A modified cellulose-loaded steel slag photocatalytic reducing agent, preparation method and application thereof

Abstract

The present invention belongs to wastewater treatment technology, specifically a modified cellulose-loaded steel slag photocatalytic reducing agent, preparation method and application. Nanocellulose is modified by polyethyleneimine, and steel slag is loaded to prepare a photocatalytic reducing agent of a cellulose-based porous composite material. A large number of amine groups are successfully introduced into the modified composite material, and steel slag can provide electrons and holes, thereby increasing the adsorption rate and adsorption performance of metal ions in high-concentration industrial wastewater. Under the condition of increasing visible light, certain components (iron oxides) in steel slag and modified cellulose can be stimulated to produce electron-hole pairs, promote the reduction of hexavalent chromium, and effectively utilize waste, which is in line with the concept of green chemistry and circular economy, and has positive significance for environmental protection.

Description

Technical Field

[0001] The invention belongs to wastewater treatment technology, and specifically relates to a modified cellulose-loaded steel slag photocatalytic reducing agent, a preparation method and an application thereof. Background Art

[0002] Hexavalent chromium wastewater mainly comes from industrial processes such as mining, metallurgy, electroplating, electronic manufacturing and chemical industry. Hexavalent chromium is highly toxic and carcinogenic, and can be absorbed through the skin, causing skin ulcers, liver and kidney damage and other health problems. If hexavalent chromium wastewater is discharged directly without treatment, it will not only pollute water and soil, but also cause long-term health hazards to humans through the food chain, bringing serious ecological and health risks.

[0003] At present, the treatment methods of hexavalent chromium are mainly divided into biological method, physical adsorption method, and photocatalytic reduction method. Among them, biological method and physical adsorption method cannot fundamentally solve the problem of hexavalent chromium pollution; Chinese patent document CN112079462A discloses a method of using low-rank coal after screening to adsorb hexavalent chromium in wastewater, but adsorption cannot solve the fundamental problem, and hexavalent chromium pollution still exists. Chinese patent document CN112159025A discloses a method of precipitating hexavalent chromium in wastewater by precipitation method and then separating it, but its operation is complicated, and hexavalent chromium precipitate pollution still exists. Therefore, reducing hexavalent chromium to low-valent chromium has become a fundamental strategy to avoid hexavalent chromium pollution. Photocatalytic reduction has become a preferred choice for solving hexavalent chromium wastewater pollution treatment. The photocatalytic process uses light energy to activate the catalyst, produce strong oxidizing species, and reduce or oxidize heavy metal ions to non-toxic or low-toxic forms. Current reports on the reduction of hexavalent chromium in wastewater have problems such as weak adsorption capacity for metal ions in high-concentration industrial wastewater, poor stability, poor economy, poor environmental friendliness, and harsh preparation conditions.

[0004] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing photocatalytic reduction technology cannot economically, effectively, quickly and non-toxicly treat high-concentration hexavalent chromium wastewater.

[0006] In order to solve the above technical problems, the inventors have obtained the technical solution of the present invention through practice and summary. The present invention adopts the following technical solution:

[0007] A method for preparing a modified cellulose-loaded steel slag photocatalytic reducing agent, the preparation steps are as follows:

[0008] S100, dispersing 4.5% nanocellulose in deionized water to obtain a dispersion;

[0009] Add steel slag and 3-aminopropyltriethoxysilane to the dispersion and stir at a constant speed for 1 ～ 2h, to obtain a mixed solution;

[0010] The mass ratio of nanocellulose: steel slag: 3-aminopropyltriethoxysilane is (2-7); (0.02 ～ 0.1):(0.3 ～ 0.6);

[0011] S200, adding polyethyleneimine to the mixed solution, stirring vigorously, and reacting for a certain period of time to obtain a composite hydrogel;

[0012] S300: After pre-freezing the composite hydrogel in a refrigerator for 1 hour, the frozen material is transferred to a dryer for freeze drying to obtain a modified cellulose-loaded steel slag photocatalytic reducing agent.

[0013] In a further embodiment, the mass ratio of nanocellulose: steel slag: 3-aminopropyltriethoxysilane is (3.5-4.5); (0.03-0.07): (0.3-0.5).

[0014] In a further embodiment, the 4.5% nanocellulose is dispersed in deionized water, and the dispersion is diluted to a concentration of 1 while stirring or while adding the nanocellulose. ～ 3%.

