Algal polysaccharide-based composite hydrogel microspheres as well as preparation method and application thereof

Abstract

The invention belongs to the field of hydrogel microsphere adsorption materials, and particularly discloses algal polysaccharide based composite hydrogel microspheres and a preparation method and application thereof.The preparation method comprises the steps that algal polysaccharide solid powder and sodium alginate are taken and added into a chitosan solution, and a polyelectrolyte compound is formed through magnetic stirring and self-assembly; dropwise adding the polyelectrolyte compound into a 2% CaCl2 saturated boric acid solution by using an injector, soaking overnight, washing with deionized water for multiple times, and performing vacuum freeze drying to prepare the algal polysaccharide based composite hydrogel microspheres. According to the algal polysaccharide based composite hydrogel microspheres, on one hand, molecular structures of algal polysaccharides, sodium alginate and chitosan raw materials contain a large number of carboxyl groups, hydroxyl groups, sulfuric acid groups and amino groups, and more cationic dye adsorption sites can be provided; on the other hand, due to a large number of mesoporous structures, the composite material has the advantage of being large in specific surface area, diffusion of cationic dye molecules in pore channels is facilitated, and therefore the adsorption treatment effect on cationic dye wastewater is good.

Description

Technical Field

[0001] The invention relates to the field of hydrogel microsphere adsorption materials, in particular to a seaweed polysaccharide-based composite hydrogel microsphere and a preparation method and application thereof. Background Art

[0002] In recent years, the use of cationic dyes has increased in industries such as leather, textiles, food processing, cosmetics, rubber and printing. The discharge of wastewater containing dyes into the aquatic environment is a serious factor causing water pollution. Adsorption, advanced oxidation, membrane filtration, microbial technology, electrochemical and photocatalytic degradation are the cutting-edge technologies for the treatment of dye industry wastewater. Compared with other technologies, adsorption technology has the advantages of simple operation, green environmental protection, low cost and high efficiency. It is one of the more commonly used technologies for treating dye wastewater. Hydrogel microspheres have great potential for development and application in the field of dye wastewater treatment due to their high porosity and good hydrophilicity. Polysaccharides are a naturally derived carbohydrate polymer. Due to their excellent adsorption performance, regeneration, biodegradability and biocompatibility, they are widely used as raw materials for hydrogel microsphere adsorbents.

[0003] Seaweed is a general term for algae that live in the ocean. Artemisia selengensis is a brown algae distributed in the waters near Dalian Lushun and Jinzhou in the Bohai Sea. It has not yet been developed and utilized by humans. At the same time, the explosive growth of green algae Enteromorpha in the intertidal zone of the Bayuquan waters of Liaodong Bay in recent years has seriously affected the coastal ecological environment. The research of the inventor's team on the bioactive components of the above two seaweeds found that seaweed polysaccharides, as a structural component of the algae cell wall, are a kind of marine bioactive macromolecule with polyanionic characteristics and complex structure. It is rich in functional groups such as hydroxyl, carboxyl, and sulfate groups. It is a natural high-quality raw material for preparing new hydrogel microsphere adsorbents.

[0004] At present, the development and utilization of seaweed polysaccharides is limited to the fact that an efficient polysaccharide extraction process has not yet been formed. On the one hand, although microwave and ultrasonic technology have improved the extraction efficiency, the molecular weight of the extracted polysaccharides is relatively large, resulting in poor water solubility. Enzymatic hydrolysis has a high specificity for the cleavage of glycosidic bonds in polysaccharide chains and cannot be used for industrial development. On the other hand, because most seaweed polysaccharides are acidic heteropolysaccharides, the interaction between polysaccharide chains is weak, and the spatial network structure of hydrogel microspheres formed by a single seaweed polysaccharide is relatively sparse, and the adsorption performance and recycling regeneration performance are poor, and the application as an adsorption material is limited.

[0005] For example, Chinese patent publication number CN114213679A discloses a seaweed polysaccharide-based hydrogel and its preparation method and application. The hydrogel is prepared by repeated freeze-thaw method using seaweed polysaccharide, chitosan and polyvinyl alcohol as raw materials, and has good biocompatibility and excellent mechanical properties. It is used for wound dressings in the field of biomedicine. However, its adsorption performance for dye wastewater is still unclear.

