Tilted Fiber Bragg Grating Hydrogen Sensor Based on UiO-66-NH2

Abstract

The invention discloses a tilted fiber grating hydrogen sensor based on UiO‑66‑NH2, which is composed of a broadband light source, a polarization controller, a first single-mode optical fiber, a tilted fiber grating, a second single-mode optical fiber, a spectrometer, a gas chamber, a UiO‑66‑NH2 film, a hydrogen gas flow control valve, a nitrogen gas flow control valve, a hydrogen bottle, a nitrogen bottle, and PDMS; wherein the tilted fiber grating is attached with PDMS, and the UiO‑66‑NH2 film is attached through PDMS. The UiO‑66‑NH2 powder prepared by a solvothermal method is uniformly coated on the tilted fiber grating through PDMS as a hydrogen sensitive layer. The invention has the advantages of fast response speed and high sensitivity, and has good practical value and application prospects.

Description

Technical Field

[0001] The invention proposes a tilted fiber grating hydrogen sensor based on UiO-66-NH2, belonging to the technical field of optical fiber sensing. Background Art

[0002] UiO-66-NH2 is a metal organic framework material (MOFS) with a three-dimensional porous structure that can be used for hydrogen adsorption. When hydrogen enters the pores, the refractive index of UiO-66-NH2 will change.

[0003] The UiO-66-NH2 powder prepared by the solvothermal method is uniformly coated on the tilted fiber grating. Under different hydrogen concentrations, the refractive index of the UiO-66-NH2 film will be different.

[0004] Since polydimethylsiloxane (PDMS) elastomer has the advantages of excellent elastic properties and good adhesion, is easy to expand when heated, is non-toxic and non-flammable, it is a very promising material in the field of optical fiber sensing.

[0005] The special structure of tilted fiber Bragg grating (TFBG) leads to the emergence of multiple complex mode couplings, among which the most special one is the coupling between core mode and cladding mode. The emergence of cladding mode makes TFBG more sensitive to the change of environmental refractive index than ordinary Bragg fiber Bragg grating. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a tilted fiber grating hydrogen sensor based on UiO-66-NH2, using the UiO-66-NH2 film as the hydrogen sensitive layer, and measuring the concentration of hydrogen by changing the wavelength of the interference pattern caused by the change in the effective refractive index of the UiO-66-NH2 film.

[0007] The present invention is realized by the following technical scheme: a tilted fiber Bragg grating hydrogen sensor based on UiO-66-NH2, comprising a broadband light source (1), a polarization controller (2), a first single-mode optical fiber (3), a tilted fiber Bragg grating (4), a second single-mode optical fiber (5), a spectrometer (6), an air chamber (7), a UiO-66-NH2 film (8), a hydrogen gas flow control valve (9), a nitrogen gas flow control valve (10), a hydrogen bottle (11), a nitrogen bottle (12), and PDMS (13), characterized in that: the broadband light source (1) is connected to the left end of the polarization controller (2), the right end of the polarization controller (2) is connected to the left end of the first single-mode optical fiber (3), the right end of the first single-mode optical fiber (3) is connected to the left end of the tilted fiber Bragg grating (4), the central wavelength of the tilted fiber Bragg grating (4) is 1548nm, and the PDMS (13) is coated on the tilted fiber Bragg grating (4). The MS (13) is then attached with a UiO-66-NH2 film (8), the thickness of the UiO-66-NH2 film (8) is 300 nm, the right end of the tilted fiber grating (4) is connected to the left end of the second single-mode optical fiber (5), the right end of the second single-mode optical fiber (5) is connected to the left end of the spectrometer (6), the lower end of the gas chamber (7) is connected to the upper end of the hydrogen gas flow control valve (9) and the upper end of the nitrogen gas flow control valve (10), the lower end of the hydrogen gas flow control valve (9) is connected to the hydrogen bottle (11), and the lower end of the nitrogen gas flow control valve (10) is connected to the nitrogen bottle (12). When the hydrogen concentration changes, the amount of hydrogen absorbed by the UiO-66-NH2 film (8) also changes, causing the refractive index of the UiO-66-NH2 film (8) to change, and the transmission spectrum of the tilted fiber grating (4) to drift, thereby measuring the hydrogen concentration and its change.

