Preparation and Application of Nitrogen and Sulfur Co-Doped Carbon Quantum Dots Derived from Waste Biomass Eggshells

Abstract

The invention discloses a preparation method and application of nitrogen and sulfur co-doped carbon quantum dots derived from waste biomass eggshells, belonging to the fields of biomass fluorescent carbon nanomaterials and chemical sensing. The preparation method of the nitrogen and sulfur co-doped carbon quantum dots comprises the steps of: 1) washing, drying and pulverizing waste biomass eggshells; 2) dispersing the pulverized eggshell powder into deionized water, adding thiourea as a nitrogen source and a sulfur source thereto, and performing a hydrothermal reaction in a reaction kettle; 3) naturally cooling the product after the reaction to room temperature, and obtaining the nitrogen and sulfur co-doped carbon quantum dots after centrifugal separation, suction filtration and dialysis. The invention provides a preparation method and application of nitrogen and sulfur co-doped carbon quantum dots derived from waste biomass eggshells. The preparation is simple, green and non-toxic, and the quantum dots prepared by this method have strong stability, show excellent anti-interference property, selectivity and high sensitivity to lead ions, and realize the detection of lead ions in actual samples.

Description

Technical Field

[0001] The present invention belongs to the fields of biomass fluorescent carbon nanomaterials and chemical sensing, and particularly relates to the preparation and application of nitrogen and sulfur co-doped carbon quantum dots derived from waste biomass eggshells. Background Art

[0002] With the rapid development of society, heavy metal ion pollution has become increasingly serious. Lead ion (Pb 2+ ) is one of the most toxic, widely distributed, and dangerous heavy metal ions recognized internationally in the environment. It easily enters the human body through bioaccumulation. Even at very low concentrations, it can bind to proteins in the body and cause lead poisoning, posing a serious threat to human health. The common methods for detecting Pb 2+ mainly include inductively coupled plasma mass spectrometry, cold atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, fluorescence spectrometry, etc. Among them, fluorescence spectrometry has attracted much attention due to its advantages such as good selectivity, high sensitivity, low cost, and simple equipment. Up to now, there have been reports of fluorescent probes containing heavy metal elements as Pb 2+ fluorescent chemical sensors. However, many of these fluorescent probes have disadvantages such as high toxicity, complex synthesis process, high cost, and long time consumption, which limit their practical applications. Therefore, there is an urgent need to develop a more environmentally friendly method for synthesizing new non-toxic fluorescent materials to achieve rapid, accurate, and quantitative analysis of Pb 2+ .

[0003] Carbon quantum dots have advantages such as high fluorescence intensity, high photo-stability, good biocompatibility, low toxicity, water solubility, and adjustable emission wavelength, and have broad application prospects in the fields of photocatalysis, bioimaging, biological macromolecules, heavy metal ion detection, etc. So far, traditional synthesis of carbon quantum dots usually uses relatively high-purity raw materials such as organic small molecules, oligomers, ionic liquids, and citric acid as carbon sources. On the one hand, this can lead to an increase in the cost of preparing carbon quantum dots, and on the other hand, the quantum yield of the prepared carbon quantum dots is relatively low, which limits their further applications. Natural biomass carbon sources (such as banana juice, domestic silk, tomato juice, etc.) are usually non-toxic and rich in elements, which can ensure the "green" nature of the carbon source, and the carbon quantum dots prepared from such carbon sources have potential excellent photoluminescence properties. However, the large consumption of precursors may cause waste of available resources. Therefore, waste biomass in life (such as eggshells, etc.) has become a potential candidate natural biomass. However, the main problem with using these biomasses to prepare carbon quantum dots is their relatively low fluorescence performance, which limits their applications. To overcome these defects, there is an urgent need to regulate the core and surface of carbon quantum dots. Introducing heteroatoms (such as nitrogen, sulfur, etc.) to dope them is an effective strategy to regulate the fluorescence performance of carbon quantum dots. Therefore, how to synthesize carbon quantum dots with excellent fluorescence performance, which can be used for Pb 2+The detected nitrogen and sulfur co-doped carbon quantum dots have become a technical problem to be solved urgently. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a method for preparing nitrogen and sulfur co-doped carbon quantum dots by using waste biomass eggshells as a novel biomass carbon source through a one-step hydrothermal method and its application. The prepared quantum dots have a particle size distribution range of 2.22 - 3.60 nm, contain groups such as hydroxyl, carboxyl, and esters on the surface, have a maximum excitation wavelength of 360 nm, and a maximum emission wavelength of 433 nm, and can be used for Pb 2+ detection. To achieve the above object, the technical solution provided by the present invention is as follows:

