Gas sensor for non-metallic pipe, manufacturing method for gas sensor, and gas monitoring method

Abstract

The present invention provides a gas sensor for a non-metallic pipe, a manufacturing method for the gas sensor, and a gas monitoring method. The manufacturing method for the gas sensor comprises: taking a dispersion liquid containing MXene nanosheets as a spinning solution, and injecting the spinning solution into a spinning guide pipe, wherein a sleeve is provided on the outer wall of the spinning guide pipe, and the temperature of the sleeve is gradually reduced in the flow direction of the spinning solution; injecting the spinning solution into a coagulating bath through the spinning guide pipe; collecting fibers formed in the coagulating bath, and then at least carrying out swelling, liquid nitrogen freezing and freeze drying to obtain MXene-based gel fibers; and using the MXene-based gel fibers to assemble the gas sensor. The gas sensor of the present invention has high sensitivity, can detect a low-concentration gas, and is suitable for monitoring gas permeation of a non-metallic pipe.

Description

Gas sensor for non-metallic pipe, preparation method thereof, and gas monitoring method Technical Field

[0001] The present invention relates to a gas sensor for a non-metallic tube, a preparation method thereof and a gas monitoring method, and belongs to the technical field of gas sensors. Background Art

[0002] Pipeline transportation plays a vital role in industrial production, with the vast majority of media being transported via pipelines. Oilfield extraction, gas transportation, and wastewater discharge generate corrosive media such as CO2, NH3, CH4, and H2S, which can cause metal pipes to corrode and age, seriously impacting the environment and human safety. Consequently, non-metallic pipes, due to their superior corrosion resistance, have gradually attracted widespread attention, and products have been developed for use in oilfield pipes, gas pipes, and drainage pipes. With the increasingly harsh oilfield extraction environment and increased mining depth, the impact of corrosive media has become more pronounced. Furthermore, with the increase in toxic and harmful gases in urban drainage processes due to increasing industrialization, the development of non-metallic pipe gas sensors for use in the oilfield, gas, and drainage sectors has become of great significance.

[0003] Connecting gas sensors to pipelines can achieve real-time monitoring of hazardous gases during oil extraction and transportation, gas transmission and drainage. This can evaluate the barrier properties of non-metallic pipes, predict the service life of pipelines, monitor the dynamic changes in corrosive gas content, and further evaluate the safety of oil extraction and transportation, gas transmission and drainage, which has important guiding significance for safe production.

[0004] Currently, to solve the problem of monitoring gas permeation during the use of non-metallic pipes, the existing technology mainly uses the pressure difference method to measure gas permeation. CN215894320U discloses a full-scale gas permeation detection device for non-metallic composite pipes. The device includes: a metal pressure autoclave for placing a test sample assembly, with a sealed annular space provided between the metal pressure autoclave and the test sample assembly; a gas source connected to the inlet of the non-metallic pipe for supplying gas to the test sample assembly; a metering and pressurizing system provided between the gas source and the test sample assembly for regulating the gas pressure output by the gas source; and a gas detection system provided on the metal pressure autoclave for detecting the gas in the annular space between the metal pressure autoclave and the test sample assembly. By inflating the interior of the non-metallic pipe and the annular space between the pipe and the outer cavity, and under long-term pressure maintenance, the test sample is leak-tested and the gas permeation in the annular space under long-term pressure maintenance is recorded. However, using the pressure difference method to measure gas permeation is not easy to achieve real-time gas monitoring and cannot provide early warning of gas anomalies during industrial production.

[0005] Two-dimensional transition metal carbon / nitride (MXene) is an emerging material with rich functional groups on its surface, which can serve as sites for gas adsorption and has excellent prospects as a gas-sensing material.

[0006] Liu et al. used vacuum-assisted layer-by-layer assembly to synthesize Ti3C2T x MXene and silver nanowires were sprayed on silk fabric substrates to prepare conductive fabrics, and their applications in electromagnetic shielding, humidity monitoring and hydrophobicity were studied (Liu-Xin Liu, Wei Chen, Hao-Bin Zhang, Qi-Wei Wang, Fanglan Guan, Zhong-Zhen Yu. Flexible and multifunctional silk textiles with biomimetic leaf-like MXene / silver nanowire nanostructures for electromagnetic interference shielding, humidity monitoring, and self-derived hydrophobicity[J]. Advanced Functional Materials, 2019, 29, 1905197).

[0007] Li et al. used a high-efficiency vacuum filtration-assisted spraying method to prepare conductive polyaniline (PANI) / MXene / cotton fabrics (PMCFs) for acid / alkali responsive and tunable EMI shielding applications (Dan-Yang Li, Liu-Xin Liu, Qi-Wei Wang, Hao-Bin Zhang, Wei Chen, Guang Yin, and Zhong-Zhen Yu. Functional Polyaniline / MXene / Cotton Fabrics with Acid / Alkali Responsive and Tunable Electromagnetic Interference Shielding Performances[J]. ACS Appl. Mater. Interfaces 2022, 14, 12703-12712).

[0008] Kim et al. studied Ti3C2T xMXene materials have a superior signal-to-noise ratio when detecting low-concentration volatile organic compound gases, revealing their advantages in the field of gas sensing (Seon Joon Kim, Hyeong-Jun Koh, Chang E. Ren, Ohmin Kwon, Kathleen Maleski, Soo-Yeon Cho, Babak Anasori, Choong-Ki Kim, Yang-Kyu Choi, Jihan Kim, Yury Gogotsi, and Hee-Tae Jung. Metallic Ti3C2T x MXene Gas Sensors with Ultrahigh Signal-to-Noise Ratio[J].ACS Nano 2018, 12, 986-993). This study provides a theoretical basis for the use of MXene as a gas-sensing material and demonstrates superior performance in gas sensing compared to black scale, molybdenum disulfide, and reduced graphene oxide.

[0009] There is no research in the existing technology on applying MXene to gas sensors in non-metallic tubes, and further improving the gas response sensitivity of MXene-based materials remains one of the research hotspots in this field.

[0010] Summary of the Invention

[0011] To address the above technical problems, the present invention provides a gas sensor for non-metallic pipes, a method for preparing the same, and a method for monitoring gas permeation. The gas sensor of the present invention has high sensitivity and can detect low-concentration gases, making it suitable for monitoring gas permeation in non-metallic pipes.

[0012] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a gas sensor for a non-metallic tube, comprising the following steps: using a dispersion containing MXene nanosheets as a spinning solution, injecting the spinning solution into a spinning tube, wherein the outer wall of the spinning tube is provided with a sleeve, and the temperature of the sleeve gradually decreases along the flow direction of the spinning solution; injecting the spinning solution into a coagulation bath through the spinning tube; collecting the fibers formed in the coagulation bath and subjecting them to at least swelling, liquid nitrogen freezing and freeze drying to obtain MXene-based gel fibers; and assembling a gas sensor using the MXene-based gel fibers to obtain the gas sensor for a non-metallic tube.

[0013] According to a specific embodiment of the present invention, preferably, the dispersion containing MXene nanosheets includes a dispersion of MXene nanosheets, a dispersion of MXene nanosheets and GO (graphene oxide) nanosheets, or a dispersion of MXene nanosheets and sodium alginate. More preferably, the dispersion containing MXene nanosheets is a dispersion of MXene nanosheets and GO nanosheets or a dispersion of MXene nanosheets and sodium alginate. It will be understood by those skilled in the art that when the dispersion is a dispersion of MXene nanosheets, the MXene-based gel fiber is a MXene gel fiber; when the dispersion is a dispersion of MXene nanosheets and GO nanosheets, the MXene-based gel fiber is a MXene / GO composite gel fiber; when the dispersion is a dispersion of MXene nanosheets and sodium alginate, the MXene-based gel fiber is a MXene / alginate composite gel fiber.

[0014] According to a specific embodiment of the present invention, preferably, the MXene nanosheets include Ti3C2T x MXene nanosheets.

[0015] According to a specific embodiment of the present invention, the MXene nanosheets are preferably prepared by the following steps: treating a MAX phase with a mixed solution of LiF and HCl, followed by ultrasonic treatment to obtain MXene nanosheets. The MAX phase used is preferably titanium aluminum carbon (Ti3AlC2).

[0016] According to a specific embodiment of the present invention, preferably, the concentration of the MXene nanosheets in the dispersion of the MXene nanosheets is 80 to 180 mg / mL, more preferably 110 to 150 mg / mL.

[0017] According to a specific embodiment of the present invention, preferably, the solvent in the dispersion of the MXene nanosheets includes dimethyl sulfoxide (DMSO) and / or N,N-dimethylformamide (DMF).

[0018] According to a specific embodiment of the present invention, preferably, the total concentration of MXene nanosheets and GO nanosheets in the dispersion of MXene nanosheets and GO nanosheets is 70-160 mg / mL, more preferably 100-140 mg / mL, and the mass ratio of MXene nanosheets to GO nanosheets is 1:9-8:2. More preferably, the thickness of the GO nanosheet is less than 2 nm, and the transverse diameter of the sheet is 8-80 μm. The transverse diameter of the GO nanosheet generally refers to the maximum straight-line distance between any two points on the nanosheet.

[0019] According to a specific embodiment of the present invention, preferably, the solvent in the dispersion of MXene nanosheets and GO nanosheets includes dimethyl sulfoxide and / or N,N-dimethylformamide.

[0020] According to a specific embodiment of the present invention, preferably, the total concentration of MXene nanosheets and sodium alginate in the dispersion of MXene nanosheets and sodium alginate is 50 to 150 mg / mL, more preferably 80 to 130 mg / mL, and the mass ratio of MXene nanosheets to sodium alginate is 1:9 to 9:1.

