Carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent as well as preparation method and application thereof

Abstract

The invention provides a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent as well as a preparation method and application thereof. The preparation method of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent comprises the following steps: (1) dissolving K-type carrageenan in carboxylated cellulose nanofibers, stirring and carrying out ultrasonic treatment to form a mixed solution; (2) dropwise adding the mixed solution into a potassium chloride solution, and stirring and cross-linking to form composite hydrogel microspheres; and (3) washing and drying the composite hydrogel microspheres, so as to obtain the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent. The method is simple in step, low in cost and environmentally friendly, and the prepared carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent has a good adsorption effect on cationic dye methylene blue and is an optional dye wastewater adsorbent.

Description

Technical Field

[0001] The present invention relates to sewage purification technology, in particular to a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, a preparation method and application thereof. Background Art

[0002] With economic and social development and growing environmental awareness, environmental pollution has become a growing global concern. Industrial wastewater generated during this process poses a serious threat to the sustainable development of the environment and ecosystems. Furthermore, dye waste generated during industrial production can cause serious illnesses, such as kidney, reproductive system, liver, brain, and central nervous system dysfunction. Furthermore, if industrial wastewater is deemed unreusable and left untreated, it can lead to a significant waste of water resources, and its discharge is also a major concern. To address the various risks and hazards associated with industrial wastewater, it is necessary to implement treatment measures to protect the environment, recycle resources, conserve water, reduce health risks, and ultimately achieve sustainable development.

[0003] Due to the high toxicity and low biodegradability of synthetic organic dyes, organic dyes in industrial wastewater are discharged into the natural environment, posing a serious threat to aquatic organisms and human health. Water-soluble dyes, such as methylene blue (MB), crystal violet (CV), and methylene orange (MO), have stable physical and chemical properties and are not easily degraded. Therefore, it is very necessary to treat dye wastewater generated in industrial production processes to achieve the recycling of polluted water. In recent years, many scholars have developed conventional methods for removing dyes from water, including membrane separation, ion exchange, coagulation / flocculation, and oxidative degradation. However, the above methods all have disadvantages to varying degrees. For example, the membrane separation method has high membrane cost, high maintenance cost, easy clogging, and short service life; the ion exchange method has a long cycle and high water quality requirements; the flocculation method has poor environmental impact and may generate by-products.

[0004] Currently, adsorption methods, known for their ease of use, cost-effectiveness, high efficiency, and environmental friendliness, are attracting significant attention in dye wastewater treatment. With its large adsorption capacity, wide applicability, and low energy consumption, adsorption is a common method for removing dyes from wastewater. Among various wastewater treatment methods, adsorption of dyes from wastewater is a preferred approach due to its low cost, high efficiency, wide availability of materials, and wide applicability. Adsorption can remove 99.9% of dye contaminants from wastewater. Adsorption can be achieved by preparing hydrogels with excellent dye adsorption properties.

[0005] Hydrogels are cross-linked hydrophilic polymer networks that can absorb large amounts of water or biological fluids, swelling without dissolving. They are "soft and wet" materials with a three-dimensional cross-linked network structure and are widely used in tissue engineering, drug delivery, microfluidics, stretchable and bio-integrated electronics, and other fields. The use of hydrogel materials in adsorption methods can effectively treat dye wastewater, adsorbing dye ions through electrostatic interactions, hydrogen bonds, π-π interactions, and other mechanisms to obtain environmentally friendly treated water. In short, the preparation of hydrogels for dye wastewater treatment not only helps protect the environment and resources, but also helps improve water quality and human health. This is an interdisciplinary research involving multiple fields such as chemistry, materials science, and environmental engineering, and has important social and economic value.

[0006] Currently, many sewage treatment plants around the world use hydrogels for adsorption purification. While these adsorbents offer remarkable adsorption performance and are environmentally friendly, they also present challenges such as complex preparation processes and the use of toxic or hazardous materials. Therefore, the search for green, efficient, low-cost adsorbents with simple and accessible preparation processes is crucial. Summary of the Invention

[0007] The purpose of the present invention is to address the above-mentioned problems and propose a method for preparing a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent. The method has simple steps, low cost, and is green and environmentally friendly. The prepared carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent has a good adsorption effect on cationic dyes and is an alternative dye wastewater adsorbent.

