Ultra-responsive and selective of formic acid sensors based on flame-made SnO<inf>2</inf> nanoparticles loaded with core-shell Ir-IrO<inf>2</inf> nanocatalysts

Abstract

0.1–2 wt% Ir-loaded tin dioxide (SnO2) nanoparticles were prepared via flame spray pyrolysis and investigated for sensing of formic acid (CH2O2). The structural morphologies of the materials were investigated by various X-ray spectroscopic and electron microscopic analyses. The results revealed that very fine secondary core-shell nanoparticles containing Ir° and Ir4+ species were decorated on the surfaces of cassiterite SnO2 nanoparticles, resulting in an increase of specific surface area and a small reduction of SnO2 crystallize size. The gas-sensing performances of all fabricated sensors were evaluated towards several volatile organic acids particularly CH2O2, volatile organic compounds and hydrocarbon gases at working temperature in the range of 200–400 °C in dry and humid air. The data revealed that the 1 wt% Ir-loaded SnO2 provided the optimal sensor response of ∼1.43 × 105 to 1000 ppm CH2O2 at an optimum working temperature of 350 °C. In addition, the sensors presented moderately low humidity effect on CH2O2 response and high CH2O2 selectivity against C2H5OH, CH3OH, C3H6O, C7H8, C6H6, C8H10, HCHO, CH4, H2, C2H4O2, C3H6O2, C4H8O2, C5H10O2 and C3H6O3. The electronic and gas-sensing mechanisms could be primarily ascribed to metal-metal-semiconductor heterojunctions and catalytic effects of Ir-IrO2 via oxygen spill-over and oxygen evolution reaction mechanisms. Therefore, the loading of catalytic core-shell Ir nanoparticles on SnO2 nanostructures was a highly promising approach to achieve ultrasensitive and selective sensing of formic acid.