N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and its preparation method and application

Abstract

The invention discloses an N-doped carbon quantum dot composite salix psammophila microcrystalline cellulose hydrogel and a preparation method and application thereof, relating to the technical field of adsorption materials. The N-doped carbon quantum dot composite salix psammophila microcrystalline cellulose hydrogel comprises N-doped carbon quantum dots and salix psammophila microcrystalline cellulose. The preparation method comprises the following steps: preparing the salix psammophila microcrystalline cellulose into a hydrogel and then immersing the hydrogel in an N-doped carbon quantum dot solution, grafting the N-doped carbon quantum dots onto the molecular chains of the salix psammophila microcrystalline cellulose hydrogel through an amidation reaction, so as to obtain the N-doped carbon quantum dot composite salix psammophila microcrystalline cellulose hydrogel. The invention also provides an application of the N-doped carbon quantum dot composite salix psammophila microcrystalline cellulose hydrogel for adsorbing heavy metal ions. The invention adopts the N-doped carbon quantum dot-salix psammophila microcrystalline cellulose-hydrogel preparation process for the first time to prepare a new material, and applies the new material to the field of detecting heavy metal ions in industrial wastewater, thus having prospects for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption materials, and in particular to an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel, and a preparation method and application thereof. Background Art

[0002] With the progress of global industrialization, heavy metals are increasingly used in industrial production. After mining and smelting, many heavy metal minerals are widely used in industrial processes such as metal surface treatment, electronic component processing, equipment manufacturing, printing and dyeing. These procedures always lead to the production of a large amount of heavy metals including Fe 3+ Industrial wastewater containing heavy metal ions, including chlorinated or chlorinated metals, has an increasing amount of wastewater discharge, posing a serious threat to our survival and development, and becoming a major obstacle to the healthy and sustainable development of the economy and society. The control of heavy metal water pollution is a major environmental problem that urgently needs to be solved.

[0003] Iron is an important trace element for human health and is essential for a variety of biological functions, including DNA and RNA synthesis, enzyme catalysis, cell metabolism and electron transport activities. 3+ Essential to most species due to its various functions, both beneficial and detrimental, Fe 3+ Detection is crucial, and activated carbon, ion exchange resins, biochar, polymer brushes, biosorbents, and hydrogels have been created for the remediation of water contamination caused by heavy metal ions.

[0004] The cross-linked three-dimensional (3D) network structure of hydrogels enables them to absorb large amounts of water while maintaining their original structure. Due to the presence of hydrophilic active groups on the surface of the hydrogel matrix, which are used to collect heavy metal ions in water, heavy metal ions in wastewater can be electrostatically attached, hydrogen bonded or chelated with the hydrogel; hydrogels can also be easily separated from wastewater because they are insoluble and maintain their stability in water, preventing subsequent pollution; due to these characteristics, hydrogels have attracted widespread attention as a new type of metal ion adsorbent.

[0005] In the existing technology, Chirag developed a cost-effective and environmentally friendly SF / PEI hydrogel, including silk fibroin (SF) and polyethyleneimine (PEI), for treating metal ions in aqueous solution. 2+ 、Zn 2+ 、Cd 2+ , Pb 2+ 、Cu 2+ and Ag +The adsorption capacities of SF / PEI hydrogels were 163.9, 185.2, 169.5, 125.0, 140.8 and 200.0 mg / g, respectively. However, the synthetic polymers used as the matrix of SF / PEI hydrogels are non-biodegradable and pose a hazard to organisms. In addition, the beneficial nanoparticles used in hydrogel adsorbents are usually expensive and difficult to use in large quantities. Summary of the Invention

[0006] Based on the above technical problems, the present invention provides an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel. Blue fluorescent carbon quantum dots were prepared using Salix psammophila as raw material, and then doped into the Salix psammophila microcrystalline cellulose hydrogel to successfully synthesize a composite hydrogel with comprehensive detection and adsorption properties, as follows:

[0007] An N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel, comprising N-doped carbon quantum dots and Salix psammophila microcrystalline cellulose;

[0008] The N-doped carbon quantum dots are blue fluorescent carbon quantum dots synthesized by high-temperature hydrothermal synthesis of Salix psammophila powder, ethylenediamine and water;

[0009] The Salix psammophila microcrystalline cellulose is a product obtained by removing lignin and hemicellulose from Salix psammophila powder;

[0010] Salix psammophila microcrystalline cellulose is prepared into a hydrogel and then immersed in an N-doped carbon quantum dot solution. The N-doped carbon quantum dots are grafted onto the molecular chains of the Salix psammophila microcrystalline cellulose hydrogel through an amidation reaction to obtain an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel.

[0011] Carbon quantum dots (CQDs) are fluorescent zero-dimensional carbon nanomaterials that offer advantages such as environmental friendliness, low biotoxicity, and numerous active sites. Many heavy metal ions can specifically quench the fluorescence emission of CQDs. This is due to the complex formation and electron transport between surface functional groups and the CQD core, similar to graphite. These properties of CQDs mean they are able to capture heavy metal ions in water.

[0012] On the other hand, the present invention provides a method for preparing N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel, comprising the following steps:

[0013] Preparation of S1. N-doped carbon quantum dots: crush the rejuvenated Salix psammophila stems as raw materials to form Salix psammophila powder. Take 1-3 g of Salix psammophila powder, 0.4-0.6 mL of ethylenediamine and 55-65 mL of water to form a Salix psammophila mixed solution. o After the reaction at 400 °C, the obtained solution was centrifuged, filtered, and freeze-dried to obtain N-doped carbon quantum dots;

[0014] S2. Preparation of Salix psammophila microcrystalline cellulose hydrogel:

[0015] S21, weigh 8-12 g of Salix psammophila powder and place it in a 1 L three-necked flask, dilute it with 1:50-70 g / mL in distilled water at 70-90°C. o C for 0.5-1.5 h, take it out and wash it to neutrality, filter it, and heat it at 90-120 o C oven dried to constant weight;

[0016] S22, add the sample prepared in S21 to 7-8 wt% sodium chlorite solution, adjust the pH to 3-4, and o C for 2.5-3.5 h, remove and wash to neutrality, then heat at 55-65 o C is dried to constant weight;

[0017] S23, then place the sample prepared in S22 in 8-12 wt % potassium hydroxide solution, 70-80 o C magnetic stirring reaction for 1.5-2.5 h, take out and wash until neutral, at 55-65 o C to constant weight, add 7-9 wt% hydrochloric acid solution, and o C for 80-100 min, take out and wash until neutral, 55-65 o C is dried to constant weight to obtain Salix psammophila microcrystalline cellulose;

[0018] S24, take 3.5-4.5% of Salix psammophila microcrystalline cellulose by mass ratio, mix it with sodium hydroxide: urea: distilled water in the ratio of 6-8:10-14:75-85 in a beaker, pre-freeze it, take it out and thaw it, add 8-10% epichlorohydrin cross-linking agent, transfer it to a 20 ml penicillin bottle, rotate it at 50-60 o After reacting in a C oven for 1.5-2.5 h, the mixture was soaked in distilled water for 40-55 h until neutral, and freeze-dried for 40-55 h to obtain Salix psammophila microcrystalline cellulose hydrogel;

[0019] Preparation of S3, N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel:

[0020] Take 0.4-0.6 g of dried N-doped carbon quantum dots and dissolve them in 400-600 mL of distilled water to obtain a 1 g / L N-doped carbon quantum dot solution. Take a 1-2 cm × 1-2 cm × 1-2 cm volume of Salix psammophila microcrystalline cellulose hydrogel and place it in the 1 g / L N-doped carbon quantum dot solution for 10-20 h. After taking it out, wash it with distilled water and freeze-dry it for 24-36 h to obtain N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0021] Moreover, in the step S1, the particle size of the Salix psammophila powder is sieved through an 80-200 mesh sieve, and the Salix psammophila mixed solution is sieved at 170-190 o C for 10-14 h, and the resulting solution was centrifuged at 1000 rpm for 8-12 min; μm Filter through a water filter; freeze-dry in a freeze dryer for 40-55 hours.