[0021] According to a specific embodiment of the present invention, preferably, the solvent in the dispersion of MXene nanosheets and sodium alginate includes water.

[0022] According to a specific embodiment of the present invention, preferably, the spinning tube has a length of 0.3 to 1 m and an inner diameter of 0.30 to 1.3 mm.

[0023] According to a specific embodiment of the present invention, the sleeve provided on the outer wall of the spinning duct is preferably a metal tube. The gradual decrease in temperature of the sleeve along the flow direction of the spinning solution is achieved by providing a cooling source at one end of the sleeve, so that the sleeve conducts cooling energy in a direction opposite to the flow direction of the spinning solution, thereby gradually decreasing the temperature along the flow direction of the spinning solution. Specifically, the sleeve may be a copper tube. Furthermore, as will be appreciated by those skilled in the art, an appropriate gap should be provided between the sleeve and the spinning duct to prevent the spinning solution from freezing and solidifying and becoming unable to flow.

[0024] According to a specific embodiment of the present invention, preferably, the temperature of the cold source provided at one end of the sleeve is -200° C. to -100° C. Specifically, the cold source may be liquid nitrogen (-196° C.).

[0025] According to a specific embodiment of the present invention, preferably, the coagulation bath comprises one or a combination of an aqueous solution of ammonium chloride, an aqueous solution of calcium chloride, an aqueous solution of aluminum chloride, aqueous ammonia, isopropyl alcohol, ethyl acetate, acetone, acetic acid, n-hexane, dichloromethane, a mixture of dimethyl sulfoxide and acetic acid, and a mixture of isopropyl alcohol and water. More preferably, when the dispersion containing MXene nanosheets is a dimethyl sulfoxide dispersion of MXene nanosheets, or a dimethyl sulfoxide dispersion of MXene nanosheets and GO nanosheets, the coagulation bath is a mixture of dimethyl sulfoxide and acetic acid, and further preferably, the volume ratio of dimethyl sulfoxide to acetic acid in the mixture is 1:3 to 3:1; when the dispersion containing MXene nanosheets is an N,N-dimethylformamide dispersion of MXene nanosheets, or an N,N-dimethylformamide dispersion of MXene nanosheets and GO nanosheets, the coagulation bath is a mixture of isopropanol and water, and further preferably, the volume ratio of isopropanol to water in the mixture is 1:2 to 3:1; when the dispersion containing MXene nanosheets is an aqueous dispersion of MXene nanosheets and sodium alginate, the coagulation bath is an aqueous ammonium chloride solution or an aqueous calcium chloride solution, and its mass concentration is 0.5 to 1%. For the spinning dope of MXene or MXene / GO inorganic nanomaterials, the present invention preferably uses an organic solvent such as DMSO for dispersion, and preferably uses a mixture of DMSO and acetic acid as the coagulation bath. DMSO can appropriately slow the coagulation rate of acetic acid on the fiber, and coagulation in this weak coagulation bath more easily results in a porous fiber structure. For the spinning dope of MXene / sodium alginate, the present invention preferably uses water as the solvent, and preferably forms the fiber in an ionic coagulation bath. During the forming process, the polymer alginate can serve as a crosslinking agent and also provide structural support. Simultaneously, the present invention controls the concentration of salts in the ionic coagulation bath to achieve an appropriate degree of crosslinking and gelation of the fiber during the forming process.

[0026] According to a specific embodiment of the present invention, preferably, the fibers formed in the coagulation bath are collected and washed, and then naturally dried. The dried fibers are swollen, and the swollen fibers are placed in liquid nitrogen for freezing, and then freeze-dried, and then vacuum-dried to obtain the MXene-based gel fibers.

[0027] According to a specific embodiment of the present invention, preferably, the fibers formed in the coagulation bath are collected and washed with a mixture of ethanol and water. More preferably, the volume ratio of ethanol to water in the mixture is 1:3 to 3:1, and further preferably 2:1.

[0028] According to a specific embodiment of the present invention, preferably, the time for naturally drying the fibers formed in the coagulation bath after being collected and washed is 0.5 to 1 day.

[0029] According to a specific embodiment of the present invention, preferably, the swelling is carried out using a mixture of alcohol and water, more preferably a mixture of ethanol and water, and the volume ratio of ethanol to water in the mixture is 3:4 to 1:3, more preferably 1:1.

[0030] According to a specific embodiment of the present invention, preferably, the dried fiber is immersed in a mixture of alcohol and water for swelling for 2 to 5 minutes.

[0031] According to a specific embodiment of the present invention, preferably, the swollen fiber is placed in liquid nitrogen for freezing for 30 to 60 minutes.

[0032] According to a specific embodiment of the present invention, preferably, the freeze-drying temperature is -45°C to -60°C. The freeze-drying can be carried out under vacuum conditions. More preferably, the freeze-drying time is 2 to 4 days.

[0033] According to a specific embodiment of the present invention, preferably, the vacuum drying temperature is 40 to 70° C. More preferably, the vacuum drying time is 0.5 to 2 days.

[0034] A second aspect of the present invention provides a gas sensor for a non-metallic tube, which is manufactured by the above-mentioned method for preparing a gas sensor for a non-metallic tube, wherein the gas sensor for a non-metallic tube includes MXene-based gel fiber.

[0035] According to a specific embodiment of the present invention, the gas sensor for non-metallic tubes preferably includes an external gas sensor, a wall-mounted gas sensor, or an embedded gas sensor. The external gas sensor is installed on the outside of the non-metallic tube, the wall-mounted gas sensor adheres to the outer wall of the non-metallic tube, and the embedded gas sensor is installed between layers within the non-metallic tube. More preferably, the gas sensor for non-metallic tubes is an external gas sensor.

[0036] According to a specific embodiment of the present invention, preferably, the external gas sensor comprises: a MXene-based gel fiber sensing element, a sealing cover, a first air duct and a second air duct;

[0037] The MXene-based gel fiber sensing element includes a chamber, a substrate, a plurality of MXene-based gel fibers, and a pair of electrodes. The plurality of MXene-based gel fibers and the electrodes are arranged on the substrate and placed in the chamber. The pair of electrodes are respectively connected to the axial ends of the plurality of MXene-based gel fibers. The chamber wall is provided with a first gas inlet and a first gas outlet.

[0038] The sealing cover is an annular shell, which is used to seal and cover the part of the non-metallic tube to be inspected; the sealing cover is provided with a second gas outlet and a second gas inlet;

[0039] One end of the first gas duct is connected to the second gas outlet, and the other end is connected to the first gas inlet; one end of the second gas duct is connected to the first gas outlet, and the other end is connected to the second gas inlet.

[0040] According to a specific embodiment of the present invention, in actual application, after the MXene-based gel fiber sensing element is energized, it converts changes in gas content into changes in resistance and can be connected to a computer for communication, thereby realizing real-time monitoring of the ambient gas and / or permeating gas of the non-metallic pipe.

[0041] According to a specific embodiment of the present invention, preferably, the MXene-based gel fiber sensing element includes 2 to 10 MXene-based gel fibers connected in parallel, more preferably 3 to 6 MXene-based gel fibers.

[0042] According to a specific embodiment of the present invention, preferably, the electrode includes one of a copper electrode, a silver electrode, a gold electrode, a platinum electrode, a titanium electrode, a nickel electrode or an aluminum electrode.

[0043] According to a specific embodiment of the present invention, preferably, the sealing cover includes an upper sealing cover and a lower sealing cover, and the upper sealing cover and the lower sealing cover are both semi-annular shell structures. The upper sealing cover and the lower sealing cover are coupled and connected to form a circular connecting port, and the circular connecting port is used to allow the non-metallic pipe to pass through, and after the upper sealing cover and the lower sealing cover are coupled and connected, a closed annular space is formed between the outer wall of the non-metallic pipe portion to be inspected.

[0044] According to a specific embodiment of the present invention, preferably, the upper sealing cover is provided with the second gas outlet, and the lower sealing cover is provided with the second gas inlet.

[0045] According to a specific embodiment of the present invention, preferably, the first gas inlet and the first gas outlet are respectively located at two ends of the axial direction of the MXene-based gel fiber.

[0046] According to a specific embodiment of the present invention, preferably, a gas pump is provided on the first air duct.

[0047] According to a specific embodiment of the present invention, the wall-attached gas sensor preferably includes at least a MXene-based gel fiber sensing element; the MXene-based gel fiber sensing element includes a substrate, a plurality of MXene-based gel fibers, and electrodes, wherein the plurality of MXene-based gel fibers and the electrodes are disposed on the substrate, and the electrodes are disposed at both axial ends of the plurality of MXene-based gel fibers; the plurality of MXene-based gel fibers and the electrodes are adhered to the outer wall of a non-metallic tube. More preferably, the wall-attached gas sensor may further include a sealing cover disposed outside the substrate for sealing the MXene-based gel fiber sensing element to the outer wall of the non-metallic tube.

[0048] According to a specific embodiment of the present invention, preferably, the embedded gas sensor includes a MXene-based gel fiber sensing element; the MXene-based gel fiber sensing element includes a substrate, a plurality of the MXene-based gel fibers, and electrodes, the plurality of the MXene-based gel fibers and the electrodes are disposed on the substrate, and the electrodes are disposed at both ends of the axial direction of the plurality of the MXene-based gel fibers; the plurality of the MXene-based gel fibers and the electrodes are adhered to the outer surface of the barrier layer in the non-metallic tube. Generally speaking, the non-metallic tube is a multi-layer composite tube, which may include an inner lining layer, a barrier layer, a reinforcement layer, etc. from the inside to the outside. The present invention does not impose any special restrictions on the multi-layer composite structure of the non-metallic tube, and only disposes the embedded gas sensor on the outer surface of the barrier layer.

