A system and method for measuring single particle adsorption isotherms

Abstract

The application discloses a kind of single-particle adsorption isotherm measurement system and method, the system includes: dark field optical imaging system, for the dark field image of sample particle is collected;Micro gas flow cell, for accommodating sample particle and controlling its atmosphere environment, the micro gas flow cell is equipped with gas inlet, gas outlet and optical transparent window;The optical transparent window is used for the light path of the dark field optical imaging system passes through;Temperature control system, for controlling the temperature of sample particle;Gas path control system, for adjusting the gas type and partial pressure that pass into the micro gas flow cell;Signal acquisition and processing system are connected with the dark field optical imaging system, for collecting dark field image and calculating the scattering light intensity change of the sample particle, to further construct adsorption isotherm.The application realizes the accurate characterization of molecular adsorption amount by real-time monitoring the optical scattering intensity change of single particle in adsorption process.

Description

Technical Field

[0001] This invention belongs to the field of materials testing technology, and relates to a measurement system and method for single-particle adsorption isotherms. Background Technology

[0002] Porous materials, with their ordered pore structure, high specific surface area, and tunable chemical environment, have significant application value in adsorption separation and gas storage. Adsorption isotherms, as the core thermodynamic curves describing the adsorbate-adsorbent interaction, are crucial for evaluating material adsorption capacity, elucidating adsorption mechanisms, and guiding material design.

[0003] Currently, existing adsorption isotherm measurement methods are mainly volumetric and gravimetric methods. Both rely on macroscopic average measurements of powder samples and cannot reveal intrinsic adsorption performance differences at the single-particle scale. Volumetric methods often calculate adsorption capacity by monitoring pressure changes between the sample chamber and the gas chamber, combined with the gas law. However, volumetric methods, based on rational gas laws, require indirect calculation of adsorption capacity through changes in gas volume and pressure, thus necessitating precise calibration of dead volumes in sample tubes, pipelines, and valves, easily introducing systematic errors. Gravimetric methods obtain adsorption capacity by directly measuring the mass change of the sample during adsorption. Typical equipment, such as a magnetic levitation balance system, can achieve dynamic or static measurements, avoiding the dead volume calibration errors of volumetric methods. However, this method requires significant equipment investment (high-sensitivity microbalances), buoyancy calibration, and is complex to operate. Furthermore, both volumetric and gravimetric methods test powder samples, failing to focus on single particles and masking the intrinsic performance heterogeneity between particles.

[0004] The common problems with the above-mentioned existing technologies are: (1) they all rely on macroscopic average measurements of powder samples, simplifying the individual behavior of a large number of single particles to statistical averages, which cannot reflect the differences in adsorption performance between particles; (2) when there are particles with significantly different adsorption capacities in the same batch of materials, a few abnormal particles may dominate macroscopic behavior, leading to systematic deviations in the structure-activity relationship established based on average data; (3) they cannot identify and screen single particles with specific adsorption properties, which restricts the precise design and quality control of high-performance adsorption materials. Therefore, it is urgent to develop a new method that can directly measure adsorption isotherms at the single particle scale to overcome the limitations of traditional measurement techniques. Summary of the Invention

[0005] Purpose of the invention: The present invention aims to solve the problems of existing adsorption measurement technology, which can only obtain the average adsorption performance of porous materials, cannot characterize the intrinsic adsorption behavior at the single particle scale, and is difficult to reveal the relationship between material heterogeneity and adsorption performance. The invention provides a measurement system and method for single particle adsorption isotherms.

[0006] Technical solution: The present invention provides a measurement system for single-particle adsorption isotherms, comprising:

[0007] Dark-field optical imaging system, used to acquire dark-field images of sample particles;

[0008] A miniature gas flow cell is used to contain sample particles and control their atmospheric environment. The miniature gas flow cell is provided with an inlet, an outlet, and an optically transparent window. The optically transparent window is used for the optical path of the dark-field optical imaging system.