[0022] Furthermore, in step S22, glacial acetic acid is used to adjust the pH.

[0023] Moreover, in the step S24, the temperature is -15-25 o C pre-freeze for 25-35 min, 20-30 o Thaw at 4°C for 25-35 min.

[0024] Furthermore, the method for washing to neutrality is: firstly removing unreacted chemical reagents with distilled water, and then washing with anhydrous ethanol to remove residual distilled water from the previous operation.

[0025] On the other hand, the present invention also provides the use of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel for adsorbing heavy metal ions.

[0026] Moreover, the metal ion is Fe 3+ .

[0027] Moreover, Fe adsorption 3+ The concentration is 1500-1600 mg / g and the temperature is 43-47 o C, pH is 2-3, and adsorption time is 60-100 min.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. In the prior art, the production of microcrystalline cellulose mainly uses natural cellulose such as cotton linter, hemp, and bamboo as raw materials, but due to resource shortages and high costs, its large-scale production is greatly limited; the raw material selected for the present invention is Salix psammophila, which has the characteristics of natural source, large reserves, and low price. It has a spatial three-dimensional polymer network structure and is a natural renewable polymer material rich in multi-scale porous structure and a large number of functional groups such as hydroxyl and carboxyl groups. Using it as an adsorption material in the treatment of heavy metal wastewater is a process of taking from nature and returning to nature, and is suitable for large-scale production; moreover, Salix psammophila is easily biodegradable and does not pollute the environment.

[0030] 2. The present invention is the first to use Salix psammophila as raw material to prepare carbon quantum dots, which are applied to the detection of heavy metal ions, providing a new technical solution for the field of heavy metal ion detection.

[0031] 3. The present invention provides an N-doped carbon quantum dot composite Salix microcrystalline cellulose hydrogel, which is a new type of material formed with Salix microcrystalline cellulose as a matrix and N-doped carbon quantum dots as a reinforcement. The advantages of carbon dots having a certain indication effect on heavy metal ions and Salix microcrystalline cellulose having a certain adsorption effect on heavy metal ions are combined with each other, so that the composite material exhibits a synergistic effect, and an intelligent fluorescent composite gel material integrating adsorption and detection is prepared.

[0032] 4. The present invention adopts the N-doped carbon quantum dots-salix microcrystalline cellulose-hydrogel (NCDs-SP-MCC-gels) preparation process for the first time to prepare a new N-doped carbon quantum dots composite salix microcrystalline cellulose hydrogel adsorption material for detecting heavy metal ions in industrial wastewater. This adsorption material not only maintains the effect of carbon quantum dots on indicating heavy metal ions, but also maintains the advantage of salix microcrystalline cellulose hydrogel in having a good adsorption effect on heavy metal ions, thereby broadening the scope of use of the two materials.

[0033] 5. The N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel prepared by the present invention is 3+ The concentration is 1500mg / g and the temperature is 45 o C. Under the conditions of pH 2.5 and adsorption time of 60 min, the adsorption capacity of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel can reach a maximum of 642.3 mg / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 (a) Transmission electron microscopy image of N-doped carbon quantum;

[0035] Figure 1 (b) Particle size distribution of N-doped carbon quanta;

[0036] Figure 1 (c) HR-TEM image of N-doped carbon quantum;

[0037] Figure 1 (d) XRD spectrum of N-doped carbon quantum;

[0038] Figure 1 (e) Raman spectrum of N-doped carbon quantum;

[0039] Figure 1 (f) FTIR spectrum of N-doped carbon quantum;

[0040] Figure 2 (a) UV-visible absorption and fluorescence emission spectra of N-doped carbon quantum dots;

[0041] Figure 2(b) Photographs of N-doped carbon quantum dots under visible light and 365 nm ultraviolet light;

[0042] Figure 2 (c) Emission spectra of N-doped carbon quantum dots at different excitation wavelengths;

[0043] Figure 2 (d) is the three-dimensional fluorescence spectrum of N-doped carbon quantum dots;

[0044] Figure 2 (e) Fluorescence stability diagram of N-doped carbon quantum dots in sodium chloride solutions with different concentrations;

[0045] Figure 2 (f) Fluorescence stability diagram of N-doped carbon quantum dots at different pH values;

[0046] Figure 2 (g) Fluorescence quenching diagram of N-doped carbon quantum dots under different metal ions;

[0047] Figure 2 (h) is different Fe 3+ Concentration and fluorescence response of N-doped carbon quantum dots;

[0048] Figure 2 (i) for different Fe 3+ Indicative linear graph of concentration and fluorescence intensity of N-doped carbon quantum dots;

[0049] Figure 3 (a) Schematic diagram of the preparation process of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel;

[0050] Figure 3 (b) SEM image of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel;

[0051] Figure 3 (c) is the magnified SEM image of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel;

[0052] Figure 3 (d) FTIR spectra of Salix psammophila microcrystalline cellulose hydrogel, N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and N-doped carbon quantum dots;

[0053] Figure 3 (e) is the XPS overall spectrum of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel;

[0054] Figure 3 (f) High-resolution C1s spectrum of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel at 528-539 eV;

[0055] Figure 3(g) is the high-resolution C1s spectrum of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel at 280-292 eV;

[0056] Figure 4 Fe 3+ Standard working curve;

[0057] Figure 5 (a) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel to different concentrations of Fe 3+ Ion adsorption capacity diagram;

[0058] Figure 5 (b) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogels react with Fe at different temperatures 3+ Adsorption capacity diagram;

[0059] Figure 5 (c) The effects of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel on Fe at different pH values 3+ Adsorption capacity diagram;

[0060] Figure 5 (d) The effect of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel on Fe 3+ Adsorption capacity diagram;

[0061] Figure 5 (e) is adsorbed Fe 3+ The pseudo-first-order kinetic model and pseudo-second-order kinetic model fitting;

[0062] Figure 5 (f) is adsorbed Fe 3+ Freundlich and Langmuir isotherm adsorption model fitting;

[0063] Figure 6 (a) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose gel and Fe 3+ Schematic diagram of quenching of solution reaction;

[0064] Figure 6 (b) Figure 6 (c) Fe adsorption on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel 3+ SEM images of

[0065] Figure 6 (d) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and Salix psammophila microcrystalline cellulose hydrogel-Fe 3+ FTIR spectrum of

[0066] Figure 6 (e) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel to Fe3+ Fluorescence response diagram of

[0067] Figure 7 Digital photos of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose gel in solutions with different pH values ​​under 365 nm ultraviolet light irradiation;

[0068] Figure 8 (a) Fe adsorption by N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel 3+ The XPS total spectrum after

[0069] Figure 8 (b) Fe adsorption on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel 3+ 2p high-resolution spectrogram after

[0070] Figure 8 (c) Fe adsorption on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel 3+ O1s spectra before and after;

[0071] Figure 8 (d) Fe adsorption on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel 3+ The C1s spectrum after .

