CN104897508B - A method for testing thermodynamic parameters of functional materials - Google Patents

Abstract

The invention relates to a method for testing thermodynamic parameters of a functional material, which comprises the steps of using a resonant micro-cantilever as a micro-mass sensor, loading the functional material on the free end of the resonant micro-cantilever, testing the adsorption quantity of the functional material to gases with different pressures at a specific temperature in real time to obtain an adsorption isotherm of the functional material, further calculating the thermodynamic parameters of the functional material, and evaluating the characteristics of the functional material according to the obtained thermodynamic parameters; the method is advanced, has practical application significance, and has the characteristics of easy operation and low cost.

Description

A method for testing thermodynamic parameters of functional materials

technical field

The invention relates to a method for testing thermodynamic parameters of materials by a temperature-variable weighing method, in particular to the testing and calculation of thermodynamic parameters of functional materials by resonant micro-cantilever beams, and belongs to the field of evaluation of adsorption characteristics of functional materials.

Background technique

The research on the adsorption direction, mode, and capacity of functional materials on gas molecules plays an important role in many fields such as public safety, environmental protection, and food safety. For example, in order to reduce the content of greenhouse gases such as carbon dioxide (CO ₂ ) in the atmosphere, it is necessary to study new adsorbent materials with a large adsorption capacity for CO ₂ and certain selectivity; Safety, it is necessary to study new materials with specific adsorption and low cost for organic phosphorus and other pesticides; for example, in order to manufacture high-performance sensors that can specifically respond to trace pesticide residues in vegetables and other agricultural products, it is urgent to understand sensitive Adsorption properties of materials for pesticide molecules. The above research fields all need to evaluate the thermodynamic properties of functional materials such as the adsorption direction, method, and capacity of gases.

Foreign literature reports have used thermodynamic parameters to evaluate the _CO adsorption properties of new materials (such as metal-organic framework compounds) (Nature, 2013, 495, 80-84). However, this type of research is based on large-scale equipment such as gas adsorption instruments, Monte Carlo calculation simulations, quartz balances, and magnetic levitation balances, which have disadvantages such as high test prices, large amounts of materials, and a single variety of test gases.

The invention points out that the resonant micro-cantilever beam can be used as a micro-mass sensor to measure the adsorption amount of a material to a specified pressure gas in real time at a constant temperature, thereby obtaining characteristic parameters such as the adsorption (or desorption) direction, mode, and capacity of the material. The invention has positive significance to the fields of evaluation of the adsorption (or desorption) characteristics of functional materials and the like, and broadens the application field of the resonant micro-cantilever beam.

Contents of the invention

The purpose of the present invention is to overcome the defects of the prior art and provide a method for testing the thermodynamic parameters of functional materials. In order to apply the resonant micro-cantilever beam to the specific evaluation field of adsorption and desorption of functional materials, the method is advanced and has practical application Meaningful, easy to operate, and inexpensive.

The present invention is achieved through the following technical solutions:

A method for testing thermodynamic parameters of functional materials, which uses a resonant micro-cantilever beam as a micro-mass sensor, loads functional materials on the free end of the resonant micro-cantilever beam, and tests the adsorption capacity of the functional material to gases at different pressures at a specific temperature in real time , to obtain the adsorption isotherm of the functional material, and then further calculate the thermodynamic parameters of the functional material, and evaluate the characteristics of the functional material based on the obtained thermodynamic parameters.

The functional material is selected from mesoporous materials, polymers, carbon nanotubes, graphene and the like.

The resonant micro-cantilever is an integrated piezoresistive silicon-based micro-cantilever.

The mass sensitivity of the resonant micro-cantilever is 1.53 Hz/pg. Among them, Hz is the frequency unit, 1pg=10 ^{- 12} g.

The thermodynamic parameters include enthalpy change, entropy change, Gibbs free energy change, adsorption/desorption equilibrium constant, and coverage.

The objects of the characteristic evaluation of the functional material include adsorption direction, desorption direction, adsorption method, adsorption capacity and the like.