[0008] The preparation process of the UiO-66-NH2 membrane (8) is as follows: 4.2 g (34.3 mmol) of benzoic acid is weighed and dispersed in 200 mL of N, N-dimethylformamide (DMF), and 0.8 g of ZrCl4 (3.4 mmol) is added after ultrasonic treatment for 2 min to make it dispersed completely, and then 0.6 g (3.4 mmol) of 2-aminoterephthalic acid is added, and ultrasonic treatment is continued for 5 min, and the dispersed solution is transferred to a hydrothermal reactor with a polytetrafluoroethylene sleeve and kept at a constant temperature of 120° C. for 24 h. After cooling to room temperature, the mixture is centrifuged at a speed of 4000 r / min for 15 min, washed with 10 mL of DMF and 10 mL of ethanol for 3 times, and then refluxed with 30 mL of methanol at 70° C. for 6 h, and the product obtained by centrifugation is vacuum dried for 10 h to prepare UiO-66-NH2.

[0009] The working principle of the present invention is: in the fiber grating sensor, when the ambient refractive index (SRI) changes, the core mode is not in contact with the outside world, so the resonant wavelength of the core mode will not shift with the change of SRI. Since the cladding is in direct contact with the outside world, the effective refractive index (n eff,clad,i ) will be affected by SRI, so the resonant wavelength of each cladding mode is the resonant wavelength of the i-th cladding mode (λ clad,i ) will shift with the change of SRI. The phase matching condition of TFBG can be expressed by the following expression:

[0010]

[0011]

[0012] because and are all zero, so the above formula can be simplified to:

[0013] Δλ Bragg =0 (2-3)

[0014]

[0015] In the formula, Δn s Indicates the change in the refractive index SRI of the external environment, λ Bragg represents the core mode resonant wavelength, Λ represents the period of TFBG, n eff,core represents the core refractive index, and θ is the tilt angle.

[0016] From equations (2-3) and (2-4), we can see that when SRI changes, the core mode resonant wavelength λ Bragg will not change, but the cladding mode resonance wavelength λ clad,i It will shift with the change of SRI. Therefore, refractive index sensing can be achieved by calibrating the relationship between the change of external refractive index and the wavelength of cladding mode.

[0017] UiO-66-NH2 is based on Zr 4+ The metal organic framework material prepared with 2-aminoterephthalic acid as a metal ion is the MOFS material with high thermal and chemical stability reported so far. It is stable in aqueous solution and acidic conditions. It has high thermal stability and thermal decomposition temperature greater than 400°C, and is a gas storage material and adsorption material. The rigid structure of UiO-66-NH2 is a good catalyst carrier, and the amino functional group is suitable for further derivatization.

[0018] The beneficial effects of the present invention are as follows: a tilted fiber grating (4) with PDMS (13) coated with a UiO-66-NH2 hydrogen sensitive film is proposed to sense hydrogen concentration. The structure is relatively sensitive to temperature changes, so that the sensitivity of the sensor to changes in external hydrogen concentration is significantly enhanced, providing a new method for hydrogen detection that is relatively simple, easy to build, reliable and highly sensitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the characteristic device of the tilted fiber Bragg grating hydrogen sensor based on UiO-66-NH2 of the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0021] See attached Figure 1 The invention discloses a tilted fiber Bragg grating hydrogen sensor based on UiO-66-NH2, comprising a broadband light source (1), a polarization controller (2), a first single-mode optical fiber (3), a tilted fiber Bragg grating (4), a second single-mode optical fiber (5), a spectrometer (6), a gas chamber (7), a UiO-66-NH2 film (8), a hydrogen gas flow control valve (9), a nitrogen gas flow control valve (10), a hydrogen bottle (11), a nitrogen bottle (12), and PDMS (13). The invention is characterized in that: the broadband light source (1) is connected to the left end of the polarization controller (2), the right end of the polarization controller (2) is connected to the left end of the first single-mode optical fiber (3), the right end of the first single-mode optical fiber (3) is connected to the left end of the tilted fiber Bragg grating (4), the central wavelength of the tilted fiber Bragg grating (4) is 1548nm, and the PDMS (13) is coated on the tilted fiber Bragg grating (4). A UiO-66-NH2 film (8) is then attached. The thickness of the UiO-66-NH2 film (8) is 300 nm. The right end of the tilted fiber grating (4) is connected to the left end of the second single-mode optical fiber (5). The right end of the second single-mode optical fiber (5) is connected to the left end of the spectrometer (6). The lower end of the gas chamber (7) is connected to the upper end of the hydrogen gas flow control valve (9) and the upper end of the nitrogen gas flow control valve (10). The lower end of the hydrogen gas flow control valve (9) is connected to the hydrogen bottle (11), and the lower end of the nitrogen gas flow control valve (10) is connected to the nitrogen bottle (12). When the hydrogen concentration changes, the amount of hydrogen absorbed by the UiO-66-NH2 film (8) also changes, causing the refractive index of the UiO-66-NH2 film (8) to change, and the transmission spectrum of the tilted fiber grating (4) to drift, thereby measuring the hydrogen concentration and its change.

