Heterocontact type CuO-modified SnO2 sensor for the detection of a ppm level H2S gas at room temperature

Thick films of SnO2 were prepared by screen printing technique. The films were modified with Cu2+ by dipping them into an aqueous solution of copper chloride for different intervals of time and fired at 550 °C for 24 h. The copper chloride would be transformed upon firing into copper oxide. The p-type CuO grains around n-type SnO2 grains would form n-SnO2/p-CuO heterojunctions. Upon exposure to H2S gas, the barrier height of n-SnO2/p-CuO heterojunctions decreases markedly due to the chemical transformation of p-CuO into well conducting Cu2S, leading to a drastic change in resistance. These sensors were observed to be operated at room temperature. An exceptional sensitivity was found to low concentrations (below threshold limit value = 10 ppm) of H2S gas at room temperature, and no cross sensitivity was observed even to high concentrations of other hazardous and polluting gases. The efforts have, therefore, been made to develop the heterocontact type gas sensor based on tin oxide surface-modified with cupric oxide. The effects of microstructure and surfactant concentration on the sensitivity, selectivity, response and recovery of the sensor in the presence of H2S gas were studied and discussed.