Optical fiber sensor for selectively detecting acetic acid concentration and detection method

Abstract

The invention discloses an optical fiber sensor for selectively detecting acetic acid concentration and a detection method. The sensor comprises an acetic acid detection optical fiber, a coupler coupled with the acetic acid detection optical fiber, and an acetic acid sensing unit arranged in the coupler, the acetic acid sensitive unit comprises a light reflecting mirror directly facing the detection end of the acetic acid detection optical fiber during use and an acetic acid sensitive film arranged on the surface of the reflecting surface of the light reflecting mirror; and the acetic acid sensitive film is a UiO-66-2CF3 / TiO2 / polyaniline film which is composed of UiO-66, a fluorine-containing group-CF3, TiO2 and polyaniline. After the acetic acid sensitive film absorbs acetic acid, the refractive index is increased, the absorption intensity of light with the wavelength of 326 nm is enhanced, the reflectivity is reduced, the intensity of light transmitted in the acetic acid detection optical fiber is reduced, and the concentration of acetic acid in the environment can be accurately measured through the variable quantity between the output light intensity and the input light intensity of the acetic acid detection optical fiber; an acetic acid measurement result is not interfered by other gas components and humidity changes, so that a linear relation exists between an output signal of the optical fiber sensor and the acetic acid concentration.

Description

Technical Field

[0001] The invention relates to the technical field of acetic acid concentration detection, and in particular to an optical fiber sensor and a detection method for selectively detecting acetic acid concentration. Background Art

[0002] Cultural relics in museums are precious and non-renewable cultural resources. They play a core role in modern society and are regarded not only as a cultural asset but also as an economic asset. Protecting and inheriting cultural heritage is a sacred mission entrusted to us by history and the nation. Over the past few decades, with the continuous enhancement of awareness of cultural relics protection, the impact of pollutant gases generated by decorative materials of cultural relics exhibits on the damage of cultural relics in museums has gradually received high attention. Common decorative materials such as wood, plastics, textiles, coatings, adhesives, etc. release volatile pollutant gases such as acetic acid, formic acid, sulfur compounds, acetaldehyde, olefins, aromatic hydrocarbons, etc., among which acetic acid is the most important organic acid in volatile organic compounds released by decorative materials. Even if the amount of acetic acid released by these decorative materials is very low, it can reach a relatively high concentration when they are used in closed spaces, such as in internal display cabinets. Acetic acid reduces the degree of polymerization of cellulose in paper, corrodes lead alloys and other metals, and degrades calcium materials (stone, ceramics). Therefore, in order to effectively prevent acetic acid gas from causing irreparable and serious damage to cultural relics in closed spaces (such as capsules), it is particularly important to detect the concentration of acetic acid in situ.

[0003] At present, the main methods for detecting acetic acid concentration are offline detection method and online detection method. Among them, the offline detection methods mainly include gas chromatography-mass spectrometry, PID photoionization detection method, ion flow tube mass spectrometry and infrared absorption spectroscopy. Gas chromatography-mass spectrometry can monitor volatile organic compounds at the ppm level and show good chemical selectivity; but the detection process is time-consuming and requires professional operation. PID photoionization detection method has fast response and strong anti-interference ability; but the analytical instrument is expensive, maintenance is complicated and cannot distinguish isomers, that is, when isomers such as acetic acid, ethyl acetate and hydroxyacetaldehyde exist in the environment at the same time, it is difficult to accurately detect the concentration of acetic acid. Ion flow tube mass spectrometry has the advantages of high sensitivity and quantitative analysis for detecting acetic acid gas, but the sample preparation process is complicated and the measurement process is time-consuming. Infrared absorption spectroscopy obtains the acetic acid concentration by testing the absorption of infrared light 730nm by the sample molecules. The method is simple to operate but has low sensitivity, and other components in the air (such as carbon dioxide, water, etc.) have great interference with the measurement results.

[0004] Among them, the online detection method of acetic acid concentration mainly uses electrochemical gas sensors, metal oxide semiconductor gas sensors, quartz crystal microbalances and optical fiber sensors to monitor the concentration of acetic acid. Electrochemical gas sensors, metal oxide semiconductor gas sensors and quartz crystal microbalance sensors have the advantages of high sensitivity and fast response speed; but there is a risk of discharge, the measurement results are affected by temperature, humidity and interfering gases, and it is difficult to achieve distributed measurement of acetic acid concentration. However, optical fiber sensors have the advantages of no discharge risk, small geometric size, high sensitivity, fast response speed, and distributed measurement, so they have become the most promising type of sensor in gas concentration online detection technology. Although optical fiber sensors have been developed for online detection of various gas concentrations such as carbon dioxide, hydrogen, acetaldehyde, hydrogen sulfide, and ethane, there are no literature reports or commercial products on optical fiber sensors for online detection of acetic acid concentration. Therefore, it is necessary to design an optical fiber sensor for online detection of acetic acid concentration. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is: how to provide an optical fiber sensor for selectively detecting the concentration of acetic acid, wherein when the acetic acid in the environment is transmitted to the acetic acid sensitive membrane, the refractive index of the acetic acid sensitive membrane increases after absorbing the acetic acid, the absorption intensity of the light with a wavelength of 326nm is enhanced and the reflectivity is reduced, causing the light intensity transmitted inside the acetic acid detection optical fiber to decrease, so that the acetic acid concentration in the environment can be accurately measured by the change between the output light intensity and the input light intensity of the acetic acid detection optical fiber; and the acetic acid measurement result is not affected by other gas components and humidity changes, so that there is a linear relationship between the output signal of the optical fiber sensor and the acetic acid concentration, and the optical fiber sensor can be widely used for in-situ online detection of acetic acid concentration in various environments.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] An optical fiber sensor for selectively detecting acetic acid concentration comprises: an acetic acid detection optical fiber, a coupler coupled to the acetic acid detection optical fiber, and an acetic acid sensitive unit arranged inside the coupler;

[0008] The acetic acid sensitive unit includes a light reflector facing the detection end of the acetic acid detection optical fiber when in use and an acetic acid sensitive film arranged on the reflective surface of the light reflector; the acetic acid sensitive film is formed by UiO-66 compound, fluorine-containing group -CF 3 、TiO 2 UiO-66-2CF composed of polyaniline 3 / TiO 2 / polyaniline film.

