Combined determination method of specific surface area and surface charge density of nano-micron charged particles

Abstract

The present invention relates to the field of performance measurement of nano-micron particles, and in particular to a method for jointly measuring the specific surface area and surface charge density of nano-micron charged particles: preparing H + Saturated sample; the anions corresponding to the two indicator ions are selected as Cl ‑ , A and B are K + 、Na + , Ca 2+ any two ions in the equilibrium system; determine the activity of the indicator ion in the equilibrium system; calculate the concentration of the indicator ion in the equilibrium system; calculate the adsorption amount of the indicator ion on the surface of the nano-micron particle: calculate the surface potential of the nano-micron particle; calculate the surface charge density of the particle; obtain the specific surface area of ​​the particle. When the ion exchange on the particle surface reaches equilibrium, the present invention only needs to determine the concentration of the two indicator ions in the equilibrium solution to directly calculate the specific surface area and surface charge density of the particle.

Description

Technical Field

[0001] The invention relates to the field of performance measurement of nano-micron particles, and in particular to a method for jointly measuring specific surface area and surface charge density of nano-micron charged particles. Background Art

[0002] Specific surface area and surface charge density are the most important surface property parameters of nano-micron particles, and their size is closely related to the particle size, shape, surface defects and pore structure of the particles. The size of specific surface area and surface charge density will have a great influence on many other physical and chemical properties of the material. In many industries, such as graphite, batteries, rare earth, ceramics, alumina, chemical industry and other industries, as well as the research and development, production, analysis and monitoring of high-efficiency powder materials, they have important applications.

[0003] The current method for determining specific surface area and surface charge density based on relative effective charge coefficient has a major drawback, that is, for the same indicator ion, the relative effective charge coefficient of the indicator ion is different in different ion combinations. For example, when the coexisting ions are K + , Ca 2+ and Mg 2+ When, Na + The effective charge coefficients are 0.756, 0.741 and 0.906 respectively. It is very inconvenient in practical application, and the determination principle is not rigorous.

[0004] Therefore, a joint determination method of specific surface area and surface charge density based on a constant absolute effective charge coefficient is urgently needed to overcome the defects of existing determination methods and achieve new breakthroughs in the study of material interface properties. Summary of the invention

[0005] In view of this, the purpose of the present invention is to overcome the above-mentioned defects and provide a method for the joint determination of the specific surface area and surface charge density of nano-micron charged particles based on the absolute effective charge coefficient, so as to realize the joint determination of the specific surface area and surface charge density under liquid phase conditions.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A combined determination method for specific surface area and surface charge density of nano-micron charged particles comprises the following steps:

[0008] S1. Sample pretreatment, preparation of H + Saturated sample;

[0009] S2. Select two indicator ions The corresponding anions are Cl - , the corresponding Cl - and The compound formed is and The indicator ion It is a non-specific adsorption cation, z A and z B is 1 or 2, and is a water-soluble salt; A and B are K + 、Na + , Ca 2+ Any two ions in

[0010] S3. Determine the activity of the indicator ion in the equilibrium system, denoted by a A and a B ;

[0011] S4. Calculate the concentration of the indicator ion in the equilibrium system, denoted as c A and c B , according to c Cl =z A c A +z B c B Calculate the corresponding anion Cl - concentration;

[0012] S5. Substitute the ion concentration measured in step S4 into the following formula to calculate the indicator ion The adsorption amount on the surface of nano-micron particles is recorded as N A and N B :

[0013] N A =(c A 0 –c A )V A 0 / m

[0014] N B =(c B 0 –c B )V B 0 / m

[0015] Where V A 0 and V B 0 They are and The total volume of the ionic solution, in L; c A 0 and c B 0 for and The initial concentration of the ion, in mol / L; m is the mass of the nano-micron particle sample, in g;

[0016] S6. Calculation of surface potential of nano-micron particles

[0017]

[0018] Where R is the gas constant, T is the absolute temperature, F is the Faraday constant, γ A and γ B are the absolute effective charge coefficients of ions A and B, respectively.

[0019] In particular, when When , the above surface potential correction is:

[0020]

[0021] S7. Based on the obtained surface potential, calculate the surface charge density (σ0) of the particles according to the following formula:

[0022] because

[0023] Therefore, in Under the two indicator ion systems, the above formula is expanded to:

[0024]

[0025] Considering the absolute effective charge coefficient of the anion to be 1. Therefore, the final result is:

[0026]

[0027] S8. Further obtain the specific surface area (S) of the particles:

[0028]

[0029] The absolute effective charge coefficient (γ) of the ions is shown in Table 1 below:

[0030] Table 1 Absolute effective charge coefficients of ions

[0031]

[0032] The specific operations of step S1 are:

[0033] S1.1. Weigh a certain mass of the sample to be tested into a centrifuge tube; if more samples need to be prepared, weigh more samples into a large container (such as a 5000mL beaker).