[0072] In the figure, NCDs represents N-doped carbon quantum dots; SP-MCC-gels represents Salix psammophila microcrystalline cellulose hydrogel; NCDs-SP-MCC-gels represents N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel. DETAILED DESCRIPTION

[0073] Example 1

[0074] A method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel comprises the following steps:

[0075] Preparation of S1. N-doped carbon quantum dots: crush Salix psammophila stems to form Salix psammophila powder, take 1 g Salix psammophila powder, 0.4 mL ethylenediamine and 55 mL water to form a Salix psammophila mixed solution, and heat the Salix psammophila mixed solution at 170 o After the reaction at 400 °C, the obtained solution was centrifuged, filtered, and freeze-dried to obtain N-doped carbon quantum dots;

[0076] S2. Preparation of Salix psammophila microcrystalline cellulose hydrogel:

[0077] S21, weigh 8 g of Salix psammophila powder, and dilute it in distilled water at 70 °C at a ratio of 1:500 g / mL. o C for 0.5 h, take out and wash until neutral, filter, 90 o C is dried to constant weight;

[0078] S22, add to 7 wt% sodium chlorite solution, adjust pH=3, at 70 o C for 2.5 h, take out, wash until neutral, and then o C is dried to constant weight;

[0079] S23, the sample prepared in S22 is placed in 8 wt % potassium hydroxide solution, 70 o C magnetic stirring reaction for 1.5 h, take out and wash to neutral, at 55 o C to constant weight, add 7 wt % hydrochloric acid solution, and o C for 80 min, take out and wash until neutral, 55 o C is dried to constant weight to obtain Salix psammophila microcrystalline cellulose;

[0080] S24, take 3.5% of Salix psammophila microcrystalline cellulose by mass ratio, mix it with sodium hydroxide, urea and distilled water in the ratio of 6:10:75, pre-freeze it, take it out and thaw it, add 8% epichlorohydrin cross-linking agent, and stir at 50 o After reacting for 1.5 h under C conditions, the mixture was soaked in distilled water for 40 h until neutral, and freeze-dried for 40 h to obtain Salix psammophila microcrystalline cellulose hydrogel;

[0081] Preparation of S3, N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel:

[0082] 0.4 g of dried N-doped carbon quantum dots was dissolved in 400 mL of distilled water to obtain a 1 g / L N-doped carbon quantum dot solution. A 1 cm × 1 cm × 1 cm volume of Salix psammophila microcrystalline cellulose hydrogel was placed in the 1 g / L N-doped carbon quantum dot solution and left for 10 h. After being taken out, it was washed with distilled water and freeze-dried for 24 h to obtain N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0083] Furthermore, in the step S1, the particle size of the Salix psammophila powder is sieved through an 80-mesh sieve, and the Salix psammophila mixed solution is sieved at 150 o C for 10 h, and the resulting solution was centrifuged at 1000 rpm for 8 min; μm Filter through a water filter and freeze-dry in a freeze dryer for 40 h.

[0084] Furthermore, in step S22, glacial acetic acid is used to adjust the pH.

[0085] Furthermore, in step S24, minus 15 o C pre-freeze for 25 min, 20 o Thaw at 37°C for 25 min.

[0086] Furthermore, the method for washing to neutrality is: first removing unreacted chemical reagents with distilled water, and then washing with anhydrous ethanol to remove distilled water remaining in the previous operation.

[0087] Example 2

[0088] A method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel comprises the following steps:

[0089] Preparation of S1. N-doped carbon quantum dots: crush Salix psammophila stems to form Salix psammophila powder, take 3 g Salix psammophila powder, 0.6 mL ethylenediamine and 65 mL water to form a Salix psammophila mixed solution, and heat the Salix psammophila mixed solution at 190 o After the reaction at 400 °C, the obtained solution was centrifuged, filtered, and freeze-dried to obtain N-doped carbon quantum dots;

[0090] S2. Preparation of Salix psammophila microcrystalline cellulose hydrogel:

[0091] S21, weigh 12 g of Salix psammophila powder, dilute with 90% distilled water at a ratio of 1:70 g / mL, o C for 1.5 h, take out and wash until neutral, filter, 120 o C is dried to constant weight;

[0092] S22, add the sample prepared in S21 to 8 wt% sodium chlorite solution, adjust the pH to 4, and o C for 3.5 h, take out, wash until neutral, and then o C is dried to constant weight;

[0093] S23, placing the sample prepared in S22 in a 12 wt % potassium hydroxide solution, 80 o C magnetic stirring reaction for 2.5 h, take out and wash to neutrality, at 65 o C to a constant weight, add 9 wt % hydrochloric acid solution, and o C for 100 min, take out and wash until neutral, 65 o C is dried to constant weight to obtain Salix psammophila microcrystalline cellulose;

[0094] S24, take 4.5% of Salix psammophila microcrystalline cellulose by mass ratio, mix it with sodium hydroxide, urea and distilled water in the ratio of 8:14:85, pre-freeze it, take it out and thaw it, add 10% epichlorohydrin cross-linking agent, and freeze it at 60 o After reacting for 2.5 h under C conditions, the mixture was soaked in distilled water for 55 h until neutral, and freeze-dried for 58 h to obtain Salix psammophila microcrystalline cellulose hydrogel;

[0095] Preparation of S3, N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel:

[0096] 0.6 g of dried N-doped carbon quantum dots was dissolved in 600 mL of distilled water to obtain a 1 g / L N-doped carbon quantum dot solution. A 2 cm × 2 cm × 2 cm volume of Salix psammophila microcrystalline cellulose hydrogel was placed in the 1 g / L N-doped carbon quantum dot solution and left for 20 h. After being taken out, it was washed with distilled water and freeze-dried for 36 h to obtain N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0097] Furthermore, in the step S1, the particle size of the Salix psammophila powder is sieved through a 200-mesh sieve, and the Salix psammophila mixed solution is sieved at 210 o C for 14 h, and the resulting solution was centrifuged at 1000 rpm for 12 min; μm Filter through a water filter and freeze-dry in a freeze dryer for 55 h.

[0098] Furthermore, in step S22, glacial acetic acid is used to adjust the pH.

[0099] Furthermore, in step S24, minus 25 o C pre-freeze for 35 min, 30 o Thaw at 37°C for 35 min.

[0100] Furthermore, the method for washing to neutrality is: first removing unreacted chemical reagents with distilled water, and then washing with anhydrous ethanol to remove distilled water remaining in the previous operation.

