Methods for detecting trace gaseous substances and preparation of thermal desorption pre-concentrator

Abstract

This application relates to the field of trace detection technology, and more specifically, to a method for detecting trace gaseous substances, a thermal desorption pre-concentrator, and its preparation method. The preparation method of the thermal desorption pre-concentrator includes: sequentially cleaning, acid-activating, drying, and cutting a metal foam sheet; immersing a metal foam substrate in an adhesive and then removing it; dispersing a particulate adsorbent phase on the surface of the metal foam substrate; guiding the particulate adsorbent phase into and adhering to the internal pore surface of the metal foam substrate through negative pressure filtration to obtain a metal foam substrate loaded with the particulate adsorbent phase; applying a DC voltage to the metal foam substrate loaded with the particulate adsorbent phase; placing the metal foam adsorbent in a housing with an airflow channel, and electrically connecting the metal foam adsorbent to a conductive electrode. This application is advantageous for achieving rapid and complete desorption of the target analyte, improving pre-concentration efficiency, and increasing detection response speed.

Description

Technical Field

[0001] This application relates to the field of trace detection technology, and more specifically, to a method for detecting trace gaseous substances, a thermal desorption pre-concentrator, and a method for preparing the same. Background Technology

[0002] In fields such as environmental monitoring, industrial safety, and healthcare, high-sensitivity detection of trace volatile organic compounds (VOCs) and other gaseous pollutants is often required. Since the concentration of these target substances in the environment or the gas being tested is usually low, direct detection is insufficient to meet sensitivity requirements. Therefore, pre-concentration technology is typically used to enrich the target gas before detection. Current pre-concentrators often use stainless steel or quartz tubes as the substrate, with adsorbents coated or filled on their inner walls. This allows the target substances to be adsorbed and enriched as the gas flows through. Subsequently, the entire adsorption structure is heated to achieve thermal desorption of the target substances, allowing them to enter the detection system. However, when using a whole-structure heating method for thermal desorption of the adsorption structure, the large heat capacity of the substrate material or structural limitations make it difficult to simultaneously achieve a high heating rate and temperature uniformity. This results in a prolonged desorption process and incomplete desorption, affecting the pre-concentration efficiency and detection response speed of gaseous pollutants, thus limiting its use in rapid detection and high-efficiency applications. Summary of the Invention

[0003] The purpose of this application is to provide a method for detecting trace gaseous substances, a thermal desorption pre-concentrator and its preparation method, in order to solve the technical problems in the related art where the pre-concentrator adopts an overall heating desorption method, which makes it difficult to balance the heating rate and temperature uniformity, resulting in low desorption efficiency and slow detection response speed.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0005] This application provides a method for preparing a thermal desorption pre-concentrator, comprising:

[0006] The metal foam sheets are sequentially cleaned, acid-activated, dried, and cut to obtain the metal foam substrate.

[0007] After the metal foam substrate is immersed in the adhesive, it is taken out, and particulate adsorbent phase is dispersed on the surface of the metal foam substrate. The particulate adsorbent phase is guided into the internal pore surface of the metal foam substrate by negative pressure filtration to obtain a metal foam substrate loaded with particulate adsorbent phase.

[0008] A DC voltage is applied to the metal foam substrate loaded with the particulate adsorbent phase, and the binder is cured by the Joule heat generated by the substrate itself to obtain a metal foam adsorbent.

[0009] The metal foam adsorbent is placed inside a housing with an airflow channel, and the metal foam adsorbent is electrically connected to a conductive electrode.

[0010] In some implementations, the cleaning process includes: ultrasonically cleaning the metal foam sheet sequentially with deionized water, acetone, and ethanol;

[0011] The acid activation treatment includes ultrasonic treatment with a hydrochloric acid solution with a concentration of 3 mol / L to 5 mol / L.

[0012] In some implementations, the binder is an aqueous solution of carboxymethyl cellulose with a mass percentage concentration of 0.5% to 2%.

[0013] In some implementations, applying a DC voltage to the metal foam substrate loaded with the particulate adsorbed phase includes:

[0014] A DC voltage of 1V to 2V is applied to the metal foam substrate for a duration of 1 to 2 minutes.

[0015] In some implementations, the particulate adsorbent phase includes at least one of poly(2,6-diphenyl-p-phenyl ether) particles, carbon adsorbent particles, molecular sieves, silica gel particles, and polymer adsorbents.

[0016] In the metal foam substrate loaded with the particulate adsorbent phase, the mass of the particulate adsorbent phase is 40% to 50% of the mass of the metal foam substrate.

[0017] In some implementations, the metal foam sheet includes at least one of nickel foam, copper foam, and aluminum foam.

[0018] This application provides a thermal desorption pre-concentrator, which is prepared by the preparation method of the thermal desorption pre-concentrator described in any of the above implementations;

[0019] The thermal desorption pre-concentrator includes: a shell, a metal foam adsorbent, and a conductive electrode. The shell has an airflow channel, the metal foam adsorbent is disposed in the airflow channel, and the conductive electrode is electrically connected to the metal foam adsorbent.

[0020] The metal foam adsorbent comprises a metal foam substrate and a particulate adsorbent phase, wherein the particulate adsorbent phase is attached to the metal foam substrate.