A method for testing thermodynamic parameters of functional materials, specifically comprising the following steps:

(1) Coating: use the micro-operating system to coat the dispersion of functional materials on the free end of the resonant micro-cantilever beam, dry and set aside;

(2) Aging: Place the resonant micro-cantilever coated with functional materials in a test pool capable of stabilizing the temperature, and age stably under high-purity nitrogen flow;

(3) Perform a baseline test: fix the flow rate of the gas, continuously feed high-purity nitrogen, and record the frequency of the resonant micro-cantilever;

(4) Sensitivity curve test: At a constant temperature, keep the same gas flow rate as in step (3), continuously feed a mixture of adsorption gas and nitrogen gas of known concentration for adsorption, and collect the frequency of the resonant micro-cantilever in real time, until After the frequency remains unchanged, the same flow rate of high-purity nitrogen is continuously introduced for purging and desorption, and the frequency of the resonant micro-cantilever is collected in real time until the frequency remains unchanged; then the concentration of the adsorbed gas in the mixed gas introduced is changed, and repeated The above test process; at this temperature, the sensitivity curve of the frequency of the resonant micro-cantilever varies with the concentration of the adsorbed gas;

(5) Adjust the temperature of the test cell to another constant temperature, repeat step (4), and obtain another sensitive curve of the frequency of the resonant micro-cantilever changing with the concentration of the adsorbed gas at another temperature;

(6) According to the mass sensitivity of the resonant micro-cantilever, the sensitivity curve obtained in steps (4) and (5) is converted into an adsorption isotherm curve: that is, the relationship curve between the gas adsorption amount and the pressure at a constant temperature;

(7) Calculate the adsorption enthalpy change ΔH° according to the adsorption isotherm curve and the Clausius-Clapeyron equation;

(8) Take any adsorption isotherm curve and transform it into a relational curve of p/V and p, and obtain the adsorption equilibrium constant K and standard equilibrium constant K° from the intercept and slope of the curve;

(9) According to the value of K, the coverage θ under the specific adsorbed gas partial pressure is obtained by the Langmuir equation;

(10) According to K° and the test temperature of the adsorption isotherm curve obtained in step (8), the Gibbs free energy change ΔG° is obtained from the Van't Hoff equation;

(11) According to the values of Gibbs free energy change ΔG° and adsorption enthalpy change ΔH°, the entropy change ΔS° is obtained from the definition formula of Gibbs free energy change.

in,

Preferably, the solvent of the dispersion liquid of the functional material is selected from deionized water, ethanol, tetrahydrofuran and the like.

Preferably, the concentration of the functional material in the dispersion of the functional material is 1-50 mg/mL; the coating amount on the free end of the resonant micro-cantilever is 0.01-1 microliter.

Preferably, the drying temperature in step (1) is 60-100°C, more preferably 80°C.

Preferably, in step (2), the stable aging time is 1-5 days, more preferably 3 days.

Preferably, the frequency is collected using a commercial frequency meter, preferably an American Agilent 5313A frequency meter.

In step (7), the calculation method of the adsorption enthalpy change ΔH° is to randomly select two numerical points with the same coverage θ from the two adsorption isotherms whose temperatures are denoted as T ₁ and T ₂ respectively, denoted as (p ₁ , θ) and (p ₂ , θ), and then calculate ΔH° according to the Clausius-Clapeyron equation. Unless otherwise specified, T in the present invention refers to temperature, p refers to pressure, and θ refers to adsorption coverage.

The Clausius-Clapeyron equation is as follows:

or its integral form:

In step (8), the relationship curve between p/V and p is the Langmuir equation:

p/V=p/V _∞ +(KV _∞ ) ^-1 (Ⅲ)

Among them, K is the adsorption equilibrium constant, and the standard equilibrium constant K° is obtained by calculating the relational formula of K°=K×p°;

Among them, p° refers to the standard pressure, that is, p°=101325 Pa, and its approximate value is taken in actual calculation Pa.

V refers to the volume under standard conditions when the adsorption gas partial pressure is p; V _∞ refers to the volume under the standard conditions when the functional material reaches saturated adsorption conditions, and the gas adsorption is converted into the volume under standard conditions, then the coverage θ=V /V∞.

The said standard conditions refer to the conditions where the temperature is 0°C (273.15K) and the pressure is 101.325 kPa (1 standard atmosphere, 760 mmHg).

