Molybdenum sulfide/citric acid composite membrane-coated long period fiber grating sensor for measuring trace hydrogen sulfide gas

Abstract

A molybdenum sulfide/citric acid composite membrane-coated long period fiber grating (LPFG) sensor was demonstrated and applied to detect the trace hydrogen sulfide gas. The sensor was fabricated by growing molybdenum sulfide/citric acid composite film on the surface of optical fiber grating by using the sol-gel and dip-coating techniques. The sensor measures the hydrogen sulfide concentration by monitoring the molecular adsorption-induced resonant wavelength shift of LPFG in near infrared (∼1555 nm) region. Experimental results show that with the increasing concentration of hydrogen sulfide, the transmission spectrum appears blue shift with time response of 89 s. In addition, a high sensitivity of 10.52 pm/ppm and a good linear relationship are achieved within a measurement range from 0 to 70 ppm. Furthermore, there is an excellent selectivity for H2S, which has also been confirmed by the surface adsorption energy results of molybdenum sulfide with five common gases in the air (H2S, N2, CO2, O2 and Ar) based on the density functional theory calculations. The proposed sensor has an excellent detection limit of hydrogen sulfide which is as low as 0.5 ppm. This sensor has the advantages of simple structure, easy manufacture, high sensitivity and low cost, and can be used in hydrogen sulfide gas sensing places such as factories, sewers, and so on.