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Formaldehyde (HCHO) is the main source of indoor air pollutant. HCHO sensors are therefore of paramount importance for timely detection in daily life. However, existing sensors do not meet the stringent performance targets, while deactivation due to sensing detection at room temperature, for example, at extremely low concentration of formaldehyde (especially lower than 0.08 ppm), is a widely unsolved problem. Herein, we present the Ag nanoparticles (Ag NPs) sensitized dispersed In2O3 nanograin via a low-fabrication-cost hydrothermal strategy, where the Ag NPs reduces the apparent activation energy for HCHO transporting into and out of the In2O3 nanoparticles, while low concentrations detection at low working temperature is realized. The pristine In2O3 exhibits a sluggish response (Ra/Rg = 4.14 to 10 ppm) with incomplete recovery to HCHO gas. After Ag functionalization, the 5%Ag-In2O3 sensor shows a dramatically enhanced response (135) with a short response time (102 s) and recovery time (157 s) to 1 ppm HCHO gas at 30 °C, which benefits from the Ag NPs that electronically and chemically sensitize the crystal In2O3 nanograin, greatly enhancing the selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

The rational design of heterojunction between different metal oxides with mesoporous structures has attracted tremendous attention due to their special physicochemical properties and vital importance for practical applications. In this paper, mesoporous Ag/Zn–LaFeO3 nanocomposite is successfully synthesized through a facile nanocasting technique using KIT‐6 as a hard template in sol–gel route and used as sensing materials to achieve an exceptionally sensitive and selective detection of trace ppm‐level ethanol. The obtained composite possesses high surface area and exhibits excellent sensing response (64.2 for 100 ppm) to ethanol at near‐room with relatively fast response/recovery time. When tested with the concentrations as low as 5 ppm, it also shows a remarkably high selectivity to the ethanol, but only minor responses to other interfering gases. These enhanced gas‐sensing properties are attributed to the combination of mesoporous nanostructure and Ag/Zn–LaFeO3 heterogeneous composites. Perovskite type metal oxide semiconductors are developed for application of gas sensors due to their numerous favorable physical/chemical properties. LaFeO3 shows considerably sensitive to reducing gases, but it still has some deficiencies. Mesoporous Ag/Zn–LaFeO3 nanocomposite synthesized through facile nanocasting technique is used as a sensing material to achieve sensitive and selective detection of trace ppm‐level ethanol at near‐room temperature. [ABSTRACT FROM AUTHOR]

Formaldehyde is a common carcinogen in daily life and harmful to health. The detection of formaldehyde by a metal oxide semiconductor gas sensor is an important research direction. In this work, cobalt-doped SnO 2 nanoparticles (Co-SnO 2 NPs) with typical zero-dimensional structure were synthesized by a simple hydrothermal method. At the optimal temperature, the selectivity and response of 0.5% Co-doped SnO 2 to formaldehyde are excellent (for 30 ppm formaldehyde, R a / R g = 163 437). Furthermore, the actual minimum detectable concentration of 0.5%Co-SnO 2 NPs is as low as 40 ppb, which exceeds the requirements for formaldehyde detection in the World Health Organization (WHO) guidelines. The significant improvement of 0.5%Co-SnO 2 NPs gas performance can be attributed to the following aspects: firstly, cobalt doping effectively improves the resistance of SnO 2 NPs in the air; moreover, doping creates more defects and oxygen vacancies, which is conducive to the adsorption and desorption of gases. In addition, the crystal size of SnO 2 NPs is vastly small and has unique physical and chemical properties of zero-dimensional materials. At the same time, compared with other gases tested, formaldehyde has a strong reducibility, so that it can be selectively detected at a lower temperature., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

To address the urgent issues of hazardous gas detection and the prevention of environmental pollution, various functional materials for gas sensing and catalytic reduction have been studied. Specifically, the p-type perovskite LaFeO 3 has been studied widely because of its promising physicochemical properties. However, there remains several problems to develop a controllable synthesis of LaFeO 3 -based p-n heterojunctions. In this work, α-Fe 2 O 3 was further compounded with LaFeO 3 to form a porous and hollow α-Fe 2 O 3 /LaFeO 3 heterojunction to improve its gas-sensing performance and photocatalytic efficiency via a microwave-assisted hydrothermal method. While evaluated as sensors of acetone gas, the optimized sample exhibits excellent performance, including a high response (48.3), excellent selectivity, good reversibility, fast response, and recovery ability. Furthermore, it is an efficient catalyst for the degradation of methylene blue. This can be attributed to the enhancement effect of its larger specific surface area, fast diffusion, enhanced surface activities, and p-n heterojunction. Additionally, this work provides a rapid and rational synthesis strategy to produce metal oxides with both enhanced gas-sensing performance and improved photocatalytic properties.

Xylene is a volatile organic compound which is harmful to the human health and requires precise detection. The detection of xylene by an oxide semiconductor gas sensor is an important research direction. In this work, Co 3 O 4 decorated flower-like SnO 2 nanorods (SnO 2 /Co 3 O 4 NRs) were synthesized by a simple and effective two-step method. The SnO 2 /Co 3 O 4 NRs show high xylene response (R g /R a  = 47.8 for 100 ppm) and selectivity at the operating temperature of 280 °C, and exhibit high stability in continuous testing. The resulting SnO 2 /Co 3 O 4 NRs nanocomposites show superior sensing performance towards xylene in comparison with pure SnO 2 nanorods. The remarkable enhancement in the gas-sensing properties of SnO 2 /Co 3 O 4 NRs are attributed to larger specific surface area and the formation of p-n heterojunction between Co 3 O 4 and SnO 2 . These results demonstrate that particular nanostructures and synergistic effect of SnO 2 and Co 3 O 4 enable gas sensors to selectively detect xylene.