[0009] Temperature control system, used to control the temperature of sample particles;

[0010] A gas path control system is used to regulate the type and partial pressure of the gas introduced into the micro gas flow cell;

[0011] The signal acquisition and processing system is connected to the dark field optical imaging system and is used to acquire dark field images and calculate the changes in the intensity of scattered light from the sample particles, thereby constructing adsorption isotherms.

[0012] Furthermore, the dark-field optical imaging system includes an inverted optical microscope equipped with a dark-field condenser, a CCD camera, and an illumination source with adjustable light intensity.

[0013] Furthermore, the micro gas flow cell has a stacked sealed structure, consisting of a transparent cap, a gasket, and a substrate from top to bottom; the gasket is provided with an air inlet and an air outlet, an optically transparent window is formed between the transparent cap and the substrate, the substrate is used to hold sample particles, and electrodes for heating are deposited on the substrate.

[0014] Furthermore, the electrode is an I-shaped gold thin film electrode, and the gold thin film electrode is electrically connected to the temperature control system.

[0015] Furthermore, the temperature control system includes an electrochemical workstation, which heats the sample particles by applying a DC voltage to the gold thin film electrode using the Joule heating effect.

[0016] Another object of the present invention is to provide a method for measuring single-particle adsorption isotherms, which is implemented using the above-mentioned single-particle adsorption isotherm measurement system and includes the following steps:

[0017] (1) The sample is ultrasonically dispersed in a solvent to form a suspension. The suspension is dropped into the optically transparent window of the micro gas flow cell. After the solvent evaporates, a sparsely distributed array of single particles is formed. Pretreatment is performed to completely remove the water molecules pre-adsorbed in the pores of the sample particles.

[0018] (2) Under the condition that the partial pressure of the target gas is zero, the dark field image of the sample particles is acquired by the dark field optical imaging system to obtain its baseline scattered light intensity I0;

[0019] (3) Introduce a mixed gas containing the target gas into the micro gas flow cell, control the partial pressure of the target gas to a set value, and continuously collect dark field images of the sample particles during the adsorption equilibrium process to obtain the real-time scattered light intensity I.

[0020] (4) Calculate the relative change in scattered light intensity ΔI / I0 based on the real-time scattered light intensity I and the baseline scattered light intensity I0, where ΔI=I-I0, and use the relative change in scattered light intensity ΔI / I0 as the index of the relative adsorption amount of the sample particles under the partial pressure of the target gas.

[0021] (5) Change the partial pressure of the target gas and repeat steps (3) to (4) to obtain the relative adsorption capacity index under multiple partial pressures;

[0022] (6) Construct an adsorption isotherm of a single sample particle with the partial pressure of the target gas as the abscissa and the relative adsorption amount index as the ordinate.

[0023] Furthermore, the particle spacing of the sample particles in step (1) is greater than 10 μm.

[0024] Further, the specific steps of the pretreatment in step (1) are as follows: high-purity nitrogen gas is introduced into the micro gas flow cell at a flow rate of 3 ml / min, and a DC voltage is applied to the gold thin film electrode to rapidly heat the sample to 100°C and keep it at a constant temperature for 10 minutes to completely remove the pre-adsorbed water molecules in the sample particle pores. The voltage is then cut off, heating is stopped, and the temperature is continuously purged with nitrogen gas to cool down to 30°C and stabilized for 10 minutes.

[0025] Furthermore, in steps (2) and (3), when acquiring dark field images through the dark field optical imaging system, a CCD camera is used to continuously acquire multiple frames of images at a set frame rate, and the position of the individual sample particles is automatically identified and its scattered light intensity is extracted through the image processing program, the relative change in scattered light intensity is calculated, and an adsorption isotherm is constructed.

