Preparation and application method of acid-resistant composite material based on chitosan and graphite phase carbon nitride

Abstract

The present invention provides a method for preparing an acid-resistant composite material based on chitosan and graphite-phase carbon nitride, comprising the following steps: (1) weighing chitosan and dissolving it in an acetic acid solution, and adding graphite-phase carbon nitride powder for ultrasonic dispersion; then, adding epichlorohydrin for primary crosslinking, crosslinking for 0.5 to 1.5 hours, and stirring for 2 to 3 hours; (2) dripping the primary crosslinked material into an alkaline condensate mixture to produce composite microspheres; washing the composite microspheres with deionized water until neutral, filtering, and then placing them in ethylene glycol glycidyl ether, ultrasonically dispersing, and performing secondary crosslinking for 2 to 3 hours; (3) washing after the secondary crosslinking, and then storing in an aqueous environment to obtain the desired composite material. The present invention also provides the use of the above-mentioned acid-resistant composite material in electroplating wastewater treatment. The present invention has the advantage that the composite material can be used in electroplating wastewater treatment to stably and efficiently adsorb Cr(VI) in the wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of electroplating wastewater treatment, and in particular to a preparation and application method of an acid-resistant composite material based on chitosan and graphite-phase carbon nitride. Background Art

[0002] With the development of the electroplating industry, large amounts of chromium (Cr)-containing electroplating wastewater, when discharged into the environment without proper treatment, can cause serious Cr pollution. Cr(VI) is listed as a key pollutant in my country, and its treatment in wastewater has become a major challenge. Photocatalysis is a green and efficient advanced oxidation technology that effectively removes Cr(VI) from water.

[0003] Graphitic carbon nitride (g-C3N4) is an ideal organic photocatalytic semiconductor material due to its simple preparation method, visible light response, and high stability. However, g-C3N4 has the following shortcomings in practical applications: (1) Graphitic carbon nitride is in powder form, has poor fluidity, and is difficult to apply; (2) Graphitic carbon nitride has limited adsorption capacity for Cr(VI), mainly due to surface adsorption, which is generally weak.

[0004] Chitosan, an important derivative of the natural polysaccharide chitin, contains reactive amino and hydroxyl groups that form stable complexes with metal ions, making it widely used in metal recovery and industrial wastewater treatment. Furthermore, chitosan's adsorption capacity for trivalent chromium is much greater than for hexavalent chromium. Therefore, combining chitosan with graphite-phase carbon nitride to create a composite material could further enhance the material's chromium adsorption capacity. Chitosan also serves to stabilize the graphite-phase carbon nitride, facilitating its application.

[0005] Furthermore, it has been discovered that, in addition to significant amounts of chromium (Cr), electroplating wastewater also contains numerous other pollutants, often rendering it acidic. Chitosan is unstable in acidic solutions and dissolves, leading to adsorbent loss. Therefore, chitosan materials used in electroplating wastewater treatment should be modified to make them resistant to acidic environments. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a preparation and application method of an acid-resistant composite material based on chitosan and graphite phase carbon nitride. The composite material is used for electroplating wastewater treatment and can efficiently adsorb Cr(VI) in the wastewater.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] A method for preparing an acid-resistant composite material based on chitosan and graphite-phase carbon nitride comprises the following steps:

[0009] (1) Chitosan was weighed and dissolved in acetic acid solution, and graphite carbon nitride powder was added and ultrasonically dispersed for 5 to 15 minutes; then, epichlorohydrin was added for primary crosslinking for 0.5 to 1.5 hours, and then stirred for 2 to 3 hours;

[0010] (2) dripping the primary cross-linked material into the alkaline coagulant mixture through a syringe to produce composite microspheres; washing the composite microspheres with deionized water for 5 to 6 times until neutral, filtering, and then placing them in ethylene glycol glycidyl ether, ultrasonically dispersing for 10 to 30 minutes, and then performing secondary cross-linking for 2 to 3 hours;

[0011] (3) After the secondary cross-linking, the composite is cleaned to remove excess cross-linking agent and then stored in an aqueous environment to obtain the desired composite material.

