A method for preparing highly nitrogen-doped carbon dots for enhancing microbial removal of pollutants

Abstract

The present invention discloses a method for preparing highly nitrogen-doped carbon dots for enhancing microbial removal of pollutants, and belongs to the technical field of carbon dot materials for enhancing microbial electrochemistry. The nitrogen-doped carbon dots provided by the present invention improve the charge conduction and storage performance of the carbon dot materials due to the high nitrogen doping ratio. The carbon dots provided by the present invention can effectively improve the degradation of organic pollutants by microbial electrochemical methods. At the same time, there are few reports on the application of carbon dots to promote microbial degradation of wastewater pollutants. The carbon dots of the present invention are prepared by condensing the precursor pentahydroxymethylfurfural and o-phenylenediamine to generate Schiff base intermediates, and then further hydrothermally synthesizing carbon dots; the nitrogen doping mass proportion of the carbon dots is 18% to 19%, wherein the nitrogen doping ratio is higher than previously reported. The carbon dots with a high nitrogen doping ratio of the present invention are used in microbial fuel cells to degrade high concentrations of the organic pollutant sulfamethoxazole.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dot material enhanced microbial electrochemistry, and specifically relates to a method for preparing highly nitrogen-doped carbon dots for enhancing microbial removal of pollutants in wastewater and its application. Background Art

[0002] Microbial electrochemical technology uses microbial fuel cells as its main device. It uses functional microorganisms as anode catalysts to convert chemical energy in organic matter into electrical energy. It has broad application prospects in the fields of wastewater pollutant treatment and green energy development. The electron transfer rate in the microbial electrochemical system is an important rate-limiting step that affects the metabolism of organic substrates by microorganisms. Since microorganisms themselves have many non-conductive components, they have a low electron transfer rate, which in turn limits their application potential in degrading pollutants in wastewater. Currently, microbial modification is an effective way to enhance electron transfer. Common enhancement strategies include genetic engineering to enhance target protein expression, artificial synthesis of conductive polymers to enhance transmembrane electron transfer, and conductive metal nanoparticle modification of microorganisms. These strategies have problems such as complex operation, high cost, and environmental unfriendliness. Carbon dot materials have been successfully used in enhancing microbial electricity production due to their high light and electrocatalytic properties and low cost. Carbon dots are zero-dimensional carbon nanomaterials composed of a carbon core and surface functional groups. The carbon core is composed of sp 2 / sp 3 The hybrid conjugated structure has excellent electron transfer properties, and its surface contains a variety of active groups, such as hydroxyl and carboxyl groups, which can undergo electrostatic adsorption or coordination with microbial proteins / peptides / enzymes. Electron-rich nitrogen atom doping can effectively change the conjugation and electrical properties of the carbon core of carbon dots. Nitrogen doping strengthens the electron donation / acceptance of the carbon core, and has high electron transfer properties while enhancing the electron storage capacity of carbon dots, effectively accelerating the electron transfer rate of microorganisms. However, the current low degree of nitrogen doping of carbon dots results in poor electron conduction and storage performance of carbon dots, and there have been no reports on the application of carbon dots for microbial degradation of wastewater pollutants. Summary of the invention

[0003] The purpose of the present invention is to create a method for preparing a carbon dot material with a high nitrogen doping ratio and apply it to the microbial degradation of organic wastewater. The carbon dots provided by the present invention can improve the problem of insufficient charge transfer and storage performance caused by the low nitrogen doping degree in the existing microbial electrochemical degradation of organic pollutants. Schiffbase precursors are synthesized by reacting aldehydes with amines, and high nitrogen doping carbon dots are prepared by hydrothermal method. Furthermore, the high nitrogen doping carbon dots are combined with functional microorganisms to enhance the degradation of organic pollutants.

[0004] The present invention uses pentahydroxymethylfurfural (5-HMF) and o-phenylenediamine (OPD) as raw materials. Due to the aldehyde group and primary amino group contained in the raw materials, it is very easy to undergo Schiff base synthesis reaction at room temperature. During the reaction, the aldehyde group loses an oxygen atom, and the primary amino group loses two hydrogen atoms. Then the two molecules combine. The obtained Schiff base is used for hydrothermal synthesis to obtain a carbon dot material with a high nitrogen doping ratio. XPS test of the obtained carbon dot material shows that the nitrogen atom accounts for 18%-19%. In order to achieve the above technical problems, the present invention adopts the following technical solutions:

[0005] The object of the present invention is to provide a carbon dot material with a high nitrogen doping ratio, wherein the heteroatoms in the carbon dots are mainly nitrogen atoms, accounting for 18% to 19%.

