Preparation method and application of carbon dot-magnesium iron layered double hydroxide-activated carbon composite material

Abstract

The invention belongs to the technical field of environmental material preparation and pollution treatment, and discloses a preparation method and application of a carbon dot-magnesium iron layered double hydroxide-activated carbon composite material. The preparation method of the composite material comprises the following steps: synthesizing a carbon dot solution through a hydrothermal method; synthesizing magnesium-iron layered double-metal hydroxide-activated carbon by a coprecipitation method; and finally, mixing the carbon dot solution with the magnesium-iron layered double-metal hydroxide-activated carbon, and heating in a reaction kettle to obtain the composite material. According to the prepared carbon dot-magnesium iron layered double hydroxide-activated carbon composite material, the carbon dots can be slowly released under the action of microorganisms, and the released carbon dots can accelerate the microbial metabolism rate and improve the anaerobic biological denitrification rate. The preparation process is simple, and the prepared composite material can effectively reduce the loss rate of free carbon dots and improve the utilization rate of the carbon dots by microorganisms, so that the composite material has great potential in the aspect of enhancing biological denitrification treatment of sewage.

Description

Technical Field

[0001] This invention belongs to the field of environmental material preparation and pollution control technology, and relates to a method for preparing a carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material and its application. Background Technology

[0002] In recent decades, with increasingly frequent human activities, including the excessive application of nitrogen-rich fertilizers and the large-scale discharge of untreated industrial wastewater, large amounts of nitrates have entered groundwater and surface water systems, causing water pollution. High-concentration nitrogen-containing wastewater easily leads to eutrophication and further induces algal blooms. The algal toxins released by abnormal algal proliferation not only threaten the safety of aquatic fish but also pose a potential risk to human health. Therefore, developing technologies that can efficiently remove nitrogen-containing pollutants from water bodies is of great significance.

[0003] Currently, the main methods for treating nitrogen-containing wastewater include physical, chemical, and biological methods. Among them, biological methods are widely used in wastewater denitrification processes due to their strong treatment capacity and low cost. However, traditional microbial treatment technologies suffer from limited denitrification efficiency. Existing research has attempted to promote anaerobic microbial metabolism by adding conductive materials such as biochar, but because these materials have large particle sizes, they can only enhance extracellular electron transfer, and their effect on improving the denitrification process remains limited. To address this, some researchers have proposed introducing novel carbon-based nanomaterials with particle sizes less than 10 nm—carbon dots. Carbon dots have good electron transfer capabilities and biocompatibility, and can effectively promote the anaerobic denitrification process. However, in practical applications, free carbon dots are easily soluble in water, leading to their easy loss during application. This characteristic has become a key issue restricting the widespread adoption of this technology.

[0004] Layered bimetallic hydroxides are a novel type of inorganic adsorbent material with a bilayer structure, mainly composed of positively charged host layers, interlayer anions, and interlayer water molecules. This unique structure endows them with excellent thermal stability, biocompatibility, and adsorption performance. However, the adsorption performance of layered bimetallic hydroxides is limited when used alone. Carbon dots possess abundant functional groups and high water solubility, but are prone to aggregation. By combining carbon dots with layered bimetallic hydroxides, not only can the positively charged surface of the layered bimetallic hydroxides stabilize the carbon dots, but the adsorption performance can also be further improved. In his study, "The Influence of Carbon Dot-Layered Double Hydroxide Composites on the Fixation and Transformation of Ammonium Nitrogen in Soil," Liu Fan demonstrated that layered bimetallic hydroxides can fix carbon dots through adsorption methods, and the prepared carbon dot-calcium-aluminum layered bimetallic hydroxides and carbon dot-magnesium-aluminum layered bimetallic hydroxides can adsorb ammonium ions in water. However, in this study, the carbon dot adsorption capacity of the materials was low, and there was a possibility of carbon dot loss after adsorption. Furthermore, this method only achieved phase transfer of nitrogen pollutants and did not achieve their final elimination from the system. Currently, in existing technologies, composite materials of layered bimetallic hydroxides and carbon dots are mostly designed to directly remove specific pollutants such as heavy metals and dyes through adsorption. Their function is limited to passive physicochemical adsorption and cannot actively regulate and enhance the biotransformation process in the environment.