[0009] Preferably, the acetic acid sensitive membrane is prepared by the following steps:

[0010] 1) Add 2,5-bis(trifluoromethyl)terephthalic acid, benzoic acid and hydrochloric acid to a beaker containing N,N-dimethylformamide in sequence, stir and seal the beaker;

[0011] 2) placing a sealed beaker in water and heating it to dissolve 2,5-bis(trifluoromethyl)terephthalic acid and benzoic acid; then adding zirconium oxychloride octahydrate to the mixture in which 2,5-bis(trifluoromethyl)terephthalic acid is completely dissolved to obtain a mixed solution; transferring the mixed solution to a polytetrafluoroethylene-lined autoclave and heating it for reaction, and then centrifuging the mixture to obtain a solid;

[0012] 3) washing the collected solid with N,N-dimethylformamide and anhydrous ethanol in sequence;

[0013] 4) The washed solid was vacuum dried to obtain UiO-66-2CF 3 ;

[0014] 5) TiO 2 Nano powder and UiO-66-2CF 3 The mixture is mixed in a mixture of deionized water and ethanol, and then vacuum dried after ultrasonic dispersion. The obtained powder is ground in a mortar and then calcined. The obtained powder is the acetic acid sensitive material UiO-66-2CF. 3 / TiO 2 ;

[0015] 7) The acetic acid sensitive material UiO-66-2CF 3 / TiO 2 Add to the polyaniline sol and stir with a magnetic stirrer to obtain UiO-66-2CF 3 / TiO 2 / polyaniline sol;

[0016] 8) UiO-66-2CF 3 / TiO 2 The polyaniline sol is coated on the reflective surface of the light reflector and dried in vacuum to obtain an acetic acid sensitive film.

[0017] Preferably, coating UiO-66-2CF 3 / TiO 2 Before the preparation of the polyaniline sol, the reflecting surface of the light reflector is firstly soaked in a mixed solution of a silane coupling agent and ethanol; and then vacuum drying is performed to achieve silane treatment of the reflecting surface of the light reflector.

[0018] Preferably, the acetic acid detection optical fiber includes a tapered incident optical fiber, a plurality of receiving optical fibers and an optical fiber fixture; the detection ends of the tapered incident optical fiber and the plurality of receiving optical fibers are fixed together by the optical fiber fixture and the plurality of receiving optical fibers are distributed around the periphery of the tapered incident optical fiber;

[0019] The detection ends of the tapered incident optical fiber and a plurality of receiving optical fibers are detection ends of the acetic acid detection optical fibers.

[0020] Preferably, the detection end of the tapered incident optical fiber is corroded with hydrofluoric acid to form a truncated cone-shaped structure with a tapered angle.

[0021] Preferably, the coupler is a hollow Teflon tube with an opening at one end and a sealed end at the other end; the acetic acid detection optical fiber is inserted into the opening of the Teflon tube through an optical fiber holder to achieve coupling with the coupler, and the tapered incident optical fiber of the acetic acid detection optical fiber and the detection ends of several receiving optical fibers are facing the inside of the Teflon tube.

[0022] Preferably, an opening area is provided on the side wall of the Teflon tube to connect the interior of the Teflon tube with the outside, so that the acetic acid-containing air can enter the interior of the Teflon tube through the opening area.

[0023] The acetic acid concentration detection method based on the optical fiber sensor is implemented based on the optical fiber sensor of the present invention, comprising:

[0024] S1: The tapered incident optical fiber of the optical fiber sensor transmits the light beam emitted by the light source;

[0025] S2: The detection end of the tapered incident optical fiber of the optical fiber sensor radiates the light beam into the interior of the Teflon tube containing acetic acid air, and the light beam is transmitted to the acetic acid sensitive unit after passing through the acetic acid air;

[0026] S3: The detection end of each receiving optical fiber of the optical fiber sensor receives the light beam reflected by the acetic acid sensitive unit; the output light intensity of the optical fiber sensor is calculated based on the light intensity output by each receiving optical fiber;

[0027] S4: Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor;

[0028] S5: Calculating the acetic acid concentration of the acetic acid-containing air by using the output signal of the optical fiber sensor and a predetermined calibration relationship between the output signal and the acetic acid concentration.

[0029] Preferably, in step S3, the processing step of calculating the output light intensity of the optical fiber sensor includes:

[0030] S301: Define the light intensity of the conical incident optical fiber radiated light as I in ;

[0031] S302: Light intensity is I in The light beam radiates to form a light intensity of I in1 and light intensity is I in2 Two types of beams;

[0032] S303: Light intensity is I in1The light beam is transmitted to the surface of the acetic acid sensitive membrane through the acetic acid-containing air, and part of the light beam is reflected back to the receiving optical fiber. The light intensity received by the receiving optical fiber is I out1 ;

[0033] The formula is:

[0034] I out1 =kI in1 R;

[0035] in:

[0036] R=R 0 exp[-(4πσ / λ) 2 ;

[0037]

[0038] n 2 =K 1 C+b;

[0039]

[0040] Where: k represents the optical coupling coefficient when the light beam is coupled into the receiving optical fiber; R is the reflectivity of the acetic acid sensitive film to light; R 0 represents the reflectivity of the acetic acid sensitive film under ideal smoothness; σ represents the root mean square roughness of the surface of the acetic acid sensitive film; λ represents the wavelength of the light beam; n 1 Represents the refractive index of air; n 2 Represents the refractive index of acetic acid sensitive film; θ 1 is the incident angle of the light beam; θ 2 is the refraction angle of the light beam; x is the core spacing between the receiving fiber and the tapered incident fiber; K 1 , b are constants; C is the concentration of acetic acid;

[0041] S304: Light intensity is I in2 After the light beam is transmitted to the surface of the acetic acid sensitive film through the acetic acid-containing air, it is coupled into the acetic acid sensitive film, and after being attenuated by the acetic acid sensitive film, it is transmitted to the interface between the acetic acid sensitive film and the reflective surface of the light reflector; then it is reflected by the reflective surface of the light reflector and enters the acetic acid sensitive film again; then it is attenuated again by the acetic acid sensitive film and transmitted to the interface between the acetic acid sensitive film and the acetic acid-containing air; finally, the light beam is refracted at the interface between the acetic acid sensitive film and the air and enters the air medium again, and the partially reflected light beam is coupled into the interior of the optical fiber by the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out2 ;

[0042] The formula is:

[0043] I out2 =kI in2 exp(2ζx / cosθ 2);

[0044] in:

[0045] ζ=2πε 2 / (λn 2 );

[0046] I out2 =kI in2 exp[4πε 2 x / (λn 2 cosθ 2 );

[0047] Where: ζ is the attenuation coefficient of the acetic acid sensitive film to light; ε 2 is the imaginary part of the complex dielectric constant of the acetic acid sensitive film;

[0048] S305: Based on the light intensity I output by each receiving optical fiber out1 and I out2 Calculate the output light intensity I of the optical fiber sensor out ;

[0049] The formula is:

[0050]

[0051] Where: n represents the number of receiving optical fibers.

[0052] Preferably, in step S4, based on the output light intensity I of the optical fiber sensor out and the light intensity I of the tapered incident fiber receiving beam in Calculate the absorbance A as the output signal of the optical fiber sensor;

[0053] The formula is:

[0054] A=log(I in / I ou )=log[I in / n(I ou +I out2 )];

[0055] Where: I in ,I ou They represent the light intensity of the cone-shaped incident optical fiber receiving light beam and the light intensity of the receiving optical fiber output light beam respectively.

