Iodine adsorbent, its preparation method and application

Abstract

The application discloses an iodine adsorbent and a preparation method and application thereof, and specifically comprises the following steps: (1) dissolving cyclodextrin and sodium hydroxide in water and ultrasonically dissolving to obtain a mixed solution; (2) adding an organic solvent into the mixed solution, ultrasonically oscillating, centrifuging and collecting the precipitate; and (3) ultrasonically washing the precipitate with ethanol, drying, grinding and obtaining the iodine adsorbent. The iodine adsorbent prepared by the application has excellent adsorption capacity, large porosity, low cost, can be quickly and massively synthesized, has high adsorption rate and is beneficial to efficient treatment of iodine; and the preparation method is simple in steps, convenient in operation and low in cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorbents, and more particularly to an iodine adsorbent, a preparation method and application thereof. BACKGROUND

[0002] With the growing demand for energy worldwide, nuclear energy has become a popular choice due to its high efficiency and environmental friendliness. However, the radioactive waste and spent nuclear fuel generated by nuclear power plants pose potential environmental risks, especially long-term exposure to radioactive iodine, which can cause thyroid disease and cancer and other health problems. Due to the long half-life of these substances and their potential harm to human health, global scholars are increasingly concerned about how to effectively capture and dispose of discharged radioactive iodine to prevent possible dangerous effects. Therefore, it is urgent to find practical and effective solutions to ensure that the use of nuclear energy does not pose potential threats to our health and the environment.

[0003] Currently, the two main methods for treating volatile iodine are wet scrubbing and solid adsorption. Among them, wet scrubbing involves the use of mercury or iodine reduction methods, but these methods require the use of large amounts of toxic and highly corrosive chemicals or expensive chemical-resistant equipment. In contrast, the solid adsorption method is considered more promising due to its simplicity, efficiency, and low pollution. Previous studies have discussed various solid adsorbents in the literature, including activated carbon, zeolites, silver-exchanged zeolites, and organic or inorganic hybrid materials. Activated carbon is cost-effective and stable in acidic or alkaline environments, but due to its unique chemical and physical properties, activated carbon has a low ignition temperature and is not suitable for use in oxygen-rich and high-temperature environments. Zeolites and silver-impregnated zeolites are popular adsorbents in industry due to their excellent thermal stability and ability to capture iodine, although zeolites have many advantages, they are also affected by nitrogen oxides and organic compounds, which affect their adsorption performance. In addition, considering the high adsorption temperature of radioactive iodine and its high kinetic energy, it is essential to use adsorbents that can form strong interactions with iodine molecules. Therefore, the efficient, green, and economical removal of radioactive iodine (I2) has attracted worldwide attention for the safe development of nuclear energy.

[0004] Metal-organic frameworks (MOFs) have received much attention in recent years due to their high porosity and tunable pore size characteristics, which have been widely pursued in gas storage, catalysis, and chemical sensing. In particular, as a potential solution for hydrogen energy, MOFs are considered to have the potential to provide good hydrogen adsorption capacity due to their large surface area and tunable pore structure. In terms of environmental protection, MOFs are also considered to be effective in treating hazardous waste such as heavy metals, uranium, and radioactive iodine (e.g. 129 I and 131The potential candidate material of I) is a MOF. The environmental and health risks caused by long half-life of radioactive iodine make effective disposal of nuclear waste a difficult problem to be solved urgently. Traditional materials have limitations in limited adsorption capacity and interaction sites for capturing radioactive iodine, while MOFs have high adsorption of iodine, good thermal stability and high repeatability. Therefore, synthesizing MOFs with adjustable structure and excellent performance for this purpose becomes an important exploration direction. These MOFs are expected to become an important tool for more effective and sustainable disposal of toxic nuclear waste.