[0034] S1.2. Add 0.10 mol / L HCl solution to a centrifuge tube or beaker at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, tighten the centrifuge tube cover, and shake thoroughly (turn over and shake, about 20 times / min) for 2 minutes; samples in large containers can be stirred with a hanging stirrer for a certain period of time to disperse the sample until there are no lumps (stirring time depends on the degree of dispersion).

[0035] S1.3. Transfer the centrifuge tube containing the particle suspension to be tested after dispersion or the suspension in the large container after dispersion into the centrifuge tube in batches (note that the amount added should not exceed 2 / 3 of the maximum range of the centrifuge tube to avoid overflow during centrifugation), and centrifuge. If the centrifugation is incomplete, increase the speed and time appropriately until the centrifugation is complete, and discard the supernatant after centrifugation;

[0036] S1.4. Repeat S1.2 and S1.3 for 4 times. After the last centrifugation, use pH test paper to test the pH of the supernatant. If pH ≤ 2.00, it means that the sample has been completely deionized. + Saturation; if pH>2.00, continue to add the same volume of 0.10 mol / L HCl solution in S1.2, and increase the number of treatments according to S1.2 and S1.3 until pH≤2.00.

[0037] S1.5. Add pure water to a centrifuge tube or beaker at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, tighten the centrifuge tube cover, and shake thoroughly (turn over and shake, about 20 times / min) for 2 minutes; samples in large containers can be stirred with a hanging stirrer for a certain period of time to disperse the sample until there are no lumps (the stirring time depends on the degree of dispersion).

[0038] S1.6, repeat the operation of step S1.3;

[0039] S1.7. Place the centrifuge tube (containing the sample, with the lid open and the opening facing upward) in an oven at 70°C for drying (the recommended drying time is no less than 24 hours), or transfer all the samples in the centrifuge tube to a mortar (the centrifuge tube can be rinsed with a small amount of pure water, and the suspension after rinsing can be transferred to the mortar), and place the mortar containing the sample in an oven at 70°C for drying (the recommended drying time is no less than 24 hours).

[0040] S1.8. Take out the centrifuge tube or mortar containing the dried sample, grind it until it passes through a 0.25mm sieve after cooling, mix it thoroughly, seal it in a plastic ziplock bag, and store it at room temperature. Grind and sieve the same samples from the same batch together, mix them thoroughly, and put them in the same ziplock bag.

[0041] The specific operation steps of step S3 are:

[0042] S3.1. Weigh a certain mass of sample into the sample cup and add the prepared K+ and Ca 2+ A KOH+Ca(OH)2 mixture with a known initial concentration in a concentration ratio of 1:1 (mix well first and then quickly absorb); the initial concentration is related to the sample weight and the number of charges of the sample to be tested; the added volume is determined by the equilibrium pH of S3.2; after adding the alkali solution, stir on a magnetic stirrer for 10 minutes;

[0043] S3.2, use a pH electrode to measure the pH of the suspension to be tested in S3.1. The initial target pH of the Na / K system is 10.5, and that of the K / Ca and Na / Ca systems is 8.0. If the pH is higher than the initial target value + 0.2, increase the sample volume for adjustment. Stir for 10 minutes after increasing the sample volume. After stirring, test the pH value again. If the pH is still higher than the initial target value + 0.2 at this time, continue to increase the sample volume for stirring. Repeat the above operation until the pH is between the initial target value ± 0.2. Conversely, if the pH value is lower than the initial target value - 0.2, increase the amount of alkali solution for adjustment. Stir for 10 minutes after increasing the amount of alkali solution. After completion, test the pH value again. If the pH value is still lower than the initial target value - 0.2 at this time, continue to increase the amount of alkali solution for stirring. Repeat the above operation until the pH value is between the initial target value ± 0.2.

[0044] S3.3. Based on S3.2, the equilibrium target value is pH 9.8 for the Na / K system; pH 6.0 for the K / Ca and Na / Ca systems; use 0.50 mol / L acetic acid solution to adjust the pH of the suspension to the corresponding equilibrium target value ±0.2.

[0045] S3.4, respectively Ion selective electrode for determination of activity.

