Tunable NH₄F-Assisted Synthesis of 3D Porous In₂O₃ Microcubes for Outstanding NO₂ Gas-Sensing Performance: Fast Equilibrium at High Temperature and Resistant to Humidity at Room Temperature

Abstract

NO2 gas sensors based on metal oxides under wild conditions are highly demanded yet an incomplete surface reaction and humidity interference on the gas-sensing performance limit their applications. Herein, we report three-dimensional (3D) porous In2O3 microcubes via a simple hydrothermal strategy to produce outstanding NO2 gas-sensing performance: fast equilibrium of the surface reaction at 150 °C and negligible humidity dependence on the NO2 gas sensing at room temperature. The 3D porous In2O3 microcubes with high surface areas, suitable pore sizes, rich oxygen vacancies, and high conductivity are testified. The underlying structural transformation mechanism for 3D porous In2O3 is investigated in detail. The as-made 3D porous In2O3 microcubic gas sensors present excellent gas-sensing performance to 50 ppm NO2 at 150 °C, including a high response value (2329), fast response/recovery time (10/9 s), a low detection limit (10 ppb), long-term stability (60 days), and strong selectivity. Furthermore, they exhibit relatively stable NO2 gas response under humidity variation (20–80%). The NO2 gas mechanism under the interference of water is also clarified.

Low-Temperature As-Doped In2O3 Nanowires for Room Temperature NO2 Gas Sensing

“…Once introduced, it will rapidly seize the free electrons on the surface of the NWs. This process consumes the electrons of the In 2 O 3 NWs and further increases the resistance of the NWs, expressed as eqs and . ,− When these NO 2 gases are evacuated, NO 2 – will return electrons to the oxygen vacancy in eqs and , and the device will return to its initial state. Figure displays the NO 2 response mechanism.…”

“…In the meanwhile, the Au catalyst is believed to be complementary metal oxide semiconductor (CMOS) technology incompatible, necessitating alternative metal catalysts. − In addition, In 2 O 3 nanostructures have also been reported with other methods to test NO 2 . For example, Liu et al used porous In 2 O 3 to improve NO 2 detection by the hydrothermal method . Zhang et al.…”

“…For example, Liu et al used porous In 2 O 3 to improve NO 2 detection by the hydrothermal method. 16 Zhang et al synthesized one-dimensional In 2 O 3 nanostructures by electrospinning and explored the gas sensing recovery under light. However, the surface of the obtained nanowires is not smooth, and the growth direction is not controllable, which affects the device design of a single nanowire.…”

Enhancing the Low/Middle‐Frequency Electromagnetic Wave Absorption of Metal Sulfides through F− Regulation Engineering

“…Ammonium fluoride (NH 4 F), which is a versatile inorganic salt, has attracted significant research interest for morphology control [1][2][3] and transition-metal anion doping [4] in the catalysis and energy fields. As a popular morphology-directing agent, previous studies have revealed that the fluorine ion (F − ), which is released from NH 4 F in the growth solution, provides numerous active sites for the nucleation and growth of nanostructures to control morphology evolution.…”

NH4F-Induced Morphology Control of CoP Nanostructures to Enhance the Hydrogen Evolution Reaction

“…The thickness of the Co­(OH)F layer dramatically decreases with the increase of NH 4 F concentration (Figure i,l,o). The changes of morphology and thickness are mainly due to the corrosion of F – and the strongly acidic condition from the excess addition of NH 4 F, which dramatically restrain the hydrolysis of urea and the following crystal growth. , Correspondingly, the EDS results also manifest that the content of fluorine element in the precursors increases with the added concentration of NH 4 F, further indicating the key factor of F – in the phase formation and morphological changes (Table S1). Afterward, the obtained cobalt carbonate hydrate and Co­(OH)F precursors with different morphologies are subsequently converted into CoP nanostructures using NaH 2 PO 2 as the phosphorus source at 350 °C for 2 h in a tubular furnace under the protection of pure Ar.…”