CN113372901A

CN113372901A - Preparation method of fluorescence double-enhanced sisal fiber carbon quantum dots

Info

Publication number: CN113372901A
Application number: CN202110587750.3A
Authority: CN
Inventors: 覃爱苗; 娄颖; 孙伟; 凡新刚; 廖雷
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2021-05-27
Filing date: 2021-05-27
Publication date: 2021-09-10

Abstract

The invention discloses a preparation method of fluorescent double-enhanced sisal fiber carbon quantum dots. Dissolving transition metal ion salt in ultrapure water, and adjusting the pH to 8-12 by using ammonia water; then, placing the cleaned sisal fibers in a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene inner liner, and adding the transition metal ion salt solution with the adjusted pH value into the reaction kettle; and (3) carrying out hydrothermal reaction, cooling to room temperature, filtering, centrifuging, and diluting with PEG to obtain the fluorescence double-enhanced sisal fiber carbon quantum dots. According to the invention, biomass sisal fibers containing rich groups are used as a carbon source, and the effect of double enhancement of fluorescence of carbon quantum dots can be realized only by introducing metal ions in a hydrothermal process and then carrying out passivation modification without participation of a metal chelating agent; the fluorescent double-enhanced sisal fiber carbon quantum dots prepared by the method are environment-friendly and nontoxic, and can be used as fluorescent probes for environmental analysis such as cell imaging, biosensing and disease diagnosis, and the fields of biomedicine and the like.

Description

Preparation method of fluorescence double-enhanced sisal fiber carbon quantum dots

Technical Field

The invention relates to a method for preparing a fluorescence double-enhanced high-quality biomass carbon quantum dot by using sisal fibers as a carbon source through transition metal ion doping and surface passivation modification, belonging to the field of nano materials.

Background

Carbon Quantum Dots (CQDs) have the advantages of excellent and stable fluorescence characteristics, good biocompatibility, rich groups and the like, and are important materials in the application fields of analysis and detection, biological imaging, drug transportation and the like.

There have been many reports on the preparation of CQDs, however, it has been found that most of CQDs are prepared from non-renewable raw materials, such as carbon nanotubes, graphene oxide and derivatives thereof. These precursors are not only expensive, but also have long preparation periods, and some procedures involve the use of a large number of toxic chemicals. Therefore, it is necessary to find a widely available raw material and develop a simple and efficient synthetic route to realize mass production of high-quality CQDs.

Due to rich biomass resources and low price, the cost of the biomass precursor is far lower than that of most other precursors (such as graphite, carbon fiber, carbon nano tube, citric acid, glucose and the like). Therefore, the biomass is a green, natural, cheap and renewable carbon source and can be used for producing CQDs with excellent biocompatibility on a large scale. However, the fluorescence performance of biomass CQDs is usually unreasonable due to a large number of defects on the surface, and heteroatom doping and surface passivation are effective ways for improving the fluorescence performance of the CQDs. Doping with metal ions can increase the fluorescence of CQDs by electron transfer as compared to doping with non-metallic heteroatoms (e.g., N, S, P, etc.). Oxygen-containing functional group modifiers can improve the fluorescence properties of CQDs by inactivating the state of their surface defects. Therefore, metal doping and surface passivation can achieve the effect of dual enhancement of fluorescence properties of CQDs. In order to change the emission wavelength of the carbon dot, the metal chelating agent and the transition metal salt are dissolved in the organic solvent for chelating, and the formed mixed solution is subjected to solvothermal reaction to obtain the metal-doped fluorescent carbon quantum dot, but the preparation method needs the organic solvent and the chelating agent, which is not environment-friendly. The prior art is only about to improve the fluorescence property of biomass CQDs by simultaneously utilizing a metal doping and surface passivation mode.

Disclosure of Invention

In view of the above problems, the present invention aims to provide a method for preparing a fluorescence double-enhanced high-quality carbon quantum dot by using biomass sisal fibers as a carbon source, using transition metal ions as a dopant, and using polyethylene glycol (PEG) as a passivating agent.

The method comprises the following specific steps:

(1) removing impurities in the sisal fibers, washing with a large amount of tap water, washing with deionized water, and drying.

(2) 0.001-0.005 mol of transition metal ion salt is weighed and dissolved in 50-75 mL of ultrapure water, and then the pH is adjusted to 8-12 by analytically pure ammonia water.

(3) Weighing 2-5 g of sisal fibers cleaned in the step (1), placing the sisal fibers in a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining and a 100mL inner container, and pouring the solution prepared in the step (2) into the inner container of the reaction kettle.

