Zeolite thin film-coated long period fiber grating sensor for measuring trace organic vapors

• Published in: Sensors and actuators. B, Chemical Chemical, 2009-01, Vol.135 (2), p.420-425
• Main Authors: Zhang, Jian, Tang, Xiling, Dong, Junhang, Wei, Tao, Xiao, Hai
• Format: Article
• Language: English
• Subjects: Crystallization; Diffraction gratings; Fibers; Gratings (spectra); Isopropanol; Long period fiber grating; Optical sensor; Sensors; Silicalite; Trace measurement; Zeolite; Zeolites
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2008.09.033

A zeolite thin film-coated long period fiber grating (LPFG) sensor was developed and tested for direct measurement of trace organic vapors with straightforward operation. The sensor was fabricated by growing pure silica MFI-type zeolite (i.e. silicalite) thin film on the optical fiber grating by in situ hydrothermal crystallization. The sensor measures chemical vapor concentration by monitoring the molecular adsorption-induced shift of LPFG resonant wavelength ( λ R) in near infrared (IR) region. Upon loading analyte molecules, the zeolite's refractive index changes in the close vicinity of the fiber index where the λ R responds with extremely high sensitivity. Because the silicalite is hydrophobic and preferentially adsorbs organic molecules, the zeolite-LPFG sensor is capable of quantifying organic vapor concentrations in lower ppm or ppb ranges without sample pre-concentration and rigorous control of operating conditions. The sensor had a much faster response speed for isopropanol than for toluene as the former has a smaller molecular kinetic size and greater diffusivity in the zeolite pores than the latter.