[0026] Furthermore, the image processing program includes the following steps during execution:

[0027] The acquired dark-field images are binarized to separate particles from the background;

[0028] The location of individual sample particles was identified and marked using a connected component labeling algorithm;

[0029] The average pixel grayscale value of the region where the particle is located is extracted as the scattered light intensity;

[0030] Calculate the relative change in scattered light intensity and construct an adsorption isotherm.

[0031] This invention is based on the following principle: after porous material particles adsorb target molecules, their effective refractive index changes, and this change is positively correlated with the amount of adsorption. According to Mie scattering theory, the intensity of dark-field scattered light from particles is highly sensitive to changes in their refractive index. Therefore, by monitoring the changes in the intensity of dark-field scattered light from a single particle during the adsorption process in real time, the amount of molecules adsorbed can be quantitatively characterized, and an adsorption isotherm can be constructed.

[0032] Beneficial effects: 1. This invention breaks through the limitations of traditional batch measurement and is used to characterize the intrinsic heterogeneity of single particle adsorption, improve the accuracy of material adsorption performance evaluation, realize the quantitative measurement of adsorption isotherms of single particles, directly capture the differences in adsorption capacity and adsorption kinetics of different single particles under various partial pressures, restore the intrinsic state of the adsorption performance of raw materials, and provide reliable experimental data for the accurate analysis of the structure-adsorption performance relationship.

[0033] 2. This invention eliminates the need for complex sample pretreatment and error correction steps. Through automated signal acquisition and processing, it simplifies the operation process of adsorption isotherm measurement and reduces operational difficulty. At the same time, the system has low energy consumption, does not require a vacuum environment (it can be adapted to atmospheric pressure), reduces equipment operating costs, significantly reduces the interference of external factors on measurement results, and improves the stability of the measurement process and the reliability of data. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0035] Figure 2 This is a schematic cross-sectional view of the micro gas flow cell of the present invention;

[0036] Figure 3 This is a schematic diagram of the I-shaped gold thin film electrode of the present invention;

[0037] Figure 4 The adsorption curves and adsorption isotherms of propylene on six representative Silicalite-1 zeolite particles were selected for Example 2 of the present invention.

[0038] Figure 5 The experimental results for the verification example are shown in the figure, where (a): adsorption curves of n-butene, propylene and ethylene on the same single Silicalite-1 nanoparticle; (b): adsorption isotherm characterization of the three olefins of Silicalite-1 powder; (c): relative relationship between the relative adsorption amount ΔI / I0 of a single particle and the macroscopic adsorption mass. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] The technical principle of this invention is based on the high sensitivity of optical imaging to changes in refractive index. Its core lies in the quantitative correlation between "molecular adsorption - refractive index change - scattered light intensity change," as detailed below:

[0041] When a single particle of a porous material adsorbs a target molecule, its refractive index changes. This is determined by the Lorentz–Lorenz equation (1).

[0042] (1)

[0043] Where n is the refractive index, N i α is the number of molecules per unit volume of component i. i The polarizability of the molecule. Under the measurement conditions of this invention, the change in refractive index caused by the adsorption of gas molecules by the particles is typically 10. -4 The refractive index of the particles is much smaller than that of the particles themselves. Therefore, a linear positive correlation between the number of adsorbed molecules and the refractive index of the particles can be established by approximation: that is, as the number of adsorbed molecules increases, the refractive index of the particles also increases monotonically.

[0044] This invention employs dark-field optical imaging technology, where the detection signal is the intensity of scattered light from the particles, and the intensity of scattered light is related to the scattering efficiency. Directly related. According to Mie scattering theory, scattering efficiency From scattering coefficient and The decision, expressed as:

[0045] (2)

[0046] in, For dimensional parameters, and Let be the Mie scattering coefficient, the specific form of which is given by equations (3) and (4):

[0047] (3)

[0048] (4)

[0049] in, is the relative refractive index of the particle relative to the surrounding medium. and It is the Ricatti-Bessel function, which describes the propagation behavior of electromagnetic waves inside and outside a particle.