In step (10), the Van't Hoff equation is:

ΔG°=-RTlnK° (Ⅳ)

In step (11), the definition formula of the Gibbs free energy change is:

ΔG°=ΔH°-TΔS° (Ⅴ)

Technical scheme described in the present invention can also be:

An application of a resonant micro-cantilever in testing the thermodynamic parameters of functional materials, in order to use the resonant micro-cantilever as a micro-mass sensor, load the functional material on the free end of the resonant micro-cantilever, and test the functional material in real time at a specific temperature. The adsorption capacity of gases at different pressures is obtained to obtain the adsorption isotherm of the functional material, and then the thermodynamic parameters of the functional material are further calculated; then the characteristics of the functional material can be evaluated by the obtained thermodynamic parameters; specifically, the following steps are included:

(1) Coating: apply the dispersion of functional materials on the free end of the resonant micro-cantilever beam by using a micro-operating system, dry it, and set aside;

(2) Aging: Place the resonant micro-cantilever coated with functional materials in a test pool capable of stabilizing the temperature, and age stably under high-purity nitrogen flow;

(3) Perform a baseline test: fix the flow rate of the gas, continuously feed high-purity nitrogen, and record the frequency of the resonant micro-cantilever;

(4) Sensitivity curve test: At a constant temperature, keep the same gas flow rate as in step (3), continuously feed a mixture of adsorption gas and nitrogen gas of known concentration for adsorption, and collect the frequency of the resonant micro-cantilever in real time, until After the frequency remains unchanged, the same flow rate of high-purity nitrogen is continuously introduced for purging and desorption, and the frequency of the resonant micro-cantilever is collected in real time until the frequency remains unchanged; then the concentration of the adsorbed gas in the mixed gas introduced is changed, and repeated The above test process; at this temperature, the sensitivity curve of the frequency of the resonant micro-cantilever varies with the concentration of the adsorbed gas;

(5) Adjust the temperature of the test cell to another constant temperature, repeat step (4), and obtain another sensitive curve of the frequency of the resonant micro-cantilever changing with the concentration of the adsorbed gas at another temperature;

(6) According to the mass sensitivity of the resonant micro-cantilever, the sensitivity curve obtained in steps (4) and (5) is converted into an adsorption isotherm curve: that is, the relationship curve between the gas adsorption amount and the pressure at a constant temperature;

(7) Calculate the adsorption enthalpy change ΔH° according to the adsorption isotherm curve and the Clausius-Clapeyron equation;

(8) Take any adsorption isotherm curve and transform it into a relational curve of p/V and p, and obtain the adsorption equilibrium constant K and standard equilibrium constant K° from the intercept and slope of the curve;

(9) According to the value of K, the coverage θ under the specific adsorbed gas partial pressure is obtained by the Langmuir equation;

(10) According to K° and the test temperature of the adsorption isotherm curve obtained in step (8), the Gibbs free energy change ΔG° is obtained from the Van't Hoff equation;

(11) According to the values of Gibbs free energy change ΔG° and adsorption enthalpy change ΔH°, the entropy change ΔS° is obtained from the definition formula of Gibbs free energy change.

The evaluation described in the present invention is based on the usual physical and chemical theory of matter. The absolute value of the adsorption enthalpy change ΔH ° value is less than 40kJ/mol and belongs to physical adsorption, and greater than 80kJ/mol belongs to chemical adsorption, and the value between the two belongs to difficult Defined forces (such as hydrogen bonds, etc.), so as to judge the adsorption form of materials for special gases.

The technical effects and advantages of the present invention are: applying the resonant micro-cantilever beam to the field of adsorption (desorption) characteristic evaluation of functional materials, the method is advanced, has practical application significance, is easy to operate, and is cheap.

