Adsorbent for treating Congo red wastewater and preparation method thereof

Abstract

The invention belongs to the technical field of printing and dyeing wastewater treatment, and particularly relates to an adsorbent for treating Congo red wastewater and a preparation method thereof.The preparation method comprises the steps that dry urea is calcined for 1-4 h at the temperature of 450-600 DEG C, washed and dried for at least 6 h at the temperature of 50-80 DEG C in sequence, and g-C3N4 is obtained; then mixing g-C3N4 with water, adding hexadecyl trimethyl ammonium bromide, and carrying out hydrothermal reaction at 160-180 DEG C for 6-24 hours to obtain a reaction product; and cooling the reaction product to room temperature, and sequentially washing and drying at 50-80 DEG C for at least 6 hours to obtain the final adsorbent. The hexadecyl trimethyl ammonium bromide is introduced to perform surface modification on the g-C3N4, so that the original negatively charged g-C3N4 is changed into positively charged g-C3N4, and the adsorption capacity and selectivity of the adsorbent on the anionic dye Congo red are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of printing and dyeing wastewater treatment, and particularly relates to an adsorbent for treating Congo red wastewater and a preparation method thereof. Background Art

[0002] In the field of wastewater treatment, especially for the treatment of wastewater containing organic dyes such as Congo red, a variety of adsorbents have been developed and applied. These adsorbents mainly include activated carbon, natural minerals (such as bentonite, zeolite), synthetic polymers, and nanomaterials that have emerged in recent years. Among them, activated carbon is widely used due to its high specific surface area and good adsorption properties, but its selective adsorption effect is poor; although natural minerals are low in cost, their adsorption efficiency is limited; and synthetic polymers may cause secondary pollution problems. In recent years, some adsorbents based on graphite phase carbon nitride (g-C3N4) have gradually attracted attention due to their excellent stability and adjustability. Although adsorbents based on g-C3N4 have shown certain potential in wastewater treatment, the existing technology still has the following problems: (1) Limited adsorption efficiency: The adsorption capacity of unmodified g-C3N4-based adsorbent for Congo red is not high, which makes it difficult to meet the needs of high-concentration wastewater treatment.

[0003] (2) Insufficient selective adsorption capacity: The unmodified g-C3N4-based adsorbent has weak selective adsorption capacity for Congo red. Summary of the Invention

[0004] The purpose of the present invention is to address the above-mentioned problems in the prior art and to provide an adsorbent with high adsorption capacity and selectivity for treating Congo red wastewater and a preparation method thereof.

[0005] To achieve the above objectives, the technical solutions of the present invention are as follows: In a first aspect, the present invention provides a method for preparing an adsorbent for treating Congo red wastewater, the preparation method comprising: The preparation method comprises: S1, calcining the dried urea at 450-600 ° C for 1-4 hours, washing, and drying at 50-80 ° C for at least 6 hours to obtain g-C3N4; S2. Mix g-C3N4 with water, add cetyltrimethylammonium bromide and hydrothermally react at 160-180°C for 6-24h to obtain a reaction product; S3. After cooling the reaction product to room temperature, washing and drying at 50-80° C. for at least 6 h are performed in sequence to obtain the final adsorbent.

[0006] The mass ratio of g-C3N4 to hexadecyltrimethylammonium bromide in S2 is 1:0.1-0.5.

[0007] The mass ratio of g-C3N4 to hexadecyltrimethylammonium bromide in S2 is 1:0.2.

[0008] The mass volume ratio of g-C3N4 to water in the S2 is 0.2g:20-80mL.

[0009] The calcination temperature is 550° C., and the calcination heating rate is 2-10° C. / min.

[0010] The drying temperature is 55°C.

[0011] The washing refers to washing with water and ethanol alternately for 3 times.

[0012] In a second aspect, the present invention provides an adsorbent for treating Congo red wastewater, wherein the adsorbent is prepared according to the aforementioned preparation method.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The preparation method of the present invention introduces cetyltrimethylammonium bromide (CTAB) to perform surface modification on g-C3N4. The modified g-C3N4 changes from being negatively charged to being positively charged, which is more conducive to the adsorption of the anionic dye Congo red, thereby significantly improving the adsorption capacity and selectivity of the adsorbent for Congo red. In addition, the raw materials of the prepared adsorbent are widely available, and no toxic or harmful reagents are used in the preparation process. The process is green, pollution-free, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 XRD patterns of modified and unmodified g-C3N4.

[0015] Figure 2 This is the SEM image of modified g-C3N4.

[0016] Figure 3 This is the SEM image of unmodified g-C3N4.

[0017] Figure 4 Zeta potential diagram of modified and unmodified g-C3N4.

[0018] Figure 5 The removal rates of different dyes by the adsorbent obtained in Example 1 are shown in FIG.

