A cross-linked modified peach gum gel and its application in the removal of hexavalent chromium

Abstract

This invention discloses a cross-linked modified gum arabic gel and its application in the removal of hexavalent chromium. The cross-linked modified gum arabic gel is prepared by placing purified gum arabic and maleic anhydride in N,N-dimethylformamide, mixing thoroughly, adding a pore-forming agent, and stirring the mixture under a nitrogen atmosphere at 60-80°C for 0.5-2 hours. Then, a solution of branched polyethyleneimine in N,N-dimethylformamide is added, and the reaction continues at 60-80°C until a light yellow granular precipitate is formed. The precipitate is then filtered under reduced pressure, washed, and dried to obtain the final product. This cross-linked modified gum arabic gel material exhibits both adsorption and reduction of hexavalent chromium in its application to the removal of hexavalent chromium, demonstrating excellent performance in treating high-concentration chromium wastewater. It is unaffected by common coexisting metal ions and exhibits good selectivity. Furthermore, the preparation method of this cross-linked modified gum arabic gel material is simple, easy to synthesize industrially, and readily applicable to the market.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of new biomass materials for water purification, specifically relating to the preparation of a cross-linked modified peach gum gel material and the application of cross-linked modified peach gum gel in the removal of hexavalent chromium. Background Technology

[0002] Chromium (Cr) is a highly toxic environmental pollutant, and excessive emissions can easily cause water and soil pollution. Hexavalent chromium in wastewater mainly exists as dichromate (Cr₂O₇). 2- Chromium exists in anionic form. Chromium pollution originates from wastewater discharged from industries such as chromium ore processing and smelting, metal surface treatment, leather tanning, and dyeing. For example, potassium dichromate is a commonly used strong oxidant in industry. Wastewater containing hexavalent chromium is highly toxic. Aerobic and anaerobic microbial treatment technologies in urban wastewater treatment plants cannot reduce chromium concentrations, and existing wastewater purification technologies also struggle to completely remove chromium ions.

[0003] Dichromate poisoning initially corrodes the human digestive tract. Once in the bloodstream, hexavalent chromium is reduced to trivalent chromium, causing a decrease in glutathione reductase activity and resulting in hemoglobin becoming methemoglobin, which loses its oxygen-carrying capacity. Therefore, hexavalent chromium is significantly more toxic than trivalent chromium and poses a greater threat to the ecological environment. There is an urgent need to develop new technologies to address industrial hexavalent chromium pollution and improve the efficiency of chromium purification.

[0004] Peach gum is a macromolecular heteropolysaccharide secreted by peach trees, possessing a well-developed branched chain structure. Peach gum polysaccharides contain many hydrophilic hydroxyl groups, making it readily soluble in water to form a homogeneous and stable hydrosol. Experiments have shown that peach gum has a strong adsorption capacity for heavy metal ions in water, demonstrating its potential as a heavy metal ion adsorbent in industrial wastewater treatment. Despite its excellent water absorption and heavy metal ion adsorption capabilities, its water solubility hinders recycling and reuse. Therefore, further chemical modification of natural peach gum to stabilize its molecular structure and enhance its heavy metal ion adsorption capacity has become crucial for technological development. Summary of the Invention

[0005] For highly toxic hexavalent chromium (Cr2O7) in industrial wastewater 2- To address the challenges of chromium purification, including the unstable structure of gum arabic, poor adsorption capacity for hexavalent chromium, and the inability to recycle and reuse it, this invention provides a cross-linked modified gum arabic gel material. This material is prepared by cross-linking gum macromolecules as biomass raw material. When applied to chromium-containing wastewater treatment, this cross-linked modified gum arabic gel material exhibits excellent adsorption-reduction capacity for hexavalent chromium and is easily recyclable.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] 1. The purification of peach gum involves soaking natural peach gum in warm water for 20-30 hours until it is fully swelled and absorbs water. Then, it is filtered under reduced pressure 2-4 times using a 100-mesh fine filter cloth to remove impurities from the peach gum. The transparent peach gum water soluble gel is then dried at 50-70℃, pulverized, and purified peach gum is obtained.