[0012] As one of the preferred embodiments of the present invention, in step (1), 2 g of chitosan is weighed and dissolved in 50 mL of 2% acetic acid solution, and 1 g of graphite phase carbon nitride powder is added and ultrasonically dispersed; then, 2 mL of epichlorohydrin is added for primary crosslinking.

[0013] As one of the preferred embodiments of the present invention, in step (2), the once cross-linked material is dropped into 500 mL of an alkaline coagulant mixture via a syringe to produce composite microspheres; then, the composite microspheres are washed and filtered with deionized water, and then placed in 100 mL of 0.5-2% ethylene glycol glycidyl ether for secondary cross-linking.

[0014] As one of the preferred embodiments of the present invention, the alkaline condensate mixture is specifically a condensation mixture of H2O, C2H5OH, and NaOH, and in terms of mass percentage, H2O:C2H5OH:NaOH=4:5:1.

[0015] As one of the preferred embodiments of the present invention, the graphite phase carbon nitride powder of step (1) is prepared by the following method:

[0016] Melamine was placed in a crucible, wrapped with tin foil, placed in a muffle furnace, heated to 500-600°C, and calcined for 1.5-2.5 hours; after cooling to 95-105°C, the calcined light yellow solid was taken out and ground in a mortar to obtain graphite phase carbon nitride powder.

[0017] As one of the preferred embodiments of the present invention, a 50 mL crucible is selected and 20 g of melamine is placed therein.

[0018] As one of the preferred embodiments of the present invention, the crucible is heated at a rate of 5° C. / min in a muffle furnace.

[0019] A method for applying an acid-resistant composite material based on chitosan and graphite-phase carbon nitride is disclosed. The acid-resistant composite material prepared according to the preparation method is used for electroplating wastewater treatment to adsorb Cr(VI) in the wastewater.

[0020] principle:

[0021] The photocatalytic reaction process usually includes the following three steps: (1) the catalyst absorbs light energy and transforms into an excited state with charge separation; (2) the catalyst generates photogenerated charges and migrates to the surface of the reactants; (3) the catalyst oxidizes and reduces organic pollutants at the catalytic site.

[0022] The composite microspheres are obtained by uniformly dispersing graphite-phase carbon nitride in chitosan gel, then alkali-setting and crosslinking. The adsorption mechanism of the composite microspheres is as follows: the catalyst g-C3N4 catalytically reduces a large amount of hexavalent chromium to trivalent chromium, which it then adsorbs in small amounts. Simultaneously, the modified chitosan stably and efficiently adsorbs the reduced trivalent chromium. Furthermore, the chitosan also adsorbs a small amount of hexavalent chromium that has not been reduced by the catalyst.

[0023] The advantages of the present invention over the prior art are:

[0024] (1) The present invention is time-saving, has high yield, uses fluorine-free and solvent-free, and is beneficial to environmental protection.

[0025] (2) Chitosan has good biocompatibility and degradability, and contains a large number of amino and hydroxyl functional groups on its molecular chain, which has a high adsorption selectivity for the anion Cr(VI); however, simple chitosan has shortcomings in the adsorption process, for example, it is unstable in acidic solution and will dissolve, causing adsorbent loss, limiting its application; therefore, it is necessary to modify chitosan in the present invention to increase its stability and improve its adsorption performance. The two-crosslinking modification process (the first with epichlorohydrin and the second with ethylene glycol glycidyl ether) greatly improves the acid resistance of the material.

[0026] (3) The graphite phase carbon nitride (g-C3N4) of the present invention is simple to prepare and has the characteristics of visible light response and high stability; at the same time, the present invention can more easily introduce a variety of adsorption sites through a composite method, improve the stability of chitosan, and give full play to the advantages of each component in the adsorption process to achieve the purpose of complementary advantages.