[0056] Compared with the prior art, the optical fiber sensor for selectively detecting acetic acid concentration in the present invention has the following beneficial effects:

[0057] The present invention designs an optical fiber sensor for selectively detecting acetic acid concentration, comprising an acetic acid detection optical fiber, an acetic acid sensitive unit and a coupler. The acetic acid sensitive unit comprises a light reflector and an acetic acid sensitive film, wherein the acetic acid sensitive film is an acetic acid sensitive material coated on the light reflector, and the acetic acid sensitive material is composed of UiO-66-2CF having a selective adsorption function for acetic acid. 3 / TiO 2 / Polyaniline composite material composition: UiO-66 has the function of selective adsorption of acetic acid, fluorinated group -CF 3 It is hydrophobic and can eliminate the interference of humidity changes on acetic acid concentration monitoring results in a humid environment; TiO 2 Used to improve UiO-66-2CF 3 / TiO 2 / Polyaniline composite material adsorption capacity for acetic acid, increase the sensor's measurement range for acetic acid and improve the sensor's sensitivity; Polyaniline is used to enhance the UiO-66-2CF 3 / TiO 2 / The adhesion strength between the polyaniline film and the light reflector and the mechanical strength of the film improve the repeatability and service life of the sensor.

[0058] When the optical fiber sensor is working, the light intensity of the optical fiber radiates into the coupler through the acetic acid detection. When the acetic acid in the external environment is transmitted to the acetic acid sensitive film (UiO-66-2CF 3 / TiO 2 / polyaniline film), the refractive index of the acetic acid sensitive film increases after absorbing acetic acid, the absorption intensity of light with a wavelength of 326nm is enhanced and the reflectivity is reduced, causing the light intensity transmitted inside the acetic acid detection optical fiber to decrease, so that the acetic acid concentration in the environment can be accurately measured through the change between the output light intensity and the input light intensity of the acetic acid detection optical fiber; and the acetic acid measurement result is not affected by other gas components and humidity changes, so that the output signal of the optical fiber sensor has a linear relationship with the acetic acid concentration, and can be widely used in the in-situ online detection of acetic acid concentration in various environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0060] Figure 1 Schematic diagram of the structure of the optical fiber sensor for selectively detecting acetic acid concentration: Figure 1 (a) is a schematic diagram of the sensor structure in which the acetic acid detection optical fiber is not coupled to the coupler; Figure 1 (b) is a schematic diagram of the sensor structure after the acetic acid detection optical fiber is coupled to the coupler.

[0061] Figure 2This is a schematic diagram of the structure of each component of the Y-type optical fiber: Figure 2 (a) is a schematic diagram of the tapered incident optical fiber structure; Figure 2 (b) is a schematic diagram of the coupling structure of the tapered incident optical fiber, the receiving optical fiber and the optical fiber holder; Figure 2 (c) is a schematic diagram of the coupling end face structure of the tapered incident optical fiber, the receiving optical fiber and the optical fiber holder; Figure 2 (d) is a schematic diagram of the optical fiber structure for acetic acid detection.

[0062] Figure 3 Schematic diagram of the structure of the acetic acid sensitive unit.

[0063] Figure 4 Schematic diagram of the optical transmission path of the fiber optic sensor.

[0064] Figure 5 This is the response curve of the sensor to acetic acid: Figure 5 (a) Sensor output spectra at different acetic acid concentrations; Figure 5 (b) is the relationship curve between the absorbance change of the sensor at 326nm and the acetic acid concentration.

[0065] Figure 6 The selectivity of the optical fiber sensor to acetic acid.

[0066] The figure marks in the drawings of the specification include: tapered incident optical fiber 1, receiving optical fiber 2, optical fiber protective cover 3, SMA optical fiber connector 4, optical fiber collimator 5, optical fiber holder 6, UV shadowless glue 61, external thread 7, coupler 8, internal thread 9, opening area 10, light reflector 11, acetic acid sensitive film 12. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but only represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0068] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0069] The following is a further detailed description through specific implementation methods:

[0070] Embodiment 1:

[0071] This embodiment discloses an optical fiber sensor for selectively detecting acetic acid concentration.

[0072] like Figure 1 As shown, the optical fiber sensor for selectively detecting the concentration of acetic acid comprises: an acetic acid detection optical fiber, a coupler coupled to the acetic acid detection optical fiber, and an acetic acid sensitive unit arranged inside the coupler;

[0073] The acetic acid sensitive unit comprises a light reflector facing the detection end of the acetic acid detection optical fiber when in use and an acetic acid sensitive membrane arranged on the reflective surface of the light reflector; the acetic acid sensitive membrane is a UiO-66 compound having a selective adsorption function for acetic acid, a hydrophobic fluorine-containing group -CF 3 , TiO for acetic acid adsorption capacity 2 UiO-66-2CF composed of titanium dioxide and polyaniline for enhancing the adhesion strength between the acetic acid sensitive film and the light reflector and the mechanical strength of the acetic acid sensitive film itself3 / TiO 2 / polyaniline film.

[0074] in:

[0075] UiO-66 compound refers to a metal organic framework compound composed of zirconium ions and organic linkers. It has the characteristics of large pore size and high surface area. The chemical formula is generally C48H24O38Zr6 and the molecular weight is 1756.03.

[0076] Fluorinated group -CF 3 It is a functional group with three fluorine atoms connected to one carbon atom, also known as trifluoromethyl, and often appears as a substituent in organic compounds.

[0077] TiO 2 (Titanium dioxide) is a white solid or powdered amphoteric oxide with a molecular weight of 79.866.

[0078] Polyaniline is a polymer compound.

[0079] The acetic acid detection optical fiber (Y-shaped optical fiber) includes a tapered incident optical fiber 1, a plurality of receiving optical fibers 2 and an optical fiber holder 6;

[0080] The first ends (i.e., detection ends) of the tapered incident optical fiber 1 and the plurality of receiving optical fibers 2 are fixed together by an optical fiber holder 6, and the plurality of receiving optical fibers 2 are distributed around the tapered incident optical fiber 1, and the second ends of the tapered incident optical fiber 1 and the plurality of receiving optical fibers 2 are separated and the plurality of receiving optical fibers 2 are fixed together;

[0081] The first ends of the tapered incident optical fiber 1 and the plurality of receiving optical fibers 2 are detection ends of the acetic acid detection optical fibers.

[0082] In this embodiment, there is one tapered incident optical fiber and six receiving optical fibers.

[0083] The first end of the tapered incident optical fiber is etched with hydrofluoric acid with a concentration of 5%-30% to form a truncated cone structure with a cone angle of 35° to 85°, so as to enhance the radiation capability of the tip of the tapered incident optical fiber to light.

[0084] The coupler 8 is a hollow Teflon tube with an opening at one end and a sealed end at the other end; the acetic acid detection optical fiber is inserted into the opening of the Teflon tube through an optical fiber holder to achieve coupling with the coupler 8, and the first ends of the tapered incident optical fiber 1 and several receiving optical fibers 2 of the acetic acid detection optical fiber are facing the inside of the Teflon tube.

