CN110093157B

CN110093157B - Method for extracting fluorescent nanostructure from carbon source through reduction reaction

Info

Publication number: CN110093157B
Application number: CN201811134955.0A
Authority: CN
Inventors: 相昌盛
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-09-29
Filing date: 2018-09-29
Publication date: 2022-06-03
Anticipated expiration: 2038-09-29
Also published as: CN110093157A

Abstract

The invention crushes the carbon source by ball milling treatment, and mixes the carbon source with the reducing agent to carry out reduction reaction to obtain the fluorescent nano structure. The invention purifies the obtained fluorescent nano structure by centrifugation, filtration, dialysis and other modes. The invention carries out fine size separation on the obtained fluorescent nanostructure in a high-speed centrifugation and molecular weight truncation mode. The invention also includes functionalizing the resulting fluorescent nanostructures.

Description

Method for extracting fluorescent nanostructure from carbon source through reduction reaction

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patent application No. 62/565,100 filed on 29/9/2017. The entire contents of the above application are incorporated herein by reference.

Technical Field

The invention belongs to the technical field of nano material preparation, and particularly relates to a method for extracting a fluorescent nano structure from a carbon source through chemical reduction reaction.

Background

The current common method for massively preparing graphene quantum dots and carbon dots is to cut a carbon source by an oxidation method. For example, a mixed acid oxidation method, a hydrothermal method, an electrochemical oxidation method, a microwave oxidation method, and the like. However, the oxidant has a large destructive effect on the carbon source structure, and a large number of structural defects exist in the generated graphene quantum dots and carbon dots. This results in a large number of electrons in the excited state transitioning back to the ground state through nonradiative transitions, thereby greatly reducing their fluorescence efficiency. Meanwhile, graphene quantum dots and carbon dots prepared by an oxidation method have the problems of poor monochromaticity and low yield of low-band-gap nanoparticles. In addition, the waste liquid obtained by the oxidation method contains strong oxidants such as sulfuric acid, nitric acid, potassium permanganate and the like, and the waste liquid treatment process is complex and has hidden dangers such as environmental pollution and the like. The present invention solves the above problems.

Disclosure of Invention

In some embodiments, the invention relates to methods of making fluorescent nanostructures from a carbon source. In some embodiments, the carbon source comprises anthracite, bituminous coal, sub-bituminous coal, kinetic coal, coke, pitch, asphaltenes, graphite, carbon black, rice hulls, cellulose, and combinations thereof.

In some embodiments, the carbon source is reduced to a powder form by ball milling.

In some embodiments, the carbon source is exposed to a reducing agent resulting in the formation of fluorescent nanostructures comprising graphene quantum dots, carbon dots.

In some embodiments, the reducing agent comprises lithium, sodium, potassium, sodium potassium alloys, sodium mercury alloys, lithium aluminum hydride, sodium borohydride, dithionate, thiosulfate, hydrazine hydrate, oxalic acid, formic acid, acetic acid, citric acid, ethylenediamine, ammonium sulfate, methanol, ethanol, and combinations thereof. In some embodiments, the carbon source is subjected to a heat treatment in the presence of a reducing agent.

In some embodiments, the fluorescent nanostructures formed are initially separated from the residual carbon source by centrifugation, filtration, or the like, to extract the fluorescent nanostructures.

In some embodiments, the fluorescent nanostructures are size separated by high speed centrifugation, cross-flow filtration, molecular weight cut-off methods, and combinations of these steps.

In some embodiments, the size of the formed fluorescent nanostructures is controlled by controlling the time, temperature, mass ratio of carbon source to reducing agent, etc. of the chemical reaction. In some embodiments, the carbon source is selected to be coal and the fluorescent nanostructures formed are about 1-80 nanometers in diameter. The carbon source is selected to be pitch and asphaltene, and the fluorescent nanostructures formed are about 1-20 nanometers in diameter. The carbon source is selected to be graphite and the fluorescent nanostructures formed are about 1-100 nanometers in diameter. In some embodiments, the fluorescent nanostructures are formed to a thickness of 0.5 to 5 nanometers.

In some embodiments, the fluorescent nanostructure formed has a fluorescence emission peak between 380-850 nanometers. In some embodiments, the fluorescent nanostructures formed have an emission peak half-width between 10 and 150 nanometers.

In some embodiments, the carbon source is selected to be coal and the fluorescent nanostructures formed have a fluorescence efficiency between 1-90%. In some embodiments, the carbon source is selected to be an asphaltene or a pitch, and the fluorescent nanostructure formed has a fluorescence efficiency between 10-80%. In some embodiments, the carbon source is selected to be graphite, and the fluorescent nanostructures formed have a fluorescence efficiency of between 25-90%.