[0021] In some implementations, the metal foam substrate includes at least one of nickel foam, copper foam, and aluminum foam.

[0022] The metal foam adsorbent is in the form of multiple pieces, which are stacked together; or, the metal foam adsorbent is formed into a columnar structure in a coiled form.

[0023] This application provides a method for detecting trace gaseous substances, wherein the method uses a thermal desorption pre-concentrator prepared by the preparation method of the thermal desorption pre-concentrator described in any of the above implementations, or uses a thermal desorption pre-concentrator described in any of the above implementations.

[0024] The method for detecting trace gaseous substances includes:

[0025] The sample gas containing the target trace gaseous substance is passed through a thermal desorption pre-concentrator at a flow rate of 10 mL / min to 500 mL / min, so that the target trace gaseous substance in the sample gas is adsorbed by the thermal desorption pre-concentrator.

[0026] Stop the gas supply to the thermal desorption pre-concentrator, apply a DC voltage of 0.9V~1.3V to the metal foam adsorbent of the thermal desorption pre-concentrator to heat it to 80℃~120℃ within 30s~90s using the Joule heating effect, and introduce carrier gas into the thermal desorption pre-concentrator to purge the desorbed target trace gaseous substances to the substance detector.

[0027] The concentration of the target trace gaseous substance is determined based on the detection information from the substance detector.

[0028] In some implementations, the trace gaseous substance detection method further includes:

[0029] Based on the detection information from the substance detector, the desorption signal curve is obtained;

[0030] Desorption peaks are determined based on the desorption signal curve.

[0031] The desorption time is calculated based on the desorption peak, wherein the desorption time The following conditions must be met:

[0032] , The point in time at which the desorption signal decays from the peak value of the desorption peak to 5% of the peak value of the desorption peak is defined. This is the starting time point of the desorption peak.

[0033] The main advantages of the trace gaseous substance detection method, thermal desorption pre-concentrator and preparation method provided in this application are as follows:

[0034] This application utilizes a metal foam substrate as the carrier of the adsorbent phase, leveraging its high porosity and three-dimensional interconnected framework structure. This not only increases the effective contact area between the target gas and the adsorbent material but also facilitates uniform and rapid heat transfer during the desorption stage. Due to the excellent conductivity of the metal foam adsorbent itself, in-situ heating using Joule heating through direct voltage application via conductive electrodes reduces the thermal inertia effect of the matrix material in external heating methods used in related technologies. This improves the heating rate and the uniformity of temperature distribution, thus promoting rapid and complete desorption of the target analyte. Furthermore, the use of negative pressure filtration during preparation guides the particulate adsorbent phase into the pores, followed by curing with a binder. This enhances the bonding force between the adsorbent material and the metal framework, reducing the probability of adsorbent phase detachment during long-term cyclic use. This integrated design improves pre-concentration efficiency and detection response speed, while its compact structure and high physical stability effectively extend the service life of the adsorption module and facilitate subsequent installation and maintenance in confined spaces. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic flowchart of the preparation method of the thermal desorption pre-concentrator provided in the embodiments of this application;

[0037] Figure 2 This is a schematic diagram of the structure of the thermal desorption pre-concentrator provided in the embodiments of this application;

[0038] Figure 3 This is a schematic diagram of the inner shell structure provided in an embodiment of this application;

[0039] Figure 4 This is a schematic diagram of the structure of the metal foam adsorbent provided in the embodiment of this application when it is disposed in the airflow channel;

[0040] Figure 5 yes Figure 3 A cross-sectional view of the inner shell;

[0041] Figure 6 This is a schematic diagram of the adsorption-desorption detection curve when using a thermal desorption pre-concentrator for detection, as provided in the embodiments of this application.

[0042] Explanation of key figure labels:

[0043] 101. Conductive electrode; 102. Airflow channel; 103. First sub-shell; 104. Second sub-shell; 105. Air inlet pipe; 106. Air outlet pipe; 107. Third sub-shell; 108. Fourth sub-shell; 109. Air inlet; 110. Air outlet; 111. Metal foam adsorbent; 112. Buckle. Detailed Implementation

[0044] In related technologies, pre-concentrators often use stainless steel or quartz tubes as the substrate, with adsorbent coated or filled on their inner walls. This allows the target analyte to be adsorbed and enriched during gas flow. Subsequently, the entire adsorption structure is heated to achieve thermal desorption of the target analyte, which then enters the detection system. To achieve miniaturization and rapid heating, some solutions introduce microchannel and thin-film heating structures based on microelectromechanical systems (MEMS). However, these pre-concentration solutions still have several shortcomings. On the one hand, metal or quartz tube structures have large heat capacities, resulting in slow heating and cooling rates, low desorption efficiency, and a tendency for desorption peak broadening and residue problems. On the other hand, uneven temperature distribution in tubular or microchannel structures affects the complete desorption of the adsorbent. Furthermore, while MEMS pre-concentrators are small and have fast response times, their adsorption capacity is limited, and their mechanical strength is low, making them unsuitable for high-flow-rate sampling and repeated thermal cycling. Additionally, their high manufacturing cost and complex system integration limit their application in rapid, portable on-site detection.