[0050] From equations (3) and (4), it can be seen that the Mie scattering coefficient and Both are functions of the relative refractive index m. When the adsorption of molecules by the particles causes an increase in the refractive index m, it results in... and The modulus is significantly improved, and according to equation (2), the scattering efficiency is... and Directly related, therefore It increases monotonically with increasing refractive index m.

[0051] In dark-field optical imaging, the signal intensity I is directly proportional to the scattered light power of the particles, and the scattered light power is in turn related to the scattering efficiency. The geometric cross section πr of the particle 2 Proportional.

[0052] Based on the quantitative correlation between "adsorption amount → refractive index → ​​scattering efficiency → dark-field optical intensity" mentioned above, a clear positive correlation can be derived between dark-field optical intensity and the adsorption amount of single-particle molecules. This relationship is the core theoretical basis for the accurate measurement of single-particle adsorption isotherms using dark-field imaging technology in this invention.

[0053] Example 1:

[0054] like Figure 1 As shown, a single-particle adsorption isotherm measurement system based on dark-field optical microscopy was constructed. This system mainly consists of the following core modules:

[0055] Dark-field optical imaging system, used to acquire dark-field images of sample particles;

[0056] The miniature gas flow cell 3 is used to contain sample particles and control their atmosphere. The miniature gas flow cell is equipped with an inlet, an outlet and an optically transparent window. The optically transparent window is used for the light path of the dark field optical imaging system. The inlet is connected to the gas source and the outlet is connected to the waste gas treatment device.

[0057] Temperature control system 4 is used to control the temperature of sample particles;

[0058] A gas path control system is used to regulate the type and partial pressure of the gas introduced into the micro gas flow cell;

[0059] The signal acquisition and processing system is connected to the dark field optical imaging system and is used to acquire dark field images and calculate the changes in the intensity of scattered light from the sample particles, thereby constructing adsorption isotherms.

[0060] In one specific embodiment, the gas path control system includes a gas source 1, an injection pump 2, and a six-way valve 9. The gas source 1 may include nitrogen and a target gas, such as n-butene, propylene, ethylene, etc. The inlet of the micro gas flow cell 3 controls the flow rate of the two gases through a high-precision injection pump 2. The dark-field optical imaging system includes an inverted optical microscope equipped with a dark-field condenser, a CCD camera 7, and an adjustable illumination source. The illumination source and the dark-field condenser 5 are located above the micro gas flow cell 3, and the objective lens 6 is located below the sample in the micro gas flow cell 3.

[0061] In one specific implementation, such as Figure 2-3 As shown, the micro gas flow cell 3 has a stacked sealed structure, consisting of a transparent cap 12, a gasket 13, and a substrate 14 from top to bottom. The substrate 14 is used to hold sample particles, and an electrode 11 for heating is deposited on the substrate 14. Further, the electrode 11 is an I-shaped gold thin-film electrode, with the sample area 10 in the middle for holding the sample particles. The temperature control system 4 includes an electrochemical workstation, with both ends of the gold thin-film electrode connected to the workstation. By applying a DC voltage to the gold thin-film electrode, the Joule heating effect is used to rapidly heat the sample particles, meeting the temperature control requirements of the pretreatment and adsorption / desorption processes.

[0062] In one specific embodiment, the upper transparent cover 12 is a transparent glass sheet; the middle component gasket 13 is a polytetrafluoroethylene gasket with a square hollow window in the center, and two stainless steel hollow needles 15 symmetrically pass through the gasket 13. The hollow needles 15 serve as ventilation channels, forming the air inlet and outlet of the micro gas flow cell 3; the lower substrate 14 is a glass sheet coated with an I-shaped gold thin film electrode. The three components are bonded together by 3M double-sided adhesive to form a closed gas flow cavity, realizing the sealed flow of trace gases and optical characterization.