[0101] Example 3

[0102] A method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel comprises the following steps:

[0103] Preparation of S1. N-doped carbon quantum dots: crush Salix psammophila stems to form Salix psammophila powder, take 2 g Salix psammophila powder, 0.5 mL ethylenediamine and 60 mL water to form a Salix psammophila mixed solution, and heat the Salix psammophila mixed solution at 180 o After the reaction at 400 °C, the obtained solution was centrifuged, filtered, and freeze-dried to obtain N-doped carbon quantum dots;

[0104] S2. Preparation of Salix psammophila microcrystalline cellulose hydrogel:

[0105] S21, weigh 8-12 g of Salix psammophila powder, dilute with distilled water at a ratio of 1:60 g / mL and 80 o C for 1 h, take out and wash until neutral, filter, 115 o C is dried to constant weight;

[0106] S22, add the sample prepared in S21 to 7.5 wt% sodium chlorite solution, adjust the pH to 3, ando C for 3 h, take out and wash until neutral, then o C is dried to constant weight;

[0107] S23, placing the sample prepared in S22 in a 10 wt % potassium hydroxide solution, 75 o C magnetic stirring reaction for 2 h, take out and wash to neutrality, at 60 o C to a constant weight, add 8 wt % hydrochloric acid solution, and o C for 90 min, take out and wash until neutral, 60 o C is dried to constant weight to obtain Salix psammophila microcrystalline cellulose;

[0108] S24, take 4% of Salix psammophila microcrystalline cellulose by mass, mix it with sodium hydroxide, urea and distilled water in a ratio of 7:12:80, pre-freeze it, take it out and thaw it, add 9% of epichlorohydrin cross-linking agent, and freeze it at 55 o After reacting for 2 h under C conditions, the mixture was soaked in distilled water for 50 h until neutral, and freeze-dried for 48 h to obtain Salix psammophila microcrystalline cellulose hydrogel;

[0109] Preparation of S3, N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel:

[0110] 0.5 g of dried N-doped carbon quantum dots was dissolved in 500 mL of distilled water to obtain a 1 g / L N-doped carbon quantum dot solution. A 1.5 cm × 1.5 cm × 1.5 cm volume of Salix psammophila microcrystalline cellulose hydrogel was placed in the 1 g / L N-doped carbon quantum dot solution and left for 15 h. After being taken out, it was washed with distilled water and freeze-dried for 30 h to obtain N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0111] Furthermore, in the step S1, the particle size of the Salix psammophila powder is sieved through a 150-mesh sieve, and the Salix psammophila mixed solution is sieved at 180 o C for 12 h, and the resulting solution was centrifuged at 1000 rpm for 10 min; μm Filter through a water filter and freeze-dry in a freeze dryer for 50 h.

[0112] Furthermore, in step S22, glacial acetic acid is used to adjust the pH.

[0113] Furthermore, in step S24, minus 20 o C pre-freeze for 30 min, 25 o Thaw at 37°C for 30 min.

[0114] Furthermore, the method for washing to neutrality is: first removing unreacted chemical reagents with distilled water, and then washing with anhydrous ethanol to remove distilled water remaining in the previous operation.

[0115] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of patent protection, should still fall within the scope of this patent. Furthermore, the technical features of this invention may be freely combined with one another, with other technical inventions, and with other technical inventions.

[0116] Experimental part

[0117] Experiment 1

[0118] The N-doped carbon quantum dots prepared in Example 3 were analyzed by TEM electron microscope. Figure 1 (a), 1(b), 1(c), from Figure 1 As can be seen from (a), the N-doped carbon quantum dots are evenly distributed and circular; Figure 1 (b) It can be seen that the average size of N-doped carbon quantum dots is 3.0 nm; Figure 1 (c) It can be seen that the lattice spacing of the N-doped carbon quantum dot lattice stripes is 0.19 nm.

[0119] The N-doped carbon quantum dots were subjected to X-ray diffraction analysis, and the results are shown in 1(d). As can be seen from the figure, due to the extremely disordered graphite structure, the XRD spectrum of the prepared N-doped carbon quantum dots shows a strong peak centered at 2θ=22.4°.

[0120] Raman analysis of N-doped carbon quantum dots showed the following results: Figure 1 As shown in (e), it can be seen from the figure that the prominent peak of the D band caused by the sp3 vibration of defective and disordered carbon atoms appears at about 1353 cm −1 The prominent peak of the G band, which is caused by the sp2 vibration of carbon atoms in the two-dimensional hexagonal lattice, appears at about 1568 cm −1 This is common for single crystals of graphite with effective structures, indicating that sp2 hybridized carbon atoms move on the plane; N-doped carbon quantum dots are structurally similar to graphite with an ID / IG of 0.98.

[0121] Infrared spectroscopy analysis was performed on N-doped carbon quantum dots to study the surface functional groups on the N-doped carbon quantum dots. The results are as follows: Figure 1 As shown in (f), it can be seen from the figure that the FTIR spectrum of N-doped carbon quantum dots is around 3300-3500 cm −1The prominent peaks at 2927 and 2856 cm are related to the OH and NH stretching vibrations. −1 The asymmetric CH stretching and symmetric CH stretching vibrations of N-doped carbon quantum dots are shown at 1650 cm −1 The peak observed at 1290 cm indicates the presence of C=O in N-doped carbon quantum dots; −1 The bands observed at approximately 1050 cm indicate the presence of C-N bonds. −1 The peaks observed at confirm the presence of C-O-C bonds; these results suggest the presence of functional groups such as –NH, CH, CN, and C=O in N-doped carbon quantum dots.

[0122] Experiment 2

[0123] The fluorescence sensing ability of the N-doped carbon quantum dots prepared in Example 3 was analyzed. A 0.5 g / L N-doped carbon quantum dot solution was placed in a four-way quartz cuvette, and then a fluorescence spectrophotometer was used to scan the emission spectrum in the range of 300 nm to 700 nm, using an excitation bandwidth of 10 nm, an emission bandwidth of 10 nm, and a gain (PMT) of 7 levels. The UV-visible absorption experiment process was to place a 0.5 g / L N-doped carbon quantum dot solution in a double-way quartz cuvette, and then use a UV-vis spectrophotometer to measure its absorption wavelength range of 200-700 nm using a slit width of 2 nm and a step size of 1 nm. The results are shown in FIG. Figure 2 As shown, Figure 2 (a) shows the UV-visible absorption spectrum, emission spectrum and emission image of N-doped carbon quantum dots. It can be seen from the figure that the UV-visible absorption spectrum of the N-doped carbon quantum dot solution has an absorption peak near 265 nm and a weak shoulder peak at 330 nm. These two absorbance peaks correspond to the π-π* transition of the C=C bond and the n-π* transition between the sp2 aromatic domain and the oxygen / nitrogen-containing group, respectively. Under the excitation wavelength of 398 nm, the maximum emission wavelength shows a strong peak at 465 nm.

[0124] Comparison of the optical properties of N-doped carbon quantum dots under visible light and ultraviolet light conditions. Figure 2 (b) shows the picture of N-doped carbon quantum dots under visible light and 365 nm ultraviolet light. It can be seen from the figure that when the N-doped carbon quantum dot solution is irradiated by 365 nm ultraviolet light, its color changes from light brown to bright blue.