[0008] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0009] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, comprising the following steps:

[0010] Step (1) dissolving K-type carrageenan in carboxylated cellulose nanofibers, stirring and ultrasonically treating to form a mixed solution;

[0011] Step (2) adding the mixed solution dropwise to a potassium chloride solution, stirring and cross-linking to form composite hydrogel microspheres;

[0012] Step (3) washing and drying the composite hydrogel microspheres to obtain the carrageenan carboxylated cellulose hydrogel microsphere cationic dye adsorbent.

[0013] Furthermore, the mass volume ratio of K-type carrageenan to carboxylated cellulose nanofibers in step (1) is 0.28:18-22 (g:ml), that is, the concentration of K-type carrageenan in the mixed solution in step (1) is 1.26-1.53 ​​wt.%.

[0014] Furthermore, the ultrasonic treatment time in step (1) is 40 to 80 minutes, preferably 60 minutes.

[0015] Furthermore, in step (2), the volume ratio of the mixed solution to the potassium chloride solution is 2 to 4:20.

[0016] Furthermore, the concentration of the potassium chloride solution in step (2) is 2.5 to 7.5 wt.%, preferably 5 wt.%.

[0017] Furthermore, the time for completing the dropwise addition of the mixed solution in step (2) is 25 to 35 minutes.

[0018] Furthermore, the cross-linking time in step (2) is 10 to 15 hours, preferably 12 hours.

[0019] Furthermore, the average particle size of the composite hydrogel microspheres prepared in step (2) is 0.8 to 1.2 mm, preferably 1 mm.

[0020] Furthermore, in step (3), the drying temperature is 50-70° C., and the drying time is 3-5 h. Preferably, the drying temperature is 60° C., and the drying time is 4 h.

[0021] Another object of the present invention is to disclose a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, which is prepared by the above method.

[0022] Furthermore, the mass percentage of the carboxylated cellulose nanofibers in the carrageenan carboxylated cellulose hydrogel microsphere cationic dye adsorbent is 97% to 99%.

[0023] Furthermore, the maximum adsorption capacity of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent is 400-450 mg / g, and preferably the maximum adsorption capacity is 426-428 mg / g.

[0024] Another object of the present invention is to disclose the application of a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent in the field of organic dye wastewater adsorption.

[0025] Furthermore, the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent is particularly suitable for cationic dye adsorption.

[0026] Furthermore, the cationic dye is methylene blue.

[0027] Furthermore, the steps of using carrageenan carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent to purify sewage are as follows: adding the carrageenan carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent to the dye solution, the volume ratio of the added amount of the carrageenan carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent to the dye solution is 1:5 to 3:5 (mg:mL), the adsorption temperature is 20 to 30°C, the adsorption time is 5 to 7h, and the pH environment of the adsorption reaction is the pH environment of the sewage itself.

[0028] Furthermore, taking the treatment of methylene blue dye solution as an example, carrageenan carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent is put into the methylene blue solution. The dye molecules in the solution reach the surface of the adsorbent and react with functional groups such as hydroxyl (-OH) and carboxyl (-COOH) on the adsorbent surface through hydrogen bonds, electrostatic interactions, etc., occupying the active sites on the adsorbent surface. When the active sites on the adsorbent surface are completely occupied, the adsorption reaction reaches equilibrium. The volume ratio of the carrageenan cellulose nanofiber hydrogel microspheres cationic dye adsorbent to the methylene blue dye solution is 2:5, the adsorption reaction system temperature is 25°C, the adsorption time is 330 minutes, and the pH environment of the reaction is the pH environment of the dye itself.

[0029] The carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, preparation method and application thereof have the following advantages over the prior art:

[0030] 1) The present invention prepares a cationic dye adsorbent made of carrageenan-carboxylated cellulose nanofiber hydrogel microspheres by cross-linking a mixed solution of K-carrageenan and carboxylated cellulose nanofibers with potassium chloride. This adsorbent exhibits excellent adsorption properties for cationic dyes (such as methylene blue). Experimental results show that, with a 20 mg adsorbent dosage and 50 mL of dye solution (with an initial dye concentration of 150 mg / L), the adsorbent achieves a cationic dye adsorption capacity of 235.79 mg / g within 330 minutes, demonstrating high adsorption efficiency.