[0063] The signal acquisition and processing system includes a computer. A CCD camera 7 is connected to the computer 8. The CCD camera 7 continuously acquires multiple frames of images at a set frame rate. An image processing program automatically identifies the position of individual sample particles, extracts their scattered light intensity, calculates the relative change in scattered light intensity, and constructs an adsorption isotherm. The image processing program includes the following steps:

[0064] The acquired dark-field images are binarized to separate particles from the background;

[0065] The location of individual sample particles was identified and marked using a connected component labeling algorithm;

[0066] The average pixel grayscale value of the region where the particle is located is extracted as the scattered light intensity;

[0067] Calculate the relative change in scattered light intensity and construct an adsorption isotherm.

[0068] In one specific implementation, real-time acquisition and storage of dark-field images are achieved using image acquisition software (commercial camera software). The image processing program is a MATLAB-based image processing program stored on the computer's storage medium. When executed, this program performs the following steps: First, the image is imported into the MATLAB-based image processing program. The image is binarized according to a specified threshold (typically 0.1) to separate particles from the background. Then, a connected component labeling function is used to label connected pixels in the binary image as independent particles. The position and bounding box of each particle are then extracted and stored as centroid coordinates, thus obtaining the position of each particle (target region). Next, based on the previously extracted target region, the average gray intensity I of each particle in each frame is extracted from all frames of images. Using the initial 100 frames (nitrogen atmosphere) as a baseline, the average intensity is I0. The intensity is converted into a relative change value, which is ΔI / I0.

[0069] Example 2: A method for measuring single-particle adsorption isotherms, implemented using the aforementioned single-particle adsorption isotherm measurement system. Taking Silicalite-1 zeolite particles as an example, 12 propylene partial pressure gradient points are set: 1 kPa, 5 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, and 100 kPa. The method includes the following steps:

[0070] 1) Sample Preparation: Silicalite-1 zeolite particles were ultrasonically dispersed in anhydrous ethanol. 5 μL of the suspension was precisely added dropwise to the center of the electrode, allowing the solvent to evaporate and form a sparsely distributed array of single particles. Optical microscopy was used to ensure that the particles were centered in the electrode gap and that the interparticle spacing was greater than 10 μm to avoid interference from scattered light between particles. A micro-gas flow cell was then encapsulated on the lower substrate for subsequent adsorption experiments.

[0071] 2) Pretreatment: High-purity nitrogen gas was introduced into the flow cell at a flow rate of 3 ml / min, while a DC voltage was applied to the gold thin-film electrode to rapidly heat the sample to 100 °C and hold it at that temperature for 10 minutes to completely remove pre-adsorbed water molecules from the particle pores. After pretreatment, the voltage was cut off, heating was stopped, and the sample was cooled to 30 °C under continuous nitrogen purging and stabilized for 10 minutes.

[0072] 3) Baseline signal acquisition: At 30 ℃, in a pure nitrogen atmosphere (propylene partial pressure P=0 kPa), 100 frames of dark field images were continuously acquired by a CCD camera at a frame rate of one frame per second. The average light intensity of a single particle was taken as the baseline signal I0 before the target gas was adsorbed.

[0073] 4) Acquisition of adsorption signals at different propylene partial pressures: Nitrogen gas was switched to propylene at a known partial pressure concentration, and optical images were continuously acquired until the optical intensity of the particles no longer changed, indicating adsorption saturation. Acquisition was then stopped. Subsequently, the gas was switched back to nitrogen, and the temperature was raised to 100 °C to promote complete desorption of propylene, preparing for the next partial pressure experiment. Twelve propylene partial pressure gradient points were set by adjusting the propylene-nitrogen ratio: 1 kPa, 5 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, and 100 kPa. The adsorption-desorption process was repeated at each partial pressure point, and optical images of the adsorption process were acquired.