[0006] For example, Chinese patent publication number CN113045681A discloses a hydrogel of Enteromorpha polysaccharide prepared by two-step crosslinking, using Enteromorpha polysaccharide as the base material, acrylic acid, acrylamide, methyl acrylate, etc. as crosslinking monomers, and epichlorohydrin, N,N'-methylenebisacrylamide, carbodiimide, etc. as crosslinking agents. The hydrogel has excellent adsorption properties for heavy metal ions in water. However, its preparation process is cumbersome, and the preparation process uses a large amount of toxic substances that are easy to pollute the environment.

[0007] For example, Chinese patent publication number CN114700046A discloses a method of preparing a polysaccharide of Sargassum fusiformis and sodium alginate by Ca 2+ The hydrogel microspheres prepared by cross-linking for adsorbing the cationic dye crystal violet are green and environmentally friendly, but their adsorption capacity for crystal violet dye is small, and their recyclability after regeneration is still unknown.

[0008] Therefore, finding a green and environmentally friendly hydrogel adsorption material with simple preparation process, large adsorption capacity and stable regeneration and recycling performance has become an urgent problem to be solved. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a seaweed polysaccharide-based composite hydrogel microsphere and a preparation method and application thereof. The prepared seaweed polysaccharide-based composite hydrogel microsphere has a large number of mesoporous structures, a large adsorption capacity for cationic dyes, and stable regeneration and recycling performance.

[0010] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0011] One of the purposes of the present invention is to provide a method for preparing seaweed polysaccharide-based composite hydrogel microspheres, comprising the following steps:

[0012] S1. Add seaweed polysaccharide solid powder and sodium alginate in a mass ratio of 1:0.5-10 to chitosan solution, and form a polyelectrolyte complex by magnetic stirring and self-assembly; the chitosan solution is prepared by first adding water to chitosan, and then adding HCl to adjust the pH value of the chitosan solution to 2.5-3.0, and the mass concentration of chitosan in the chitosan solution is 0.5-1.5%; the mass ratio of seaweed polysaccharide to chitosan is 1:0.25-3.0, and the mass ratio of sodium alginate to chitosan is 1:0.1-1.5;

[0013] S2. The polyelectrolyte complex was dripped into a 2% CaCl2 saturated boric acid solution using a syringe, and after soaking overnight, it was washed with deionized water for several times, and vacuum freeze-dried to prepare seaweed polysaccharide-based composite hydrogel microspheres.

[0014] Furthermore, the seaweed polysaccharide is a low molecular weight water-soluble seaweed polysaccharide, and the preparation method thereof is as follows:

[0015] 1) Wash and dry the seaweed to constant weight, and crush and sieve to obtain seaweed powder;

[0016] 2) extracting the seaweed powder by reflux extraction with anhydrous ethanol, filtering and drying after cooling to obtain defatted and depigmented seaweed powder;

[0017] 3) Disperse the defatted and depigmented seaweed powder into deionized water and add 30% H2O2 and V c The solution is placed in a sealed container of a microwave reactor and continuously stirred with magnetic stirring for 10 to 20 minutes to obtain a crude seaweed polysaccharide extract;

[0018] 4) Centrifuging the crude seaweed polysaccharide extract, taking the supernatant, concentrating it to obtain a concentrated solution, adding anhydrous ethanol to the concentrated solution for precipitation at 4°C overnight;

[0019] 5) Centrifuging the alcohol precipitate in step 4), taking the precipitate, dissolving it with deionized water, removing the impurities in the crude polysaccharide solution by Sevage method, dialyzing the aqueous phase solution with deionized water overnight, concentrating and freeze-drying to obtain seaweed polysaccharide solid powder.

[0020] Furthermore, the seaweed is the brown algae Sargassum marinum or the green algae Enteromorpha.

[0021] Furthermore, in the step 2), the volume ratio of seaweed powder to anhydrous ethanol is 1 g:40-60 mL, the reflux temperature is 70-90° C., and the reflux time is 1-3 h.

