Highly sensitive and selective Gd2O3-doped SnO2 ethanol sensors synthesized by a high temperature and pressure solvothermal method in a microreactor

Abstract

Gd2O3-doped SnO2 nanoparticles as highly sensitive and selective ethanol sensor materials with uniform size distributions were synthesized in ethylene glycol at 250°C and 20bar in a continuous tubular microreactor. The samples were characterized by DLS, XRD, SEM, EDX, TEM, FTIR, and BET surface area measurement techniques. As 5wt% Gd2O3 is added to SnO2, the average particle and crystallite sizes of the samples decrease from 22 and 11.9nm to 10 and 3.8nm, respectively. The responses of Gd2O3-doped SnO2 sensors containing 0–10.0wt% Gd2O3 calcined at 450°C were measured in presence of 300ppm CO, 10–1000ppm ethanol and 1.0 vol% of methane in air at 150–430°C. The sensor containing 10wt% Gd2O3 is highly sensitive and selective to ethanol in presence of CO, methane, and three volatile organic compounds, at 150°C. At the same low temperature, as the Gd2O3 content of the sensor increases from 2.5 to 10%, its response to ethanol dramatically enhances by about 263 times and the resistance in air changes by more than 4 orders of magnitude. Relative humidities higher than 50% eliminate the 10% Gd2O3–SnO2 sensor responses to CO and CH4 and the sensor shows absolute selectivity to ethanol.