[0005] Therefore, how to further study MOFs with higher adsorption capacity, selectivity, rapid mass synthesis and low cost is a problem to be solved by those skilled in the art. SUMMARY

[0006] Therefore, the purpose of the present application is to provide a cyclodextrin MOF adsorbent for efficient capture of iodine and a room temperature rapid preparation method and application thereof, aiming to solve the problem of iodine adsorption and prevent the danger related to radioactive iodine.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of an iodine adsorbent, specifically comprising the following steps:

[0009] (1) Dissolve cyclodextrin and sodium hydroxide in water, ultrasonically dissolve to obtain a mixed solution;

[0010] (2) Add an organic solvent to the mixed solution, ultrasonically shake, centrifuge and collect the precipitate;

[0011] (3) Ultrasonically wash the precipitate with ethanol, dry and grind to obtain the iodine adsorbent.

[0012] Further, in the above step (1), the cyclodextrin is γ-cyclodextrin (γ-CD); the ratio of the amount of cyclodextrin, sodium hydroxide and water is 1.25 mmol:(7.5-12.5) mmol:(20-30) mL.

[0013] The above further beneficial effect is that it is found through research that the γ-cyclodextrin sodium MOF adsorbent synthesized from cyclodextrin and sodium hydroxide has strong affinity for iodine.

[0014] Further, in the above step (2), the organic solvent is N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), ethanol (EtOH) or methanol (MeOH); the ratio of the amount of the mixed solution and the organic solvent is 8 mL:(20-30) mL; the ultrasonic shaking time is 1-10 min.

[0015] The further beneficial effect of the above is that the product (sodium γ-cyclodextrin MOF adsorbent) of the present application is insoluble in organic solvents, so that the product can be quickly precipitated from the solution by adding an organic solvent. By ultrasonic shaking, the reaction system can be quickly and fully mixed, and compared with manual shaking, the ultrasonic shaking operation is simple, more sufficient and controllable.

[0016] Further, in the above step (3), the ultrasonic washing is performed for 3 times, each time for 5-15 min; the drying temperature is 60-80 DEG C, and the time is 8-12 h; and the grinding is performed to a particle size of 1-4 mu m.

[0017] The further beneficial effect of the above is that by ultrasonic washing, the residual organic solvent and unreacted raw material in the sodium γ-cyclodextrin MOF adsorbent can be washed away. Meanwhile, the sodium γ-cyclodextrin MOF adsorbent will be caked at room temperature after washing and drying, and the grinding can expose more adsorption sites of the sodium γ-cyclodextrin MOF adsorbent, thereby improving the dispersibility of the product.

[0018] The present application also claims a iodine adsorbent prepared by the above preparation method.

[0019] The present application also claims the application of the iodine adsorbent prepared by the above preparation method in capturing iodine.

[0020] A gas phase adsorption and desorption treatment method of the iodine adsorbent prepared by the above preparation method, specifically comprising the following steps:

[0021] (1) the iodine adsorbent is added into a glass vial, and then is placed into a sample bottle containing iodine, sealed, and adsorbed;

[0022] (2) after the adsorption is completed, the desorption is performed.

[0023] Further, in the above step (1), the dosage ratio of the iodine adsorbent to iodine is (50-55) mg:200 mg; the sealing is performed by using tin paper plus a screw cap; the adsorption temperature is 65-85 DEG C, preferably 75 DEG C; and the adsorption time is 1-24 h, preferably 6 h.

[0024] Further, in the above step (2), the desorption temperature is 150 DEG C.

[0025] A liquid phase adsorption and desorption treatment method of the iodine adsorbent prepared by the above preparation method, specifically comprising the following steps:

[0026] (1) the iodine adsorbent is added into a solution containing iodine, and adsorbed;

[0027] (2) after the adsorption is completed, the desorption is performed in an ethanol solution.

[0028] Further, in the step (1), the iodine-containing solution is an iodine-containing cyclohexane solution, the iodine content is 50-1000 mg / L; the iodine adsorbent is added in an amount of 0.45-0.5 mg / mL; the adsorption is carried out at room temperature under static condition for 0.5-72 h.

[0029] Compared with the prior art, the present application has the following advantages:

[0030] 1. The present application uses cheap edible γ-cyclodextrin as a raw material for synthesizing iodine adsorbent, which is economical and has a preparation condition of room temperature vibration, uses water and DMA, DMF, ethanol, methanol and other organic solvents as solvents, is energy-saving and environment-friendly, and conforms to the concept of green chemistry.