[0049] According to a specific embodiment of the present invention, the external gas sensor can mainly detect the permeation gas and / or ambient gas of the entire non-metallic tube, the wall-mounted gas sensor can mainly detect the ambient gas and permeation gas of the non-metallic tube, and the embedded gas sensor can mainly detect the permeation gas of the non-metallic tube.

[0050] According to a specific embodiment of the present invention, preferably, the absolute value of the H2S response value of the gas sensor for non-metallic pipes (i.e., |ΔR / R0|) is greater than 3%; wherein, the testing method for the absolute value of the H2S response value includes: using the gas sensor for non-metallic pipes to detect the permeated gas of the non-metallic pipe with an H2S gas content of 80 to 100 ppm in the pipeline, and using a digital multimeter to detect the resistance change of the MXene-based gel fiber sensing element to obtain the absolute value of the H2S response value.

[0051] According to a specific embodiment of the present invention, preferably, the absolute value of the CH4 response value of the gas sensor for non-metallic tubes (i.e., |ΔR / R0|) is greater than 4%; wherein, the testing method for the absolute value of the CH4 response value includes: using the gas sensor for non-metallic tubes to detect the permeated gas of the non-metallic tube with a CH4 gas content of 500 to 600 ppm in the pipeline, and using a digital multimeter to detect the resistance change of the MXene-based gel fiber sensing element to obtain the absolute value of the CH4 response value.

[0052] According to a specific embodiment of the present invention, preferably, the absolute value of the NH3 response value of the gas sensor for non-metallic tubes (i.e., |ΔR / R0|) is greater than 12%; wherein, the testing method for the absolute value of the NH3 response value includes: using the gas sensor for non-metallic tubes to detect the permeated gas of the non-metallic tube with an NH3 gas content of 700 ppm in the pipeline, and using a digital multimeter to detect the resistance change of the MXene-based gel fiber sensing element to obtain the absolute value of the NH3 response value.

[0053] According to a specific embodiment of the present invention, preferably, the absolute value of the H2O response value of the gas sensor for non-metallic tubes (i.e., |ΔR / R0|) is greater than 5%; wherein, the method for testing the absolute value of the H2O response value includes: using the gas sensor for non-metallic tubes to detect the permeated gas of the non-metallic tube with an H2O gas content of 700 ppm in the pipeline, and using a digital multimeter to detect the resistance change of the MXene-based gel fiber sensing element to obtain the absolute value of the H2O response value.

[0054] According to a specific embodiment of the present invention, preferably, the absolute value of the CO2 response value of the gas sensor for non-metallic tubes (i.e., |ΔR / R0|) is greater than 4%; wherein, the testing method for the absolute value of the CO2 response value includes: using the gas sensor for non-metallic tubes to detect the permeated gas of the non-metallic tube with a CO2 gas content of 500 ppm in the pipeline, and using a digital multimeter to detect the resistance change of the MXene-based gel fiber sensing element to obtain the absolute value of the CO2 response value.

[0055] It should be noted that in the above-mentioned test method for the absolute value of the gas response value, ΔR is the resistance change value of the MXene-based gel fiber sensing element, and R0 is the initial resistance value of the MXene-based gel fiber sensing element. The non-metallic tube can specifically be a polyethylene tube (PE), but is not limited thereto. Polypropylene (PP), polyvinylidene fluoride (PVDF) or polyvinyl chloride (PVC) can also be used. The test temperature can be room temperature (23±2°C), the test pressure can be standard atmospheric pressure (101.325kPa), and the detection gas in the pipeline can be diluted with nitrogen. It will be understood by those skilled in the art that the gas sensor of the present invention is not limited to detecting the gas of the above-mentioned content, and the test temperature and pressure are not limited to the above-mentioned temperature and pressure. The gas sensor of the present invention has a high absolute value of the response value for different gases (including CO2, NH3, CH4, H2S, H2O or H2, etc.) under a variety of test conditions (including any temperature, pressure, humidity and gas content in the pipeline).

[0056] The present invention preferably employs an external gas sensor. First and second air ducts connect the sealed annular space outside the non-metallic tube to a MXene-based gel fiber sensing element. Gas permeating from the non-metallic tube enters the MXene-based gel fiber sensing element through the first air duct. The conductive properties of the MXene-based gel fiber are used to convert changes in gas content into changes in resistance. The resistance change signal is then transmitted to a computer, enabling real-time monitoring of gas permeating the non-metallic tube. The gas sensor signal of the present invention can be transmitted in real time to a monitoring room at the base. For example, a computer can be located near the gas sensor and another in the monitoring room. This allows data changes to be observed both at the actual monitoring location and in the monitoring room. Furthermore, the gel fibers in the MXene-based gel fiber sensing element are preferably arranged in parallel, which increases the contact area between the gel fibers and the gas, reduces the overall resistance, and thus improves the sensitivity of the response. Furthermore, the gas pump on the first air duct ensures gas flow in a single direction. Furthermore, by arranging the second gas outlet and second gas inlet on the upper and lower sealing covers, respectively, and maintaining a maximum vertical distance between the second gas outlet and second gas inlet, gas flow can be more fully achieved. In addition, the present invention preferably adopts an external gas sensor, which can ensure the long-term use of the gas sensor by conveniently replacing the MXene-based gel fiber sensing element.

[0057] The present invention provides a gas sensor for non-metallic pipes. This gas sensor includes a MXene-based gel fiber sensing element and is a resistive gas sensor. Connected to the non-metallic pipe, the sensor utilizes the conductive properties of the MXene-based gel fiber to convert gas variations into resistance signal changes. This sensor can visually display the gas permeation status of the non-metallic pipe, enabling real-time monitoring of gas permeation within the pipe.

[0058] The present invention uses MXene as a gas-sensitive material. MXene has two-dimensional layered structure, single-atom thickness, large specific surface area, high conductivity, adjustable band gap and other characteristics. Studies have confirmed that MXene can be used for gas detection. There are many types of MXene materials, generally MXene is used as a gas-sensitive material. n+1 X n T x Represents its structure, in which transition metal atoms (M) are stacked into a honeycomb two-dimensional lattice; carbon and / or nitrogen (X) occupy the octahedral sites of adjacent M layers; T x It represents the end group connected to M, and n varies from 1 to 4 according to the number of M and X layers. The most mature MXene material currently studied is Ti3C2T x However, the gas response sensitivity of MXene materials in the existing technology needs to be further improved.

[0059] This invention creatively uses low-temperature wet freezing technology to prepare MXene-based gel fibers. A sleeve is installed on the outer wall of the spinning tube, and the temperature of the sleeve is gradually reduced along the flow direction of the spinning solution. This allows the formation of orderly growing ice crystals in the spinning solution, which play a role in pore formation during the gel fiber formation process. Furthermore, the present invention uses a spinning tube with a length of 0.3 to 1 meter and an inner diameter of 0.30 to 1.3 mm, which acts as a size confinement. The spinning solution gradually becomes oriented during its flow in the spinning tube, which helps improve the orientation of the fiber structure. Furthermore, the hydrogel fibers formed in the coagulation bath are washed and naturally dried, then immersed in a mixture of alcohol and water to swell. The fibers are then quenched in liquid nitrogen at -196°C, freezing the hydrogel fibers into a solid state containing ice crystals. During the subsequent freeze-drying process at -45°C to -60°C, the ice crystals sublime, leaving numerous voids. Thanks to the ordered ice crystal band structure formed in the spinning solution, the resulting MXene-based gel fibers have a highly porous structure. The inventors of this case were pleasantly surprised to find that the MXene-based gel fiber prepared by the low-temperature wet freezing technology of the present invention has higher gas response sensitivity than the MXene-based gel fiber prepared by the method in the prior art, and is suitable for detecting gases such as CO2, NH3, CH4, H2S, H2O and H2.

[0060] A third aspect of the present invention provides a gas monitoring method, which comprises the following steps:

[0061] (1) Preparation of MXene-based gel fibers;

[0062] (2) assembling a gas sensor using the MXene-based gel fiber;

[0063] (3) The gas sensor is used to detect the ambient gas and / or permeated gas of the non-metallic pipe, and the signal obtained by the gas sensor is transmitted to a computer to achieve real-time monitoring of the ambient gas and / or permeated gas of the non-metallic pipe.

[0064] According to a specific embodiment of the present invention, preferably, step (1) comprises: using a dispersion containing MXene nanosheets as a spinning solution, injecting the spinning solution into a spinning tube, wherein the outer wall of the spinning tube is provided with a sleeve, and the temperature of the sleeve gradually decreases along the flow direction of the spinning solution; injecting the spinning solution into a coagulation bath through the spinning tube; collecting the fibers formed in the coagulation bath and performing at least swelling, liquid nitrogen freezing and freeze drying to obtain the MXene-based gel fiber.

[0065] According to a specific embodiment of the present invention, preferably, step (2) includes: using the MXene-based gel fiber to assemble an external gas sensor, a wall-mounted gas sensor, or an embedded gas sensor. More preferably, the MXene-based gel fiber is used to assemble an external gas sensor.

[0066] According to a specific embodiment of the present invention, preferably, step (2) specifically includes: placing a plurality of the MXene-based gel fibers and a pair of electrodes in a chamber, wherein the pair of electrodes are respectively arranged at the axial ends of the plurality of the MXene-based gel fibers, and the chamber wall is provided with a first gas inlet and a first gas outlet, to obtain a MXene-based gel fiber sensing element; covering the portion of the non-metallic tube to be detected with a sealing cover, wherein the sealing cover is an annular shell and is provided with a second gas outlet and a second gas inlet; connecting the second gas outlet and the first gas inlet through a first gas duct; connecting the first gas outlet and the second gas inlet through a second gas duct to obtain the gas sensor.