[0022] Furthermore, in step 3), the liquid ratio of defatted and depigmented seaweed powder to deionized water is 1 g:40-60 mL, the volume of H2O2 added is 0.1-0.3 mL, and V c The volume is 1~3mL, V c The concentration is 0.5~1.5mol / L.

[0023] Furthermore, in the step 4), the amount of anhydrous ethanol added is 2 to 10 times that of the concentrated solution, and the overnight precipitation time is 12 to 24 hours.

[0024] Furthermore, in the step 5), the freeze-drying temperature is -50 to -30°C.

[0025] The second object of the present invention is to provide a seaweed polysaccharide-based composite hydrogel microsphere prepared by the above method.

[0026] The third object of the present invention is to provide an application of seaweed polysaccharide-based composite hydrogel microspheres in cationic dye adsorption.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The present invention utilizes microwave-assisted H2O2 and V c Low molecular weight water-soluble seaweed polysaccharides are prepared by degradation, the extraction process is short, and the obtained seaweed polysaccharides have good water solubility, which is conducive to their further application.

[0029] 2) Based on the polyelectrolyte single network complex formed by seaweed polysaccharide, sodium alginate and chitosan, the present invention uses a syringe to drip and add Ca 2+ As a bridge, under the dual effects of copolymerization and cross-linking, hydrogel microspheres with easy solid-liquid separation and stable performance are formed.

[0030] 3) The seaweed polysaccharide-based composite hydrogel microspheres of the present invention, on the one hand, contain a large number of carboxyl groups, hydroxyl groups, sulfate groups, and amino groups in the molecular structure of the seaweed polysaccharide, sodium alginate, and chitosan raw materials, which can provide more cationic dye adsorption sites; on the other hand, a large number of mesoporous structures give it the advantage of a large specific surface area, which is conducive to the diffusion of cationic dye molecules in the pore channels, and therefore has a better adsorption treatment effect on cationic dye wastewater.

[0031] 4) The preparation of the seaweed polysaccharide-based composite hydrogel microspheres of the present invention has a simple process, a short flow, a wide source of raw materials and is green and environmentally friendly, while achieving high-value development and utilization of algae resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a graph showing the adsorption removal rate of two cationic dyes, crystal violet and methylene blue, by 12 kinds of hydrogel microspheres prepared in Examples 1 to 4 of the present invention and Comparative Examples 1, 2 and 3;

[0033] Figure 2 This is a pore volume-pore size distribution diagram of the hydrogel microspheres SPP4 prepared in Example 4 of the present invention;

[0034] Figure 3 is a scanning electron microscope image of the hydrogel microspheres SPP4 prepared in Example 4 of the present invention;

[0035] Figure 4 This is a graph showing the regeneration adsorption performance of the hydrogel microspheres SPP4 prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0037] The seaweed samples used in the following examples are the seaweed samples distributed in the waters near Dalian Lushun and Jinzhou in the Bohai Sea and the green algae Enteromorpha that broke out in the coastal areas of Bayuquan, Yingkou, Liaoning.

[0038] Example 1

[0039] S1. Wash and dry the collected seaweed or green algae Enteromorpha to constant weight, and grind and sieve to obtain seaweed powder.

[0040] S2. The seaweed powder was mixed with anhydrous ethanol at a solid-liquid ratio of 1:50 (g / mL), and refluxed at 80°C for 2 h. After cooling, the mixture was filtered and dried to obtain defatted and depigmented seaweed powder.

[0041] S3. Mix the defatted and depigmented seaweed powder with deionized water at a solid-liquid ratio of 1:50 (g / mL), and add 0.2 mL 30% H2O2 and 2 mL 1.0 mol / LV c The solution was placed in a sealed container of a microwave reactor and continuously magnetically stirred for 15 min to obtain a crude seaweed polysaccharide extract.

[0042] S4. Centrifuge the above extract, concentrate the supernatant, add 8 times the volume of anhydrous ethanol and precipitate at 4°C for 18 hours.

[0043] S5. The alcohol precipitate is centrifuged, the precipitate is dissolved in deionized water, and the impurity protein in the crude polysaccharide solution is removed by Sevage method. The aqueous phase solution is dialyzed against deionized water overnight, concentrated and freeze-dried at -40°C to obtain a solid powder of Artemisia seagrass polysaccharide or Enteromorpha enteromorpha polysaccharide.