[0031] 2. The iodine adsorbent of the present application is generated almost instantaneously after adding another solvent, and the iodine adsorbent generated rapidly and in large quantities at room temperature is applied to gas-phase iodine adsorption and liquid-phase iodine adsorption, and has a high adsorption rate and a high adsorption capacity.

[0032] 3. The iodine adsorbent prepared by the present application has excellent adsorption capacity, high porosity, low cost, can be synthesized rapidly and in large quantities, has a high adsorption rate, and is conducive to efficient treatment of iodine. The iodine adsorbent prepared by the present application has extremely excellent iodine adsorption performance at 75℃, the adsorption capacity reaches 1.05 g / g within 2 h, and the equilibrium capacity (6 h) reaches 2.256 g / g; for a relatively low-concentration iodine-containing solution, the adsorption is colorless, and the adsorption rate reaches 87%.

[0033] 4. The preparation method of the present application is simple, easy to operate, and low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 SEM images of the iodine adsorbent prepared in Examples 1-4;

[0035] Figure 2 XRD images of the iodine adsorbent CD-Na-DMA prepared in Example 1 before and after adsorbing iodine;

[0036] Figure 3 Effects of different temperatures on the adsorption capacity of the iodine adsorbent CD-Na-DMA prepared in Example 1 and the iodine adsorbent CD-Na-DMF prepared in Example 2;

[0037] Figure 4 Effects of different times on the adsorption capacity of the iodine adsorbent CD-Na-DMA prepared in Example 1;

[0038] Figure 5 Effects of different times on the adsorption capacity of the iodine adsorbent CD-Na-DMF prepared in Example 2;

[0039] Figure 6Adsorption rate curve of iodine on the iodine adsorbent CD-Na-DMA prepared in Example 1;

[0040] Figure 7 Adsorption amount curve of iodine on the iodine adsorbent CD-Na-DMA prepared in Example 1. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments are clearly and completely described below. Apparently, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0042] Example 1

[0043] The preparation method of the iodine adsorbent specifically comprises the following steps:

[0044] (1) Put 1.25 mmol (1.625 g) of γ-cyclodextrin and 10 mmol (0.4 g) of sodium hydroxide into a beaker, add 24 mL of deionized water, and ultrasonically dissolve to obtain a mixed solution;

[0045] (2) Use a syringe to suck out 8 mL of the mixed solution, and filter into a centrifuge tube through a filter head, add 24 mL of N,N-dimethylacetamide, ultrasonically shake for 10 min, centrifugally separate, and collect the precipitate;

[0046] (3) Ultrasonically wash the precipitate with ethanol for 3 times, each time for 15 min, then put it into an 80℃ oven to dry for 12 h, and grind to a particle size of 1-4 μm, to obtain the iodine adsorbent, which is named as CD-Na-DMA.

[0047] Example 2

[0048] The preparation method of the iodine adsorbent specifically comprises the following steps:

[0049] (1) Put 1.25 mmol (1.625 g) of γ-cyclodextrin and 10 mmol (0.4 g) of sodium hydroxide into a beaker, add 24 mL of deionized water, and ultrasonically dissolve to obtain a mixed solution;

[0050] (2) Use a syringe to suck out 8 mL of the mixed solution, and filter into a centrifuge tube through a filter head, add 24 mL of N,N-dimethylacetamide, ultrasonically shake for 10 min, centrifugally separate, and collect the precipitate;

[0051] (3) Ultrasonically wash the precipitate with ethanol for 3 times, each time for 15 min, then put it into an 80℃ oven to dry for 12 h, and grind to a particle size of 1-4 μm, to obtain the iodine adsorbent, which is named as CD-Na-DMA.