[0045] Therefore, this application provides a method for detecting trace gaseous substances, a thermal desorption pre-concentrator and its preparation method, to solve the problems in related technologies.

[0046] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0047] See Figure 1 As shown, the preparation method of the thermal desorption pre-concentrator provided in the embodiments of this application may include at least some or all of the following steps.

[0048] Step S10: The metal foam sheet is sequentially cleaned, acid-activated, dried, and cut to obtain a metal foam substrate. Cleaning the surface of the metal foam sheet removes surface impurities and grease, which increases the micro-roughness of the metal skeleton surface and reduces the interfacial contact resistance. This helps to enhance the adhesion of the subsequent binder and adsorbed phase to the metal skeleton and reduces the probability of adsorbed phase detachment under high-speed airflow.

[0049] Step S20: After impregnating the metal foam substrate with the binder, remove it and disperse particulate adsorbent phase on the surface of the metal foam substrate. Then, guide the particulate adsorbent phase into and adhere to the internal pore surface of the metal foam substrate using negative pressure filtration to obtain a metal foam substrate loaded with particulate adsorbent phase. This achieves a uniform spatial distribution of the adsorbent phase, avoiding the accumulation and blockage of particulate adsorbent phase on the surface. Therefore, while maintaining low gas resistance, it maximizes the contact area between the target gas and the adsorbent material, improving the capture efficiency.

[0050] Step S30: Apply a DC voltage to the metal foam substrate loaded with particulate adsorbent phase, and use the Joule heat generated by the substrate itself to cure the binder to obtain metal foam adsorbent 111. By using DC voltage, in-situ heating can be performed directly on the skeleton interface. This method has low heat loss and extremely fast heating, which is conducive to the uniform curing of the binder in microseconds / seconds, forming a tight heat transfer chain of metal skeleton, binder and adsorbent particles.

[0051] Step S40: Place the metal foam adsorbent 111 inside the housing with the airflow channel 102, and electrically connect the metal foam adsorbent 111 to the conductive electrode 101. Due to the high strength characteristics of the metal foam, this structure provides a large adsorption capacity while overcoming the shortcomings of insufficient mechanical strength in MEMS structures in related technologies. This facilitates achieving a high desorption heating rate through high current in actual detection, shortening the detection cycle, and providing a reliable guarantee for the portability and high-frequency reusability of the thermal desorption pre-concentrator.

[0052] The method for preparing a thermal desorption pre-concentrator provided in this application uses a metal foam substrate as the carrier of the adsorbent phase. Utilizing its high porosity and three-dimensional interconnected framework structure, it not only increases the effective contact area between the target gas and the adsorbent material but also facilitates uniform and rapid heat transfer during the desorption stage. Because the metal foam adsorbent 111 itself has good conductivity, in-situ heating using Joule heating is achieved by directly applying voltage through the conductive electrode 101. This reduces the thermal inertia effect of the matrix material in external heating methods used in related technologies, improving the heating rate and the uniformity of temperature distribution. It also reduces the probability of desorption peak broadening and target residue, thus promoting rapid and complete desorption of the target analyte. Furthermore, the negative pressure filtration process guides the particulate adsorbent phase into the pores, and the binder is used for curing, enhancing the bonding force between the adsorbent material and the metal framework and reducing the probability of adsorbent phase detachment during long-term cyclic use. This integrated design improves pre-concentration efficiency and detection response speed. Due to its compact structure and high physical stability, it also effectively extends the service life of the adsorption component and facilitates subsequent installation and maintenance in confined spaces.

[0053] In some embodiments, in step S10, the cleaning process includes: sequentially ultrasonically cleaning the metal foam sheet with deionized water, acetone, and ethanol; the acid activation process includes: ultrasonic treatment with a hydrochloric acid solution with a concentration of 3 mol / L to 5 mol / L. This removes surface oxides such as NiO and Ni(OH)2 from the metal foam sheet, thereby enhancing the surface cleanliness and activity of the metal foam substrate. This facilitates subsequent negative pressure filtration and Joule thermal curing processes, enhancing the adhesion stability of the particulate adsorbent phase on the pore surface and reducing the probability of adsorbent material loss under airflow impact.

[0054] For example, when using deionized water, acetone and ethanol to perform ultrasonic cleaning on metal foam sheets, the ultrasonic cleaning time for each cleaning step can be the same or different; the ultrasonic cleaning time for each liquid cleaning step is 8 min to 30 min, for example 8 min, 9 min, 10 min, 11 min, 15 min, 19 min, 20 min, 25 min or 30 min.

[0055] The concentration of the hydrochloric acid solution can be 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L. When using hydrochloric acid solution for ultrasonic treatment, the ultrasonic treatment time can be 25 min to 35 min, for example, 25 min, 30 min, or 35 min.

[0056] It is understood that, in some possible embodiments, the drying process in step S10 may include: placing the cleaned and activated metal foam sheet in a vacuum drying oven and drying it at 60°C to 80°C for 30 to 60 minutes. Using vacuum low-temperature drying is beneficial for quickly removing residual liquid from the metal micropores, preventing secondary oxidation of the metal skeleton in a humid and high-temperature environment, and ensuring the purity of the substrate surface. For example, the temperature in the vacuum drying oven can be 60°C, 65°C, 70°C, or 80°C; the drying time can be 30 minutes, 45 minutes, 50 minutes, or 60 minutes.