(4) And (3) placing the reaction kettle in the step (3) in an oven, carrying out hydrothermal reaction for 10-26 hours at the temperature of 150-190 ℃, naturally cooling to room temperature, filtering and centrifuging the product, and obtaining supernatant, namely the transition metal ion doped sisal fiber carbon quantum dot stock solution.

(5) Passivating and modifying the solution obtained in the step (4) by 10-100 times by using polyethylene glycol to obtain polyethylene glycol passivated and modified transition metal ion doped sisal fiber carbon quantum dots (PEG-M)ⁿ⁺CQDs) solution, namely the fluorescent double-enhanced sisal fiber carbon quantum dots.

The transition metal ion salt is CuCl₂、ZnCl₂、MnCl₂、CdCl₂、BiCl₃、CrCl₃、FeCl₃And CeCl₃One kind of (1).

The polyethylene glycol is one of PEG-200, PEG-400 and PEG-600.

The fluorescent carbon quantum dot prepared by the preparation method is arrangedDetecting in a fluorescence spectrophotometer with excitation voltage of 500-650V and excitation slit and emission slit of 5nm, and detecting PEG-M when excitation wavelength is 300-360 nmⁿ ⁺The emission peak of the CQDs solution is maximum at 390-430 nm. The doping of transition metal ions and the surface passivation modification of PEG can realize the double enhancement effect of the fluorescence intensity of sisal fiber CQDs. Transmission Electron Microscope (TEM) observation shows that the prepared CQDs are spherical, are uniformly dispersed, and have an average particle size of 1.5-3.5 nm.

Compared with the prior art, the invention has the advantages that:

1. the invention has the advantages of low cost of raw materials, environmental protection and simple preparation process. The sisal fiber is used as the raw material, so that the pollution caused by burning the sisal fiber as waste can be effectively reduced, and the residual value of the sisal fiber is fully exerted. Compared with a small molecular carbon source, the biomass sisal fiber has abundant groups, which provides a greater possibility for improving the fluorescence property of CQDs.

2. The invention can realize the effect of double enhancement of the fluorescence of the carbon quantum dots by introducing metal ions in the hydrothermal process and then carrying out passivation modification without the participation of a metal chelating agent. Compared with solvothermal reaction, the method effectively avoids the use of organic solvents in the reaction process, reduces the production cost, and provides greater possibility for the mass production of high-quality CQDs.

3. The fluorescence double-enhanced sisal fiber carbon quantum dots prepared by the method are environment-friendly and non-toxic, and can be used as fluorescent probes for environmental analysis such as cell imaging, biosensing and disease diagnosis, and the fields of biomedicine and the like.

Drawings

FIG. 1 is a comparison graph of fluorescence emission spectra of different transition metal ion-doped sisal fiber carbon quantum dots in the examples.

FIG. 2 is a comparison graph of fluorescence emission spectra of different PEGs passivated and modified transition metal ion doped sisal fiber carbon quantum dots in the example.

FIG. 3 shows Mn in example²⁺TEM images of sisal fiber doped carbon quantum dots.

FIG. 4 shows Mn in example²⁺The particle size distribution diagram of the sisal fiber-doped carbon quantum dots.

FIG. 5 shows Mn in example²⁺XPS (X-ray photoelectron spectroscopy) of the doped sisal fiber carbon quantum dots, (a) X-ray photoelectron spectroscopy of Mn-CQDs; (b) and (c), (d) and (e) are high resolution spectra of carbon, nitrogen, oxygen and manganese, respectively.

Detailed Description

Example (b):

passivation modification of Mn with PEG²⁺Sisal fiber-doped carbon quantum dots are taken as an example, namely PEG-Mn-CQDs:

(2) 0.001mol of MnCl is weighed₂Dissolved in 50mL of ultrapure water, followed by adjustment of the pH to 12 with analytically pure ammonia.

(3) Weighing 2.5g of the sisal fibers cleaned in the step (1), placing the sisal fibers in a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining and a 100mL inner container, and pouring the solution prepared in the step (2) into the inner container of the reaction kettle.

(4) And (4) placing the reaction kettle in the step (3) in an oven, carrying out hydrothermal reaction for 16 hours at 180 ℃, naturally cooling to room temperature, filtering and centrifuging the product, and obtaining supernatant, namely Mn-CQDs stock solution.

