CN112095113B - Method for preparing carbon quantum dots by taking coal as raw material - Google Patents
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Abstract
The invention belongs to the field of carbon nano materials, and particularly relates to a preparation method of carbon quantum dots. Compared with the raw materials such as small organic molecules, graphite or graphene, the preparation method has the advantages that the cost is relatively low when the coal powder is used as a carbon source to prepare the carbon quantum dots, and the high-value utilization of the coal is facilitated. In addition, compared with a coal rod serving as a working electrode, the method for preparing the carbon quantum dots by directly carrying out electrochemical oxidation on the coal water slurry has the advantages of easiness in scale up and reusability of the electrode.
Description
Technical Field
The invention particularly relates to a preparation method of carbon quantum dots, and belongs to the field of carbon nano materials.
Background
The carbon quantum dot is a novel zero-dimensional carbon-based nanomaterial, has a size smaller than 10nm and has a quasi-spherical structure. The structure comprises two parts: surface groups and carbonaceous cores. The surface groups being predominantly oxygen-containing functional groups, e.g. hydroxy, carboxy, etc., the carbonaceous core being predominantly internally bound by sp 2 And sp (sp) 3 The hybridized carbon is formed into amorphous carbon, graphite microcrystals, single-layer or multi-layer graphene fragments and the like. Compared with the original semiconductor quantum dot and other materials, the carbon quantum dot not only maintains the special advantages of carbon materials, such as low toxicity, good biocompatibility and the like, but also has better light stability, adjustable luminous wavelength, easy surface functionalization and abundant raw material sourcesRich and simple preparation method, and the like. The existing synthesis strategies of carbon quantum dots can be summarized into two main categories: "top-down" and "bottom-up". The 'bottom-up' rule adopts small molecular organic matters and the like as carbon sources, and the carbon quantum dots are finally synthesized by a series of changes such as polycondensation reaction and the like through reaction operations such as dehydration, carbonization and the like. The top-down method generally adopts graphite, graphene or carbon nano tube with a macromolecular structure as a carbon source, and the macromolecular structure of the carbon source is partially degraded or modified by means of oxidization, etching and the like, so that the carbon quantum dot is prepared.
Disclosure of Invention
The invention discloses a method for preparing carbon quantum dots, which comprises the following steps of dissolving coal and sodium chloride in water to prepare coal water slurry, and carrying out electrochemical oxidation to prepare the carbon quantum dots.
The preparation method of the carbon quantum dot comprises the following steps:
1) Coal is used as a carbon source, raw material coal is crushed into pulverized coal, and then the pulverized coal is uniformly dispersed in an aqueous solution containing chloride ions with a certain molar concentration to prepare coal water slurry;
2) Using graphite or titanium coated with ruthenium oxide as an anode, and using graphite or nickel screen as a cathode, and electrifying the coal water slurry to perform electrolytic oxidation reaction;
3) After the reaction is finished, centrifugally separating the obtained mixture, filtering supernatant obtained by centrifugal separation, and putting the obtained filtrate into a dialysis bag with the molecular weight cutoff of 3500Da, dialyzing for 3 days, and changing water every 12 hours;
4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying.
Further, the molar concentration of chloride ions in the aqueous solution containing chloride ions is 0.1mol/L to 3mol/L.
Further, in the coal water slurry, the concentration of the coal powder is preferably 2g/L to 30g/L.
Further, the current density during the electrolytic oxidation reaction is preferably 0.1A/cm 2 To 2A/cm 2 The electrolysis time is0.5h to 10h.
In a preferred technical scheme, in the technical scheme, the raw coal is any one of lignite, subbituminous coal, bituminous coal and anthracite coal, and is crushed to more than 100 meshes before use.