[0046] The specific operations of step S4 are:

[0047] S4.1. In the iterative operation, the measured The activity is set to The initial concentration value, i.e. c A (0) = a A , c B (0) = a B , then the first iteration The concentration is:

[0048]

[0049] In the formula π is the circumference of a circle 3.14, F is the Faraday constant 96487C / mol, e0 is the charge of an electron 1.6×10 -19 C, ε is the dielectric constant of water 8.9×10 -10 C2 / (J·dm), R gas is a constant of 8.314 J / (K·mol), T is the system Kelvin temperature (298.15 K at 25°C); I(0) is the initial ionic strength and

[0050] S4.2, calculated according to the first iteration Concentration A (1) and c B (1), and the second iteration is calculated by the following equation:

[0051]

[0052] Where I(1) is the initial ionic strength and

[0053] S4.3, Similarly, repeat the above process until the difference between the nth and n+1th results is [c(n+1)-c(n)] / c(n+1)<0.001. The concentration is the corresponding pH value in the suspension. Concentration, i.e. c A and c B .

[0054] The beneficial effect of the present invention is that when the ion exchange on the particle surface reaches equilibrium, the specific surface area and surface charge density of the particle can be directly calculated by simply measuring the concentrations of the two indicator ions in the equilibrium solution. The method relies on the adsorption of the two indicator ions that do not undergo specific adsorption in the system, and has nothing to do with whether there are other specific adsorbed ions on the surface, and is applicable to any charged substance, such as the surface of a variable charge substance, the surface of a constant charge substance, and a mixture of the two. The ion effective charge coefficient is a constant value and does not change with changes in the ion composition. DETAILED DESCRIPTION

[0055] The specific technical solution of the present invention is explained in conjunction with embodiments.

[0056] The present invention comprises the following steps:

[0057] S1. Sample pretreatment, preparation of H + Saturated sample:

[0058] S1.1. Weigh a certain mass of the sample to be tested into a centrifuge tube.

[0059] S1.2. Add 0.10 mol / L HCl solution into the centrifuge tube at a solid-liquid mass ratio of 1:10. Stir with a glass rod to disperse the sample until there is no lumps. Tighten the cap of the centrifuge tube and shake thoroughly (turn over and shake, about 20 times / min) for 2 minutes.

[0060] S1.3. Place the centrifuge tube containing the dispersed particle suspension into the centrifuge for centrifugation. If the centrifugation is incomplete, increase the speed and time appropriately until the centrifugation is complete, and discard the supernatant after centrifugation.

[0061] S1.4. Repeat S1.2 and S1.3 for 4 times. After the last centrifugation, use pH test paper to test the pH of the supernatant. If pH ≤ 2.00, it means that the sample has been completely deionized. + Saturation; if pH>2.00, continue to add the same volume of 0.10 mol / L HCl solution as in 2), and increase the number of treatments according to S1.2 and S1.3 until pH≤2.00.

[0062] S1.5) Add pure water to the centrifuge tube at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, tighten the centrifuge tube cap, and shake thoroughly (turn over and shake, about 20 times / min) for 2 minutes.

[0063] S1.6. Repeat the operation in step S1.3.

[0064] S1.7. Place the centrifuge tube (containing the sample, with the lid open and the opening facing upward) in an oven and dry it at 70°C (the recommended drying time is no less than 24 hours).

[0065] S1.8. Take out the centrifuge tube containing the dried sample, grind it until it passes through a 0.25 mm sieve after cooling, mix it thoroughly, seal it in a plastic ziplock bag, and store it at room temperature. Grind and sieve the same samples from the same batch together, mix them thoroughly, and put them in the same ziplock bag.

[0066] S2. Select two indicator ions K + , Ca 2+ , the corresponding anion OH - , whose chemical formula is KOH and Ca(OH)2. Ca(OH)2 solution is prepared with saturated solution of Ca(OH)2 and its concentration is calibrated.

[0067] S3. Determine the activity of the indicator ion in the equilibrium system, denoted by a K and a Ca ;

[0068] S3.1. Weigh a certain mass of sample into the sample cup and add the prepared K + and Ca 2+ A KOH+Ca(OH)2 mixture with a known initial concentration of 1:1 (the initial concentration is related to the sample weight and the number of charges of the sample to be tested. Mix well first and then quickly absorb. The added volume is determined by the equilibrium pH of S3.2). After adding alkali solution, stir on a magnetic stirrer for 10 minutes. The initial target pH of the K / Ca system is 8.0.

