Guar gum and sodium alginate crosslinking-based Congo red adsorbent as well as preparation method and application thereof

Abstract

The invention provides a guar gum and sodium alginate crosslinking-based Congo red adsorbent and a preparation method and application thereof, the preparation method of the adsorbent comprises the following steps: step 1, firing sodium alginate in a tubular furnace at 850-950 DEG C for 7-9 h to obtain carbonized sodium alginate; step 2, dissolving carbonized sodium alginate in deionized water, adding guar gum after ultrasonic dispersion, stirring to form a polysaccharide mixed solution, and cooling to 20-30 DEG C; and step 3, dropwise adding the polysaccharide mixed solution into the borax solution for crosslinking to form hydrogel, washing the hydrogel with deionized water, and drying to obtain the Congo red adsorbent based on guar gum and sodium alginate crosslinking. The process is simple and environmentally friendly, and the prepared Congo red adsorbent based on crosslinking of guar gum and sodium alginate has high adsorption efficiency and high capacity, is suitable for the field of dye wastewater treatment, and is particularly suitable for efficient removal of Congo red (CR) in dye wastewater.

Description

Technical Field

[0001] The present invention relates to the technology of adsorbents, and particularly to a Congo red adsorbent based on the crosslinking of guar gum and sodium alginate, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogels are three-dimensional porous network polymers formed by the crosslinking of one or more molecules, and their structures can absorb and lock a large amount of water in the swollen state. The water absorption capacity of hydrogels stems from the hydrophilic groups inherent in the polymer chains, while their high-efficiency adsorption performance for pollutants depends on the functional groups in the network, including hydroxyl groups (-OH), amino groups (-NH 2 ), sulfonic acid groups (-SO 3 H), carboxylic acid groups (-COOH), and amide groups (-CONH 2 ), etc. Pollutants can be captured through two ways: being adsorbed on the surface by connecting with functional groups, or being adsorbed in the polymer network.

[0003] In recent years, significant progress has been made in the research of hydrogels as high-efficiency adsorbents. Vinod Kumar Gupta et al. mixed guar gum with activated carbon, added glyoxal to the mixed solution and crosslinked it for 24 hours, and then used acetone precipitation to obtain a mortar powder-like hydrogel. Cai used polyethylene glycol as a pore-forming agent to prepare a novel self-supporting polysaccharide-based hydrogel film by adding cellulose nanofibers and micron-scale biochar to sodium alginate hydrogels. Mohammad et al. successfully produced graphene oxide / polyacrylamide-2-acrylamide-methylpropanesulfonic acid / sodium alginate (GO / PA-AMPS / SA) hydrogels using the method of free radical polymerization. Heqin used sodium alginate as the hydrogel skeleton material, and sodium carboxymethyl cellulose and protonated chitosan as strength-enhancing materials to prepare a magnetic hydrogel adsorbent Fe 3 O 4 @SA@CMC@CTS. Feng Yuefeng et al. prepared ternary composite hydrogel beads SCP@PE using sodium alginate, cellulose nanofibers, and polyethyleneimine as raw materials.

[0004] Although various preparation methods have been developed for guar gum hydrogels and sodium alginate hydrogels, there are still significant technical bottlenecks. For sodium alginate hydrogels, their intrinsic adsorption performance is weak, and composite modification is often required to enhance the adsorption capacity. This process leads to complex preparation processes and long flowcharts, restricting their large-scale application. The limitations of guar gum hydrogels are even more prominent: due to the lack of effective reaction sites in the molecular chains, it is difficult to form a stable cross-linked network with conventional inorganic cross-linking agents, forcing researchers to use organic cross-linking systems. Such cross-linking agents not only pose a risk of acute toxicity, threatening the health of experimental personnel, but their potential environmental cumulative hazards are even more worrying - if cross-linking dissociation occurs, the released organic cross-linking agents may cause persistent pollution to the ecosystem. Summary of the Invention

[0005] The purpose of the present invention is to propose a preparation method of a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate, aiming at the problems of low adsorption efficiency of traditional sodium alginate adsorbents and the need to use toxic organic cross-linking agents for guar gum. This method is simple and environmentally friendly, and the prepared Congo red adsorbent based on the cross-linking of guar gum and sodium alginate has both high efficiency and high capacity (the equilibrium adsorption capacity reaches 942.33 mg / g), and is applicable to the field of dye wastewater treatment, especially for the efficient removal of Congo red (CR) in dye wastewater.