[0005] Therefore, this invention successfully constructed a novel composite material with slow-release function by loading carbon dots onto the surface of a magnesium-iron layered bimetallic hydroxide-activated carbon composite carrier. This structure not only enables the controlled and slow release of carbon dots but also continuously enhances electron transfer and microbial activity in the anaerobic denitrification process, thereby significantly improving nitrogen removal efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide a composite material, its preparation method, and its application, which aims to achieve efficient removal of nitrates from water.

[0007] The technical solution of the present invention:

[0008] A method for preparing a carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material includes the following steps:

[0009] (1) Synthesis of carbon dots:

[0010] Citric acid, FeCl3 . 6H₂O and diethylenetriamine were dissolved in ultrapure water and transferred to an autoclave for reaction at 180–230 °C for 12–18 h to obtain a brown mixture. The brown mixture was centrifuged, filtered, purified, and freeze-dried to obtain carbon dot powder. Citric acid and FeCl₃ were present in the powder. . The mass ratio of 6H2O to diethylenetriamine is 650:75:24.

[0011] (2) Preparation of magnesium-iron layered bimetallic hydroxide-activated carbon material by co-precipitation method:

[0012] MgCl2 . 6H2O and FeCl3 . 6H2O was dissolved in 100 mL of ultrapure water to obtain a mixed metal solution. The mixed metal solution was slowly added dropwise to a 0.55~0.75 mol / L sodium hydroxide solution, and the pH of the system was maintained at around 10 during the addition process to obtain a magnesium-iron layered bimetallic hydroxide suspension. Activated carbon was then added to the magnesium-iron layered bimetallic hydroxide suspension and stirred evenly. The suspension was then sealed and placed in an oven for aging. After filtration, washing, and drying, a magnesium-iron layered bimetallic hydroxide-activated carbon composite material was finally obtained.

[0013] (3) Synthesis of carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material:

[0014] The magnesium-iron layered bimetallic hydroxide-activated carbon material was uniformly mixed with a carbon dot solution, and then transferred to a polytetrafluoroethylene-lined autoclave for heating and reaction. After cooling, the resulting product was centrifuged, washed, and dried to obtain the carbon dot-magnesium-iron layered bimetallic hydroxide-activated carbon composite material.

[0015] The MgCl2 . 6H2O and FeCl3 . The molar ratio of 6H2O is 2:1 to 5:1.

[0016] The metal mixture solution contains MgCl2 . The concentration of 6H2O is 22.4~56 g / L.

[0017] The volume ratio of the sodium hydroxide solution to the metal mixture is 1:1.

[0018] The concentration of activated carbon in the magnesium-iron layered bimetallic hydroxide suspension is 2.5~10 g / L.

[0019] The aging temperature is 80~120 ℃, and the aging time is 8~12 h.

[0020] The concentration of the carbon dot solution is 2~4 g / L.

[0021] The mass ratio of the magnesium-iron layered bimetallic hydroxide-activated carbon composite material to the carbon dot solution is 1:1 to 1:1.5.

[0022] The heating reaction is carried out at a temperature of 100~140 ℃ for a duration of 2~6 h.

[0023] The beneficial effects of this invention are:

[0024] (1) The magnesium-iron layered bimetallic hydroxide-activated carbon prepared by the present invention has a good ability to adsorb carbon dots, thereby solving the problem of easy loss of free carbon dots and providing an effective carrier for the development of high-performance and high-stability carbon dot composite materials.

[0025] (2) By controlling the slow release of carbon dots, the present invention can maintain the effective concentration of carbon dots in the water for a long time, continuously enhance the electron transfer efficiency in the anaerobic denitrification process, significantly promote the metabolic activity of denitrifying functional bacteria, and thus comprehensively improve the denitrification efficiency. Attached Figure Description

[0026] Figure 1 XRD patterns of magnesium-iron layered bimetallic hydroxide-activated carbon and carbon dots-magnesium-iron layered bimetallic hydroxide-activated carbon.

