Alginate fiber silver complex photocatalyst and preparation method thereof

Abstract

The invention discloses an alginate fiber silver complex photocatalyst and a preparation method thereof, the alginate fiber silver complex photocatalyst is prepared by coordination reaction of alginate fibers and silver ions, and the silver matching amount in the alginate fiber silver complex photocatalyst is 0.5 mmol / g to 3.0 mmol / g. The photocatalyst can serve as a heterogeneous photocatalyst to be applied to oxidative degradation treatment of printing and dyeing wastewater, keeps good photocatalytic oxidation performance, not only has higher visible light response performance and photocatalytic oxidation activity compared with a silver complex photocatalyst in the prior art, but also can be recycled for multiple times. The photocatalyst is simple in preparation process, mild in condition and free of special equipment, the application method is simple, feasible, easy to operate and low in operation cost, and industrial application has obvious economic benefits.

Description

Technical Field

[0001] The present invention relates to the technology of chemical catalysts, and particularly to a seaweed fiber silver complex photocatalyst and a preparation method thereof. Background Art

[0002] The rapid development of social economy and industrial modernization has led to an increasingly serious problem of ecological environment pollution, and the problem of water environmental pollution is particularly prominent. Under this background, a variety of technical means for treating water pollution have developed rapidly. Among them, the semiconductor photocatalytic oxidation technology based on chemical oxidation method has been widely used for the removal of organic pollutants due to its high efficiency, low cost and no secondary pollution. As is well known, polymer metal complexes (PMCs) usually exhibit unique catalytic activity due to their complex and variable molecular structures. Among them, silver complexes with semiconductor properties can be synthesized by coordinating silver ions with a variety of organic ligands, which can photocatalytically oxidize and decompose organic pollutants without adding oxidants. However, most of the silver complex photocatalysts prepared at present [see Yin Z C, et al. A 3D supramolecular Ag(I)-based coordination polymer as stable photocatalyst for dye degradation[J]. Inorganic Chemistry Communications, 2021, 131: 108805.] are synthesized using small molecule ligands under harsh reaction conditions such as high temperature and high pressure or hydrothermal environment. The reaction process is complex and energy consumption is high. Moreover, the obtained silver complexes usually only show photocatalytic oxidation degradation reaction performance for organic pollutants such as dyes in water under ultraviolet light conditions. More importantly, the previous silver complex photocatalysts are usually in the form of particles, with deficiencies such as complex preparation, difficult recovery or high cost.Although fiber materials are mostly used as organic polymer ligands to prepare PMCs with special catalytic properties due to their large specific surface area, good adsorption performance, and flexible shape and size design, especially the amidoxime-modified polyacrylonitrile fiber silver complex photocatalyst prepared using amidoxime-modified polyacrylonitrile fiber ligands [see Yan Y, et al. Modified polyacrylonitrile fiber silver complexes to display semiconducting behavior: synthesis, characterization and photocatalytic oxidative capacity[J]. Industrial & Engineering Chemistry Research, 2023, 62(27), 10330-10341.], there are still the following deficiencies in this method: (1) The fiber ligands used are synthetic fibers with poor biodegradability; (2) There are problems with the modification reaction of polyacrylonitrile fibers, such as complex processes, difficult-to-control reaction conditions, and chemical reagent pollution; (3) The operating cost is high, making it difficult to adapt to future industrial production and applications. Seaweed fiber not only has excellent biocompatibility and metal ion adsorption characteristics, but also its macromolecular structure contains a large number of carboxyl groups that can coordinate with a variety of transition metal ions to form complexes. Compared with modified polyacrylonitrile fibers, the unique carboxyl structure in its molecules makes the preparation process of PMCs photocatalysts simpler and the processing cost lower. However, there is currently no report on the research of seaweed fiber silver complexes with photocatalytic oxidation performance prepared using seaweed fiber as a polymer ligand. Summary of the Invention

[0003] Object of the Invention: To overcome the shortcomings and deficiencies of the prior art, the technical problem to be solved by this invention is to provide a seaweed fiber silver complex photocatalyst and its preparation method. The organic polymer ligand used in this photocatalyst is natural carboxyl-containing seaweed fiber, which can coordinate with silver ions without complex modification, greatly shortening the preparation process of the seaweed fiber silver complex photocatalyst, simplifying the preparation process, being easy to operate without special equipment, and being easy to promote industrially.

