Lignin-based photocatalytic composites and their use in removing pollutants from water

Abstract

The present application belongs to the technical field of photocatalytic composite materials, and particularly relates to a lignin-based photocatalytic composite material and application thereof in removal of pollutants in water. By utilizing electrostatic interaction and hydrogen bond interaction between lignin and polyethylene imine, a bio-based material with a nano-porous structure is formed, and then by utilizing complexation between TiO2 and amine groups in polyethylene imine, the bio-based material is anchored, the material not only can utilize photocatalytic effect of TiO2 to catalytically degrade dyes and formaldehyde in water, but also can synergistically adsorb and degrade heavy metals, dyes and formaldehyde in water through complexation, hydrogen bond interaction and hydrogen bond interaction between -OH and -NH2 in lignin and polyethylene imine and heavy metals, dyes and formaldehyde, so as to realize multifunctionality of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic composite materials, and particularly relates to a lignin-based photocatalytic composite material and application thereof in removal of pollutants in water. BACKGROUND

[0002] With the development of modern industry, water quality and air pollution are increasingly serious, and seriously threaten human health, such as various heavy metals, dyes, formaldehyde and the like, which can be enriched along the biological chain or directly inhaled into the human body, and damage the human brain, kidney, nervous system, endocrine system and the like. Therefore, it is essential to take effective measures to remove pollutants in water and air.

[0003] In existing water purification materials, TiO2 is usually used as an ideal catalytic material for removing water pollutants due to its characteristics of non-toxicity, high activity, strong oxidation, good stability, low cost, and the like, and can oxidize or reduce pollutants into small molecules such as H2O and CO2 through sunlight, without causing secondary pollution to the surrounding environment. However, TiO2 directly used to remove water pollutants has the problem of difficult recovery after treatment, and therefore, it is necessary to load TiO2 onto the surface of various solid materials to solve the problem of recovery of TiO2 after purifying water. At present, commonly used solid materials mainly include activated carbon, graphene oxide, molybdenum sulfide and various organic materials, and the loading mode is mainly through physical adsorption of TiO2 and the surface of the above solid materials. Although this can solve the problem of recovery of TiO2 to some extent, TiO2 falls off the surface of the solid material during use, and therefore, chemical methods for loading TiO2 onto the surface of solid material are an important way to solve the above problems.

[0004] Chinese patent CN 112495354A discloses a TiO2-polyethyleneimine-graphene composite adsorption and degradation material. Mesoporous nanometer titanium dioxide is coordinated with 3,4-dihydroxybenzoic acid to obtain carboxylated mesoporous nanometer titanium dioxide, and carboxylated graphene hydrogel has a three-dimensional network structure. The two are respectively reacted with polyethyleneimine through covalent grafting, and polyethyleneimine is grafted onto the surface of the carboxylated three-dimensional graphene hydrogel, and titanium dioxide is uniformly dispersed in the polyethyleneimine-graphene hydrogel matrix. The method disclosed in the patent has many organic solvents and a complex preparation method, which is not conducive to industrial production. SUMMARY

[0005] The present application utilizes the electrostatic interaction and hydrogen bond interaction between lignin and polyethylene imine to form a bio-based material with a nano-porous structure, and then utilizes the complexation between TiO2 and the amine group in polyethylene imine to anchor the bio-based material, the material can not only utilize the photocatalytic effect of TiO2 to catalytically degrade dyes and formaldehyde in water, but also can synergistically adsorb and degrade heavy metals, dyes and formaldehyde in water through the complexation, hydrogen bond interaction and hydrogen bond interaction between -OH and -NH2 in lignin and polyethylene imine and heavy metals, dyes and formaldehyde, so as to realize the multifunctionality of the material.

[0006] The technical scheme of the present application is as follows:

[0007] A lignin-based photocatalytic composite material comprises the following components in a weight ratio:

[0008] Lignin: 1-10 parts; polyethylene imine: 1-10 parts; nano-titanium dioxide: 1-10 parts.

[0009] Preferably, the nano-titanium dioxide is an anatase nano-titanium dioxide with a diameter of 5-300 nm.

[0010] Preferably, the molecular weight of the polyethylene imine is 600-10000 g / mol.