[0005] 1. Provide a method for preparing nitrogen and sulfur co-doped carbon quantum dots derived from waste biomass eggshells, including the following specific steps:

[0006] (1) Wash and dry the waste biomass eggshells, and ball-mill and pulverize them in a high-speed ball mill at a rotation speed of 1000 - 1500 r min -1 .

[0007] (2) According to the mass-volume ratio of eggshell powder to deionized water of 1.0 g:30 mL, disperse the eggshell powder obtained in step (1) in deionized water, and add thiourea as a nitrogen source and a sulfur source to it according to the mass ratio of eggshell powder to thiourea of 1:(0.1 - 1). After mixing evenly, transfer it to a reaction kettle and carry out hydrothermal reaction at 140 - 220 °C for 4 - 12 h;

[0008] (3) Wait for the product obtained in step (2) to cool naturally to room temperature, centrifuge and separate it at a rotation speed of 8000 - 10000 r min -1 for 10 - 20 min, then filter it by suction with a 0.22 μm water-based filter membrane, and then dialyze the obtained filtrate with a dialysis bag with a molecular weight cut-off of 1000 Da for 24 - 48 h, and collect the solution in the dialysis bag to obtain nitrogen and sulfur co-doped carbon quantum dots.

[0009] 2. Provide an application of the above nitrogen and sulfur co-doped carbon quantum dots in the field of lead ion detection.

[0010] The beneficial effects of the present invention are as follows:

[0011] The present invention uses waste biomass eggshells as a carbon source and thiourea as a sulfur source and a nitrogen source to obtain nitrogen and sulfur co-doped carbon quantum dots by a one-step hydrothermal method. The quantum dots can be used for the detection of lead ions. This method not only has natural and easily available raw materials, is green and pollution-free, the prepared quantum dots have high purity and few impurities, are suitable for large-scale production, but also have a wide detection range for lead ions, low detection limit, good selectivity and anti-interference ability, and can be used for the detection of actual samples. Brief Description of the Drawings

[0012] Figure 1 (a) Transmission electron microscopy image and (b) particle size distribution diagram of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1

[0013] Figure 2 (a) XPS survey spectrum and high-resolution spectra of (b) C 1s, (c) O 1s, (d) N 1s, and (e) S 2p of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1

[0014] Figure 3 (a) XRD pattern and (b) FT-IR spectrum of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1

[0015] Figure 4 UV-visible absorption spectrum of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1

[0016] Figure 5 (a) Fluorescence emission spectra of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1 at different excitation wavelengths, (b) fluorescence spectra at different pH values, (c) fluorescence spectra at different NaCl concentrations, and (d) anti-photobleaching property

[0017] Figure 6 Fluorescence spectrum of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 2

[0018] Figure 7 Fluorescence spectrum of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 3

[0019] Figure 8 Selectivity of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1 for Pb 2+ and (b) anti-interference ability

[0020] Figure 9 (a) Fluorescence spectra of the nitrogen and sulfur co-doped carbon quantum dots prepared in Example 1 after adding different concentrations of Pb 2+ and (b) fitting curve of the relative fluorescence intensity versus concentration linear relationship Detailed implementation manners

[0021] To further understand the present invention, the preparation and application of the waste biomass eggshell-derived nitrogen and sulfur co-doped carbon quantum dots provided by the present invention are further described below in conjunction with the implementation examples, but it is not intended to limit the present invention

[0022] Example 1

[0023] (1) Wash and dry the waste biomass eggshells, and grind them into powder in a high-speed ball mill at a rotation speed of 1500 r min -1 ;

[0024] (2) Disperse 1.0 g of the eggshell powder obtained in step (1) in 30 mL of deionized water, add 0.6 g of thiourea as the nitrogen and sulfur source thereto, transfer the mixture to a reaction kettle after mixing evenly, and perform hydrothermal reaction at 200 °C for 10 h;

[0025] (3) Wait for the product obtained in step (2) to cool naturally to room temperature, centrifuge at 10000 r min -1 speed for 10 min, then filter by suction with a 0.22 μm water-based filter membrane, and dialyze the obtained filtrate with a dialysis bag with a molecular weight cut-off of 1000 Da for 48 h. Collect the solution in the dialysis bag to obtain nitrogen and sulfur co-doped carbon quantum dots.