In another preferred technical scheme, in the technical scheme, the aqueous solution containing chloride ions can be seawater or industrial wastewater containing chloride ions. In the technical scheme of the invention, the electrolyte solution adopts the seawater or the salt lake water rich in sodium chloride, has the advantages of extremely abundant raw materials, low production and operation cost and easy large-scale industrialized application, and the electrolyte solution adopts the industrial wastewater containing chloride ions, so that the high-value utilization of the industrial salt-containing wastewater can be realized, waste is changed into valuable, and the environmental protection benefit is very remarkable.
The principle of the method of the invention is as follows: the microstructure of the coal comprises amorphous carbon regions composed of aliphatic groups and nano-sized crystalline carbon regions formed from condensed aromatic hydrocarbons. Crystalline carbon in the coal structure is easily oxidized, producing nano-sized carbon quantum dots with amorphous carbon attached at the edges. The invention uses coal as a carbon source, prepares coal powder into water coal slurry by using an aqueous solution containing chloride ions, and then uses the water coal slurry as electrolyte to carry out electrochemical oxidation reaction. After the coal water slurry containing chlorine ions is electrified, the chlorine ions can be anodized at an electrode to generate chlorine, then the chlorine ions are dissolved in an aqueous solution to generate hypochlorite ions with high stability and strong oxidability, and the hypochlorite ions can effectively attack coal dust dispersed in an electrolyte to oxidize a crystalline carbon area in the structure of the coal water slurry to generate carbon quantum dots.
Compared with the preparation method of the quantum dot in the prior art, the preparation method has the following beneficial effects:
(1) According to the preparation method of the carbon quantum dots, coal resources with rich coal reserves in China are used as main raw materials, the raw material cost is low, the added value of the prepared carbon quantum dots is high, and a new way for realizing high-value utilization of the coal resources is provided.
(2) Compared with a coal rod serving as a working electrode, the preparation method has the advantages of simple preparation process, easy scale-up and repeated use of the electrode.
(3) A considerable part of industrial wastewater belongs to industrial wastewater with higher chloride content, for example, the chloride ion concentration of pickling wastewater in the pickle industry can reach 1153000mg/L, if the pickling wastewater is directly discharged into a water body without control, the water environment is seriously endangered, the water balance is destroyed, the water quality is influenced, the fishery production, the agricultural irrigation and the fresh water resource are influenced, and even the underground water and a quoted water source are polluted in serious cases. In a further preferred embodiment of the invention, the electrolyte raw material adopts industrial wastewater containing chloride ions, so that the high-value utilization of the industrial saline wastewater can be realized, and the environmental protection benefit is very remarkable.
Drawings
FIG. 1 is a transmission electron microscope image and a particle size distribution diagram of a nitrogen-sulfur co-doped carbon quantum dot prepared in example 1 of the present invention, wherein (a) is a transmission electron microscope image of a carbon quantum dot prepared by using coal as a carbon source; (b) histogram of particle size distribution of carbon quantum dots.
Fig. 2 is an ultraviolet-visible absorption spectrum and a fluorescence emission spectrum of a carbon quantum dot prepared by using coal as a carbon source.
Detailed Description
The invention is further described below with reference to examples.
Example 1
(1) Selecting Zhaotong brown coal as a raw material, crushing the raw material to above 100 meshes, and uniformly dispersing pulverized coal into a sodium chloride aqueous solution with the chloride ion concentration of 3mol/L by stirring to prepare the coal water slurry with the concentration of 2 g/L.
(2) The titanium coated with ruthenium oxide is used as an anode, a nickel screen is used as a cathode, and the current density is 0.5A/cm 2 And (3) electrifying the coal water slurry obtained in the step (1) to carry out electrolytic oxidation for 1.5h.
(3) After the reaction, the mixture obtained in the step (2) is centrifuged at a high speed, unreacted residues are filtered out, the obtained filtrate is put into a dialysis bag with the molecular weight cut-off of 3500Da, and the dialysis is carried out for 3 days, and water is changed every 12 hours.
(4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying, wherein the quantum yield of the carbon quantum dots is 0.9%.