[0052] Example 3

[0053] The preparation method of the iodine adsorbent specifically comprises the following steps:

[0054] (1) Put 1.25 mmol (1.625 g) of γ-cyclodextrin and 10 mmol (0.4 g) of sodium hydroxide into a beaker, add 24 mL of deionized water, and ultrasonically dissolve to obtain a mixed solution;

[0055] (2) Use a syringe to suck out 8 mL of the mixed solution, and filter into a centrifuge tube with a filter head, add 24 mL of ethanol, ultrasonically shake for 10 min, centrifugal separate, and collect the precipitate;

[0056] (3) The precipitate is ultrasonically washed with ethanol for 3 times, each time for 15 min, then put into a 80℃ oven to dry for 12 h, and grind to a particle size of 1-4 μm, to obtain the iodine adsorbent, named as CD-Na-EtOH.

[0057] Example 4

[0058] The preparation method of the iodine adsorbent specifically comprises the following steps:

[0059] (1) Put 1.25 mmol (1.625 g) of γ-cyclodextrin and 10 mmol (0.4 g) of sodium hydroxide into a beaker, add 24 mL of deionized water, and ultrasonically dissolve to obtain a mixed solution;

[0060] (2) Use a syringe to suck out 8 mL of the mixed solution, and filter into a centrifuge tube with a filter head, add 24 mL of methanol, ultrasonically shake for 10 min, centrifugal separate, and collect the precipitate;

[0061] (3) The precipitate is ultrasonically washed with ethanol for 3 times, each time for 15 min, then put into a 80℃ oven to dry for 12 h, and grind to a particle size of 1-4 μm, to obtain the iodine adsorbent, named as CD-Na-MeOH.

[0062] Performance test

[0063] 1. Scanning electron microscope (SEM) image

[0064] The scanning electron microscope (SEM) images of the iodine adsorbents prepared in Examples 1-4 are shown in Figure 1 Fig. 1, wherein, Figure 1 Fig. 1a is a scanning electron microscope (SEM) image of the CD-Na-DMF iodine adsorbent prepared in Example 2, Figure 1 Fig. 1b is a scanning electron microscope (SEM) image of the CD-Na-DMA iodine adsorbent prepared in Example 1, Figure 1 Fig. 1c is a scanning electron microscope (SEM) image of the CD-Na-MeOH iodine adsorbent prepared in Example 4, Figure 1In the image d, we see a scanning electron microscope (SEM) image of the CD-Na-EtOH iodine adsorbent prepared in Example 3.

[0065] Depend on Figure 1 It can be seen that the particle size of the CD-Na-DMF iodine adsorbent prepared in Example 2 is 1 μm, and the crystal shape is mostly spindle-shaped; the particle size of the CD-Na-DMA iodine adsorbent prepared in Example 1 is 2 μm, and the crystal shape is twisted; the particle size of the CD-Na-MeOH iodine adsorbent prepared in Example 4 is 1.5 μm, and the crystal shape is cubic; the particle size of the CD-Na-EtOH iodine adsorbent prepared in Example 3 is 4 μm, and the crystal shape is square plate-like.

[0066] 2. Powder X-ray diffraction (XRD) images

[0067] The CD-Na-DMA iodine adsorbent prepared in Example 1 was subjected to powder X-ray diffraction (XRD) analysis before and after iodine adsorption. The results are as follows: Figure 2 As shown.

[0068] Depend on Figure 2 It can be seen that the CD-Na-DMA iodine adsorbent (before adsorption) prepared in Example 1 has characteristic diffraction peaks at 5.7°, 6.98°, 8.06°, and 16.6°, indicating that the synthesized material has high crystallinity and the preparation was successful.

[0069] At the same time, by Figure 2 It can be seen that the crystallinity of I2@CD-Na-DMA iodine adsorbent (after adsorption) disappears. This is due to the strong binding interaction between a large amount of iodine and CD-Na-DMA adsorbent, which is consistent with the literature.