[0011] The preparation method of the above lignin-based photocatalytic composite material comprises the following steps:

[0012] (1) Dissolve lignin and polyethylene imine in a solvent respectively, mix after complete dissolution, and stir until uniform;

[0013] (2) Disperse titanium dioxide in the solvent, then slowly add the mixed solution of step (1) under stirring at a rate of 1-3 mL / min;

[0014] (3) Slowly add a basic or acidic solution to the solution of step (2) under stirring at a rate of 1-3 mL / min, and adjust the pH value of the mixed solution to 4-9; stand still;

[0015] (4) Remove the supernatant, filter, wash and dry the precipitate to obtain an adsorption material.

[0016] Further, the solvent in steps (1) and (2) is water.

[0017] Further, the preparation method is completed at room temperature.

[0018] Further, the preparation method is completed at 25°C.

[0019] Another object of the present application is to protect the application of the lignin-based photocatalytic composite material in removing formaldehyde.

[0020] Another object of the present application is to protect the application of the lignin-based photocatalytic composite material in removing methyl blue.

[0021] Another object of the present application is to protect the application of the lignin-based photocatalytic composite material in removing heavy metal.

[0022] The lignin-based photocatalytic composite material for adsorbing pollutants in water according to the present application is based on the electrostatic interaction, hydrogen bond interaction between the hydroxyl or amine groups in lignin and polyethylene imine and different dyes, and the catalytic degradation of TiO2 on dyes. In addition, there is a condensation reaction between the amine groups in polyethylene imine and formaldehyde, and the photocatalytic effect of TiO2 on formaldehyde.

[0023] The present application has the following advantages:

[0024] (1) The preparation method of the material is green and environmentally friendly, and no organic solvent or toxic catalyst or initiator is added during the synthesis process.

[0025] (2) The material has a high specific surface area, which provides favorable conditions for the transfer of pollutants in the material, increases the contact probability between pollutants and the adsorption functional groups of the material and TiO2, and thus improves the removal effect of the material on pollutants;

[0026] (3) TiO2 is anchored in the material by chemical action and will not fall off from the surface of the material during the treatment of pollutants, thereby greatly increasing the use efficiency of TiO2, and at the same time, avoiding secondary pollution of the material to water quality during the adsorption process;

[0027] (4) The material has multiple effects of removing heavy metals, dyes and formaldehyde. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of TiO2 with a size of 150 nm;

[0029] Figure 2 SEM image of the material prepared for Comparative Example 4;

[0030] Figure 3 SEM image of the composite material prepared for Example 4.

[0031] Figure 4 XRD spectrum of lignin, polyethylene imine and lignin-polyethylene imine composite material. DETAILED DESCRIPTION

[0032] Example 1

[0033] A preparation method of a lignin-based photocatalytic composite material, comprising the following steps:

[0034] (1) 1 g of lignin and 10 g of polyethyleneimine with a molecular weight of 600 g / mol are dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 200 r / min at 25°C;

[0035] (2) 10 g of nano-TiO2 with a diameter of 5 nm is dispersed in an aqueous solution, and then slowly added to the mixed solution of step (1) under stirring, with an addition rate controlled at 1 mL / min;

[0036] (3) 1 mol / L of HCl solution is slowly added to the solution of step (2) at a rate of 1 mL / min until the pH of the solution is 7, at which time a large amount of flocculent material appears in the mixed solution, and the product is allowed to stand for 2 h;

[0037] (4) The supernatant is removed, the precipitate is suction filtered, and the precipitate is repeatedly washed with distilled water for 3 times, and then placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0038] Example 2

[0039] A preparation method of a lignin-based photocatalytic composite material, comprising the following steps:

[0040] (1) 10 g of lignin and 1 g of polyethyleneimine with a molecular weight of 10000 g / mol are dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 200 r / min at 25°C;

[0041] (2) 1 g of nano-TiO2 with a diameter of 300 nm is dispersed in an aqueous solution, and then slowly added to the mixed solution of step (1) under stirring, with an addition rate controlled at 3 mL / min;

[0042] (3) 1 mol / L of NaOH solution is slowly added to the solution of step (2) at a rate of 3 mL / min until the pH of the solution is 9, at which time a large amount of flocculent material appears in the mixed solution, and the product is allowed to stand for 2 h;

[0043] (4) The supernatant is removed, the precipitate is suction filtered, and the precipitate is repeatedly washed with distilled water for 3 times, and then placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0044] Example 3

[0045] A preparation method of a lignin-based photocatalytic composite material, comprising the following steps:

[0046] (1) 5 g of lignin and 5 g of polyethyleneimine with a molecular weight of 2000 g / mol were dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 25°C and 200 r / min;

[0047] (2) 5 g of nano-TiO2 with a diameter of 200 nm was dispersed in an aqueous solution, and then slowly added to the mixed solution of step (1) under stirring, at an addition rate of 2 mL / min;

[0048] (3) 1 mol / L of HCl solution was slowly added to the solution of step (2) at a rate of 2 mL / min until the pH of the solution was 4, at which time a large amount of flocculent material appeared in the mixed solution, and the product was allowed to stand for 2 h;

[0049] (4) The supernatant was removed, the precipitate was suction filtered, and the precipitate was repeatedly washed with distilled water for 3 times, and then was placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0050] Example 4

[0051] A preparation method of a lignin-based photocatalytic composite material, comprising the following steps:

[0052] (1) 8 g of lignin and 5 g of polyethyleneimine with a molecular weight of 2000 g / mol were dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 25°C and 200 r / min;

[0053] (2) 3 g of nano-TiO2 with a diameter of 150 nm was dispersed in an aqueous solution, and then slowly added to the mixed solution of step (1) under stirring, at an addition rate of 1 mL / min;

[0054] (3) 1 mol / L of NaOH solution was slowly added to the solution of step (2) at a rate of 1 mL / min until the pH of the solution was 8, at which time a large amount of flocculent material appeared in the mixed solution, and the product was allowed to stand for 2 h;

[0055] (4) The supernatant was removed, the precipitate was suction filtered, and the precipitate was repeatedly washed with distilled water for 3 times, and then was placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0056] Comparative Example 1 Compared with Example 1, Comparative Example 1 does not contain TiO2.

[0057] A preparation method of a lignin-based composite material, comprising the following steps:

[0058] (1) 1 g of lignin and 10 g of polyethyleneimine with a molecular weight of 600 g / mol were dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 200 r / min at 25°C;

[0059] (2) 1 mol / L HCl solution was slowly added to the solution of step (1) at a rate of 1 mL / min until the pH of the solution was 7, and the product was allowed to stand for 2 h;

[0060] (3) The supernatant was removed, the precipitate was suction filtered, the precipitate was repeatedly washed with distilled water for 3 times, and then it was placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0061] Comparative Example 2 does not contain TiO2 compared with Example 2.

[0062] A preparation method of a lignin-based composite material, comprising the following steps:

[0063] (1) 10 g of lignin and 1 g of polyethyleneimine with a molecular weight of 10000 g / mol were dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 200 r / min at 25°C;

[0064] (2) 1 mol / L NaOH solution was slowly added to the solution of step (1) at a rate of 3 mL / min until the pH of the solution was 9, and the product was allowed to stand for 2 h;

[0065] (3) The supernatant was removed, the precipitate was suction filtered, the precipitate was repeatedly washed with distilled water for 3 times, and then it was placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0066] Comparative Example 3 does not contain TiO2 compared with Example 3.

[0067] A preparation method of a lignin-based composite material, comprising the following steps:

[0068] (1) 5 g of lignin and 5 g of polyethyleneimine with a molecular weight of 2000 g / mol were dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 200 r / min at 25°C;

[0069] (2) 1 mol / L HCl solution was slowly added to the solution of step (1) at a rate of 2 mL / min until the pH of the solution was 4, and the product was allowed to stand for 2 h;

[0070] (3) The supernatant was removed, the precipitate was suction filtered, the precipitate was repeatedly washed with distilled water for 3 times, and then it was placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0071] Comparative Example 4 does not contain TiO2 as compared with Example 4.

[0072] A preparation method of a lignin-based composite material, comprising the following steps:

[0073] (1) 8 g of lignin and 5 g of polyethyleneimine with a molecular weight of 2000 g / mol were dissolved in 500 mL of distilled water respectively, mixed, and uniformly mixed under the action of mechanical stirring at 25°C and 200 r / min;

[0074] (2) 1 mol / L NaOH solution was slowly added to the solution of step (1) at a rate of 1 mL / min until the pH of the solution was 8, and the product was allowed to stand for 2 h;

[0075] (3) The supernatant was removed, the precipitate was suction filtered, and the precipitate was repeatedly washed with distilled water for 3 times, and then it was placed in a vacuum freeze dryer for drying for 48 h to obtain the final product.