(5) Diluting the Mn-CQDs stock solution obtained in the step (4) by 50 times by using PEG-200 to obtain a PEG-Mn-CQDs solution; for comparison, the Mn-CQDs stock solution obtained in the step (4) is diluted by 50 times with ultrapure water to obtain a Mn-CQDs solution.

If the dopant in the examples is MnCl₂Replacement with CuCl₂、ZnCl₂、CdCl₂、BiCl₃、CrCl₃、FeCl₃And CeCl₃Taking PEG-200 as a passivating agent, and preparing PEG-Cu-CQDs, PEG-Zn-CQDs, PEG-Cd-CQDs, PEG-Bi-CQDs, PEG-Cr-CQDs, PEG-Fe-CQDs and PEG-Ce-CQDs by the similar method; for comparison, Cu-CQDs, Zn-CQDs, Cd-CQDs, Bi-CQDs, Cr-CQDs, Fe-CQDs and Ce-CQDs can be prepared by diluting with ultrapure water.

Using a voltage of 600VAll the solutions were detected by a spectrofluorometer with 5nm excitation and emission slits, and PEG-M was detected at 326nm excitation wavelengthⁿ⁺The emission peak of the CQDs solution is maximum at 390-430 nm. Compared with CQDs (blank) which are not doped and have passivated surfaces, the fluorescence intensity of the carbon quantum dots obtained after doping of the transition metal ions is improved to a certain extent (see figure 1); the fluorescence intensity of the carbon quantum dots after transition metal ion doping and surface passivation is greatly improved (see figure 2). Wherein under the same condition, MnCl is used₂The Mn-CQDs and the PEG-Mn-CQDs prepared respectively from the doping agents have the highest fluorescence intensity.

With MnCl₂The samples prepared for the dopants are the best examples, and therefore the Mn-CQDs are characterized as follows:

1. the prepared Mn-CQDs are spherical in shape (see FIG. 3) and have an average particle diameter of 2.3nm (see FIG. 4) as observed by a Transmission Electron Microscope (TEM).

2. The peak of Mn-CQDs was observed at 641.0, 284.8, 400.1 and 532.1eV for Mn2p, C1s, N1s and O1s (see FIG. 5a) by XPS characterization. From the high resolution spectrum of C1s, the 5 main peaks at 284.1, 285.1, 286.0, 286.6 and 288.4eV correspond to Csp2(C-C/C ═ C), Csp, respectively³(C-N/C-O, C ═ N/C ═ O) and hcooonh₄(see FIG. 5 b); high resolution spectral display of N1s, sp³Hybrid N (N-H) has a binding energy at 401.3eV and pyridine nitrogen (C ═ N-C/C-N) has a binding energy at 399.5eV (see fig. 5C); the O1s map of Mn-CQDs indicated that it contained O-H and C-O groups, located at 531.0eV and 531.8eV, respectively (see FIG. 5 d); the high resolution XPS spectrum of Mn2p shows a major peak at 641.0eV (see FIG. 5e), Mn²⁺Successfully realizes the doping of sisal fiber CQDs.

Claims

1. A preparation method of fluorescence double-enhanced sisal fiber carbon quantum dots is characterized by comprising the following specific steps:

(1) removing impurities in the sisal fibers, washing with a large amount of tap water, washing with deionized water and drying;

(2) weighing 0.001-0.005 mol of transition metal ion salt, dissolving in 50-75 mL of ultrapure water, and then adjusting the pH to 8-12 by using analytically pure ammonia water;

(3) weighing 2-5 g of sisal fibers cleaned in the step (1), placing the sisal fibers in a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene inner liner and a 100mL inner liner, and pouring the solution prepared in the step (2) into the inner liner of the reaction kettle;

(4) placing the reaction kettle in the step (3) in an oven, performing hydrothermal reaction for 10-26 hours at 150-190 ℃, naturally cooling to room temperature, filtering and centrifuging a product, and obtaining a supernatant, namely the transition metal ion doped sisal fiber carbon quantum dot stock solution;

(5) carrying out polyethylene glycol passivation modification treatment on the solution obtained in the step (4) by 10-100 times to obtain a polyethylene glycol passivation modified transition metal ion doped sisal fiber carbon quantum dot solution, namely the fluorescence double-enhanced sisal fiber carbon quantum dot;

the transition metal ion salt is CuCl₂、ZnCl₂、MnCl₂、CdCl₂、BiCl₃、CrCl₃、FeCl₃And CeCl₃One of (1);

the polyethylene glycol is one of PEG-200, PEG-400 and PEG-600.