[0044] S6. Add 0.5 g chitosan into 40 mL deionized water, adjust the pH value of the chitosan solution to 2.5 with 6 mol / L HCl, and dissolve by magnetic stirring.

[0045] S7. Add 1.0 g of the seaweed polysaccharide solid powder of step S5 and 0.75 g of sodium alginate to the chitosan solution of step S6, and perform magnetic stirring self-assembly to obtain a polyelectrolyte single network complex.

[0046] S8. Dissolve a sufficient amount of boric acid in hot water, stir thoroughly for a certain period of time, cool naturally, take 100 mL of the upper clear solution, add 2.0 g of CaCl2 thereto, and obtain a 2% CaCl2 saturated boric acid solution.

[0047] S9. The polyelectrolyte single network complex in step S7 is dripped into the 2% CaCl2 saturated boric acid solution in step S3 using a 5 mL disposable syringe, soaked overnight, washed with deionized water several times, and vacuum freeze-dried to prepare hydrogel microspheres.

[0048] Example 2

[0049] The difference from Example 1 is that the mass of chitosan in step S6 is 0.2 g; the mass of seaweed polysaccharide in step S7 is 0.4 g; and the mass of sodium alginate is 0.3 g.

[0050] Example 3

[0051] The difference from Example 1 is that the mass of chitosan in step S6 is 0.4 g; the mass of seaweed polysaccharide in step S7 is 0.8 g; and the mass of sodium alginate is 0.6 g.

[0052] Example 4

[0053] The difference from Example 1 is that the mass of chitosan in step S6 is 0.6 g; the mass of seaweed polysaccharide in step S7 is 1.2 g; and the mass of sodium alginate is 0.9 g.

[0054] In the hydrogel microspheres prepared in Example 2, the hydrogel microspheres prepared using wormwood polysaccharide and enteromorpha polysaccharide were marked as SPP1 and EPP1, respectively; in the hydrogel microspheres prepared in Example 3, the hydrogel microspheres prepared using wormwood polysaccharide and enteromorpha polysaccharide were marked as SPP2 and EPP2, respectively; in the hydrogel microspheres prepared in Example 1, the hydrogel microspheres prepared using wormwood polysaccharide and enteromorpha polysaccharide were marked as SPP3 and EPP3, respectively; in the hydrogel microspheres prepared in Example 4, the hydrogel microspheres prepared using wormwood polysaccharide and enteromorpha polysaccharide were marked as SPP4 and EPP4, respectively.

[0055] Comparative Example 1

[0056] S1. Add 1.0 g of the low molecular weight water-soluble seaweed polysaccharide extracted in Example 1 and 1.0 g of sodium alginate into 40 mL of deionized water, and stir magnetically to dissolve into a uniform viscous liquid.

[0057] S2. Dissolve sufficient boric acid in hot water, stir thoroughly for a certain period of time, cool naturally, take 100 mL of the upper clear solution, add 2.0 g of CaCl2 thereto, and obtain a 2% CaCl2 saturated boric acid solution.

[0058] S3. The viscous liquid in step S1 is dripped into the 2% CaCl2 saturated boric acid solution in step S2 using a 5mL disposable syringe. After soaking overnight, the mixture is washed with deionized water several times and freeze-dried in vacuum to prepare hydrogel microspheres. The hydrogel microspheres prepared with Artemisia seagrass polysaccharide are labeled as SPP-SA, and the hydrogel microspheres prepared with Enteromorpha polysaccharide are labeled as EPP-SA.

[0059] Comparative Example 2

[0060] S1. Add 0.5 g chitosan into 40 mL deionized water, adjust the pH value of the chitosan solution to 2.5 with 6 mol / L HCl, and dissolve by magnetic stirring.

[0061] S2. Add 1.0 g of sodium alginate to the chitosan solution of step S1, and perform magnetic stirring self-assembly to obtain a polyelectrolyte single network complex.

[0062] S3. Dissolve sufficient boric acid in hot water, stir thoroughly for a certain period of time, cool naturally, take 100 mL of the upper clear solution, add 2.0 g of CaCl2 thereto, and obtain a 2% CaCl2 saturated boric acid solution.

