Facile synthesis of mesoporous hierarchical Co₃O₄–TiO₂ p–n heterojunctions with greatly enhanced gas sensing performance

Abstract

The development of highly active, sensitive and durable gas sensing materials for the detection of volatile organic compounds (VOCs) is extremely desirable in gas sensors. Herein, a series of mesoporous hierarchical Co3O4-TiO2 p-n heterojunctions have been prepared for the first time via the facile thermal conversion of hierarchical CoTi layered double hydroxides (CoTi-LDH) precursors at 300-400 ºC. The resulting Co3O4-TiO2 nanocomposites showed superior sensing performance towards toluene and xylene in comparison with Co3O4 and TiO2 at low temperature, and the sample with a Co/Ti molar ratio of 4 shows optimal response (Rg/Ra = 113, Rg and Ra denote the sensor resistance in a target gas and in air, respectively) to 50 ppm xylene at 115 ºC. The ultrahigh sensing activity of theses Co3O4-TiO2 p-n heterojunctions originates from their hierarchical structure, high specific surface area (>120 m 2 g −1 ), and the formation of numerous p-n heterojunctions, which results in full exposure of active sites, easy adsorption of oxygen and target gases, and large modulation of resistance. Importantly, hierarchical Co3O4-TiO2 heterojunctions possess advantages of simple preparation, structural stability, good selectivity and long-term durability. Therefore, this work provides a facile approach for the preparation of hierarchical Co3O4-TiO2 p-n heterojunctions with excellent activity, sensitivity and durability, which can be used as a promising material for the development of high-performance gas sensors.

Interior Supported Hierarchical TiO2@Co3O4 Derived from MOF‐on‐MOF Architecture with Enhanced Electrochemical Properties for Lithium Storage

“…The relative stronger Co 3+ intensity and higher calculated ratio of Co 3+ /Co (Table S1) of TiO 2 @Co 3 O 4 , further confirming the existence of CoTiO 3 intermediate phase. The O 1s spectra (Figure S6b) is divided into three peaks at 530.2, 531.4 and 532.6 eV corresponding to the lattice oxygen (O lat ), the deficient oxygen (O def ) and adsorbed oxygen (O abs ), respectively . Notably, the O def peak of TiO 2 @Co 3 O 4 is slightly higher than that of Co 3 O 4 /TiO 2 , suggesting that more oxygen vacancies were created after annealing attributed to the noble structure of TiO 2 @Co 3 O 4 .…”

Expanded graphite/NiAl layered double hydroxide nanowires for ultra-sensitive, ultra-low detection limits and selective NOx gas detection at room temperature

“…In particular, due to their excellent physical and electrical properties, carbon materials, such as carbon nanotubes (CNTs), carbon black (CB), graphene (GN), and carbon nitride (g-C 3 N 4 ) nanomaterials, have received great attention as gas sensor materials. 8 Seekaew et al 9 obtained 3D TiO 2 /graphene-carbon nanotube (TiO 2 /G-CNT) composites by chemical vapor deposition and sparking. It was found that 3D TiO 2 /G-CNT composites with optimum spark time of 60 s at RT showed high response to toluene (500 ppm, $42%).…”

Graphene Oxide@3D Hierarchical SnO2 Nanofiber/Nanosheets Nanocomposites for Highly Sensitive and Low-Temperature Formaldehyde Detection

“…It demonstrated that BET surface area of the nanocomposites could further increase after the introduction of GO nanosheets. The larger BET surface area of 1% GO@SnO 2 NF/NSs could provide more active sites for the adsorption of gas molecules, which could facilitate the improvement of gas-sensing performance [36,37]. With respect to the pore size distribution of these sensing materials, as can be observed in Figure S2b, the GO@SnO 2 nanocomposites have a smaller pore size (25.7 nm) than that of pure SnO 2 (37.8 nm), which may be ascribed to introduction and wrapping of GO on hierarchical SnO 2 .…”