[0006] It is further defined that the surface groups of the carbon dots mainly include -COOH, -COOH, and -NH2.

[0007] It is further defined that the core of the carbon dots is composed of a nitrogen-doped π-conjugated structure, and the nitrogen doping pattern is mainly graphitic nitrogen, pyridinic nitrogen, and pyrrolic nitrogen.

[0008] It is further defined that the particle size of the carbon dots is mainly 3.1±0.7 nm.

[0009] Another object of the present application is to provide a method for preparing a carbon dot material with a high nitrogen doping ratio, which is specifically achieved by the following steps: adding pentahydroxymethylfurfural (5-HMF) and o-phenylenediamine (OPD) to deionized water, causing an aldehyde-amine condensation reaction at room temperature to generate a Schiff base, then performing a hydrothermal reaction for at least 2 hours, performing high-speed centrifugation, taking a supernatant, and then freeze-drying the supernatant to obtain a carbon dot powder.

[0010] Further defined, 0.252 g of pentahydroxymethylfurfural (5-HMF) and 0.108 g of o-phenylenediamine (OPD) were added to 20 mL of deionized water.

[0011] It is further defined that the hydrothermal reaction temperature is 200°C.

[0012] The carbon dot material or the carbon dot material prepared by the method is used to degrade the organic pollutant sulfamethoxazole.

[0013] It is further defined that the degradation is carried out using a microbial fuel cell, and the carbon dots are added to the anolyte at a concentration of 100 μg mL -1 .

[0014] It is further specified that the microorganisms used in the anode come from a mixture of bacteria found in cow dung.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention proposes a high nitrogen doping ratio carbon dot material, which forms many surface active sites by introducing electron-rich nitrogen atoms, and can react with microbial proteins / peptides / enzymes, etc. At the same time, nitrogen atom doping strengthens the electron storage and electron transfer capabilities of the carbon core, and accelerates the electron transfer rate of microorganisms; at the same time, the carbon dot nitrogen doping method proposed by the present invention is to first generate a Schiff base precursor by an aldehyde-amine condensation reaction of the raw materials, and then hydrothermally synthesize carbon dots, so that the nitrogen doping ratio of the carbon dots is higher than before; furthermore, the carbon dots proposed by the present invention are conducive to the mutual cross-linking between carbon dots due to the introduction of nitrogen atoms, thereby enhancing the stability of carbon dots. The preparation method of the carbon dot material proposed by the present invention is simple, and only the aldehyde precursor and the amine precursor need to be put into the reactor together, and the carbon dots are prepared by one-pot hydrothermal method. Therefore, the preparation method of the carbon dot material proposed by the present invention has a simple process and low operating cost, which is conducive to the promotion and use of carbon dot materials.

[0017] The present invention proposes a microbial fuel cell based on the use of the carbon dot material. In the microbial fuel cell, the carbon dot material is added to the anode chamber, which is beneficial to the microbial fuel cell to degrade organic pollutants.

[0018] The concentration of the organic pollutant sulfamethoxazole degraded by the present invention (10 mg L -1 ) compared with the previously reported concentration (2 mg L -1 ) is higher.

[0019] The degradation efficiency of the microbial fuel cell under the action of the carbon point material involved in the present invention is 3.8 times that of the microbial fuel cell without the action of the carbon point material.

[0020] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the attached drawings are only provided for reference and illustration and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the process of synthesizing carbon dot materials;

[0022] Figure 2 It is the degradation reaction of the anode chamber;

[0023] Figure 3 H-NMR spectra of Schiff base and carbon dot materials;

[0024] Figure 4 This is a transmission electron microscope (TEM) image of carbon dot materials;

[0025] Figure 5 is the particle size distribution histogram.