[0004] This invention provides a seaweed fiber silver complex photocatalyst, which is prepared by the coordination reaction of seaweed fiber and silver ions. The silver ion content in the seaweed fiber silver complex photocatalyst is 0.5 mmol / g to 3.0 mmol / g. The carboxyl group content in the molecular structure of the seaweed fiber is greater than 2.0 mmol / g.

[0005] The present invention also provides a method for preparing a seaweed fiber silver complex photocatalyst, which includes the step of performing a coordination reaction between seaweed fiber and a silver ion solution. The silver ion solution is a 0.05 - 0.20 mol / L silver nitrate solution, and the weight - to - volume ratio of the seaweed fiber to the silver ion solution is 1:50. The coordination reaction is carried out under stirring for 0.5 - 2.0 hours at a reaction temperature of 20 - 60°C. After the reaction, it is washed with distilled water and dried.

[0006] Furthermore, the seaweed fiber needs to be pretreated before the coordination reaction. The pretreatment steps are as follows: First, wash the seaweed fiber with an aqueous solution of a non - ionic surfactant under stirring at room temperature for 30 - 60 minutes, then wash it with distilled water, and finally dry it for standby. The non - ionic surfactant is of the fatty alcohol polyoxyethylene ether type or the alkylphenol polyoxyethylene ether type. The concentration of the non - ionic surfactant is 2 - 5 g / L.

[0007] Furthermore, after the coordination reaction is completed, the seaweed fiber silver complex needs to be post - treated. The post - treatment process is to wash it with distilled water and then dry it to obtain the seaweed fiber silver complex.

[0008] The present invention also provides the application of the seaweed fiber silver complex photocatalyst in the oxidative degradation treatment of textile printing and dyeing wastewater.

[0009] Beneficial effects: Compared with the prior art, the organic polymer ligand used in the photocatalyst of the present invention is natural seaweed fiber containing carboxyl groups, which can undergo a coordination reaction with silver ions without complex modification. The carboxyl groups in the molecular structure of the seaweed fiber can form a silver complex with stable structure with silver ions through monodentate or bidentate chelation, overcoming the problems of traditional silver complex photocatalysts being sensitive to light and water. In addition, the silver - affinity in the complex endows it with the characteristics of a semiconductor photocatalyst. Compared with the Fenton reaction photocatalyst, it has photocatalytic oxidation activity without the need to be used in combination with an oxidant. Under visible light irradiation conditions, the photocatalyst of the present invention can be used as a heterogeneous photocatalyst in the oxidative degradation treatment of printing and dyeing wastewater and maintain good photocatalytic oxidation performance. It not only has higher visible - light response performance and photocatalytic oxidation activity than the existing photocatalysts, but also can be recycled multiple times. The preparation process of the photocatalyst of the present invention is simple, the conditions are mild, no special equipment is required, its application method is simple and feasible, easy to operate, and the operation cost is low. The industrial application has obvious economic benefits. Description of the Drawings

[0010] Figure 1Comparison of the photocatalytic oxidation degradation effects of three embodiments (Ag-Alginate-1, Ag-Alginate-2, and Ag-Alginate-3) of the photocatalyst described in the present invention on Reactive Red 195 under the condition of pH = 6 (test conditions: Reactive Red 195: 0.05 mmol / L, 50 mL; catalyst: 0.5 g; pH = 6.0; LED radiation light (visible light: 400 - 1000 nm; intensity: 14.95 mWcm -2 ) Figure 2 Comparison chart of the degradation rate changes of an embodiment (Ag-Alginate-1) of the photocatalyst described in the present invention and a prior art catalyst (Fe-Alginate) in the oxidation degradation reaction of Reactive Red 195 under different concentrations of hydrogen peroxide (the test time is 100 minutes, and other test conditions are the same as Figure 1 ) Figure 3 Comparison chart of the degradation rate changes of an embodiment (Ag-Alginate-1) of the photocatalyst described in the present invention and a prior art catalyst (Ag-AO-PAN) in the oxidation degradation reaction of Reactive Red 195 (the test conditions are the same as Figure 1 ) Figure 4 Curve graph of the degradation rate changes of an embodiment (Ag-Alginate-1) of the photocatalyst described in the present invention during repeated use on Reactive Red 195 (the test conditions are the same as Figure 1 ) Detailed implementation manners

