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 SWCNT5-Ag-LaFeO3 were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), respectively. Indirect-heating sensors using SWCNT5-Ag-LaFeO3 sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. Gas-sensing characteristic of SWCNT5-Ag-LaFeO3 to formaldehyde was investigated. It is found that the structure of SWCNT5-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%SWCNT5-Ag-LaFeO3) are the best. The response of 0.75%SWCNT5-Ag-LaFeO3 powder to 0.5 ppm formaldehyde is 23 at 86 degrees C. The detect limit to formaldehyde is 0.2 ppm. The response and recovery times are 6s and 20s, respectively. Those good properties make them the promising candidates for practical detectors to formaldehyde. (C) 2014 Elsevier B.V. All rights reserved.