[0067] According to a specific embodiment of the present invention, preferably, the non-metallic pipe includes one or a combination of oilfield pipes, gas pipes, drainage pipes, etc.

[0068] According to a specific embodiment of the present invention, preferably, the gas detected by the gas sensor includes one or a combination of CO2, NH3, CH4, H2S, H2O and H2.

[0069] In summary, the present invention provides a gas sensor for non-metallic pipes, a preparation method thereof, and a gas monitoring method. The present invention has at least the following beneficial effects: the gas sensor of the present invention comprises MXene-based gel fibers. The MXene-based gel fibers of the present invention are prepared using a low-temperature wet freezing technique, have a porous structure and a large specific surface area, and have adjustable filament length. The low-temperature wet freezing technique of the present invention enhances the gel structure of the fibers and increases their porosity. The MXene-based gel fibers of the present invention have a larger contact area with gas and a higher gas response sensitivity. The gas sensor of the present invention has high sensitivity, can detect low-concentration gases, and exhibits strong gas detection stability. It is applicable to fields such as oil and gas transportation, drainage, and other fields, and can monitor ambient gas and / or permeated gas in real time within non-metallic pipes. The gas sensor of the present invention can be positioned differently to detect the ambient gas and / or permeated gas content at different locations within the non-metallic pipe. The monitoring results of the gas sensor of the present invention can guide the design and development of materials and structures for non-metallic pipes and serve as a warning against the dangers of gas permeation or leakage in industrial production. The signal of the gas sensor of the present invention can be transmitted to the monitoring room of the base in real time, which has important research significance for realizing the construction of smart oil fields and digital pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] FIG1 is a schematic structural diagram of an external gas sensor provided in Example 1.

[0071] Figure 2 shows the MAX phase Ti3AlC2 and Ti3C2T in Example 1 x Scanning electron microscope image of MXene nanosheets.

[0072] Figure 3 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the pure MXene gel fiber in Example 1.

[0073] Figure 4 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the MXene / GO composite gel fiber in Example 2.

[0074] Figure 5 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the pure MXene gel fiber in Comparative Example 1.

[0075] Figure 6 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the MXene / GO composite gel fiber in Comparative Example 2.

[0076] Explanation of the accompanying figures: 1-MXene-based gel fiber sensing element; 2-sealing cover; 3-first air duct; 4-second air duct; 5-gas pump; 11-chamber; 12-substrate; 13-MXene-based gel fiber; 14-electrode; 111-first gas inlet; 112-first gas outlet; 21-second gas outlet; 22-second gas inlet; 23-upper sealing cover; 24-lower sealing cover. DETAILED DESCRIPTION

[0077] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0078] The raw materials used in the following examples and comparative examples include:

[0079] Titanium aluminum carbon compound (Ti3AlC2, 400 mesh): purchased from Jilin Yiyi Technology Co., Ltd.

[0080] Lithium fluoride (LiF, 99.99%): purchased from Shanghai Aladdin.

[0081] Hydrochloric acid (HCl, 37%): purchased from Beijing Chemical Plant.

[0082] Dimethyl sulfoxide (DMSO, 99%): purchased from Tianjin Damao Chemical.

[0083] N,N-Dimethylformamide (DMF, 99%): purchased from Tianjin Damao Chemical.

[0084] Graphene oxide (GO, sheet lateral diameter 8-80 μm, thickness less than 2 nm): purchased from Hangzhou Gaoxin Technology Co., Ltd.

[0085] Sodium alginate (SA, 1% viscosity 5000 mPa·s): purchased from Maclean.

[0086] Acetic acid (AC, 99.9%): purchased from Tianjin Damao Chemical.

[0087] Ammonium chloride (NH4Cl): purchased from Tianjin Guangfu.

[0088] Calcium chloride (CaCl2): Purchased from Tianjin Guangfu.

[0089] Example 1

[0090] The present embodiment provides a gas sensor for a non-metallic tube, which includes a MXene-based gel fiber, wherein the MXene-based gel fiber is a pure MXene gel fiber prepared by the low-temperature wet freezing technology of the present invention. The low-temperature wet freezing technology comprises at least the following steps: using a mixed solution of LiF and HCl (which is obtained by dissolving 8g LiF in 100mL 9M HCl solution) to etch Ti3AlC2 in a 35°C constant temperature water bath environment for about 40 hours, then ultrasonically peeling in a nitrogen atmosphere for about 1 hour, and finally centrifuging at 3500rpm in a centrifuge for 1 hour to obtain a Ti3C2T containing a single layer or a few layers. x Mixed solution of MXene nanosheets; Ti3C2T x The MXene nanosheets were centrifuged at high speed and prepared into a 120 mg / mL dispersion in DMSO using a solvent replacement method. The dispersion was used as a spinning solution, which was uniformly injected into a spinning tube with a length of 0.5 m and an inner diameter of 0.80 mm through a syringe pump at an injection speed of 200 μL min. -1 The outer wall of the spinning duct is provided with a sleeve, and there should be an appropriate gap between the sleeve and the spinning duct. The sleeve is a copper tube, and liquid nitrogen is provided at the lower end of the sleeve along the flow direction of the spinning solution. The sleeve conducts cold energy from bottom to top (i.e., in the opposite direction of the flow direction of the spinning solution), so that the temperature of the sleeve gradually decreases from top to bottom (i.e., in the flow direction of the spinning solution); the spinning solution is injected into a coagulation bath through the spinning duct, and the coagulation bath is a mixture of DMSO and acetic acid (wherein the volume ratio of DMSO to acetic acid is 1:1). The fibers formed in the coagulation bath were collected and washed twice by immersion in a mixture of ethanol and water (the volume ratio of ethanol to water was 2:1), and then naturally dried for 0.5 days at room temperature; the dried fibers were immersed in a mixture of ethanol and water (the volume ratio of ethanol to water was 1:1) and swelled for 2 minutes, and then the swollen fibers were frozen in liquid nitrogen for 30 minutes, and then dried in a freeze dryer at -57°C for 3 days, and then dried in a vacuum oven at 60°C for 1 day to obtain pure MXene gel fibers.

[0091] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, as shown in FIG1 , which includes: a MXene-based gel fiber sensing element 1, a sealing cover 2, a first gas guide tube 3, a second gas guide tube 4, and a gas pump 5;

[0092] The MXene-based gel fiber sensing element 1 includes a chamber 11, a substrate 12, four parallel MXene-based gel fibers 13, and a pair of electrodes 14. The four parallel MXene-based gel fibers 13 and the electrodes 14 are arranged on the substrate 12 and placed in the chamber 11. The pair of electrodes 14 are respectively connected to the axial ends of the four parallel MXene-based gel fibers 13. The chamber wall of the chamber 11 is provided with a first gas inlet 111 and a first gas outlet 112.

[0093] The sealing cover 2 is an annular shell, which is used to seal and cover the portion of the non-metallic tube to be inspected; the sealing cover 2 is provided with a second gas outlet 21 and a second gas inlet 22;

[0094] One end of the first gas duct 3 is connected to the second gas outlet 21 , and the other end is connected to the first gas inlet 111 ;

[0095] One end of the second gas duct 4 is connected to the first gas outlet 112 , and the other end is connected to the second gas inlet 22 ;

[0096] The gas pump 5 is disposed on the first air duct 3 .

[0097] In this embodiment, the pair of electrodes 14 are both copper electrodes.

[0098] In this embodiment, the sealing cover 2 includes an upper sealing cover 23 and a lower sealing cover 24. The upper sealing cover 23 and the lower sealing cover 24 are both semi-annular shell structures. The upper sealing cover 23 and the lower sealing cover 24 are connected to form a circular connecting port, which is used to allow the non-metallic pipe to pass through. After the upper sealing cover 23 and the lower sealing cover 24 are connected to each other, a closed annular space is formed between the outer wall of the non-metallic pipe to be inspected.

[0099] In this embodiment, the upper sealing cover 23 is provided with a second gas outlet 21 , and the lower sealing cover 24 is provided with a second gas inlet 22 .

[0100] In this embodiment, the first gas inlet 111 and the first gas outlet 112 are respectively located at two ends of the axial direction of the MXene-based gel fiber 13 .

[0101] Figure 1 also shows a digital multimeter and a computer. The digital multimeter can serve as a signal converter, converting the gas change signal from the MXene-based gel fiber sensing element 1 into a resistance signal to test the sensitivity of the gas sensor of this embodiment. The converted signal is then input into a computer to enable real-time monitoring of the ambient gas and / or permeating gas in the non-metallic pipe.

[0102] This embodiment monitors the ambient gas and / or permeated gas in a polyethylene pipeline. In practical applications, a MXene-based gel fiber sensing element 1 can be placed on the ground near the polyethylene pipeline. Pipeline permeation is introduced into the MXene-based gel fiber sensing element 1 through a first gas conduit 3. Changes in gas content cause changes in the resistance signal of the MXene-based gel fiber sensing element 1, thereby evaluating the pipeline's gas permeability.

[0103] To test the sensitivity of the gas sensor of this embodiment, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor of this embodiment was used to detect the change in the content of the H2S gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor of this embodiment was used to detect the change in the content of the CH4 gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and the CH4 response value measured in this embodiment are shown in Table 1.

