CN114674879A - Method for judging adsorption rate control step based on electrochemical impedance spectrum - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 48
- 238000001453 impedance spectrum Methods 0.000 title claims abstract description 14
- 238000002791 soaking Methods 0.000 claims abstract description 48
- 239000000463 material Substances 0.000 claims abstract description 38
- 239000003344 environmental pollutant Substances 0.000 claims abstract description 37
- 231100000719 pollutant Toxicity 0.000 claims abstract description 37
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 49
- 239000007772 electrode material Substances 0.000 claims description 35
- 238000009792 diffusion process Methods 0.000 claims description 22
- 238000010586 diagram Methods 0.000 claims description 15
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 12
- 238000000157 electrochemical-induced impedance spectroscopy Methods 0.000 claims description 10
- 238000005259 measurement Methods 0.000 claims description 10
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- 239000000356 contaminant Substances 0.000 claims description 6
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 claims description 6
- 239000003792 electrolyte Substances 0.000 claims description 6
- 229910052697 platinum Inorganic materials 0.000 claims description 6
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- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 3
- 239000006230 acetylene black Substances 0.000 claims description 3
- 238000001035 drying Methods 0.000 claims description 3
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- 229910021607 Silver chloride Inorganic materials 0.000 claims description 2
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Abstract
The invention provides a method for simply, clearly, directly and accurately judging the adsorption rate control step. The method comprises the steps of preparing an adsorption material into a working electrode by adopting an electrochemical three-electrode system, soaking the working electrode in a solution containing a target pollutant, carrying out electrochemical impedance spectrum test on the soaked adsorption material, solving the time for adsorbing the target pollutant by the electrode according to the parameters of the electrochemical impedance spectrum, and determining the adsorption rate control step according to the adsorption time. The method realizes accurate judgment of the adsorption rate control step, and provides a foundation for research of the adsorption mechanism of the material and improvement of the adsorption performance.
Description
Technical Field
The invention relates to the field of removing target pollutants by using an adsorption method, in particular to a method for judging an adsorption rate control step based on an electrochemical impedance spectrum.
Background
Due to the increasing population and environmental pollution of the world, more and more areas around the world are facing shortages of water resources, and further food production and human diseases. The existing methods for treating wastewater mainly comprise a chemical precipitation method, an oxidation-reduction method, an ion exchange method, a biological treatment method, an adsorption method and the like. Compared with other technologies, the adsorption method is a mature and simple wastewater treatment technology, has low energy consumption, and is particularly suitable for a water treatment system with large quantity and low concentration.
The effect of the adsorption method mainly depends on the aperture, specific surface area, surface functional groups and the like of the adsorption material, so that the adsorption of target pollutants by the adsorption material is usually influenced by three steps of internal diffusion, external diffusion and chemical bond adsorption, the slowest of the three steps is a rate control step, and the whole adsorption process is determined, namely the adsorption rate control step can be divided into diffusion control and adsorption control.
At present, the adsorption control step can be preliminarily determined through experimental data dynamics fitting, however, the dynamics fitting can be influenced by various factors, other means or methods are needed to be assisted to comprehensively determine the rate control step, and then even if the experimental data and the dynamics model are well fitted, the adsorption control step cannot be intuitively revealed, and moreover, the adsorption dynamics fitting needs a large amount of experimental data and consumes a large amount of manpower, financial resources and time.
In view of the above, there is a need to provide a method for determining an adsorption rate control step based on electrochemical impedance spectroscopy, which solves or at least alleviates the above-mentioned problems of poor intuitiveness of conventional fitting and large data dependence.
Disclosure of Invention
The invention mainly aims to provide a method for judging an adsorption rate control step based on an electrochemical impedance spectrum, and aims to solve the problems of poor fitting intuitiveness and large data dependence of the traditional method.
