EFFECT OF ADDITIVES AND PARTICLE-SIZE ON THE SENSITIVITY OF SNO2-BASED SENSORS FOR OFFENSIVE-ODOR COMPONENTS

The sensing mechanism of an SnO2 sensor as well as the effects of addi tives on its sensitivity for trimethylamine (TMA), (CH3)3N, have been studied. The conductance changes reversibly and greatly upon the chang e between N2 and N2+(CH3)3N, while the change is small upon exposure t o O2. Hence, it is concluded that the electron-donating adsorption of TMA is the key step in determining the change in the conductance. The addition of La to SnO2 greatly enhances the sensitivity, whereas trans ition metals like Cr, Cu, Mn, etc., have opposite effects. The sensiti vity is correlated almost inversely with the catalytic activity of the sensor for oxidation of TMA. The particle size of SnO2 and the loadin g amount of La are also influential in determining the sensitivity. Th erefore, a probable mechanism for the increase in sensitivity is that La enhances, by suppressing the catalytic oxidation of trimethylamine, the supply of trimethylamine to the neck formed between SnO2 particle s, at which the conductance is mainly determined.