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

•WO3/g-C3N4 composites were successfully synthesized by a one step microwave irradiation method.•WO3/g-C3N4 has high sensitivity, fast response and recovery time towards ethanol gas.•The enhancement has been explained by surface O2 and ethanol gas.•WO3/g-C3N4 would be promising potential application in gas sensor field.