Description of drawings

Figure 1 (a1) Transmission electron micrograph of carboxyl-functionalized mesoporous nanoparticles

(a2) Time-frequency response curve of resonant microcantilever loaded with carboxyl-functionalized mesoporous nanoparticles (298K)

(a3) Time-frequency response curve of resonant microcantilever loaded with carboxyl-functionalized mesoporous nanoparticles (318K)

(a4) Adsorption isotherms of carboxyl-functionalized mesoporous nanoparticles for trimethylamine gas (298K, 318K)

(b1) Transmission electron micrograph of sulfonic acid functionalized mesoporous nanoparticles

(b2) Time-frequency response curve of resonant microcantilever loaded with sulfonic acid functionalized mesoporous nanoparticles (298K)

(b3) Time-frequency response curve of resonant microcantilever loaded with sulfonic acid functionalized mesoporous nanoparticles (318K)

(b4) Adsorption isotherms of trimethylamine gas on sulfonic acid functionalized mesoporous nanoparticles (298K, 318K)

(c1) Transmission electron micrograph of unmodified mesoporous nanoparticles

(c2) Time-frequency response curve of resonant microcantilever loaded with unmodified mesoporous nanoparticles (298K)

(c3) Time-frequency response curve of resonant microcantilever loaded with unmodified mesoporous nanoparticles (318K)

(c4) Adsorption isotherms of unmodified mesoporous nanoparticles for trimethylamine gas (298K, 318K)

The functionalized hyperbranched polymer molecular structure diagram described in Fig. 2 embodiment 2

Fig. 3(a) Time-frequency response curve of resonant microcantilever loaded with functionalized hyperbranched polymer (283K)

(b) Time-frequency response curve of resonant microcantilever loaded with functionalized hyperbranched polymer (298K)

(c) Adsorption isotherms of functionalized hyperbranched polymers on DMMP (dimethyl methylphosphonate) (283K, 298K)

Detailed ways

The technical solutions of the present invention are illustrated below through specific examples. It should be understood that one or more method steps mentioned in the present invention do not exclude that there are other method steps before and after the combined steps or other method steps can be inserted between these explicitly mentioned steps; it should also be understood that these The examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. Moreover, unless otherwise stated, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the sequence of each method step or limit the scope of the present invention. The change or adjustment of its relative relationship is in In the case of no substantive change in the technical content, it shall also be regarded as the applicable scope of the present invention.

Example 1: Evaluation of the Adsorption Characteristics of Three Kinds of Mesoporous Nanoparticles to Trimethylamine

(1) Synthesis of three mesoporous nanoparticles samples

① Three kinds of mesoporous nanoparticles refer to: a. carboxyl functionalized mesoporous nanoparticles; b. sulfonic acid functionalized mesoporous nanoparticles; C. unmodified mesoporous nanoparticles

②For the synthesis method of carboxyl-functionalized mesoporous nanoparticles, please refer to the patent application: Manufacturing method of carboxyl-functionalized mesoporous nanoparticles with helical channels (patent application number: 201210306247.7).

③The synthesis method of sulfonic acid functionalized mesoporous nanoparticles is the same as that described in the document (patent application number: 201210306247.7), but the reagent trihydroxysilyl acetate sodium solution is replaced by 2-(4-chlorosulfonylphenyl)ethyl trimethoxy silane [English name is 2-(4-Chlorosulfonylphenyl)ethyltrimethoxy silane, 50wt% dichloromethane solution], and other reaction conditions are the same, and the sulfonic acid functionalized mesoporous nanoparticles can be obtained.

④ The synthesis method of unmodified mesoporous nanoparticles is the same as that described in the document (patent application number: 201210306247.7), but without using an aqueous solution of sodium trihydroxysilyl acetate, and other reaction conditions are the same, unmodified mesoporous nanoparticles can be obtained.

⑤ Transmission electron micrographs of three kinds of mesoporous nanoparticles are shown in Fig. 1 (a1), (b1), (c1);

(2) Sample preparation (loading mesoporous nanoparticles on the free end of the integrated piezoresistive silicon-based micro-cantilever to form a micro-load sensor) and aging:

① Pre-disperse three kinds of mesoporous nanoparticles (both with a weight of about 10 mg) in 1 ml of deionized water to prepare three dispersions of mesoporous nanoparticles;

②Using a microscopic operating system, apply 1 microliter of the dispersion of mesoporous nanoparticles to the free end of the resonant microcantilever, dry at 80°C, and set aside;

③ Place the resonant micro-cantilever beam coated with mesoporous nanoparticle material in a test cell with a constant temperature function, and age it stably under high-purity nitrogen flow for 3 days;

(3) Test (taking carboxyl functionalized mesoporous nanoparticles as an example)

