Ultra-responsive and selective of formic acid sensors based on flame-made SnO_2 nanoparticles loaded with core-shell Ir-IrO_2 nanocatalysts

摘要

0.1-2 wt% Ir-loaded tin dioxide (SnO_2) nanoparticles were prepared via flame spray pyrolysis and investigated for sensing of formic acid (CH_2O_2). 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~o and Ir~(4＋) species were decorated on the surfaces of cassiterite SnO_2 nanoparticles, resulting in an increase of specific surface area and a small reduction of SnO_2 crystallize size. The gas-sensing performances of all fabricated sensors were evaluated towards several volatile organic acids particularly CH_2O_2, 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 SnO_2 provided the optimal sensor response of ～1.43 × 10~5 to 1000 ppm CH_2O_2 at an optimum working temperature of 350 °C. In addition, the sensors presented moderately low humidity effect on CH_2O_2 response and high CH_2O_2 selectivity against C_2H_5OH, CH_3OH, C_3H_6O, C_7H_8, C_6H_6, C_8H_(10), HCHO, CH_4, H_2, C_2H_4O_2, C_3H_6O_2, C_4H_8O_2, C_5H_(10)O_2 and C_3H_6O_3. The electronic and gas-sensing mechanisms could be primarily ascribed to metal-metal-semiconductor hetero-junctions and catalytic effects of Ir-IrO_2 via oxygen spill-over and oxygen evolution reaction mechanisms. Therefore, the loading of catalytic core-shell Ir nanoparticles on SnO_2 nanostructures was a highly promising approach to achieve ultrasensitive and selective sensing of formic acid.