A method for preparing fluorescent carbon dots by hydraulic cavitation stripping of coal gasification slag

Abstract

The invention discloses a method for preparing fluorescent carbon dots by hydraulic cavitation stripping of coal gasification slag, wherein the coal gasification slag is added to a solvent to prepare a gasification slag solution, and then pumped into a hydraulic cavitation element at a flow rate of 0.5 to 5000 L / h, the cavitation pressure is controlled to be 0.1 to 50 MPa, the temperature does not exceed 50°C, and the process is circulated for 90 to 210 minutes to obtain a gasification slag dispersion; then filtered through filter paper and centrifuged, and the supernatant is dried. The invention proposes and successfully adopts hydraulic cavitation stripping of residual carbon in coal gasification slag to prepare fluorescent carbon dots for the first time, which not only avoids the dissolution of silicon-aluminum minerals by strong acids and strong alkalis in chemical oxidation methods, but also avoids the requirements of other "top-down" methods for high-purity block carbon sources, providing a new idea for realizing the scientific and resource utilization of coal gasification slag, and reducing the pressure on the ecological environment. The method of the invention has simple equipment, low cost, short time consumption, and environmentally friendly preparation process, and is also easy to scale up to achieve large-scale industrial production, with good adaptability and application prospects.

Description

Technical Field

[0001] The invention relates to a method for preparing fluorescent carbon dots by hydraulic cavitation stripping of coal gasification slag. Background Art

[0002] Coal gasification is one of the core contents of my country's clean coal utilization. Using coal chemical technology to convert coal into gas, oil and other energy forms can not only control coal-burning pollution at the source, but more importantly, it can provide a certain strategic guarantee for my country's "poor oil and little gas" energy endowment. Therefore, in recent years, my country has successively established a number of large-scale modern coal chemical bases in the coal-rich western regions, and with the increase in production capacity, the scale has initially emerged.

[0003] During the coal gasification process, the associated minerals and residual carbon particles (residual carbon) in the coal will form coal gasification slag through complex physical and chemical changes. The coal gasification slag contains rich inorganic minerals such as SiO2, Al2O3, Fe2O3, CaO and some residual carbon, showing a structure in which amorphous silicate and porous residual carbon are interlocked. Due to the high content of residual carbon, the gasification slag cannot meet the requirements of the loss on burn of raw materials for construction materials, and cannot even be used for paving. At the same time, due to the structural characteristics of fusion, coating and adhesion of carbon and ash and the high water content, there are serious constraints between the components during the mixing and other high-value utilization of circulating fluidized bed. Therefore, the current effective utilization of gasification slag is not high, and it is mainly landfilled, causing surface dust, water and heavy metal pollution, and seriously affecting the geological and ecological environment. And with the continuous promotion of gasification technology, the output of gasification slag has also increased significantly. Therefore, how to scientifically utilize and turn waste into treasure has become a national and people's livelihood issue that needs to be solved urgently.

[0004] At present, the research on resource utilization of coal gasification slag mainly includes: 1) construction materials: such as replacing river sand as aggregate, concrete, sintered bricks, wall materials, etc., which is the most direct way of large-scale consumption; 2) soil and water: such as soil improvement, ecological fertilizer, water body remediation, etc.; 3) residual carbon utilization: such as fluidized bed co-combustion, catalytic graphitization, etc.; 4) high added value utilization, such as preparation of molecular sieves, catalysts, polymer fillers, etc., but there are no reports on using it as a raw material for the preparation of carbon quantum dots.

[0005] Carbon Quantum Dots (CQDs), also known as carbon dots or carbon nanodots, are a type of zero-dimensional carbon nanomaterials with significant fluorescent properties. They have the characteristics of high fluorescence quantum yield, stable optical and chemical properties, adjustable luminescent color, and excellent photoelectric properties. Therefore, they are expected to replace highly toxic heavy metal semiconductor quantum dots such as tin and cadmium, become high-end fluorescent nanomaterials, and have broad prospects for application in many fields such as optoelectronic devices, optical communications, display technology, energy conversion, photocatalysis, and photoelectric sensors.