The carbon quantum dots prepared in example 1 were characterized using transmission electron microscopy. As shown in FIG. 1, it was found that the carbon quanta were uniformly distributed, the particle diameter was narrow in the range of 0.5 to 3.5nm, and the average diameter was 1.81nm. The optical properties of the carbon quantum dots in example 1 were studied using an ultraviolet-visible spectrophotometer and a fluorescence spectrophotometer, and as shown in fig. 2, the carbon quantum dots have strong absorption in the ultraviolet region, and the shorter the wavelength, the more remarkable the absorption. The maximum emission peak (450 nm) of the carbon quantum dots is obtained under 340nm excitation, and a shoulder peak at 400nm is also observed in the emission peak.
XPS test was performed on the elements on the surface of the carbon quantum dots prepared in example 1, and the results are shown in Table 1. From the data in table 1, it can be found that the carbon quantum dots mainly contain two elements of carbon (284.79 eV) and oxygen (531.94 eV), wherein the content of the carbon element is 60.86%, and the content of the oxygen element is 30.41%. And because the raw material is brown coal, the content of nitrogen and sulfur elements is relatively high, and a small amount of nitrogen elements and sulfur elements are also contained in the generated carbon quantum dots. In addition, since the electrolyte containing chloride ions is used in the preparation method, a small amount of chlorine element is inevitably contained in the prepared carbon quantum dots.
TABLE 1 XPS data for carbon Quantum dots prepared with coal as carbon source
Example 2
(1) And selecting the Yining sub-bituminous coal as a raw material, crushing the raw material to more than 100 meshes, and uniformly dispersing the pulverized coal into a potassium chloride aqueous solution with the chloride ion concentration of 3mol/L by stirring to prepare the coal water slurry with the concentration of 10 g/L.
(2) The titanium coated with ruthenium oxide is used as an anode, a nickel screen is used as a cathode, and the current density is 0.5A/cm 2 Lower pair of(1) And electrifying the obtained coal water slurry to carry out electrolytic oxidation for 1.0h.
(3) After the reaction, the mixture obtained in the step (2) is centrifuged at a high speed, unreacted residues are filtered out, the obtained filtrate is put into a dialysis bag with the molecular weight cut-off of 3500Da, and the dialysis is carried out for 3 days, and water is changed every 12 hours.
(4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying, wherein the quantum yield of the carbon quantum dots is 0.99%.
Example 3
(1) Selecting Zhaotong brown coal as a raw material, crushing the raw material to more than 100 meshes, and uniformly dispersing pulverized coal into a magnesium chloride aqueous solution with the chloride ion concentration of 0.6mol/L by stirring to prepare the coal water slurry with the concentration of 10 g/L.
(2) The titanium coated with ruthenium oxide is used as an anode, a nickel screen is used as a cathode, and the current density is 0.5A/cm 2 And (3) electrifying the coal water slurry obtained in the step (1) to carry out electrolytic oxidation for 1.0h.
(3) After the reaction, the mixture obtained in the step (2) is centrifuged at a high speed, unreacted residues are filtered out, the obtained filtrate is put into a dialysis bag with the molecular weight cut-off of 3500Da, and the dialysis is carried out for 3 days, and water is changed every 12 hours.
(4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying, wherein the quantum yield of the carbon quantum dots is 0.84%.
Example 4
(1) Lv Liang bituminous coal is selected as a raw material, crushed to more than 100 meshes, and then evenly dispersed in industrial salt-containing wastewater with the chloride ion concentration of 3mol/L by stirring to prepare the coal water slurry with the concentration of 10 g/L.
(2) The titanium coated with ruthenium oxide is used as an anode, a nickel screen is used as a cathode, and the current density is 0.5A/cm 2 And (3) electrifying the coal water slurry obtained in the step (1) to carry out electrolytic oxidation for 1.0h.