[0027] (4) The alkaline solution used in the present invention is an alkaline condensate mixture (H2O:C2H5OH:NaOH=4:5:1, w / w) which is more conducive to the formation of small balls than other alkaline solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a real shot of the composite microspheres in Example 3;

[0029] Figure 2 is a SEM photograph of the composite microspheres in Example 3;

[0030] Figure 3 is the FT-IR spectrum of g-C3N4, chitosan and composite microspheres in Example 3;

[0031] Figure 4 This is the experimental principle diagram in Experimental Example 2;

[0032] Figure 5 is the g-C3N4 adsorption performance curve in Experimental Example 2;

[0033] Figure 6 This is the g-C3N4 kinetic fitting curve in Experimental Example 2;

[0034] Figure 7 is a graph showing the adsorption performance of the composite microspheres in Experimental Example 2;

[0035] Figure 8 is a kinetic fitting curve diagram of the composite microspheres in Experimental Example 2;

[0036] Figure 9 This is a real shot of the composite microspheres prepared in Comparative Example 3. DETAILED DESCRIPTION

[0037] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0038] Example 1

[0039] The acid-resistant composite microspheres based on chitosan and graphite carbon nitride in this embodiment are prepared as follows:

[0040] (1) Take 20g of melamine and put it into a 50mL crucible, wrap it with tin foil, place it in a muffle furnace, heat it to 500℃ at a rate of 5℃ / min, and roast it for 2.5h; after cooling to 95℃, take out the roasted light yellow solid and grind it in a mortar to obtain graphite phase carbon nitride powder.

[0041] (2) Weigh 2 g of chitosan and dissolve it in 50 mL of 2% (v / v) acetic acid solution. Add 1 g of graphite-phase carbon nitride powder and disperse it ultrasonically for 5 min. Then, add 2 mL of epichlorohydrin for primary crosslinking. Crosslink for 0.5 h and stir for 2 h.

[0042] (3) The primary cross-linked material was added dropwise into 500 mL of an alkaline coagulant mixture (H2O: C2H5OH: NaOH = 4:5:1, w / w) via a syringe to produce composite microspheres. The composite microspheres were washed five times with deionized water until neutral, filtered, and then placed in 100 mL of 0.5% ethylene glycol glycidyl ether. After ultrasonic dispersion for 10 min, secondary cross-linking was performed for 2 h.

[0043] (4) After the secondary cross-linking, the microspheres are cleaned to remove excess cross-linking agent and then stored in a water environment to obtain the desired composite microspheres.

[0044] Example 2

[0045] The acid-resistant composite microspheres based on chitosan and graphite carbon nitride in this embodiment are prepared as follows:

[0046] (1) Take 20g of melamine and put it into a 50mL crucible, wrap it with tin foil, place it in a muffle furnace, heat it to 600℃ at a rate of 5℃ / min, and roast it for 1.5h; after cooling to 105℃, take out the roasted light yellow solid and grind it in a mortar to obtain graphite phase carbon nitride powder.

[0047] (2) 2 g of chitosan was weighed and dissolved in 50 mL of 2% (v / v) acetic acid solution, and 1 g of graphite-phase carbon nitride powder was added and ultrasonically dispersed for 15 min. Then, 2 mL of epichlorohydrin was added for primary crosslinking, and the crosslinking was carried out for 1.5 h, followed by stirring for 3 h.

[0048] (3) The primary cross-linked material was added dropwise into 500 mL of an alkaline coagulant mixture (H2O: C2H5OH: NaOH = 4:5:1, w / w) via a syringe to produce composite microspheres. The composite microspheres were washed six times with deionized water until neutral, filtered, and then placed in 100 mL of 2% ethylene glycol glycidyl ether. After ultrasonic dispersion for 30 min, secondary cross-linking was performed for 3 h.

[0049] (4) After the secondary cross-linking, the microspheres are cleaned to remove excess cross-linking agent and then stored in a water environment to obtain the desired composite microspheres.

[0050] Example 3

[0051] The acid-resistant composite microspheres based on chitosan and graphite carbon nitride in this embodiment are prepared as follows:

[0052] (1) Take 20g of melamine and put it into a 50mL crucible, wrap it with tin foil, place it in a muffle furnace, heat it to 550℃ at a rate of 5℃ / min, and roast it for 2h; after cooling to 100℃, take out the roasted light yellow solid and grind it in a mortar to obtain graphite phase carbon nitride powder.

[0053] (2) Weigh 2 g of chitosan and dissolve it in 50 mL of 2% (v / v) acetic acid solution. Add 1 g of graphite-phase carbon nitride powder and disperse it ultrasonically for 10 min. Then, add 2 mL of epichlorohydrin for primary crosslinking. Crosslink for 1.0 h and stir for 2.5 h.