[0006] It should be noted that in the present invention, unless otherwise specified, the specific meaning of "including" involving composition limitations and descriptions includes both the open "including", "containing" and their similar meanings, as well as the closed "consisting of", "constituted by" and their similar meanings.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is: a preparation method of a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate, including the following steps:

[0008] Step 1: Burn sodium alginate at 850 - 950 °C for 7 - 9 h to obtain carbonized sodium alginate (CSA); the burning equipment can use a tube furnace;

[0009] Step 2: Dissolve carbonized sodium alginate in deionized water, add guar gum after ultrasonic dispersion, and stir to form a polysaccharide mixed solution. Since the viscosity of the guar gum solution decreases with the increase of temperature, cooling to 20 - 30 °C is beneficial to reducing the system viscosity;

[0010] Step 3: In order to obtain well-defined hydrogel spheres and avoid the generation of shapeless hydrogel spheres, the polysaccharide mixed solution is dropped into the borax solution drop by drop for cross-linking. After forming the hydrogel, it is rinsed with deionized water and dried to obtain a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate (the adsorbent is also called sodium alginate / guar gum composite hydrogel SA / GG composite hydrogel).

[0011] Further, the ultrasonic dispersion time in Step 2 is 2 - 7 h.

[0012] Further, the mass ratio of sodium alginate carbide to guar gum in Step 2 is 1:17.5 - 1:20.

[0013] Further, the ratio of sodium alginate carbide to deionized water in Step 2 is 1:1250 - 3:1250.

[0014] Further, the concentration of the borax solution in Step 3 is 2 - 3% wt.

[0015] Further, the mass ratio of the mixed solution to the borax solution in Step 3 is 2000:10000 - 3000:10000, and preferably the mass ratio is 2537:10000 - 2542:10000. The present invention uses a borax solution as a cross - linker to avoid the toxicity problem of organic reagents.

[0016] Further, the cross - linking time in Step 3 is 12 - 16 h.

[0017] Further, the drying temperature in Step 3 is 40 - 60 °C, and the drying time is 4 - 6 h.

[0018] Another object of the present invention also discloses a Congo red adsorbent based on the cross - linking of guar gum and sodium alginate, which is prepared by the above - mentioned method.

[0019] Further, the pore size of the Congo red adsorbent based on the cross - linking of guar gum and sodium alginate is 3.4 - 3.5 nm. The main adsorption groups of the Congo red adsorbent based on the cross - linking of guar gum and sodium alginate are hydroxyl groups (-OH) and carboxyl groups (-COOH).

[0020] Further, for the Congo red adsorbent based on the cross - linking of guar gum and sodium alginate, the adsorption capacity is 730.00 - 960 mg / g, and preferably 942.33 - 952.33 mg / g.

[0021] Another object of the present invention also discloses the application of a Congo red adsorbent based on the cross - linking of guar gum and sodium alginate in the field of dye wastewater treatment.

[0022] Further, the Congo red adsorbent based on the cross - linking of guar gum and sodium alginate is particularly suitable for the adsorption of industrial wastewater containing Congo red.

[0023] Furthermore, the method for the Congo red adsorbent based on the crosslinking of guar gum and sodium alginate to adsorb Congo red is as follows: at pH = 2 - 13, adsorption temperature of 25 - 45 °C, adsorption time of 4 - 8 h, and adsorbent dosage of 0.05 - 0.4 mg / ml. For example, when the volume of the Congo red solution is 200 ml, the adsorbent dosage is 10 - 80 mg.

[0024] Furthermore, the concentration of the Congo red solution is 50 mg / L - 600 mg / L.

[0025] Furthermore, the preferred adsorption temperature is 40 - 45 °C.

[0026] The adsorption mechanism of the Congo red adsorbent based on the crosslinking of guar gum and sodium alginate in the present invention:

[0027] Through the characterization and analysis of the hydrogel by SEM, XPS, FT-IR, and BET, as shown in the appendix Figure 2-5 it can be known that the adsorption of the SA / GG hydrogel is mainly chemical adsorption, and the main groups participating in the adsorption are -OH and -COO - . Moreover, through the analysis of B in XPS, it can be known that the borate diester bond is the root cause of the crosslinking. The existence of the borate diester bond has two effects: First, since the crosslinking reaction is a chemical crosslinking, the hydrogel spheres are very dense. And it can be confirmed by BET detection that the pore size is 3.391 nm, which is very narrow. This determines that the main adsorption principle of the hydrogel spheres cannot be pore adsorption. Second, the binding energy of B detected by XPS in the hydrogel is very low and relatively unstable. The borate diester bond in the hydrogel in water may be broken by water molecules, resulting in the release or partial release of the crosslinking.