[0027] Figure 2 This diagram illustrates the promoting effect of carbon dots-magnesium-iron layered bimetallic hydroxide-activated carbon on denitrification. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0029] Example 1

[0030] Preparation of carbon dots: 1.3 g citric acid, 0.15 g FeCl3 . 6H₂O and 0.05 mL of diethylenetriamine were dissolved in 20 mL of ultrapure water, transferred to a polytetrafluoroethylene-lined autoclave, and heated in an oven at 230 °C for 12 h. The resulting brown mixture was centrifuged, filtered, and purified using a 1 KD dialysis bag for 6 h. Finally, the resulting solution was freeze-dried to obtain carbon dot powder.

[0031] Preparation of magnesium-iron layered bimetallic hydroxide-activated carbon material: A mixture containing 22.4 g / L MgCl2... . 6H₂O, 14.9 g / L FeCl₃ . A metal mixture solution of 6H₂O was slowly added dropwise to a 0.665 mol / L alkaline solution to obtain a magnesium-iron layered hydroxide suspension. Then, 2.5 g / L activated carbon was added to the magnesium-iron layered bimetallic hydroxide suspension, stirred thoroughly, sealed, and placed in an oven at 80℃ for 8 h of aging. After filtration, washing, and drying, magnesium-iron layered bimetallic hydroxide-activated carbon was obtained.

[0032] Preparation of carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material: 60 mg of magnesium iron layered bimetallic hydroxide-activated carbon powder was added to a 2 g / L carbon dot solution and transferred to a 100 mL polytetrafluoroethylene-lined autoclave. The reaction was carried out at 100 °C for 2 h. After cooling, the resulting product was centrifuged, washed and dried to obtain the carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material.

[0033] Example 2

[0034] Preparation of carbon dots: The preparation method is the same as in Example 1.

[0035] Preparation of magnesium-iron layered bimetallic hydroxide-activated carbon material: A mixture containing 39.2 g / L MgCl2... . 6H₂O, 14.9 g / L FeCl₃ . A metal mixture solution of 6H₂O was slowly added dropwise to a 0.665 mol / L alkaline solution to obtain a magnesium-iron layered hydroxide suspension. Then, 6.25 g / L activated carbon was added to the magnesium-iron layered bimetallic hydroxide suspension, stirred thoroughly, sealed, and placed in an oven at 100℃ for 10 h of aging. After filtration, washing, and drying, magnesium-iron layered bimetallic hydroxide-activated carbon was obtained.

[0036] Preparation of carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material: 70 mg of magnesium iron layered bimetallic hydroxide-activated carbon powder was added to a 3 g / L carbon dot solution and transferred to a 100 mL polytetrafluoroethylene-lined autoclave. The reaction was carried out at 120 °C for 4 h. After cooling, the resulting product was centrifuged, washed and dried to obtain the carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material.

[0037] Example 3

[0038] Preparation of carbon dots: The preparation method is the same as in Example 1.

[0039] Preparation of magnesium-iron layered bimetallic hydroxide-activated carbon material: A mixture containing 56 g / L MgCl2... . 6H2O, 14.9 g / L FeCl3 . A metal mixture solution of 6H₂O was slowly added dropwise to a 0.665 mol / L alkaline solution to obtain a magnesium-iron layered hydroxide suspension. Then, 10 g / L activated carbon was added to the magnesium-iron layered bimetallic hydroxide suspension, stirred thoroughly, sealed, and placed in an oven at 120℃ for 12 h of aging. After filtration, washing, and drying, magnesium-iron layered bimetallic hydroxide-activated carbon was obtained.

[0040] Preparation of carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material: 80 mg of magnesium iron layered bimetallic hydroxide-activated carbon powder was added to 4 g / L carbon dot solution and transferred to a 100 mL polytetrafluoroethylene-lined autoclave. The reaction was carried out at 140 °C for 6 h. After cooling, the resulting product was centrifuged, washed and dried to obtain the carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon composite material.

