Au-Pd Co-Modified LaFeO3 for Low-Concentration n-Butanol Sensing and Composition Analysis of n-Butanol/HCHO Mixtures

To improve the response of LaFeO3 to low concentrations of n-butanol, LaFeO3 co-modified with 3 wt% Au and 5 wt% Pd was prepared by a citrate-assisted sol–gel method. At 180 °C, the resulting sensor exhibited a response of 16.92 to 1 ppm n-butanol, corresponding to 5.90 times the maximum response of pristine LaFeO3. The optimal operating temperature decreased from 200 to 180 °C, and a distinguishable response was observed at the lowest tested concentration of 0.1 ppm. However, selectivity tests revealed a substantial cross-response to formaldehyde (HCHO), motivating further analysis of binary n-butanol/HCHO mixtures. Responses to these mixtures were measured at 160, 180, and 200 °C. The ratio of the response increments at 160 and 180 °C reduced the influence of total concentration while retaining composition-related information. A support vector regression model with a radial basis function kernel was trained using the dataset obtained at a total concentration of 1.0 ppm. Without refitting, the model predicted n-butanol fractions for five predefined mixture compositions at total concentrations of 0.5 and 2.0 ppm. The mean absolute errors were 0.075 and 0.033, with R2 values of 0.921 and 0.981, respectively. These results demonstrate the potential of combining Au-Pd modification with temperature-response normalization for low-concentration n-butanol sensing and binary-mixture composition analysis using a single LaFeO3 sensor.