Green preparation method of biomass carbon quantum dots for rapid detection of hexavalent chromium ions in water

Abstract

The application discloses a green preparation method of modified carbon quantum dots capable of rapidly detecting hexavalent chromium ions in water. The method comprises the following steps: 1) preparing a pretreated biomass solution; 2) preparing a modified carbon quantum dot precursor solution doped with a modifier; 3) preparing biomass carbon quantum dots by one-step method; and 4) detecting hexavalent chromium ions by using the biomass carbon quantum dots. The biomass precursor can realize resource recycling, the prepared carbon quantum dots have good dispersity, regular morphology and stable fluorescence performance, and the carbon quantum dot preparation process is simple and easy to implement, so that the carbon quantum dots can be used as a feasible scheme for conveniently and efficiently detecting hexavalent chromium ions in water.

Description

Technical Field

[0001] This invention belongs to the fields of materials synthesis and environmental science, and specifically relates to a green preparation method of biomass carbon quantum dots that enables rapid detection of hexavalent chromium ions in water. Background Technology

[0002] In recent years, with the increasing demand for environmental health, the detection of hexavalent chromium ions in water has received growing attention. Consequently, hexavalent chromium ion sensors based on nanomaterials have seen rapid development. Fast detection speed and low detection concentration are advantages and prerequisites for the application of novel nanoprobes. However, whether based on organic dyes (indigo, rhodamine B, methylene blue, Congo red, etc.) or inorganic nanoparticles (nano-gold, nano-silver, single-atom nanozymes, or transition metal quantum dots), besides the drawbacks of complex material synthesis processes and high costs, their application is also limited by detection instruments and methods. Therefore, developing and designing novel nanomaterials for rapid and sensitive detection of hexavalent chromium ions in water is a crucial problem urgently needing to be solved in the field of environmental science.

[0003] In recent years, thanks to the development of carbon materials, especially carbon quantum dots, nanomaterials based on modified carbon quantum dots have achieved remarkable success not only in disease diagnosis and treatment and biopharmaceuticals, but have also greatly promoted the development of technologies such as chemical sensing and fluorescence analysis. Currently, carbon quantum dots are mainly prepared by using carbon-rich chemical reagents through top-down or bottom-up methods. Although a large number of carbon quantum dot-based nanomaterials are already used in environmental monitoring, waste materials such as plant vines and roots, crop straw, and kitchen waste, which are rich in carbon and other elements, can actually be used as raw materials for carbon quantum dot preparation. Therefore, after proper pretreatment, these materials can be used to prepare biomass carbon quantum dots capable of rapid detection of hexavalent chromium ions in water. This not only meets the concepts and inherent requirements of sustainable development and carbon cycling, but also serves as an important supplement to the methods and applications of carbon quantum dot preparation. Summary of the Invention

[0004] The purpose of this invention is to provide a green preparation method for biomass carbon quantum dots that enables rapid detection of hexavalent chromium ions in water.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A green preparation method for biomass carbon quantum dots that enables rapid detection of hexavalent chromium ions in water, comprising the following steps:

[0006] (1) After pretreatment of the biomass precursor, it is dried and thoroughly ground, sieved (80 mesh), and the material passing through the sieve is collected to obtain biomass powder;

[0007] (2) Under stirring conditions, biomass powder is uniformly dispersed in water to obtain a biomass solution; wherein, the stirring speed is 1000~1200 rpm and the stirring time is 12~24 h;

[0008] (3) Mix the biomass solution with the modifier solution, remove oxygen, and immediately place it in a sealed container and stir to mix evenly to obtain the reaction solution;

[0009] (4) The reaction solution is fully reacted under the reaction conditions, cooled to room temperature, centrifuged, and the supernatant is filtered through a 0.22 µm filter membrane to obtain biomass carbon quantum dots; the biomass carbon quantum dots are water soluble.

[0010] The biomass precursors in this invention include, but are not limited to, plant-derived biomass, such as plant-derived waste, including tree roots, stems and vines, residues after extraction of active ingredients from traditional Chinese medicine, straw and wood ash before and after crop burning, fruit peels and cores, vegetable leaves and roots, etc.

[0011] To avoid uneven carbonization of carbon sources in biomass precursors, different pretreatment methods should be selected based on the lipid content of the biomass precursors. If the lipid content of the biomass precursor is low, the pretreatment method is to first air-dry the precursor in a dry, cool place, and then place it in a 60℃ oven for 24 hours to completely remove moisture. If the biomass precursor contains a large amount of lipids, the pretreatment method is to first crush and grind the precursor, add ultrapure water for stirring and sonication, and then remove the lipids from the precursor using an extraction system that can separate lipids, such as water and ethyl acetate or water and phosphate ester. Subsequently, the residue in the aqueous phase is freeze-dried and placed in a 60℃ oven for 24 hours to remove moisture. All pretreated biomass precursors must be thoroughly ground before use.