In some embodiments, the formed fluorescent nanostructures are functionalized to improve their dispersibility, including hydroxyl, carboxyl, alkyl, ester, amino, amide, and combinations thereof. In some embodiments, the formed fluorescent nanostructure is matched with a dispersing agent to improve the dispersibility of the fluorescent nanostructure in high salinity water and inhibit agglomeration.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the field of quantum dot displays. The backlight of the liquid crystal display technology mainly adopts fluorescent powder, and the color gamut can only reach 70% of NTSC, so that the defect of unreal color expression exists. The quantum dot backlight replaces old fluorescent powder with a quantum dot material, red light and green light are excited by irradiating quantum dots with different sizes through backlight LED blue light, and then the blue light is combined with the blue light to be mixed into white light, so that the high color gamut range of 110% NTSC can be reached, and the color expression is purer and closer to the real color. At present, toxic and high-cost metal quantum dots such as cadmium selenide and indium phosphide are used for quantum dot display. The metal quantum dots are usually oxidized by water and oxygen, so that the service life of the metal quantum dots is reduced, and a water and oxygen barrier film is required for protection, so that additional cost is increased. The graphene quantum dots are non-toxic, stable in chemical property and free of a water-oxygen barrier film. Therefore, the metal quantum dots with toxicity can be replaced, and the color gamut of the display can be improved by adopting a photoluminescence or electric-to-luminescence mode.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the photovoltaic field. The graphene quantum dots or the carbon dots can increase the number of carriers and expand the absorption range of solar spectrum, thereby improving the photoelectric conversion efficiency.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the field of lighting. The light quality of the common LED illumination is lower than that of the traditional light source, compared with full-color warm light of the traditional incandescent lamp, the artificial white light high-energy photons of the LED, namely blue light, are too much, and medical science proves that the too much blue light is harmful to human health. The white light using the quantum dot LED can be completely consistent with an ideal illumination light source in principle, is closer to natural light, and generates heat to be further reduced, so that the energy consumption is reduced.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the biomedical field. In order to analyze the outcome and the response mechanism of transplanted cells after they have entered the body, the cells entering the body must be monitored. The monitoring process takes a long time, so that the marker is required to have the characteristics of long luminescence time and no toxic harm to organisms. The graphene quantum dots and the carbon dots have good performances such as no toxicity, high fluorescence intensity, strong photobleaching resistance and the like, so that the graphene quantum dots and the carbon dots play a great role in research directions such as cell positioning, signal transduction, movement and migration of components in cells, clinical diagnosis and the like.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the field of optical brighteners. Fluorescent whitening agents are an additive used in the field of household chemicals. It can be attached to the surface of an object to absorb ultraviolet light and convert it into blue light. For example, most garments yellow over time, and blue and yellow are complementary colors, so that the blue-emitting optical brightener counteracts the yellow color, and the garment looks visually very white. The chemical component of the common fluorescent whitening agent is sodium diphenylethylene biphenyl disulfonate, and the harmfulness to human bodies is controversial and blamed. The blue-light-emitting graphene quantum dots or carbon dots prepared by the method are non-toxic and can replace the existing fluorescent whitening agent.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the field of anti-counterfeiting labels. And mixing the graphene quantum dots or the carbon dots with polyvinyl alcohol to prepare the anti-counterfeiting ink. The anti-counterfeiting ink can emit fluorescence under the irradiation of ultraviolet light and laser. In addition, phosphorescence is also associated within 2 seconds after the ultraviolet light is turned off. This property can be used as anti-counterfeiting material, and can improve the complexity and security of anti-counterfeiting.

In some embodiments, the formed graphene quantum dots or carbon dots are used in the field of oilfield tracers. In the oil exploitation process, communication conditions between different water injection wells and production wells need to be detected so as to judge the oil displacement efficiency of the water injection wells. The graphene quantum dots or the carbon dots have stable chemical properties under high-temperature and high-pressure conditions, are free from environmental hazards, have good dispersibility, have high penetration rate in an oil layer, and are easy to detect. Can be used as an excellent oil field tracer product.

In some embodiments, the formed graphene quantum dots also possess all of the properties of graphene. Such as high electrical and thermal conductivity, zero gas permeability, high tensile strength, etc. Therefore, the graphene material can be used in the fields related to graphene materials, such as lithium ion batteries, supercapacitors, electric and heat conducting films, composite materials, gas barrier materials and the like.