[0008] 2. Dissolve the purified peach gum and maleic anhydride in N,N-dimethylformamide, mix well, add a pore-forming agent, purge with nitrogen, and stir at 60-80℃ for 0.5-2 hours under nitrogen atmosphere. Then add N,N-dimethylformamide solution of branched polyethyleneimine and continue to react at 60-80℃ until a large amount of light yellow granular precipitate is generated. Filter under reduced pressure, and wash and dry the granular precipitate with ethanol to obtain cross-linked modified peach gum gel.

[0009] The mass ratio of purified peach gum to maleic anhydride is 1-3:1, the mass ratio of purified peach gum to pore-forming agent is 15-25:1, and the mass ratio of purified peach gum to branched polyethyleneimine is 1-1.5:1.

[0010] The pore-forming agent used is ammonium bicarbonate;

[0011] 3. The above-mentioned cross-linked modified gum arabic gel was applied to the removal of hexavalent chromium (Cr2O7). 2- In the study, experimental results showed that the cross-linked modified gum arabic gel achieved a chromium removal rate of 98-99% in hexavalent chromium solutions with concentrations ranging from 100-600 mg / L after 1 hour of adsorption. Furthermore, after adsorbing hexavalent chromium, this material could also reduce some of the hexavalent chromium to the less toxic trivalent chromium (Cr). 3+ It has both adsorption and reduction functions.

[0012] The recycled cross-linked modified peach gum gel was regenerated by elution with sodium hydroxide solution and reused to treat aqueous solutions containing hexavalent chromium. After six consecutive cycles, the removal rate of hexavalent chromium remained at 99%. Furthermore, the cross-linked modified peach gum gel of this invention is not affected by Cu during use. 2+ Co 2+ Fe 3+ Al 3+ Ca 2+ Na + The influence of coexisting metal ions.

[0013] Advantages and technical effects of the present invention:

[0014] 1. The branched polyethyleneimine used in this invention has a well-developed branched structure. The amino groups at the ends of the branches form a supramolecular network structure with the gum olean molecules through intermolecular hydrogen bonds. The introduction of amino groups can further enhance the supramolecular network's ability to adsorb hexavalent chromium. Through maleic anhydride crosslinking modification, stable ester bonds and amide bonds can be generated in the supramolecular network structure, forming a gum olean polysaccharide-maleic acid-branched polyethyleneimine crosslinked polymer with a three-dimensional network structure. This makes the crosslinked modified gum olean gel insoluble in water, achieving the purpose of recycling and reuse.

[0015] 2. The cross-linked modified gum arabic gel of this invention has both adsorption and reduction effects in the removal of hexavalent chromium. It also shows excellent results in the treatment of high-concentration chromium waste liquid and is not affected by common coexisting metal ions. In addition to retaining most of the hydroxyl groups of gum arabic polysaccharide, the molecular chain of the cross-linked modified gum arabic gel also has a large number of amino groups of polyethyleneimine, as well as ester groups and amide groups generated by the reaction with maleic anhydride. These active groups are the active sites for adsorbing hexavalent chromium. The presence of a large number of hydroxyl, amino and amide groups gives the cross-linked modified gum arabic gel good hydrophilicity and water absorption, which is beneficial for the rapid adsorption of hexavalent chromium from aqueous solutions.

[0016] 3. The cross-linked modified peach gum gel preparation method of the present invention is simple and easy to industrialize and promote in the market. Attached Figure Description

[0017] Figure 1 Schematic diagrams of the morphology of purified peach gum and cross-linked modified peach gum gel;

[0018] Figure 2 This is a scanning electron microscope image of cross-linked modified peach gum gel;

[0019] Figure 3 The infrared spectrum of cross-linked modified peach gum gel;

[0020] Figure 4 The X-ray photoelectron spectra of cross-linked modified gum arabic gel are shown in Figure a, where Figure a is the full spectrum, Figure b is the C 1s spectrum, Figure c is the N 1s spectrum, and Figure d is the O 1s spectrum.

[0021] Figure 5 This is a schematic diagram of the network structure of cross-linked modified peach gum gel macromolecules;

[0022] Figure 6 The fitted curves show the isothermal adsorption data of hexavalent chromium on cross-linked modified gum arabic gel.