[0085] The working logic of the optical fiber sensor is:

[0086] 1) The second end of the tapered input optical fiber transmits the light beam emitted by the light source;

[0087] 2) The first end of the tapered incident optical fiber radiates the light beam into the interior of the Teflon tube containing acetic acid air, and the light beam is transmitted to the acetic acid sensitive unit after passing through the acetic acid air;

[0088] 3) The first end of each receiving optical fiber receives the light beam reflected by the acetic acid sensitive unit and transmits it to the second end; the output light intensity of the optical fiber sensor is calculated based on the light intensity output from the second end of each receiving optical fiber;

[0089] 4) Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor;

[0090] 5) Calculating the acetic acid concentration of the acetic acid-containing air by using the output signal of the optical fiber sensor and a predetermined calibration relationship between the output signal and the acetic acid concentration.

[0091] The present invention designs an optical fiber sensor for selectively detecting acetic acid concentration, comprising an acetic acid detection optical fiber, an acetic acid sensitive unit and a coupler. The acetic acid detection optical fiber is composed of a tapered incident optical fiber, a plurality of receiving optical fibers and an optical fiber holder, wherein the first ends of the tapered incident optical fiber and the receiving optical fiber are fixed in the optical fiber holder, and the receiving optical fibers are distributed around the tapered incident optical fiber, and the tapered incident optical fiber and the receiving optical fiber are fixed and packaged with the optical fiber holder using UV shadowless adhesive. The acetic acid sensitive unit comprises a light reflector and an acetic acid sensitive film, wherein the acetic acid sensitive film is an acetic acid sensitive material coated on the light reflector, and the acetic acid sensitive material is made of UiO-66-2CF having a selective adsorption function for acetic acid. 3 / TiO 2 / Polyaniline composite material composition: UiO-66 has the function of selective adsorption of acetic acid, fluorinated group -CF 3 It is hydrophobic and can eliminate the interference of humidity changes on acetic acid concentration monitoring results in a humid environment; TiO 2 Used to improve UiO-66-2CF 3 / TiO 2 / Polyaniline composite material adsorption capacity for acetic acid, increase the sensor's measurement range for acetic acid and improve the sensor's sensitivity; Polyaniline is used to enhance the UiO-66-2CF 3 / TiO 2 / The adhesion strength between the polyaniline film and the light reflector and the mechanical strength of the film improve the repeatability and service life of the sensor. The coupler is a hollow Teflon tube with an opening at one end and a seal at the other end. The opening area set on the Teflon tube is convenient for acetic acid in the environment to pass through the Teflon tube freely; the acetic acid sensitive unit is fixed to the end of the coupler with UV shadowless glue; the coupler has an internal thread structure and is fixed with the external thread on the optical fiber holder to form an optical fiber sensor for acetic acid measurement.

[0092] When the optical fiber sensor is working, the light intensity of the optical fiber radiates into the coupler through the acetic acid detection. When the acetic acid in the external environment is transmitted to the acetic acid sensitive film (UiO-66-2CF 3 / TiO 2 / polyaniline film), the refractive index of the acetic acid sensitive film increases after absorbing acetic acid, the absorption intensity of light with a wavelength of 326nm is enhanced and the reflectivity is reduced, causing the light intensity transmitted inside the acetic acid detection optical fiber to decrease, so that the acetic acid concentration in the environment can be accurately measured through the change between the output light intensity and the input light intensity of the acetic acid detection optical fiber; and the acetic acid measurement result is not affected by other gas components and humidity changes, so that the output signal of the optical fiber sensor has a linear relationship with the acetic acid concentration, and can be widely used in the in-situ online detection of acetic acid concentration in various environments.

[0093] In order to better introduce the technical solution of the present invention, this embodiment is described through the following parts.

[0094] 1. Acetic acid detection optical fiber (Y-shaped optical fiber)

[0095] In order to improve the sensitivity of the optical fiber sensor in detecting acetic acid, firstly cut seven quartz optical fibers with a length of 0.2 to 10 m and a diameter of 100 to 5000 μm, use optical fiber polishing paper to grind the end face of the optical fiber flat and smooth, then rinse the surface of the optical fiber with deionized water, and use high-purity nitrogen to blow it dry for use. Then, one end of one of the optical fibers is corroded with hydrofluoric acid at a concentration of 5%-30%. After corrosion, the optical fiber has a truncated cone structure with a cone angle of 35° to 85°. The optical fiber with a cone angle is the sensor cone incident optical fiber, which is used to enhance the radiation capacity of the tip of the cone incident optical fiber to light. Then, the cone optical fiber is cleaned with alcohol and deionized water in turn to remove the corrosion products attached to the surface of the optical fiber and set aside. The schematic diagram of the end face structure of the cone incident optical fiber is shown in the figure. Figure 2 (a) As shown. Secondly, a tapered incident optical fiber and the first ends of six receiving optical fibers are fixed in an optical fiber holder made of Teflon, with a length of 10 to 100 mm and a diameter of 5 to 30 mm, one end of which has an external thread 7. The diameters of the seven holes in the optical fiber holder are 110-5100 μm, and the length of the external thread 7 is 5 to 50 mm. The receiving optical fibers are distributed around the tapered incident optical fiber, and the core spacing between the receiving optical fiber and the tapered incident optical fiber is 2 to 5 mm. UV shadowless glue 61 is used to fill and fix the optical fiber and the holder to achieve coupling between the tapered incident optical fiber and the receiving optical fiber, as shown in FIG. Figure 2 (b) and Figure 2(c) As shown. The other end (second end) of the tapered incident optical fiber and the receiving optical fiber are fixed in the optical fiber protective sleeve 3 with UV shadowless glue for later use. Finally, the SMA optical fiber connector 4 is connected to the second end of the tapered incident optical fiber, and the optical fiber collimator 5 and the SMA optical fiber connector 4 are connected to the second end of the receiving optical fiber in sequence to form an acetic acid detection optical fiber (Y-shaped optical fiber), as shown in FIG. Figure 2 (d) as shown.

[0096] During the specific implementation process, the preparation of acetic acid detection optical fiber (Y-shaped optical fiber) is as follows:

[0097] The length of the quartz optical fiber is 1m, the diameter of the tapered incident optical fiber is 1500μm, and the cone angle of the tapered incident optical fiber is 45°; the diameter of the six receiving optical fibers is 500μm; the core spacing between the tapered incident optical fiber and the receiving optical fiber is 3mm. The optical fiber holder with external threads is 50mm long and 10mm in diameter, the diameter of the middle hole of the holder is 1510μm, the diameter of the other six holes is 510μm, and the length of the external threads is 20mm. The first end of the receiving optical fiber is inserted into the hole in the middle of the optical fiber holder, and the first ends of the six receiving optical fibers are respectively inserted into the other six holes of the optical fiber holder. UV shadowless glue is used to fill and fix the package between the optical fiber and the holder, and an SMA optical fiber connector is connected to the second end of the tapered incident optical fiber, and an optical fiber collimator and an SMA optical fiber connector are connected to the second end of the receiving optical fiber in sequence to form an acetic acid detection optical fiber.

