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Low-temperature operating chemiresistive gas sensors are attractive for a variety of real-time gas monitoring applications, with benefits such as low power consumption, profitability, and miniaturization of devices. In this regard, we developed a low-temperature operating H 2 gas sensor using solvothermal-processed novel amine-functionalized zinc-based metal-organic framework (Zn-BDC-NH 2) as a detection material. The Zn-BDC-NH 2 structure is consists of the Zn 4 O secondary building units and 2–aminoterephthalate acidic linker that form the 3D frame structure. Prior to sensing studies, various techniques were employed to confirm -NH 2 functionalization and to characterize structure, surface morphology, thermal stability, surface area, and surface chemistry of synthesized Zn-BDC-NH 2 materials. Benefitting from the simple synthesis process and larger surface area (880 m2g-1) with adequate porosity (~13 Å), Zn-BDC-NH 2 has proven to be an excellent chemiresistive sensor for the effective sensing of low concentrations of H 2 at 50 °C. Moreover, the sensor shown significant sensitivity to the detection of lower H 2 concentrations of 1–10 ppm, a response value of 2.93–10 ppm H 2 , and complete recovery characteristics at 50 °C. We discussed the mechanisms for attaining the excellent H 2 sensing. The utilized room temperature solvothermal approach opens up a perspective for synthesizing Zn-BDC-NH 2 material with suitable functionalities and their use in low temperature H 2 sensors. [Display omitted] • A highly effective H 2 gas sensor using a novel Zn-BDC-NH 2 as the detection material was developed. • Solvothermal-processed Zn-BDC-NH 2 features an ultra-high surface area of 880 m2g-1. • Zn-BDC-NH 2 was an excellent sensor for the selective detection of low-concentration H 2 at 50 °C. • Adding -NH 2 groups to Zn-BDC MOFs increased the binding energy for H 2 gas, ultimately improving H 2 adsorption. [ABSTRACT FROM AUTHOR]

This work demonstrates the potential of a novel iron-based metal-organic framework (Fe-MOF or VNU-15) to effectively detect low-concentration volatile organic compounds (VOCs), particularly acetone (CH 3 COCH 3). A facile solvothermal strategy was used to synthesize Fe-MOFs, comprising Fe(II)/Fe(III) and two distinct linkers—BDC (benzene-1,4-dicarboxylate) and NDC (naphthalene-2,6-dicarboxylic acid). As a first step, Fe-MOFs were characterized to determine their pure phase formation and identify their structural and morphological characteristics. Fe-MOFs processed via the solvothermal method demonstrated high crystallinity, high thermal stability, polyhedral crystal-shaped surface morphology, and a surface area of 735 m2g−1, making them suitable for gas-sensing applications. Laboratory-scale gas-sensing devices were fabricated by printing Fe-MOF powder onto patterned interdigitated electrodes, with performance measurements conducted on these devices in response to exposure to various target gases at temperatures between 25 and 200 °C and gas concentrations between 1 and 10 ppm. Gas-sensing tests confirmed that the VNU-15 sensor selectivity detects CH 3 COCH 3 with a gas response of 1.68–10 ppm and a response time of 64 s, followed by a recovery time of 166 s at 50 °C. This study demonstrates the feasibility of using novel MOF-based sensing channels as low-temperature gas sensors, providing new insights into gas-sensing technology. • Facile low-temperature solvothermal synthesis approach of Fe-MOFs with ultra-high surface area of 735 m2g−1. • The use of Fe-MOFs as an active gas-sensing material has been demonstrated. • Fe-MOF has proven to be an excellent chemiresistive material for detecting low-level CH 3 COCH 3 at 50 °C. • Fe-MOF detects 1 ppm CH 3 COCH 3 , being lower than the breath value for people with diabetes. [ABSTRACT FROM AUTHOR]