[0063] S4. The polyelectrolyte single network complex in step S2 was dripped into the 2% CaCl2 saturated boric acid solution in step S3 using a 5 mL disposable syringe, and then soaked overnight, washed with deionized water several times, and vacuum freeze-dried to prepare hydrogel microspheres, which were labeled as CTS-SA.

[0064] Comparative Example 3

[0065] S1. Add 1.0 g of sodium alginate into 40 mL of deionized water and dissolve it into a uniform viscous liquid by magnetic stirring.

[0066] S2. Dissolve sufficient boric acid in hot water, stir thoroughly for a certain period of time, cool naturally, take 100 mL of the upper clear solution, add 2.0 g of CaCl2 thereto, and obtain a 2% CaCl2 saturated boric acid solution.

[0067] S4. The viscous liquid in step S1 was dripped into the 2% CaCl2 saturated boric acid solution in step S2 using a 5 mL disposable syringe, and then washed with deionized water several times after being soaked overnight. The hydrogel microspheres were prepared by vacuum freeze-drying and labeled as SA.

[0068] The adsorption performance of cationic dye wastewater was tested using the hydrogel microspheres of 8 different seaweeds with different polysaccharide contents prepared in Example 1 to Example 4 and the hydrogel microspheres in Comparative Example 1, Comparative Example 2, and Comparative Example 3. The above 12 hydrogel microspheres were used for the adsorption treatment of cationic dye wastewater, including the following steps (all materials were treated with the same steps): Crystal violet and methylene blue dye solutions with a mass concentration of 100 mg / L were prepared respectively, 12 portions of 25 mL of each dye solution were measured and placed in a 150 mL stoppered conical flask, two portions of each of the 12 hydrogel microspheres that had been swollen overnight (the mass of the dry gel microspheres was 0.025 g) were added to the above stoppered conical flask, and the adsorption was carried out by shaking at 25°C and 180 r / min for 24 hours, and the concentration of the dye solution was measured by a spectrophotometer. The adsorption performance of the hydrogel microspheres of 12 different seaweeds with different polysaccharide contents on two cationic dyes was tested, and the results are as follows Figure 1shown.

[0069] Depend on Figure 1 It can be seen that the removal rates of the hydrogel microspheres in Comparative Examples 1, 2 and 3 for the cationic dyes crystal violet and methylene blue are all lower than 80%. The removal rates of the hydrogel microspheres prepared from two different seaweed polysaccharides for the cationic dyes crystal violet and methylene blue gradually increase with the increase of polysaccharide concentration, and the removal rates of the hydrogel microspheres SPP4 prepared using Artemisia seaweed polysaccharide for the two cationic dyes are both above 96%.

[0070] The specific surface area, pore size and total pore volume of the hydrogel microspheres SPP4 prepared using the polysaccharide from Artemisia seagrass in Example 4 were tested. Figure 2 As shown. Figure 2 It can be seen that the pore size distribution of hydrogel microspheres SPP4 is relatively wide, mainly concentrated between 1.7 and 28.5 nm, and the specific surface area is 25.4557 m 2 / g, adsorption pore volume 0.066426cm 3 / g.

[0071] The hydrogel microsphere SPP4 in Example 4 was fractured by liquid nitrogen, polished to make the cut surface smooth, and the cross section of the microsphere was sprayed with gold by a gold spraying instrument. The cross-sectional morphology of the sample was observed by a scanning electron microscope. Figure 3 As shown. Figure 3 It can be seen that the cross-section of the hydrogel microspheres SPP4 prepared in Example 4 has a large number of pore structures, which provides a larger specific surface area for the adsorption of cationic dyes inside the microspheres and improves its adsorption performance.

[0072] After the hydrogel microspheres SPP4 in Example 4 adsorbed the three cationic dyes, they were added to 25 mL of 95% ethanol solution and desorbed in a constant temperature oscillator at 25°C and 180 r / min for 30 min. The ethanol solution was replaced every 30 min, and this process was repeated 3 times. After being taken out, they were washed several times with deionized water to clean the ethanol on the surface of the hydrogel microspheres. After vacuum freeze-drying, they were used for the next adsorption. The above process was repeated 5 times to test the adsorption regeneration ability of the hydrogel microspheres. Figure 4 shown.