[0070] 3. Test on the effect of different temperatures on adsorption capacity

[0071] The effects of different temperatures on the adsorption capacity of the CD-Na-DMA iodine adsorbent prepared in Example 1 and the CD-Na-DMF iodine adsorbent prepared in Example 2 were tested. The specific test methods are as follows:

[0072] 50 mg of the CD-Na-DMA iodine adsorbent prepared in Example 1 and the CD-Na-DMF iodine adsorbent prepared in Example 2 were added to glass vials, respectively. These vials were then placed into sample vials containing 200 mg of iodine. The sample vials were sealed with aluminum foil and screw caps. Adsorption was performed under different temperature conditions (65℃, 75℃, 85℃, 95℃, 105℃). After 8 hours, the vials were removed and weighed. The adsorption capacity Q was calculated using the following formula. e (g / g): Q e =(m e -m0) / m0, where m0 is the initial mass of the iodine adsorbent, m eThe mass of the iodine adsorbent after adsorption is shown in the following figure. Figure 3 As shown.

[0073] Depend on Figure 3 It can be seen that, under 75℃ conditions, the CD-Na-DMA iodine adsorbent prepared in Example 1 and the CD-Na-DMF iodine adsorbent prepared in Example 2 exhibit the best adsorption performance for iodine. Therefore, subsequent tests were conducted at 75℃ to test the effect of different time periods on the adsorption capacity.

[0074] 4. Test on the effect of different times on adsorption capacity

[0075] The effect of different time intervals on the adsorption capacity of the CD-Na-DMA iodine adsorbent prepared in Example 1 was tested. The specific test method is as follows:

[0076] 50 mg of the CD-Na-DMA iodine adsorbent prepared in Example 1 was added to a glass vial, which was then placed into a sample vial containing 200 mg of iodine. The sample vial was sealed with aluminum foil and a screw cap, and adsorption was performed at 75°C. The vial was taken out and weighed at regular intervals (0 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h). The adsorption capacity Q was calculated using the following formula. e (g / g): Q e =(m e -m0) / m0, where m0 is the initial mass of the CD-Na-DMA iodine adsorbent, m e The mass of CD-Na-DMA iodine adsorbent after adsorption is shown in the following figures. Figure 4 As shown.

[0077] Depend on Figure 4 It can be seen that, under the condition of 75℃, the CD-Na-DMA iodine adsorbent prepared in Example 1 can adsorb 1.05 g / g of iodine within 2 hours, and the equilibrium adsorption capacity of iodine can reach 2.256 g / g after 6 hours.

[0078] 5. Test on the effect of different times on adsorption capacity

[0079] The effect of different time intervals on the adsorption capacity of the CD-Na-DMF iodine adsorbent prepared in Example 2 was tested. The specific test method is as follows:

[0080] 50 mg of the CD-Na-DMF iodine adsorbent prepared in Example 2 was added to a glass vial, which was then placed into a sample vial containing 200 mg of iodine. The sample vial was sealed with aluminum foil and a screw cap, and adsorption was performed at 75°C. The vial was removed and weighed at regular intervals (0 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h). The adsorption capacity Q was calculated using the following formula. e (g / g): Q e =(me - (m0- m1) / m0, wherein m0 is the initial mass of the CD-Na-DMF iodine adsorbent, and m1 is the mass of the CD-Na-DMF iodine adsorbent after adsorption of iodine, and the results are shown in Table 1. e Figure 7

[0081] As can be seen from Table 1, the equilibrium adsorption capacity of the CD-Na-DMF iodine adsorbent prepared in Example 2 for iodine can reach 1.877 g / g at 75°C. Figure 5

[0082] 6. Adsorption rate test of iodine in liquid phase

[0083] The adsorption rate test of iodine in liquid phase was carried out on the CD-Na-DMA iodine adsorbent prepared in Example 1, and the specific test method was as follows:

[0084] (1) 5 mg of the CD-Na-DMA iodine adsorbent prepared in Example 1 was weighed and then added to 100 mL of 200 mg / L iodine-containing cyclohexane solution, and adsorption was carried out at room temperature. Samples were taken every 0 h, 0.5 h, 1 h, 2.5 h, 5 h, 8 h, 12 h, 24 h, 48 h, and 72 h, and each time 4 mL was taken.

[0085] (2) Centrifugation was carried out in a centrifuge at a speed of 8500 r / min for 3 min, and 3 mL of supernatant was taken, and then the iodine adsorption was analyzed and tested using a UV-2600 ultraviolet-visible spectrometer, and the absorbance value at 523 nm wavelength was recorded.