[0012] Furthermore, in step (2), the mass ratio of biomass powder to water is 1:5~30.

[0013] Furthermore, in step (2), surfactants such as low molecular weight polyethylene glycol, hexadecyltrimethylammonium bromide, Tween 80 and Triton 100 may also be added; the amount of surfactant added is 0.01~0.05% of the mass of biomass powder; the surfactant is added in the form of a solution, and the concentration of the surfactant solution is 0.01~0.05 mg / L.

[0014] Furthermore, the modifier in step (3) includes, but is not limited to, reducing organic acids such as citric acid, ascorbic acid, ethylenediaminetetraacetic acid, formic acid, and glyoxylic acid, as well as inorganic substances and organic amines such as ammonia, sodium borohydride, urea, ethylenediamine, and diethylamine. The volume ratio of the biomass solution to the modifier solution is 3:1 to 1:3; the concentration of the modifier solution is 1 to 3 mol / L.

[0015] Furthermore, the reaction in step (4) can be completed by hydrothermal method, or by microwave radiation method, electrochemical method and sol-gel method, but oxygen in the reaction system must be removed by means of ultrasound, nitrogen gas or other means before the reaction.

[0016] Furthermore, the reaction described in step (4) is a hydrothermal reaction, with a hydrothermal reaction temperature of 150–210°C and a reaction time of 4–12 h.

[0017] Due to the unique chemical composition of biomass, the biomass carbon quantum dots produced contain a rich variety of elemental impurities. The participation of modifiers not only ensures that the quantum dots have good water solubility, but also improves their dispersibility. At the same time, it causes a large number of polar groups with redox capabilities to be distributed on the surface of the quantum dots, thereby enabling rapid detection of hexavalent chromium ions in water through coordination and chemical reactions.

[0018] Specifically, a rapid detection method for hexavalent chromium ions in water is as follows: A certain amount of biomass carbon quantum dots is measured and prepared into carbon quantum dot solutions of different concentrations. These solutions are placed in quartz cuvettes, and their fluorescence excitation spectra are measured using a fluorescence spectrophotometer. The fluorescence spectrophotometer is then adjusted to the optimal excitation wavelength, and the fluorescence emission spectra of the carbon quantum dot solutions are measured. Standard hexavalent chromium ion solutions and Al2O3 solutions are prepared separately. 3+ Zn 2+ Cr 3+ Mg 2+ Ni 2+ Ca 2+ Cu 2+ Mn 2+ Fe 3+ K + Na + A specific detection experiment was conducted on heavy metal ions using carbon quantum dot solution. The fluorescence spectrophotometer was set to the optimal excitation wavelength of the carbon quantum dot solution, and the fluorescence intensity of the carbon quantum dot solution mixed with different heavy metal ions was measured.

[0019] When preparing quantum dot solutions, in addition to using deionized water as a solvent, solvents that are miscible with water, such as methanol, ethanol, and glycerol, can also be used.

[0020] The biomass carbon quantum dots prepared by this invention can selectively detect hexavalent chromium ions in water, exhibiting advantages such as rapid detection and high sensitivity. In one exemplary embodiment of this invention, the prepared biomass carbon quantum dots selectively detect hexavalent chromium ions in water. 6+ The detection limit is 0.07 μmol / L.

[0021] The beneficial effects of this invention are: the reuse of biomass not only meets the inherent requirements of sustainable development and the carbon cycle concept, but also the quantum dot preparation process is green and environmentally friendly. While avoiding environmental pollution and potential health hazards, it can achieve rapid and sensitive detection of hexavalent chromium ions, and is an important supplement to the preparation method and application of carbon quantum dots. Attached Figure Description

[0022] Figure 1 Transmission electron microscope (TEM) and high-magnification TEM images of the biomass carbon quantum dots prepared in Example 1.

[0023] Figure 2 The particle size distribution of the biomass carbon quantum dots prepared in Example 1 is shown in the figure.

[0024] Figure 3 The fluorescence excitation and fluorescence emission spectra of the biomass carbon quantum dots prepared in Example 1 are shown.

[0025] Figure 4 The image shows the detection effect of the biomass carbon quantum dots prepared in Example 1 on hexavalent chromium ions.

[0026] Figure 5 The linear relationship diagram for the detection of hexavalent chromium using biomass carbon quantum dots prepared in Example 1 is shown.