[0069] S3.2, use a pH electrode to measure the pH of the suspension to be tested in S3.1. If the pH value is higher than 8.2, increase the sample amount for adjustment, stir for 10 minutes after increasing the sample amount, and test the pH value again after stirring. If the pH value is still higher than 8.2 at this time, continue to increase the sample amount and stir, and repeat the above operation until the pH value is between 7.8 and 8.2. On the contrary, if the pH value is lower than 7.8, increase the amount of alkali solution for adjustment, stir for 10 minutes after increasing the amount of alkali solution, and test the pH value again after completion. If the pH value is still lower than 7.8 at this time, continue to increase the amount of alkali solution and stir, and repeat the above operation until the pH value is between 7.8 and 8.2.

[0070] S3.3. Based on S3.2, use 0.50 mol / L acetic acid solution to adjust the suspension equilibrium pH to 5.8-6.2.

[0071] S3.4, respectively use K + , Ca 2+ Determination of K in Suspension by Ion Selective Electrode + , Ca 2+ activity.

[0072] S4. Calculate the concentration of the indicator ion in the equilibrium system, denoted as c K and c Ca , anion Cl - The concentration of c Cl =c K +2c Ca (Note: Due to the low equilibrium pH, the anions in the system are mainly Cl in the HCl solution in the pretreatment - );

[0073] S4.1. In the iterative operation, the measured K + , Ca 2+ The activity is set as K + , Ca 2+ The initial concentration value, i.e. c K (0) = a K , c Ca (0) = a Ca , then the K of the first iteration + , Ca 2+ The concentration is:

[0074]

[0075] In the formula π is the circumference of a circle 3.14, F is the Faraday constant 96487C / mol, e0 is the charge of an electron 1.6×10 -19 C, ε is the dielectric constant of water 8.9×10 -10 C2 / (J·dm), R gas is a constant of 8.314 J / (K·mol), T is the system Kelvin temperature (298.15 K at 25°C); I(0) is the initial ionic strength and

[0076] S4.2. K calculated based on the first iteration + , Ca 2+ Concentration K (1) and c Ca (1), and the second iteration is calculated by the following equation:

[0077]

[0078] Where I(1) is the initial ionic strength and I(1) = c K (1)+3c Ca (1).

[0079] S4.3, Similarly, repeat the above process until the difference between the nth and n+1th results is [c(n+1)-c(n)] / c(n+1)<0.001. At this time, the iteration K + , Ca 2+ The concentration is the K at the corresponding pH in the suspension. + , Ca 2+ Concentration, i.e. c K and c Ca .

[0080] S5. Substitute the ion concentration measured in step S4 into the following formula to calculate the indicator ion K + , Ca 2+ The adsorption amount on the surface of nano-micron particles is recorded as N K and N Ca :

[0081] N K =(c K 0 –c K )V K 0 / m

[0082] N Ca =(c Ca 0 –c Ca )V Ca 0 / m

[0083] Where V K 0 and V Ca 0 Add K + and Ca2+ The total volume of the ionic alkali solution, in this case K + and Ca 2+ is a mixed solution, so V K 0 =V Ca 0 , unit is L; c K 0 and c Ca 0 K + and Ca 2+ The initial alkali concentration is in mol / L; m is the mass of the nano-micron particle sample in g;

[0084] S6. Calculate the surface potential of the system

[0085]

[0086] Where R is the gas constant, T is the absolute temperature, F is the Faraday constant, γ K and γ Ca K + and Ca 2+ The absolute effective charge coefficient.

[0087] In particular, when When , the above surface potential correction is:

[0088]

[0089] S7. Based on the obtained surface potential, calculate the surface charge density (σ0) of the particles according to the following formula:

[0090]

[0091] S8. Further obtain the specific surface area (S) of the particles:

[0092]

[0093] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A combined determination method for specific surface area and surface charge density of nano-micron charged particles, characterized in that: The steps include: S1. Sample pretreatment, preparation of H + Saturated sample; S2. Select two indicator ions The corresponding anions are Cl - , the corresponding Cl - and The compound formed is and The indicator ion It is a non-specific adsorption cation, z A and z B is 1 or 2, and is a water-soluble salt; A and B are K + 、Na + , Ca 2+ Any two ions in S3. Determine the activity of the indicator ion in the equilibrium system, denoted by a A and a B ; S4. Calculate the concentration of the indicator ion in the equilibrium system, denoted as c A and c B , according to c Cl =z A c A +z B c B Calculate the corresponding anion Cl - concentration; S5. Substitute the ion concentration measured in step S4 into the following formula to calculate the indicator ion The adsorption amount on the surface of nano-micron particles is recorded as N A and N B : N A =(c A 0 -c A )V A 0 / m N B =(c B 0 -c B )V B 0 / m Where V A 0 and V B 0 They are and The total volume of the ionic solution, in L; c A 0 and c B 0 for and The initial concentration of the ion, in mol / L; m is the mass of the nano-micron particle sample, in g; S6. Calculation of surface potential of nano-micron particles Where R is the gas constant, T is the absolute temperature, F is the Faraday constant, γ A and γ B are the absolute effective charge coefficients of ions A and B, respectively; when When , the above surface potential correction is: S7. According to the obtained surface potential, the surface charge density σ0 of the particles is calculated according to the following formula: ε is the dielectric constant of water; S8. Further obtain the specific surface area S of the particles:

2. The combined determination method of specific surface area and surface charge density of nano-micron charged particles according to claim 1, characterized in that: Step S1 includes the following sub-steps: S1.

1. Weigh the sample to be tested into a container; S1.

2. Add 0.10 mol / L HCl solution into the container at a solid-liquid mass ratio of 1:10 and shake well to mix; S1.3, transfer the suspension in the container containing the particle suspension to be tested into centrifuge tubes in batches, put them into a centrifuge for centrifugation, and discard the supernatant after centrifugation; S1.

4. Repeat S1.2 and S1.3 for 4 times. After the last centrifugation, use pH test paper to test the pH of the supernatant. If pH ≤ 2.00, it means that the sample has been completely deionized. + Saturation; if pH>2.00, continue to add the same volume of 0.10 mol / L HCl solution in S1.2, and increase the number of treatments according to S1.2 and S1.3 until pH≤2.00; S1.

5. Add pure water into the container at a solid-liquid mass ratio of 1:10 to disperse the sample until there is no agglomeration; S1.6, repeat the operation of step S1.3; S1.

7. Place the container in an oven and dry it at 70°C, or transfer all the samples in the container to a mortar and place the mortar with the samples in an oven and dry it at 70°C; S1.

8. Take out the container or mortar containing the dried sample, cool it down, grind it until all of it passes through a 0.25 mm sieve, and mix it thoroughly.

3. The combined determination method of specific surface area and surface charge density of nano-micron charged particles according to claim 1, characterized in that: Step S3 includes the following sub-steps: S3.

1. Weigh a certain mass of sample into the sample cup and add the prepared K + and Ca 2+ A KOH+Ca(OH)2 mixture with a known initial concentration in a concentration ratio of 1:1 is first mixed and then quickly aspirated; the initial concentration is related to the sample weight and the number of charges of the sample to be tested; the added volume is determined by the equilibrium pH of S3.2; after adding the alkali solution, stir on a magnetic stirrer for 10 minutes; S3.2, use a pH electrode to measure the pH of the suspension to be tested in S3.

1. If the pH is higher than the initial target value +0.2, increase the sample amount for adjustment. Stir for 10 minutes after increasing the sample amount. After stirring, test the pH value again. If the pH is still higher than the initial target value +0.2 at this time, continue to increase the sample amount and stir. Repeat the above operation until the pH is between the initial target value ±0.2; conversely, if the pH value is lower than the initial target value -0.2, increase the amount of alkali solution for adjustment. Stir for 10 minutes after increasing the amount of alkali solution. After completion, test the pH value again. If the pH value is still lower than the initial target value -0.2 at this time, continue to increase the amount of alkali solution and stir. Repeat the above operation until the pH value is between the initial target value ±0.2; S3.3, based on S3.2, adjust the pH of the suspension to the equilibrium target value ± 0.2 with 0.50 mol / L acetic acid solution; S3.4, respectively Ion selective electrode for determination of activity.

4. The combined determination method of specific surface area and surface charge density of nano-micron charged particles according to claim 1, characterized in that: Step S4 includes the following sub-steps: S4.

1. In the iterative operation, the measured The activity is set to The initial concentration value, i.e. c A (0) = a A , c B (0) = a B , then the first iteration The concentration is: In the formula π is the circumference of a circle 3.14, F is the Faraday constant 96487C / mol, e0 is the charge of an electron 1.6×10 -19 C, ε is the dielectric constant of water 8.9×10 -10 C 2 / (J·dm), R gas is a constant of 8.314 J / (K·mol), T is the system temperature in Kelvin; I(0) is the initial ionic strength and S4.2, calculated according to the first iteration Concentration A (1) and c B (1), and the second iteration is calculated by the following equation: Where I(1) is the initial ionic strength and S4.3, repeat the iterative operation until the difference between the nth and n+1th results is [c(n+1)-c(n)] / c(n+1)<0.

001. The concentration is the corresponding pH value in the suspension. Concentration, i.e. c A and c B .

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