Effect of pore structure of the metakaolin-based porous substrate on the growth of SnO2 nanowires and their H2S sensing properties

Abstract

The metakaolin-based porous substrates were used as the growth substrate to synthesize SnO2 nanowires (SNWs) gas sensing materials via the gold-catalyzed vapor-liquid-solid growth mechanism. The porous substrates were fabricated by a pore-forming method with poly methyl methacrylate (PMMA) microspheres as the pore former. The effect of the porous structure of different as-prepared substrates on their product morphologies were characterized using X-ray diffraction and scanning electron microscopy. The resulting structural and morphological properties showed that all SNWs had a tetragonal rutile structure, and the aspect ratio of the SNWs enhanced with the increase in the apparent porosity or total pore area of substrates. The growth mechanism of the SNWs was discussed with respect to the effect of temperature gradient inside and outside the pores. The SNWs synthesized on the porous substrates with the PMMA content of 30 wt% exhibited the highest sensing performance towards 0.5–10 ppm H2S at the operating temperature of 85 °C, accompanying with the SNWs synthesized on a dense substrate and the substrate with the PMMA content of 20 wt% for comparison. It demonstrates that the porous structure of the metakaolin-based substrates significantly improves the aspect ratio and gas sensing properties of the SNWs.