Improved TEA Sensitivity and Selectivity of In₂O₃ Porous Nanospheres by Modification with Ag Nanoparticles

A highly sensitive and selective detection of volatile organic compounds (VOCs) by using gas sensors based on metal oxide semiconductor (MOS) has attracted increasing interest, but still remains a challenge in gas sensitivity and selectivity. In order to improve the sensitivity and selectivity of In₂O₃ to triethylamine (TEA), herein, a silver (Ag)-modification strategy is proposed. Ag nanoparticles with a size around 25-30 nm were modified on pre-synthesized In₂O₃ PNSs via a simple room-temperature chemical reduction method by using NaBH₄ as a reductant. The results of gas sensing tests indicate that after functionalization with Ag, the gas sensing performance of In₂O₃ PNSs for VOCs, especially for TEA, was remarkably improved. At a lower optimal working temperature (OWT) of 300 °C (bare In₂O₃ sensor: 320 °C), the best Ag/In₂O₃-2 sensor (Ag/In₂O₃ PNSs with an optimized Ag content of 2.90 wt%) shows a sensitivity of 116.86/ppm to 1-50 ppm TEA, about 170 times higher than that of bare In₂O₃ sensor (0.69/ppm). Significantly, the Ag/In₂O₃-2 sensor can provide a response (R_a/R_g) as high as 5697 to 50 ppm TEA, which is superior to most previous TEA sensors. Besides lower OWT and higher sensitivity, the Ag/In₂O₃-2 sensor also shows a remarkably improved selectivity to TEA, whose selectivity coefficient (S_TEA/S_ethanol) is as high as 5.30, about 3.3 times higher than that of bare In₂O₃ (1.59). The sensitization mechanism of Ag on In₂O₃ is discussed in detail.