[0019] Figure 6 The removal rates of Congo red dye by the adsorbents obtained in Examples 1-3 and the comparative example are shown. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0021] A method for preparing an adsorbent for treating Congo red wastewater, the preparation method comprising: S1, calcining the dried urea at 450-600 ° C for 1-4 hours, washing, and drying at 50-80 ° C for at least 6 hours to obtain g-C3N4; S2. Mix g-C3N4 with water, add cetyltrimethylammonium bromide and hydrothermally react at 160-180°C for 6-24h to obtain a reaction product; S3. After cooling the reaction product to room temperature, washing and drying at 50-80° C. for at least 6 h are performed in sequence to obtain the final adsorbent.

[0022] The mass ratio of g-C3N4 to hexadecyltrimethylammonium bromide in S2 is 1:0.1-0.5.

[0023] The mass ratio of g-C3N4 to hexadecyltrimethylammonium bromide in S2 is 1:0.2.

[0024] The mass volume ratio of g-C3N4 to water in the S2 is 0.2g:20-80mL.

[0025] The calcination temperature is 550° C., and the calcination heating rate is 2-10° C. / min.

[0026] The drying temperature is 55°C.

[0027] The washing refers to washing with water and ethanol alternately for 3 times.

[0028] An adsorbent for treating Congo red wastewater, wherein the adsorbent is prepared according to the above-mentioned preparation method.

[0029] Example 1: S1. Weigh 20 g of urea and bake it in an oven for 10 min. Grind it in an agate mortar for 10 min, then transfer it to a crucible and place it in a muffle furnace. Calcined it at 550 ° C for 2 h at a heating rate of 10 ° C / min; cooled to room temperature, washed it with pure water and ethanol alternately three times, and dried it in a 55 ° C oven for 6 h to obtain g-C3N4; S2. Weigh 0.2 g of g-C3N4, put it into a reactor filled with 60 mL of pure water and stir it at 300 rpm for 5 minutes, then add 0.04 g of hexadecyltrimethylammonium bromide (the mass ratio of g-C3N4 to CTAB is 1:0.2), stir for 30 minutes, remove the magnet, hydrothermally react at 170°C for 8 hours, cool to room temperature, wash it alternately with water and ethanol three times, and finally dry the obtained solid in a 55°C oven for 6 hours to obtain CTAB-modified g-C3N4, which is the final adsorbent.

[0030] Performance testing: (1) XRD patterns of modified and unmodified g-C3N4 are shown in Figure 2. Figure 1 As shown, it can be seen that g-C3N4 was successfully synthesized, and the crystallinity of g-C3N4 after modification was better.

[0031] (2) The SEM images of modified and unmodified g-C3N4 are shown in Figure 2. Figure 2 、 Figure 3 As shown, it can be seen that both modified and unmodified g-C3N4 are nanosheet structures, and the modified g-C3N4 nanostructure is finer.

[0032] (3) Zeta potential of modified and unmodified g-C3N4 Figure 4 As shown in the figure, it can be seen that the modified g-C3N4 changes from negatively charged to positively charged.

[0033] (4) Prepare 50 mL of 100 mg / L dye solution, take 10 mg of adsorbent and put it in, stir at 20 ° C for 3 h, centrifuge and take the supernatant to test under UV-visible spectrophotometer, calculate the removal rate of adsorbent for different dyes, removal rate (%) = (1-absorbance of dye solution after adsorption / absorbance of initial dye solution) × 100%; Congo red (CR), methyl orange (MO), rhodamine B (RhB), methylene blue (MB), crystal violet (CV) corresponding to the UV spectrophotometer test wavelength is 498 nm, 464 nm, 554 nm, 664 nm, 588 nm. The calculation results are as follows: Figure 5 As shown, it can be seen that the modified g-C3N4 has good adsorption selectivity for Congo red and the removal rate is as high as 99%, while the removal rate for methyl orange is only 23.2%, and there is no adsorption effect on rhodamine B, methylene blue and crystal violet.

[0034] This is likely due to electrostatic adsorption of the anionic dye Congo red by the positively charged surface of the modified g-C3N4, π-π interactions between the π-conjugated system of the modified g-C3N4 and the aromatic structure of the Congo red molecule, and hydrogen bonding interactions between H-donors (such as hydroxyl groups) in the Congo red molecule and H-acceptor atoms (such as nitrogen atoms) in the modified g-C3N4. These three factors together give the modified g-C3N4 good adsorption selectivity for Congo red. Rhodamine B, methylene blue, and crystal violet are all cationic dyes, and the positively charged surface of the modified g-C3N4 makes them less likely to adsorb cationic dyes. Although methyl orange (MO) is also an anionic dye, the Congo red molecule contains multiple sulfonic acid and hydroxyl groups, which are potential hydrogen bond donors or acceptors. Sulfonic acid groups can ionize in water, releasing negative charges while retaining some hydrogen ions, making them less likely to form hydrogen bond donors. However, hydroxyl groups can directly act as hydrogen bond donors. Methyl orange also contains hydroxyl groups, thus also having the potential to act as hydrogen bond donors. However, compared to Congo red, methyl orange has fewer hydroxyl groups and a relatively simple molecular structure, resulting in fewer hydrogen bond donors or acceptors. Furthermore, Congo red is a dye containing multiple aromatic rings and a complex structure, including multiple aromatic moieties that can interact with the π-electron cloud of modified g-C3N4. Methyl orange, on the other hand, primarily contains a larger azo group and a smaller aromatic ring. While it also contains aromatic structures, it has fewer aromatic moieties than Congo red. Because Congo red has more aromatic rings, it is more likely to interact extensively with the π-electron cloud of modified g-C3N4.