[0125] The emission spectra of N-doped carbon quantum dots under different fluorescence excitation wavelengths were compared. The emission spectra of 0.5 g / L N-doped carbon quantum dot solution were scanned with an excitation wavelength of 370-450 nm at an interval of 10 nm. Figure 2(c) shows the emission spectra of N-doped carbon quantum dots at different excitation wavelengths. The emission spectra of N-doped carbon quantum dots at excitation wavelengths ranging from 370 to 450 nm, with the maximum fluorescence level observed at 400 nm. For carbon-based fluorescent materials, the fluorescence intensity and emission wavelength usually depend on the excitation. This phenomenon is mainly attributed to the emission states generated by various functional groups or particle size dispersion.

[0126] The three-dimensional spectrum of N-doped carbon quantum dots was analyzed. The three-dimensional emission spectrum of 0.5 g / L N-doped carbon quantum dot solution was measured using a fluorescence spectrophotometer in the excitation wavelength range of 250-550 nm, the interval of 10 nm, and the emission wavelength range of 350-650 nm. The excitation bandwidth of the fluorescence spectrophotometer was 10 nm, the emission bandwidth was 10 nm, and the gain (PMT) was 7 levels. Figure 2 (d) is a three-dimensional fluorescence image of N-doped carbon quantum dots. The fluorescence spectrum shows a strong correlation with the surface defects of N-doped carbon quantum dots. This is because N-doped carbon quantum dots overcome size dependence. The purpose of fluorescence-based applications is to achieve excellent fluorescence stability. Therefore, the fluorescence stability of N-doped carbon quantum dot solutions was tested at different pH and sodium chloride concentrations. Only under strong acid conditions will obvious fluorescence quenching occur.

[0127] The stability of the fluorescence performance of N-doped carbon quantum dots was analyzed by taking 2 ml of 0.5 g / L N-doped carbon quantum dot solution and 1 ml of sodium chloride solution with different concentrations and placing them in a four-way cuvette. The stability was tested by fluorescence spectrophotometer at an excitation wavelength of 398 nm. The results are shown in the figure. Figure 2 As shown in (e), N-doped carbon quantum dots still exhibit excellent fluorescence stability in high concentrations of sodium chloride up to 1 mol / L. This is because the surface functional groups of N-doped quantum dots do not react with chloride ions or sodium ions in sodium chloride, which indicates that N-doped quantum dots still have good application prospects in saline wastewater.

[0128] The stability of the fluorescence performance of N-doped carbon quantum dots at different pH values ​​was analyzed. 3 ml of 0.5 g / L N-doped carbon quantum dot solutions with pH values ​​of 1, 3, 5, 7, 9, and 11 were placed in a four-way cuvette and tested using a fluorescence spectrophotometer at an excitation wavelength of 398 nm. The results are shown in Figure 2. Figure 2 As shown in (f), it can be seen from the figure that N-doped carbon quantum dots can maintain strong fluorescence intensity in the pH range of 3-11. This is because the surface functional groups of N-doped quantum dots are less affected by pH and no major fluorescence quenching occurs. This shows that N-doped quantum dots still have good application prospects in wastewaters with different pH values.

[0129] In order to analyze the selectivity of N-doped carbon quantum dots, the fluorescence spectra of N-doped carbon quantum dots obtained under the influence of different metal cations were examined, including 400 M Fe 3+ 、Ba 2+ 、Hg 2+ 、Ni 2+ , Ca 2+ 、Cd 2+ 、Fe 2+ 、Zn 2+ 、Mn 2+ 、Cu 2+ Cr 3+ Mg 2+ and Pb 2+ Various metal cations including N-doped carbon quantum dots react with the results such as Figure 2 (g) As can be seen from the figure, N-doped carbon quantum dots show fluorescence quenching under different metal ions, but Fe 3+ The fluorescence quenching intensity of N-doped carbon quantum dots is the most obvious, indicating that the fluorescence quenching of Fe 3+ Has a good quenching effect.

[0130] The concentrations are 37.5, 75, 112.5, 150, 187.5, 225, 262.5, and 300 respectively. μm Fe 3+ Solution, take 1 ml and place it in 2 ml four-way cuvette, add N-doped carbon quantum dots, and detect the effect of N-doped carbon quantum dots on different concentrations of Fe 3+ The quenching situation, such as Figure 2 (h) As shown in the figure, it can be seen that different concentrations of Fe 3+ The solution will react with the N-doped carbon quantum dots to produce fluorescence. The peak of the fluorescence intensity at the emission wavelength of 453 nm is observed by fluorescence spectrophotometer under the condition of 398 nm excitation wavelength. The fluorescence intensity increases with the Fe 3+ continued to decrease with increasing concentration.

[0131] The concentrations are 37.5, 75, 112.5, 150, 187.5, 225, 262.5, and 300 respectively. μm Fe 3+ Solution, take 1 ml of Fe 3+ The solution was placed in a four-way cuvette containing 2 ml of N-doped carbon quantum dot solution, and the fluorescence intensity changes were detected with different Fe 3+ The relationship between concentrations, such as Figure 2 (i) shows the fluorescence intensity changes with different Fe 3+ The relationship between the relative peak fluorescence intensity (F0 / F) and Fe 3+The slope of the line showing the linear relationship between the two results was 0.99029, indicating very good linearity.

[0132] Experiment 3

[0133] The structure of the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel prepared in Example 3 was analyzed. Figure 3 As shown, Figure 3 (a) Schematic diagram of the preparation process of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0134] The morphology of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel was analyzed. Figure 3 (b) is the SEM image of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel, which shows that the freeze-dried N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel has a 3D network pore structure and the network structure of N-doped carbon quantum dots embedded in the Salix psammophila microcrystalline cellulose gel; Figure 3 (c) is the SEM magnified image of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel. Further magnification shows that the skeleton of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel is mainly composed of wall shapes connected by Salix psammophila microcrystalline cellulose.

[0135] FTIR analysis of Salix psammophila microcrystalline cellulose hydrogel, N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and N-doped carbon quantum dots was performed. Figure 3 As shown in (d), it can be seen from the figure that the Salix psammophila microcrystalline cellulose hydrogel has a −1 The unique C=O absorption bands of carboxyl and aldehyde groups appear at 1290 cm-1, which is due to the oxidation of sodium chlorite causing the hydroxyl groups on the cellulose surface to be partially oxidized to aldehyde or carboxyl groups. −1 The prominent absorption band at 1050 cm is attributed to the CN stretching vibration; −1 The sharp band observed at 1650 cm-1 is caused by COC stretching vibration. The characteristic peaks of all the above N-doped carbon quantum dots were also found in the spectrum of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel. The spectrum comparison between N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel and Salix microcrystalline cellulose revealed that the peaks at 1650 cm-1 and 1603 cm-1 were significantly different from those at 1650 cm-1. −1 The two new absorption bands at 1650 cm-1 correspond to amide I and II bands respectively; these amide bands partially cover the carboxyl group of microcrystalline cellulose oxidized by sodium chlorite at 1650 cm-1. −1 The C=O stretching band at 3000–3400 cm was observed in all spectra. This finding indicates that the carboxyl groups of Salix psammophila microcrystalline cellulose are bonded to the amino-rich N-doped carbon quantum dots through an amide reaction. −1Among them, N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel showed a band intensity higher than that of Salix psammophila microcrystalline cellulose hydrogel and N-doped carbon quantum dots; this intensity difference was due to the numerous -NH2 on the surface of N-doped carbon quantum dots, which allowed the N-doped carbon quantum dots to covalently bond with the hydroxyl and carboxyl groups of Salix psammophila microcrystalline cellulose hydrogel through nucleophilic reactions, and also self-assembled with the Salix psammophila microcrystalline cellulose hydrogel through electrostatic and hydrogen bonding interactions.