[0028] Time, temperature, and pH value have a significant impact on the adsorption of the hydrogel. The relationship diagrams of the three with the adsorption effect are as follows Figure 6-8 shown. Within the first 60 min of adsorption, the rate of the hydrogel adsorbing water molecules is much greater than the rate of adsorbing CR molecules. As time progresses, the adsorption capacity of the SA / GG hydrogel for CR continuously increases and finally reaches equilibrium at about 4 h. In addition, for the hydrogel, in a neutral acid-base environment and at a higher temperature, its adsorption capacity for CR is higher. However, it should be noted that due to the relatively weak mechanical properties of the hydrogel itself, it will break due to adsorbing too many water molecules and dye molecules. This phenomenon will gradually intensify with the increase in temperature.

[0029] The adsorption mechanism and adsorption process of the SA / GG hydrogel spheres for CR more conform to the pseudo-first-order kinetic model and the Tekmin isotherm model. The fitting results are as follows Figure 6 and Figure 7As shown. During the adsorption of CR by the hydrogel, the rate of binding of the adsorbed substance to the surface of the adsorbent may be proportional to the amount of the adsorbed substance already present on the adsorbent, and, neglecting the influence of concentration, the relationship between temperature and adsorption capacity is proportional. The relationship diagram is as Figure 9 shown.

[0030] The adsorption of CR by SA / GG hydrogel spheres is an endothermic reaction, and as the temperature increases, the adsorption effect of SA / GG hydrogel spheres on CR gradually increases. Moreover, the adsorption of the hydrogel occurs spontaneously. The relationship diagram is as follows Figure 10 shown.

[0031] Working principle:

[0032] The adsorption process can be divided into the following steps. First, the substance to be adsorbed is transported to the surface of the adsorbent; then, chemical bonds such as hydrogen bonds, ionic interactions, and charge interactions are formed with the various groups of the hydrogel, and thus it is adsorbed by the hydrogel; finally, the hydrogel reaches a critical point due to the ratio of the adsorbed substance to the external substance, presenting a dynamic equilibrium. Generally speaking, the adsorption process is a process that is fast first and then slow and tends to equilibrium.

[0033] Adsorption kinetic models such as the pseudo-first-order model and the pseudo-second-order model can be used to explore the influence of adsorption time on adsorption capacity. The formulas of the two models are as follows.

[0034] Pseudo-first-order kinetic model:

[0035] ln(q e -q t ) = lnq e -k 1 t

[0036] Pseudo-second-order kinetic model:

[0037]

[0038] Currently, the adsorption isotherm of a liquid refers to the relationship between adsorption capacity and equilibrium concentration when the adsorbent reaches adsorption equilibrium. In addition to describing the relationship between the adsorbate on the adsorbent and the adsorbate in the solution, the adsorption isotherm also provides information about the adsorption mechanism, adsorption capacity, and surface properties.

[0039] The Langmuir, Freundlich, and Temkin isotherm models are commonly used models. The Langmuir isotherm model theory assumes that the energy of the active sites on the solid surface is the same, which also indicates that the distribution of adsorbate molecules is uniform. The adsorbate is adsorbed on the active sites in a monolayer form, and all the active sites are occupied. Further adsorption will no longer occur. The formula is as follows.

[0040]

[0041] The Freundlich model assumes that the adsorption of adsorbate by the adsorbent is multilayered. The model is expressed as follows.

[0042] q e = K F C e 1 / n

[0043] The Temkin isotherm model ignores the influence of concentration and assumes that the relationship between the adsorption capacity and temperature is linear, rather than logarithmic as in the Freundlich model. Its model can be expressed by the following formula.

[0044]

[0045] During the adsorption process, in order to study the adsorption mechanism of SA / GG composite hydrogel beads more deeply, the spontaneity and thermal changes of adsorption can be studied starting from adsorption thermodynamics. And in order to determine these two values, three thermodynamic parameters, enthalpy (ΔH 0 ), entropy (ΔS 0 ), and Gibbs free energy (ΔG 0 ), are required. And these thermodynamic parameters can be calculated by the following three formulas.