[0015] In a further embodiment, the dispersion dilution concentration is 2 ～ 3%.

[0016] In a further embodiment, the slag material is in powder form with a particle size of 400 ～ 600 mesh.

[0017] In a further embodiment, the stirring speed is 400 ～ 500r / min, stirring time is 1h.

[0018] In a further embodiment, the mass of the polyethyleneimine is the same as the mass of 3-aminopropyltriethoxysilane.

[0019] In a further embodiment, the vigorous stirring in step S200 is performed by a magnetic stirrer at a speed of 800 ～ 1500r / min, reaction time is 15min.

[0020] A modified cellulose-loaded steel slag photocatalytic reducing agent is prepared by the preparation method. The modified cellulose-loaded steel slag photocatalytic reducing agent is a porous composite material with modified cellulose as a skeleton to fix steel slag.

[0021] The invention discloses an application of a modified cellulose-loaded steel slag photocatalytic reducing agent. The photocatalytic reducing agent adsorbs hexavalent chromium ion compounds under acidic or neutral conditions, and the steel slag reduces the hexavalent chromium ion compounds to non-toxic trivalent chromium under light conditions.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] In this application, nanocellulose and steel slag are key raw materials, serving as carriers and photocatalysts, respectively. Modified cellulose can not only provide excellent adsorption capacity, but also enhance the mechanical strength and durability of the composite material. The iron oxides contained in steel slag can generate active oxygen species under light conditions, degrading and reducing organic pollutants and heavy metal ions. Loading steel slag on modified cellulose can effectively combine the excellent adsorption properties of modified cellulose and the photocatalytic activity of steel slag, improve the treatment efficiency through synergistic effects, and thus achieve economical, effective, rapid and harmless treatment of high-concentration hexavalent chromium wastewater. It has a series of excellent characteristics: efficient photocatalytic activity, good reproducibility and environmental friendliness; in addition, it has the characteristics of simple production process and mild preparation conditions, making it an ideal choice for treating high-concentration hexavalent chromium industrial wastewater. Its advantages of simple operation, low cost and high efficiency have been fully reflected in the actual treatment process.

[0024] This application uses polyethyleneimine to modify nanocellulose in a targeted manner, and loads steel slag to prepare a photocatalytic reducing agent for a cellulose-based porous composite material. A large number of amino groups are successfully introduced into the modified composite material, and the steel slag can provide electrons and holes, thereby increasing the adsorption rate and adsorption performance of metal ions in high-concentration industrial wastewater. It can also be used for adsorption-reduction of high-concentration hexavalent chromium industrial wastewater produced by electroplating plants under visible light irradiation: modified cellulose can effectively adsorb anionic compounds such as hexavalent chromium in acidic or neutral solutions. Under the condition of increasing visible light, it can stimulate certain components (iron oxides) in steel slag and the generation of electron-hole pairs on modified cellulose, promote the reduction of hexavalent chromium, and effectively utilize waste, which is in line with the concept of green chemistry and circular economy and has positive significance for environmental protection.

[0025] Compared with the homogeneous hydrogel material, the composite material of modified cellulose loaded with steel slag in this application can avoid the following problems: first, when the hydrogel absorbs water and swells, the distance between the crosslinking points increases, which will cause the pores inside the gel to compress, thereby reducing the porosity. Secondly, the hydrophilic group absorbs a large amount of water molecules, causing the gel volume to expand. The lower degree of crosslinking allows more water molecules to enter the gel network, resulting in greater swelling. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a scanning electron microscope image of the surface of the material of the present invention.

[0027] Figure 2 It is the infrared spectrum diagram of the material of the present invention before and after the reaction.

[0028] Figure 3 is a photocurrent diagram of the material of the present invention.

[0029] Figure 4 It is the ultraviolet diffuse reflection spectrum diagram of the material of the present invention.