[0027] Figure 6 The image shows a comparison of the quenching effects of hexavalent chromium on different biomass carbon quantum dots prepared in Examples 1-4. Detailed Implementation

[0028] The present invention will be further described in conjunction with specific embodiments. The following embodiments are intended to illustrate the present invention and not to further limit the present invention. Example 1

[0029] (1) Collect a certain amount of kudzu root residue and air dry it in a ventilated place. Place it in a 60℃ oven for 24 h to completely remove moisture. Grind the completely dried kudzu root residue thoroughly. Take 1 g of the powder obtained from grinding and disperse it in 10 mL of ultrapure water. Stir it magnetically at 1000 rpm for 20 h to mix it thoroughly, and then obtain the pretreated biomass solution.

[0030] (2) Prepare a 1 mol / L urea solution, take 10 mL and mix it with the pretreated biomass solution, place it in a sealed container and stir magnetically at 1000 rpm for 15 min, immediately place it in a high-pressure reactor and send it to a 200℃ oven to react for 6 h, cool to room temperature, centrifuge and take the supernatant to pass through a 0.22 µm filter membrane to obtain kudzu carbon quantum dots ( Figure 1 , Figure 2 ).

[0031] (3) Measure out kudzu carbon quantum dots and prepare an aqueous solution of carbon quantum dots, place it in a quartz cuvette, and use a fluorescence spectrophotometer to test its fluorescence excitation spectrum; then adjust the fluorescence spectrophotometer to the optimal emission wavelength of 425 nm and measure the fluorescence emission spectrum of the kudzu carbon quantum dot solution. Figure 3 ).

[0032] (4) Prepare standard hexavalent chromium ion solutions and Al solutions respectively. 3+ Zn 2+ Cr 3+ Mg 2+ Ni 2+ Ca 2+ Cu 2+ Mn 2+ Fe 3 + K + Na + The fluorescence intensity of the carbon quantum dot solution mixed with different heavy metal ions was measured by setting the fluorescence spectrophotometer to the optimal excitation wavelength of 352 nm for the kudzu carbon quantum dot solution. Figure 4 ).

[0033] (5) A solution of kudzu carbon quantum dots of a certain concentration was mixed with ultrapure water and potassium dichromate standard solutions of varying concentrations. The mixture was placed in a quartz cuvette, and the fluorescence intensity was recorded at the optimal excitation wavelength of 352 nm using a fluorescence spectrophotometer. F0 is the fluorescence intensity of kudzu carbon quantum dots mixed with ultrapure water in equal volumes, and F is the fluorescence intensity of kudzu carbon quantum dots mixed with potassium dichromate standard solutions of different concentrations. A correlation between (F0-F) / F0 and Cr can be established. 6+ The linear relationship between concentrations is: (F0-F) / F0 = 0.0072C + 0.0145, where C is the concentration of Cr. 6+ Solution concentration, Cr 6+ The detection limit is 0.07 μmol / L. Figure 5 ). Example 2

[0034] (1) Collect a certain amount of kudzu root residue and air dry it in a ventilated place. Place it in a 60℃ oven for 24 h to completely remove moisture. Grind the completely dried kudzu root residue thoroughly. Take 1 g of the powder obtained from grinding and disperse it in 10 mL of ultrapure water. Prepare a 0.01 mg / L hexadecyltrimethylammonium bromide aqueous solution and add 10 mL of it. Stir magnetically at 1000 rpm for 20 h to mix it thoroughly, and obtain the pretreated biomass solution.

[0035] (2) Prepare kudzu 2-carbon quantum dots in the same way as in Example 1 (2).

[0036] (3) The fluorescence excitation and emission spectra of the 2-carbon quantum dot solution of kudzu root were measured in the same manner as in Example 1 to determine the optimal excitation wavelength of 345 nm; a standard hexavalent chromium ion solution was prepared in the same manner as in Example 1, and the fluorescence intensity of the mixture of 2-carbon quantum dots of kudzu root and hexavalent chromium solution was measured at the optimal excitation wavelength. The results were compared with those of Example 1. Figure 6 ). Example 3

[0037] (1) Biomass solution pretreated in the same way as in Example 1.

[0038] (2) Prepare a 1 mol / L EDTA solution, take 10 mL and mix it with the pretreated biomass solution, place it in a sealed container and stir magnetically at 1000 rpm for 15 min, then immediately place it in a high-pressure reactor and send it to a 200℃ oven for 6 h. After cooling to room temperature, centrifuge and take the supernatant to pass through a 0.22 µm filter membrane to obtain kudzu carbon quantum dots.