[0057] In some embodiments, step S10, the cutting process may include: cutting the metal foam sheet into rectangular pieces to form a metal foam base. The length of the rectangular piece is 14mm to 18mm, and the width is 6mm to 10mm; for example, the length of the rectangular piece may be 14mm, 15mm, 16mm, or 18mm, and the width may be 6mm, 8mm, 9mm, or 10mm.

[0058] In some embodiments, the metal foam sheet includes at least one of nickel foam, copper foam, and aluminum foam. These metallic materials have high electrical conductivity and low resistivity, allowing the metal foam adsorbent 111 to be directly connected to the circuit as a heating element, utilizing Joule heating for in-situ heating. Compared to materials such as stainless steel in related technologies, the high thermal conductivity of nickel, copper, and aluminum in this embodiment facilitates rapid heat transfer from the metal skeleton to the particulate adsorbed phase, reducing the temperature gradient during desorption, thereby helping to increase the heating rate and ensure sufficient desorption. Nickel foam exhibits good interfacial activity after acid activation treatment, which helps to enhance the bonding force with the binder; while copper foam and aluminum foam have lighter weight or higher thermal conductivity.

[0059] For example, the metal foam sheet can be a nickel foam sheet with a pore density of 20 PPI to 40 PPI, such as 20 PPI, 30 PPI, or 40 PPI; and a thickness of 1.0 mm to 2.0 mm, such as 1.0 mm, 1.5 mm, or 2.0 mm. When a nickel foam sheet with a pore density of 30 PPI is selected as the metal foam sheet, it serves not only as a mechanical support for the adsorbent phase but also as an electric heating element and a gas guiding unit. This three-dimensional interconnected structure with its high pore density generates microscale disturbances and local turbulence when gas flows through it. Compared to the smooth microchannel structure in MEMS pre-concentrators in related technologies, this significantly increases the effective collision probability between VOC molecules and the adsorbent, thereby improving the adsorption efficiency per unit volume.

[0060] In some embodiments, the binder is a carboxymethyl cellulose (CMC) aqueous solution with a mass percentage concentration of 0.5% to 2%. Using a low-concentration CMC aqueous solution as the binder ensures efficient loading of the adsorbent particles and facilitates the formation of a film layer with appropriate thickness using Joule heating, reducing the impact on porosity and lowering the probability of binder failure and adsorbent phase detachment during high-temperature cycling. Exemplarily, the mass percentage concentration of CMC can be 0.5%, 1%, 1.25%, or 2%. The water in the CMC aqueous solution is deionized water.

[0061] It is understood that, in some possible embodiments, after step S20 and before step S30, the preparation method of the thermal desorption pre-concentrator provided in this application may further include: naturally air-drying the metal foam substrate loaded with the particulate adsorbent phase or hot air purging at 40°C~50°C for 5min~10min before applying DC voltage for curing. This can remove most of the solvent moisture, preventing the moisture from drastically vaporizing due to excessively rapid local heating when applying DC voltage in subsequent step S30, thereby reducing the probability of bubbles or cracks forming in the adhesive layer and helping to improve the uniformity of adsorbent phase adhesion. For example, the hot air purging temperature can be 40°C, 45°C, or 50°C; the drying time can be 5min, 6min, 7min, or 10min.

[0062] In some embodiments, the method of applying a DC voltage to a metal foam substrate loaded with a particulate adsorbed phase in step S30 includes:

[0063] A DC voltage of 1V to 2V is applied to the metal foam substrate for a duration of 1 to 3 minutes. This ensures uniform film formation of the binder and reduces the potential thermal damage to the activity of the adsorbed phase caused by prolonged high temperatures, thus lowering the probability of adhesion failure and particle detachment during subsequent high-temperature thermal desorption cycles. Furthermore, this heating method generates heat from the inside out of the metal foam substrate. Compared to the outside-to-inside heat transfer method in related technologies, this embodiment avoids the problem of premature surface crusting of the binder while the interior remains insufficiently cured. This allows the binder to harden preferentially at the interface between the metal foam substrate and the adsorbed phase, significantly enhancing the bonding strength of the adsorbed phase within the three-dimensional pores and effectively preventing displacement or detachment of the adsorbed phase during subsequent gas scouring and multiple thermal cycles. For example, the voltage applied to the metal foam substrate is 1V, 1.1V, 1.5V, or 2V for durations of 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes, or 3 minutes. When the metal foam sheet includes a nickel foam sheet, a low voltage of 1.1V can be applied to Joule heating to cure the binder in situ during the adsorption phase loading process.

[0064] In some embodiments, the particulate adsorbent phase includes at least one of poly(2,6-diphenyl-p-phenylene ether) particles, carbon adsorbent particles, molecular sieves, silica gel particles, and polymer adsorbents. By utilizing their varying micropore sizes and surface chemical polarities, targeted capture of volatile organic compounds (VOCs) of different molecular sizes or functional groups can be achieved, thereby broadening the response range of the pre-concentrator to complex component gases and meeting diverse detection needs. For example, the particulate adsorbent phase may include poly(2,6-diphenyl-p-phenylene ether) particles.