[0030] Figure 5 It is a superoxide radical diagram of the material of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0032] A method for preparing a modified cellulose-loaded steel slag photocatalytic reducing agent, the preparation steps are as follows:

[0033] S100, dispersing 4.5% nanocellulose in deionized water to obtain a dispersion;

[0034] Add steel slag and 3-aminopropyltriethoxysilane to the dispersion and stir at a constant speed for 1 ～ 2h, to obtain a mixed solution;

[0035] The mass ratio of nanocellulose: steel slag: 3-aminopropyltriethoxysilane is (2-7); (0.02 ～ 0.1):(0.3 ～ 0.6);

[0036] S200, adding polyethyleneimine to the mixed solution, stirring vigorously, and reacting for a certain period of time to obtain a composite hydrogel;

[0037] S300: After pre-freezing the composite hydrogel in a refrigerator for 1 hour, the frozen material is transferred to a dryer for freeze drying to obtain a modified cellulose-loaded steel slag photocatalytic reducing agent.

[0038] In a further embodiment, the mass ratio of nanocellulose: steel slag: 3-aminopropyltriethoxysilane is (3.5-4.5); (0.03-0.07): (0.3-0.5).

[0039] In a further embodiment, the 4.5% nanocellulose is dispersed in deionized water, and the dispersion is diluted to a concentration of 1 while stirring or while adding the nanocellulose. ～ 3%.

[0040] In a further embodiment, the dispersion dilution concentration is 2 ～ 3%.

[0041] In a further embodiment, the slag material is in powder form with a particle size of 400 ～ 600 mesh.

[0042] In a further embodiment, the stirring speed is 400 ～ 500r / min, preferably 400r / min, stirring time is 1h.

[0043] In a further embodiment, the mass of the polyethyleneimine is the same as the mass of 3-aminopropyltriethoxysilane.

[0044] In a further embodiment, the vigorous stirring in step S200 is performed by a magnetic stirrer at a speed of 800 ～ 1500r / min, preferably 1000r / min, and the reaction time is 15min.

[0045] A modified cellulose-loaded steel slag photocatalytic reducing agent is prepared by the preparation method. The modified cellulose-loaded steel slag photocatalytic reducing agent is a porous composite material with modified cellulose as a skeleton to fix steel slag.

[0046] The invention discloses an application of a modified cellulose-loaded steel slag photocatalytic reducing agent. The photocatalytic reducing agent adsorbs hexavalent chromium ion compounds under acidic or neutral conditions, and the steel slag reduces the hexavalent chromium ion compounds to non-toxic trivalent chromium under light conditions.

[0047] Example 1

[0048] A method for preparing a modified cellulose-loaded steel slag photocatalytic reducing agent, the preparation steps are as follows:

[0049] S100, dissolving 2.22 g of 4.5% cellulose in 7.77 mL of deionized water, then adding 0.05 g of steel slag and 0.4 g of 3-aminopropyltriethoxysilane, stirring at a constant speed for 1 h to obtain a mixed solution;

[0050] S200, adding polyethyleneimine to the mixed solution, stirring vigorously for 15 minutes to obtain a composite hydrogel;

[0051] S300: After pre-freezing the composite hydrogel in a refrigerator for 12 hours, the frozen material is transferred to a dryer for freeze drying for 24 hours to obtain a modified cellulose-loaded steel slag photocatalytic reducing agent.

[0052] Example 2

[0053] A method for preparing a modified cellulose-loaded steel slag photocatalytic reducing agent, the preparation steps are as follows:

[0054] S100, dissolving 4.44 g of 4.5% cellulose in 5.56 mL of deionized water, then adding 0.05 g of steel slag and 0.4 g of 3-aminopropyltriethoxysilane, stirring at a constant speed for 1 h to obtain a mixed solution;

[0055] S200, adding polyethyleneimine to the mixed solution, stirring vigorously for 15 minutes to obtain a composite hydrogel;

[0056] S300: After pre-freezing the composite hydrogel in a refrigerator for 12 hours, the frozen material is transferred to a dryer for freeze drying for 24 hours to obtain a modified cellulose-loaded steel slag photocatalytic reducing agent.

[0057] Example 3

[0058] A method for preparing a modified cellulose-loaded steel slag photocatalytic reducing agent, the preparation steps are as follows:

[0059] S100, dissolving 6.66 g of 4.5% cellulose in 3.34 mL of deionized water, then adding 0.05 g of steel slag and 0.4 g of 3-aminopropyltriethoxysilane, stirring at a constant speed for 1 h to obtain a mixed solution;

[0060] S200, adding polyethyleneimine to the mixed solution, stirring vigorously for 15 minutes to obtain a composite hydrogel;

[0061] S300: After pre-freezing the composite hydrogel in a refrigerator for 12 hours, the frozen material is transferred to a dryer for freeze drying for 24 hours to obtain a modified cellulose-loaded steel slag photocatalytic reducing agent.