[0011] To deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0012] The silver complex photocatalyst designed by the present invention is composed of a seaweed fiber ligand with good biodegradability and natural carboxylic acid groups and a silver ion coordination reactant, and its appearance is white to reddish-brown, fibrous. A large number of hydroxyl and carboxyl groups exist in the molecular structure of the seaweed fiber, resulting in its extremely strong hydrophilicity. The oxygen atoms therein can provide lone pair electrons to metal ions and form coordination bonds with them. On the one hand, this is conducive to the rapid adsorption of silver ions by the seaweed fiber, enabling the two to obtain more silver ion content within a shorter coordination reaction time, thus showing higher photocatalytic activity in the oxidation degradation reaction of dyes and other pollutants. On the other hand, the carboxyl groups in the molecular structure of the seaweed fiber can generate silver complexes with stable structures through monodentate or bidentate chelation with silver ions, making it not easy to have the problem of metal ion shedding during use. In addition, the special eggshell structure in the seaweed fiber molecule can encapsulate silver ions in the molecular chain, avoiding the inactivation of the active center silver ions during use and overcoming the problems of traditional silver complex photocatalysts being sensitive to light and water. More importantly, due to the existence of a metallophilic interaction between two closed-shell metal ions with a d 10 valence electron shell distribution, the argentophilic interaction formed between the two silver ions in the silver complex of seaweed fiber endows the catalyst with excellent light absorption properties and makes it possible to be a visible light-responsive semiconductor photocatalyst.

[0013] In the embodiment of the present invention, the silver coordination amount ( Q Ag ) and the dye degradation rate ( D %) of the silver complex of seaweed fiber are calculated by the following formulas (1-2): (1) In formula (1), C 0 and C 1 are respectively the silver ion concentrations (mol / L) in the silver nitrate solution before and after the coordination reaction, V 0 and V 1 are respectively the volumes (mL) of the silver ion aqueous solution before and after the coordination reaction, m is the weight (g) of the silver complex of seaweed fiber.

[0014] (2) In formula (2), C 0 and C t are respectively the concentrations (mmol / L) of the dye in water before and after the oxidation degradation reaction in the presence of the silver complex of seaweed fiber.

[0015] The following introduces the specific embodiments of the present invention, but the claims of the present invention are not limited by these specific embodiments.

[0016] Source of alginate fiber: The alginate fiber used in this invention is provided by China National Textile and Apparel Council, with a fineness of 5.53 dtex (dtex, the symbol for decitex, refers to the number of grams of weight of a 10,000-meter-long yarn at the official regain. 1 dtex = 1 g / 10,000 m). The content of carboxyl groups in the molecular structure of the alginate fiber in the examples is 2.23 mmol / g.

[0017] Example 1 Preparation of silver complex of alginate fiber 1) Pretreatment of alginate fiber: First, wash the alginate fiber with an aqueous solution of non-ionic surfactant OP-10 with a concentration of 2.0 g / L at room temperature and under stirring conditions for 30 minutes. Then take it out and wash it with distilled water 3 times. Finally, dry it in vacuum at 50 °C for later use. 2) Coordination reaction between alginate fiber and silver ion solution: Accurately weigh 1.0 g of the above-pretreated alginate fiber and immerse it in a silver nitrate solution with a concentration of 0.20 mol / L and a volume of 50 mL. Carry out the coordination reaction at 50 °C and under stirring conditions for 2.0 hours. Then wash it repeatedly with distilled water 3 times and dry it. 3) Post-treatment process: Wash it with distilled water 3 times, and then dry it in vacuum at 50 °C to obtain the silver complex photocatalyst of alginate fiber (denoted as Ag-Alginate-1). Through measurement and calculation, the silver coordination amount of this photocatalyst is 2.816 mmol / g.

[0018] Example 2 The preparation steps are the same as those in Example 1, except that the concentration of the silver nitrate aqueous solution is adjusted to 0.10 mol / L. Denote the obtained silver complex photocatalyst of alginate fiber as Ag-Alginate-2. Through measurement and calculation, the silver coordination amount of this photocatalyst is 2.158 mmol / g.