[0098] 2. Acetic acid sensitive unit

[0099] The preparation steps of the acetic acid sensitive unit include:

[0100] 1. Preparation of acetic acid sensitive materials:

[0101] 1) In order to obtain UiO-66 with selective adsorption and hydrophobic function for acetic acid, 500-650 mg of 2,5-bis(trifluoromethyl)terephthalic acid, 2.0-3.0 g of benzoic acid and 0.5-1.5 mL of hydrochloric acid were sequentially added into a beaker containing 20-100 mL of N,N-dimethylformamide, and the beaker was sealed after stirring for 5-10 minutes;

[0102] 2) placing a sealed beaker in a water area at 50 to 90° C. and heating for 1 to 2 hours to dissolve 2,5-bis(trifluoromethyl)terephthalic acid and benzoic acid; then adding 600 to 700 mg of zirconium oxychloride octahydrate to the mixture in which 2,5-bis(trifluoromethyl)terephthalic acid and benzoic acid are completely dissolved to obtain a mixed solution; transferring the mixed solution to a polytetrafluoroethylene-lined autoclave, heating and reacting at 90 to 150° C. for 20 to 24 hours, and then centrifuging the mixture to obtain a solid;

[0103] 3) washing the collected solids with N,N-dimethylformamide and anhydrous ethanol for 2 to 5 times in sequence;

[0104] 4) The washed solid was vacuum dried at 60-100°C for 10-20 hours to obtain UiO-66-2CF 3 ;

[0105] 5) In order to enhance the adsorption capacity of acetic acid sensitive materials for acetic acid, increase the sensor's measurement range for acetic acid and improve the sensor's sensitivity, 1 to 8 mg of TiO 2 Nano powder and 5-10 mg of UiO-66-2CF 3 The mixture is mixed in a mixture of 1-3 mL of deionized water and 1-4 mL of ethanol for 1-2 hours, ultrasonically dispersed for 10-30 minutes, and then vacuum dried at 90-120° C. for 10-20 hours. The obtained powder is ground in a mortar; then calcined at 80-150° C. for 3-4 hours (heating rate is 2-5° C. / min), and the obtained powder is the acetic acid sensitive material UiO-66-2CF. 3 / TiO 2 ;

[0106] 2. Preparation of acetic acid sensitive unit:

[0107] 7) To enhance UiO-66-2CF 3 / TiO 2 Adhesion strength between the reflector and the light reflector, 5-20 mg of acetic acid sensitive material UiO-66-2CF 3 / TiO 2 (Powder) was added to 20-50 μL of polyaniline sol and stirred for 1-2 hours using a magnetic stirrer to obtain UiO-66-2CF 3 / TiO 2 / polyaniline sol;

[0108] 8) soaking the reflective surface of the light reflector in a mixed solution of 1 to 3 wt% silane coupling agent and ethanol for 5 to 20 minutes; then vacuum drying at 70 to 90° C. for 20 to 30 minutes to achieve silane treatment of the reflective surface of the light reflector;

[0109] 9) Spin coating UiO-66-2CF 3 / TiO 2 The polyaniline sol was evenly coated on the reflective surface of the light reflector treated with silane, and vacuum dried at 50-90°C for 1-3 hours to obtain an acetic acid sensitive film (i.e., UiO-66-2CF 3 / TiO 2 / polyaniline film); finally, a light reflector coated with an acetic acid selectively adsorbing, hydrophobic acetic acid sensitive film is used as an acetic acid sensitive unit, such as Figure 3 shown.

[0110] In the specific implementation process, the preparation of the acetic acid sensitive unit is as follows:

[0111] 1. UiO-66-2CF 3 / TiO 2 / Polyaniline sol preparation:

[0112] 1) 604 mg of 2,5-bis(trifluoromethyl)terephthalic acid, 2.44 g of benzoic acid and 0.99 mL of hydrochloric acid (37% aqueous solution) were added to 36 mL of N,N-dimethylformamide in a 50 mL beaker and stirred, and then a layer of plastic wrap was covered on the beaker, and the mixed solution was heated at 60°C for 1 hour. After dissolution, 644 mg of zirconium oxychloride octahydrate was added, and the solution was transferred to a polytetrafluoroethylene-lined autoclave, heated in a drying oven at 120°C for 24 hours, centrifuged, washed 3 times with N,N-dimethylformamide, washed 3 times with anhydrous ethanol, and finally the washed solid was vacuum dried at 80°C for 12 hours to obtain UiO-66-2CF 3 .

[0113] 2) 6.4 mg of TiO with a diameter of 10 nm 2 Nano powder with 8.6mgUiO-66-2CF 3 The mixture was mixed in a mixture of 2 mL of deionized water and 3 mL of ethanol for 1 h, ultrasonically dispersed for 15 min, and then vacuum dried at 100 ° C for 15 h. The obtained powder was ground in a mortar; then calcined at 120 ° C for 3 h (heating rate of 3 ° C / min) to obtain a powder, which is the acetic acid sensitive material UiO-66-2CF. 3 / TiO 2 (3) 15 mg UiO-66-2CF 3 / TiO 2 The powder was added to 36 μL of polyaniline sol and stirred for 2 h using a magnetic stirrer to obtain UiO-66-2CF 3 / TiO 2 / polyaniline sol.

[0114] 2. Silane treatment of light reflector:

[0115] The glass area of ​​the lens was soaked in an ethanol solution containing 1% silane coupling agent (KH-560) for 10 minutes, and then placed in a 90°C vacuum drying oven for drying for 20 minutes.

[0116] 3. Acetic acid sensitive film coating on the surface of light reflector:

[0117] UiO-66-2CF3 / TiO 2 / polyaniline sol was dropped on the light reflector, and the sensitive film was evenly coated on the surface of the light reflector by spin coating. After coating, the light reflector was placed horizontally at room temperature for 10 minutes, and then placed in a 60℃ vacuum drying oven for 1 hour to obtain an acetic acid selective sensitive film (UiO-66-2CF) with a thickness of 120μm. 3 / TiO 2 / polyaniline film), the light reflecting mirror coated with the acetic acid selective sensitive film is the acetic acid sensitive unit.

[0118] The above scheme is the optimal ratio of various components when preparing the acetic acid sensitive unit (see Case 3 in Table 1). Through this optimal ratio, the absorption intensity and reflectivity of the acetic acid sensitive film can be best taken into account.

[0119] In other preferred embodiments, acetic acid sensitive units can also be prepared by the component ratios of other cases in Table 1, but compared with Case 3, the absorption intensity of the acetic acid sensitive membrane in Case 1 and Case 2 is better, but the reflectivity effect is worse, and the absorption intensity of the acetic acid sensitive membrane in Case 4 and Case 5 is better, but the reflectivity effect is worse; only Case 3 can make the absorption intensity and reflectivity of the acetic acid sensitive membrane reach excellent.