[0104] Table 1 Absolute values ​​of gas response of pure MXene gel fibers prepared by low-temperature wet freezing technology

[0105] The raw materials Ti3AlC2 and Ti3C2T prepared in this embodiment are x The scanning electron micrographs of MXene nanosheets are shown in Figure 2, where (a) in Figure 2 is a scanning electron micrograph of MAX phase Ti3AlC2, and (b) in Figure 2 is a scanning electron micrograph of Ti3C2T x Scanning electron micrograph of MXene nanosheets. Figure 3 is a scanning electron micrograph of the cross-sectional pore structure of the pure MXene gel fiber prepared in this example.

[0106] Example 2

[0107] The present embodiment provides a gas sensor for a non-metallic tube, which includes a MXene-based gel fiber, wherein the MXene-based gel fiber is a MXene / GO composite gel fiber prepared by the low-temperature wet freezing technology of the present invention. The low-temperature wet freezing technology comprises at least the following steps: using a mixed solution of LiF and HCl (which is obtained by dissolving 8g LiF in 100mL 9M HCl solution) to etch Ti3AlC2 in a 35°C constant temperature water bath environment for about 40 hours, then ultrasonically peeling in a nitrogen atmosphere for about 1 hour, and finally centrifuging at 3500rpm in a centrifuge for 1 hour to obtain a Ti3C2T containing a single layer or a few layers. x Mixed solution of MXene nanosheets; Ti3C2T x MXene nanosheets were centrifuged at high speed and mixed with GO nanosheets by solvent replacement to prepare a dispersion in DMSO with a total concentration of MXene and GO of 100 mg / mL, wherein the mass ratio of MXene nanosheets to GO nanosheets was 3:7. The dispersion was used as the spinning solution, and the spinning solution was uniformly injected into a spinning tube with a length of 0.5 m and an inner diameter of 0.80 mm through a syringe pump at an injection speed of 200 μL min. -1 The outer wall of the spinning duct is provided with a sleeve, and there should be an appropriate gap between the sleeve and the spinning duct. The sleeve is a copper tube, and liquid nitrogen is provided at the lower end of the sleeve along the flow direction of the spinning solution. The sleeve conducts cold energy from bottom to top (i.e., in the opposite direction of the flow direction of the spinning solution), so that the temperature of the sleeve gradually decreases from top to bottom (i.e., in the flow direction of the spinning solution); the spinning solution is injected into a coagulation bath through the spinning duct, and the coagulation bath is a mixture of DMSO and acetic acid (wherein the volume ratio of DMSO to acetic acid is 1:1). :1); the fibers formed in the coagulation bath were collected and washed twice by immersion in a mixture of ethanol and water (the volume ratio of ethanol to water was 2:1), and then naturally dried at room temperature for 0.5 days; the dried fibers were immersed in a mixture of ethanol and water (the volume ratio of ethanol to water was 1:1) to swell for 2 minutes, and then the swollen fibers were frozen in liquid nitrogen for 30 minutes, and then dried in a freeze dryer at -57°C for 3 days, and then dried in a vacuum oven at 60°C for 1 day to obtain MXene / GO composite gel fibers.

[0108] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, and its structure is the same as that of embodiment 1.

[0109] To test the sensitivity of the gas sensor of this embodiment, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor of this embodiment was used to detect the change in the content of the H2S gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor of this embodiment was used to detect the change in the content of the CH4 gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and the CH4 response value measured in this embodiment are shown in Table 2.

[0110] Table 2 Absolute values ​​of gas response of MXene / GO composite gel fibers prepared by low-temperature wet freezing technology

[0111] FIG4 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the MXene / GO composite gel fiber prepared in this example.

[0112] Example 3

[0113] The present embodiment provides a gas sensor for a non-metallic tube, which includes a MXene-based gel fiber, wherein the MXene-based gel fiber is a MXene / alginate composite gel fiber prepared by the low-temperature wet freezing technology of the present invention. The low-temperature wet freezing technology comprises at least the following steps: using a mixed solution of LiF and HCl (which is obtained by dissolving 8g LiF in 100mL 9M HCl solution) to etch Ti3AlC2 in a 35°C constant temperature water bath environment for about 40 hours, then ultrasonically peeling in a nitrogen atmosphere for about 1 hour, and finally centrifuging at 3500rpm in a centrifuge for 1 hour to obtain a Ti3C2T containing a single layer or a few layers. x Mixed solution of MXene nanosheets; Ti3C2T x MXene nanosheets and sodium alginate were mixed to prepare a dispersion in water with a total concentration of 90 mg / mL of MXene nanosheets and sodium alginate, wherein the mass ratio of MXene nanosheets to sodium alginate was 9:1. The dispersion was used as a spinning solution, and the spinning solution was uniformly injected into a spinning tube through a syringe pump. The spinning tube had a length of 0.3 m and an inner diameter of 1.3 mm, and the injection speed was 260 μL min -1The outer wall of the spinning tube is provided with a sleeve, and there should be an appropriate gap between the sleeve and the spinning tube. The sleeve is a copper tube, and liquid nitrogen is provided at the lower end of the sleeve along the flow direction of the spinning solution. The sleeve conducts cold energy from bottom to top (i.e., in the opposite direction of the flow direction of the spinning solution), so that the temperature of the sleeve gradually decreases from top to bottom (i.e., in the flow direction of the spinning solution); the spinning solution is injected into the coagulation bath through the spinning tube, and the coagulation bath is an ammonium chloride aqueous solution with a mass concentration of 1%; the coagulation The fibers formed in the solid bath were collected and washed twice by immersion in a mixture of ethanol and water (the volume ratio of ethanol to water was 2:1), and then naturally dried at room temperature for 1 day; the dried fibers were immersed in a mixture of ethanol and water (the volume ratio of ethanol to water was 1:1) to swell for 3 minutes, and then the swollen fibers were frozen in liquid nitrogen for 40 minutes, and then dried in a freeze dryer at -45°C for 4 days, and then vacuum dried at 70°C for 1 day to obtain MXene / alginate composite gel fibers.

[0114] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, and its structure is the same as that of embodiment 1.

[0115] To test the sensitivity of the gas sensor of this embodiment, NH3 gas diluted with nitrogen was introduced into a polyethylene pipe to a concentration of 700 ppm. The gas sensor of this embodiment was used to detect changes in the content of NH3 gas permeating the pipe, and a digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1 to obtain the NH3 response value. Under the same conditions, H2O gas diluted with nitrogen was introduced into a polyethylene pipe to a concentration of 700 ppm. The gas sensor of this embodiment was used to detect changes in the content of H2O gas permeating the pipe, and a digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1 to obtain the H2O response value. The absolute values ​​of the H2S response value and the CH4 response value measured in this embodiment are shown in Table 3.

[0116] Table 3 Absolute values ​​of gas response of MXene / alginate composite gel fibers prepared by low-temperature wet freezing technology

[0117] Example 4

[0118] This embodiment provides a gas sensor for a non-metallic tube, comprising a MXene-based gel fiber, which is a MXene / GO composite gel fiber prepared using the low-temperature wet freezing technique of the present invention. The preparation method of the MXene / GO composite gel fiber is substantially the same as that of Example 2, except that: the dispersion is a DMF-based dispersion with a total concentration of 70 mg / mL of MXene and GO, wherein the mass ratio of MXene nanosheets to GO nanosheets is 1:9; the spinning conduit is 0.8 m long and has an inner diameter of 0.50 mm; and the coagulation bath is a mixture of isopropyl alcohol and water (wherein the volume ratio of isopropyl alcohol to water is 3:1).

[0119] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, and its structure is the same as that of embodiment 1.

[0120] To test the sensitivity of the gas sensor of this embodiment, CO2 gas diluted with nitrogen was introduced into a polyethylene pipe. The CO2 gas content in the pipe was 500 ppm. The gas sensor of this embodiment was used to detect the change in the content of CO2 gas that permeated the pipe. A digital multimeter was used to detect the change in resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CO2 response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 500 ppm. The gas sensor of this embodiment was used to detect the change in the content of CH4 gas that permeated the pipe. A digital multimeter was used to detect the change in resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and CH4 response value measured in this embodiment are shown in Table 4.

[0121] Table 4 Absolute values ​​of gas response of MXene / GO composite gel fibers prepared by low-temperature wet freezing technology

[0122] Example 5

[0123] This embodiment provides a gas sensor for a non-metallic tube, comprising a MXene-based gel fiber. The MXene-based gel fiber is a MXene / GO composite gel fiber prepared using the low-temperature wet freezing technique of the present invention. The preparation method for this MXene / GO composite gel fiber is essentially the same as that of Example 2, except that the dispersion is a DMSO-based dispersion with a total MXene and GO concentration of 160 mg / mL, and the mass ratio of the MXene nanosheets to the GO nanosheets is 8:2. The spinning conduit is 0.3 m long and has an inner diameter of 0.60 mm.

[0124] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, and its structure is the same as that of embodiment 1.

[0125] To test the sensitivity of the gas sensor of this embodiment, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor of this embodiment was used to detect the change in the content of the H2S gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor of this embodiment was used to detect the change in the content of the CH4 gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and the CH4 response value measured in this embodiment are shown in Table 5.

[0126] Table 5 Absolute values ​​of gas response of MXene / GO composite gel fibers prepared by low-temperature wet freezing technology

[0127] Example 6

[0128] This embodiment provides a gas sensor for a non-metallic tube, comprising a MXene-based gel fiber, which is a MXene / alginate composite gel fiber prepared using the low-temperature wet freezing technique of the present invention. The preparation method for this MXene / alginate composite gel fiber is substantially the same as that of Example 3, except that the dispersion is a water-based dispersion containing MXene nanosheets and sodium alginate at a total concentration of 150 mg / mL, with a mass ratio of 6:4. The spinning conduit has a length of 0.4 m and an inner diameter of 0.6 mm. The coagulation bath is a 1% calcium chloride aqueous solution.