In order to achieve the above object, the present invention provides a method for determining an adsorption rate control step of an adsorbent material based on electrochemical impedance spectroscopy, comprising the steps of:
s1, providing N parts of electrode material and N parts of soak solution, wherein N is more than or equal to 2; each part of the electrode material has the same content of the adsorption material to be detected; the soak solution contains target pollutants corresponding to the adsorption capacity of the adsorption material to be detected, and the concentrations of the target pollutants of N parts of soak solution are different;
s2, respectively and independently soaking the electrode materials into each soaking solution correspondingly;
s3, measuring the electrochemical impedance spectrum of each part of the electrode material after soaking in a three-electrode system; wherein the electrolyte adopted by the three-electrode system contains the target pollutant;
s4, obtaining the parameter omega of each electrode material according to the measurement resultoAnd the parameter ω; wherein, the ω isoThe angular frequency corresponding to an impedance angular peak or an inductive reactance angular valley in the baud diagram is shown, and omega is the characteristic angular frequency of the maximum response of the imaginary part of the electrochemical impedance complex plane diagram;
s5, calculating the tau value of each electrode material according to a formula I and a formula II, and then calculating the ratio of any two tau values;
wherein, the first formula is:
the second formula is:
s6, judging the adsorption rate control step of the adsorption material according to the ratio; when each ratio is smaller than a preset threshold value, judging that the adsorption rate control step of the adsorption material to be detected for adsorbing the target pollutant is adsorption control; and when at least one of the ratios is not less than the preset threshold value, judging that the adsorption rate control step of the adsorption material to be detected for adsorbing the target pollutant is diffusion control.
Further, the preparation process of the electrode material comprises the following steps:
mixing the adsorbing material to be detected with acetylene black and polyvinylidene fluoride, and then mixing with methyl-2-pyrrolidone to obtain a mixture; and sequentially carrying out pressing treatment and drying treatment on the mixture to obtain the electrode material.
Further, the working electrode in the three-electrode system comprises the electrode material, the counter electrode comprises one of a platinum electrode, a lead electrode, a titanium electrode, a graphite electrode and a carbon electrode, and the reference electrode comprises one of a saturated calomel electrode, a mercurous sulfate electrode and a silver/silver chloride electrode.
Further, the soaking time of each part of the electrode material is consistent, and the soaking time is 5-300 min.
Further, the N is 2-6, and the concentration of the target pollutant in the soaking solution is selected from 0-M g/L; and M is the corresponding target pollutant concentration when the adsorption material to be detected reaches adsorption saturation in the relationship of initial concentration-equilibrium adsorption capacity.
Further, the concentration difference between each soaking solution is not less than M/20-M/10.
Further, the working electrode potentials in the three-electrode system range from open circuit potentials to polarization potentials.
Further, the working electrode potential in the three-electrode system is a polarization potential.
Further, the preset threshold value is 8-12.
Further, the target contaminant includes one or more of an anion, a cation, and an organic.
In the invention, the adsorption course of the adsorption material for the pollutants is as follows: the contaminants are mass transferred to the adsorbent interface by diffusion and then chemically or physically adsorbed. When the adsorption material is soaked in the solution for a certain time in advance, the adsorption material is saturated. The adsorption material with saturated adsorption is prepared into an electrode and applied with voltage, and mass transfer driving can be increased by continuously increasing the applied voltage. Changing the concentration of the soak solution can improve the concentration gradient of the target pollutant and increase the mass transfer drive. Tau values are different, which shows that the adsorption time can be effectively shortened by increasing the mass transfer drive, and the mass transfer (diffusion) belongs to the control step; the tau value is not different, which shows that the increase of the mass transfer driving has no influence on the adsorption time, and the adsorption belongs to the control step.
Compared with the prior art, the invention has the following advantages:
1. the method for judging the adsorption rate control step is simpler and more effective and is easy to realize; and the temperature is not required to be changed for carrying out the experiment, so that the experiment difficulty is reduced, the experiment content is reduced, and the experiment flow is shortened.
2. The method is simple, clear, direct and accurate, and the adsorption rate control step can be determined by solving the time for the electrode material to adsorb a target pollutant again.
