Improvement of response to formaldehyde at Ag-LaFeO3 based gas sensors through incorporation of SWCNTs

The LaFeO3 modified by silver (Ag-LaFeO3) further modified by single-walled carbon nanotubes (SWCNTs-Ag-LaFeO3) with different weight ratio were prepared using a sol-gel method combined with the microwave chemical synthesis. The phase structures and micro-morphology of SWCNTs-Ag-LaFeO3 were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), respectively. Indirect-heating sensors using SWCNTs-Ag-LaFeO3 sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. Gas-sensing characteristic of SWCNTs-Ag-LaFeO3 to formaldehyde was investigated. It is found that the structure of SWCNTs-Ag-LaFeO3 is of orthogonal perovskite. The gas-sensing properties of the Ag-LaFeO3 sample modified by SWCNTs with 0.75% weight ratio (0.75%SWCNTs-Ag-LaFeO3) are the best. The response of 0.75%SWCNTs-Ag-LaFeO3 powder to 0.5 ppm formaldehyde is 23 at 86 °C. The detect limit to formaldehyde is 0.2 ppm. The response and recovery times are 6 s and 20 s, respectively. Those good properties make them the promising candidates for practical detectors to formaldehyde.