Composite flocculant as well as preparation method and application thereof

Abstract

The invention discloses a composite flocculant and a preparation method and application thereof, and relates to the technical field of flocculants.The preparation method of the composite flocculant comprises the following steps that S1, titanium dioxide nanoparticles are dispersed in a mixed solvent, then aminopropyltriethoxysilane is added for surface modification, and dispersion liquid is obtained; s2, sequentially adding polydopamine and chitosan into the dispersion liquid prepared in S1 under a heating condition, and continuously stirring to prepare a composite material through a Schiff base reaction; s3, centrifuging, washing and drying the composite material prepared in S2 to obtain a composite flocculant; the invention also provides the composite flocculant prepared by the method and application of the composite flocculant in treatment of sewage containing diclofenac sodium.

Description

Technical Field

[0001] The present invention relates to the technical field of flocculants, and in particular to a composite flocculant and a preparation method and application thereof. Background Art

[0002] The treatment of wastewater containing diclofenac sodium is an important environmental issue because diclofenac is a widely used nonsteroidal anti-inflammatory drug that is persistent, bioaccumulative, and potentially ecotoxic.

[0003] Existing treatment methods for diclofenac sodium-containing wastewater generally include adsorption, membrane separation, and advanced oxidation processes. Adsorption is mostly used to treat low-concentration wastewater, and after adsorption saturation, the adsorption material needs to be regenerated or replaced, which is costly and easily generates hazardous waste. Membrane separation requires frequent membrane treatment, increasing treatment costs. Advanced oxidation processes are prone to generating various wastewaters or waste residues that require recycling. Chinese invention patent publication number CN103193352A discloses a method for deep treatment of diclofenac production wastewater, which uses an "adsorption + flocculation" approach to treat diclofenac sodium-containing wastewater. However, this method still cannot avoid the common problems of adsorption materials.

[0004] In the prior art, there are methods for treating diclofenac sodium-containing wastewater using flocculants. However, since diclofenac sodium is a soluble small-molecule organic matter, the effect of existing flocculants in directly treating diclofenac sodium-containing wastewater is limited. Generally, these flocculants are used as pretreatment for diclofenac sodium-containing wastewater to remove suspended matter, colloids, or some coexisting organic matter in the wastewater, thereby creating conditions for subsequent deep treatment. Therefore, there is an urgent need to develop an efficient and stable flocculant for directly treating diclofenac sodium-containing wastewater. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a composite flocculant and its preparation method and application, so as to solve the problem that the flocculants in the prior art have poor treatment effect on wastewater containing diclofenac sodium.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a composite flocculant comprises the following steps:

[0008] S1. The titanium dioxide nanoparticles are dispersed in a mixed solvent, and then aminopropyltriethoxysilane is added for surface modification to obtain a dispersion;

[0009] S2. Polydopamine and chitosan were sequentially added to the dispersion prepared in S1 under heating conditions, and the composite material was obtained by Schiff base reaction with continuous stirring;

[0010] S3. The composite material prepared in S2 is centrifuged, washed, and dried to obtain a composite flocculant.

[0011] Preferably, in step S1, the molar ratio of titanium dioxide nanoparticles, aminopropyltriethoxysilane and mixed solvent is 0.3-0.8:8-15:3-8.

[0012] Preferably, in step S1, the mixed solvent is formed by mixing anhydrous ethanol and deionized water in a volume ratio of 1:3.

[0013] Preferably, in step S1, the titanium dioxide nanoparticles are ultrasonically dispersed in the mixed solvent for 10 to 30 minutes.

[0014] Preferably, in step S1, aminopropyltriethoxysilane needs to be slowly added dropwise at a rate of 1 to 2 mL / min.

[0015] Preferably, in step S2, the heating temperature is 60-80°C, the stirring speed is 200-500 rpm, and the stirring time is 3 hours.

[0016] Preferably, in step S2, the molar ratio of polydopamine to chitosan is 1:1.

[0017] Preferably, in step S3, the centrifugal speed is 3000 rpm, the centrifugal time is 10 min, and the washing method is to use deionized water and alcohol for three times respectively.

[0018] The present invention also provides a composite flocculant prepared by the preparation method.