[0046]

[0047] ΔG 0 = -RTlnK D

[0048]

[0049] The present invention relates to a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate, its preparation method and application, and has the following advantages compared with the prior art:

[0050] 1) The preparation method of the Congo red adsorbent based on the cross-linking of guar gum and sodium alginate in the present invention is simple, has a short production cycle, and the raw materials are all easy to obtain and economical.

[0051] 2) In the present invention, by high-temperature calcination, the pore size of sodium alginate is increased and the attraction to dyes is enhanced. The present invention combines carbonized sodium alginate (CSA) with guar gum (GG) to form a dense and porous three-dimensional network structure. The Congo red adsorbent based on the cross-linking of guar gum and sodium alginate has excellent adsorption performance while maintaining a relatively fast adsorption rate. For example, at an environmental temperature of 45 °C and an initial Congo red solution concentration of 400 mg / L, the equilibrium adsorption capacity of the sodium alginate / guar gum hydrogel is as high as 942.33 mg / g.

[0052] 3) The raw materials of the Congo red adsorbent based on the crosslinking of guar gum and sodium alginate in the present invention are all inorganic substances, which will not cause secondary pollution to the environment and have significant environmentally friendly characteristics.

[0053] The Congo red adsorbent based on the crosslinking of guar gum and sodium alginate in the present invention solves the problems of low adsorption efficiency of traditional sodium alginate adsorbents and the need to use toxic organic crosslinking agents for guar gum. It has the advantages of simple process, environmental protection, high adsorption capacity (the equilibrium adsorption capacity reaches 942.33 mg / g), etc., and has good application prospects and great potential for large-scale promotion in the field of dye wastewater treatment. Description of the Drawings

[0054] Figure 1 It is a flow chart for the preparation of SA / GG composite hydrogel.

[0055] Figure 2 It is the SEM image of the SA / GG hydrogel beads in Example 1. (a), (c), (e) are the SEM images at the microscopic scales of 5 μm, 40 μm, and 300 μm before adsorption; (b), (d), (f) are the SEM images at the microscopic scales of 5 μm, 40 μm, and 300 μm after adsorption.

[0056] Figure 3 It is the FT-IR spectrum of the SA / GG hydrogel beads in Example 1.

[0057] Figure 4 It is the XPS hydrogel binding energy status of the SA / GG hydrogel beads in Example 1; (a) hydrogel binding energy status; (b) O 1s binding energy; (c) C 1s binding energy; (d) Na 1s binding energy; (e) B 1s binding energy; (f) N 1s binding energy.

[0058] Figure 5 It is the N 2 adsorption-desorption isotherm and the corresponding pore size distribution diagram of the SA / GG hydrogel beads in Example 1.

[0059] Figure 6 It is the adsorption kinetic curve of the SA / GG hydrogel beads in Example 1. (a) is the adsorption kinetics of the SA / GG hydrogel beads for CR in a 100 mg / L solution; (b) is the adsorption kinetics of the SA / GG hydrogel beads for CR in a 200 mg / L solution.

[0060] Figure 7 It is the adsorption isotherm. (a) Adsorption isotherm of the SA / GG hydrogel beads for CR; (b) Fitting of the Langmuir adsorption isotherm model; (c) Fitting of the Freundlich isotherm model; (d) Fitting of the Temkin isotherm model.

[0061] Figure 8It is the relationship curve between pH value and Cr removal rate.

[0062] Figure 9 It is the relationship diagram between adsorbent mass and adsorption capacity.

[0063] Figure 10 It is for adsorption thermodynamics (a) C e reciprocal of and lnK d relationship diagram with; (b) reciprocal of adsorption temperature (1 / T) and ln K 0 relationship diagram

[0064] Meanings represented by reference numerals in the drawings

[0065] Figure 4 In, Binding energy refers to binding energy and Intensity refers to intensity. Figure 5 In, Relative Pressure refers to relative pressure, while Volume refers to the nitrogen adsorption capacity of the hydrogel under relative pressure. Figure 6 In, t refers to adsorption time, Q t refers to the adsorption amount of the hydrogel for Congo red dye at a certain moment. Figure 7 In, Ce refers to the concentration of the Congo red solution after the hydrogel is put into the Congo red solution and reaches adsorption equilibrium. Figure 9 In, m refers to the mass of the hydrogel used for adsorption. Figure 10 In, 1 / T refers to the derivative of temperature, K D is the adsorbate distribution coefficient. Detailed implementation manners

[0066] Hereinafter, the present invention will be further described in conjunction with embodiments. The descriptions of the technical features recorded below are 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:

[0067] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the systematic errors inevitable in industrial production.