[0129] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, and its structure is the same as that of embodiment 1.

[0130] To test the sensitivity of the gas sensor of this embodiment, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor of this embodiment was used to detect the change in the content of H2S gas that permeated the pipe. A digital multimeter was used to detect the change in resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor of this embodiment was used to detect the change in the content of CH4 gas that permeated the pipe. A digital multimeter was used to detect the change in resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and the CH4 response value measured in this embodiment are shown in Table 6.

[0131] Table 6 Absolute values ​​of gas response of MXene / alginate composite gel fibers prepared by low-temperature wet freezing technology

[0132] Example 7

[0133] This embodiment provides a gas sensor for a non-metallic tube, comprising a MXene-based gel fiber, which is a MXene / alginate composite gel fiber prepared by the low-temperature wet freezing technology of the present invention. The preparation method of the MXene / alginate composite gel fiber is substantially the same as that of Example 3, except that: the dispersion liquid is a dispersion liquid with a total concentration of 50 mg / mL of MXene nanosheets and sodium alginate in water as the solvent, wherein the mass ratio of MXene nanosheets to sodium alginate is 1:9; the spinning tube has a length of 1 m, an inner diameter of 0.6 mm, and an injection speed of 300 μL min -1 ; The coagulation bath is a calcium chloride aqueous solution with a mass concentration of 1%.

[0134] The gas sensor for non-metallic tubes provided in this embodiment is an external gas sensor, and its structure is the same as that of embodiment 1.

[0135] To test the sensitivity of the gas sensor of this embodiment, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 80 ppm. The gas sensor of this embodiment was used to detect the change in the content of the H2S gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 500 ppm. The gas sensor of this embodiment was used to detect the change in the content of the CH4 gas that permeated the pipe. A digital multimeter was used to detect the change in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and the CH4 response value measured in this embodiment are shown in Table 7.

[0136] Table 7 Absolute values ​​of gas response of MXene / alginate composite gel fibers prepared by low-temperature wet freezing technology

[0137] Example 8

[0138] This embodiment provides a gas monitoring method, which includes the following steps:

[0139] (1) Preparation of MXene-based gel fibers

[0140] A dispersion containing MXene nanosheets is used as a spinning solution, and the spinning solution is injected into a spinning conduit, wherein the outer wall of the spinning conduit is provided with a sleeve, and the temperature of the sleeve gradually decreases along the flow direction of the spinning solution; the spinning solution is injected into a coagulation bath through the spinning conduit; and the fibers formed in the coagulation bath are collected and subjected to at least swelling, liquid nitrogen freezing, and freeze drying to obtain the MXene-based gel fibers.

[0141] (2) Assembling a gas sensor using the MXene-based gel fiber

[0142] Specifically, the MXene-based gel fiber is used to assemble an external gas sensor, a wall-mounted gas sensor, or an embedded gas sensor;

[0143] (3) The gas sensor is used to detect the ambient gas and / or permeated gas of the non-metallic pipe, and the signal obtained by the gas sensor is transmitted to a computer to achieve real-time monitoring of the ambient gas and / or permeated gas of the non-metallic pipe.

[0144] In this embodiment, the dispersion containing MXene nanosheets includes a dispersion of MXene nanosheets, a dispersion of MXene nanosheets and GO nanosheets, or a dispersion of MXene nanosheets and sodium alginate. Preferably, the dispersion containing MXene nanosheets is a dispersion of MXene nanosheets and GO nanosheets or a dispersion of MXene nanosheets and sodium alginate. When the dispersion is a dispersion of MXene nanosheets, the MXene-based gel fiber is a MXene gel fiber; when the dispersion is a dispersion of MXene nanosheets and GO nanosheets, the MXene-based gel fiber is a MXene / GO composite gel fiber; when the dispersion is a dispersion of MXene nanosheets and sodium alginate, the MXene-based gel fiber is a MXene / alginate composite gel fiber.

[0145] In this embodiment, the MXene nanosheets include Ti3C2T x MXene nanosheets.

[0146] In this embodiment, the MXene nanosheets are prepared by treating a MAX phase with a mixed solution of LiF and HCl, followed by ultrasonic treatment to obtain MXene nanosheets. The MAX phase used is preferably titanium aluminum carbon (Ti3AlC2).

[0147] In this embodiment, the concentration of the MXene nanosheets in the dispersion of the MXene nanosheets is 80 to 180 mg / mL, preferably 110 to 150 mg / mL.

[0148] In this embodiment, the solvent in the dispersion of the MXene nanosheets includes dimethyl sulfoxide (DMSO) and / or N,N-dimethylformamide (DMF).

[0149] In this embodiment, the total concentration of the MXene nanosheets and GO nanosheets in the dispersion is 70 to 160 mg / mL, preferably 100 to 140 mg / mL, and the mass ratio of the MXene nanosheets to the GO nanosheets is 1:9 to 8:2. Preferably, the GO nanosheets have a thickness of less than 2 nm and a transverse diameter of 8 to 80 μm.

[0150] In this embodiment, the total concentration of MXene nanosheets and sodium alginate in the dispersion of MXene nanosheets and sodium alginate is 50 to 150 mg / mL, preferably 80 to 130 mg / mL, and the mass ratio of MXene nanosheets to sodium alginate is 1:9 to 9:1.

[0151] In this embodiment, the spinning tube has a length of 0.3 to 1 m and an inner diameter of 0.30 to 1.3 mm.

[0152] In this embodiment, the outer wall of the spinning duct is provided with a metal tube. The temperature of the tube is gradually reduced along the flow direction of the spinning solution by providing a cooling source at one end of the tube. This allows the tube to conduct cooling energy in a direction opposite to the flow direction of the spinning solution, thereby gradually reducing the temperature along the flow direction of the spinning solution. Specifically, the tube can be a copper tube. Furthermore, as will be appreciated by those skilled in the art, an appropriate gap should be provided between the tube and the spinning duct to prevent the spinning solution from freezing and solidifying and becoming unable to flow.

[0153] In this embodiment, the temperature of the cold source provided at one end of the sleeve is -200° C. to -100° C. Specifically, the cold source is liquid nitrogen (-196° C.).

[0154] In this embodiment, the coagulation bath includes one or more of an aqueous solution of ammonium chloride, an aqueous solution of calcium chloride, an aqueous solution of aluminum chloride, aqueous ammonia, isopropyl alcohol, ethyl acetate, acetone, dimethyl sulfoxide, acetic acid, n-hexane, dichloromethane, a mixture of dimethyl sulfoxide and acetic acid, and a mixture of isopropyl alcohol and water. Preferably, when the dispersion containing MXene nanosheets is a dimethyl sulfoxide dispersion of MXene nanosheets, or a dimethyl sulfoxide dispersion of MXene nanosheets and GO nanosheets, the coagulation bath is a mixture of dimethyl sulfoxide and acetic acid. Further preferably, the volume ratio of dimethyl sulfoxide to acetic acid in the mixture is 1:3 to 3:1; when the dispersion containing MXene nanosheets is an N,N-dimethylformamide dispersion of MXene nanosheets, or an N,N-dimethylformamide dispersion of MXene nanosheets and GO nanosheets, the coagulation bath is a mixture of isopropanol and water. Further preferably, the volume ratio of isopropanol to water in the mixture is 1:2 to 3:1; when the dispersion containing MXene nanosheets is an aqueous dispersion of MXene nanosheets and sodium alginate, the coagulation bath is an aqueous ammonium chloride solution or an aqueous calcium chloride solution, with a mass concentration of 0.5 to 1%.

[0155] In this embodiment, the fibers formed in the coagulation bath are collected and washed, and then naturally dried. The dried fibers are swollen, and the swollen fibers are placed in liquid nitrogen for freezing, and then freeze-dried. Thereafter, they are vacuum-dried to obtain the MXene-based gel fibers.

[0156] In this embodiment, the fibers formed in the coagulation bath are collected and then washed with a mixture of ethanol and water. Preferably, the volume ratio of ethanol to water in the mixture is 1:3 to 3:1, more preferably 2:1.

[0157] In this embodiment, the fibers formed in the coagulation bath are collected and washed and then naturally dried for 0.5 to 1 day.

[0158] In this embodiment, the swelling is performed using a mixture of alcohol and water, preferably a mixture of ethanol and water, wherein the volume ratio of ethanol to water in the mixture is 3:4 to 1:3, preferably 1:1.

[0159] In this embodiment, the dried fibers are immersed in a mixture of alcohol and water for swelling for 2 to 5 minutes.

[0160] In this embodiment, the swollen fibers are placed in liquid nitrogen for freezing for 30 to 60 minutes.

[0161] In this embodiment, the freeze-drying temperature is -45°C to -60°C. The freeze-drying can be performed under vacuum conditions. Preferably, the freeze-drying time is 2 to 4 days.

[0162] In this embodiment, the vacuum drying temperature is 40-70° C. Preferably, the vacuum drying time is 0.5-2 days.

[0163] In this embodiment, the MXene-based gel fiber is used to assemble an external gas sensor. Step (2) specifically includes: placing a plurality of the MXene-based gel fibers and a pair of electrodes in a chamber, wherein the pair of electrodes are respectively disposed at the axial ends of the plurality of the MXene-based gel fibers, and the chamber wall is provided with a first gas inlet and a first gas outlet, thereby obtaining a MXene-based gel fiber sensing element; covering the portion of the non-metallic tube to be detected with a sealing cover, wherein the sealing cover is an annular shell and is provided with a second gas outlet and a second gas inlet; connecting the second gas outlet and the first gas inlet through a first gas duct; and connecting the first gas outlet and the second gas inlet through a second gas duct, thereby obtaining the gas sensor.

