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Carbon dots (CDs) played increasingly important roles in biotechnology due to their potential as alternatives of natural enzymes. However, the fabrication of highly active and durable CDs remains challenging and catalytic reaction mechanisms over CDs needs to be better clarified for future advances. Herein, we synthesized manganese-doped carbon dots (Mn-CDs, ∼5 nm) with excellent oxidase properties which exhibits stable catalytic capacity in various salt solutions at different temperatures. Moreover, by thoroughly investigating catalytic ability of Mn-CDs, we found that doped Mn atoms effectively modulated the spin density and charge distribution of CDs, thus reducing the band gap by forming intermediate energy levels. Besides, it is found that the content of pyrrolic N positively correlated to catalytic capacity of Mn-CDs. As a demonstration, the prepared Mn-CDs could work as pseudo-oxidase in real cell environment. They can easily enter into cells, induce the production of ·O 2 − under ultraviolet light irradiation, and eventually inhibit the activity of HeLa cells and 4T1 cells. We believe that the as-prepared Mn-CDs would find wide applications as metal-doped artificial nanozymes, and lay a foundation for the application and development of Mn-CDs. [ABSTRACT FROM AUTHOR]

We report for the first time using pure cobaltous tungstate (CoWO 4) as an efficient ethanol sensor by controlling the Co3+-Co2+ redox couple in CoWO 4. The prepared Co x WO 4 has a flower-like structure self-assembled by a mesoporous microbelt. Moreover, the Co x WO 4 sensor with a Co3+/Co2+ ratio of 38.9% exhibits a high response (42.9–100 ppm ethanol), fast response/recovery time (11/13 s), low detection limit (0.42 ppm), as well as remarkable short-term and long-term repeatability. Notably, the Co x WO 4 sample maintains a constant response value over a wide range of humidity (30–90 RH%), manifesting its good anti-humidity properties. The outstanding sensing performance is owing to the Co3+-Co2+ redox couple, high surface area and moderate porosity of the obtained samples. The self-transforming of the Co3+-Co2+ redox couple contributes to the formation of absorbed oxygen (O 2 -), oxygen vacancies and the reduction of the band gap, which is a crucial factor in improving the sensing properties of Co x WO 4. • Pure cobalt tungstate was used for the first time as an efficient ethanol sensor. • The sensor shows a fast response/recovery time and low detection limit. • The self-transforming of Co3+-Co2+ redox on the surface is also a crucial factor. [ABSTRACT FROM AUTHOR]

Regulation based on the crystalline structure modulations is capable of optimizing the band gap and chemisorbed oxygen components thus adjusting the gas sensing characteristics of sensing materials. Herein, In 2 O 3 hierarchical-assembled microspheres with diverse crystalline structures were synthesized via a simple hydrothermal method combined with calcinating procedure under different temperatures. The gas sensor based on rhombohedral In 2 O 3 (rh-In 2 O 3) microspheres assembled by pine needle shaped nanorods annealed at 350 ℃ (350-In 2 O 3) exhibited superior H 2 S sensing performances at relative low operating temperature of 100 ℃ with low detection limit (50 ppb) and optimized stability compared with cubic In 2 O 3 (c-In 2 O 3). Notably, H 2 S sensing characteristics of In 2 O 3 samples with different crystalline structures certificated that crystal structures can dominate the H 2 S sensing reactions with different mechanisms. This work enlightened a novel prospect for designing rh-In 2 O 3 based sensors and provides an innovative pathway for analyzing the feasible H 2 S sensing mechanisms. [Display omitted] • In 2 O 3 materials with diverse crystalline structures were prepared for H 2 S detections. • Rhombohedral In 2 O 3 microspheres is composed of nanorods (diameter of 8 nm). • Rhombohedral In 2 O 3 based sensor displayed the optimized H 2 S sensitivity. • Crystalline structure controls H 2 S sensing mechanism. [ABSTRACT FROM AUTHOR]