① Baseline test: Under the high-purity nitrogen gas flow, the frequency of the resonant micro-cantilever (the free end of which is loaded with carboxyl-functionalized mesoporous nanoparticles) was recorded with a commercial frequency meter;

②Sensitivity curve test at a temperature of 298K (25°C): at a temperature of 298K, 90ppb (ppb refers to a volume concentration of one part per billion) of trimethylamine gas is injected, and the frequency of the resonant microcantilever is collected in real time. After the frequency remains constant, a nitrogen flow is introduced to desorb the carboxyl-functionalized mesoporous nanoparticles adsorbed with trimethylamine gas. After the frequency of the resonant micro-cantilever remains constant, adjust the concentration of trimethylamine gas to 180ppb. Repeat the test to obtain the frequency data of the micro-cantilever beam in the gas atmosphere of this concentration; using this method, adjust the concentration of trimethylamine gas to 360ppb and 900ppb respectively, and test the frequency of the resonant micro-cantilever beam under these two concentrations data. Thus, at the temperature of 298K, the real-time test curve of the frequency of the micro-cantilever changing with the concentration of trimethylamine gas is obtained (as shown in Figure 1 (a2));

③Adjust the temperature of the test pool to 318K, and according to the test process of step ②, obtain another real-time test curve of the frequency of the resonant micro-cantilever changing with the concentration of trimethylamine gas at 318K (as shown in Figure 1 (a3));

④ Using the same method, fix the temperature of the test chamber at 298K and 318K respectively, and obtain the real-time test curve of the frequency of the resonant microcantilever supported by sulfonic acid functionalized mesoporous nanoparticles with the concentration of trimethylamine gas (as shown in Figure 1 (b2) and (b3));

⑤ Using the same method, fix the temperature of the test chamber at 298K and 318K respectively, and obtain the real-time test curve of the frequency of the unmodified mesoporous nanoparticle-loaded resonant microcantilever corresponding to the change of the gas concentration of trimethylamine (as shown in Figure 1 ( c2) and (c3));

(4) Calculation of thermodynamic parameters and evaluation of adsorption characteristics

① Draw the isotherm curve: according to the mass sensitivity of the resonant microcantilever, convert the test curve (shown in (a2) and (a3), (b2) and (b3), (c2) and (c3) in Figure 1) into adsorption Isotherm curves (respectively shown in (a4), (b4) and (c4) in Figure 1); the adsorption isotherm curve is the relationship curve between the adsorption amount of trimethylamine gas and the pressure at a constant temperature;

②Calculation of enthalpy change (ΔH°): draw a horizontal line randomly and intersect with two adsorption isotherms, and the two intersection points are the partial pressure values of trimethylamine under the same coverage. As shown in (a4) in Figure 1, the partial pressure of trimethylamine at 298K is 18 mPa, and the partial pressure of trimethylamine at 318K is 90 mPa, and the corresponding partial pressure and temperature values are brought into Clausius- Clapeyron equation

That is to say, the adsorption enthalpy change ΔH° of carboxyl-functionalized mesoporous nanoparticles to trimethylamine can be calculated as -63.4kJ/mol. Using the same method, the adsorption enthalpy change ΔH° of sulfonic acid functionalized mesoporous nanoparticles to trimethylamine can be calculated as -149.6kJ/mol; the adsorption enthalpy change ΔH° of unmodified mesoporous nanoparticles to trimethylamine is -23.0kJ /mol.

③ Calculation of other thermodynamic parameters (entropy change, Gibbs free curve (energy change, adsorption/desorption equilibrium constant and coverage) of carboxyl-functionalized mesoporous nanoparticles: transform an adsorption isotherm into p/V and p Among them, p is the partial pressure of the gas, V is the volume of the adsorbed gas under the corresponding partial pressure p converted into standard conditions), according to the Langmuir equation

p/V=p/V _∞ +(KV _∞ ) ^-1 ,

The adsorption equilibrium constant K=63Pa ^-1 was obtained from the intercept and slope of the curve. Since the present invention only involves gas-solid two-phase adsorption reactions (specifically referring to the adsorption of a gaseous substance on the surface of a solid substance to produce another solid substance with gas adsorbed on its surface), the standard equilibrium constant K°=K ×p° (p° refers to the standard pressure, that is, p°=101325 Pa, take its approximate value in actual calculation Pa), that is, K°=63×10 ⁵ =6.3×10 ⁶ . Since the coverage of the material surface is different under different gas partial pressures before reaching saturated adsorption, it is necessary to calculate the coverage at a specified partial pressure. According to the adsorption/desorption equilibrium constant K=63Pa ^-1 and the specified partial pressure (such as p=9×10 ^-3 Pa), another form of the Langmuir equation