[0006] When carbon dots are prepared from coal gasification slag as raw material, the structural morphology of amorphous silicate and porous residual carbon interlocking determines that only a "top-down" etching or stripping method can be used. The commonly used etching or stripping methods currently include chemical corrosion, arc discharge, laser ablation, electrochemical stripping, etc. These methods generally require the carbon source to be in a high-purity block, and the etching process requires the addition of strong oxidizing agents such as strong acids and strong alkalis or the use of other etching equipment. Not only are the operations complicated and expensive, but they may also cause the dissolution of the silicon and aluminum components in the gasification slag, increasing the difficulty of subsequent processing, and are not suitable for the preparation of carbon dots from coal gasification slag. Therefore, combined with the structural characteristics of residual carbon in coal gasification slag, the development of a green, low-cost, and large-scale etching method has become an urgent problem to be solved. Summary of the invention

[0007] In view of the above problems and in order to achieve the above objectives, the present invention provides a method for preparing fluorescent carbon dots by stripping coal gasification slag with hydraulic cavitation, which utilizes the mechanical action and hot spot effect formed by the collapse and explosion of hydraulic cavitation bubbles to strip the residual carbon in the coal gasification slag to prepare fluorescent carbon dots, which not only avoids the dissolution of silicon-aluminum minerals by strong acids and alkalis, but also achieves the objectives of simple operation, low energy consumption, high flux and efficiency, and clean, green and pollution-free. The specific technical scheme is as follows:

[0008] First, the present invention provides a method for preparing fluorescent carbon dots by hydraulic cavitation stripping of coal gasification slag, comprising the following steps:

[0009] 1) Weigh a certain amount of coal gasification slag and add it to the solvent, stir it thoroughly to obtain a gasification slag solution;

[0010] 2) The prepared gasified slag solution is pumped into the hydraulic cavitation element at a flow rate of 0.5 to 5000 L / h, the cavitation pressure is controlled to be 0.1 to 50 MPa, the cavitation temperature does not exceed 50°C, and the circulated treatment is performed for 90 to 210 minutes to obtain a gasified slag dispersion;

[0011] 3) Collect the gasified slag dispersion after cavitation, filter it through filter paper, centrifuge it at 5000-10000 rpm for 10-30 min, take the supernatant, and dry it to obtain fluorescent carbon dots.

[0012] As a preferred technical solution, in step 1), the solvent is water or ethanol or a mixture of both.

[0013] Further preferably, the solvent is a mixture of water and ethanol, and the volume ratio of the mixture is ethanol:water=1:19.

[0014] As a preferred technical solution, in step 1), the concentration of the gasified slag solution is 1 to 200 g / L.

[0015] Further preferably, the concentration of the gasified slag solution is 50-100 g / L.

[0016] As a preferred technical solution, in step 2), the hydrodynamic cavitation element is an orifice plate, a nozzle, a venturi tube, a vortex diode or a rotating jet cavitator.

[0017] Further preferably, the opening size of the hydrodynamic cavitation element is 0.01-100 mm.

[0018] As a preferred technical solution, in step 2), the flow rate of the gasified slag solution pumped into the hydraulic cavitation element is 30 to 2000 L / h, the cavitation pressure is controlled to be 0.1 to 30 MPa, the cavitation temperature is 5 to 45° C., and the cavitation cycle time is 120 to 180 min.

[0019] As a preferred technical solution, in step 3), the filter paper filtration is carried out by sequentially filtering with three types of filter papers of quantitative fast, medium and slow speeds with a diameter of 12 cm; the centrifugal speed is 5000-10000 rpm, and the centrifugal time is 10-30 min.

[0020] As a preferred technical solution, in step 3), the drying is vacuum drying at a temperature of 40 to 50° C. for a time of 6 to 18 hours.

[0021] The principle of preparing fluorescent carbon dots by stripping the residual carbon in the hydraulic cavitation of coal gasification slag is: cavitation refers to the whole process of the initiation, growth and collapse of cavitation bubbles in liquid as the flow velocity and flow state change. Hydraulic cavitation mainly utilizes the mechanical action and hot spot effect formed at the moment of cavitation collapse and explosion. The present invention utilizes the mechanical action formed when the hydraulic cavitation cavitation bubble collapses, such as micro jets, shock waves, etc., to effectively cut the residual carbon and form fluorescent carbon dots.