3. The method has wide application range, and can be widely used for judging the adsorption process of various adsorption materials and target pollutants.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a schematic flow chart of the adsorption rate determining control step in the present invention;
FIG. 2 is a graph showing the effect of chloride ion adsorption data of activated carbon at different temperatures in comparative example 1.
The implementation, functional features and advantages of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Moreover, the technical solutions in the embodiments of the present invention may be combined with each other, but it is necessary to be based on the realization of the technical solutions by those skilled in the art, and when the technical solutions are contradictory to each other or cannot be realized, such a combination of the technical solutions should not be considered to exist, and is not within the protection scope claimed by the present invention.
When numerical ranges are given in the examples, it is understood that both endpoints of each of the numerical ranges and any value therebetween can be selected unless the invention otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and the description of the present invention, and any methods, apparatuses, and materials similar or equivalent to those described in the examples of the present invention may be used to practice the present invention.
Referring to fig. 1, the method for determining the adsorption rate control step based on electrochemical impedance spectroscopy of the present invention includes the following core steps:
s1, providing N parts of electrode material and N parts of soak solution, wherein N is more than or equal to 2; each part of the electrode material has the same content of the adsorption material to be detected; the soak solution contains target pollutants corresponding to the adsorption capacity of the adsorption material to be detected, and the concentrations of the target pollutants of N parts of soak solution are different;
the selection of the soaking concentration needs to be determined according to the actual conditions of the adsorbing material to be detected and the target pollutant, for example: the upper limit of the soaking concentration can be the concentration of the target pollutant corresponding to the adsorption saturation degree of the adsorption material to be detected, and specifically can be the concentration of the target pollutant corresponding to the adsorption saturation degree of the adsorption material to be detected in the experiment of the relationship between different initial concentrations of the target pollutant and the equilibrium adsorption capacity of the adsorption material at normal temperature and normal pressure.
S2, respectively and independently soaking the electrode materials into each part of the soaking solution;
s3, measuring the electrochemical impedance spectrum of each part of the electrode material after soaking in a three-electrode system; wherein the electrolyte adopted by the three-electrode system contains the target pollutant; the electrode material is used as a working electrode in a three-electrode system.
S4, obtaining the parameter omega of each electrode material according to the measurement resultoAnd a parameter ω; wherein, the ω isoThe angular frequency corresponding to an impedance angular peak or an inductive reactance angular valley in the baud diagram is shown, and omega is the characteristic angular frequency of the maximum response of the imaginary part of the electrochemical impedance complex plane diagram;
and S5, calculating the tau value of each electrode material according to the first formula and the second formula, and then calculating the ratio of any two tau values. Of course, in this process, only the ratio of not less than 1 may be retained; or sequencing the concentration of the soaking solution from small to large according to gradient, then sequencing the tau value corresponding to each soaking solution in sequence corresponding to the sequence of the soaking solution, and reserving the ratio of the two tau values after sequencing.
Wherein, the first formula is:
the second formula is:
s6, judging the adsorption rate control step of the adsorption material according to the ratio; when each ratio is smaller than a preset threshold value, judging that the adsorption rate control step of the adsorption material to be detected for adsorbing the target pollutant is adsorption control; and when at least one of the ratios is not less than the preset threshold value, judging that the adsorption rate control step of the adsorption material to be detected for adsorbing the target pollutant is diffusion control.
It should be understood by those skilled in the art that the application of voltage can improve the mass transfer driving, and therefore, the determination process of the present invention needs to be performed under the condition of electrochemical reaction, so as to more effectively determine the adsorption rate control step of the adsorption material to be detected and the target pollutant in the action process, and the determination process can be applied to various scenarios of electro-adsorption and non-electro-adsorption. In addition, in the present invention, a portion of the electrode material is soaked with the soaking solution of each concentration alone, thereby achieving the correspondence of the soaking solution concentration to each τ value. Of course, a plurality of parallel tests can be performed, that is, a plurality of soaking solutions with each concentration are provided, and one electrode material corresponds to a plurality of electrode materials, so that the test accuracy is improved.