Drawings

FIG. 1 is a schematic diagram of a method for preparing fluorescent nanostructures from a carbon source. The method comprises the following steps: the carbon source is ball milled (step 10), chemically reacted under reducing conditions (step 12), the fluorescent nanostructures are extracted (step 14), size separated (step 16), and functionalized (step 18).

Fig. 2 is data for characterization of ultraviolet and fluorescence properties of graphene quantum dots extracted from bituminous coal. The concentration of the tested graphene quantum dot aqueous solution is 1 mg/mL. The maximum peak of the ultraviolet absorbance appears around 365 nm. Under the excitation condition of 365 nm wavelength, the obtained fluorescence emission peak value is about 485 nm.

Fig. 3 is a graph showing the fluorescence intensity contrast of graphene quantum dots extracted from the same bituminous coal by the reduction method and the mixed acid oxidation method (concentrated sulfuric acid and concentrated nitric acid 3:1, heating at 100 ℃ for 12 hours) according to the present invention, and the excitation wavelength is 365 nm. The fluorescence intensity of the graphene quantum dots obtained by the reduction method is far higher than that of the graphene quantum dots obtained by the oxidation method.

FIG. 4 is data representing carbon points extracted from asphaltenes by reduction. The maximum peak of the ultraviolet absorbance of the obtained carbon dot aqueous solution (1mg/mL) appeared at about 350 nm. Under the excitation condition of 350 nm wavelength, the obtained fluorescence emission spectrum is shown as a dotted line in the figure, two emission peaks appear at 410nm and 450nm, and the fluorescence presents blue.

Fig. 5 is a graphene quantum dot dispersibility study. Fig. 5a is a picture of 1mg/mL graphene quantum dots uniformly dispersed in deionized water. FIG. 5b is a 2% concentration of CaCl with 1mg/mL graphene quantum dots₂Picture of agglomeration phenomenon occurred in the solution. Fig. 5c is a picture of graphene quantum dots uniformly dispersed again after a proper amount of dispersant is added in fig. 5 b.

Detailed Description

The following detailed description is exemplary and explanatory only and is not restrictive of the subject matter claimed. Various changes and modifications can be made in the embodiments by the applicant without departing from the spirit and scope of the invention.

Embodiment 1, 300 mg of bituminous coal after ball milling treatment was mixed with 3 g of potassium and packed in a glass tube sealed in a vacuum environment. The mixture was heated through a sand bath at 350 degrees celsius for 5 hours. After cooling, the solid powder was washed with methanol and sonicated by a sonicator for 5 hours. 100 mg of the treated solid was dispersed in 100 ml of methanol and placed in a Parr bench reactor for chemical reaction. The reaction temperature is 250 ℃, the torque is 1.76 N.m., the stirring speed is 300 r/min, and the reaction time is 10 hours. After cooling, the solution was placed in a centrifuge (3000 rpm) to separate the remaining graphite solids that were not reacted from the solution. Dialyzing the separated solution in a 1000-Da dialysis bag for 3 days, and then processing the solution by a rotary evaporator to obtain the graphene quantum dot solid.

Example 2, 100 mg of asphaltenes were dissolved in 100 ml of tetrahydrofuran and 10 mg of citric acid was added. The solution was heated at 180 degrees celsius for 10 hours. After cooling, the solution was placed in a centrifuge (3000 rpm) to separate the remaining asphaltene solids that were not reacted from the solution. The separated solution was dialyzed in a 1000-Da dialysis bag for 3 days, after which it was treated by a rotary evaporator to obtain a carbon point solid.

Claims

1. A method for extracting fluorescent nanostructures from a carbon source, wherein the fluorescent nanostructures are graphene quantum dots, and the method comprises the following steps: mixing 300 mg of bituminous coal subjected to ball milling treatment with 3 g of potassium, packaging in a vacuum environment sealed glass tube to obtain a mixture, heating the mixture at 350 ℃ for 5 hours by using a sand bath to obtain solid powder, cooling, cleaning the solid powder by using methanol, and carrying out ultrasonic treatment for 5 hours by using an ultrasonic instrument; dispersing 100 mg of the treated solid powder in 100 ml of methanol, and putting the solid powder into a Parr bench reaction kettle to perform chemical reaction under the following conditions: the reaction temperature is 250 ℃, the torque is 1.76 N.m., the stirring speed is 300 r/min, and the reaction time is 10 hours; after cooling, placing the solution obtained by the reaction in a centrifuge for separation, wherein the centrifugal speed of the separation is 3000 r/min; dialyzing the separated solution in a 1000-Da dialysis bag for 3 days, and then processing the solution by a rotary evaporator to obtain the graphene quantum dot solid.