Mesoporous Fe-doped In 2 O 3 nanorods derived from metal-organic frameworks (In/Fe-MIL-68s) were synthesized for NO 2 detection. The morphologies, structures and NO 2 gas-sensing performances of the Fe–In 2 O 3 nanorods were systematically investigated. Texture characterizations demonstrate that the as-prepared Fe–In 2 O 3 nanorods show rich porous structures, high specific surface areas and reduced grain sizes. Gas-sensing measurements display that the Fe–In 2 O 3 nanorods derived from In/Fe-MIL-68s with the Fe(Ⅲ) content of 5 mol.% (Fe(5)-In 2 O 3) exhibit high response (82) and short response/recovery time (70/65 s) towards 2 ppm NO 2 at 80 °C compared with their counterparts. Besides, superior selectivity and good stability are observed. The sensing mechanism studies reveal that the improved gas-sensing performances are attributed to the decrease in the gran size, the formation of rich oxygen vacancies and band gaps narrowing caused by Fe(Ⅲ) doping. Therefore, this work indicates that the Fe–In 2 O 3 nanorods derived from metal-organic frameworks precursors can be a promising candidate for NO 2 detection. [ABSTRACT FROM AUTHOR]

Due to the intrinsic properties of wide band gap and the 5d shell being vacant, WO 3 still has the disadvantages of low response dynamics, slow response/recovery speed and high detection limit for real-time gas monitoring. To address such issues, the Ni3+ doped WO 3 hierarchical hollow structure composed of irregular nanosheets was achieved and the content of adsorbed oxygen was adjusted by Ni3+ doping to further improve the gas sensing performance of WO 3. In comparison to pure WO 3 , the 3 wt%Ni-WO 3 sensor exhibited remarkable response value (396), short response/recovery speed (13 s/6 s) and low detection limit (510 ppt) at 160 ℃. The impressive gas properties could be attributed to the reduced band gap and oxygen inhibiting effect of Ni3+ doping, which provides more NO 2 adsorption sites and making it easier for NO 2 to capture more electrons in the conduction band by restraining the oxygen ions chemisorbed on the surface. The unique sensing characteristics of the Ni3+ doped WO 3 suggest its wonderful potential applications in environmental pollution gas detection. The mechanism of oxygen inhibiting effect induced by Ni3+ doping was also discussed in detail [Display omitted] • The Ni3+ doped WO 3 was synthesized via soaking and oil bath evaporation. • The sensor based on Ni3+ doped WO 3 presented rapid response/recovery speed and low detection limit. • The superior sensing characteristic can be attributed to the oxygen inhibiting effect. [ABSTRACT FROM AUTHOR]

Triethylamine (TEA) is a typical pollution in chemical industry and Corrupt markers of aquatic products. TEA emissions have a serious impact on human health, industrial production and food safety. In this study, hierarchical flower-like Pt-loaded/Ce-doped In 2 O 3 microspheres are synthesized via simple hydrothermal and in-situ reduction methods. The triethylamine (TEA) sensing measurements display the 0.5Pt-3CeIn gas sensor exhibits high sensitivity (R a /R g = 900–100 ppm triethylamine), ultra-low optimal working temperature (100 ℃), enhanced responding and recovering speed (158/45 s) and excellent selectivity towards different target gases (ethanol, acetone, xylene, methanol, nitrogen dioxide and methane) including amine (response towards 50 ppm NH 3 is lower than 10). The TEA detection limit is as low as 5 ppb and the sensor exhibits a wide TEA detection range. The introduction of Pt and Ce components into In 2 O 3 effectively reduces the operating temperature, promotes the chemisorbed oxygen content (18.14 %) and wildly decreases the band gap (2.97 eV). The gas sensing mechanism of Pt/Ce-In 2 O 3 , which is dominated by electronic and chemical sensitization of Pt, catalytic function of Ce dopants and the functional interface between Pt nanoparticles and Ce-doped In 2 O 3 microspheres, is proposed. This work as well testifies the feasibility for multi-components cooperative optimization of MOS in gas sensing applications. [Display omitted] [ABSTRACT FROM AUTHOR]