[0022] The beneficial effects of the present invention are:

[0023] 1) This invention proposes for the first time to prepare fluorescent carbon dots using coal gasification slag as raw material, which provides a new idea for the scientific and resourceful utilization of coal gasification slag and reduces the pressure on the ecological environment.

[0024] 2) Based on the structural characteristics of the interlocking of amorphous aluminosilicates and porous residual carbon in coal gasification slag, the present invention proposes for the first time the method of hydraulic cavitation stripping, which not only avoids the dissolution of aluminosilicate minerals by strong acids and alkalis in the chemical oxidation method, but also avoids the requirement of other "top-down" methods for high-purity block carbon sources. It is a practical method for preparing fluorescent carbon dots by stripping gasification slag.

[0025] 3) The present invention adopts hydraulic cavitation exfoliation to prepare fluorescent carbon dots, which not only has simple equipment, low cost and short time consumption, but also has an environmentally friendly preparation process and is also easy to scale up to achieve large-scale industrial production.

[0026] 4) The fluorescent carbon dots prepared by the present invention have good dispersibility and a carbon dot size distribution between 1 and 15 nanometers. They emit obvious blue fluorescence under 320 nanometer light with a wavelength of 440 to 480 nanometers, have good photoelectric properties, and have good development prospects.

[0027] 5) The hydraulic cavitation etching stripping method proposed in the present invention is not only applicable to coal gasification slag but also applicable to the preparation of carbon dots from other carbonaceous materials, and has good adaptability and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the device for preparing fluorescent carbon dots by hydraulic cavitation stripping of coal gasification slag according to the present invention

[0029] Figure 2 This is a transmission electron microscope photo of fluorescent carbon dots prepared by hydraulic cavitation stripping of coal gasification slag in the present invention;

[0030] Figure 3 The fluorescence curves of the fluorescent carbon dots prepared by hydraulic cavitation stripping of coal gasification slag under different excitation light wavelengths of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments and drawings.

[0032] The present invention is to prepare fluorescent carbon dots by stripping the residual carbon in the hydraulic cavitation of coal gasification slag. Cavitation refers to the whole process of the initiation, growth and collapse of cavitation bubbles in liquid as the flow velocity and flow state change. Hydraulic cavitation mainly utilizes the mechanical action and hot spot effect formed at the moment of cavitation collapse and explosion. The present invention utilizes the mechanical action formed when the cavitation bubble collapses in hydraulic cavitation, such as micro jets, shock waves, etc., which can effectively cut the residual carbon and form fluorescent carbon dots.

[0033] To achieve the above purpose, the present invention makes a hydraulic cavitation device, the structure of which is as follows Figure 1 As shown, it includes a liquid storage tank, valve 1, a circulation pump, valve 2, and a hydraulic cavitation element. These components are connected in series through pipelines to form a closed loop, and the liquid in the liquid storage tank can circulate in the loop through the circulation pump. The cavitation element is a venturi tube, an orifice plate, a nozzle, an eddy current diode or a rotating jet cavitator, etc., and the opening size is 0.01 to 100 mm. The gasification slag is prepared into a gasification slag solution, which is injected into the liquid storage tank and pumped into the hydraulic cavitation element under the action of the circulation pump, and circulates in the loop.

[0034] The specific preparation method is as follows:

[0035] Example 1

[0036] 1) First, put 300g of coal gasification slag into a 2L container, add deionized water, stir thoroughly, and obtain a dispersion of gasification slag. Considering that the opening size of the hydraulic cavitation element is 0.01-100mm, the coal gasification slag used is powdered gasification fine slag, and its particle size is smaller than the opening size of the hydraulic cavitation element; if gasification coarse slag is used, or if there are larger particles, pretreatment is required to avoid clogging of the hydraulic cavitation element and affect the operation of the system. The role of the solvent is the working fluid, which forms a suspension of coal gasification slag and circulates in the system under the action of the circulating pump. Therefore, in general, deionized water can be used as the solvent, and some ethanol can also be appropriately added to dissolve the residual organic components in the gasification slag to ensure the effective stripping of carbon dots and optimize the purity of the stripped carbon dots. The concentration of the coal gasification slag solution affects the efficiency of preparing carbon dots. The higher the concentration, the faster the preparation. However, too high a concentration will affect the flow rate and even block the papermaking cavitation element. Therefore, the concentration of the coal gasification slag solution can be controlled to 1-200 g / L, preferably 50-100 g / L.