[0023] Figure 7 The figure shows the fitting curves for the adsorption kinetics of hexavalent chromium on cross-linked modified gum arabic gel. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of the present invention is not limited to the contents described. Unless otherwise specified, the reagents and methods used in the embodiments are all commercially available reagents and conventional methods.

[0025] Example 1: Preparation of cross-linked modified peach gum gel material

[0026] 1. Soak the coarse peach gum in warm water for 24 hours until it is fully swelled and absorbs water. Stir to allow impurities to settle. Then, use a 100-mesh fine-mesh filter cloth to repeatedly filter under reduced pressure three times to remove impurities. Dry the filtered peach gum in a 50℃ oven, then pulverize it to 200 mesh to obtain purified peach gum (PG). See [link to product description]. Figure 1 Left image;

[0027] 2. Weigh 2g of purified peach gum (PG) and 1g of maleic anhydride (MAH) into a 100mL round-bottom flask. Add 50mL of N,N-dimethylformamide (DMF) as the reaction solvent, and then add 0.1g of ammonium bicarbonate as a pore-forming agent. Purge with nitrogen and place the flask in a 70℃ water bath for heating and stirring for 1 hour to allow the peach gum and maleic anhydride to fully undergo esterification. Then, slowly add an N,N-dimethylformamide solution containing 1.5g of branched polyethyleneimine (PEI), and continue the reaction at 70℃ for 1 hour. A large amount of light yellow granular precipitate is formed. After the reaction is complete, filter to remove the N,N-dimethylformamide solvent. Wash the light yellow solid product with anhydrous ethanol at least three times, and then dry it in a 50℃ oven for 48 hours to obtain cross-linked modified peach gum gel (PG-MAH-PEI). See [link to relevant documentation]. Figure 1 The image on the right.

[0028] 3. Structural characteristics of cross-linked modified peach gum gel

[0029] Using a scanning electron microscope ( Figure 2 ), infrared spectrum ( Figure 3 X-ray photoelectron spectroscopy (XPS) Figure 4 The morphology and structure of the above-mentioned cross-linked modified peach gum gel were characterized.

[0030] Figure 2 The results show that the cross-linked modified peach gum gel has a uniform internal texture and a large number of pores.

[0031] Figure 3 The results show that the gum molecule is at 3440 cm⁻¹ -1 The peak at 2929 cm⁻¹ belongs to the -OH stretching vibration peak. -1 The peak at 1629 cm⁻¹ belongs to the CH bond stretching vibration peak. -1 The peak at 1036 cm⁻¹ is attributed to the stretching vibration peak of uronic acid in the gum molecule. -1The peak at 1729 cm⁻¹ belongs to the COC stretching vibration peak. The cross-linked modified gum arabic gel at 1729 cm⁻¹... -1 The characteristic peak of the stretching vibration of the ester group appeared at 1662 cm⁻¹. -1 The presence of a stretching vibration characteristic peak of amide indicates that the gum-maleic anhydride-polyethyleneimine have been successfully cross-linked.

[0032] Figure 4 The results show that the cross-linked modified gum arabic contains C, O, and N elements, and has chemical bonds such as CC, CO, C=O, CN, and NC=O, further proving that gum arabic-maleic anhydride-polyethyleneimine has been successfully cross-linked.

[0033] The crosslinked modified peach gum prepared in this invention uses natural peach gum polysaccharide (PG) as the matrix and maleic anhydride (MAH) as the crosslinking bridge agent to undergo a covalent crosslinking reaction with polyethyleneimine (PEI) to form a peach gum polysaccharide-maleic acid-branched polyethyleneimine crosslinked polymer (PG-MAH-PEI) with a three-dimensional network structure. A schematic diagram of its molecular structure is shown below. Figure 5 The cross-linked modified gum arabic gel has the following three structural characteristics:

[0034] (1) The molecular chain of natural peach gum polysaccharide contains a large number of hydroxyl groups (-OH). Under the action of a 70°C water bath and DMF solvent, maleic anhydride first undergoes a ring-opening reaction. The carboxyl group (-COOH) in its molecule undergoes an esterification reaction with the hydroxyl group of peach gum polysaccharide, grafting unsaturated carboxylic acid groups onto the main chain of peach gum polysaccharide to form a peach gum-maleic anhydride intermediate containing carboxyl and ester groups.