[0065] In the metal foam substrate loaded with a particulate adsorbent phase, the mass of the particulate adsorbent phase is 40%–50% of the mass of the metal foam substrate. Due to the high three-dimensional interconnected porosity of the metal foam substrate, this loading ratio ensures that the particles fully and uniformly cover the surface of the metal framework. This provides sufficient adsorption capacity to meet trace substance enrichment requirements while avoiding pore blockage or agglomeration due to excessive particles. This configuration reduces the pressure drop resistance during gas flow, ensuring smooth flow during high-flow-rate sampling. Furthermore, this loading ratio allows for optimal contact between the particulate adsorbent phase and the metal framework, facilitating efficient heat transfer during desorption via Joule heating generated by the framework, reducing thermal hysteresis, and helping to maintain the mechanical structural stability of the adsorbate during multiple thermal cycles. This reduces the risk of particle detachment, thereby extending component life and improving detection repeatability.

[0066] For example, the mass of the particulate adsorbent phase is 40%, 45%, or 50% of the mass of the metal foam substrate.

[0067] Combination Figures 2 to 5 As shown in the embodiments, this application also provides a thermal desorption pre-concentrator, which is prepared using the preparation method of the thermal desorption pre-concentrator provided in any of the above embodiments. The above-mentioned thermal desorption pre-concentrator has the same technical effects as the manufacturing method of the thermal desorption pre-concentrator provided in the foregoing embodiments, and will not be repeated here. The thermal desorption pre-concentrator can be directly integrated with portable mass spectrometers, gas sensors, and other detection systems, and is suitable for applications such as indoor and outdoor air quality monitoring, industrial safety early warning, and on-site emergency detection.

[0068] In this embodiment of the application, the thermal desorption pre-concentrator includes: a shell, a metal foam adsorbent 111 and a conductive electrode 101. The shell has an airflow channel 102, the metal foam adsorbent 111 is disposed in the airflow channel 102, and the conductive electrode 101 is electrically connected to the metal foam adsorbent 111. The metal foam adsorbent 111 includes a metal foam substrate and a particulate adsorbent phase, and the particulate adsorbent phase is attached to the metal foam substrate.

[0069] For example, the housing includes an inner shell and an outer shell. The outer shell includes a first sub-shell 103 and a second sub-shell 104. The first sub-shell 103 and the second sub-shell 104 cooperate to form a receiving cavity, and the inner shell is fixed in the receiving cavity. The first sub-shell 103 and the second sub-shell 104 are detachably fixedly connected by screws or clips 112. The first sub-shell 103 has an air inlet pipe 105 and an air outlet pipe 106. An airflow channel 102 is formed in the inner shell. The inner shell may include a third sub-shell 107 and a fourth sub-shell 108, which are joined together. The airflow channel 102 has corresponding air inlets 109 and air outlets 110. The air inlet pipe 105 is connected to the air inlet 109 of the airflow channel 102, and the air outlet pipe 106 is connected to the air outlet 110 of the airflow channel 102. The metal foam adsorbent 111 can be disposed in the middle of the airflow channel 102. The sample gas enters the airflow channel 102 through the inlet pipe 105, then flows through the metal foam adsorbent 111, and then flows out through the outlet pipe 106. The metal foam adsorbent 111 has a first connection end and a second connection end. The first connection end is electrically connected to a conductive electrode 101, and the second connection end is electrically connected to another conductive electrode 101. The positive and negative terminals of the linear power supply are respectively electrically connected to the two conductive electrodes 101 to supply power to the metal foam adsorbent 111.

[0070] The first sub-shell 103 and the second sub-shell 104 are sealed together, for example, with a sealing ring at the contact point between them to ensure airtightness. This allows the sample gas to flow entirely through the airflow channel 102 after entering through the inlet pipe 105, and finally exit through the outlet pipe 106. Because the joint between the first sub-shell 103 and the second sub-shell 104 is sealed, leakage of the sample gas from the connection point is prevented. Both the inlet pipe 105 and the outlet pipe 106 can use a standard 6mm inner diameter, and both the outer surfaces of the inlet pipe 105 and the outlet pipe 106 can have external threads, facilitating quick connection to other pipelines using compression fittings with internal thread connectors.

[0071] The cross-section of the airflow channel 102 can be circular or rectangular; the cross-section of the airflow channel 102 is perpendicular to its length direction; the length of the airflow channel 102 can be 50mm to 70mm, for example, 50mm, 55mm, 60mm, 65mm, or 70mm. When the cross-section of the airflow channel 102 is rectangular, the width of the airflow channel 102 is 15mm to 720mm, for example, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm; the height of the airflow channel 102 is 5mm to 710mm, for example, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm, and the height can also be referred to as the depth. The shape of the cross-section of the airflow channel is adapted to the shape of the metal foam adsorbent, so that after the metal foam adsorbent is placed in the airflow channel, it can completely fill the cross-section of the airflow channel, thereby ensuring that the sample gas can completely pass through the metal foam adsorbent after entering the airflow channel; for example, when the shape of the metal foam adsorbent 111 is rectangular, the cross-section of the airflow channel 102 is rectangular.

