Synthesis and optimization strategies of nanostructured metal oxides for chemiresistive methanol sensors

Hollow Urchin-Like Ag-Doped In2O3 Nanomaterials for Enhanced Low-Temperature Methanol Sensing Under UV Irradiations

“… However, the adsorbed oxygen O 2 (ads) on the hollow urchin-like In 2 O 3 surface is reactivated by the photogenerated electrons to form the highly reactive O 2 – species (reaction ). Finally, when the sensor is exposed to methanol, it will react with the O 2 – to release the electrons to the conduction band of In 2 O 3 (reaction ), contributing to the resistance decline of gas sensors. Therefore, the UV-mediated methanol-sensing performances of the hollow urchin-like Ag-doped In 2 O 3 should drive from the effective participation of photogenerated electrons. h ν → h + ( h ν ) + e − ( h ν ) normalO 2 − ( ads ) + h + ( h ν ) → O 2 ( des ) O 2 ( ads ) + e − ( h ν ) → normalO 2 − ( h ν ) 2 CH 3 OH ( ads ) + normalO 2 − ( h ν ) → 2 CHOH ( ads ) + 2 H 2 normalO (…”

“…4 The Chinese authorities stipulate that the exposure threshold values of methanol are the permissible concentration-short-term exposure limit of 50 mg/m 3 (35 ppm). 5 Therefore, it is of great significance to detect methanol accurately for human health. 6 Indium oxide (In 2 O 3 ) is a wide bandgap n-type semiconductor 7 with superior surface activity and high carrier conductivity, which has been widely investigated and used as a high-performance gas sensor.…”

“…Excessive inhalation of methanol affects the human nervous and blood systems, even to cause death . The Chinese authorities stipulate that the exposure threshold values of methanol are the permissible concentration-short-term exposure limit of 50 mg/m 3 (35 ppm) . Therefore, it is of great significance to detect methanol accurately for human health …”

Nanostructured metal oxide heterojunctions for chemiresistive gas sensors

“…The preparation of nanostructured heterojunctions involves a heterogeneous chemical reaction, where the solution concentration, the reaction temperature (130–250 °C) and time (12–48 hours) can be regulated. 39,127,128 Its distinctive advantage is that it can prepare metal oxides with high crystallization properties without the need for calcination at high temperatures, avoiding the aggregation of nanocrystals and residual impurities. Hydrothermally synthesized metal oxide-based sensing materials exhibit high-purity characteristics, and their grain size can be easily modulated just by changing the reaction conditions ( i.e.…”

“…35–37 However, the high working temperature will exert adverse effects, such as inducing the thermal growth of grains inside metal oxides or the decomposition of the target gas, on the long-term stability and durability of sensors. 38,39 Therefore, metal oxides are required to operate at a low temperature while simultaneously maintaining their superior gas-sensing properties. Besides, metal oxide-based gas sensors are sensitive to the target gas and have high sensitivity to other interfering gases and even humidity, displaying poor selectivity.…”