[0076] Implementation effect example

[0077] I. The specific surface area and pore size distribution of the above-mentioned adsorption materials were determined by a specific surface analyzer, and the results are shown in Table 1.

[0078] Table 1 Specific surface area and pore size distribution of adsorption materials

[0079]

[0080] From the above data, it can be clearly seen that in the preparation process of the material, the material formed by the interaction between lignin and polyethyleneimine has a high specific surface area. When TiO2 is not added to lignin and polyethyleneimine, although the specific surface area of the material is reduced, it is still higher than the specific surface area of lignin and polyethyleneimine itself, which is helpful for the mass transfer of the adsorbate in the material.

[0081] Figure 1 SEM image of TiO2 with a size of 150 nm; Figure 2 SEM image of the material prepared in Comparative Example 4; Figure 3 SEM image of the composite material prepared in Example 4; From the comparison of the three, it can be seen that after the assembly of lignin-polyethyleneimine, there is a obvious nano-porous structure in the material, and after the combination of TiO2, the material still maintains a good nano-porous structure and the specific surface area increases, which will be conducive to the mass transfer of formaldehyde, heavy metals and dyes in the material. XRD can reflect the change of the crystal structure of the material before and after self-assembly, Figure 4XRD spectra of lignin, polyethyleneimine and lignin-polyethyleneimine. As can be seen from the figure, lignin has a diffraction peak at 21.7°; polyethyleneimine has a diffraction peak at 19.9°, and lignin-polyethyleneimine has a diffraction peak at 21.52° after self-assembly, which shows that the hydrogen bonding between lignin and polyethyleneimine can improve the binding force between them, and make the crystallization region move to the right.

[0082] II. The removal rate of the adsorption material on low-concentration Ni 2+ , Zn 2+ , Pb 2+ , Cu 2+ , Cd 2+ is detected by ICP-OES, and the results are shown in Table 2.

[0083] Table 2 Removal rate of adsorption material on heavy metals

[0084]

[0085] It can be observed from Table 2 that the adsorption material prepared by the scheme of the application has a high removal rate on heavy metals, and the content of TiO2 in the material has little effect on the adsorption of heavy metals.

[0086] III. According to the detection method of GBZ / T 300.99-2017, the adsorption amount of the material on formaldehyde is detected by ultraviolet-visible spectrophotometer. The results are shown in Table 3.

[0087] Table 3 Adsorption of adsorption material on formaldehyde

[0088]

[0089] It can be observed from Table 3 that the adsorption material prepared by the scheme of the application has a high adsorption amount on formaldehyde in water, and the adsorption amount of the material containing TiO2 (Examples 1-4) on formaldehyde is obviously higher than that of the material not containing TiO2 (Comparative Examples 1-4), which is mainly because TiO2 plays an important role in the photocatalytic reaction of formaldehyde.

[0090] IV. The adsorption amount of the adsorption material on methyl blue is detected by ultraviolet-visible spectrophotometer, and the results are shown in Table 4.

[0091] Table 4 Adsorption of adsorption material on dye

[0092]

[0093] It can be observed from Table 4 that the adsorption material prepared by the scheme of the application has a high adsorption capacity for methyl blue and methyl orange in water, and there is the following rule: the adsorption capacity of methyl blue > the adsorption capacity of methyl orange, the adsorption capacity of the material containing titanium dioxide for methyl blue > the adsorption capacity of the material not containing titanium dioxide for methyl blue, and the adsorption capacity of the material containing titanium dioxide for methyl orange is much greater than the adsorption capacity of the material not containing titanium dioxide for methyl orange, which shows that the photocatalysis of TiO2 on the dye plays an important role, in addition, the surface of methyl blue shows negative charge, the surface of methyl orange shows positive charge, and the material contains more amine groups, so in the process of adsorbing methyl orange, in addition to the photocatalysis of titanium dioxide, the electrostatic interaction between the material and the dye also plays an important role. The removal of the dye by the material is not limited to methyl blue and methyl orange.

[0094] The removal of low-concentration heavy metals in water by the adsorption material is completed by the following specific process:

[0095] Adsorption process:

[0096] 0.3g of the above-prepared adsorption material was respectively placed in 100mL of 10mg / L Ni 2+ , Zn 2+ , Pb 2+ , Cu 2+ , and Cd 2+ aqueous solution, and adsorption was carried out in a constant-temperature oscillator, the adsorption reaction was carried out at 25℃ for 1h, ICP-OES was used to detect the concentrations of the above heavy metals before and after adsorption, and the removal rate was calculated.