[0136] The elemental composition and surface chemical structure of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel were tested by XPS analysis. Figure 3 (e) Figure 3 (e) is the XPS overall spectrum of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel, showing different peaks at 285, 400 and 532 eV, which are attributed to C1s, N1s and O1s, respectively, indicating that the nitrogen element has been successfully introduced into the N-doped carbon quantum dots and composite hydrogel by the hydrothermal method. The full spectrum confirms the presence of C, N and O.

[0137] XPS fine spectrum analysis of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel was performed, such as Figure 3 (f) High-resolution C1s spectrum of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel at 528-539 eV. The figure shows that the two peaks observed at 531.7 and 532.2 eV at 528-539 eV correspond to C–O and C=O bonds, respectively, and can be fitted into the O1s spectrum of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel.

[0138] Figure 3 (g) High-resolution C1s spectrum of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel at 280-292 eV, which is used to analyze the bond configuration of C and O atoms in N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel. It can be seen that the peaks observed at 284.6, 285.6, 286.4 and 287.7 eV are identified as CC, CN, CO and C=O, respectively, and it also confirms that the preparation of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel is successful.

[0139] Experiment 4 Adsorption performance of N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel for heavy metal ions

[0140] 1. Fe 3+ Standard working curve

[0141] 50 mg / L Fe 3+2.00, 4.00, 6.00, 8.00, and 10.00 ml of the standard solution were placed in a 50 ml volumetric flask, diluted to the mark with distilled water, and shaken. The absorbance of the solution was measured using a Perkin Elmer flame atomic absorption spectrometer. The absorbance was measured using a blank reagent as a reference. A standard working curve was drawn with the concentration of Fe (III) as the horizontal axis and the absorbance as the vertical axis. The Fe 3+ The standard curve equation is as follows: Figure 4 shown.

[0142] 2. Fe 3+ Effect of initial concentration on adsorption capacity

[0143] Weigh 0.05 g of six portions of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and place them in 200, 400, 600, 800, 1000, 1200, 1400, 1500, 1600, and 1700 mg / L of Fe-containing solutions. 3+ The adsorption capacity test was carried out in the ion solution, wherein the adsorbent dosage was 0.05 g, and the Fe 3+ The pH value of the ion is 3.0 and the adsorption temperature is 25 o C, adsorption time 120 min, absorbance determination, the results showed that when Fe 3+ When the concentration is 1500 mg / L, the adsorption capacity reaches the maximum. After calculating the adsorption capacity, the final adsorption capacity is 273.1 mg / g. Figure 5 (a) shown.

[0144] 3. Effect of reaction temperature on Fe 3+ Effect of ion adsorption

[0145] Weigh 0.05 g of six portions of N-doped carbon quantum dots composite microcrystalline cellulose hydrogel and heat them to a system temperature of 25 o C, 30 o C, 35 o C, 40 o C, 45 o C, 50 o C, the adsorption capacity test was carried out, in which Fe 3+ The initial concentration of Fe ions was 1500 mg / L, pH value was 3.0, adsorbent dosage was 0.05 g, adsorption time was 120 min, and absorbance was measured. The results showed that when Fe 3+ The adsorption temperature is 45 o C, the adsorption capacity reaches the maximum, and the final adsorption capacity is 475.4 mg / g after calculation. Figure 5 (b)

[0146] 4. Fe 3+Effect of initial solution pH on Fe 3+ Effect of ion adsorption

[0147] Weigh 0.05 g of six portions of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and place them in Fe-containing solutions at pH values ​​of 1.56, 1.88, 2.45, 2.90, and 3.40. 3 + ion solution was used to test the adsorption capacity, in which Fe 3 The initial concentration of + ions was 1500 mg / L, the adsorbent dosage was 0.05 g, and the adsorption temperature was 45 o C, adsorption time 120 min, absorbance determination, the results showed that when Fe 3+ When the pH value is 2.5, the adsorption capacity reaches the maximum. After calculating the adsorption capacity, the final adsorption capacity is 642.3 mg / g. Figure 5 (c) shown.

[0148] 5. Effect of reaction time on Fe 3+ Effect of ion adsorption

[0149] Weigh 0.05 g of six portions of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and place them in a 1500 mg / L Fe-containing 3+ In the ion solution, 10 min, 20 min, 40 min, 60 min, 90 min and 120 min were selected for adsorption capacity test. 3+ The initial concentration of ions was 1500 mg / L, the adsorbent dosage was 0.05 g, the pH value was 2.5, and the adsorption temperature was 45 o C, measured absorbance, the results showed that when Fe 3+ When the adsorption time reaches 60 min, the adsorption reaches equilibrium, and the final adsorption amount is calculated to be 610.5 mg / g. Figure 5 (d) shown.

[0150] 6. Adsorption performance study

[0151] In order to analyze the system in depth, adsorption kinetics was studied. Six portions of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel (0.05 g) were placed in a 1500 mg / L Fe 3+ In the ion solution, 10 min, 20 min, 40 min, 60 min, 90 min and 120 min were selected for adsorption capacity test. 3+ The initial concentration of ions was 1500 mg / L, the adsorbent dosage was 0.05 g, the pH value was 2.5, and the adsorption temperature was 45 o C, measure the absorbance, the result is as follows Figure 5 As shown in (e), the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel reached adsorption equilibrium after about 60 min of adsorption.

[0152] The rate data were fitted to pseudo-first-order kinetic models and pseudo-second-order kinetic models, as Figure 5 As shown in (f), the pseudo-second-order kinetic model is more consistent with the adsorption model, and the fitting effect is poor when the pseudo-first-order kinetic model is used. Therefore, the adsorption process conforms to the pseudo-second-order kinetic model. The fitting results show that the rate-limiting step is not the resistance of the boundary layer; on the contrary, chemical adsorption on Fe 3+ The capture process is dominated by the isotherm model, and the interaction between the adsorbent and the adsorbate is then elucidated. Figure 5 (f) The data are fitted with the Langmuir and Freundlich models. At 318 K, the R 2 The values ​​are better than those of the Freundlich model, and the fitting results are consistent with the monolayer adsorption; in addition, all 1 / n values ​​are in the range of 0 to 1, which is the ideal value for the effective adsorption of aqueous Fe 3+ Systematic prediction of ions.

[0153] The effect of temperature on the stability of N-doped carbon quantum dots composite Salix microcrystalline cellulose gel was studied to further evaluate its adsorption capacity. Table 1 illustrates how the adsorption capacity increases with increasing temperature in the temperature range of 293 to 323 K. According to the observed positive ΔH values, Fe 3+ The removal of Fe 3+ The adsorption of Fe is dominated by entropy (ΔG), and all ΔG values ​​are negative. The number of negative ΔG values ​​increases with increasing temperature, indicating that the adsorption effect is enhanced at high temperature. Therefore, it can be proved that the adsorption process of Fe 3+ The removal of ions is due to the porous structure and different functional groups.