[0068] In this specification, the numerical range represented by "numerical value A to numerical value B" refers to the range including the endpoint numerical values A and B.

[0069] In this specification, the numerical range represented by "above" or "below" refers to the numerical range including this number.

[0070] In this specification, the meaning represented by "can" includes the meanings of both performing a certain treatment and not performing a certain treatment.

[0071] In this specification, the use of "optional" or "optionally" indicates that certain substances, components, implementation steps, application conditions and other factors are used or not used.

[0072] In this specification, when "normal temperature" or "room temperature" is used, the temperature can be 15 - 25 °C.

[0073] In this specification, for reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0074] Example 1

[0075] This example discloses a Congo red adsorbent based on the cross - linking of guar gum and sodium alginate, and its preparation method is as Figure 1 shown, specifically including the following steps:

[0076] 1. Place 10 g of sodium alginate in a crucible, calcine it in a tube furnace at 900 °C for 8 h to obtain CSA powder.

[0077] 2. Take 0.02 g of CSA powder, dissolve it in 25 mL of deionized water, ultrasonically disperse it for 2 h, add 375 mg of guar gum, stir to obtain a polysaccharide mixture, and cool it to 25 °C.

[0078] 3. Drop the polysaccharide mixture into a 3% wt borax solution, and the mass ratio of the polysaccharide mixture to the 3% wt borax solution is 2539.5:10000. Let it stand for cross - linking for 12 h to form hydrogel beads.

[0079] 4. Rinse it 5 times with deionized water and dry it at 40 °C for 4 h to obtain a Congo red adsorbent (SA / GG hydrogel beads) based on the cross - linking of guar gum and sodium alginate.

[0080] In the present invention, by high - temperature carbonization of sodium alginate (900 °C, 8 h) to increase its pore size and combining with an inorganic borax solution as a cross - linker, a Congo red adsorbent based on the cross - linking of guar gum and sodium alginate with high adsorption performance is successfully prepared. The adsorption experiment proves that the Congo red adsorbent based on the cross - linking of guar gum and sodium alginate reaches the adsorption equilibrium within 4 h under the conditions of pH = 7 and 45 °C, and the adsorption capacity reaches 942.33 mg / g.

[0081] As Figure 2-5 shown, the adsorption of the SA / GG hydrogel is mainly chemical adsorption, and the main groups participating in the adsorption are - OH and - COO - . As Figure 6-8 shown, time, temperature, and pH value have a significant impact on the adsorption of the hydrogel. As Figure 9As shown, the rate of binding of the adsorbate to the adsorbent surface may be proportional to the amount of adsorbate already present on the adsorbent, and, ignoring the influence of concentration, the relationship between temperature and adsorption capacity is proportional. As Figure 10 shown, the adsorption of CR by SA / GG hydrogel beads is an endothermic reaction, and as the temperature increases, the adsorption effect of SA / GG hydrogel beads on CR gradually increases. Moreover, the adsorption of the hydrogel occurs spontaneously.

[0082] Example 2

[0083] This example discloses a Congo red adsorbent based on the crosslinking of guar gum and sodium alginate, and its preparation method is as Figure 1 shown, and specifically includes the following steps:

[0084] 1. Place 10 g of sodium alginate in a crucible and calcine it in a tube furnace at 910 °C for 8 h to obtain CSA powder.

[0085] 2. Take 0.02 g of CSA powder and dissolve it in 25 mL of deionized water, ultrasonically disperse it for 2 h, add 375 mg of guar gum, stir to obtain a polysaccharide mixture, and cool it to 25 °C.

[0086] 3. Drop the polysaccharide mixture into a 3% wt borax solution, and the mass ratio of the polysaccharide mixture to the 3% wt borax solution is 2539.5:10000. Let it stand for crosslinking for 12 h to form hydrogel beads.