[0054] (3) The primary cross-linked material was added dropwise into 500 mL of an alkaline coagulant mixture (H2O: C2H5OH: NaOH = 4:5:1, w / w) via a syringe to produce composite microspheres. The composite microspheres were washed five times with deionized water until neutral, filtered, and then placed in 100 mL of 1% ethylene glycol diglyceride. After ultrasonic dispersion for 20 min, secondary cross-linking was performed for 2.5 h.

[0055] (4) After the secondary cross-linking, the microspheres are cleaned to remove excess cross-linking agent and then stored in a water environment to obtain the desired composite microspheres.

[0056] The actual photos and SEM photos of the composite microspheres prepared in this embodiment are shown in Figure 2. Figure 1 、 Figure 2 As shown; FT-IR results of g-C3N4, chitosan and composite microspheres are shown Figure 3 shown.

[0057] Comparative Example 1

[0058] The preparation method of the composite microspheres based on chitosan and graphite carbon nitride in this comparative example is basically the same as that in Example 3, with the main difference being that the cross-linking step of epichlorohydrin is omitted.

[0059] Comparative Example 2

[0060] The preparation method of the composite microspheres based on chitosan and graphite carbon nitride in this comparative example is basically the same as that in Example 3, with the main difference being that the cross-linking operation of ethylene glycol glycidyl ether is omitted.

[0061] Comparative Example 3

[0062] The preparation method of the composite microspheres based on chitosan and graphite phase carbon nitride in this comparative example is basically the same as that in Example 3, the main difference being that NaOH is used instead of the "alkaline condensate mixture (H2O:C2H5OH:NaOH=4:5:1, w / w)".

[0063] Experimental Example 1

[0064] This experimental example is used to test the effect of “double cross-linking modification” on the acid resistance of the composite microsphere material of the present invention.

[0065] Experimental method: 2 g of the composite microspheres prepared in Example 3 of the present invention and Comparative Examples 1 and 2 were respectively soaked in 0.5 mol / L hydrochloric acid, and the hydrolysis of the three was observed.

[0066] Experimental results: The composite microspheres of Example 3 did not show any hydrolysis within 360 hours; the composite microspheres of Comparative Example 1 were hydrolyzed in about 100 hours; and the composite microspheres of Comparative Example 2 were hydrolyzed in about 20 to 40 hours.

[0067] It can be seen from this that the present invention can effectively improve the acid resistance of the material through two cross-linking reactions (the first one is epichlorohydrin and the second one is ethylene glycol glycidyl ether), which is beneficial to the stable and efficient adsorption of Cr(VI) by the composite material in acidic wastewater.

[0068] Experimental Example 2

[0069] This experimental example is used to specifically test the adsorption performance of the composite material of the present invention under different acidic conditions.

[0070] Experimental method: g-C3N4 and the composite microsphere material prepared by the present invention (taking Example 3 as an example) were respectively added to hexavalent chromium standard solutions (same concentration) with different pH values ​​(2, 5, 8); after addition, the solution was placed under sunlight illumination, and timing was started. An appropriate amount of the supernatant was taken and filtered through a 0.45-μm filter. The adsorption effect of g-C3N4 and the composite microsphere material on hexavalent chromium was determined by diphenylcarbazide spectrophotometry at different time periods (0 to 250 min).

[0071] Experimental principle: refer to Figure 4 The catalyst g-C3N4 in the composite microspheres catalytically reduces a large amount of hexavalent chromium to trivalent chromium and performs a certain amount of adsorption; at the same time, the chitosan (CTS) in the composite microspheres also stably and efficiently adsorbs the reduced trivalent chromium.

[0072] Experimental results: g-C3N4 adsorption performance curve is as follows Figure 5 The kinetic fitting curve is shown in Figure 6 As shown; the adsorption performance curve of the composite microspheres is shown Figure 7 The kinetic fitting curve is shown in Figure 8 shown.

[0073] Depend on Figures 5 to 8 The results show that the removal efficiency of g-C3N4 and the composite microspheres for hexavalent chromium increases with lower pH, thus acid resistance is essential, and the performance of the composite microspheres is far superior to that of pure g-C3N4. Kinetic fitting results show that the degradation processes of g-C3N4 and the composite microspheres conform to the first-order kinetic model, and the lower the pH, the faster the hexavalent chromium removal rate.