This study proposes a solvothermal method for synthesizing sulfate-functionalized hafnium-organic frameworks (Hf-BTC-SO 4) for application in low-temperature NH 3 gas sensors. Prior to the gas-sensing studies, solvothermal-processed Hf-BTC-SO 4 is characterized using various techniques to obtain structural, elemental, morphological, and thermal stability information. Results of structural and thermal-stability analysis demonstrate that Hf-BTC-SO 4 exhibits good crystallinity and high thermal stability with the functionalization of SO 4 in the Hf-framework. Microstructural analysis reveals that nanoparticles aggregated to form compact clusters of Hf-BTC-SO 4. In addition, Hf-BTC-SO 4 has an ultra-high specific surface area of 1100 m2g−1 (with a pore size of 15 Å), suitable for gas detection owing to enhanced surface reactions. Gas-sensing studies confirm that the fabricated Hf-BTC-SO 4 sensor exhibits selective detection of NH 3 gas at a lower working temperature of 100 ºC. Notably, the Hf-BTC-SO 4 sensor detected up to 1 ppm of NH 3 (response = 1.41), with excellent response reversibility. The functionalized sulfate bonds and Hf-clusters within the framework form strong bonds with NH 3 , enhancing their interaction with the metal-organic frameworks. This study can motivate future research on the synthesis of functional organic frameworks for applications in low-temperature NH 3 detection devices. [Display omitted] • A novel sensing material based on Hf-BTC-SO 4 was synthesized and characterized as a chemiresistive gas sensor. • As-synthesized Hf-BTC-SO 4 features an ultra-high surface area of 1100 m2g−1. • Hf-BTC-SO 4 sensor showed a selective detection of NH 3 gas at a low temperature of 100 ºC. • Functionalized sulfate bonds and Hf-clusters enable NH 3 molecules to adsorb by strong host-guest interactions to realize low-level NH 3 detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhancement of the humidity resistance of the semiconductor metal oxide gas sensors. • Coating of SnO 2 nanowires (NWs) with a humidity resistant nanomembrane. • Molecular layer deposition (MLD) was used for the synthesis of the nanomembrane. • The membrane coated SnO 2 NWs gas sensors shows a remarkable gas response under humid conditions. • The sensor showed stability and repeatability in humid conditions like relative humidity (RH %) 30 and 90 %. We report a novel route for enhancing the humidity resistance of SnO 2 nanowires (NWs; widely used metal oxide semiconductor gas sensors) based on their coating with a humidity-resistant nanomembrane. A conformal thin film was deposited by Molecular Layer Deposition (MLD) on the SnO 2 NWs using trimethylaluminum and ethylene glycol as precursors (100 MLD cycles), followed by oxidation in air at 400 °C. In conditions of increasing relative humidity, the SnO 2 NW gas sensor coated with a microporous, 10-nm thick nanomembrane layer of converted alucone obtained by MLD and calcination showed a remarkable gas response compared with the pristine SnO 2 NW gas sensor. This sensor was stable and displayed good recovery times in humid conditions (30 and 90 % of relative humidity). This work shows the benefits and the practical application of MLD-prepared nanomaterials. This original strategy applied to NW-based gas sensors paves the way for other complex 3D designs and different applications that require gas or ion selectivity, such as photocatalysts and biosensors, in humid atmosphere. [ABSTRACT FROM AUTHOR]

The effect of shell thickness and noble metal decoration on the gas-sensing characteristics of two-dimensional (2D) materials has not been reported yet. Herein, we synthesized 2D pristine and Au-decorated WS 2 -SnO 2 core-shell nanosheets (Au NSs). SnO 2 shells with various thicknesses (up to 60 nm) were deposited on the WS 2 NSs. Subsequently, Au was deposited on the synthesized WS 2 -SnO 2 core-shell NSs (WS 2 -SnO 2 NSs) under UV irradiation. Flexible polyamide substrates were used to fabricate gas sensors, which operated in self-heating mode upon applying different voltages for CO detection. Bare and Au-decorated gas sensors with shell thicknesses of 15 and 30 nm revealed the highest CO sensing performance at a low voltage of 3.4 V. The flexibility of the gas sensors was demonstrated by the negligible degradation of the sensing performance after 10,000 bending cycles. We also evaluated the sensing characteristics under humid conditions. The developed gas sensors with very low applied voltage and high performance for CO gas sensing are very promising for commercial applications. • We synthesized Au-decorated WS 2 -SnO 2 core-shell nanosheets on flexible polyamide substrates. • Sensors were operated in self-heating mode upon applying different voltages for CO detection. • Au-decorated gas sensors with shell thicknesses of 30 nm indicated the highest response to CO gas at 3.4 V. • Formation of heterojunctions and the promising effect of Au NPs led to enhanced sensing. [ABSTRACT FROM AUTHOR]

The effect of shell thickness and noble metal decoration on the gas-sensing characteristics of two-dimensional (2D) materials has not been reported yet. Herein, we synthesized 2D pristine and Au-decorated WS 2 -SnO 2 core-shell nanosheets (Au NSs). SnO 2 shells with various thicknesses (up to 60 nm) were deposited on the WS 2 NSs. Subsequently, Au was deposited on the synthesized WS 2 -SnO 2 core-shell NSs (WS 2 -SnO 2 NSs) under UV irradiation. Flexible polyamide substrates were used to fabricate gas sensors, which operated in self-heating mode upon applying different voltages for CO detection. Bare and Au-decorated gas sensors with shell thicknesses of 15 and 30 nm revealed the highest CO sensing performance at a low voltage of 3.4 V. The flexibility of the gas sensors was demonstrated by the negligible degradation of the sensing performance after 10,000 bending cycles. We also evaluated the sensing characteristics under humid conditions. The developed gas sensors with very low applied voltage and high performance for CO gas sensing are very promising for commercial applications. • We synthesized Au-decorated WS 2 -SnO 2 core-shell nanosheets on flexible polyamide substrates. • Sensors were operated in self-heating mode upon applying different voltages for CO detection. • Au-decorated gas sensors with shell thicknesses of 30 nm indicated the highest response to CO gas at 3.4 V. • Formation of heterojunctions and the promising effect of Au NPs led to enhanced sensing. [ABSTRACT FROM AUTHOR]