[0074] 5) Signal Extraction and Definition of Relative Adsorption Capacity: Using an image processing program, the time series of scattered light intensity for each particle in the image is automatically extracted. The average optical intensity during the unadsorbed stage is defined as I0, and the optical intensity of the particle during propylene adsorption is defined as I. The relative intensity change ΔI / I0 = (I-I0) / I0 is defined as the relative adsorption capacity index at that partial pressure. The ΔI / I0 value at saturated adsorption is defined as the saturated adsorption capacity index of the particle, used to characterize its maximum adsorption capacity.

[0075] 6) Construction of single-particle adsorption isotherms: Adsorption isotherm curves for each single particle were plotted with the partial pressure of propylene (P, unit kPa) as the x-axis and the relative adsorption amount (ΔI / I0) at the corresponding partial pressure as the y-axis. The Langmuir model was then used to fit the single-particle adsorption isotherms to obtain key thermodynamic parameters such as the adsorption equilibrium constant and saturated adsorption amount, thus achieving a quantitative characterization of the intrinsic adsorption behavior of single particles.

[0076] like Figure 4 As shown, the adsorption kinetic curves and adsorption isotherms of six representative Silicalite-1 single particles under different propylene partial pressures are presented, along with the equilibrium constant K calculated based on the Langmuir model. A This figure, as an important result, directly demonstrates that this method can effectively measure the adsorption isotherm of a single zeolite particle.

[0077] Verification example: Comparison and verification of single-particle experimental results (ΔI / I0) with macroscopic methods.

[0078] To verify the accuracy of the method of this invention, the relative adsorption amounts (ΔI / I0) of three olefins (n-butene, propylene, and ethylene) measured on the same single particle were compared with the adsorption amounts of powder samples measured by traditional macroscopic methods. The macroscopic method involved using powder-grade samples and measuring adsorption isotherms using a gas adsorption analyzer and the static equilibrium method.

[0079] Experimental results are as follows Figure 5As shown, (a): adsorption kinetics curves of n-butene, propylene, and ethylene on the same single Silicalite-1 nanoparticle; (b): adsorption isotherms characterizing the three olefins from Silicalite-1 powder; (c): the relative relationship between the relative adsorption amount ΔI / I0 of a single particle and the macroscopic adsorption mass. Figure 5 (a) shows that there are significant differences in the adsorption curves of the same single particle for the three olefins, with the adsorption capacity ranked as n-butene > propylene > ethylene; Figure 5 (b) shows the adsorption isotherms of the macroscopic powder sample for the three olefins. It can be seen that the trend of the single-particle results is consistent with that of the macroscopic results. Figure 5 (c) shows a strong linear positive correlation between the relative adsorption capacity of a single particle (ΔI / I0) and the macroscopic adsorption capacity (R0). 2 >0.99).

[0080] The above results show that the relative adsorption amount of a single particle characterized by the change in dark field scattered light intensity has a consistent quantitative correspondence with the absolute adsorption amount measured by traditional macroscopic methods, verifying the accuracy and reliability of the method of the present invention. While retaining the intrinsic information of a single particle, the measurement results of the present invention are still comparable in effectiveness to those of macroscopic methods.

Claims

1. A measurement system for single-particle adsorption isotherms, characterized in that, include: Dark-field optical imaging system, used to acquire dark-field images of sample particles; A miniature gas flow cell is used to contain sample particles and control their atmospheric environment. The miniature gas flow cell is provided with an inlet, an outlet, and an optically transparent window. The optically transparent window is used for the optical path of the dark-field optical imaging system. Temperature control system, used to control the temperature of sample particles; A gas path control system is used to regulate the type and partial pressure of the gas introduced into the micro gas flow cell; The signal acquisition and processing system is connected to the dark field optical imaging system and is used to acquire dark field images and calculate the changes in the intensity of scattered light from the sample particles, thereby constructing adsorption isotherms.

2. The measurement system for single-particle adsorption isotherms according to claim 1, characterized in that, The dark-field optical imaging system includes an inverted optical microscope equipped with a dark-field condenser, a CCD camera, and an adjustable illumination source.

