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

• Gd2O3-doped SnO2 nanoparticles as highly sensitive and selective ethanol sensor materials with narrow size distribution are produced in a capillary tube microreactor at 250 °C and 20 bar in 5 s.
• The average particle and crystallite sizes of the samples decrease from 22 and 11.9 nm to 10 and 3.8 nm, respectively, as 5 wt% Gd2O3 was added to SnO2.
• At 150 °C, about 5 orders of magnitude increase in the sensor resistance is observed, when 5% Gd2O3 is added to SnO2.
• Adding 10% Gd2O3 to SnO2 dramatically enhances the sensor responses and selectivity to ethanol in presence of CO, methane, and three volatile organic compounds, at low operating temperatures.

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 20 bar in a continuous tubular microreactor. The samples were characterized by DLS, XRD, SEM, EDX, TEM, FTIR, and BET surface area measurement techniques. As 5 wt% Gd2O3 is added to SnO2, the average particle and crystallite sizes of the samples decrease from 22 and 11.9 nm to 10 and 3.8 nm, respectively. The responses of Gd2O3-doped SnO2 sensors containing 0–10.0 wt% Gd2O3 calcined at 450 °C were measured in presence of 300 ppm CO, 10–1000 ppm ethanol and 1.0 vol% of methane in air at 150–430 °C. The sensor containing 10 wt% 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.