[0120] Table 1 Ratios of various components in the preparation of acetic acid sensitive units

[0121]

[0122] 3. Coupler

[0123] In order to obtain a reflective acetic acid concentration optical fiber sensor, firstly, a Teflon rod with a diameter of 10 to 35 mm and a length of 10 to 200 mm is cut. Then, a hole with a diameter of 6 to 22 mm and a depth of 8 to 190 mm is drilled at one end of the Teflon rod. Secondly, in order to facilitate the free entry and exit of the substances in the Teflon hole and the substances outside the Teflon, an opening area 10 connected to the outside is set on both sides of the Teflon central area with a hole, and the width of the opening area 10 is 3 to 15 mm and the length is 4 to 150 mm, that is, the side wall of the Teflon round tube is provided with an opening area 10 that connects the inside of the Teflon round tube with the outside, so that the acetic acid-containing air can enter the inside of the Teflon round tube through the opening area 10. Next, one end of the Teflon material with a hole drilled inside and an opening area on the side is processed into an internal thread 9 by turning. The diameter of the internal thread 9 is 5 to 30 mm and the length is 5 to 50 mm. The internal thread 9 matches the structural dimensions of the external thread of the optical fiber holder. The Teflon material with the internal thread 9 is the coupler. Finally, the acetic acid sensitive unit is fixed to the bottom of the coupler using UV shadowless glue. The coupling and fixation between the coupler and the optical fiber holder of the acetic acid detection optical fiber are achieved by thread rotation, forming an optical fiber sensor for acetic acid measurement. The schematic diagram of the structure of the reflective optical fiber sensor for selective detection of acetic acid concentration is shown in the figure. Figure 1 shown.

[0124] In the specific implementation process, for the reflective acetic acid concentration optical fiber sensor packaging:

[0125] First, a Teflon rod with a diameter of 15mm and a length of 50mm is cut. Then, a hole with a diameter of 10mm and a depth of 40mm is drilled in the center of the Teflon rod. Then, openings connected to the outside world are set on both sides of the central area of ​​the Teflon with a hole, and the opening width is 7mm and the length is 20mm. Secondly, one end of the Teflon material with a hole drilled inside and an opening on the side is processed into an internal thread by turning. The internal thread diameter is 10mm and the length is 20mm. The Teflon material with the internal thread is a coupler. UV shadowless glue is used again to fix the acetic acid sensitive unit at the bottom of the coupler. Finally, the coupler and the optical fiber holder of the acetic acid detection optical fiber are fixed by threaded rotation coupling, and the distance between the optical fiber end face and the light reflection mirror surface is kept at 2mm. The packaged and fixed sensor is the optical fiber sensor for selective measurement of acetic acid concentration.

[0126] Embodiment 2:

[0127] This embodiment discloses a method for detecting acetic acid concentration based on an optical fiber sensor, which is implemented based on the optical fiber sensor in the first embodiment.

[0128] The acetic acid concentration detection method based on the optical fiber sensor comprises:

[0129] S1: The second end of the tapered incident optical fiber of the optical fiber sensor transmits the light beam emitted by the light source;

[0130] S2: The first end of the tapered incident optical fiber of the optical fiber sensor radiates the light beam into the interior of the Teflon tube containing acetic acid air, and the light beam is transmitted to the acetic acid sensitive unit after passing through the acetic acid air;

[0131] S3: The first end of each receiving optical fiber of the optical fiber sensor receives the light beam reflected by the acetic acid sensitive unit and transmits it to the second end; the output light intensity of the optical fiber sensor is calculated based on the light intensity outputted from the second end of each receiving optical fiber;

[0132] S4: Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor;

[0133] S5: Calculating the acetic acid concentration of the acetic acid-containing air by using the output signal of the optical fiber sensor and a predetermined calibration relationship between the output signal and the acetic acid concentration.

[0134] The reflective optical fiber acetic acid concentration sensor in the first embodiment mainly utilizes the increase in the refractive index of the acetic acid selective sensitive membrane after adsorbing acetic acid gas molecules, which causes the light intensity transmitted to the receiving optical fiber to weaken. By measuring the relative attenuation of the light intensity or absorbance at the output end of the receiving optical fiber, the selective measurement of acetic acid concentration is achieved. The schematic diagram of the light transmission path during the sensor selective detection of acetic acid is as follows: Figure 4 shown.

[0135] Combination Figure 4 As shown, the output light intensity of the optical fiber sensor is calculated by the following steps:

[0136] S301: Define the light intensity of the conical incident optical fiber radiated light as I in ;

[0137] S302: Light intensity is I in The light beam radiates to form a light intensity of I in1 and light intensity is I in2 Two types of beams;

[0138] I in =I in1 +I in2 ; (1)

[0139] S303: Light intensity is I in1 The light beam is transmitted to the surface of the acetic acid sensitive membrane through the acetic acid-containing air, and part of the light beam is reflected back to the receiving optical fiber. The light intensity received by the receiving optical fiber is I out1 ;

[0140] For the tapered incident fiber output light intensity I in1 After being transmitted to the surface of the acetic acid sensitive film and reflected, the light intensity received by the receiving optical fiber can be expressed as:

[0141] I oit1 =kI in1 R; (2)

[0142] in:

[0143] R=R 0 exp[-(4πσ / λ) 2 ; (3)

[0144] When the refractive index of air is n 1 The refractive index of the acetic acid sensitive film is n 2 , the incident angle is θ 1 , the refraction angle is θ 2 When R 0 It can be expressed by the Fresnel formula:

[0145]

[0146] In formula (4), n 1 sinθ 1 =n 2 sinθ 2 θ 1 =arctan(x / y), x is the core distance between the receiving fiber and the tapered incident fiber, and y is the distance between the incident fiber and the acetic acid sensitive film. 2 is a function of the acetic acid concentration C, so n 2 The functional relationship between and C can be described as:

[0147] n 2 =K 1 C+b; (5)

[0148]

[0149] Where: k represents the optical coupling coefficient of the light beam transmitted in the air containing acetic acid coupled into the receiving optical fiber; R is the reflectivity of the acetic acid sensitive film to light; R 0 represents the reflectivity of the acetic acid sensitive film under ideal smoothness; σ represents the root mean square roughness of the surface of the acetic acid sensitive film; λ represents the wavelength of the light beam; n 1 Represents the refractive index of air; n 2 Represents the refractive index of acetic acid sensitive film; θ 1 is the incident angle; θ 2 is the refraction angle; x is the core spacing between the receiving fiber and the tapered incident fiber; K 1 , b are constants; C is the concentration of acetic acid;

[0150] S304: Light intensity is I in2After the light beam is transmitted to the surface of the acetic acid sensitive film through the acetic acid-containing air, it is coupled into the acetic acid sensitive film, and after being attenuated by the acetic acid sensitive film, it is transmitted to the interface between the acetic acid sensitive film and the reflective surface of the light reflector; then it is reflected by the reflective surface of the light reflector and enters the acetic acid sensitive film again; then it is attenuated again by the acetic acid sensitive film and transmitted to the interface between the acetic acid sensitive film and the acetic acid-containing air; finally, the light beam is refracted at the interface between the acetic acid sensitive film and the air and enters the air medium again, and the partially reflected light beam is coupled into the interior of the optical fiber by the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out2 ;

[0151] For the tapered incident fiber output light intensity I in2 After being transmitted into the acetic acid sensitive film, light attenuation will occur. The light intensity of the light beam coupled into the output optical fiber after attenuation by the acetic acid sensitive film can be described as:

[0152] I outs2 =kI in2 exp(2ζx / cosθ 2 ); (7)

[0153] in:

[0154] ζ=2πε 2 / (λn 2 ); (8)

[0155] Substituting equation (8) into equation (7) yields the output light intensity I of the tapered incident fiber: in2 After being absorbed by the acetic acid sensitive film, the light intensity coupled into the output optical fiber is:

[0156] I outs2 =kI in2 exp[4πε 2 x / (λn 2 cosθ 2 ); (9)

[0157] Where: ζ is the attenuation coefficient of the acetic acid sensitive film to light, and the refractive index n of the acetic acid sensitive film 2 Related to; 2 Acetic acid sensitive membrane (UiO-66-2CF 3 / TiO 2 / polyaniline film) imaginary part of the complex dielectric constant;

[0158] S305: Based on the light intensity I output by each receiving optical fiber out1 and I out2 Calculate the output light intensity I of the optical fiber sensor out ;

[0159] Substituting equations (5), (6) and (9) into equation (1), we know that the total light intensity I output by the sensor is outIt can be described as:

[0160]

[0161] In addition, according to the Lambert-Beer law, the absorbance A of the sensor output signal can be described as:

[0162] A=log(I in / I out )=log[I in / n(I out1 +I out2 )]∝C (11);

[0163] Where: I in ,I ou They represent the light intensity of the cone-shaped incident optical fiber receiving light beam and the light intensity of the receiving optical fiber output light beam respectively; C represents the acetic acid concentration; ∝ represents proportionality.

[0164] In this embodiment, after the acetic acid sensitive film selectively absorbs acetic acid molecules, the refractive index n of the acetic acid sensitive film is 2 increases, resulting in θ 2 Reduce, cosθ 2 Increase. 1 ≈1,θ 1 Constant, so I out1 and I out2 As the concentration of acetic acid C in the external environment increases, it decreases, that is, I out As the acetic acid concentration C of the external environment increases, it decreases; therefore, the sensor output signal (absorbance A) increases as the acetic acid concentration C of the external environment increases, that is, the absorbance A of the sensor output signal is proportional to the acetic acid concentration, as shown in formula (11). Therefore, the measurement of the acetic acid concentration C can be achieved by measuring the change in absorbance A.

[0165] It should be noted that the above calculation logic is an introduction to the internal working principle of the optical fiber sensor, which is mainly used to determine the calibration relationship between the output signal and the acetic acid concentration. In the actual detection process, the optical fiber sensor can directly obtain the light intensity of the received light beam and the light intensity of the output light beam, and then use formula (11) to calculate the absorbance, that is, the output signal, and then determine the acetic acid concentration through the calibration relationship between the output signal and the acetic acid concentration.

[0166] When the optical fiber sensor is working, the light intensity of the optical fiber radiates into the coupler through the acetic acid detection. When the acetic acid in the external environment is transmitted to the acetic acid sensitive film (UiO-66-2CF 3 / TiO 2 / polyaniline film), the refractive index of the acetic acid sensitive film increases after absorbing acetic acid, the absorption intensity of light with a wavelength of 326nm is enhanced and the reflectivity is reduced, causing the light intensity transmitted inside the acetic acid detection optical fiber to decrease, so that the acetic acid concentration in the environment can be accurately measured through the change between the output light intensity and the input light intensity of the acetic acid detection optical fiber; and the acetic acid measurement result is not affected by other gas components and humidity changes, so that the output signal of the optical fiber sensor has a linear relationship with the acetic acid concentration, and can be widely used in the in-situ online detection of acetic acid concentration in various environments.

[0167] Performance test of optical fiber sensor for detecting acetic acid

[0168] The prepared optical fiber sensor was placed in an acetic acid environment (ambient temperature of 25°C and relative humidity of 50% RH). When the acetic acid concentration was 0-500ppm, the response spectrum of the optical fiber sensor to acetic acid and the relationship between the absorbance and the acetic acid gas concentration were as follows: Figure 5 In order to characterize the selectivity of the fiber optic sensor for acetic acid measurement, the fiber optic sensor was placed in a SO 2 , acetone, acetic acid, CO 2 and formic acid gas, the optical fiber sensor absorbance is as follows Figure 6 shown.

[0169] Figure 5 (a) shows that the optical fiber sensor produces a characteristic absorption peak at 326 nm, and the absorbance increases with the increase of acetic acid concentration. The reason is that with the increase of acetic acid concentration, the number of acetic acid molecules adsorbed by the sensitive material increases, resulting in an increase in the refractive index of the acetic acid sensitive film, which causes the optical attenuation of the optical fiber sensor to increase. Therefore, the absorbance of the sensor output spectrum increases, which is consistent with the theoretical model analysis results of formula (11). Figure 5 (b) shows that when the wavelength of the light source is 326 nm, there is a linear relationship between the output signal (absorbance) of the optical fiber sensor and the acetic acid concentration, A = 0.00041C-0.025 (R 2 =0.99506), the sensitivity of the optical fiber sensor reached 0.00041AU / ppm. The reason for this is that UiO-66-CF 3 TiO has selective adsorption for acetic acid. 2 Doping improves the UiO-66-2CF 3 / TiO 2 / Polyaniline composite material's adsorption capacity for acetic acid. When acetic acid molecules are transmitted to the acetic acid sensitive membrane, they will be adsorbed, thereby increasing its refractive index and causing light attenuation; the greater the acetic acid concentration, the greater the refractive index increment, the greater the light attenuation, and the greater the absorbance A of the optical fiber sensor.

[0170] Figure 6The fiber optic sensor is sensitive to 500ppm SO 2 , acetone, acetic acid, CO 2 The absorption characteristic wavelength of formic acid gas is different, and the optical fiber sensor has a higher response sensitivity to acetic acid than other gases at the same concentration; the reason is that UiO-66-CF 3 Highly selective for acetic acid. Figure 5 and Figure 6 It shows that the optical fiber sensor of the present invention can realize selective and accurate detection of acetic acid gas at a light wavelength of 326 nm.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. An optical fiber sensor for selectively detecting acetic acid concentration, characterized in that: include: An acetic acid detection optical fiber, a coupler coupled to the acetic acid detection optical fiber, and an acetic acid sensitive unit disposed inside the coupler; The acetic acid sensitive unit comprises a light reflector facing the detection end of the acetic acid detection optical fiber when in use and an acetic acid sensitive film arranged on the reflection surface of the light reflector; the acetic acid sensitive film is a UiO-66-2CF3 / TiO2 / polyaniline film composed of UiO-66 compound, fluorine-containing group -CF3, TiO2 and polyaniline.