[0026] Figure 6This is a high-resolution transmission electron microscopy image (HR-TEM) of carbon dots;

[0027] Figure 7 is the X-ray diffraction (XRD) spectrum of carbon dot materials;

[0028] Figure 8 is the Raman spectrum of carbon dot materials;

[0029] Fig. 9 This is the X-ray photoelectron (XPS) spectrum of carbon dot materials;

[0030] Fig.10 is the Fourier transform infrared (FT-IR) spectrum of carbon dot materials;

[0031] Fig.11 This is the voltage curve of carbon dot materials in microbial fuel cells;

[0032] Fig.12 The microbial fuel cell with carbon dots can degrade 10 mg L -1 Sulfamethoxazole degradation efficiency;

[0033] Fig.13 The degradation of 10 mg L in a microbial fuel cell without adding carbon dots -1 Sulfamethoxazole degradation efficiency. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0035] Example 1: In this example, a carbon dot material with a high nitrogen doping ratio and a preparation method thereof are carried out according to the following steps: 0.252 g of 5-HMF and 0.108 g of OPD are added to 20 mL of deionized water, and an aldehyde-amine reaction is carried out at room temperature to generate a Schiff base. The obtained mixture is placed in a 50 mL reactor and subjected to a hydrothermal reaction at 200 ° C for 10 h to obtain a carbon dot solution;

[0036] The obtained carbon dot solution was centrifuged at 8000 rpm for 15 min, the supernatant was taken, and then the supernatant was freeze-dried at -60°C to obtain carbon dot powder.

[0037] The carbon dot material prepared in this embodiment contains 18.27% nitrogen; has multiple chemical bonds such as NH, CN, C=N, etc.; contains organic matter such as hydroxyl, carbonyl, nitrogen-containing groups, etc.; and has a particle size of 3.1±0.7nm.

[0038] A microbial fuel cell, comprising a microbial catalyst in the anode chamber that acts as an electricity-producing microorganism and is derived from mixed bacteria in cow dung; and a prepared carbon dot material, wherein the carbon dots in the anode chamber are used at a concentration of 100 μg mL -1 ; Finally, there is the organic pollutant sulfamethoxazole (10 mg L -1 )PBS (50mmol L -1 ) buffer solution.

[0039] The cathode chamber uses potassium ferrocyanide (16.46 g L -1 )PBS (50mmol L -1 ) buffer solution, the ferrocyanide reduction reaction occurs in the cathode chamber:

[0040] Anode chamber degradation reaction Figure 2 As shown, the NH2 on the benzene ring of sulfamethoxazole is oxidized to NO2 to obtain N-(5-methylisoxazol-3-yl)-4-nitrobenzenesulfonamide; then the sulfonamide bond of N-(5-methylisoxazol-3-yl)-4-nitrobenzenesulfonamide is hydrolyzed and cleaved to further obtain 4-nitrobenzenesulfonicacid and 5-methylisoxazol-3-amine. The sulfonamide bond of sulfamethoxazole can also be directly hydrolyzed and cleaved to obtain 5-methylisoxazol-3-amine and 4-aminobenzenesulfonic acid, and then 4-aminobenzenesulfonicacid is derived into 4-aminobenzenesulfinic acid. In addition, the isoxazole ring of sulfamethoxazole is also oxidized to generate 4-amino-N-(4-hydroxy-5-methylisoxazol-3-yl)benzenesulfonamide containing an OH functional group.

[0041] The H-NMR spectra of the Schiff base and carbon dot materials in this example are shown in Figure 3 As shown by Figure 3It can be seen that the chemical shift of the active hydrogen of the aldehyde functional group in the raw material 5-HMF is δ=9.5, and the chemical shift of the active hydrogen of the amino functional group in OPD is δ=4.3 (these two are standard substances, used as references here). In the H-NMR spectra corresponding to the Schiff base and the carbon dot material, it can be clearly seen that these two characteristic peaks have obviously decreased or even disappeared, proving that the two raw materials reacted and consumed the aldehyde group and the amino group.

[0042] The TEM image of the carbon dot material in this embodiment is as follows Figure 4 As shown in Figure 5, the particle size distribution histogram is shown in Figure 5. From the TEM image and the particle size distribution histogram, it can be seen that the carbon dots are zero-dimensional point-like materials with a size of 1-7 nm, and the particle size is concentrated in the range of 3.1±0.7 nm.

[0043] In this embodiment, the lattice spacing of the carbon dot material is as follows: Figure 6 As shown; high-resolution TEM images show that the lattice spacing of the carbon dot material is about 0.22nm, which is similar to the in-plane spacing of graphite (100).

[0044] The XRD spectrum of the carbon dot material in this embodiment is as follows Figure 7 As shown; the XRD spectrum of the carbon dot material shows an obvious broad peak at 23.5°, which is almost the same as the interlayer spacing of graphite.

[0045] The Raman spectrum of the carbon dot material in this example is as follows Figure 8 As shown; Raman spectrum shows that at about 1565cm -1 and 1610cm -1 There are obvious peaks, namely the D peak and G peak of the carbon dot material, and I G / I D It is about 2.4, which indicates that the graphitized structure in the carbon dot material is higher than the disordered carbon structure.