[0026] The transmission electron microscope photograph of the nitrogen and sulfur co-doped carbon quantum dots obtained in this example is shown in Figure 1 (a). From Figure 1 (a), it can be seen that the prepared nitrogen and sulfur co-doped carbon quantum dots have good dispersion, no obvious agglomeration, and the shape is nearly spherical. Figure 1 (b) is the particle size distribution diagram. From Figure 1 (b), it can be seen that the particle size distribution range of the prepared nitrogen and sulfur co-doped carbon quantum dots is 2.22 - 3.60 nm. Figure 2 (a) is the XPS full spectrum of the nitrogen and sulfur co-doped carbon quantum dots. From Figure 2 (a), it can be seen that the XPS full spectrum of the nitrogen and sulfur co-doped carbon quantum dots has 4 obvious peaks at 168.31, 285.35, 400.89, and 531.29 eV, which are S2p, C 1s, N 1s, and O1s respectively. The high-resolution spectrum of C1s ( Figure 2 b) has three main peaks at 284.02 eV, 285.18 eV, and 286.96 eV, which are attributed to C-O / C=O, C-N / C-O, and -COOH respectively. In the high-resolution spectrum of O1s ( Figure 2 c), the peak with a binding energy of 530.18 eV corresponds to C=O, and the peak with a binding energy of 530.96 eV comes from C-O. The high-resolution spectrum of N 1s ( Figure 2 d) shows that the two peaks at binding energies of 398.87 eV and 400.36 eV correspond to C-N-H bonds and C-N-C bonds respectively, indicating that N is doped into the carbon quantum dots. In the high-resolution spectrum of S2p ( Figure 2 e), the two peaks with binding energies of 167.04 and 168.20 eV are attributed to C-S and C-SO x , indicating that S is successfully doped into the carbon quantum dots. The XPS results show the successful preparation of the nitrogen and sulfur co-doped carbon quantum dots and the presence of various functional groups. Figure 3 (a) is the XRD pattern of the obtained nitrogen and sulfur co-doped carbon quantum dots. From Figure 3(a) It can be seen that the nitrogen-sulfur co-doped carbon quantum dots have a broad diffraction peak at 2θ = 26.38°, corresponding to the (002) crystal plane of typical graphene, indicating that the nitrogen-sulfur co-doped carbon quantum dots contain a graphene structure. Figure 3 (b) is the FT-IR spectrum of the obtained nitrogen-sulfur co-doped carbon quantum dots. From Figure 3 (b), it can be seen that the strong broad absorption peak at 3124 cm -1 should be the stretching vibration of O-H, attributed to the edge functional groups such as carboxylic acid, amino or hydroxyl groups of the nitrogen-sulfur co-doped carbon quantum dots. The absorption peak at 1610 cm -1 is caused by C=O, and the absorption peak at 1399 cm -1 is attributed to -O-C=O-. The absorption peaks at 1123 cm -1 and 618 cm -1 are attributed to C-O and C-S respectively. The results show that the nitrogen-sulfur co-doped carbon quantum dots contain rich hydrophilic functional groups, endowing them with good hydrophilicity. The UV-visible absorption spectrum of the nitrogen-sulfur co-doped carbon quantum dots is shown in Figure 4 . From Figure 4 , it can be seen that as the wavelength increases, the absorption intensity gradually decreases. The absorption peak at 280 nm is attributed to the n-π* electronic transition of the C=O bond of the oxygen-containing group, and the peak around 340 nm may originate from the n-π* electronic transition of the C-N and -C-OH bonds. Figure 5 (a) is the fluorescence emission spectrum of the nitrogen-sulfur co-doped carbon quantum dots at different excitation wavelengths. From Figure 5 (a), it can be seen that as the excitation wavelength increases, the fluorescence intensity shows a trend of first increasing and then decreasing. When the excitation wavelength is 360 nm, the optimal emission wavelength is 433 nm. In addition, as the excitation wavelength increases, the emission wavelength undergoes a red shift, showing an excitation-dependent phenomenon. The fluorescence spectra of the nitrogen-sulfur co-doped carbon quantum dots at different pH values are shown in Figure 5 (b). From Figure 5 (b), it can be seen that the fluorescence performance is stable and the intensity is relatively high in the range of pH = 3 - 11, indicating that the quantum dots have good stability in solutions with different pH values. Figure 5 (c) is the fluorescence spectrum of the nitrogen-sulfur co-doped carbon quantum dots at different NaCl concentrations. From Figure 5 (c), it can be seen that as the NaCl concentration increases, the fluorescence intensity of the nitrogen-sulfur co-doped carbon quantum dots remains basically unchanged, indicating that the nitrogen-sulfur co-doped carbon quantum dots have good stability in NaCl solutions. The prepared nitrogen-sulfur co-doped carbon quantum dots were continuously scanned 6 times at an excitation wavelength of 360 nm, and the results are shown in Figure 5 (d). From Figure 5 (d), it can be found that the fluorescence spectrum is almost unchanged, indicating that the prepared nitrogen-sulfur co-doped carbon quantum dots have good anti-photobleaching performance.