[0035] (2) Polyethyleneimine (PEI) is a linear polymer containing a large number of active amino groups (-NH2). The amino groups on its molecular chain undergo amidation with maleic anhydride. At the same time, the amino groups on the polyethyleneimine molecule can combine with the carboxyl groups on the molecular chains of different gum arabic-maleic anhydride intermediates, thereby crosslinking multiple gum arabic polysaccharide molecular chains through the "PG-MAH-PEI" linkage, ultimately forming a stable three-dimensional network crosslinked structure. The formation of the three-dimensional network crosslinked structure gives the crosslinked modified gum arabic gel good structural stability and a well-developed pore structure. Figure 5 );

[0036] (3) In addition to retaining most of the hydroxyl groups of peach gum polysaccharide, the molecular chain of cross-linked modified peach gum gel also has a large number of amino groups of polyethyleneimine, as well as ester groups and amide groups generated by the reaction with maleic anhydride. These active groups are the active sites for adsorbing hexavalent chromium. The presence of a large number of hydroxyl, amino and amide groups makes the cross-linked modified peach gum gel have good hydrophilicity and water absorption, which is conducive to the rapid adsorption of hexavalent chromium from aqueous solution.

[0037] Example 2: Application of cross-linked modified peach gum gel in the removal of hexavalent chromium

[0038] 1. Weigh 100 mg of cross-linked modified peach gum gel (PG-MAH-PEI) into a 100 mL beaker, add 25 mL of K2Cr2O7 solution with a concentration of 100 mg / L and pH=2, place the beaker in a 25℃ water bath, and adsorb for 1 hour under magnetic stirring at 700 r / min. Filter and recover the cross-linked modified peach gum gel, detect the concentration of hexavalent chromium in the filtrate, and calculate the hexavalent chromium removal rate.

[0039] The results showed that the removal rate of hexavalent chromium was 99% after 1 h of adsorption by cross-linked modified gum arabic gel, demonstrating excellent adsorption effect.

[0040] Following the above method, under conditions of 25℃ and pH=2, 100 mg of cross-linked modified gum arabic gel was used as the adsorbent to increase the concentration of hexavalent chromium solution (K2Cr2O7) to 600 mg / L for adsorption experiments. The experimental results showed that the removal rate of hexavalent chromium was 98% after 1 h of adsorption by the cross-linked modified gum arabic gel. This result indicates that the cross-linked modified gum arabic gel still has excellent adsorption effect on high-concentration hexavalent chromium solution and can be used for the adsorption treatment of high-concentration chromium waste liquid.

[0041] Notably, trivalent chromium (Cr) was detected in the cross-linked modified gum gel after adsorption was complete. 3+ This indicates that after adsorbing hexavalent chromium, the modified gum gel can also reduce some of the hexavalent chromium to trivalent chromium (Cr2O7), which has lower toxicity. 2- →Cr 3+ This invention combines the functions of adsorption and reduction. The cross-linked modified gum arabic gel contains a large number of amino groups, which are reducing agents. Within the modified gum arabic gel, when adsorbed hexavalent chromium migrates to the amino group, it is reduced to trivalent chromium. We refer to this in-situ reduction reaction of hexavalent chromium in the modified gum arabic gel as "intragel migration reduction".

[0042] 2. Experiment on the recycling of cross-linked modified peach gum gel

[0043] The cross-linked modified gum arabic gel recovered from filtration in step 1 was subjected to ultrasonic-assisted elution for 1 hour using 20 mL of NaOH solution with pH=12. After elution, the cross-linked modified gum arabic gel was dried at 50°C and subjected to a second adsorption test for dichromate ions (100 mg / L) (method as above). The results showed that the cross-linked modified gum arabic gel regenerated by elution with NaOH could maintain an adsorption efficiency of 99% after 6 consecutive adsorption cycles. The experiment shows that the cross-linked modified gum arabic gel of the present invention has excellent recyclability, which is both environmentally friendly and saves on usage costs.

[0044] .

