Search

The construction of composites based on metal oxides with exposed high-energy facets is very significant in a wide range of applications including gas detection, catalysis, and energy storage. However, the synthesis of such composites is always hindered by the smooth exposed surface of metal oxides, which is difficult to nucleate and grow a second component. To solve this problem, a novel metal–organic framework-assisted method was proposed to anchor ZnO nanoparticles on {221} facets of SnO2octahedrons simply by a coating and oxidation process of ZIF-8 on the smooth {221} surface. It was found that a high nucleation energy results from an appropriate ratio of Zn2+and 2-methylimidazole, giving priority to the heterogeneous nucleation and growth process for ZIF-8 on the surface of SnO2octahedral nanoparticles. The coverage of ZnO on the smooth surface can also be modulated by the ZIF-8 film. Thanks to the newly designed composites with special structure, the gas-sensing performances of {221} SnO2were improved extensively, whose response toward 100 ppm triethylamine (TEA) can be increased more than triple times from 5.68 to 18.37 (Ra/Rg) by the combination of ZnO nanoparticles. This intensively improved gas-sensing performance was attributed to the special structure with extra sensitive depletion layers at the heterojunction as well as the single-crystalline feature of SnO2octahedral nanoparticles. These composites are thus promising gas-sensing materials for TEA detection with excellent performances. More significantly, it can also pave a new way to combine metal oxides with exposed high-energy facets, providing a unique and effective means for enhancing the properties and functionality of materials in a range of fields.

The formation of p–n junctions has attracted much attention for improving the gas-sensing performances in the field of gas detection. Although the p–n heterojunctions with a defined interfacial contact are crucial in investigating their roles on gas-sensing properties, the design of such well-defined p–n heterojunctions has been sparse until now. Herein, a p–n heterostructure composed of well-defined {001}-faceted Co3O4as backbones and Fe2O3nanorods as shells was synthesized using a simple hydrothermal method without the requirement of seed crystals. During the reaction, it was demonstrated that the acetic acid holds the key to the epitaxial growth of Fe2O3nanorods on the surface of Co3O4nanocubes. The response of this as-designed Fe2O3@Co3O4composite (Ra/Rg= 134.9) toward 100 ppm triethylamine was about 6 times higher than that of pristine Co3O4(Ra/Rg= 23.1) and 5 times higher than that of pristine Fe2O3(Ra/Rg= 28.9). The highly boosted gas-sensing performances were attributed to the positive effects of the heterointerface on the gas adsorption process that were revealed through the first-principles method based on the defined heterointerfacial contacts, as well as the enlarged signal of gas–solid reactions through the heterojunctions. This work not only provides a strategy to improve gas-sensing performances but also provides guidance for the investigation of the effects of p–n heterojunctions on gas-sensing properties by designing interfacial contact with defined crystal facets.