Alternatively, the same electrode material can be subjected to repeated tests, for example: firstly, obtaining a tau value of a certain electrode material under the condition of specific soaking concentration, then changing the concentration of the soaking solution, and then testing the tau value, thereby obtaining the tau corresponding to different soaking solution concentrations.
As a preferred embodiment, in the present invention, the electrochemical impedance can be performed by increasing the soaking time and selecting the polarization potential. Mainly because: when the soaking time is longer and the potential of electrochemical impedance measurement is polarization potential, the difference of tau is more obvious, and the influence of soaking concentration change on tau can be reflected better.
As an explanation of the electrode material, reference may be made to the preparation process of the activated carbon electrode (working electrode) in the present invention, specifically:
1. uniformly mixing the activated carbon, acetylene black and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:0.5:1.5, then adding 0.4mL of 1-methyl-2-pyrrolidone, and uniformly stirring to obtain a mixture.
2. After uniformly stirring, cold-pressing the mixture into an electrode with the thickness of 0.5cm in a circular grinding tool with the diameter of 13mm under the pressure of 30 MPa; then drying the mixture for 10 hours at the temperature of 110 ℃ for standby.
3. The prepared electrode is bonded with a copper wire with the diameter of 2-3mm, and AB glue is fixed and coated on the surface of the electrode (except the surface parallel to the counter electrode).
Wherein, the working electrode adopted in the invention is the activated carbon electrode, the diameter is 1.3cm, and the working electrode is polished by 1200-mesh sand paper in a test; the counter electrode is a platinum electrode, and 1200# metallographic abrasive paper and 0.5 micron alumina powder are used for polishing; the reference electrode is a saturated calomel electrode.
The following details are given to the physical meaning of τ and the calculation formula derivation:
in the present invention, the physical meaning of τ is defined as: the time, s (units), required for adsorbing one more contaminant on the surface of the electrode on which the target contaminant has been adsorbed.
To facilitate a more detailed understanding of the present invention by those skilled in the art, the derivation of τ is now set forth as follows:
the target pollutant is adsorbed on the electrode and has inductive reactance response, and the process impedance of the surface of the electrode is expressed by formula (1)
In the formula: cdIs an electric double layer differential capacitance, F; rtIs the charge transfer resistance, Ω; r0The equivalent resistance, omega, caused by the adsorption of the target pollutant on the surface of the electrode; l is equivalent inductance generated by target pollutant adsorption, H cm2(ii) a Omega is angular frequency, rad s-1。
In general, the relaxation time constant τ due to adsorption is larger than the electric double layer charging time constant, and therefore:
is obtained by the above formula
L＞＞RtCd(Rt+R0)＞RtCdR0 (3)
Substituting the formula (3) into the formula (1) to obtain:
and (4) deducing an electrochemical impedance complex plane diagram of the electrode material for adsorbing the target pollutant according to the formula (4).
1) In the high frequency region, ω → ∞ and the terms in equation (4) that do not contain ω can be omitted, and equation (4) is simplified to equation (5)
Formula (5) shows the high frequency region Cl-The impedance response of the charge transfer reaction occurs, and equation (5) is a semicircle in the high frequency region in the complex plane.
2) Low frequency region, ω → 0, formula (4) contains ω2Can be omitted, equation (4) reduces to equation (6):
the above formula is arranged to obtain
Equation (7) shows that in the low frequency region, the complex plane diagram of the process impedance of the electrode surface is a semicircle of the fourth quadrant, and is the inductive reactance response. The complex plan view of electrochemical impedance obtained by the formula is composed of a capacitive reactance arc and an inductive reactance arc.
Thus, a can be solved by the following formula
In the formula: theta is the coverage of the target pollutant adsorbed on the electrode; omegaoWhen the state variable theta is adopted, the angular frequency corresponding to the impedance angular peak or the inductive reactance angular valley in the baud diagram; ω is the characteristic angular frequency of the imaginary maximum response of the electrochemical impedance complex plane plot when the state variable is θ. OmegaoAnd ω from the bode plot and the electrochemistry, respectivelyAnd obtaining an impedance complex plane diagram.