[0164] In this embodiment, the number of the plurality of MXene-based gel fibers is 2 to 10, preferably 3 to 6, and the plurality of MXene-based gel fibers are arranged in parallel in the chamber.

[0165] In this embodiment, the electrode includes one of a copper electrode, a silver electrode, a gold electrode, a platinum electrode, a titanium electrode, a nickel electrode or an aluminum electrode.

[0166] In this embodiment, the sealing cover includes an upper sealing cover and a lower sealing cover, and the upper sealing cover and the lower sealing cover are both semi-annular shell structures. The upper sealing cover and the lower sealing cover are connected to form a circular connecting port, and the circular connecting port is used to allow non-metallic pipes to pass through. After the upper sealing cover and the lower sealing cover are connected to each other, a closed annular space is formed between the outer wall of the non-metallic pipe to be inspected.

[0167] In this embodiment, the second gas outlet is provided on the upper sealing cover, and the second gas inlet is provided on the lower sealing cover.

[0168] In this embodiment, the first gas inlet and the first gas outlet are respectively located at two ends of the axial direction of the MXene-based gel fiber.

[0169] In this embodiment, a gas pump is provided on the first air duct.

[0170] In this embodiment, the non-metallic pipe includes one or a combination of oilfield pipes, gas pipes, and drainage pipes.

[0171] In this embodiment, the gas detected by the gas sensor includes one or a combination of CO2, NH3, CH4, H2S, H2O and H2.

[0172] Comparative Example 1

[0173] This comparative example provides a gas sensor for a non-metallic tube, which includes a MXene-based gel fiber, wherein the MXene-based gel fiber is a pure MXene gel fiber prepared by conventional wet spinning technology. The preparation method of the pure MXene gel fiber in this comparative example comprises the following steps: using a mixed solution of LiF and HCl (which is obtained by dissolving 8g LiF in 100mL 9M HCl solution) to etch Ti3AlC2 in a constant temperature water bath environment at 35°C for about 40h, then ultrasonically stripping in a nitrogen atmosphere for about 1h, and finally centrifuging at 3500rpm in a centrifuge for 1h to obtain a Ti3C2T containing a single layer or a few layers. x Mixed solution of MXene nanosheets; Ti3C2T x The MXene nanosheets were centrifuged at high speed and prepared into a 120 mg / mL dispersion in DMSO by solvent replacement method. The dispersion was used as the spinning solution, and the spinning solution was uniformly injected into the coagulation bath through an injection pump at an injection speed of 200 μL min. -1The coagulation bath is a mixture of DMSO and acetic acid (the volume ratio of DMSO to acetic acid is 1:1); the fibers formed in the coagulation bath are collected and soaked and washed twice with a mixture of ethanol and water (the volume ratio of ethanol to water is 2:1), and then naturally dried at room temperature for 1 day to obtain pure MXene gel fibers.

[0174] The gas sensor for non-metallic tubes provided in this comparative example is an external gas sensor, and its structure is the same as that of Example 1.

[0175] To test the sensitivity of the gas sensor in this comparative example, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor in this comparative example was used to detect changes in the content of H2S gas that permeated the pipe. A digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into the polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor in this comparative example was used to detect changes in the content of CH4 gas that permeated the pipe. A digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and CH4 response value measured in this comparative example are shown in Table 8.

[0176] Table 8 Absolute values ​​of gas response of pure MXene gel fibers prepared by conventional wet spinning technology

[0177] Figure 5 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the pure MXene gel fiber prepared in this comparative example.

[0178] Comparative Example 2

[0179] This comparative example provides a gas sensor for a non-metallic tube, which includes a MXene-based gel fiber, wherein the MXene-based gel fiber is a MXene / GO composite gel fiber prepared by conventional wet spinning technology. The preparation method of the MXene / GO composite gel fiber in this comparative example comprises the following steps: using a mixed solution of LiF and HCl (which is obtained by dissolving 8g of LiF in 100mL of 9M HCl solution) to etch Ti3AlC2 in a constant temperature water bath environment at 35°C for about 40h, then ultrasonically stripping in a nitrogen atmosphere for about 1h, and finally centrifuging at 3500rpm in a centrifuge for 1h to obtain a Ti3C2T containing a single layer or a few layers. x Mixed solution of MXene nanosheets; Ti3C2T xMXene nanosheets were centrifuged at high speed and mixed with GO nanosheets by solvent replacement method to prepare a dispersion with a total concentration of MXene and GO of 100 mg / mL in DMSO as solvent, wherein the mass ratio of MXene nanosheets to GO nanosheets was 3:7. The dispersion was used as the spinning solution, and the spinning solution was uniformly injected into the coagulation bath through a syringe pump at an injection speed of 200 μL min. -1 The coagulation bath is a mixture of DMSO and acetic acid (the volume ratio of DMSO to acetic acid is 1:1); the fibers formed in the coagulation bath are collected and soaked and washed twice with a mixture of ethanol and water (the volume ratio of ethanol to water is 2:1), and then naturally dried at room temperature for 1 day to obtain MXene / GO composite gel fibers.

[0180] The gas sensor for non-metallic tubes provided in this comparative example is an external gas sensor, and its structure is the same as that of Example 1.

[0181] To test the sensitivity of the gas sensor in this comparative example, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor in this comparative example was used to detect changes in the content of H2S gas that permeated the pipe. A digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into the polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor in this comparative example was used to detect changes in the content of CH4 gas that permeated the pipe. A digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and CH4 response value measured in this comparative example are shown in Table 9.

[0182] Table 9 Absolute values ​​of gas response of MXene / GO composite gel fibers prepared by conventional wet spinning technology

[0183] Figure 6 is a scanning electron microscope photograph of the cross-sectional pore structure morphology of the MXene / GO composite gel fiber prepared in this comparative example.

[0184] Comparative Example 3

[0185] This comparative example provides a gas sensor for a non-metallic tube, comprising a MXene-based gel fiber. The MXene-based gel fiber is a MXene / GO composite gel fiber prepared using the low-temperature wet freezing technique of the present invention. The preparation method for the MXene / GO composite gel fiber in this comparative example is essentially the same as that in Example 2, except that the solvent in the dispersion of MXene nanosheets and GO nanosheets in this comparative example is water, and the coagulation bath is a 1% aqueous ammonium chloride solution. The remaining steps are the same as those in Example 2.

[0186] The gas sensor for non-metallic tubes provided in this comparative example is an external gas sensor, and its structure is the same as that of Example 1.

[0187] To test the sensitivity of the gas sensor in this comparative example, H2S gas diluted with nitrogen was introduced into a polyethylene pipe. The H2S gas content in the pipe was 100 ppm. The gas sensor in this comparative example was used to detect changes in the content of H2S gas that permeated the pipe. A digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the H2S response value. Under the same conditions, CH4 gas diluted with nitrogen was introduced into a polyethylene pipe. The CH4 concentration in the pipe was 600 ppm. The gas sensor in this comparative example was used to detect changes in the content of CH4 gas that permeated the pipe. A digital multimeter was used to detect changes in the resistance of the MXene-based gel fiber sensing element 1, thereby obtaining the CH4 response value. The absolute values ​​of the H2S response value and CH4 response value measured in this comparative example are shown in Table 10.

[0188] Table 10 Absolute values ​​of gas response of MXene / GO composite gel fibers prepared by low-temperature wet freezing technology and ion coagulation bath

[0189] By comparing the scanning electron micrographs (FIGS. 3 and 5) of the pure MXene gel fibers prepared in Example 1 and Comparative Example 1, and by comparing the scanning electron micrographs (FIGS. 4 and 6) of the MXene / GO composite gel fibers prepared in Example 2 and Comparative Example 2, it can be seen that the MXene-based gel fibers prepared by the low-temperature wet freezing technology of the present invention have a significantly enhanced gel structure, improved porosity, and a larger specific surface area than the MXene-based gel fibers prepared by the conventional wet spinning technology. By comparing the absolute values ​​of the H2S response values ​​and CH4 response values ​​of Example 1 and Comparative Example 1 (Tables 1 and 8), and the absolute values ​​of the H2S response values ​​and CH4 response values ​​of Example 2 and Comparative Example 2 (Tables 2 and 9), it can be seen that the MXene-based gel fibers prepared by the low-temperature wet freezing technology of the present invention have significantly improved response values ​​to H2S and CH4 gases compared to the MXene-based gel fibers prepared by the conventional wet spinning technology, and therefore have higher gas response sensitivity and can detect low-concentration gases.

[0190] From the comparative data of the MXene / GO composite gel fibers prepared in Example 2 and Comparative Example 3 (Table 2 and Table 10), it can be seen that the present invention adopts an organic solvent such as DMSO to disperse the spinning solution of the MXene / GO inorganic nanomaterial, and adopts a mixed solution of dimethyl sulfoxide and acetic acid as a coagulation bath. Coagulation in such a weak coagulation bath makes it easier for the fiber to present a porous structure. Therefore, the MXene / GO composite gel fiber prepared in the present invention has a significantly improved response value to H2S and CH4 gases compared with the MXene / GO composite gel fiber prepared by using water as a solvent and using an ion coagulation bath.

[0191] Comparing Example 2 with Example 1 shows that the MXene / GO composite gel fiber of the present invention has higher gas response sensitivity than pure MXene gel fiber. GO enhances the mechanical properties of the MXene-based gel fiber and facilitates fiber gelation, making the porous structure more robust. GO itself is also gas-responsive, creating a synergistic effect between MXene and GO, significantly improving the gas response sensitivity of the MXene / GO composite gel fiber of the present invention.