[0027] Example 2

[0028] (1) Wash and dry the waste biomass eggshells, and ball-mill and crush them in a high-speed ball mill at a rotational speed of 1200 r / min -1 ;

[0029] (2) Disperse 1.0 g of the eggshell powder obtained in step (1) in 30 mL of deionized water, add 0.1 g of thiourea as the nitrogen and sulfur source, mix evenly, transfer it to a reaction kettle, and carry out a hydrothermal reaction at 140 °C for 12 h;

[0030] (3) Wait for the product obtained in step (2) to cool naturally to room temperature, centrifuge and separate it at a rotational speed of 10000 r / min for 15 min, then filter it with a 0.22-μm aqueous filter membrane, and then dialyze the obtained filtrate with a dialysis bag with a molecular weight cut-off of 1000 Da for 24 h. Collect the solution in the dialysis bag to obtain nitrogen and sulfur co-doped carbon quantum dots, and their fluorescence spectra are shown in -1 ; Figure 6 .

[0031] Example 3

[0032] (1) Wash and dry the waste biomass eggshells, and ball-mill and crush them in a high-speed ball mill at a rotational speed of 1000 r / min -1 ;

[0033] (2) Disperse 1.0 g of the eggshell powder obtained in step (1) in 30 mL of deionized water, add 1.0 g of thiourea as the nitrogen and sulfur source, mix evenly, transfer it to a reaction kettle, and carry out a hydrothermal reaction at 220 °C for 4 h;

[0034] (3) Wait for the product obtained in step (2) to cool naturally to room temperature, centrifuge and separate it at a rotational speed of 8000 r / min for 20 min, then filter it with a 0.22-μm aqueous filter membrane, and then dialyze the obtained filtrate with a dialysis bag with a molecular weight cut-off of 1000 Da for 36 h. Collect the solution in the dialysis bag to obtain nitrogen and sulfur co-doped carbon quantum dots, and their fluorescence spectra are shown in -1 ; Figure 7 .

[0035] Example 4

[0036] Test the selectivity, anti-interference ability, detection range, and detection limit of the nitrogen and sulfur co-doped carbon quantum dots prepared in Application Example 1 for Pb 2+ as follows:

[0037] (1) Add 0.15 mL of 10 -2 M metal ion solution (Ag + , Al 3+ , Ba 2+ , Ca 2+ , Cd2+ 、Cu 2+ 、K + 、Hg 2+ 、Pb 2+ 、Mg 2 + 、Mn 2+ 、Na + 、Ni 2+ 、Sn 4+ 、Zn 2+ 、Co 2+ 、Cr 3+ 、Fe 3+ ) were respectively added to 0.3 mL of the nitrogen and sulfur co-doped carbon quantum dot solution, mixed evenly. After reacting for 3 - 5 min, the fluorescence spectrum at 433 nm was recorded using a fluorescence spectrophotometer, and the measurement was repeated three times in parallel. The results are shown in Figure 8 (a). As can be seen from Figure 8 (a), after adding Pb 2+ , the relative fluorescence intensity F0 / F of the nitrogen and sulfur co-doped carbon quantum dots changed significantly, while the addition of other metal ions had little change in F0 / F, indicating that the prepared nitrogen and sulfur co-doped carbon quantum dots have high selectivity for Pb 2+ .