[0019] Example 3 The preparation steps are the same as those in Example 1, except that the concentration of the silver nitrate aqueous solution is adjusted to 0.05 mol / L. Denote the obtained silver complex photocatalyst of alginate fiber as Ag-Alginate-3. Through measurement and calculation, the silver coordination amount of this photocatalyst is 0.935 mmol / g.

[0020] Comparative Example 1 Iron complex of alginate fiber This example is a comparative example for the effect. Use a 0.20 mol / L ferric chloride solution to replace the silver nitrate solution in Step 2 of Example 1, and the rest of the process is the same as that in Example 1 to obtain the iron complex of alginate fiber (denoted as Fe-Alginate). Through measurement and calculation, the iron coordination amount of this catalyst is 2.884 mmol / g.

[0021] Comparative Example 2: Amidoxime-Modified Polyacrylonitrile Fiber Silver Complex This example is a comparative example for the effect, and the specific steps are as follows: 1) Amidoxime modification reaction of polyacrylonitrile fiber: Accurately weigh 1.0 g of pretreated polyacrylonitrile yarn and immerse it in 50 mL of an aqueous hydroxylamine hydrochloride solution with a concentration of 30 g / L. Use sodium hydroxide to adjust the pH value of the aqueous hydroxylamine hydrochloride solution to 9.5, and then react at 98 °C under stirring conditions for 2 hours. Take out the obtained light yellow fiber, wash it repeatedly with distilled water 3 times, and then dry it to obtain amidoxime-modified polyacrylonitrile fiber.

[0022] 2) Coordination reaction of amidoxime-modified polyacrylonitrile fiber with silver ions: Immerse 1.0 g of the above modified polyacrylonitrile fiber in 50 mL of a silver nitrate solution with a concentration of 0.20 mol / L, let it react at 50 °C under stirring conditions for 1 hour, then take it out, wash it repeatedly with distilled water 3 times, and dry it to obtain amidoxime-modified polyacrylonitrile fiber silver complex (denoted as Ag-AO-PAN). After measurement and calculation, the silver coordination amount of this photocatalyst is 2.797 mmol / g.

[0023] Figure 1 Shows the photocatalytic oxidation degradation performance of three samples of Ag-Alginate-1, Ag-Alginate-2, and Ag-Alginate-3 prepared in Examples 1-3 of the present invention for Reactive Red 195, and the effect comparison of the photocatalytic oxidation degradation of Reactive Red 195 under the condition of pH = 6 (test conditions: Reactive Red 195: 0.05 mmol / L, 50 mL; catalyst: 0.5 g; pH = 6.0; LED radiation light (visible light: 400 - 1000 nm; intensity: 14.95 mWcm -2 ) As can be seen from the figure, under the premise of not adding hydrogen peroxide, the degradation rate of the photocatalyst of the present invention for Reactive Red 195 increases rapidly with the extension of the reaction time, and with the increase of the silver coordination amount in the alginate fiber silver complex, the degradation rate of Reactive Red 195 continues to increase. It is actually proved that the photocatalyst of the present invention has high photocatalytic activity for the oxidation degradation reaction of dyes, and the increase of the silver coordination amount of the complex can significantly enhance its photocatalytic oxidation performance.

[0024] Figure 2 Shows the photocatalytic oxidation degradation performance of a sample of Ag-Alginate-1 prepared by the present invention and a sample of Fe-Alginate prepared by the prior art for Reactive Red 195 under different hydrogen peroxide concentration conditions (the test time is 100 minutes, and other test conditions are the same as Figure 1 ). From Figure 2It can be seen that without adding hydrogen peroxide, the degradation rate of the dye in the presence of Ag-Alginate-1 is significantly higher than the corresponding value in the presence of Fe-Alginate at the same reaction time. In the case of adding hydrogen peroxide, the degradation rates of the two dyes are at a similar level and show an upward trend with the increase of hydrogen peroxide concentration. This proves that Fe-Alginate can only act as a heterogeneous Fenton reaction photocatalyst in the presence of hydrogen peroxide, while the photocatalyst Ag-Alginate-1 of the present invention can act as a heterogeneous photocatalyst to oxidize and degrade the dye in both the presence and absence of hydrogen peroxide.