[0019] The present invention also provides an application of the composite flocculant in the treatment of sewage containing diclofenac sodium.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. In the composite flocculant prepared by the present invention, aminopropyltriethoxysilane forms Si-O-Ti covalent bonds on the surface of titanium dioxide nanoparticles through hydrolysis and condensation reaction, so that the organic-inorganic interface is firmly bonded and the nanoparticles are prevented from agglomerating or falling off. In addition, the Si-O-Ti bonds are stable at room temperature and are not easily destroyed by water molecules. Polydopamine reacts with amino groups to form a Schiff base to form a stable chemical cross-linked network. At the same time, the π-π stacking effect in polydopamine further enhances the mechanical stability of the composite material. In addition, chitosan combines with polydopamine / titanium dioxide nanoparticles through hydrogen bonds and electrostatic effects to form a dense coating layer, which reduces the erosion of the internal structure by the external environment. Therefore, through the synergistic effect of the above three effects, the composite flocculant prepared by the present invention has good stability and still has a good removal effect after long-term storage.

[0022] 2. The phenolic hydroxyl groups in the polydopamine in the composite flocculant prepared by the present invention can quench active oxygen species, thereby protecting chitosan and aminopropyltriethoxysilane from oxidation. At the same time, the chitosan coating layer can reduce the direct irradiation of ultraviolet light on titanium dioxide nanoparticles, thereby inhibiting the photocatalytic self-degradation of titanium dioxide nanoparticles, so that the composite flocculant has good antioxidant and anti-photolysis properties.

[0023] 3. In the composite flocculant prepared by the present invention, since hydrogen bonds and electrostatic adsorption can be reversibly broken under alkaline conditions, the composite flocculant can be regenerated under mild alkaline conditions. In addition, aminopropyltriethoxysilane-modified titanium dioxide nanoparticles provide a rigid skeleton, which can prevent polydopamine / chitosan from swelling or structural collapse during the regeneration process, thereby ensuring the morphological stability of the material. Although polydopamine will partially depolymerize under alkaline conditions, the cross-linked structure can be restored after re-drying, and it has self-repairing properties. Chitosan will be deprotonated under alkaline conditions, thereby releasing pollutants and achieving regeneration.

[0024] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0025] In order to make the technical means, creative features, objectives and effects of the present invention clearer and easier to understand, the present invention is further described below in conjunction with specific embodiments:

[0026] Example 1

[0027] S1. Titanium dioxide nanoparticles were dispersed in a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 1:3 for 30 min, and then aminopropyltriethoxysilane was slowly added dropwise at a rate of 1 mL / min to obtain a dispersion in which the molar ratio of titanium dioxide nanoparticles, aminopropyltriethoxysilane, and the mixed solvent was 0.3:8:3;

[0028] S2. To the dispersion prepared in S1, polydopamine and chitosan were added in a molar ratio of 1:1, sequentially, at 70°C, and stirred at 200 rpm for 3 h to obtain a composite material via a Schiff base reaction.

[0029] S3. The composite material prepared in S2 was centrifuged at 3000 rpm for 10 min, then washed three times with deionized water and three times with alcohol, and finally dried for more than 24 h to obtain a composite flocculant.

[0030] Example 2

[0031] S1. Titanium dioxide nanoparticles were dispersed in a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 1:3 for 10 min, and then aminopropyltriethoxysilane was slowly added dropwise at a rate of 2 mL / min to obtain a dispersion in which the molar ratio of titanium dioxide nanoparticles, aminopropyltriethoxysilane, and the mixed solvent was 0.5:10:8;

[0032] S2. To the dispersion prepared in S1, polydopamine and chitosan were added in a molar ratio of 1:1, respectively, at 60°C, and stirred at 500 rpm for 3 h to obtain a composite material through a Schiff base reaction.

[0033] S3. The composite material prepared in S2 was centrifuged at 3000 rpm for 10 min, then washed three times with deionized water and three times with alcohol, and finally dried for more than 24 h to obtain a composite flocculant.