[0086] The adsorption rate of iodine under different time conditions is shown in Table 2. Figure 6

[0087] As can be seen from Table 2, the CD-Na-DMA iodine adsorbent prepared in Example 1 adsorbed the 200 mg / L iodine-containing cyclohexane solution to light pink at room temperature. Figure 6

[0088] 7. Adsorption capacity test of iodine in liquid phase

[0089] The adsorption capacity test of iodine in liquid phase was carried out on the CD-Na-DMA iodine adsorbent prepared in Example 1, and the specific test method was as follows:

[0090] (1) 5 mg of the CD-Na-DMA iodine adsorbent prepared in Example 1 was weighed and then added to 100 mL of 200 mg / L iodine-containing cyclohexane solution, and adsorption was carried out at room temperature. Samples were taken every 0 h, 0.5 h, 1 h, 2.5 h, 5 h, 8 h, 12 h, 24 h, 48 h, and 72 h, and each time 4 mL was taken.

[0091] ​​​​​(2) Centrifuge in a centrifuge at a speed of 8000 r / min for 5 min, take 3 mL of supernatant, and then use a UV-2600 UV-Vis spectrometer to analyze and test the iodine adsorption and record the absorbance value at a wavelength of 523 nm.

[0092] The absorbance and concentration conform to Beer-Lambert law. Using a standard curve of the iodine-containing cyclohexane solution, the concentration of the remaining dye in the supernatant can be determined from the absorbance obtained by the above UV test. The adsorption amount Q can then be calculated using the following formula. e (mg / g): Q e =(C0-C e )V / m, where C0 is the initial concentration of the iodine-containing cyclohexane solution, C e Let V be the equilibrium concentration after adsorption, V be the volume of the iodine-containing cyclohexane solution, and m be the mass of the CD-Na-DMA iodine adsorbent. The amount of iodine adsorbed in the liquid phase can be calculated from these values, as shown below. Figure 7 As shown.

[0093] Depend on Figure 7 It can be seen that, under room temperature conditions, the maximum adsorption capacity of the CD-Na-DMA iodine adsorbent prepared in Example 1 for liquid iodine is 701.2 mg / g.

[0094] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an iodine adsorbent, characterized by, Specifically comprising the following steps: (1) Put 1.25 mmol of γ-cyclodextrin and 10 mmol of sodium hydroxide into a beaker, add 24 mL of deionized water, and ultrasonically dissolve to obtain a mixed solution; (2) Use a syringe to suck out 8 mL of the mixed solution and filter into a centrifuge tube with a filter head, add 24 mL of N,N-dimethylacetamide, ultrasonically shake for 10 min, centrifuge and collect the precipitate; (3) Wash the precipitate with ethanol for 3 times, 15 min each time, then put it into an 80℃ oven to dry for 12 h, and grind to a particle size of 1-4 μm to obtain the iodine adsorbent.

2. The iodine adsorbent prepared by the preparation method of claim 1.

3. The use of the iodine adsorbent prepared by the preparation method of claim 1 in capturing iodine.

4. A method for gas phase adsorption and desorption of the iodine adsorbent prepared by the production method according to claim 1, characterized by, Specifically comprising the following steps: (1) Put the iodine adsorbent into a glass vial, then put it into a sample bottle containing iodine, seal and adsorb; The ratio of the amount of the iodine adsorbent to the amount of iodine is 50 mg:200 mg; The sealing is sealed with tin paper and a screw cap; The adsorption temperature is 75℃ and the time is 6 h; (2) After adsorption, desorption is performed; The desorption temperature is 150℃.

5. A method for liquid phase adsorption and desorption of the iodine adsorbent prepared by the production method according to claim 1, characterized by, Specifically comprising the following steps: (1) Put the iodine adsorbent into a solution containing iodine and adsorb; The solution containing iodine is a cyclohexane solution containing iodine, and the iodine content is 200 mg / L; The amount of the iodine adsorbent added is 0.5 mg / mL; The adsorption temperature is room temperature, the condition is standing, and the time is 0.5-72 h; (2) After adsorption, desorption is performed in an ethanol solution.

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