[0039] (3) The fluorescence excitation and emission spectra of the 2-carbon quantum dot solution of Pueraria lobata were measured in the same manner as in Example 1 to determine the optimal excitation wavelength of 340 nm; a standard hexavalent chromium ion solution was prepared in the same manner as in Example 1, and the fluorescence intensity of the mixture of the new Pueraria lobata carbon quantum dots and the hexavalent chromium solution was measured at the optimal excitation wavelength. The results were compared with those of Example 1. Figure 6 ). Example 4

[0040] (1) Collect a certain amount of grape skins and grape seeds and air dry them in a ventilated place. Place them in a 60℃ oven for 24 h to completely remove moisture. Grind the completely dried grape skins and seeds thoroughly. Take 0.5 g of the powder obtained from grinding and disperse it in 10 mL of ultrapure water. Stir magnetically at 1000 rpm for 20 h to mix it thoroughly, and then obtain the pretreated biomass solution.

[0041] (2) Prepare a 1 mol / L citric acid solution, take 10 mL and mix it with the pretreated biomass solution, place it in a sealed container and stir magnetically at 1000 rpm for 15 min, then immediately place it in a high-pressure reactor and send it to a 200℃ oven for 6 h. After cooling to room temperature, centrifuge and take the supernatant to pass through a 0.22 µm filter membrane to obtain grape pomace carbon quantum dots.

[0042] (3) The fluorescence excitation and emission spectra of the grape pomace carbon quantum dot solution were measured in the same manner as in Example 1 to determine the optimal excitation wavelength of 336 nm; a standard hexavalent chromium ion solution was prepared in the same manner as in Example 1, and the fluorescence intensity of the mixture of grape pomace carbon quantum dots and hexavalent chromium solution was measured at the optimal excitation wavelength. The results were compared with those of Example 1. Figure 6 ).

[0043] Figure 6The fluorescence intensity of different carbon dots and the fluorescence intensity of the solution after adding the same concentration of hexavalent chromium stock solution were measured, indicating that the methods in Examples 1, 2, 3, and 4 can all prepare carbon quantum dots that specifically react with hexavalent chromium. The figure shows that the carbon dots prepared in Example 3 have the strongest fluorescence intensity, but the quenching effect of hexavalent chromium on them is only moderate; while the carbon dots in Example 1 show the most significant quenching effect, thus obtaining a more accurate detection limit and linear range for hexavalent chromium.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A green preparation method of biomass carbon quantum dots capable of realizing rapid detection of hexavalent chromium ions in water, characterized in that: The method comprises the following steps: (1) drying and grinding the pretreated biomass precursor to obtain a biomass powder; the biomass precursor is radix puerariae residue; (2) uniformly dispersing the biomass powder in water under stirring to obtain a biomass solution; the stirring speed is 1000-1200 rpm, and the stirring time is 12-24 h; (3) mixing the biomass solution with a modifier solution, stirring the mixture in a sealed container immediately after removing oxygen to obtain a reaction solution; the modifier is urea; (4) performing hydrothermal reaction on the reaction solution under reaction conditions, centrifuging the reaction solution after cooling to room temperature, filtering the supernatant through a 0.22 µm filter membrane to obtain the biomass carbon quantum dots; the biomass carbon quantum dots are water-soluble.

2. The green preparation method of biomass carbon quantum dots for rapid detection of hexavalent chromium ions in water according to claim 1, characterized in that: The pretreatment method of the biomass precursor is selected according to the content of lipid substances in the biomass precursor: if the content of lipid substances in the biomass precursor is low, the pretreatment method is to first dry the precursor naturally in a dry and cool place and then dry the precursor completely to remove water; if the biomass precursor contains a large amount of lipid substances, the pretreatment method is to first crush and grind the precursor, wash the precursor with ultrapure water, and then remove the lipid substances in the precursor with an extraction system capable of separating lipids, and dry the residual substances in the water phase completely to remove water. 3.The green preparation method of biomass carbon quantum dots capable of realizing rapid detection of hexavalent chromium ions in water according to claim 1, characterized in that: The mass ratio of the biomass powder to water in step (2) is 1:5-30. 4.The green preparation method of biomass carbon quantum dots capable of realizing rapid detection of hexavalent chromium ions in water according to claim 1, characterized in that: A surfactant can also be added in step (2), and the addition amount of the surfactant is 0.01-0.05% of the mass of the biomass powder. 5.The green preparation method of biomass carbon quantum dots capable of realizing rapid detection of hexavalent chromium ions in water according to claim 1, characterized in that: In step (3), the volume ratio of the biomass solution to the modifier solution is 3:1-1:3; and / or, the concentration of the modifier solution is 1-3 mol / L. 6.The green preparation method of biomass carbon quantum dots capable of realizing rapid detection of hexavalent chromium ions in water according to claim 1, characterized in that: The reaction in step (4) is a hydrothermal reaction, the hydrothermal reaction temperature is 150-210 o C, and the reaction time is 4-12 h.

7. Application of the biomass carbon quantum dots prepared by the method of any one of claims 1-6 in detection of hexavalent chromium ions in water.

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