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The strategy of combining different semiconductor materials is adjudged an effective approach to improve the sensing performances of semiconductor materials. However, the specific synergistic mechanism for the excellent gas‐sensitive performances of composite materials has not been elucidated. Herein, a facile solvothermal method is employed to synthesize SnXTi1‐XO2‐TiXSn1‐XO2 core–shell heterostructures using SnCl4•5H2O and tetrabutyl titanate (TBOT) as raw materials. When the molar ratio of SnCl4•5H2O/TBOT is 1.8/3.0, the afforded composite exhibited the highest gas sensing performances compared with other composites prepared with other molar ratios. The enhanced sensing performance is attributed to the simultaneous incorporation of Sn and Ti ions into each other's lattice, leading to an increase in the density of unsaturated Sn and Ti atoms on the surface. Ultimately, more oxygen vacancies are formed by the unsaturated Sn and Ti atoms, which benefits electron capture and the redox reaction of adsorbed gases. Thus, the concept of increased unsaturated metal atoms and oxygen vacancy resulting from the doping of different metal ions into each other's lattice has deepened the understanding of gas sensing and the catalytic reaction mechanisms. The lattice synergy of different metals provides a pathway for the design of advanced gas‐sensing materials and catalysts. [ABSTRACT FROM AUTHOR]

Co3O4 octahedrons enclosed by {111} facets were synthesized using Cl− ions as a crystal facet control agent. The Co3O4 octahedrons show higher responses than Co3O4 commercial particles to ethanol, methanol, acetone and triethylamine, and the responses are further enhanced by increasing the numbers of 3-coordinated Co atoms (Co3c) with one dangling bond at Co–Co3O4 (111) plane by eliminating surface Cl− ions and OH groups. Accordingly, we deem that the Co3c atom at (111) plane acts as an active center for sensing reaction and present an atomic and molecular level sensing mechanism. The Co3c atoms can produce free electrons, absorb O2 molecules and catalyze the gas-sensing reactions. The surface engineering may be used to bolster gas-sensing properties of other metallic oxides. The concept of Co3c atom as an active center will contribute to understand the true nature of the gas sensing and provide guidance on designing highly performance sensing materials. [ABSTRACT FROM AUTHOR]

The hollow microspheres assembled with ZnO nanoflakes exposing {001} facets have been successfully synthesized by annealing ZnS nanospheres at 550 °C for 2 h. Response of the hollow microspheres assembled from ZnO nanoflakes for ethanol, acetone, or triethylamine is significantly higher than hollow microspheres assembled from ZnO nanorod with dominant {100} facets. The exposed Zn-terminated (001) face is considered to be an active surface for gas sensing. Threefold coordinated Zn (Zn3c) atom with a dangling bond on the Zn-terminated (001) surface serves as a gas-sensing active atom, and thus a gas-sensing mechanism at atomic and molecular level is proposed. The concept of unsaturated Zn3c atoms as a gas-sensing active atoms will be useful for designing of high-performance sensing materials. [ABSTRACT FROM AUTHOR]

Abstract The ZnO foam structure assembled from nanoflakes with exposed {001} facets has been successfully prepared by heating aqueous Zn(NO 3) 2 -polyvinyl pyrrolidone mixed solution. Response of the ZnO foam structure towards ethanol, acetone and n-Butylamine was observably increased by increasing the amounts of 3-coordinated Zn (Zn 3c) atoms on the ZnO (001) surface through hydrogenation. The unsaturated Zn 3c atoms are regarded as the reaction active sites and they contribute to generating free electrons, adsorbing oxygen molecules and catalyzing the reaction of the target gas with chemisorbed oxygen. The sensing mechanism will be instructive for the understanding of the gas sensing and heterogeneous catalytic reactions and the design of high performance sensing materials and catalysts. The hydrogenation optimizing surface-structural engineering may be a general strategy to enhancing sensing and catalytic properties. Highlights • ZnO foam structure with exposed {001} facets were synthesized. • The enhanced gas-sensing property is attributed to the exposed Zn-ZnO (001) facet. • The unsaturated Zn atom at the (001) facet serves as a sensing reaction active site. • A sensing reaction mechanism at molecule level is proposed. [ABSTRACT FROM AUTHOR]

• Sensitivity of {111} faced Cu 2 O octahedron is signally enhanced by hydrogenation. • Density of 1-coordinated Cu atoms at (111) surface is increased by hydrogenation. • The 1-coordinated Cu atoms are regarded to function as the sensing reactive centers. • They can adsorb O 2 , generate free electrons and catalyze the sensing reaction. • The hydrogenation may be a universal strategy for improving sensing properties. Sensitivity of the Cu 2 O octahedral structures towards ethanol, acetone, triethylamine and formaldehyde has been significantly enhanced by increasing the numbers of 1-coordinated Cu (Cu 1c) atoms on the (111) facet of Cu 2 O octahedrons through hydrogenation. The Cu 1c atom with one dangling bond is considered to be a reaction active center. The active center has three kinds of functions: adsorbing oxygen, creating free electrons and catalyzing the redox reaction between the adsorbed oxygen and the detected gas. The findings can deepen comprehending gas sensing mechanisms and give guidance to design high performance sensing material. In addition, the hydrogenation surface-engineering strategy can be employed to enhance sensing performances of other materials. [ABSTRACT FROM AUTHOR]