Fiber optic ethanol gas sensor based WO3 and WO3/gC3N4 nanocomposites by a novel microwave technique

Abstract

In this report, WO3/graphitic carbon nitride (g-C3N4) composites were successfully prepared through one step microwave irradiation technique followed by direct calcining of a combination of WO3 and g-C3N4 at 400 °C for 2 h. The nanocomposites were analyzed by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Raman, X-ray photoelectron spectra and N2-sorption analysis. Powder XRD results reveal that pure WO3 could be well indexed as the monoclinic structure (JCPDF 43-1035) and the two characteristic peaks of g-C3N4 bulk appearing at 13.2° and 27.6° could be assigned to the (1 0 0) and (0 0 2) planes respectively. The XPS results verify that presence of g-C3N4 in WO3 and tungsten in 6+ states in WO3 nanocrystals. TEM images showed that a serious agglomeration of nanoparticles (25–30 nm), which can be dispersed on the g-C3N4 nanosheets. The high surface area of WO3/g-C3N4 (138 m2·g−1) and the interaction between 2-D g-C3N4 and WO3 could strongly favour of the elevated gas-sensing property. Fiber optic gas sensors with nanostructures of WO3/g-C3N4 as the cladding of a PMMA fiber have been proposed and investigate the ethanol gas sensing test. The WO3/g-C3N4 nanocomposites exhibit excellent selectivity to ethanol gas, such as high sensitivity (62.5 at 500 ppm), faster response (30 s) and recovery time (25 s) than those of the pure WO3. The possible mechanism for the enhanced ethanol gas sensing properties of WO3/g-C3N4 nanostructures is proposed.