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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]

Sensing reaction mechanism is decisive for improvement of the sensing property of metal oxide sensing materials. Herein, we demonstrated a conceptually different approach to improving sensing property of ZnO nanoparticles by increasing quantity of the surface unsaturated 3-coordinated Zn atoms through hydrogenation. The surface 3-coordinated Zn atoms play a pivotal role in sensing reaction. They can produce electrons, adsorb O2 and catalyze the gas sensing reaction between the adsorbed oxygen and test gas. A sensing mechanism of the unsaturated Zn atom serving as a sensing reactive site is presented for the first time. The mechanism provides a deep understanding for sensing and catalytic reaction mechanisms. In addition, the sensing performance of other sensing materials and reactive activity of catalysts may be enhanced by increasing concentration of surface unsaturated metal atom through hydrogenation. [ABSTRACT FROM AUTHOR]

We demonstrated a new approach to increasing response of Fe 2 O 3 nanoparticles and sea urchin-like nanostructures towards methanol, ethanol, formaldehyde, acetone, triethlamine and n-Butylamine by increasing number of surface Fe atoms having dangling bonds through hydrogenation. The surface Fe atoms having dangling bonds are believed to serve as the reactive atoms for sensing reaction, thus, a gas sensing mechanism at atomic and molecular level is presented for the first time. The surface unsaturated active Fe atoms can adsorb oxygen molecules, produce electrons and catalyze the chemical reaction of the adsorbed oxygen with target gas. Hydrogenation may be a universal approach to increasing gas sensing performances of metal oxides. The gas sensing mechanism can deepen comprehending electron transfer during the gas sensing process and offer guidance to design the gas sensing materials with higher performances. • Hydrogenation is successfully used to improve the sensitivity of α-Fe 2 O 3 gas sensors. • Density of unsaturated Fe atoms at the surface is increased by hydrogenation. • The unsaturated Fe atoms are regarded to act as an active site for sensing reaction. • They generate free electrons, adsorb oxygen and catalyze the gas sensing reaction. • Hydrogenation may be used to improve gas sensing properties of other metal oxides. [ABSTRACT FROM AUTHOR]

In this work, we successfully developed a strategy for enhancing sensing performances of WO 3 nanoparticles by increasing density of the 5-fold coordinated unsaturated W atoms at the surface of WO 3 nanoparticles through hydrogenation. Responses of the hydrogenated WO 3 nanoparticles sensors towards alcohol, methanol and formaldehyde were found to be 2–3 times higher than that of the WO 3 nanoparticles without hydrogenation. We believed that the 5-fold coordinated W atoms function as the sensing reactive sites and elaborated the sensing reaction mechanism at atomic and molecule level. The 5-fold coordinated W atoms can absorb O 2 molecules, create conductive electrons and catalyze the sensing reaction between the chemisorbed oxygen species with the detected gas. The concept of unsaturated 5-fold coordinated W atoms acting as the reaction active sites will be instructive for the in-depth understanding of sensing and other catalytic reaction as well as design of sensing materials and catalysts with outstanding performance. In addition, the hydrogenation activating surface strategy can be applied to increasing sensing and catalytic properties of other metallic oxides. [ABSTRACT FROM AUTHOR]

Abstract: We report on the near-infrared (NIR) luminescent properties of Bi2O3–GeO2 glass. Apparent differences of NIR luminescence, decay properties and thermal stability manifest the co-existence of more than one active center in this system. The effects of Al ions introduced both unintentionally and intentionally were investigated. 27Al NMR analysis proposes 4-fold Al coordination as dominant structure which can also provide the environment for active centers. We suggest that Al ions play a crucial role to restrain concentration quenching at higher Bi2O3 concentration instead of assisting to construct Bi centers. [Copyright &y& Elsevier]