[0041] Anaerobic denitrification experiments were conducted on the prepared layered bimetallic hydroxide-activated carbon and carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon.

[0042] In a 100 mL biological system, inorganic salt culture medium, 0.2 g / L carbon dot-magnesium iron layered bimetallic hydroxide-activated carbon, 0.869 g / L sodium acetate, 1.557 g / L sodium citrate, 0.858 g / L sodium succinate, 0.5 g / L glycerol, and 15 mM nitrate were added. The system was sealed, purged with N2, and sterilized at high temperature. After cooling, the inoculum was added at a concentration of 90 mg / L. A blank control group was used without the composite material. Figure 2 As shown, after incubating the serum bottles in a 30 ℃ constant temperature incubator for 12 h, the nitrate concentration was measured. The results showed that the nitrate removal rate of the experimental group was 46% higher than that of the blank control group.

Claims

1. A method for preparing a carbon dot-maghemite layered double hydroxide-activated carbon composite material, characterized by, Comprising the following steps: (1) Synthesis of carbon dots: Citric acid, FeCl3 . 6H2O and diethylenetriamine were dissolved in ultrapure water and transferred to an autoclave for reaction at 180-230 °C for 12-18 h to obtain a brown mixture; the brown mixture was centrifuged, suction filtered, purified, and freeze-dried to obtain a carbon dot powder; (2) Preparation of magnesium-iron layered double hydroxide-activated carbon material by coprecipitation method: MgCl2 . 6H2O and FeCl3 . 6H2O was dissolved in ultrapure water to obtain a metal mixed solution; the metal mixed solution was slowly dropped into a 0.55-0.75 mol / L sodium hydroxide solution to obtain a magnesium-iron layered double hydroxide suspension; Subsequently, the activated carbon is added to the magnesium-iron layered double hydroxide suspension, stirred uniformly, then the suspension is sealed and placed in an oven for aging, filtered, washed, dried, and finally the magnesium-iron layered double hydroxide-activated carbon composite material is obtained; (3) Synthesis of carbon dot-magnesium-iron layered double hydroxide-activated carbon composite material: The magnesium-iron layered double hydroxide-activated carbon composite material is uniformly mixed with the carbon dot solution, then transferred to a polytetrafluoroethylene-lined autoclave for heating reaction, and after cooling, the obtained product is centrifuged, washed and dried to obtain the carbon dot-magnesium-iron layered double hydroxide-activated carbon composite material.

2. The preparation method of carbon dot-magnesium-iron layered double hydroxide-activated carbon composite material according to claim 1, characterized in that, The citric acid, FeCl3 . 6H2O and diethylenetriamine in a mass ratio of 650:75:

24.

3. The preparation method of carbon dot-magnesium-iron layered double hydroxide-activated carbon composite material according to claim 1, characterized in that, said MgCl2 . 6H2O and FeCl3 . a molar ratio of 2:1 to 5:

1. The concentration of MgCl2 in the metal mixed solution . 6H2O is 22.4-56 g / L; The volume ratio of the sodium hydroxide solution and the metal mixed solution is 1:1; The concentration of the activated carbon in the magnesium-iron layered double hydroxide suspension is 2.5-10 g / L; The aging temperature is 80-120℃, and the aging time is 8-12h.

4. The preparation method of carbon dot-magnesium-iron layered double hydroxide-activated carbon composite material according to claim 1, characterized in that, The concentration of the carbon dot solution is 2-4 g / L; The mass ratio of the magnesium-iron layered double hydroxide-activated carbon composite material to the carbon dot solution is 1:1-1:1.5; The heating reaction temperature is 100-140℃, and the heating reaction time is 2-6h.

5. The application of carbon dot-magnesium-iron layered double hydroxide-activated carbon composite material prepared by the preparation method of any one of claims 1-4 in anaerobic biological denitrification.

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