2. The optical fiber sensor for selectively detecting acetic acid concentration according to claim 1, characterized in that: The acetic acid sensitive membrane was prepared by the following steps: 1) Add 2,5-bis(trifluoromethyl)terephthalic acid, benzoic acid and hydrochloric acid to a beaker containing N,N-dimethylformamide in sequence, stir and seal the beaker; 2) placing a sealed beaker in water and heating it to dissolve 2,5-bis(trifluoromethyl)terephthalic acid and benzoic acid; then adding zirconium oxychloride octahydrate to the mixture in which 2,5-bis(trifluoromethyl)terephthalic acid is completely dissolved to obtain a mixed solution; transferring the mixed solution to a polytetrafluoroethylene-lined autoclave and heating it for reaction, and then centrifuging the mixture to obtain a solid; 3) washing the collected solid with N,N-dimethylformamide and anhydrous ethanol in sequence; 4) vacuum drying the washed solid to obtain UiO-66-2CF3; 5) mixing TiO2 nanopowder and UiO-66-2CF3 in a mixture of deionized water and ethanol, performing vacuum drying after ultrasonic dispersion, grinding the obtained powder in a mortar and calcining the obtained powder, and obtaining the acetic acid sensitive material UiO-66-2CF3 / TiO2; 7) adding the acetic acid sensitive material UiO-66-2CF3 / TiO2 into the polyaniline sol and stirring with a magnetic stirrer to obtain UiO-66-2CF3 / TiO2 / polyaniline sol; 8) The UiO-66-2CF3 / TiO2 / polyaniline sol is coated on the reflective surface of the light reflector and vacuum dried to obtain an acetic acid sensitive film.

3. The optical fiber sensor for selectively detecting acetic acid concentration according to claim 2, characterized in that: Before coating the UiO-66-2CF3 / TiO2 / polyaniline sol, the reflecting surface of the light reflector is firstly soaked in a mixed solution of a silane coupling agent and ethanol; and then vacuum drying is performed to achieve silane treatment of the reflecting surface of the light reflector.

4. The optical fiber sensor for selectively detecting acetic acid concentration according to claim 1, characterized in that: The acetic acid detection optical fiber includes a tapered incident optical fiber, a plurality of receiving optical fibers and an optical fiber holder; the detection ends of the tapered incident optical fiber and the plurality of receiving optical fibers are fixed together by the optical fiber holder and the plurality of receiving optical fibers are distributed around the tapered incident optical fiber; The detection ends of the tapered incident optical fiber and a plurality of receiving optical fibers are detection ends of the acetic acid detection optical fibers.

5. The optical fiber sensor for selectively detecting acetic acid concentration according to claim 4, characterized in that: The detection end of the tapered incident optical fiber is etched with hydrofluoric acid to form a truncated cone-shaped structure with a tapered angle.

6. The optical fiber sensor for selectively detecting acetic acid concentration according to claim 4, characterized in that: The coupler is a hollow Teflon tube with an opening at one end and a sealed end at the other end; the acetic acid detection optical fiber is inserted into the opening of the Teflon tube through an optical fiber holder to achieve coupling with the coupler, and the tapered incident optical fiber of the acetic acid detection optical fiber and the detection ends of several receiving optical fibers are facing the inside of the Teflon tube.

7. The optical fiber sensor for selectively detecting acetic acid concentration according to claim 6, characterized in that: An opening area is provided on the side wall of the Teflon tube to connect the inside of the Teflon tube with the outside, so that the acetic acid-containing air can enter the inside of the Teflon tube through the opening area.

8. A method for detecting acetic acid concentration based on an optical fiber sensor, characterized in that: The optical fiber sensor according to claim 4 is implemented as follows: S1: The tapered incident optical fiber of the optical fiber sensor transmits the light beam emitted by the light source; S2: The detection end of the tapered incident optical fiber of the optical fiber sensor radiates the light beam into the interior of the Teflon tube containing acetic acid air, and the light beam is transmitted to the acetic acid sensitive unit after passing through the acetic acid air; S3: The detection end of each receiving optical fiber of the optical fiber sensor receives the light beam reflected by the acetic acid sensitive unit; the output light intensity of the optical fiber sensor is calculated based on the light intensity output by each receiving optical fiber; S4: Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor; S5: Calculating the acetic acid concentration of the acetic acid-containing air by using the output signal of the optical fiber sensor and a predetermined calibration relationship between the output signal and the acetic acid concentration.

9. The method for detecting acetic acid concentration based on an optical fiber sensor according to claim 8, characterized in that: In step S3, the processing steps of calculating the output light intensity of the optical fiber sensor include: S301: Define the light intensity of the conical incident optical fiber radiated light as I in ; S302: Light intensity is I in The light beam radiates to form a light intensity of I in1 and light intensity is I in2 Two types of beams; S303: Light intensity is I in1 The light beam is transmitted to the surface of the acetic acid sensitive membrane through the acetic acid-containing air, and part of the light beam is reflected back to the receiving optical fiber. The light intensity received by the receiving optical fiber is I out1 ; The formula is: I out1 =kI in1 R; in: R=R0exp[-(4π / λ) 2 ; n2=K1C+b; Where: k represents the optical coupling coefficient when the light beam is coupled into the receiving optical fiber; R is the reflectivity of the acetic acid sensitive film to light; R0 represents the reflectivity of the acetic acid sensitive film under ideal smoothness; σ represents the root mean square roughness of the surface of the acetic acid sensitive film; λ represents the wavelength of the light beam; n1 represents the refractive index of air; n2 represents the refractive index of the acetic acid sensitive film; θ1 is the incident angle of the light beam; θ is the refraction angle of the light beam; x is the core spacing between the receiving optical fiber and the tapered incident optical fiber; K1 and b are both constants; C is the acetic acid concentration; S304: Light intensity is I in2 After the light beam is transmitted to the surface of the acetic acid sensitive film through the acetic acid-containing air, it is coupled into the acetic acid sensitive film, and after being attenuated by the acetic acid sensitive film, it is transmitted to the interface between the acetic acid sensitive film and the reflective surface of the light reflector; then it is reflected by the reflective surface of the light reflector and enters the acetic acid sensitive film again; then it is attenuated again by the acetic acid sensitive film and transmitted to the interface between the acetic acid sensitive film and the acetic acid-containing air; finally, the light beam is refracted at the interface between the acetic acid sensitive film and the air and enters the air medium again, and the partially reflected light beam is coupled into the interior of the optical fiber by the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out2 ; The formula is: I out2 =kI in2 exp(2ζx / cosθ2); in: ζ=2πε2 / (λn2); I out2 =kI in2 exp[4πε2x / (λn2cosθ2); Where: ζ is the attenuation coefficient of the acetic acid sensitive film to light; ε2 is the imaginary part of the complex dielectric constant of the acetic acid sensitive film; S305: Based on the light intensity I output by each receiving optical fiber out1 and I out2 Calculate the output light intensity I of the optical fiber sensor out ; The formula is: Where: n represents the number of receiving optical fibers.

10. The method for detecting acetic acid concentration based on an optical fiber sensor according to claim 9, characterized in that: In step S4, based on the output light intensity I of the optical fiber sensor out and the light intensity I of the tapered incident fiber receiving beam in Calculate the absorbance A as the output signal of the optical fiber sensor; The formula is: A=log(I in / I out )=log[I in / n(I out1 +I out2 )]; Where: I in ,I ou They represent the light intensity of the cone-shaped incident optical fiber receiving light beam and the light intensity of the receiving optical fiber output light beam respectively.

Images