θ=Kp/(1+Kp),

Find the coverage θ=0.36. According to the Van't Hoff equation ΔG°=-RTlnK°, where the temperature T is 298K from the isotherm curve in Figure 1 (a4), and K°=6.3×10 ⁶ is substituted, the Gibbs freedom of the adsorption process can be calculated Energy change ΔG°=-38.8kJ·mol ^-1 . Finally, from the definition of Gibbs free energy change ΔG°=ΔH°-TΔS°, the entropy change ΔS°=-82.6J·K ^-1 can be obtained.

④ Adsorption characteristic evaluation: Physical and chemical theory generally believes that the absolute value of the adsorption enthalpy change ΔH° is less than 40kJ/mol, which belongs to physical adsorption, and greater than 80kJ/mol belongs to chemical adsorption, and the value between the two belongs to the force that is difficult to define (such as hydrogen bonds, etc.). Therefore, according to the calculated adsorption enthalpy change ΔH° value, it can be known that trimethylamine molecules are adsorbed on the surface of carboxyl-functionalized mesoporous nanoparticles by hydrogen bonding, and adsorbed on the surface of sulfonic acid mesoporous nanoparticles by chemical adsorption. Adsorption mode Adsorption on the surface of unmodified mesoporous nanoparticles. Among them, carboxyl-functionalized mesoporous nanoparticles have a certain selective adsorption to trimethylamine and can be desorbed, and are suitable for use as sensitive materials for amine gases; sulfonic acid-functionalized mesoporous nanoparticles have strong Adsorption, and it is difficult to desorb after adsorption, suitable for use as an adsorbent for amine gases.

Example 2: Functionalized hyperbranched polymer (its synthesis method is the same as that of the document Chem.Mater.2004, 16, 5357-5364, and the molecular structure diagram of the functionalized hyperbranched polymer as shown in Figure 2) simulates organophosphorus Evaluation of the adsorption properties of the agent DMMP (dimethyl methylphosphonate):

(1) Sample preparation (load the functionalized hyperbranched polymer on the free end of the resonant micro-cantilever to form a micro-load sensor) and aging

① Pre-disperse about 10 mg of functionalized hyperbranched polymer in 1 ml of tetrahydrofuran;

②Using a microscopic operating system, apply 1 microliter of tetrahydrofuran dispersion of hyperbranched polymer on the free end of the resonant microcantilever, dry at 80°C, and set aside;

③Place the resonant micro-cantilever coated with functional materials in a test cell with a constant temperature function, and age it stably under a high-purity nitrogen flow for 3 days.

(2) test

① Baseline test: Under high-purity nitrogen flow, use a commercial frequency meter to record the frequency of the resonant micro-cantilever;

②Sensitivity curve test at a temperature of 283K (10°C): at a temperature of 283K, DMMP gas of 80ppb (ppb refers to a volume concentration of one billionth) is introduced to collect the frequency of the resonant micro-cantilever beam in real time. After keeping it constant, a nitrogen flow is introduced to desorb the sensor of the adsorbed gas; after the frequency of the micro-cantilever remains unchanged, adjust the concentration of DMMP gas to 160ppb, repeat the test, and obtain the concentration of the micro-cantilever under the gas atmosphere of this concentration. Using this method, adjust the concentration of DMMP gas to 270ppb and test the frequency data of the resonant microcantilever at this concentration. Thus, at the temperature of 283K, the real-time test curve of the frequency of the micro-cantilever changing with the concentration of DMMP gas was obtained (as shown in Fig. 3(a)).

③Adjust the temperature of the test cell to 298K, and according to the steps in ②, obtain another real-time test curve of the frequency of the micro-cantilever changing with the concentration of DMMP gas at this temperature (as shown in Figure 3(b)).