[0062] Adsorption test: Prepare two different Cr(VI) standard solutions with pH values ​​of 1 and 2, with a concentration of 100 mg / L. Take 100 mg of each of the three catalysts prepared above, place them in 100 mL of Cr(VI) solutions with different pH values, and place them in a dark environment for 12 hours for adsorption. The labels are:

[0063] a1-1 / a1-2 / a1-3 / b2-1 / b2-2 / b2-3, the test results are as follows.

[0064] Table 1 Concentration of hexavalent chromium in solution after adsorption

[0065] Example 1 a1-1 b2-1 Cr(VI)(mg / L) 10.4 15.4 Example 2 a1-2 b2-2 Cr(VI)(mg / L) 7.4 13.6 Example 3 a1-3 b2-3 Cr(VI)(mg / L) 14.2 19.1

[0066] Photocatalytic test: Prepare a Cr(VI) standard solution with a pH of 1 and a concentration of 50 mg / L. Take 100 mg of each of the three catalysts prepared above and place them in the Cr(VI) standard solution with a volume of 100 mL. Perform photocatalytic reduction under visible light irradiation. Take samples every 10 minutes to measure the Cr(VI) concentration. The labels are:

[0067] c1 / c2 / c3 / c4 / c5 / c6 / d1 / d2 / d3 / d4 / d5 / d6 / e1 / e2 / e3 / e4 / e5 / e6, the test results are as follows.

[0068] Table 2 Remaining Cr(VI) concentration in solution after photocatalytic experiment

[0069] Example 1 c1 c2 c3 c4 c5 c6 Cr(VI)(mg / L) 54.0 32.6 22.8 17.2 7.4 3.4 Example 2 d1 d2 d3 d4 d5 d6 Cr(VI)(mg / L) 39.5 12.0 2.6 0 0 0 Example 3 e1 e2 e3 e4 e5 e6 Cr(VI)(mg / L) 53.8 31.4 20.6 15.7 6.9 3.0

[0070] Comparative experiment: A Cr(VI) standard solution with a pH of 1 and a concentration of 100 mg / L was prepared. The modified cellulose-loaded steel slag photocatalytic reducing agent prepared by the optimal preparation scheme was selected and the experiments were carried out under dark and visible light conditions, respectively. The concentration of Cr(VI) was tested by sampling every 1 hour and 10 minutes under dark and visible light conditions, respectively. The labels are:

[0071] f1 / f2 / f3 / f4 / f5 / f6 / f7 / f8 / f9 / f10 / f11 / f12 / g1 / g2 / g3 / g4 / g5 / g6 / g7 / g8 / g9 / g10 / g11 / g12, the test results are as follows.

[0072] Table 3: Concentration of residual Cr(VI) in solution after experiment under dark and visible light conditions in Example 2

[0073]

[0074] Detection and analysis: The catalyst prepared with the most preferred formula was ground into powder to detect its instantaneous photocurrent and absorption characteristics of visible light; the Cr(VI) standard solution after adsorption and photocatalytic experiments was used to detect the concentration of residual hexavalent chromium in the solution using an ultraviolet spectrophotometer; adsorbents with regular morphology were selected for SEM analysis.

[0075] It can be seen from Table 1 that the modified cellulose-loaded steel slag photocatalytic reducing agents prepared with three different formulas have better removal capabilities for Cr(VI) at pH 1 than at pH 2. This is because the amino groups on the modified catalysts have stronger protonation capabilities under strong acidic conditions, and by comparison, it can be seen that Example 2 has the best removal capability for Cr(VI). Therefore, Example 2 is used as the optimal preparation scheme.

[0076] As shown in Table 2, the results of the photocatalytic reduction test on the photocatalysts prepared in different embodiments show that the modified cellulose-loaded steel slag photocatalytic reducing agent prepared in Example 2 can completely remove Cr(VI) within 40 minutes. In addition, the adsorption-catalytic reduction ability of Example 2 on Cr(VI) is more significant than that of Examples 1 and 3.

[0077] As shown in Table 3, the modified cellulose-loaded steel slag photocatalytic reducing agent of Example 2 of the present invention takes about 6 hours to remove about 60% of Cr(VI) in the solution under dark conditions, but only takes 10 minutes under visible light irradiation, and Cr(VI) in the solution is completely removed after 40 minutes. From this comparison, it can be seen that the efficiency of removing Cr(VI) is increased by more than 30 times under the condition of increasing visible light.