[0037] 2) Control the temperature below 50°C, use a pump to deliver the gasified slag dispersion into the venturi tube at a flow rate of 120L / h, maintain the cavitation pressure at 0.2Mpa, and circulate for 120min. The pressure of the system in the present invention is the prerequisite for ensuring the cavitation effect. Depending on the equipment, the required cavitation pressure is also different. The pressure range is controlled to 0.1-30Mpa to ensure the occurrence of cavitation; in addition, it should be noted that if the pressure is too high, the pipeline is prone to dripping; if the pressure is too low, cavitation cannot occur. For the flow rate of the system, the present invention has no specific requirements. Under the condition of maintaining the pressure required for cavitation, the greater the flow rate, the higher the efficiency of preparing carbon slag. Generally, the flow rate can be controlled to be 30-2000L / h. Hydraulic cavitation is not greatly affected by temperature, and it can be below 50°C, preferably 5-45°C. It is generally selected at room temperature for easy operation. The cavitation cycle time is another important parameter for the preparation of carbon dots, which is related to the solution concentration and flow rate. Generally, the desired fluorescent carbon dots can be prepared by controlling the cavitation cycle time to 120 to 180 minutes.

[0038] 3) Collect the dispersion obtained after cyclic cavitation, filter it with quantitative fast, medium and slow filter papers in turn, centrifuge it at 6000rpm for 15min, take the upper clear liquid, which is the carbon dot solution; take 100ml of the carbon dot solution, vacuum dry it at 50℃ for 10h, and solid carbon dots, i.e. fluorescent carbon dots, can be obtained.

[0039] The size and morphology of the solid fluorescent carbon dots prepared in this way were observed by transmission electron microscopy. Figure 2 As shown, the size distribution is between 1 and 10 nanometers, with an average size of 5.1 nanometers; and the fluorescence spectrum of the solid fluorescent carbon dots prepared in this embodiment is detected by different excitation light wavelengths, such as Figure 3As shown, it emits obvious blue fluorescence with a wavelength of 460 nanometers under 320 nanometer light excitation. This shows that the method of the present invention successfully uses hydraulic cavitation to etch coal gasification slag to obtain fluorescent carbon dots with application value.

[0040] Example 2

[0041] 1) First, put 100g of coal gasification crude slag into a 1L container, add 50ml of ethanol and 950ml of deionized water in sequence, and stir well to obtain a gasification slag dispersion;

[0042] 2) At room temperature, use a pump to deliver the gasified slag dispersion into the orifice plate cavitation device at a flow rate of 30L / h, maintain the cavitation pressure at 0.3Mpa, and circulate for 180min;

[0043] 3) Collect the dispersion obtained after cyclic cavitation, filter it with quantitative fast, medium and slow filter papers in turn, centrifuge it at 8000 rpm for 15 min, take the upper clear liquid, which is the carbon dot solution; take 100 ml of the carbon dot solution and vacuum dry it at 50°C for 10 h to obtain solid fluorescent carbon dots.

[0044] The solid fluorescent carbon dots prepared in this embodiment were observed by transmission electron microscopy, and their size distribution was between 2 and 11 nanometers, with an average size of 5.3 nanometers. The fluorescence spectrum of the solid fluorescent carbon dots was detected by different excitation light wavelengths, and under the excitation of 320 nanometers light, they emitted obvious blue fluorescence with a wavelength of 452 nanometers.

[0045] Example 3

[0046] 1) First, put 50g of coal gasification crude slag into a 1L container, add ethanol, and stir thoroughly to obtain a gasification slag dispersion;

[0047] 2) At room temperature, use a pump to deliver the gasified slag dispersion into the eddy current diode at a flow rate of 200L / h, maintain the cavitation pressure at 2Mpa, and circulate for 150min;

[0048] 3) Collect the dispersion obtained after cyclic cavitation, filter it with quantitative fast, medium and slow filter papers in turn, centrifuge it at 10,000 rpm for 30 min, take the supernatant, which is the carbon dot solution; take 100 ml of the carbon dot solution and vacuum dry it at 50°C for 10 h to obtain solid fluorescent carbon dots.