[0035] Example 2: The difference from Example 1 is that the mass ratio of g-C3N4 to CTAB in S2 is set to 1:0.1.

[0036] Example 3: The difference from Example 1 is that the mass ratio of g-C3N4 to CTAB in S2 is set to 1:0.5.

[0037] Comparative Example: The difference from Example 1 is that the mass ratio of g-C3N4 to CTAB in S2 is set to 1:0.

[0038] Calculate the removal rate of Congo red dye by the adsorbent obtained in Examples 1-3 and Comparative Example. The calculation results are as follows: Figure 6 As shown, it can be seen that the removal rate of Congo red dye in Examples 1-3 reached more than 90%, and the removal rate was best when the mass ratio of g-C3N4 to CTAB was 1:0.2.

[0039] Example 4: S1. Weigh 20 g of urea and bake it in an oven for 10 min. Grind it in an agate mortar for 10 min, then transfer it to a crucible and place it in a muffle furnace. Calcine it at 450 ° C for 4 h at a heating rate of 2 ° C / min; cool it to room temperature, wash it with pure water and ethanol alternately three times, and dry it in a 60 ° C oven for 12 h to obtain g-C3N4; S2. Weigh 0.2 g of g-C3N4, put it into a reactor filled with 20 mL of pure water and stir it at 300 rpm for 5 minutes, then add 0.04 g of hexadecyltrimethylammonium bromide, stir for 30 minutes, remove the magnet, hydrothermally react at 160°C for 24 hours, cool to room temperature, wash it alternately with water and ethanol three times, and finally dry the obtained solid in an oven at 60°C for 12 hours to obtain CTAB-modified g-C3N4, which is the final adsorbent.

[0040] Example 5: S1. Weigh 20 g of urea and bake it in an oven for 10 min. Grind it in an agate mortar for 10 min, then transfer it to a crucible and place it in a muffle furnace. Calcine it at 600 ° C for 1 h at a heating rate of 10 ° C / min; cool it to room temperature, wash it with pure water and ethanol alternately three times, and dry it in an 80 ° C oven for 6 h to obtain g-C3N4; S2. Weigh 0.2 g of g-C3N4, put it into a reactor filled with 800 mL of pure water and stir it at 300 rpm for 5 minutes, then add 0.04 g of hexadecyltrimethylammonium bromide, stir for 30 minutes, remove the magnet, hydrothermally react at 180°C for 10 hours, cool to room temperature, wash it alternately with water and ethanol three times, and finally dry the obtained solid in an oven at 80°C for 6 hours to obtain CTAB-modified g-C3N4, which is the final adsorbent.

Claims

1. A method for preparing an adsorbent for treating Congo red wastewater, characterized in that: The preparation method comprises: S1, calcining the dried urea at 450-600 ° C for 1-4 hours, washing, and drying at 50-80 ° C for at least 6 hours to obtain g-C3N4; S2. Mix g-C3N4 with water, add cetyltrimethylammonium bromide and hydrothermally react at 160-180°C for 6-24h to obtain a reaction product; S3. After cooling the reaction product to room temperature, washing and drying at 50-80° C. for at least 6 hours are performed in sequence to obtain the final adsorbent.

2. The method for preparing an adsorbent for treating Congo red wastewater according to claim 1, wherein: The mass ratio of g-C3N4 to hexadecyltrimethylammonium bromide in S2 is 1:0.1-0.

5.

3. The method for preparing an adsorbent for treating Congo red wastewater according to claim 2, wherein: The mass ratio of g-C3N4 to hexadecyltrimethylammonium bromide in S2 is 1:0.

2.

4. The method for preparing an adsorbent for treating Congo red wastewater according to claim 1, wherein: The mass volume ratio of g-C3N4 to water in the S2 is 0.2g:20-80mL.

5. The method for preparing an adsorbent for treating Congo red wastewater according to claim 1, wherein: The calcination temperature is 550° C., and the calcination heating rate is 2-10° C. / min.

6. The method for preparing an adsorbent for treating Congo red wastewater according to claim 1, wherein: The drying temperature is 55°C.

7. The method for preparing an adsorbent for treating Congo red wastewater according to claim 1, wherein: The washing refers to washing with water and ethanol alternately for 3 times.

8. An adsorbent for treating Congo red wastewater, characterized in that: The adsorbent is prepared according to the preparation method according to any one of claims 1 to 7.

Images