[0087] 4. Rinse it 5 times with deionized water and dry it at 40 °C for 6 h to obtain a Congo red adsorbent (SA / GG hydrogel beads) based on the crosslinking of guar gum and sodium alginate

[0088] In the present invention, sodium alginate is carbonized at a high temperature (900 °C, 8 h) to increase its pore size, and an inorganic borax solution is used as a crosslinking agent to successfully prepare a Congo red adsorbent based on the crosslinking of guar gum and sodium alginate with high adsorption performance. Adsorption experiments prove that the Congo red adsorbent based on the crosslinking of guar gum and sodium alginate reaches the adsorption equilibrium within 4 h at pH = 7 and 45 °C, and the adsorption capacity reaches 934.33 mg / g.

[0089] The adsorption process of SA / GG hydrogel for CR (Congo red) is mainly dominated by chemisorption, and its main active groups are hydroxyl (-OH) and carboxylate (-COO-). The kinetic and thermodynamic characteristics of this adsorption system are significantly regulated by three key parameters: time, temperature, and pH value. Kinetic studies have shown that the rate of binding of the adsorbate to the surface of the adsorbent may be positively correlated with the amount of adsorbate already loaded on the surface of the adsorbent, which conforms to the characteristic law of chemisorption. Thermodynamic analysis indicates that, under the condition of neglecting the influence of solution concentration, an increase in temperature will significantly enhance the adsorption capacity of the hydrogel. Experimental data show that the adsorption of CR by SA / GG hydrogel is a spontaneous (ΔG < 0) and endothermic (ΔH > 0) process. As the temperature rises from 25 °C to 45 °C, the adsorption efficiency shows a systematic increasing trend, which confirms that temperature has a dual promoting effect on the adsorption process by changing the activity of adsorption sites and the molecular diffusion rate.

[0090] Example 3

[0091] This example discloses a Congo red adsorbent based on the crosslinking of guar gum and sodium alginate, and its preparation method is as Figure 1 shown, specifically including the following steps:

[0092] 1. Place 10 g of sodium alginate in a crucible and calcine it at 890 °C in a tube furnace for 7 h to obtain CSA powder.

[0093] 2. Take 0.02 g of CSA powder and dissolve it in 25 mL of deionized water. Ultrasonically disperse it for 5 h, add 375 mg of guar gum, stir to obtain a polysaccharide mixture, and cool it to 25 °C.

[0094] 3. Drop the polysaccharide mixture into a 3% wt borax solution. The mass ratio of the polysaccharide mixture to the 3% wt borax solution is 2539.5:10000. Let it stand for crosslinking for 12 h to form hydrogel beads.

[0095] 4. Rinse it 5 times with deionized water and dry it at 40 °C for 4 h to obtain a Congo red adsorbent based on the crosslinking of guar gum and sodium alginate (SA / GG hydrogel beads)

[0096] In this invention, sodium alginate is carbonized at high temperature (900 °C, 8 h) to increase its pore size, and an inorganic borax solution is used as a crosslinking agent to successfully prepare a Congo red adsorbent based on the crosslinking of guar gum and sodium alginate with high adsorption performance. Adsorption experiments have proved that the Congo red adsorbent based on the crosslinking of guar gum and sodium alginate reaches the adsorption equilibrium within 6 h at pH = 7 and 35 °C, and the adsorption capacity reaches 731.63 mg / g.

[0097] The adsorption process of Congo red (CR) by SA / GG hydrogel is mainly dominated by chemisorption mechanism. Its surface hydroxyl groups (-OH) and carboxylate groups (-COO-) form stable bonds with CR molecules through coordination or electrostatic interactions. Experiments show that the efficiency of this adsorption system is co-regulated by time, temperature, and pH value: the adsorption rate is positively correlated with the amount of CR already loaded on the adsorbent surface, conforming to the dynamic equilibrium characteristics of chemisorption; within the range of 25–45 °C, the adsorption capacity increases significantly with the increase of temperature, confirming that it is a spontaneous (ΔG<0) and endothermic (ΔH>0) process. The increase in temperature achieves a dual promotion effect by enhancing the activity of adsorption sites and the molecular diffusion driving force. At the same time, the solution pH directly affects the adsorption efficiency by regulating the surface charge distribution of the hydrogel and the dissociation state of CR molecules. The optimal adsorption conditions mostly concentrate in a neutral or weakly acidic environment.