3. The measurement system for single-particle adsorption isotherms according to claim 1, characterized in that, The micro gas flow cell has a layered sealed structure, consisting of a transparent cap, a gasket, and a substrate from top to bottom. The gasket has an air inlet and an air outlet. An optically transparent window is formed between the transparent cap and the substrate. The substrate is used to hold sample particles, and electrodes for heating are deposited on the substrate.

4. The measurement system for single-particle adsorption isotherms according to claim 3, characterized in that, The electrode is an I-shaped gold thin film electrode, which is electrically connected to the temperature control system.

5. The measurement system for single-particle adsorption isotherms according to claim 4, characterized in that, The temperature control system includes an electrochemical workstation, which heats the sample particles by applying a DC voltage to the gold thin film electrode and utilizing the Joule heating effect.

6. A method for measuring single-particle adsorption isotherms, characterized in that, The measurement system for single-particle adsorption isotherms according to any one of claims 1-5 includes the following steps: (1) The sample is ultrasonically dispersed in a solvent to form a suspension. The suspension is dropped into the optically transparent window of the micro gas flow cell. After the solvent evaporates, a sparsely distributed array of single particles is formed. Pretreatment is performed to completely remove the water molecules pre-adsorbed in the pores of the sample particles. (2) Under the condition that the partial pressure of the target gas is zero, the dark field image of the sample particles is acquired by the dark field optical imaging system to obtain its baseline scattered light intensity I0; (3) Introduce a mixed gas containing the target gas into the micro gas flow cell, control the partial pressure of the target gas to a set value, and continuously collect dark field images of the sample particles during the adsorption equilibrium process to obtain the real-time scattered light intensity I. (4) Calculate the relative change in scattered light intensity ΔI / I0 based on the real-time scattered light intensity I and the baseline scattered light intensity I0, where ΔI=I-I0, and use the relative change in scattered light intensity ΔI / I0 as the index of the relative adsorption amount of the sample particles under the partial pressure of the target gas. (5) Change the partial pressure of the target gas and repeat steps (3) to (4) to obtain the relative adsorption capacity index under multiple partial pressures; (6) Construct an adsorption isotherm of a single sample particle with the partial pressure of the target gas as the abscissa and the relative adsorption amount index as the ordinate.

7. The method for measuring single-particle adsorption isotherms according to claim 6, characterized in that, The particle spacing of the sample particles in step (1) is greater than 10 μm.

8. The method for measuring single-particle adsorption isotherms according to claim 6, characterized in that, The specific steps of the pretreatment in step (1) are as follows: High-purity nitrogen gas is introduced into the micro gas flow cell at a flow rate of 3 ml / min, and DC voltage is applied to the gold thin film electrode to rapidly heat the sample to 100°C and keep it at a constant temperature for 10 minutes to completely remove the pre-adsorbed water molecules in the sample particle pores. The voltage is then cut off, heating is stopped, and the temperature is continuously purged with nitrogen gas to cool down to 30°C and stabilized for 10 minutes.

9. The method for measuring single-particle adsorption isotherms according to claim 6, characterized in that, In steps (2) and (3), when acquiring dark field images through the dark field optical imaging system, a CCD camera is used to continuously acquire multiple frames of images at a set frame rate, and the position of the individual sample particles is automatically identified and its scattered light intensity is extracted through the image processing program, the relative change in scattered light intensity is calculated, and an adsorption isotherm is constructed.

10. The method for measuring single-particle adsorption isotherms according to claim 9, characterized in that, The image processing program includes the following steps during operation: The acquired dark-field images are binarized to separate particles from the background; The location of individual sample particles was identified and marked using a connected component labeling algorithm; The average pixel grayscale value of the region where the particle is located is extracted as the scattered light intensity; Calculate the relative change in scattered light intensity and construct an adsorption isotherm.

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