[0097] υ= V(C0-C) / VC0×100%

[0098] Wherein:

[0099] υ-removal rate of the adsorption material for heavy metals, %;

[0100] V-volume of the heavy metal solution, mL;

[0101] C0-concentration of heavy metals before adsorption, mg / L;

[0102] C-concentration of heavy metals after adsorption, mg / L.

[0103] The adsorption capacity of the adsorption material for formaldehyde in water is completed by the following specific process:

[0104] 0.2g of the above-prepared adsorption material was respectively placed in 200mL of 500mg / L formaldehyde aqueous solution, and adsorption was carried out in a constant-temperature oscillator under sunlight for 2h, the concentration of formaldehyde in the solution after adsorption was detected by the method described in GBZ / T 300.99-2017, and the adsorption capacity was calculated.

[0105] Q = V(C0-C) / 1000G

[0106] wherein:

[0107] Q - adsorption capacity of the adsorbent material for formaldehyde, mg / g;

[0108] V - solution volume, mL;

[0109] C0- concentration of formaldehyde before adsorption, mg / L;

[0110] C - concentration of formaldehyde after adsorption, mg / L;

[0111] G - adsorbent material dosage, g.

[0112] The adsorption capacity of the adsorbent material for dyes methyl blue and methyl orange in water is completed by the following specific process:

[0113] 0.2 g of the above-prepared adsorbent material is taken and placed in 200 mL of a 500 mg / L aqueous solution of methyl blue or methyl orange, and adsorption reaction is carried out under a constant-temperature oscillator under sunlight for 2 h, the concentration of the dye before and after adsorption is detected using a UV-visible spectrophotometer, and the adsorption capacity is calculated.

[0114] Q' = V'(C0'-C') / 1000G'

[0115] wherein:

[0116] Q' - adsorption capacity of the adsorbent material for the dye, mg / g;

[0117] V' - solution volume, mL;

[0118] C0' - concentration of the dye before adsorption, mg / L;

[0119] C' - concentration of the dye after adsorption, mg / L;

[0120] G' - adsorbent material dosage, g.

Claims

1. A lignin-based photocatalytic composite material, characterized in that, The components include the following weight ratios: Lignin: 1-10 parts; Polyethyleneimine: 1-10 parts; Nano titanium dioxide: 1-10 parts; The pore size distribution of the lignin-based photocatalytic composite material is 5-30 nm; In the lignin-based photocatalytic composite material, a bio-based material with a nanoporous structure is formed through electrostatic interactions and hydrogen bonding between the lignin and the polyethyleneimine. The nano-titanium dioxide is anchored to the bio-based material by utilizing the complexation between the nano-titanium dioxide and the amine groups in the polyethyleneimine.

2. The lignin-based photocatalytic composite material according to claim 1, characterized in that, The nano-titanium dioxide is anatase nano-titanium dioxide with a diameter of 5~300nm.

3. The lignin-based photocatalytic composite material according to claim 1, characterized in that, The molecular weight of the polyethyleneimine is 600~10000 g / mol.

4. A method for preparing the lignin-based photocatalytic composite material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Dissolve lignin and polyethyleneimine separately in a solvent, mix them after they are completely dissolved, and stir until homogeneous; (2) Disperse titanium dioxide in a solvent and then slowly add it to the mixed solution of step (1) under stirring. The addition rate is controlled at 1~3 mL / min. (3) Add an alkaline or acidic solution slowly to the solution in step (2) under stirring, at a rate of 1-3 mL / min, and adjust the pH of the mixed solution to 4-9; let it stand; (4) Remove the supernatant, filter, wash and dry the precipitate to obtain the adsorbent material.

5. The preparation method according to claim 4, characterized in that, The solvent used in steps (1) and (2) is water.

6. The preparation method according to claim 4, characterized in that, The preparation method described herein is carried out at room temperature.

7. The preparation method according to claim 4, characterized in that, The preparation method described herein is carried out at 25°C.

8. The application of the lignin-based photocatalytic composite material according to claim 1 in formaldehyde removal.

9. The application of the lignin-based photocatalytic composite material according to claim 1 in the removal of methylene blue.

10. The application of the lignin-based photocatalytic composite material according to claim 1 in the removal of heavy metals.

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