[0031] The present invention uses the seaweed polysaccharide carrageenan (KC) as a base material to prepare composite hydrogel microspheres as a cationic dye adsorbent. Carrageenan is a high-molecular-weight hydrophilic polysaccharide extracted from red algae. Its unique structure enables it to exhibit excellent adsorption properties. Carrageenan cannot dissolve in cold water, but it can swell in water to form a gel-like structure. This characteristic gives carrageenan unique advantages in specific application areas. In addition, carrageenan has unique gel properties and can form a thermoreversible gel in the presence of potassium ions. Under the synergistic effect of colloids such as xanthan gum, konjac gum and locust bean gum, the elasticity and water retention of carrageenan hydrogels are improved. Carrageenan has the advantages of high adsorption performance, good selectivity, easy operation, environmental friendliness, and strong adaptability. Therefore, carrageenan hydrogels can be used in sewage treatment. It is expected that adsorbents with better adsorption capacity can be prepared using carrageenan, which has great potential and commercial value in sewage treatment.

[0032] Carrageenan is a sulfonated polysaccharide composed of alternating 3-chain β-d-galactosyl and 4-chain α-d-galactosyl residues. As a novel, renewable, natural polymer derived from marine red algae, it is the primary structural component of their cell walls. The various hydroxyl groups on the polymer chain are typically replaced by sulfate ester groups. These biopolymers have long been used as thickeners, gelling agents, and stabilizers in the food and pharmaceutical industries. Carrageenan's ability to replace fats and interact with other hydrocolloids and proteins enhances its utility in various food applications. For example, carrageenan is frequently used in yogurt, salad dressings, and infant formula to thicken and improve food texture.

[0033] One of the major commercial applications of carrageenan in recent years stems from its inherent cation-dependent hydrogel formation. Carrageenan can be categorized as kappa, iota, and lambda carrageenan. Kappa and iota carrageenan exhibit gelation in the presence of monovalent and divalent cations, respectively. In contrast, lambda carrageenan does not form gels with monovalent or divalent cations, exhibiting only viscous behavior. Although the presence of excess cations can promote the binding of these hydrocolloid chains, and upon binding, both lambda and kappa carrageenans undergo a coil-to-helix transition, helical formation in kappa carrageenan is accompanied by helical aggregation, which does not occur in lambda carrageenan due to the greater electrostatic chain repulsion caused by the two sulfate groups in its molecular structure. Thus far, gelation of lambda carrageenan has not been achieved. Kappa and iota carrageenan each form an ordered three-dimensional network composed of double helices, resulting from "crosslinking" of adjacent chains, with the sulfate groups facing outward. In lambda carrageenan, the sulfate group at the 2-position faces inward, hindering crosslinking and the formation of an ordered network. Based on the characteristics of different types of carrageenan, the present invention selects kappa carrageenan as the base material and mixes it with carboxylated cellulose nanofibers, a natural polymer material with excellent biocompatibility, high specific surface area and unique nanostructure. The gelation property of kappa carrageenan in the presence of monovalent cations is utilized, and potassium chloride is selected as a cross-linking agent to achieve the gelation of carrageenan composite hydrogel microspheres.

[0034] Carrageenan has excellent water solubility and thermoreversibility, and can form a stable hydrogel. This gel structure has a large specific surface area and adsorption capacity, effectively adsorbing a variety of substances. Carrageenan's adsorption process is selective, specifically targeting specific dye molecules. This selective adsorption helps reduce interference with other substances and improve wastewater treatment efficiency.

[0035] 2) The preparation process of the carrageenan-carboxylated cellulose nanofiber hydrogel microspheres as cationic dye adsorbents is simple, requiring no complex equipment or expensive raw materials. Furthermore, carrageenan polysaccharides are widely available, resulting in low production costs. The entire preparation process is environmentally friendly, in line with the principles of green chemistry, and has broad application prospects in the treatment of cationic dye wastewater.

[0036] 3) Compared with existing adsorption materials, the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of the present invention has stronger adsorption capacity and higher adsorption efficiency, and can more effectively remove cationic dye pollutants in wastewater.