The definition is as follows:
in the formula, H is the change rate of the coverage degree theta:
thus define
The following specifically shows the effect of the electrode potential on τ:
before the electrochemical impedance spectrum measurement, the activated carbon electrode is soaked in Cl in advance-Concentration 1.0g L-1In the solution with pH of 2.0, the activated carbon electrode is enabled to adsorb Cl in advance-And the adsorption time is 120min, and after the reaction is finished, the electrochemical impedance spectroscopy is carried out.
Electrochemical impedance spectroscopy measurement is carried out by adopting a three-electrode system, the anode is a self-made activated carbon electrode, the diameter of the electrode is 1.3cm, the counter electrode is a platinum electrode, the reference electrode is a saturated calomel electrode, and the electrolyte is 1.0g L-1Cl-containing pH of 2.0-And (3) solution.
The control anode potential was: open circuit potential, 0.9V, 1.2V, 1.5V. Under different anode potentials, the characteristic angular frequency omega of the imaginary part maximum response of the electrochemical impedance complex plane diagram and the angular frequency omega corresponding to the inductive reactance valley of the baud diagramoCan be obtained according to electrochemical impedance spectroscopy, and the tau result under different anode potentials can be obtained by calculation, and is shown in table 1.
TABLE 1 Effect of Anode potential on τ
As shown in Table 1, the anode potential was increased so that Cl was adsorbed-Then adsorbing a Cl on the surface of the activated carbon-The time required was shortened, indicating that the adsorption rate was increased by increasing the anode potential.
The effect of the soaking period on τ is specified below:
before the electrochemical impedance spectrum measurement, the activated carbon electrode is soaked in Cl in advance-Concentration 1.0g L-1Adsorbing Cl in the solution with pH of 2.0 by the activated carbon electrode-The adsorption time is respectively 30min, 60min, 120min and 180min, and after the reaction is finished, the electrochemical impedance spectroscopy measurement is carried out.
Electrochemical impedance spectroscopy measurement is carried out by adopting a three-electrode system, the anode is a self-made activated carbon electrode, the diameter of the electrode is 1.3cm, the counter electrode is a platinum electrode, the reference electrode is a saturated calomel electrode, and the electrolyte is 1.0g L-1Cl-containing pH of 2.0-The anode potential of the solution was controlled to 1.5V.
Characteristic angular frequency omega of imaginary part maximum value response of electrochemical impedance complex plane diagram and angular frequency omega corresponding to inductive reactance valley of baud diagramoCan be obtained according to electrochemical impedance spectrum, and tau under different soaking time lengths can be obtained by calculation, and the specific result is shown in table 2.
TABLE 2 Effect of electrode soak time on τ
As shown in Table 2, Cl increased with increasing pre-soaking time of the activated carbon electrode-After having adsorbed Cl-Further adsorbing a Cl on the surface of the electrode-The time required increased significantly, indicating that as the soaking time increased, Cl-The adsorption rate of (a) is slower because the closer to equilibrium the lower the adsorption rate, the longer the soaking time the closer to equilibrium.
Example 1
Calculation of Cl adsorption of activated carbon Material-The adsorption rate control step of (2):
it is to be understood that the above-described,in combination with the above analysis, the polarization potential and the longer soaking time can shorten τ, so that the polarization potential and the longer soaking time can make the difference of τ more obvious. In view of this, the anode potential adopted in this embodiment is 1.5V, and the soaking time is 3 hours; in addition, in this embodiment, the adsorbing material to be detected is activated carbon, and the target pollutant is Cl-。
Electrochemical impedance spectrum measurement is carried out by adopting a three-electrode system, the anode is a self-made activated carbon electrode (working electrode), the diameter of the electrode is 1.3cm, the counter electrode is a platinum electrode, the reference electrode is a saturated calomel electrode, and the electrolyte is 1.0g L-1Cl-containing pH of 2.0-And (3) solution.