[0025] Figure 3 Figure showing the comparison of the degradation rate changes of an embodiment of the photocatalyst of the present invention (Ag-Alginate-1) and the prior art catalyst (Ag-AO-PAN) in the oxidation degradation reaction of Reactive Red 195 (the test conditions are the same as Figure 1 ) Figure 3 It shows the photocatalytic oxidation degradation performance of the catalyst Ag-Alginate-1 of the present invention and the prior art catalyst as heterogeneous reaction photocatalysts in the application of Reactive Red 195 under the conditions of the same usage amount, the same metal coordination amount, and pH = 6. When Ag-Alginate-1 and Ag-AO-PAN are present, the degradation rate of the dye gradually increases with the prolongation of the reaction time. It should be noted that the degradation rate of the dye in the presence of Ag-Alginate-1 is significantly higher than the corresponding value in the presence of Ag-AO-PAN at the same reaction time, indicating that Ag-Alginate-1 shows higher photocatalytic oxidation activity in the process of oxidizing and degrading Reactive Red 195 under the same reaction conditions.

[0026] Figure 4 Figure showing the change curve of the degradation rate of Reactive Red 195 when an embodiment of the photocatalyst of the present invention (Ag-Alginate-1) is reused (the test conditions are the same as Figure 1 ) Figure 4 It shows that with the prolongation of the reaction time, the degradation rate of the Reactive Red 195 dye by the photocatalyst Ag-Alginate-1 of the present invention gradually increases, and with the increase of the number of repeated uses, it still maintains a high degradation rate for the Reactive Red 195 dye, actually proving that the photocatalyst of the present invention has good stability and can be repeatedly applied to the oxidation degradation process of printing and dyeing wastewater.

[0027] In summary, the photocatalyst of the present invention not only has the characteristics of high photocatalytic activity and good reusability, but also does not require the addition of oxidants during use, which can greatly reduce the operating cost and save energy and reduce consumption. The preparation process of the present invention is simple, does not require special equipment, is easy to operate, and is easy to promote industrially.

[0028] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A seaweed fiber silver complex photocatalyst, characterized in that, It is prepared by the coordination reaction of alginate fiber and silver ions, and the silver coordination amount in the alginate fiber silver complex photocatalyst is 0.5 mmol / g to 3.0 mmol / g.

2. The silver complex photocatalyst of seaweed fiber according to claim 1, characterized in that, The carboxylic acid group content in the molecular structure of the alginate fiber is greater than 2.0 mmol / g.

3. A preparation method of the seaweed fiber silver complex photocatalyst as described in claim 1 or 2, characterized in that, It includes the step of carrying out a coordination reaction between alginate fiber and a silver ion solution.

4. The preparation method according to claim 3, characterized in that, The silver ion solution is a 0.05 - 0.20 mol / L silver nitrate solution, and the weight ratio of the alginate fiber to the volume of the silver ion solution is 1:

50.

5. The preparation method according to claim 3, characterized in that, The coordination reaction is carried out under stirring conditions, the reaction time is 0.5 - 2.0 hours, the reaction temperature is 20 - 60 °C, and after the reaction, it is washed with distilled water and dried.

6. The preparation method according to claim 3, characterized in that, The alginate fiber needs to be pretreated before the coordination reaction. The pretreatment steps are as follows: First, stir and wash the alginate fiber with an aqueous solution of a non-ionic surfactant at room temperature for 30 - 60 minutes, then wash it with distilled water, and finally dry it for standby.

7. The preparation method according to claim 3, wherein After the coordination reaction, the obtained alginate fiber silver complex is post-treated. The post-treatment process is to wash it with distilled water and then dry it to obtain the alginate fiber silver complex.

8. The preparation method according to claim 6, characterized in that, The non-ionic surfactant is a fatty alcohol polyoxyethylene ether type or an alkylphenol polyoxyethylene ether type.

9. The preparation method according to claim 8, wherein The concentration of the non-ionic surfactant is 2 - 5 g / L.

10. Application of the alginate fiber silver complex photocatalyst according to any one of claims 1 - 9 in the oxidative degradation treatment of textile printing and dyeing wastewater.

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