[0046] The XPS spectrum of the carbon dot material in this example is as follows Fig. 9 As shown; according to the XPS spectrum, the carbon dot material is mainly composed of three substances: C, N, and O, and the corresponding atomic ratios are 73; 18; 9.

[0047] The FT-IR spectrum of the carbon dot material in this example is as follows Fig.10 As shown; FTIR spectrum shows that at 3150cm -1 The characteristic broad peak of C-OH / NH stretching vibration is 2840 cm -1 The peak at 1710 cm-1 is the stretching vibration of CH in the aromatic structure, and the stretching vibration of C=O corresponds to 1710 cm-1. -1 The strong peak at 1610 cm-1 corresponds to the stretching vibration of C=C. -1 Peak at 1520cm -1The peak at 1200 cm-1 corresponds to the stretching vibration of NH -1 The peak at 1015 cm corresponds to the stretching vibration of CN. -1 The sharp peak at 740 cm-1 corresponds to the bending vibration of COC. -1 The strong peak at corresponds to the bending vibration of the aromatic ring.

[0048] In this embodiment, the voltage curve of the carbon dot material in the microbial fuel cell is as follows: Fig.11 As shown in the figure, the DC voltage of the microbial fuel cell with carbon dot material (CDs group) rises rapidly within 4 hours, with the maximum voltage being about 0.32V. However, the output voltage of the microbial fuel cell without carbon dot material (NO-CDs group) rises slowly, and it takes about 60 hours to reach a voltage output peak of about 0.19V. It can be concluded that the CDs group can reach a higher voltage output faster than the NO-CDs group, and it is reasonable to infer that the CDs group also metabolizes and consumes organic substrates faster than the NO-CDs group.

[0049] In this example, the microbial fuel cell with carbon dot material can degrade 10 mg L -1 Sulfamethoxazole degradation efficiency Fig.12 As shown; the microbial fuel cell without added carbon dots degrades 10 mg L -1 Sulfamethoxazole degradation efficiency Fig.13 As shown in the figure, after 144 hours, the remaining sulfamethoxazole concentration in the anolyte of the CDs group was about 2.7 mg L -1 The degradation efficiency was 73%. After 144 hours, the remaining sulfamethoxazole concentration in the NO-CDs group was 8.1 mg L -1 , the degradation efficiency was only 19%, and the degradation efficiency of the CDs group was 3.8 times that of the NO-CDs group.

[0050] The above describes the specific embodiments of the present invention. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essential content of the present invention.

Claims

1. A highly nitrogen-doped carbon dot for enhancing microbial removal of pollutants, characterized in that: The heteroatoms in the carbon dots are mainly nitrogen atoms, and the mass proportion of nitrogen elements is 18% to 19%; they are prepared by the following steps: pentahydroxymethylfurfural and o-phenylenediamine are added to deionized water, an aldehyde amine condensation reaction occurs at room temperature to generate a Schiff base, and then a hydrothermal reaction is performed for 10 hours, high-speed centrifugation is performed, the supernatant is taken, and then the supernatant is freeze-dried to obtain a carbon dot powder; the particle size of the carbon dots is 3.1±0.7 nm.

2. The method for preparing highly nitrogen-doped carbon dots for enhancing microbial removal of pollutants as claimed in claim 1, characterized in that: The method is achieved by the following steps: adding pentahydroxymethylfurfural and o-phenylenediamine into deionized water, generating Schiff base by aldehyde-amine condensation reaction at room temperature, then hydrothermally reacting for 10 h, centrifuging at high speed, taking the supernatant, and then freeze-drying the supernatant to obtain carbon dot powder.

3. The method according to claim 2, characterized in that 0.252 g of pentahydroxymethylfurfural and 0.108 g of o-phenylenediamine were added to 20 mL of deionized water.

4. The method according to claim 2, characterized in that The hydrothermal reaction temperature is 200°C.

5. The carbon dots according to claim 1 or the carbon dots prepared by the method according to any one of claims 2 to 4 are used to degrade sulfamethoxazole.

6. The use according to claim 5, characterized in that: The degradation was carried out using a microbial fuel cell, with the carbon dot material being one of the main components of the anolyte at a concentration of 100 μg / mL.

7. The use according to claim 5, characterized in that: The microorganisms used in the anode come from a mixture of bacteria found in cow dung.

Images