(3) After the reaction, the mixture obtained in the step (2) is centrifuged at a high speed, unreacted residues are filtered out, the obtained filtrate is put into a dialysis bag with the molecular weight cut-off of 3500Da, and the dialysis is carried out for 3 days, and water is changed every 12 hours.
(4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying, wherein the quantum yield of the carbon quantum dots is 1.14%.
Example 5
(1) Selecting Zhaotong lignite as a raw material, crushing the raw material to above 100 meshes, and uniformly dispersing coal dust into industrial salt-containing wastewater with the chloride ion concentration of 0.1mol/L by stirring to prepare the coal water slurry with the concentration of 10 g/L.
(2) The titanium coated with ruthenium oxide is used as an anode, a nickel screen is used as a cathode, and the current density is 1.0A/cm 2 And (3) electrifying the coal water slurry obtained in the step (1) to carry out electrolytic oxidation for 1.0h.
(3) After the reaction, the mixture obtained in the step (2) is centrifuged at a high speed, unreacted residues are filtered out, the obtained filtrate is put into a dialysis bag with the molecular weight cut-off of 3500Da, and the dialysis is carried out for 3 days, and water is changed every 12 hours.
(4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying, wherein the quantum yield of the carbon quantum dots is 0.91%.
Example 6
(1) And (3) selecting Jincheng anthracite as a raw material, crushing the raw material to more than 100 meshes, and uniformly dispersing the coal powder into salty salt lake water with the chloride ion concentration of 3mol/L by stirring to prepare the coal water slurry with the concentration of 30g/L.
(2) Graphite flake is used as anode and cathode materials respectively, and the current density is 2.0A/cm 2 And (3) electrifying the coal water slurry obtained in the step (1) to carry out electrolytic oxidation for 10h.
(3) After the reaction, the mixture obtained in the step (2) is centrifuged at a high speed, unreacted residues are filtered out, the obtained filtrate is put into a dialysis bag with the molecular weight cut-off of 3500Da, and the dialysis is carried out for 3 days, and water is changed every 12 hours.
(4) Concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying, wherein the quantum yield of the carbon quantum dots is 0.95%.
Claims (5)
1. The preparation method of the carbon quantum dot is characterized in that coal water slurry containing chloride ions with a certain molar concentration is used as electrolyte, graphite sheets are respectively used as an anode and a cathode, and the coal water slurry is electrified for electrolysis; after the reaction is finished, centrifugally separating the obtained mixture at a high speed, filtering supernatant obtained by centrifugal separation, putting obtained filtrate into a dialysis bag with the molecular weight cut-off of 3500Da, dialyzing for 3 days, changing water every 12 hours, concentrating the solution in the dialysis bag through reduced pressure distillation, and then obtaining the solid carbon quantum dots through freeze drying;
the molar concentration of chloride ions in the coal water slurry is 0.1mol/L to 3mol/L;
in the coal water slurry, the mass concentration of coal powder is 2g/L to 30g/L.
2. The method for preparing carbon quantum dots according to claim 1, wherein the raw materials for preparing the coal water slurry are coal and an aqueous solution containing chloride ions, and the coal water slurry is prepared by crushing coal into pulverized coal and then uniformly dispersing the pulverized coal into the aqueous solution containing chloride ions.
3. The method for preparing carbon quantum dots according to claim 1, wherein the current density is 0.1A/cm during the electrolytic oxidation reaction 2 To 2A/cm 2 The electrolysis time is 0.5h to 10h.
4. The method for producing carbon quantum dots according to any one of claims 1 to 3, wherein the raw coal for producing the coal water slurry is any one of lignite, subbituminous coal, bituminous coal and anthracite coal, and is pulverized to 100 mesh or more before use.
5. The method for preparing carbon quantum dots according to any one of claim 2, wherein the aqueous solution containing chloride ions is seawater, salt lake water or industrial wastewater containing chloride ions.
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