(3) Calculation of thermodynamic parameters and evaluation of adsorption characteristics

① Draw the isotherm curve: according to the mass sensitivity of the resonant microcantilever, convert the test curve (Figure 3 (a) and (b)) into an adsorption isotherm curve (that is, the relationship between the amount of DMMP gas adsorption and the pressure at a constant temperature, such as Figure 3(c));

②Calculation of enthalpy change (ΔH°): draw a horizontal line randomly and intersect with two adsorption isotherms, and the two intersection points are the partial pressure values of DMMP under the same coverage (as shown in Figure 3(c), 283K The partial pressure of DMMP under 298K is 8 mPa, and the partial pressure of DMMP under 298K is 19.5 mPa), and the corresponding partial pressure value and temperature value are brought into the Clausius-Clapeyron equation to calculate the adsorption enthalpy change ΔH° -41.6kJ/mol;

③Adsorption characteristic evaluation: Physicochemical theory generally believes that the absolute value of the adsorption enthalpy change ΔH° is less than 40kJ/mol belongs to physical adsorption, greater than 80kJ/mol belongs to chemical adsorption, and the value between the two belongs to the force that is difficult to define (such as hydrogen bonds, etc.). Therefore, according to the calculated adsorption enthalpy change ΔH° value (-41.6kJ/mol), it can be seen that DMMP molecules are adsorbed on the surface of functionalized hyperbranched polymers in the form of hydrogen bonds, which has certain selectivity and can be desorbed. , suitable for use as a sensitive material for organophosphorous gases.

Claims (8)