[0154] Table 1 Thermodynamic analysis of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel

[0155]

[0156] 7. Fe 3+ Adsorption model study

[0157] The adsorption process of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel was analyzed. Figure 6 (a) Describes the N-doped carbon quantum dots composite Salix microcrystalline cellulose gel (diameter: 2 cm, height: 2 cm) immersed in 100 ml of 1 g / L Fe 3+The quenching diagram in the solution shows that the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel is immersed in Fe 3+ After the solution was prepared, compared with the initially prepared N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel, Figure 3 (a), the fluorescence is basically quenched, indicating that Fe 3+ It produced a good quenching effect on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0158] The morphology of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel after adsorption was analyzed. Figure 6 (b) Figure 6 (c) shows the adsorption of Fe by N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel 3+ SEM image of Fe 3+ Uniformly dispersed in N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

[0159] FTIR analysis of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel before and after adsorption was performed. Figure 6 (d) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel and Salix psammophila microcrystalline cellulose hydrogel-Fe 3+ FTIR spectrum of Fe 3+ After the addition of N-doped carbon quantum dots, the NH and OH stretching vibration bands of Salix psammophila microcrystalline cellulose hydrogel were slightly weakened, which indicated that Fe 3+ Adsorbed on amino and hydroxyl groups; adding Fe 3+ After that, the amide I and II bands (1650 and 1603 cm -1 ) disappears and a new sharp band appears (1642 cm -1 This result shows that Fe 3+ Reacted with amide bonds.

[0160] Figure 6 (e) N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel to Fe 3+ The fluorescence response of Figure 6 (e) The left side shows a wide range of concentration limits from 200 to 1000 mg / L, indicating that Fe 3+ There is a strong linear relationship between the concentration and the relative fluorescence peak intensity ((F0 / F)) of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose gel (R 2 =0.99796), for N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose gel, Fe 3+ The detection limit is 3.90583 mg / L. Figure 6(e) The right side shows the fluorescence intensity gradient of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel, indicating that at different Fe 3+ At concentrations below 400 nm, the fluorescence of these gels gradually extinguished.

[0161] The pH analysis of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel was performed before adsorption. The solution with pH of 1.6–7.2 was irradiated with 365 nm ultraviolet light. The results were as follows: Figure 7 As shown, in the pH range of 1.6-7.2, the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel exhibited relatively stable and undisturbed fluorescence emission intensity, which proves that the composite hydrogel can simultaneously detect heavy metal ions under acidic conditions.

[0162] 8. Fe 3+ Adsorption mechanism analysis

[0163] XPS analysis of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel before and after adsorption of Fe 3+ The elemental composition and surface chemical structure of Figure 8 (a) Fe adsorption by N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel 3+ The XPS spectrum after adsorption shows that peaks of multiple chemical elements appeared on the surface of the N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel after adsorption, indicating that the nitrogen element was successfully introduced into the N-doped carbon quantum dots and composite hydrogel during the hydrothermal method. The full spectrum confirmed the presence of C, N, O, and Fe elements. It also shows that Fe was successfully introduced into the composite hydrogel during the adsorption process.

[0164] The fine spectrum of Fe element was further characterized by XPS test after N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel adsorption. 3+ The elemental composition and surface chemical structure of Figure 8 (b) is the 2p high-resolution spectrum of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel after adsorption of Fe. It can be seen from the figure that the iron on the surface of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel is in two valence states (Fe 3+ and Fe 2+ ) exists, indicating that Fe 3+ The ions are partially reduced and Fe is found between 710.2 and 723.7 eV. 3+ peaks, while Fe 2+ Fe 3+ The relative amount is greater than Fe 2+ , which indicates that N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel aggregated iron oxides.

[0165] Figure 8(c) Fe adsorption on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel 3+ C1s spectra before and after, from Figure 8 (c) It can be seen that the peaks observed at 284.6, 285.6, 286.4 and 287.7 eV were identified as CC, CN, CO and C=O, respectively; the adsorption of Fe by N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel was observed. 3+ The CN spectrum intensity of the N-doped carbon quantum dots composite microcrystalline cellulose hydrogel is much lower than that of the N-doped carbon quantum dots composite microcrystalline cellulose hydrogel. This finding indicates that the N-containing groups and Fe 3+ Complexation occurs, adsorption of Fe 3+ The active sites include amino and amide.

[0166] Figure 8 (d) Fe adsorption on N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel 3+ The O1s spectrum after Figure 8 (d) It can be seen that the two peaks observed at 531.7 and 532.2 eV correspond to the C–O and C=O bonds, respectively. The Fe adsorbed by N-doped carbon quantum dots composite microcrystalline cellulose gel 3+ A new peak corresponding to iron oxide is shown in the O1s spectrum at 531 eV, a finding that suggests that many O atoms are bound to Fe 3+ Oxidation reaction occurs, Fe is adsorbed 3+ The active sites include hydroxyl and carboxyl groups.

[0167] Experiment 5 Adsorption capacity of NCDs-SP-MCC-gels and SP-MCC-gels

[0168] The Fe(III) adsorption capacity of the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel (NCDs-SP-MCC-gels) prepared in Example 3 of the present invention was compared with that of the Salix psammophila microcrystalline cellulose hydrogel (SP-MCC-gels). The results are shown in Table 2.

[0169] Table 2 Comparison of Fe(III) adsorption capacity of NCDs-SP-MCC-gels and SP-MCC-gels

[0170]

[0171] From the data in Table 2, it can be seen that compared with the Salix psammophila microcrystalline cellulose hydrogel, the adsorption capacity of the prepared N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel for Fe(III) is increased by three times due to the introduction of N-doped carbon quantum dots. This is because the N-doped carbon quantum dots contain a large number of amino groups, which are introduced into the Salix psammophila microcrystalline cellulose hydrogel to undergo amidation reaction, so that the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel produces a large number of amide groups, which can react with Fe(III) to form a complex, thereby increasing the adsorption capacity of the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel for heavy metal ions; at the same time, Figure 6 (e) As far as we know, the introduction of N-doped carbon quantum dots can increase the quenching effect of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel under different heavy metal ion concentrations, which is an effect that Salix microcrystalline cellulose hydrogel cannot achieve. This fully demonstrates that the introduction of N-doped carbon quantum dots has a synergistic effect on the adsorption and detection of N-doped carbon quantum dots composite Salix microcrystalline cellulose hydrogel.