Before electrochemical measurement, multiple parts of activated carbon electrodes are taken, and each part of activated carbon electrodes is independently soaked in each part of soaking solution, wherein the pH of each part of soaking solution is 2.0, and Cl in the soaking solution-The concentrations are respectively 1.5g L-1、2.0g L-1、3.0g L-1、4.0g L-1The soaking time is 3 hours.
After soaking, each activated carbon electrode is respectively placed in a three-electrode system for electrochemical impedance spectrum measurement, and the anode potential is controlled to be 1.5V.
Characteristic angular frequency omega of maximum response of imaginary part of electrochemical impedance complex plane diagram and angular frequency omega corresponding to inductive reactance angle valleyoCan be obtained according to electrochemical impedance spectroscopy, and the tau results under different anode potentials can be obtained by calculation, and specific numerical values are shown in table 3.
TABLE 3 influence of initial concentration of the soaking solution on τ
As shown in Table 3, Cl was added to the soaking solution-Under the condition of concentration, the change of soaking concentration has no obvious influence on tau, which shows that the active carbon has no obvious influence on Cl when different concentrations are adsorbed in advance-Do not differ much (the ratio between τ is less than 10). Due to the Cl on the surface of the activated carbon-Is already close to saturation, so increasing the adsorption driving force to accelerate diffusion is not obviousObviously improves the equilibrium adsorption quantity, shows that Cl-The adsorption rate is less than the diffusion rate and is the rate control step of the adsorption process.
Comparative example 1
Dynamic experiment verifies that activated carbon material electrically adsorbs Cl-The adsorption rate control step of (2):
the following tests were carried out at temperatures of 288K (15 ℃), 303K (30 ℃), 313K (40 ℃) and 323K (50 ℃): adopting a three-dimensional electrode reaction device, taking 42g of granular activated carbon as anode filling, and circularly introducing 500mL of active carbon with the concentration of 1000 mg.L-1NaCl solution at pH 2.0 and electrochemical adsorption was performed at an electrode potential of 1.2V.
Sampling at different time nodes, and measuring the Cl of the effluent by ion chromatography after the reaction is finished-Content and calculating the equilibrium adsorption quantity.
Respectively adopting a first-stage dynamic model and a second-stage dynamic model to carry out Cl treatment at different temperatures-Adsorption equilibrium data on activated carbon were fitted and the results are shown in table 4.
From table 4, compared with the second-order kinetics, the fitting degree of the first-order kinetic equation is above 0.9751, and the correlation coefficient of the fitting of the first-order kinetic model is higher, which indicates that the first-order kinetic model is suitable for describing the process, but the control step of the whole reaction process cannot be determined. Therefore, further fitting of the model of internal diffusion and external diffusion is required, and the relevant parameters obtained by fitting the model of internal diffusion and external diffusion are shown in table 5.
TABLE 4 adsorption of Cl by activated carbon electrodes at different temperatures-First and second order dynamics fitting parameters of
TABLE 5 kinetic parameters of the internal and external diffusion models
BNThe inner diffusion is better than the outer diffusionA criterion of diffusion, when BNAbove 100, the adsorption process is mainly controlled by the internal diffusion mechanism. As can be seen from Table 5, B was obtainedNAre all greater than 100, indicating out-diffusion to Cl-Migration is not of interest and intra-particle diffusion may determine the step of the rate.
However, as shown in FIG. 2, the experiment of the effect of temperature on the adsorption capacity of activated carbon in this example shows that the adsorption capacity gradually decreases as the temperature increases. This is because the diffusion process is endothermic and the adsorption process is exothermic, resulting in diminished electrosorption capacity as the solution temperature increases, i.e. intraparticle diffusion is not the only mechanism of action and adsorption is the primary mechanism for rate limiting.