[0074] Experimental Example 3

[0075] This experimental example is used to test the effect of the alkaline coagulant mixture (H2O:C2H5OH:NaOH=4:5:1, w / w) on the composite microsphere material of the present invention.

[0076] Experimental method: Composite microspheres were prepared according to the methods of Example 3 and Comparative Example 3 respectively.

[0077] Experimental results: The composite microspheres prepared in Comparative Example 3 have the following appearance: Figure 9 As shown, the composite microspheres prepared in Example 3 of the present invention have an appearance as shown Figure 1 As shown, the spheres are more rounded than those in Comparative Example 3, have good spherical fluidity and good collision stability.

[0078] It can be seen from this that the alkaline solution used in the present invention is an "alkaline condensate mixture (H2O:C2H5OH:NaOH=4:5:1, w / w)". Compared with other alkaline solutions, this alkaline mixture is more conducive to the formation of round balls.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an acid-resistant composite material based on chitosan and graphite phase carbon nitride, characterized in that: The steps include: (1) Weigh chitosan and dissolve it in acetic acid solution, then add graphite carbon nitride powder and ultrasonically disperse it for 5-15 min; then add epichlorohydrin for primary crosslinking, crosslink for 0.5-1.5 h, and stir for 2-3 h; (2) dripping the primary cross-linked material into an alkaline coagulant mixture through a syringe to produce composite microspheres; washing the composite microspheres with deionized water for 5 to 6 times until neutral, filtering, and then placing them in ethylene glycol glycidyl ether, ultrasonically dispersing for 10 to 30 minutes, and then performing secondary cross-linking for 2 to 3 hours; the alkaline coagulant mixture is a coagulant mixture of H2O, C2H5OH, and NaOH; (3) After the secondary cross-linking, the composite is cleaned to remove excess cross-linking agent and then stored in a water environment to obtain the desired composite material.

2. The method for preparing the acid-resistant composite material based on chitosan and graphite phase carbon nitride according to claim 1, wherein: In the step (1), 2 g of chitosan is weighed and dissolved in 50 mL of 2% acetic acid solution, and 1 g of graphite phase carbon nitride powder is added for ultrasonic dispersion; then, 2 mL of epichlorohydrin is added for primary cross-linking.

3. The method for preparing the acid-resistant composite material based on chitosan and graphite phase carbon nitride according to claim 1, wherein: In the step (2), the primary cross-linked material is dropped into 500 mL of the alkaline coagulant mixture through a syringe to produce composite microspheres; then, the composite microspheres are washed and filtered with deionized water, and then placed in 100 mL of 0.5-2% ethylene glycol glycidyl ether for secondary cross-linking.

4. The method for preparing the acid-resistant composite material based on chitosan and graphite phase carbon nitride according to claim 1, wherein: In the alkaline condensate mixture, by mass percentage, H2O:C2H5OH:NaOH=4:5:

1.

5. The method for preparing the acid-resistant composite material based on chitosan and graphite phase carbon nitride according to any one of claims 1 to 4, characterized in that: The graphite phase carbon nitride powder of step (1) is prepared by the following method: Melamine was placed in a crucible, wrapped with tin foil, placed in a muffle furnace, heated to 500-600°C, and calcined for 1.5-2.5 hours. After cooling to 95-105°C, the calcined light yellow solid was taken out and ground in a mortar to obtain graphite phase carbon nitride powder.

6. The method for preparing the acid-resistant composite material based on chitosan and graphite phase carbon nitride according to claim 5, characterized in that: A 50 mL crucible was selected and 20 g of melamine was placed in it.

7. The method for preparing the acid-resistant composite material based on chitosan and graphite phase carbon nitride according to claim 5, characterized in that: The crucible was heated in a muffle furnace at 5°C / min.

8. An application method of an acid-resistant composite material based on chitosan and graphite carbon nitride, characterized in that: The acid-resistant composite material prepared according to any one of claims 1 to 7 is used to treat electroplating wastewater to adsorb Cr(VI) in the wastewater.

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