[0192] In summary, the gas sensor of the present invention has high sensitivity, can detect low-concentration gases, and has strong stability in gas detection. It is used in the fields of oil transportation, gas transportation, drainage, etc., and can monitor the ambient gas and / or permeated gas in non-metallic pipes in real time.

Claims

1. A method for preparing a gas sensor for a non-metallic tube, wherein: The preparation method comprises the following steps: A dispersion containing MXene nanosheets is used as a spinning solution, and the spinning solution is injected into a spinning duct, wherein the outer wall of the spinning duct is provided with a sleeve, and the temperature of the sleeve is gradually reduced along the flow direction of the spinning solution; the spinning solution is injected into a coagulation bath through the spinning duct; the fibers formed in the coagulation bath are collected and at least swollen, liquid nitrogen frozen and freeze-dried to obtain MXene-based gel fibers; and, The MXene-based gel fiber is used to assemble a gas sensor to obtain the gas sensor for the non-metallic tube.

2. The method for preparing a gas sensor for a non-metallic tube according to claim 1, wherein: The dispersion containing MXene nanosheets includes a dispersion of MXene nanosheets, a dispersion of MXene nanosheets and GO nanosheets, or a dispersion of MXene nanosheets and sodium alginate.

3. The method for preparing a gas sensor for a non-metallic tube according to claim 1, wherein: The MXene nanosheets include Ti3C2T x MXene nanosheets.

4. The method for preparing a gas sensor for a non-metallic tube according to claim 2, wherein: The concentration of the MXene nanosheets in the dispersion of the MXene nanosheets is 80 to 180 mg / mL.

5. The method for preparing a gas sensor for a non-metallic tube according to claim 2, wherein: The total concentration of the MXene nanosheets and the GO nanosheets in the dispersion of the MXene nanosheets and the GO nanosheets is 70 to 160 mg / mL, and the mass ratio of the MXene nanosheets to the GO nanosheets is 1:9 to 8:

2.

6. The method for preparing a gas sensor for a non-metallic tube according to claim 2, wherein: The total concentration of the MXene nanosheets and sodium alginate in the dispersion of the MXene nanosheets and sodium alginate is 50 to 150 mg / mL, and the mass ratio of the MXene nanosheets to the sodium alginate is 1:9 to 9:

1.

7. The method for preparing a gas sensor for a non-metallic tube according to claim 1, wherein: The spinning tube has a length of 0.3 to 1 m and an inner diameter of 0.30 to 1.3 mm.

8. The method for preparing a gas sensor for a non-metallic tube according to claim 1, wherein: The sleeve arranged on the outer wall of the spinning tube is a metal tube, and the temperature of the sleeve is gradually reduced along the flow direction of the spinning solution in the following manner: a cold source is arranged at one end of the sleeve, so that the sleeve conducts cold energy in the direction opposite to the flow direction of the spinning solution, thereby achieving a gradual reduction in temperature along the flow direction of the spinning solution; the temperature of the cold source is -200°C to -100°C.

9. The method for preparing a gas sensor for a non-metallic tube according to claim 1, wherein: The coagulation bath comprises one or a combination of ammonium chloride aqueous solution, calcium chloride aqueous solution, aluminum chloride aqueous solution, ammonia water, isopropanol, ethyl acetate, acetone, acetic acid, n-hexane, dichloromethane, a mixed solution of dimethyl sulfoxide and acetic acid, and a mixed solution of isopropanol and water.

10. The method for preparing a gas sensor for a non-metallic tube according to claim 9, wherein: When the dispersion containing MXene nanosheets is a dimethyl sulfoxide dispersion of MXene nanosheets, or a dimethyl sulfoxide dispersion of MXene nanosheets and GO nanosheets, the coagulation bath is a mixture of dimethyl sulfoxide and acetic acid; When the dispersion containing MXene nanosheets is an N,N-dimethylformamide dispersion of MXene nanosheets, or an N,N-dimethylformamide dispersion of MXene nanosheets and GO nanosheets, the coagulation bath is a mixture of isopropanol and water; When the dispersion containing MXene nanosheets is an aqueous dispersion of MXene nanosheets and sodium alginate, the coagulation bath is an aqueous solution of ammonium chloride or an aqueous solution of calcium chloride, and the mass concentration thereof is 0.5-1%.

11. A gas sensor for a non-metallic tube, wherein: The gas sensor for non-metallic tubes is prepared by the method for preparing a gas sensor for non-metallic tubes according to any one of claims 1 to 10, and the gas sensor for non-metallic tubes includes MXene-based gel fibers.

12. The gas sensor for non-metallic pipe according to claim 11, wherein: The gas sensor for the non-metallic tube includes an external gas sensor, a wall-attached gas sensor or an embedded gas sensor; the external gas sensor is arranged on the outside of the non-metallic tube, the wall-attached gas sensor is attached to the outer wall of the non-metallic tube, and the embedded gas sensor is arranged between layers in the non-metallic tube.

13. The gas sensor for non-metallic pipe according to claim 12, wherein: The gas sensor used for the non-metallic pipe is an external gas sensor.

14. The gas sensor for non-metallic pipe according to claim 13, wherein: The external gas sensor comprises: a MXene-based gel fiber sensing element, a sealing cover, a first air duct and a second air duct; The MXene-based gel fiber sensing element comprises a chamber, a substrate, a plurality of the MXene-based gel fibers, and a pair of electrodes. The plurality of the MXene-based gel fibers and the electrodes are arranged on the substrate and placed in the chamber, and the pair of electrodes are respectively connected to the two ends of the axial direction of the plurality of the MXene-based gel fibers; the chamber wall of the chamber is provided with a first gas inlet and a first gas outlet; The sealing cover is an annular shell, which is used to seal and cover the part of the non-metallic pipe to be inspected; the sealing cover is provided with a second gas outlet and a second gas inlet; One end of the first gas duct is connected to the second gas outlet, and the other end is connected to the first gas inlet; one end of the second gas duct is connected to the first gas outlet, and the other end is connected to the second gas inlet.

15. The gas sensor for non-metallic pipe according to claim 14, wherein: The MXene-based gel fiber sensing element includes 2 to 10 MXene-based gel fibers connected in parallel.

16. The gas sensor for non-metallic pipe according to claim 14, wherein: The sealing cover comprises an upper sealing cover and a lower sealing cover, both of which are semi-annular shell structures, and the upper sealing cover and the lower sealing cover are coupled and connected to form a circular connecting port, and the circular connecting port is used to allow non-metallic pipes to pass through, and after the upper sealing cover and the lower sealing cover are coupled and connected, a closed annular space is formed between the outer wall of the non-metallic pipe portion to be inspected.

17. The gas sensor for non-metallic pipe according to claim 16, wherein: The upper sealing cover is provided with the second gas outlet, and the lower sealing cover is provided with the second gas inlet.

18. The gas sensor for non-metallic pipe according to claim 14, wherein: The first gas inlet and the first gas outlet are respectively located at two ends of the axial direction of the MXene-based gel fiber.

19. The gas sensor for non-metallic pipe according to claim 12, wherein: The wall-attached gas sensor at least includes a MXene-based gel fiber sensing element; the MXene-based gel fiber sensing element includes a substrate, a plurality of the MXene-based gel fibers, and electrodes, the plurality of the MXene-based gel fibers and the electrodes are both arranged on the substrate, and the electrodes are arranged at both ends of the axial direction of the plurality of the MXene-based gel fibers; the plurality of the MXene-based gel fibers and the electrodes are attached to the outer wall of the non-metallic tube.

20. The gas sensor for non-metallic pipe according to claim 12, wherein: The embedded gas sensor includes a MXene-based gel fiber sensing element; the MXene-based gel fiber sensing element includes a substrate, a plurality of the MXene-based gel fibers and an electrode, the plurality of the MXene-based gel fibers and the electrode are both arranged on the substrate, and the electrode is arranged at both ends of the axial direction of the plurality of the MXene-based gel fibers; the plurality of the MXene-based gel fibers and the electrode are adhered to the outer surface of the barrier layer in the non-metallic tube.

21. A gas monitoring method, wherein: The gas monitoring method comprises the following steps: (1) Preparation of MXene-based gel fibers; (2) assembling a gas sensor using the MXene-based gel fiber; (3) The gas sensor is used to detect the ambient gas and / or permeated gas of the non-metallic pipe, and the signal obtained by the gas sensor is transmitted to a computer to achieve real-time monitoring of the ambient gas and / or permeated gas of the non-metallic pipe.

22. The gas monitoring method according to claim 21, wherein: Step (1) comprises: using a dispersion containing MXene nanosheets as a spinning solution, injecting the spinning solution into a spinning tube, wherein the outer wall of the spinning tube is provided with a sleeve, and the temperature of the sleeve gradually decreases along the flow direction of the spinning solution; injecting the spinning solution into a coagulation bath through the spinning tube; collecting the fibers formed in the coagulation bath and subjecting them to at least swelling, liquid nitrogen freezing and freeze drying to obtain the MXene-based gel fibers.

23. The gas monitoring method according to claim 21, wherein: Step (2) includes: using the MXene-based gel fiber to assemble an external gas sensor, a wall-mounted gas sensor or an embedded gas sensor.

24. The gas monitoring method according to claim 21, wherein: The non-metallic pipe includes one or a combination of oilfield pipes, gas pipes and drainage pipes.

25. The gas monitoring method according to claim 21, wherein: The gas detected by the gas sensor includes one or a combination of CO2, NH3, CH4, H2S, H2O and H2.

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