Search

A novel fiber-optic surface plasmon resonance (SPR) hydrogen sulfide gas sensor based on silver/3-aminpropyltriethoxysilane/cuprous oxide modified graphene sheets (Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS) composite membrane coated no-core fiber (NCF) was proposed and fabricated. The NCF is sandwiched between two segments of multi-mode fiber (MMF), forming the fiber-optic sensing unit with MMF1-NCF-MMF2 structure. The comparative experiment of sensing performance of two sensors coated respectively by Ag/APTES and Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS film is investigated in detail. The results show that the sensor with Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS film has better sensing performance for hydrogen sulfide in the concentration range of 10–60 ppm. After adsorption of hydrogen sulfide, the resonance wavelength of the sensor with Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS film shows the red shift, and the total shift is about 132.642 nm. In the concentration range of 10–40 ppm, the sensitivity is 3385.67 pm/ppm, the detection limit is 0.56±0.12 ppm, and the response time is 27 s. The sensor has good temperature, humidity, time stability and excellent selectivity, and can be potentially used in the trace hydrogen sulfide detection. [ABSTRACT FROM AUTHOR]

A novel hydrogen sulfide (H2S) gas sensor based on multimode interference is proposed and presented. The sensor is constructed by a 30 mm no-core fiber (NCF) and two 30 mm thin-core fibers (TCFs). The first part of the TCF is excited by the high-order modes, in the second part of TCF, the basic core and high-order modes are coupled to the last single-mode fiber, which can induce inter-mode interference. Titanium dioxide–zinc oxide (TiO2–ZnO) composite film is coated on the outside surface of the NCF by the dip-coating method. The experimental results indicate that there is a good linear relationship between the wavelength shift and the different H2S gas concentrations. The sensor has a sensitivity of 21.26 pm ppm−1 in the gas range of 0–50 ppm H2S. In addition, the TiO2–ZnO composite sensing membrane has good selectivity for H2S gas. The response and recovery times are about 90 s and 115 s, respectively. The sensor has the advantages of simple structure, high sensitivity, easy manufacture and could be used in toxic H2S gas monitoring. [ABSTRACT FROM AUTHOR]

A highly sensitive hydrogen sulfide gas sensor based on NH2-rGO-coated thin-core-fibre (TCF) Michelson interferometer (MI) is proposed and evaluated. Two sections of TCFs are alternately sandwiched between three single-mode-fibres (SMFs). A Faraday rotator mirror (FRM) is fixed to the end of the last SMF to reflect the light signal and enhance the interference. Then the structure SMF-TCF-SMF-TCF-SMF-FRM (STSTS-F) is successfully constructed. NH2-rGO, as sensing film, is coated on two TCFs and is used to detect traces of hydrogen sulfide gas. Raman spectra and XPS analysis show that NH2-rGO has been successfully synthesised. The thickness of the NH2-rGO film coated on the TCF surface is about 500 nm. By introducing 0–60 ppm hydrogen sulfide gas into the chamber, with the increase in concentration of the gas, the monitoring trough exhibits a blue shift. Our experimental results show that the sensor has good linearity (R2 = 0.98096) and selectivity for hydrogen sulfide gas. The sensitivity is 21.3 pm/ppm, and the response and recovery times are about 72 and 90 s, respectively. The sensor has the advantages of high sensitivity, high selectivity, and small size, enabling the detection of trace hydrogen sulfide in toxic gas environments. [ABSTRACT FROM AUTHOR]

A hydrogen sulfide (H2S) gas sensor based on copper (Cu) nanoparticle deposited graphene oxide (GO) composite membrane with two waist-enlarged tapers is proposed. Three segments of the single-mode fibres (SMFs) are sequentially fused to obtain two waist-enlarged bitapers of Mach–Zehnder interferometer (MZI). When the light of a broadband light source transmits through the first bitaper, some light enters the fiber cladding; the lights of core mode and cladding mode are coupled at the second taper and an MZI is successfully fabricated. The copper/graphene oxide (Cu/GO) composite sensing film is coated on the surface of the second SMF, and the effective refractive index of the coating is changed when the sensitive film adsorbs the target gas. The correlation between the gas concentration and the wavelength shift is achieved and the H2S can be measured effectively. The results show that a uniform Cu/GO film is successfully coated on the surface of the fiber, and when the thickness of the sensitive film is about 1.2 μm, the sensor has a sensitivity of 4.42 pm/ppm and a good linearity and selectivity for H2S in the range of 0–60 ppm, and the limit of detection is 2.79 ppm. The response time and recovery time are approximately 31 and 48 s, respectively. The sensor has the advantages of small volume, low cost, simple structure, and easy manufacture and so on, which is suitable for on-line monitoring of H2S. [ABSTRACT FROM AUTHOR]

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 H 2 S, which has also been confirmed by the surface adsorption energy results of molybdenum sulfide with five common gases in the air (H 2 S, N 2 , CO 2 , O 2 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. [ABSTRACT FROM AUTHOR]

A novel fiber-optic hydrogen sulfide sensor based on a thin-core Mach-Zehnder fiber modal interferometer (TMZFI) is demonstrated and fabricated. This in-line interferometer is composed of a short section of thin-core fiber sandwiched between two standard single mode fibers, and the fast response to hydrogen sulfide is achieved via the construction of tungsten sulfide film on the outside surface of the TMZFI using the dip-coating and calcination technique. The fabricated sensing nanofilm is characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) spectrometer, Fourier transform infrared (FTIR) and spectroscopic analysis technology, etc. Experimental results showed that the WS 2 sensing film has a hexagonal structure with a compact and porous morphology. The XPS and FTIR indicate that the existence of two elements (W and S) is demonstrated. With the increasing concentration of hydrogen sulfide, the interference spectra appear blue shift. In addition, a high sensitivity of 18.37 pm/ppm and a good linear relationship are obtained within a measurement range from 0 to 80 ppm. In addition, there is an excellent selectivity for H 2 S, which has also been proved by the surface adsorption energy results of tungsten sulfide with four gases (H 2 S, N 2 , O 2 and CO 2 ) by using the density functional theory calculations. This interferometer has the advantages of simple structure, high sensitivity and easy manufacture, and could be used in the safety monitoring field of hydrogen sulfide gas. [ABSTRACT FROM AUTHOR]

A hydrogen sulfide gas sensor based on graphene-coated tapered photonic crystal fiber (GTPCF) Mach-Zehnder interferometer (MZI) was proposed and experimentally demonstrated. The GTPCF-MZI is formed by fusion splicing a short length of tapered PCF between two single-mode fibers. The air holes of PCF in the splicing regions are fully collapsed and so that it is conducive to the mode coupling. The GTPCF-MZI was coated with a layer of graphene by using a dip-coating and sintering process. Experimental results show that with the increasing concentration of hydrogen sulfide, the interference spectra appear blue shift. In addition, a high sensitivity of 0.03143 nm/ppm and a good linear relationship are obtained within a measurement range from 0 to 45 ppm. The sensor has the advantages of simple structure, high sensitivity, easy manufacture and low cost, and can be used in indoor gas sensing fields such as factories and laboratories and so on. [ABSTRACT FROM AUTHOR]