[0073] Depend on Figure 4 It can be seen that after 5 cycles of reuse, the removal rate of the hydrogel microspheres SPP4 for the two cationic dyes declined slightly, but still remained above 90%, showing good adsorption regeneration ability.

[0074] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing seaweed polysaccharide-based composite hydrogel microspheres, characterized in that: The following steps are involved: S1. Add seaweed polysaccharide solid powder and sodium alginate in a mass ratio of 1:0.5-10 to chitosan solution, and form a polyelectrolyte complex by magnetic stirring and self-assembly; the chitosan solution is prepared by first adding water to chitosan, and then adding HCl to adjust the pH value of the chitosan solution to 2.5-3.0, and the mass concentration of chitosan in the chitosan solution is 0.5-1.5%; the mass ratio of seaweed polysaccharide to chitosan is 1:0.25-3.0, and the mass ratio of sodium alginate to chitosan is 1:0.1-1.5; S2. The polyelectrolyte complex was dripped into a 2% CaCl2 saturated boric acid solution using a syringe, and after soaking overnight, it was washed with deionized water for several times, and then vacuum freeze-dried to prepare seaweed polysaccharide-based composite hydrogel microspheres.

2. The method for preparing seaweed polysaccharide-based composite hydrogel microspheres according to claim 1, characterized in that: The seaweed polysaccharide is a low molecular weight water-soluble seaweed polysaccharide, and the preparation method thereof is as follows: 1) Wash and dry the seaweed to constant weight, and crush and sieve to obtain seaweed powder; 2) extracting the seaweed powder by reflux extraction with anhydrous ethanol, filtering and drying after cooling to obtain defatted and depigmented seaweed powder; 3) Dispersing the defatted and depigmented seaweed powder into deionized water, adding 30% H2O2 and Vc solution respectively, placing in a sealed container of a microwave reactor, and continuously stirring with magnetic stirring for 10 to 20 minutes to obtain a crude seaweed polysaccharide extract; 4) Centrifuging the crude seaweed polysaccharide extract, taking the supernatant, concentrating it to obtain a concentrated solution, adding anhydrous ethanol to the concentrated solution for precipitation at 4°C overnight; 5) Centrifuging the alcohol precipitate in step 4), taking the precipitate, dissolving it with deionized water, removing the impurities in the crude polysaccharide solution by Sevage method, dialyzing the aqueous phase solution with deionized water overnight, concentrating and freeze-drying to obtain seaweed polysaccharide solid powder.

3. The method for preparing seaweed polysaccharide-based composite hydrogel microspheres according to claim 2, characterized in that: The seaweed is the brown algae Sargassum marinum or the green alga Enteromorpha.

4. The method for preparing seaweed polysaccharide-based composite hydrogel microspheres according to claim 2, characterized in that: In the step 2), the volume ratio of seaweed powder to anhydrous ethanol is 1 g:40-60 mL, the reflux temperature is 70-90° C., and the reflux time is 1-3 h.

5. The method for preparing seaweed polysaccharide-based composite hydrogel microspheres according to claim 2, characterized in that: In the step 3), the liquid ratio of defatted and depigmented seaweed powder to deionized water is 1 g:40-60 mL, the volume of H2O2 added is 0.1-0.3 mL, and V c The volume is 1~3mL, V c The concentration is 0.5~1.5mol / L.

6. The method for preparing seaweed polysaccharide-based composite hydrogel microspheres according to claim 2, characterized in that: In the step 4), the amount of anhydrous ethanol added is 2 to 10 times that of the concentrated solution, and the overnight precipitation time is 12 to 24 hours.

7. The method for preparing seaweed polysaccharide-based composite hydrogel microspheres according to claim 2, characterized in that: In the step 5), the freeze-drying temperature is -50 to -30°C.

8. Seaweed polysaccharide-based composite hydrogel microspheres prepared by the method according to any one of claims 1 to 7.

9. Use of the seaweed polysaccharide-based composite hydrogel microspheres as claimed in claim 8 in the adsorption of cationic dyes.

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