1. A method for testing thermodynamic parameters of functional materials, for using a resonant micro-cantilever as a micro-mass sensor, loading the functional material on the free end of the resonant micro-cantilever, and testing in real time how the functional material responds to gases with different concentrations at a specific temperature The amount of adsorption is obtained to obtain the adsorption isotherm of the functional material, and then the thermodynamic parameters of the functional material are further calculated, and the characteristics of the functional material are evaluated by the obtained thermodynamic parameters. The thermodynamic parameters include enthalpy change, adsorption equilibrium constant, adsorption Equilibrium constant, degree of coverage, Gibbs free energy change and entropy change; Described method comprises the following steps at least: (1) Coating: apply the dispersion of the functional material to the free end of the resonant micro-cantilever beam by using a micro-operating system, dry it, and set aside; (2) Aging: Place the resonant micro-cantilever coated with functional materials in a test pool capable of stabilizing the temperature, and age stably under high-purity nitrogen gas flow; (3) Perform a baseline test: fix the flow rate of the gas, continuously feed high-purity nitrogen, and record the frequency of the resonant micro-cantilever; (4) Sensitivity curve test: at a constant temperature, maintain the same gas flow rate as in step (3), continuously feed a mixture of adsorption gas and nitrogen gas of known concentration for adsorption, and collect the frequency of the resonant micro-cantilever in real time, until After the frequency remains unchanged, the same flow rate of high-purity nitrogen is continuously introduced for purging and desorption, and the frequency of the resonant micro-cantilever is collected in real time until the frequency remains unchanged; then the concentration of the adsorbed gas in the mixed gas introduced is changed, and repeated The above test process; at this temperature, the sensitivity curve of the frequency of the resonant micro-cantilever varies with the concentration of the adsorbed gas; (5) adjust the temperature of the test cell to another constant temperature, repeat step (4), obtain another sensitivity curve that the frequency of the resonant micro-cantilever varies with the concentration of the adsorbed gas at another temperature; (6) According to the mass sensitivity of the resonant micro-cantilever, the sensitivity curve obtained in steps (4) and (5) is converted into an adsorption isotherm: that is, at a constant temperature, the relationship curve between the gas adsorption amount and the pressure; (7) Calculate the adsorption enthalpy change ΔH° according to the adsorption isotherm curve and the Clausius-Clapeyron equation; (8) Take an adsorption isotherm curve arbitrarily, transform it into the relational curve of P/V and P, obtain the adsorption equilibrium constant K and the standard equilibrium constant K° from the intercept and slope of the curve; (9) According to the value of K, the coverage θ under the specific adsorbed gas partial pressure is obtained by the Langmuir equation; (10) According to the test temperature of the adsorption isotherm curve described in K° and step (8), obtain Gibbs free energy and change ΔG° by Van't Hoff equation; (11) According to the values of Gibbs free energy change ΔG° and adsorption enthalpy change ΔH°, the entropy change ΔS° is obtained from the definition formula of Gibbs free energy change. 2. the test method of a kind of functional material thermodynamic parameter as claimed in claim 1, is characterized in that, described functional material is selected from mesoporous material, polymkeric substance, carbon nanotube and graphene. 3. The method for testing thermodynamic parameters of a functional material according to claim 1, wherein the resonant micro-cantilever is an integrated piezoresistive silicon-based micro-cantilever. 4. The method for testing thermodynamic parameters of a functional material according to claim 1, wherein the mass sensitivity of the resonant micro-cantilever is 1.53 Hz/pg. 5. the test method of a kind of functional material thermodynamic parameter as claimed in claim 1, is characterized in that, in the dispersion liquid of described functional material, functional material concentration is 1-50mg/mL; The coating amount of the terminal is 0.01-1 microliter; the solvent of the dispersion liquid of the functional material is selected from deionized water, ethanol and tetrahydrofuran. 6. A method for testing thermodynamic parameters of functional materials as claimed in claim 1, characterized in that, in step (2), the time for the stable aging is 1-5 days. 7. The method for testing the thermodynamic parameters of a functional material according to claim 1, wherein the collection of the frequency uses an American Agilent 5313A frequency meter. 8. The application of a resonant micro-cantilever beam in the thermodynamic parameter testing of functional materials, in order to use the resonant micro-cantilever beam as a micro-mass sensor, load the functional material on the free end of the resonant micro-cantilever beam, and test the functional material at a specific temperature in real time , to obtain the adsorption isotherm of the functional material for the adsorption capacity of gases at different pressures, and then further calculate the thermodynamic parameters of the functional material; then, the characteristic evaluation of the functional material can be performed based on the obtained thermodynamic parameters, which specifically includes the following steps: (1) Coating: apply the dispersion of the functional material to the free end of the resonant micro-cantilever beam by using a micro-operating system, dry it, and set aside; (2) Aging: Place the resonant micro-cantilever coated with functional materials in a test pool capable of stabilizing the temperature, and age stably under high-purity nitrogen gas flow; (3) Perform a baseline test: fix the flow rate of the gas, continuously feed high-purity nitrogen, and record the frequency of the resonant micro-cantilever; (4) Sensitivity curve test: at a constant temperature, maintain the same gas flow rate as in step (3), continuously feed a mixture of adsorption gas and nitrogen gas of known concentration for adsorption, and collect the frequency of the resonant micro-cantilever in real time, until After the frequency remains unchanged, the same flow rate of high-purity nitrogen is continuously introduced for purging and desorption, and the frequency of the resonant micro-cantilever is collected in real time until the frequency remains unchanged; then the concentration of the adsorbed gas in the mixed gas introduced is changed, and repeated The above test process; at this temperature, the sensitivity curve of the frequency of the resonant micro-cantilever varies with the concentration of the adsorbed gas; (5) adjust the temperature of the test cell to another constant temperature, repeat step (4), obtain another sensitivity curve that the frequency of the resonant micro-cantilever varies with the concentration of the adsorbed gas at another temperature; (6) According to the mass sensitivity of the resonant micro-cantilever, the sensitivity curve obtained in steps (4) and (5) is converted into an adsorption isotherm: that is, at a constant temperature, the relationship curve between the gas adsorption amount and the pressure; (7) Calculate the adsorption enthalpy change ΔH° according to the adsorption isotherm curve and the Clausius-Clapeyron equation; (8) Take an adsorption isotherm curve arbitrarily, transform it into a relational curve of p/V and p, obtain the adsorption equilibrium constant K and the standard equilibrium constant K° from the intercept and slope of the curve; (9) According to the value of K, the coverage θ under the specific adsorbed gas partial pressure is obtained by the Langmuir equation; (10) According to the test temperature of the adsorption isotherm curve described in K° and step (8), obtain Gibbs free energy and change ΔG° by Van't Hoff equation; (11) According to the values of Gibbs free energy change ΔG° and adsorption enthalpy change ΔH°, the entropy change ΔS° is obtained from the definition formula of Gibbs free energy change.