[0037] 4) The preparation method of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of the present invention is simple, the process is stable, and it is easy to scale up production, and has good industrial application potential.

[0038] The carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of the present invention has good application prospects and large-scale promotion potential in the field of cationic dye adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of the present invention;

[0040] Figure 2 The SEM morphology images of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent in Example 1 at different magnifications, wherein (a) is magnified 50 times, and (b) is magnified 20,000 times;

[0041] Figure 3 This is a comparison of the adsorption capacity of methylene blue dye by the cationic dye adsorbent of carrageenan carboxylated cellulose nanofiber hydrogel microspheres in Example 1, wherein the bar graph represents the mass fraction of carboxylated cellulose nanofibers in the adsorbent from left to right as 0%, 97.3%, 98.6%, 99.1%, and 99.3%, respectively;

[0042] Figure 4 The adsorption of methylene blue dye at different initial concentrations by the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of Example 1, as well as the fitting of different isotherm models;

[0043] Figure 5 The adsorption of methylene blue dye by the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent changes with reaction time in Example 1;

[0044] Figure 6 The linear fitting of the quasi-first-order and pseudo-second-order kinetic models for the adsorption of methylene blue dye by carrageenan-carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent in Example 1, wherein (a) shows the linear fitting of the kinetic data to the quasi-first-order model, and (b) shows the linear fitting of the kinetic data to the quasi-second-order model;

[0045] Figure 7 This is the fitting of the intra-particle diffusion model of the cationic dye adsorbent of carrageenan carboxylated cellulose nanofiber hydrogel microspheres adsorbing methylene blue dye in Example 1. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to the following examples. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0047] Unless otherwise stated, the units used in this specification are international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0048] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0049] In this specification, the numerical range expressed using "above" or "below" means a numerical range including the number.

[0050] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0051] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0052] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0053] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0054] Example 1

[0055] This embodiment discloses a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, the preparation method of which is as follows:

[0056] Step (1) weighing 0.28 g of K-carrageenan (KC) powder, adding 20 mL of carboxylated cellulose nanofibers, and initially stirring with a glass rod to dissolve the K-carrageenan, then ultrasonicating the mixed solution for 1 hour to fully dissolve the K-carrageenan, thereby obtaining a uniform mixed solution of K-carrageenan and carboxylated cellulose nanofibers.

[0057] Step (2) Using a syringe, a mixed solution of K-type carrageenan and carboxylated cellulose nanofibers is dripped dropwise into a 5 wt.% KCl solution at a rate of 2.5 ml / min for cross-linking. The volume ratio of the two is 1:10. During this process, a magnet should be placed in the KCl solution, and then the solution is placed on a magnetic heating stirrer and stirred for 12 hours.

[0058] After stirring in step (3), the mixture was rinsed three times with deionized water to remove components not involved in the reaction, thereby obtaining K-type carrageenan composite hydrogel microspheres before drying. Finally, the mixture was dried in a drying oven at 60°C for 4 hours to obtain carrageenan carboxylated cellulose nanofiber hydrogel microspheres as cationic dye adsorbents, wherein the mass fraction of the carboxylated cellulose nanofibers was 98.6%.

[0059] After testing, the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent prepared by the above method has a maximum adsorption capacity of 427.65271 mg / g for 50 mL of methylene blue dye with an initial concentration of 800 mg / L at 25°C.

[0060] Comparative Example 2

[0061] Weigh 0.28 g of K-carrageenan (KC) powder, mix 10 mL of carboxylated cellulose nanofibers with 10 mL of deionized water to create a 20 mL solution, and mix this solution with the K-carrageenan powder. Carrageenan-based carboxylated cellulose nanofiber hydrogel microspheres with a 97.3% mass fraction of carboxylated cellulose nanofibers were prepared according to the process described in Example 1.

[0062] Comparative Example 1

[0063] 0.28 g of K-carrageenan (KC) powder was weighed and mixed with 20 mL of deionized water. Pure carrageenan hydrogel microspheres (with a carboxylated cellulose nanofiber content of 0%) were prepared according to the process described in Example 1.