[0172] Experiment 6 Adsorption capacity of different adsorbents for Fe(III)

[0173] The adsorbents in the prior art: fluorescent nanocellulose hydrogel CQDs @HG, carbon dot / layered zirconium phosphate composite material, hydrophilic P (Am-CD-AMPS) microgel, novel fluorescent carbon quantum dot / hydrogel, and N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel (NCDs-SP-MCC-gels) prepared in Example 3 of the present invention were subjected to adsorption of heavy metal ions and the adsorption amount of heavy metal ions was tested; the maximum adsorption amount was reached when the initial concentration of the fluorescent nanocellulose hydrogel CQDs @HG was 50 mg / L, Ph=5, and the adsorption time was 105 min, as shown in Table 3; the maximum adsorption amount was reached when the initial concentration of the carbon dot / layered zirconium phosphate composite material was 500 mg / L, Ph=8, and the adsorption time was 90 min, as shown in Table 3; the initial concentration of the hydrophilic P (Am-CD-AMPS) microgel was 600 mg / L, Ph=5, and the adsorption time was 30 The maximum adsorption capacity was reached at 1500 μg / L, as shown in Table 3. The initial concentration of the new fluorescent carbon quantum dots / hydrogel was 300 mg / L, and the pH was 5.5. The maximum adsorption capacity was reached at 12 h, as shown in Table 3. The experiment of NCDs-SP-MCC-gels was the same as Experiment 4.

[0174] Table 3 Maximum adsorption capacity of Fe(III) by different adsorbents

[0175]

[0176] As can be seen from Table 3, the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel prepared by chemical bonding method in Example 3 of the present invention has significantly better adsorption performance for Fe(III) than other adsorption materials in the prior art.

[0177] Experimental Conclusion

[0178] The present invention uses Salix psammophila as raw material to prepare blue light carbon quantum dots - N-doped carbon quantum dots, and dopes them into Salix psammophila microcrystalline cellulose hydrogel, successfully synthesizing a composite hydrogel - N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel with detection and adsorption properties. The shape, chemical composition, synthesis and optical properties of the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel are investigated. Its network presents a cross-linked three-dimensional structure. The N-doped carbon quantum dots are cross-linked with the Salix psammophila microcrystalline cellulose through amide bonds. Under ultraviolet light excitation, the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel emits stable blue fluorescence; the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel has good absorption and adsorption properties. 3+ The fluorescence response and adsorption of N-doped carbon quantum dots were studied. 3+ Fluorescence resonance energy conversion between N-doped carbon quantum dots and Salix psammophila microcrystalline cellulose hydrogel 3+ (200-1000 mg / L) showed a wide range of linear fluorescence responses; due to the N and O groups of the hydrogel and Fe 3+ Chemical and physical reactions between the two groups occur when N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel is exposed to Fe 3+ The concentration is 1500 mg / g and the temperature is 45 o Under the conditions of C, pH 2.5, and adsorption time of 60 min, it was calculated that the adsorption capacity of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel can reach up to 642.3 mg / g; the introduction of N-doped carbon quantum dots has a synergistic effect on the adsorption and detection of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel; the adsorption performance of N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel on Fe(III) is better than that of the existing technology; all of these can prove that the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel prepared by the present invention has good effects in the adsorption and monitoring of heavy metal ions.

Claims

1. An N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel, characterized in that: Including N-doped carbon quantum dots and Salix psammophila microcrystalline cellulose; The N-doped carbon quantum dots are blue fluorescent carbon quantum dots synthesized by high-temperature hydrothermal synthesis of Salix psammophila powder, ethylenediamine and water; The Salix psammophila microcrystalline cellulose is a product obtained by removing lignin and hemicellulose from Salix psammophila powder; Salix psammophila microcrystalline cellulose is prepared into a hydrogel and then immersed in an N-doped carbon quantum dot solution. The N-doped carbon quantum dots are grafted onto the molecular chains of the Salix psammophila microcrystalline cellulose hydrogel through an amidation reaction to obtain an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel.

2. A method for preparing N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel, characterized in that: The steps include: Preparation of S1. N-doped carbon quantum dots: crush Salix psammophila stems to form Salix psammophila powder, take 1-3 g Salix psammophila powder, 0.4-0.6 mL ethylenediamine and 55-65 mL water to form a Salix psammophila mixed solution, and heat the Salix psammophila mixed solution at 170-190 o After the reaction at 400 °C, the obtained solution was centrifuged, filtered, and freeze-dried to obtain N-doped carbon quantum dots; S2. Preparation of Salix psammophila microcrystalline cellulose hydrogel: S21, weigh 8-12 g of Salix psammophila powder, dilute with 70-90% distilled water at a ratio of 1:50-70 g / mL. o C for 0.5-1.5 h, take out and wash until neutral, filter, 90-120 o C is dried to constant weight; S22, add the sample prepared in S21 to 7-8 wt% sodium chlorite solution, adjust the pH to 3-4, and o C for 2.5-3.5 h, remove and wash to neutrality, then heat at 55-65 o C is dried to constant weight; S23, then place the sample prepared in S22 in 8-12 wt % potassium hydroxide solution, 70-80 o C magnetic stirring reaction for 1.5-2.5 h, take out and wash until neutral, at 55-65 o C to constant weight, add 7-9 wt% hydrochloric acid solution, and o C for 80-100 min, take out and wash until neutral, 55-65 o C is dried to constant weight to obtain Salix psammophila microcrystalline cellulose; S24, take 3.5-4.5% of Salix psammophila microcrystalline cellulose by mass ratio, mix it with sodium hydroxide: urea: distilled water in the ratio of 6-8: 10-14: 75-85, pre-freeze it, take it out and thaw it, add 8-10% epichlorohydrin crosslinking agent, and stir at 50-60 o After reacting for 1.5-2.5 h under C conditions, the mixture was soaked in distilled water for 40-55 h until neutral, and freeze-dried for 40-55 h to obtain Salix psammophila microcrystalline cellulose hydrogel; S3. Preparation of N-doped carbon quantum dots composited with Salix psammophila microcrystalline cellulose hydrogel: Take 0.4-0.6 g of dried N-doped carbon quantum dots and dissolve them in 400-600 mL of distilled water to obtain a 1 g / L N-doped carbon quantum dots solution. Take a volume of 1-2 cm × 1-2 cm × 1-2 cm Salix psammophila microcrystalline cellulose hydrogel and place it in the 1 g / L N-doped carbon quantum dots solution for 10-20 h. After taking it out, wash it with distilled water and freeze-dry it for 24-36 h to obtain the N-doped carbon quantum dots composite Salix psammophila microcrystalline cellulose hydrogel.

3. The method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel according to claim 2, characterized in that: In the step S1, the particle size of the Salix psammophila powder is sieved through an 80-200 mesh sieve, and the Salix psammophila mixed solution is sieved at 170-190 o The reaction was carried out at 400 °C for 10-14 h, and the resulting solution was centrifuged at 1000 rpm for 8-12 min; filtered using a 0.22 μm water filter; and freeze-dried in a freeze dryer for 40-55 h.

4. The method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel according to claim 2, characterized in that: In step S22, glacial acetic acid is used to adjust the pH.

5. The method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel according to claim 2, characterized in that: In the step S24, the temperature is -15-25 o C pre-freeze for 25-35 min, 20-30 o Thaw at 4°C for 25-35 min.

6. The method for preparing an N-doped carbon quantum dot composite Salix psammophila microcrystalline cellulose hydrogel according to claim 2, characterized in that: The method for washing to neutrality is: first use distilled water to remove unreacted chemical reagents, and then use anhydrous ethanol to wash to remove distilled water remaining in the previous operation.

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