[0072] In some embodiments, the outer shell can be made of stainless steel or aluminum alloy; while the inner shell can be made of plastic, such as polytetrafluoroethylene, ceramic, or glass. When the inner shell is made of PTFE, it has a lower surface adsorption tendency for high-boiling-point VOCs compared to metal materials, which can significantly reduce secondary adsorption and residue of gas on the wall of the gas flow channel 102, thereby reducing the memory effect generated during multiple sampling-desorption cycles and improving the repeatability and reliability of the detection results.

[0073] In some embodiments, the metal foam substrate includes at least one of nickel foam, copper foam, and aluminum foam; the number of metal foam adsorbents 111 is multiple, and the multiple metal foam adsorbents 111 are stacked; or, the metal foam adsorbents 111 are formed into a columnar structure in a wound form. By stacking multiple metal foam adsorbents 111, the adsorption capacity of the thermal desorption pre-concentrator can be flexibly adjusted according to the concentration and flow rate requirements of the gas to be measured, thereby facilitating the on-demand customization of detection sensitivity without changing the single-piece preparation process. Furthermore, forming the metal foam adsorbents 111 into a columnar structure in a wound form ensures a large specific surface area while further increasing the adsorbent phase loading density per unit volume, effectively eliminating the edge leakage risk that may exist in the stacked structure, making the gas flow field distribution more uniform, and helping to reduce the broadening of the desorption peak.

[0074] For example, the length direction of the columnar structure can be perpendicular to the length direction of the airflow channel 102; after multiple metal foam adsorbents 111 are stacked, the stacking direction can be perpendicular to the length direction of the airflow channel 102; the airflow channel 102 can have multiple columnar structures.

[0075] It is understood that in some other possible embodiments, when there are multiple metal foam adsorbents 111, the pore density of the metal foam substrate in the multiple metal foam adsorbents 111 can be the same or different from each other. When the pore density is different from each other, the pore density of the metal foam substrate in the multiple metal foam adsorbents 111 stacked along the airflow direction can gradually increase to form a gradient structure, for example, gradually transitioning from 20 PPI to 40 PPI. This can reduce airflow resistance, improve gas distribution uniformity, and increase adsorption efficiency. In addition, the metal foam adsorbents 111 can also be installed in the airflow channel 102 in a honeycomb form.

[0076] This application also provides a method for detecting trace gaseous substances. The method uses a thermal desorption pre-concentrator prepared by the method described in any of the above embodiments, or uses the thermal desorption pre-concentrator provided in any of the above embodiments. The above-described method for detecting trace gaseous substances has the same technical effects as the manufacturing method of the thermal desorption pre-concentrator provided in the foregoing embodiments, and will not be repeated here.

[0077] The trace gaseous substance detection method provided in this application embodiment may include at least some or all of the following steps, which can not only be used to detect trace gaseous substances in the gas to be tested, but also to calibrate the thermal desorption pre-concentrator and evaluate the desorption performance of the thermal desorption pre-concentrator.

[0078] The trace gaseous substance detection method provided in this application embodiment may include at least some or all of the following steps; the trace gaseous substance detection method can not only be used to detect trace gaseous substances in the sample gas to be tested, but also to calibrate the thermal desorption pre-concentrator and to evaluate the desorption performance of the thermal desorption pre-concentrator.

[0079] The trace gaseous substance detection method provided in this application includes:

[0080] Step S100: Pass the sample gas containing the target trace gaseous substance through a thermal desorption pre-concentrator at a flow rate of 10 mL / min to 500 mL / min, so as to adsorb the target trace gaseous substance in the sample gas through the thermal desorption pre-concentrator. For example, the flow rate of the sample gas can be 10 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min; the continuous flow time of the sample gas can be 0.5 min to 15 min, for example, 0.5 min, 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3 min, 5 min, 10 min or 15 min.

[0081] Step S200: Stop the gas supply to the thermal desorption pre-concentrator, apply a DC voltage of 0.9V~1.3V to the metal foam adsorbent 111 of the thermal desorption pre-concentrator to heat it to 80℃~120℃ within 30s~90s using the Joule heating effect, and introduce carrier gas into the thermal desorption pre-concentrator to purge the desorbed target trace gaseous substance to the substance detector. For example, the DC voltage can be 0.9V, 1.0V, 1.1V, 1.2V, or 1.3V; the heating time can be 30s, 45s, 60s, 75s, or 90s; and the heating temperature can be 80℃, 90℃, 100℃, 110℃, or 120℃.

[0082] In some embodiments, the carrier gas may pass through the thermal desorption pre-concentrator at a flow rate of 50 mL / min to 400 mL / min; exemplaryly, the sample gas flow rate may be, for example, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, 350 mL / min, or 400 mL / min. The inert carrier gas may be nitrogen, helium, or argon.

[0083] Step S300: Determine the concentration of the target trace gaseous substance based on the detection information from the substance detector.

[0084] Understandably, after testing a sample gas using a thermal desorption pre-concentrator, the next round of sampling can be prepared after the thermal desorption pre-concentrator stops heating and allows it to cool naturally to room temperature within 1 to 3 minutes.