[0064] Comparative Example 2

[0065] Weigh 0.28g of K-carrageenan (KC) powder and mix it with 30mL of carboxylated cellulose nanofibers to fully dissolve the carrageenan powder. Carrageenan-based carboxylated cellulose nanofiber hydrogel microspheres containing 99.1% carboxylated cellulose nanofibers were prepared according to the process described in Example 1. Only the carboxylated cellulose nanofiber content was varied, and the adsorbent with the best adsorption performance was selected for dye adsorption.

[0066] Comparative Example 3

[0067] Weigh 0.28g of K-carrageenan (KC) powder and mix it with 40mL of carboxylated cellulose nanofibers to fully dissolve the carrageenan powder. Carrageenan-based carboxylated cellulose nanofiber hydrogel microspheres containing 99.3% carboxylated cellulose nanofibers were prepared according to the process described in Example 1. The adsorbent with the best dye adsorption performance was selected by comparing the dye adsorption capacity, while only the carboxylated cellulose nanofiber content was varied.

[0068] The carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbents of Examples 1-2 and Comparative Examples 1-3 were tested, and the test methods and test results are as follows:

[0069] Only the content of carboxylated cellulose nanofibers was changed, and the adsorbent with the best adsorption effect was selected for dye adsorption through dye adsorption capacity comparison.

[0070] For methylene blue dye with an initial concentration of 200 mg / L, the maximum adsorption capacity of the carrageenan-carboxylated cellulose hydrogel microsphere cationic dye adsorbent in Example 1 at 298 K was 311.12731 mg / g. Comparison of the methylene blue adsorption capacity of carrageenan composite hydrogel microspheres with varying cellulose nanofiber contents revealed that the carrageenan-carboxylated cellulose hydrogel microsphere cationic dye adsorbent in Example 1 (with a carboxylated cellulose nanofiber mass fraction of 98.6%) had the optimal adsorption capacity.

[0071] Figure 1 The preparation process of carrageenan-carboxylated cellulose nanofiber hydrogel microspheres as cationic dye adsorbent is demonstrated;

[0072] Figure 2 SEM images at different magnifications show that the carrageenan-carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent intuitively presents a spherical structure (a), and its surface is relatively rough, with unevenly distributed pores of varying sizes, which is conducive to the occupation of dye molecules. The SEM image at a magnification of 20,000 times (b) shows that the carrageenan-carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent exhibits an unevenly distributed lamellar structure, which is conducive to dye adsorption;

[0073] Figure 3 Comparative experimental data show that the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of Example 1 has the best adsorption capacity for methylene blue;

[0074] Figure 4 Adsorption results for methylene blue dye solutions of varying initial concentrations indicate that the adsorption capacity of the carrageenan-carboxylated cellulose nanofiber hydrogel microspheres for cationic dye adsorbents increases with increasing initial dye concentration, reaching saturation at a certain concentration. Furthermore, isotherm model fitting results indicate that the adsorption of methylene blue by the carrageenan-carboxylated cellulose nanofiber hydrogel microspheres for cationic dye adsorbents conforms to the Freundlich isotherm model, indicating that adsorption is multilayered and occurs on the surface of the heterogeneous adsorbent.

[0075] Figure 5The effect of reaction time on adsorption showed that the adsorption of methylene blue dye by carrageenan carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent began to approach equilibrium after 180 min and reached complete adsorption equilibrium within 330 min.

[0076] Figure 6 The linear fitting of the adsorption kinetic model of methylene blue dye with an initial concentration of 150 mg / L by carrageenan carboxylated cellulose nanofiber hydrogel microspheres showed that the adsorption reaction was more consistent with the pseudo-first-order kinetic model (a), indicating that the adsorption was physical adsorption, and the hydrogen bonding and electrostatic interaction between the carrageenan carboxylated cellulose nanofiber hydrogel microspheres and the methylene blue dye played a key role.

[0077] Figure 7 The adsorption of methylene blue dye by carrageenan carboxylated cellulose nanofiber hydrogel microspheres cationic dye adsorbent and the fitting of the intra-particle diffusion model show that the adsorption of methylene blue on carrageenan cellulose nanofiber hydrogel microspheres can be divided into three stages. The first stage is from 0 to 100 min. From the slope of the linear equation, it can be seen that the adsorption rate in this stage is relatively rapid; the second stage is from 100 to 180 min. The adsorption of methylene blue by the adsorbent increases rapidly in this stage; the third stage is from 180 to 330 min. The adsorption rate in this stage is very slow, indicating that the adsorption reaction has reached equilibrium.