[0038] (2) 0.45 mL of the nitrogen and sulfur co-doped carbon quantum dot solution containing Pb 2+ (10 -2 M) was mixed evenly with 0.15 mL of other ionic solutions (Ag + , Al 3+ , Ba 2+ , Ca 2+ , Cd 2+ , Cu 2+ , K + , Hg 2+ , Mg 2+ , Mn 2+ , Na + , Ni 2+ , Sn 4+ , Zn 2+ , Co 2+ , Cr 3+ , Fe 3+ ). After reacting for 3 - 5 min, the fluorescence spectrum at 433 nm was recorded using a fluorescence spectrophotometer, and the measurement was repeated three times in parallel. The results are shown in Figure 8 (b). As can be seen from Figure 8 (b), the relative fluorescence intensity of the nitrogen and sulfur co-doped carbon quantum dots showed almost no obvious change, indicating that the nitrogen and sulfur co-doped carbon quantum dots have excellent anti-interference performance for the detection of Pb 2+ .

[0039] (3) Add different concentrations of Pb to the nitrogen-sulfur co-doped carbon quantum dot solution. 2+ (0~10 -2 M), and tested its fluorescence spectrum. The results are shown in Figure 9 (a). With the increase of Pb 2+ With the increase of concentration, the fluorescence intensity of nitrogen-sulfur co-doped carbon quantum dots gradually quenched. Figure 9 (b) It can be seen that the fluorescence intensity of nitrogen-sulfur co-doped carbon quantum dots is in the range of 5 to 250 μM and is comparable to that of Pb 2+ The concentration of β-catenin showed a good linear relationship, and the detection limit calculated based on the 3-fold signal-to-noise ratio was 17.69 μM.

Claims

1. Application of waste biomass eggshell-derived nitrogen and sulfur co-doped carbon quantum dots in fluorescent detection of lead ions in a solution, characterized in that, The carbon quantum dots are synthesized by a hydrothermal reaction using waste biomass eggshells and thiourea as raw materials. The particle size distribution range of the carbon quantum dots is 2.22 - 3.60 nm, the surface contains hydroxyl groups, carboxyl groups and esters, the maximum excitation wavelength is 360 nm, and the maximum emission wavelength is 433 nm; the mass ratio of eggshells to thiourea is 1:(0.1 - 1).

2. The application according to claim 1, characterized in that The steps of the preparation method of the carbon quantum dots are as follows: (1) Wash and dry the discarded biomass eggshells, and ball-mill and crush them in a high-speed ball mill at a rotational speed of 1000 - 1500 r min -1 ; (2) Disperse the eggshell powder obtained in step (1) in deionized water according to the mass - volume ratio of eggshell powder to deionized water of 1.0 g:30 mL, and add thiourea as a nitrogen source and a sulfur source thereto according to the mass ratio of eggshell powder to thiourea of 1:(0.1 - 1). After mixing evenly, transfer it to a reaction kettle and carry out a hydrothermal reaction at 140 - 220 °C for 4 - 12 h; (3) Wait for the product obtained in step (2) to cool naturally to room temperature, and centrifuge at 8000 - 10000 r min -1 for 10 - 20 min at a rotation speed, then filter by suction using a 0.22 μm aqueous filter membrane, and then dialyze the obtained filtrate with a dialysis bag having a molecular weight cut-off of 1000 Da for 24 - 48 h. Collect the solution inside the dialysis bag to obtain the carbon quantum dots.

3. The application according to claim 1, characterized in that Add the waste biomass eggshell - derived nitrogen - sulfur co - doped carbon quantum dots to the test solution, test their fluorescence intensity for the detection of lead ion concentration; the detection range is 5 - 250 μM, the detection limit is 17.69 μM, and it has excellent anti - interference and selectivity, and can be used for the detection of lead ions in actual samples.

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