[0045] 3. To further elucidate the adsorption mechanism of hexavalent chromium by cross-linked modified gum arabic gel, isothermal adsorption and adsorption kinetic studies were conducted.

[0046] (1) Isothermal adsorption experiment

[0047] 100 mg of cross-linked modified gum arabic (PG-MAH-PEI) was weighed into six 100 mL beakers. 25 mL of K₂Cr₂O₇ solution with concentrations of 100, 200, 300, 400, 500, and 600 mg / L were added to each beaker, respectively. The beakers were placed in a 25°C water bath and subjected to magnetic stirring at 700 r / min for 1 hour for adsorption. After 1 hour, the absorbance of the hexavalent chromium solution in the beakers was measured. The adsorption data were fitted using Langmuir and Freundlich isotherm adsorption models, respectively. The fitting results showed that the process conformed to the Langmuir isotherm adsorption model (…). Figure 6 The maximum adsorption capacity of cross-linked modified gum arabic gel for hexavalent chromium is 129 mg / g.

[0048] (2) Adsorption kinetics experiment

[0049] 100 mg of cross-linked modified peach gum gel (PG-MAH-PEI) was weighed into a 100 mL beaker, and 25 mL of a 100 mg / L hexavalent chromium solution was added to the beaker. Adsorption experiments were conducted in a 25 °C water bath with stirring at 700 r / min. Samples were taken at 5, 10, 15, 30, 45, 60, 75, and 90 min to detect the concentration of hexavalent chromium in the solution. The adsorption data were fitted using pseudo-first-order and pseudo-second-order kinetic models, respectively. The fitting results showed that the adsorption process of hexavalent chromium by the cross-linked modified peach gum gel conformed to the pseudo-second-order kinetic model (…). Figure 7 ).

[0050] 4. Experiment on the resistance of cross-linked modified peach gum gel to metal ion interference

[0051] The experimental method is the same as in step 1, except that Cu with a concentration of 100 mg / L is added to the K2Cr2O7 solution (100 mg / L). 2+ Co 2+ Fe 3+ After adsorption for 1 hour, the concentration of hexavalent chromium in the solution was measured, and the results showed that Cu... 2+ Co 2+ Fe 3+ When coexisting, the removal rates of hexavalent chromium by cross-linked modified gum arabic gel were 96.2%, 97.8%, and 95.3%, respectively; the results show that cross-linked modified gum arabic gel (PG-MAH-PEI) can resist the interference of other metal ions in water.

[0052] In addition, Al with a concentration of 100 mg / L was added to the K2Cr2O7 solution. 3+ Ca 2+ and Na + After 1 hour of adsorption, the cross-linked modified gum arabic gel maintained a 99% removal rate of hexavalent chromium, indicating that Al... 3+ Ca 2+ and Na + It had no significant impact on the removal rate of hexavalent chromium.

Claims

1. The application of a cross-linked modified gum arabic gel in the adsorption and reduction of hexavalent chromium, characterized in that: Crosslinked modified gum arabic gel is prepared by dissolving purified gum arabic and maleic anhydride in N,N-dimethylformamide, mixing well, adding a pore-forming agent, and stirring the mixture under a nitrogen atmosphere at 60-80°C for 0.5-2 hours. Then, a solution of branched polyethyleneimine in N,N-dimethylformamide is added, and the reaction continues at 60-80°C until a light yellow granular precipitate is formed. The precipitate is then filtered under reduced pressure, washed with ethanol, and dried to obtain the gel.

2. The application according to claim 1, characterized in that: The purification of peach gum involves soaking natural peach gum in warm water for 20-30 hours until it fully absorbs water and swells. Then, it is filtered repeatedly under reduced pressure 2-4 times using a 100-mesh fine-pore filter cloth to remove impurities. Finally, the transparent peach gum water soluble gel is dried at 50-70℃, pulverized, and purified peach gum is obtained.

3. The application according to claim 1, characterized in that: The mass ratio of purified peach gum to maleic anhydride is 1-3:1, the mass ratio of purified peach gum to pore-forming agent is 15-25:1, and the mass ratio of purified peach gum to branched polyethyleneimine is 1-1.5:

1.

4. The application according to claim 1, characterized in that: The pore-forming agent is ammonium bicarbonate.

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