[0085] See Figure 6 As shown, Figure 6 In the vertical axis, C represents concentration, and in the horizontal axis, t represents time. In some embodiments, the trace gaseous substance detection method further includes:

[0086] Step S400: Obtain the desorption signal curve of the desorption stage based on the detection information of the substance detector.

[0087] Step S401: Determine the desorption peak based on the desorption signal curve.

[0088] Step S402: Calculate the desorption time based on the desorption peak, where the desorption time... The following conditions must be met:

[0089] , The point in time at which the desorption signal decays from the peak value of the desorption peak to 5% of the peak value of the desorption peak is defined. This is the starting time point of the desorption peak.

[0090] For example, in step S400, based on the detection information from the substance detector, an adsorption signal curve for the adsorption stage can be obtained; in step S401, the adsorption valley can be determined based on the adsorption signal curve; and in step S402, the adsorption time can be calculated based on the adsorption valley. .

[0091] In the calibration process using trace gaseous substance detection methods, the sample gas is a standard reference gas containing known components and concentrations. The substance detector can be a PID sensor used to monitor the concentration of known components (i.e., the target trace gaseous substance) at the inlet pipe 105 and outlet pipe 106 of the thermal desorption pre-concentrator. During the desorption stage, the concentration of known components at the outlet pipe 106 of the thermal desorption pre-concentrator is continuously monitored to obtain a complete desorption signal curve (i.e., the desorption peak concentration change curve). The time point from the peak value of the desorption peak to 5% of the peak value is determined from the desorption signal curve. The desorption time of the pre-concentrator can be obtained through the desorption time calculation formula, and a standard working curve is plotted by combining the response intensity of standard gas at different concentrations, thereby completing the calibration of the desorption efficiency and quantitative accuracy of the pre-concentrator. During the calibration process, based on the peak value of the desorption peak... (i.e., the maximum concentration measured during the desorption stage) and the concentrations of known components in the sample gas before it enters the thermal desorption pre-concentrator. The pre-concentration factor can be calculated. Pre-concentrated factor It is defined as the ratio of the maximum concentration measured during the desorption phase to the initial concentration of the target trace gaseous substance in the injected gas; the pre-concentration factor. The following conditions must be met:

[0092] .

[0093] It should be noted that in related technologies, desorption time is defined as the time required for the desorption peak to return to the baseline from its starting point; however, it is easily affected by baseline drift and noise interference, leading to significant fluctuations in thermal desorption kinetics analysis. The desorption time in the embodiments of this application... By focusing on the peak decay to a set threshold rather than returning to the baseline completely, the sensitivity of desorption time to baseline fluctuations and noise is reduced, which more realistically reflects the transient desorption behavior under Joule heating conditions. This provides a stable and repeatable evaluation basis for the quantitative comparison of the performance of thermal desorption pre-concentrators under different structural parameters and process conditions.

[0094] In one example, the thermal desorption pre-concentrator can complete a full adsorption cycle within 3 minutes. The desorption cycle achieves a pre-concentration factor of up to 22, reducing the detection limit for toluene to 4.8 ppb. This thermal desorption pre-concentrator exhibits stable performance over 30 consecutive cycles, with a relative standard deviation of less than 6% and an overall power consumption of less than 25W. It is suitable for portable gas chromatography, photoionization detectors, and other on-site trace gas detection systems. The limit of detection (LOD) refers to the lowest concentration of an analyte that a substance detector can reliably detect. The power consumption refers to the energy required for a single desorption cycle in the thermal desorption pre-concentrator, expressed in watts (W).

[0095] When using trace gaseous substance detection methods to detect trace gaseous substances in the sample gas, the thermal desorption pre-concentrator has been calibrated, and the pre-concentration factor is known. By using the thermal desorption pre-concentrator and the substance detector in conjunction, during the desorption stage of the thermal desorption pre-concentrator, the substance detector can detect the concentration of the target trace gaseous substance. Combining the pre-concentration factor and the maximum concentration measured during the desorption stage, the initial concentration of the target trace gaseous substance in the sample gas can be obtained.

[0096] In one embodiment, when nickel foam sheets are selected as the metal foam sheet, the thermal desorption pre-concentrator can achieve a rapid thermal response with a heating rate of approximately 4°C / s, resulting in uniform overall temperature distribution and significantly shortening the desorption start-up time. Rapid and efficient desorption of adsorbed VOCs can be achieved at desorption temperatures less than or equal to 100°C, such as 90°C, with concentrated and reproducible desorption peaks. This effectively reduces system energy consumption while ensuring desorption efficiency, making it suitable for portable or battery-powered detection equipment.

[0097] It should be understood that, in the embodiments of this application, unless otherwise expressly specified and limited, the terms "connection," "fixed connection," "contact," etc., should be interpreted broadly. Those skilled in the art can understand the specific meanings of the various terms in the embodiments of this application according to the specific circumstances.

[0098] For example, the "connection" can be a fixed connection, a rotating connection, a flexible connection, a sliding connection, a one-piece molding, an electrical connection, a contact connection, or other connection methods; it can be a direct connection, or an indirect connection through an intermediate medium, or a connection within two components or an interaction between two components.