[0034] Example 3

[0035] S1. Titanium dioxide nanoparticles were dispersed in a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 1:3 for 20 min, and then aminopropyltriethoxysilane was slowly added dropwise at a rate of 2 mL / min to obtain a dispersion in which the molar ratio of titanium dioxide nanoparticles, aminopropyltriethoxysilane, and the mixed solvent was 0.8:15:5;

[0036] S2. To the dispersion prepared in S1, polydopamine and chitosan were added in a molar ratio of 1:1, sequentially, at 80°C, and the mixture was stirred at 350 rpm for 3 h to obtain a composite material via a Schiff base reaction.

[0037] S3. The composite material prepared in S2 was centrifuged at 3000 rpm for 10 min, then washed three times with deionized water and three times with alcohol, and finally dried for more than 24 h to obtain a composite flocculant.

[0038] Taking Example 1 as an example, the performance of the composite flocculant prepared therefrom in the treatment of wastewater containing diclofenac sodium was tested, wherein the addition amount of the composite flocculant was 0.5 g / L. The test results are shown in the following table.

[0039]

[0040]

[0041] As shown in the table above, the flocculant prepared by the present invention can have an excellent removal rate at different initial concentrations of diclofenac sodium, pH values and temperatures.

[0042] Moreover, it can be seen from the 1st to 3rd tests that when the initial concentration of diclofenac sodium and the temperature remain unchanged, the composite flocculant does not have a significant effect on the removal rate of diclofenac sodium as the pH value changes.

[0043] Secondly, it can be seen from the 4th to 6th tests that when the initial concentration and pH value of diclofenac sodium remain unchanged, the removal rate of diclofenac sodium by the composite flocculant gradually increases with the increase of temperature.

[0044] Finally, it can be seen from the 2nd, 5th and 7th tests that when the pH value and temperature remain unchanged, the removal rate of diclofenac sodium by the composite flocculant gradually increases with the increase of the initial concentration of diclofenac sodium.

[0045] Next, the composite flocculant used in the second test is regenerated. The specific steps are as follows:

[0046] S1. The used composite flocculant was washed with ethanol and water;

[0047] S2. The washed product in S1 is immersed in a 0.1 M sodium hydroxide solution (pH = 12) for 2 hours, and then centrifuged and dried to obtain a regenerated composite flocculant.

[0048] Subsequently, the performance of the composite flocculant in treating diclofenac sodium-containing wastewater after being regenerated 1, 3, and 5 times in the above manner was tested, and the test results are shown in the following table.

[0049]

[0050]

[0051] As can be seen from the above table, the composite flocculant prepared by the present invention still has a good removal rate after being regenerated 5 times. At the same time, during the continuous regeneration process, the adsorption capacity retention rate of the composite flocculant does not decrease too much, indicating that the composite flocculant can maintain good stability during the regeneration process.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a composite flocculant, characterized in that: The following steps are involved: S1. The titanium dioxide nanoparticles are dispersed in a mixed solvent, and then aminopropyltriethoxysilane is added for surface modification to obtain a dispersion; S2. Polydopamine and chitosan were sequentially added to the dispersion prepared in S1 under heating conditions, and the composite material was obtained by Schiff base reaction with continuous stirring; S3. The composite material prepared in S2 is centrifuged, washed, and dried to obtain a composite flocculant.

2. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S1 , the molar ratio of titanium dioxide nanoparticles, aminopropyltriethoxysilane, and the mixed solvent is 0.3-0.8:8-15:3-8.

3. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S1, the mixed solvent is prepared by mixing anhydrous ethanol and deionized water in a volume ratio of 1:

3.

4. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S1, the titanium dioxide nanoparticles are ultrasonically dispersed in the mixed solvent for 10 to 30 minutes.

5. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S1, aminopropyltriethoxysilane needs to be slowly added dropwise at a rate of 1 to 2 mL / min.

6. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S2, the heating temperature is 60-80°C, the stirring speed is 200-500 rpm, and the stirring time is 3 hours.

7. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S2, the molar ratio of polydopamine to chitosan is 1:

1.

8. The method for preparing a composite flocculant according to claim 1, characterized in that: In step S3, the centrifugal speed is 3000 rpm, the centrifugal time is 10 min, and the washing method is to use deionized water and alcohol for three times respectively.

9. A composite flocculant, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the composite flocculant according to claim 9 in the treatment of wastewater containing diclofenac sodium.

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