[0078] The dye adsorption rate and adsorption capacity of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent of the present invention are determined as follows.

[0079] A dye solution with an initial concentration of 50-800 mg / L and 20 mg of the prepared hydrogel spheres were placed in a 100 mL beaker and then placed in a constant temperature oscillator for oscillation adsorption. After the oscillation reached adsorption equilibrium, a sample was taken. The absorbance of the adsorbed dye was measured at the maximum absorption wavelength of the dye using a UV / visible spectrophotometer. The adsorption capacity qt (mg / g) at time t (min) and the adsorption capacity qe (mg / g) at equilibrium were calculated according to the following formulas:

[0080]

[0081] Where C0, Ct, and Ce are the initial dye concentration, the dye concentration after oscillation adsorption for a certain period of time, and the dye concentration at adsorption equilibrium (mg / L), respectively; V is the volume of the dye solution (L); and m is the mass of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent (g).

[0082] The effect of the carboxylated cellulose nanofiber content in the carrageenan cellulose nanofiber hydrogel microsphere cationic dye adsorbent of the present invention on the adsorption of methylene blue by the adsorbent, the determination of the maximum adsorption amount, and the determination method of the adsorption equilibrium time are as follows.

[0083] The carboxylated cellulose nanofiber (CCN) content in the carrageenan-CCN mixture was varied to maintain the CNCN content at 0%, 97.3%, 98.6%, 99.1%, and 99.3% during the dissolution of the carrageenan. Hydrogel microspheres containing varying CNCN content were then used to adsorb methylene blue at an initial concentration of 200 mg / L to determine the CNCN content in the hydrogel microspheres that was most conducive to adsorption. The maximum equilibrium adsorption capacity was determined for solutions containing methylene blue at initial concentrations of 50 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, 500 mg / L, 600 mg / L, 700 mg / L, and 800 mg / L, using the same mass of adsorbent in a thermostatic oscillator at 298 K and 120 rpm. The adsorption equilibrium time of hydrogel microspheres is determined by taking a methylene blue solution with an initial concentration of 150 mg / L as the adsorption object, taking the adsorption reaction solution in sequence at a certain time interval to measure the adsorption capacity at that time point until the adsorption reaches equilibrium, so as to determine the adsorption equilibrium time of hydrogel microspheres with a mass fraction of carboxylated cellulose nanofibers of 98.6% for methylene blue dye.

[0084] Finally, it should be noted that the above 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 with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, characterized in that: The following steps are involved: Step (1) dissolving K-type carrageenan in carboxylated cellulose nanofibers, stirring and ultrasonically treating to form a mixed solution; Step (2) adding the mixed solution dropwise to a potassium chloride solution, stirring and cross-linking to form composite hydrogel microspheres; Step (3) washing and drying the composite hydrogel microspheres to obtain the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent.

2. The method for preparing the carrageenan carboxylated cellulose hydrogel microsphere cationic dye adsorbent according to claim 1, characterized in that: In step (1), the mass volume ratio of K-type carrageenan to carboxylated cellulose nanofibers is 0.28:18-22 (g:ml).

3. The method for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 1, characterized in that: The ultrasonic treatment time in step (1) is 40 to 80 minutes.

4. The method for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 1, characterized in that: The volume ratio of the mixed solution to the potassium chloride solution in step (2) is 2 to 4:

20.

5. The method for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 1 or 4, characterized in that: The concentration of the potassium chloride solution in step (2) is 2.5 to 7.5 wt.%.

6. The method for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 1, characterized in that: The cross-linking time in step (2) is 10 to 15 hours.

7. The method for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 1, characterized in that: The average particle size of the composite hydrogel microspheres prepared in step (2) is 0.8 to 1.2 mm.

8. The method for preparing the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 1, characterized in that: The drying temperature in step (3) is 50-70° C., and the drying time is 3-5 hours.

9. A carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent, characterized in that: The invention is prepared by the method according to any one of claims 1 to 8.

10. Use of the carrageenan carboxylated cellulose nanofiber hydrogel microsphere cationic dye adsorbent according to claim 9 in the field of organic dye wastewater adsorption.

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