[0078] Figure 2 ] are the infrared spectra of Example 2 and steel slag. By comparison, it can be seen that the peaks of the cellulose-loaded steel slag photocatalytic reducing agent in Example 2 at 3400, 1600 and 1100 cm-1 are -OH, -NH2 and COC, respectively. Figure 3 2 is the photocurrent transient response diagram of Example 2 and the steel slag loading material. It can be seen from the figure that the current intensity of Example 2 is significantly higher than that of the loading material. Figure 4 The ultraviolet diffuse reflectance spectra of steel slag, the photocatalytic reducing agent of Example 2 and the loaded steel slag photocatalytic reducing agent are shown in Figure 2. By comparison, it can be seen that the absorption intensity of the loaded steel slag material to visible light is significantly enhanced after the wavelength range of 450nm. Figure 5 This is the superoxide radical diagram of the modified cellulose-loaded steel slag photocatalytic reducing agent prepared in this experiment. It is known that the material can generate superoxide radicals to reduce hexavalent chromium under the irradiation of visible light. In summary, the material of the present invention can catalyze the reduction of Cr(VI) under the irradiation of visible light under acidic and neutral conditions.

[0079] According to the above experimental results, the modified cellulose-loaded steel slag photocatalytic reductant prepared by this method shows efficient adsorption and catalytic reduction performance for Cr(VI). The composite material also has good photocurrent response characteristics and absorption capacity for visible light, so it can treat other high-valent metal ions in the solution by photocatalytic reduction, and has broad application prospects and important significance in reducing heavy metal pollution in industrial wastewater.

Claims

1. A method for preparing a modified cellulose-loaded steel slag photocatalytic reducing agent, characterized in that: The preparation steps are as follows: S100, dispersing 4.5% nanocellulose in deionized water to obtain a dispersion; Add steel slag and 3-aminopropyltriethoxysilane to the dispersion and stir at a constant speed for 1 ～ 2h, to obtain a mixed solution; The mass ratio of nanocellulose: steel slag: 3-aminopropyltriethoxysilane is (2-7): (0.02 ～ 0.1):(0.3 ～ 0.6); S200, adding polyethyleneimine to the mixed solution, stirring vigorously, and reacting for a certain period of time to obtain a composite hydrogel; S300: After pre-freezing the composite hydrogel in a refrigerator for 1 hour, the frozen material is transferred to a dryer for freeze drying to obtain a modified cellulose-loaded steel slag photocatalytic reducing agent.

2. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 1, characterized in that: The mass ratio of the nanocellulose: steel slag: 3-aminopropyltriethoxysilane is (3.5-4.5): (0.03-0.07): (0.3-0.5).

3. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 1, characterized in that: When the 4.5% nanocellulose is dispersed in deionized water, the dispersion is diluted to a concentration of 1 by stirring or ultrasonic treatment while adding the nanocellulose. ～ 3%.

4. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 3, characterized in that: The dilution concentration of the dispersion is 2 ～ 3%.

5. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 1, characterized in that: The steel slag material is in powder form with a particle size of 400 ～ 600 mesh.

6. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 1, characterized in that: The stirring speed of the uniform stirring is 400 ～ 500r / min, stirring time is 1h.

7. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 1, characterized in that: The mass of the polyethyleneimine is the same as that of 3-aminopropyltriethoxysilane.

8. The method for preparing a modified cellulose-supported steel slag photocatalytic reducing agent according to claim 1, characterized in that: The vigorous stirring in step S200 is carried out by using a magnetic stirrer at a speed of 800 ～ 1500r / min, reaction time is 15min.

9. A modified cellulose-loaded steel slag photocatalytic reducing agent, prepared by the preparation method according to any one of claims 1 to 8, wherein the modified cellulose-loaded steel slag photocatalytic reducing agent is a porous composite material with modified cellulose as a skeleton to fix steel slag.

10. An application of the modified cellulose-supported steel slag photocatalytic reducing agent as claimed in claim 9, characterized in that: The photocatalytic reducing agent adsorbs hexavalent chromium ion compounds under acidic or neutral conditions, and the steel slag reduces the hexavalent chromium ion compounds to non-toxic trivalent chromium under light conditions.

Images