[0049] The solid fluorescent carbon dots prepared in this embodiment were observed by transmission electron microscopy, and their size distribution was between 1 and 8 nanometers, with an average size of 4.5 nanometers. The fluorescence spectrum of the solid fluorescent carbon dots was detected by different excitation light wavelengths, and under the excitation of 320 nanometers light, they emitted obvious blue fluorescence with a wavelength of 455 nanometers.

[0050] In general, based on the structural characteristics of the interlocking amorphous aluminosilicates and porous residual carbon in coal gasification slag, the present invention proposes and realizes for the first time the use of coal gasification slag as raw material and the use of hydraulic cavitation to strip the residual carbon thereon to prepare fluorescent carbon dots, which provides a new idea for the scientific and resourceful utilization of coal gasification slag and reduces the pressure on the ecological environment.

[0051] The present invention adopts the method of hydraulic cavitation stripping, which not only avoids the dissolution of silicon-aluminum minerals by strong acids and strong bases in the chemical oxidation method, but also avoids the requirement of other "top-down" methods for high-purity block carbon sources. The results show that it is a practical method for preparing fluorescent carbon dots by stripping gasified slag.

[0052] In addition, the present invention adopts hydraulic cavitation exfoliation to prepare carbon dots, which has simple equipment, low cost, short time consumption, and environmentally friendly preparation process. It is also easy to scale up and realize large-scale industrial production.

[0053] The present invention discloses that hydraulic cavitation shows great application potential in the field of preparing carbon dots by stripping gasified slag. It is not only applicable to gasified slag but also to preparing fluorescent carbon dots from other carbonaceous materials, and has good adaptability and application prospects.

[0054] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view. In addition, it should be understood that although this specification is described in accordance with the implementation mode, it does not include only one technical solution. This narrative mode of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing fluorescent carbon dots by hydraulic cavitation stripping of coal gasification slag, characterized in that: The steps include: 1) Weigh a certain amount of coal gasification slag and add it to the solvent, stir it thoroughly to obtain a gasification slag solution; 2) Pumping the prepared gasified slag solution into the hydraulic cavitation element at a flow rate of 30 to 2000 L / h, controlling the cavitation pressure to 0.1 to 50 MPa, and circulating the solution for 90 to 210 min to obtain a gasified slag dispersion; 3) Collect the gasified slag dispersion after cavitation, filter it through filter paper, centrifuge it at 5000-10000 rpm for 10-30 min, take the supernatant, and dry it to obtain fluorescent carbon dots with a size distribution between 1 and 15 nanometers.

2. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 1, characterized in that: In step 1), the solvent is water or ethanol or a mixture of both.

3. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 2, characterized in that: The solvent is a mixture of water and ethanol, and the volume ratio of the mixture is ethanol:water=1:

19.

4. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 1, characterized in that: In step 1), the concentration of the gasified slag solution is 1-200 g / L.

5. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 4, characterized in that: The concentration of the gasified slag solution is 50-100 g / L.

6. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 1, characterized in that: In step 2), the hydrodynamic cavitation element is an orifice plate, a nozzle, a venturi tube, a vortex diode or a rotating jet cavitator.

7. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 6, characterized in that: The opening size of the hydrodynamic cavitation element is 0.01-100 mm.

8. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 1, characterized in that: In step 2), the cavitation pressure of the gasified slag solution pumped into the hydraulic cavitation element is controlled to be 0.1-30 MPa, the cavitation temperature is 5-45° C., and the cavitation cycle time is 120-180 min.

9. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 1, characterized in that: In step 3), the filter paper filtration is carried out by using filter papers with quantitative fast, medium and slow speeds in sequence; the centrifugal speed is 5000-10000 rpm, and the centrifugal time is 10-30 min; the drying is vacuum drying at a temperature of 40-50° C. and a time of 6-18 h.

10. The method for preparing fluorescent carbon dots by hydrodynamic cavitation stripping of coal gasification slag according to claim 1, characterized in that: In step 3), the fluorescent carbon dots emit blue fluorescence under 320 nanometer light, with a wavelength between 440 and 480 nanometers.

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