarily attributed to a stable heterojunction formation between Co 3 O 4 and SnO 2, causing significant resistance variation. Since Co x + can substitute Sn 4+, Co 3 O 4 doping increases oxygen vacancy concentration on the material surface. Core–shell structured composite materials inherit the high surface area characteristic of mesoporous materials, providing abundant active sites for target gas and oxygen molecule reactions, which also contributes to performance improvement. This paper thoroughly analyzes the gas-sensing mechanism and the role of SnO 2 @Co 3 O 4 . The results demonstrate that SnO 2 @Co 3 O 4 is an excellent toluene detection material.