[0098] Example 4

[0099] This example discloses a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate, and its preparation method is as Figure 1 shown, specifically including the following steps:

[0100] 1. Place 10 g of sodium alginate in a crucible and calcine it in a tube furnace at 860 °C for 8 h to obtain CSA powder.

[0101] 2. Take 0.02 g of CSA powder and dissolve it in 24 mL of deionized water. Ultrasonically disperse it for 2 h, add 375 mg of guar gum, stir to obtain a polysaccharide mixture, and cool it to 25 °C.

[0102] 3. Drop the polysaccharide mixture into a 3% wt borax solution. The mass ratio of the polysaccharide mixture to the 3% wt borax solution is 2539.5:10000. Let it stand and cross-link for 12 h to form hydrogel beads.

[0103] 4. Rinse it 5 times with deionized water and dry it at 60 °C for 5 h to obtain a Congo red adsorbent (SA / GG hydrogel beads) based on the cross-linking of guar gum and sodium alginate.

[0104] In this invention, sodium alginate is carbonized at high temperature (900 °C, 8 h) to increase its pore size, and an inorganic borax solution is used as a cross-linking agent to successfully prepare a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate with high adsorption performance. Adsorption experiments prove that the Congo red adsorbent based on the cross-linking of guar gum and sodium alginate reaches the adsorption equilibrium within 4 h at pH = 7 and 45 °C, and the adsorption capacity reaches 952.33 mg / g.

[0105] The adsorption of Congo red (CR) by the SA / GG hydrogel is mainly driven by chemisorption, and its surface hydroxyl groups (-OH) and carboxylate groups (-COO-) form stable bonds with CR molecules through coordination or electrostatic interactions. It has been found that time, temperature, and pH have significant synergistic regulatory effects on this process: the adsorption rate is dynamically positively correlated with the CR loading on the adsorbent surface, which conforms to the kinetic characteristics of chemisorption; in the range of 25–45 °C, increasing the temperature not only enhances the activity of adsorption sites but also accelerates molecular diffusion, causing the adsorption capacity to continuously increase with increasing temperature. The thermodynamic parameters (ΔG < 0, ΔH > 0) further confirm that it is a spontaneous endothermic process. At the same time, the solution pH significantly affects the adsorption efficiency by regulating the surface charge of the hydrogel and the dissociation state of CR molecules, and the adsorption performance is optimal under neutral to weakly acidic conditions.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and 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 Congo red adsorbent based on guar gum and sodium alginate cross-linking, characterized in that: The following steps are involved: Step 1, calcining sodium alginate at 850-950°C for 7-9h to obtain carbonized sodium alginate; Step 2, dissolving carbonized sodium alginate in deionized water, adding guar gum after ultrasonic dispersion, stirring to form a polysaccharide mixed solution, and cooling to 20-30° C.; Step 3: drop the polysaccharide mixed solution into the borax solution drop by drop for cross-linking, and after forming a hydrogel, rinse with deionized water and dry to obtain a Congo red adsorbent based on the cross-linking of guar gum and sodium alginate.

2. The method for preparing the Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 1, characterized in that: Step 2: The mass ratio of carbonized sodium alginate to guar gum is 1:17.5-1:

20.

3. The method for preparing the Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 1, characterized in that: Step 3 The concentration of the borax solution is 2-3%wt.

4. The method for preparing the Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 1, characterized in that: The mass ratio of the mixed solution in step 3 to the borax solution is 2000:10000-3000:10000.

5. The method for preparing the Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 1, characterized in that: The cross-linking time in step 3 is 12-16 hours.

6. The method for preparing the Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 1, characterized in that: Step 3: The drying temperature is 40-60°C and the drying time is 4-6h.

7. A Congo red adsorbent based on guar gum and sodium alginate cross-linking, characterized in that: The method is prepared by any one of claims 1 to 6.

8. The Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 7, characterized in that: Its pore size is 3.4-3.5nm.

9. Use of the Congo red adsorbent based on guar gum and sodium alginate cross-linking according to claim 7 or 8 in the field of dye wastewater treatment.

10. The use according to claim 9, characterized in that: The method for adsorbing Congo red by the Congo red adsorbent based on the cross-linking of guar gum and sodium alginate is as follows: at pH=2-13, adsorption temperature 25-45°C, adsorption time 4-8h, and adsorption amount of the adsorbent is 0.05-0.4mg / ml.

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