[0022] The UiO-66-NH2 powder prepared by the solvent thermal method is uniformly coated on the tilted fiber grating (4) through PDMS (13) as a hydrogen sensitive layer.

Claims

1. A tilted fiber Bragg grating hydrogen sensor based on UiO-66-NH2, comprising a broadband light source (1), a polarization controller (2), a first single-mode optical fiber (3), a tilted fiber Bragg grating (4), a second single-mode optical fiber (5), a spectrometer (6), a gas chamber (7), a UiO-66-NH2 film (8), a hydrogen gas flow control valve (9), a nitrogen gas flow control valve (10), a hydrogen bottle (11), a nitrogen bottle (12), and PDMS (13), characterized in that: A broadband light source (1) is connected to the left end of a polarization controller (2), the right end of the polarization controller (2) is connected to the left end of a first single-mode optical fiber (3), the right end of the first single-mode optical fiber (3) is connected to the left end of a tilted optical fiber grating (4), the central wavelength of the tilted optical fiber grating (4) is 1548nm, and it is coated with PDMS (13), and a UiO-66-NH2 film (8) is attached through the PDMS (13), the thickness of the UiO-66-NH2 film (8) is 300nm, and the UiO-66-NH2 The synthesis process of membrane (8) is as follows: 4.2 g (34.3 mmol) of benzoic acid is dispersed in 200 mL of N, N-dimethylformamide, and after ultrasonic treatment for 2 min, 0.8 g of ZrCl4 (3.4 mmol) is added to make it dispersed completely, and then 0.6 g (3.4 mmol) of 2-aminoterephthalic acid is added, and ultrasonic treatment is continued for 5 min. The dispersed solution is transferred to a hydrothermal reactor with a polytetrafluoroethylene sleeve and kept at a constant temperature of 120°C for 24 h; after cooling to room temperature, The mixture was centrifuged at 4000 r / min for 15 min, washed three times with 10 mL of DMF and 10 mL of ethanol, and then refluxed with 30 mL of methanol at 70° C. for 6 h. The product obtained by centrifugation was vacuum dried for 10 h to obtain UiO-66-NH2. The right end of the tilted fiber grating (4) was connected to the left end of the second single-mode optical fiber (5), the right end of the second single-mode optical fiber (5) was connected to the left end of the spectrometer (6), and the lower end of the gas chamber (7) was connected to the hydrogen gas flow control valve ( 9) is connected to the upper end of the nitrogen gas flow control valve (10), the lower end of the hydrogen gas flow control valve (9) is connected to the hydrogen bottle (11), and the lower end of the nitrogen gas flow control valve (10) is connected to the nitrogen bottle (12). When the hydrogen concentration changes, the amount of hydrogen absorbed by the UiO-66-NH2 film (8) also changes, causing the refractive index of the UiO-66-NH2 film (8) to change, and the transmission spectrum of the tilted fiber grating (4) to drift, thereby measuring the hydrogen concentration and its change.

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