[0099] For example, a "fixed connection" can be a component that can be directly or indirectly fixedly connected to another component; a fixed connection can include mechanical connection, welding, bonding or integral molding, etc., wherein mechanical connection can include riveting, bolting, threaded connection, keying, snap-fit ​​connection, locking connection, plugging, etc., and bonding can include adhesive bonding and solvent bonding, etc.

[0100] It should also be understood that the “parallel” or “perpendicular” described in the embodiments of this application can be understood as “approximately parallel” or “approximately perpendicular”.

[0101] It should also be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Features specified as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0102] In the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature and the second feature are in direct contact, or that the first feature and the second feature are in indirect contact through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0103] It should also be understood that the terms “length,” “width,” “up,” “down,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship (if any) based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0104] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims. In conclusion, the above description is merely a preferred embodiment of the technical solution of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a thermal desorption pre-concentrator, characterized in that, include: The metal foam sheets are sequentially cleaned, acid-activated, dried, and cut to obtain the metal foam substrate. The metal foam substrate is impregnated with a binder and then removed. A particulate adsorbent phase is dispersed on the surface of the metal foam substrate. The particulate adsorbent phase is guided into and adheres to the internal pore surface of the metal foam substrate by negative pressure filtration, thus obtaining a metal foam substrate loaded with a particulate adsorbent phase. The binder is a carboxymethyl cellulose aqueous solution with a mass percentage concentration of 0.5% to 2%. The particulate adsorbent phase includes at least one of poly(2,6-diphenyl-p-phenylene ether) particles, carbon adsorbent particles, molecular sieves, silica gel particles, and polymer adsorbents. In the metal foam substrate loaded with the particulate adsorbent phase, the mass of the particulate adsorbent phase is 40% to 50% of the mass of the metal foam substrate. A DC voltage is applied to the metal foam substrate loaded with the particulate adsorbent phase, and the binder is cured by the Joule heat generated by the substrate itself to obtain a metal foam adsorbent. The metal foam adsorbent is placed inside a housing with an airflow channel, and the metal foam adsorbent is electrically connected to a conductive electrode. The cleaning process includes: sequentially ultrasonically cleaning the metal foam sheet with deionized water, acetone and ethanol; The acid activation treatment includes: ultrasonic treatment with a hydrochloric acid solution with a concentration of 3 mol / L to 5 mol / L; The step of applying a DC voltage to the metal foam substrate loaded with the particulate adsorbed phase includes: applying a DC voltage of 1V to 2V to the metal foam substrate for a duration of 1min to 2min. The thermal desorption pre-concentrator includes: a shell, a metal foam adsorbent, and a conductive electrode. The shell has an airflow channel, the metal foam adsorbent is disposed in the airflow channel, and the conductive electrode is electrically connected to the metal foam adsorbent. The metal foam adsorbent comprises a metal foam substrate and a particulate adsorbent phase, wherein the particulate adsorbent phase is attached to the metal foam substrate.

2. The method for preparing the thermal desorption pre-concentrator as described in claim 1, characterized in that, The metal foam sheet includes at least one of nickel foam sheet, copper foam sheet, and aluminum foam sheet.

3. The method for preparing the thermal desorption pre-concentrator as described in claim 1, characterized in that, The metal foam substrate includes at least one of nickel foam, copper foam, and aluminum foam. The metal foam adsorbent is in the form of multiple pieces, which are stacked together; or, the metal foam adsorbent is formed into a columnar structure in a coiled form.

4. A method for detecting trace gaseous substances, characterized in that, The method for detecting trace gaseous substances uses a thermal desorption pre-concentrator prepared by the method described in any one of claims 1-3. The thermal desorption pre-concentrator includes: a shell, a metal foam adsorbent, and a conductive electrode. The shell has an airflow channel, the metal foam adsorbent is disposed in the airflow channel, and the conductive electrode is electrically connected to the metal foam adsorbent. The metal foam adsorbent comprises a metal foam substrate and a particulate adsorbent phase, wherein the particulate adsorbent phase is attached to the metal foam substrate; The method for detecting trace gaseous substances includes: The sample gas containing the target trace gaseous substance is passed through a thermal desorption pre-concentrator at a flow rate of 10 mL / min to 500 mL / min, so that the target trace gaseous substance in the sample gas is adsorbed by the thermal desorption pre-concentrator. Stop the gas supply to the thermal desorption pre-concentrator, apply a DC voltage of 0.9V~1.3V to the metal foam adsorbent of the thermal desorption pre-concentrator to heat it to 80℃~120℃ within 30s~90s using the Joule heating effect, and introduce carrier gas into the thermal desorption pre-concentrator to purge the desorbed target trace gaseous substances to the substance detector. The concentration of the target trace gaseous substance is determined based on the detection information from the substance detector; The method for detecting trace gaseous substances also includes: Based on the detection information from the substance detector, the desorption signal curve is obtained; Desorption peaks are determined based on the desorption signal curve. The desorption time is calculated based on the desorption peak, wherein the desorption time The following conditions must be met: , The point in time at which the desorption signal decays from the peak value of the desorption peak to 5% of the peak value of the desorption peak is defined. This is the starting time point of the desorption peak.

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