On the basis, the consistency of the adsorption rate control step calculated in example 1 and that in comparative example 1 is demonstrated, and therefore, compared with the adsorption rate control step determined by a kinetic experiment, the method provided by the invention is simpler, clearer, more direct and has higher accuracy.
In the above technical solutions, the above are only preferred embodiments of the present invention, and the technical scope of the present invention is not limited thereby, and all the technical concepts of the present invention include the claims of the present invention, which are directly or indirectly applied to other related technical fields by using the equivalent structural changes made in the content of the description and the drawings of the present invention.
Claims (10)
1. A method for determining an adsorption rate control step based on electrochemical impedance spectroscopy, comprising the steps of:
s1, providing N parts of electrode material and N parts of soak solution, wherein N is more than or equal to 2; each part of the electrode material has the same content of the adsorption material to be detected; the soak solution contains target pollutants corresponding to the adsorption capacity of the adsorption material to be detected, and the concentrations of the target pollutants of N parts of soak solution are different;
s2, respectively and independently soaking the electrode materials into each soaking solution correspondingly;
s3, measuring the electrochemical impedance spectrum of each part of the electrode material after soaking in a three-electrode system; wherein the electrolyte adopted by the three-electrode system contains the target pollutant;
s4, obtaining the parameter omega of each electrode material according to the measurement resultoAnd the parameter ω; wherein, the ω isoThe angular frequency corresponding to an impedance angular peak or an inductance angular valley in the bode diagram is shown, and omega is the characteristic angular frequency of the maximum value response of the imaginary part of the electrochemical impedance complex plane diagram;
s5, calculating the tau value of each electrode material according to a formula I and a formula II, and then calculating the ratio of any two tau values;
wherein, the first formula is:
the second formula is:
s6, judging the adsorption rate control step of the adsorption material according to the ratio; when each ratio is smaller than a preset threshold value, judging that the adsorption rate control step of the adsorption material to be detected for adsorbing the target pollutant is adsorption control; and when at least one of the ratios is not less than the preset threshold value, judging that the adsorption rate control step of the adsorption material to be detected for adsorbing the target pollutant is diffusion control.
2. The method of determining an adsorption rate control step according to claim 1, wherein the preparation process of the electrode material comprises:
mixing the adsorbing material to be detected with acetylene black and polyvinylidene fluoride, and then mixing with methyl-2-pyrrolidone to obtain a mixture; and sequentially carrying out pressing treatment and drying treatment on the mixture to obtain the electrode material.
3. The method of determining an adsorption rate control step of claim 1, wherein the working electrode in the three-electrode system comprises the electrode material, the counter electrode comprises one of a platinum electrode, a lead electrode, a titanium electrode, a graphite electrode, and a carbon electrode, and the reference electrode comprises one of a saturated calomel electrode, a mercurous sulfate electrode, and a silver/silver chloride electrode.
4. The method for determining an adsorption rate control step according to claim 1, wherein the soaking time is uniform for each of the electrode materials, and the soaking time is 5 to 300 min.
5. The method for determining an adsorption rate control step of claim 1, wherein N is 2 to 6, and the concentration of the target contaminant in the soaking solution is selected from 0 to Mg/L; and M is the corresponding target pollutant concentration when the adsorption material to be detected reaches adsorption saturation in the relationship of initial concentration-equilibrium adsorption capacity.
6. The method for determining the adsorption rate control step according to claim 5, wherein the concentration difference between each soaking solution is not less than M/20-M/10.
7. The method of determining an adsorption rate controlling step of claim 1, wherein the working electrode potential in the three-electrode system ranges from an open circuit potential to a polarizing potential.
8. The method of determining an adsorption rate controlling step according to claim 7, wherein the working electrode potential in the three-electrode system is a polarization potential.
9. The method of determining a sorption rate control step according to claim 1, wherein the preset threshold value is 8-12.
10. The method of determining an adsorption rate control step of any one of claims 1 to 9, wherein the target contaminant comprises one or more of an anion, a cation and an organic substance.
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