The new sensing material, LiFe0.995Y0.0025Ag0.0025PO4 was synthesized using hydro-thermal methods, and characterized by X-ray diffraction, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The as prepared products were subsequently utilized in a self assembled optical waveguide gases testing apparatus and a WS-30A electro-chemical gas sensing apparatus for xylene detection. A glass optical waveguide gas sensor was fabricated by spin-coating a LiFe0.995Y0.0025Ag0.0025PO4 thin film on the surface of single-mode tin-diffused glass Optical Waveguide. The sensing elements for electro-chemical gas sensor were made by dip-coating a LiFe0.995Y0.0025Ag0.0025PO4 thin film on the surface of an alumina ceramic tube, assembled with platinum wire. The experimental results indicated that, at room temperature, LiFe0.995Y0.0025Ag0.0025PO4 thin film/tin-diffused optical waveguide sensing element exhibited higher response to xylene in the range of 0.1–100 ppm; at an optimum operating temperature (300 °C), the response (Sr) of LiFe0.995Y0.0025Ag0.0025PO4 to 100 ppm of xylene was 5.29, as measured by the WS-30A electro-chemical gases sensing apparatus.

A composite optical waveguide sensor, consisting of lithium iron phosphate (LiFePO4, LFP) as the sensing material, was constructed and utilized for the detection of volatile organic compound gases. Nano-LFP powder was prepared via the hydrothermal method and was subsequently utilized in a dip-coating procedure for the fabrication of LFP thin films. The effect of heat treating temperature on the refractive index of the thin films was studied. A glass optical waveguide gas sensor was fabricated by coating an LFP thin film on the surface of single-mode tin-diffused glass optical waveguide. The sensor was found to exhibit a linear response to xylene in the range of 50–1000 ppm, with response times of less than 5 s.Highlights► LiFePO4 was selected as sensing material for xylene detection. ► Refractive index of LiFePO4 thin films increases with annealing temperature from 120 to 450 °C. ► LiFePO4 optical waveguide sensor easily detects 50 ppm of xylene gas with response < 5 s. ► Below 100 ppm, no interference is caused by other volatile organic compounds.

In this study, a sensitive optical waveguide (OWG) sensor for the detection and identification of volatile organic compounds (VOCs) was reported. The sensing membrane is constructed by immobilization of peroxopolytungsten acid (PTA) thin film over a single-mode potassium ion (K+) exchanged glass OWG by spin-coating method. A laser beam was coupled into and out of the glass optical waveguide using prism couplers, and dry air functioned as a carrier gas. The sensor was tested for various volatile organic compounds (VOCs), and it showed higher response to the chlorobenzene gas compared to other VOCs. Therefore, we used the OWG sensor to detect chlorobenzene gas as a typical example of VOCs. The sensor exhibits a linear response to chlorobenzene gas in the range of 0.4–1000 ppm with rapid response and good reversibility. The constructed sensor is easy to fabricate and it has some unique qualities which can be characterized as inexpensive, sensitive, and reusable.

An optical sensor sensitive to BTX has been developed by spin coating a thin film of polyacrylate resin onto a tin- diffused glass optical waveguide. A pair of prism coupler was employed for optical coupling matched with diiodomethane (CH2I2). The guided wave transmits in waveguide layer and passes through the film as an evanescent wave. Polyacrylate film has a strong capacity of absorbing oil gases. The film is stable in N2 but benzene exposure at room temperature can result in rapid and reversible changes of transmittance (T) and refractive index (n1) of this film. It has been demonstrated that the sensor containing a 10 mm board and about a hundred nanometers thick resin film can detect lower than 8 ppm BTX.

An optical waveguide (OWG) sensor for the detection of BTX gases is reported. The highly sensitive element of this sensor was made by coating the copper Nafion film over a single-mode potassium ion exchanged glass OWG. We used the OWG sensor to detect toluene gas as a typical example BTX gas. The sensor exhibits a linear response to toluene in the range of 0.25−4250 ppm with response and recovery times less than 25 s. The sensor has a short response time, high sensitivity, and good reversibility.