A method for preparing carbon quantum dots by using oily sludge

Abstract

This invention relates to the field of harmless treatment technology for oily sludge, specifically to a method for preparing carbon quantum dots from oily sludge. Conventional methods for preparing carbon quantum dots from oily sludge have limitations in yield and fluorescence intensity. To address these issues, this invention provides a method for preparing carbon quantum dots from oily sludge. Considering the complex composition of oily sludge, this invention designs a multi-stage purification process chain of "ultrasonic extraction—water washing—Soxhlet extraction—acidification treatment." Each step works synergistically, purifying the sludge step by step to ultimately obtain a high-purity refined organic carbon source. The refined organic carbon source removes impurities through gentle solvent extraction and acid washing, maximizing the preservation of the organic carbon source's chemical activity and structural integrity. In the hydrothermal reaction, it can be effectively converted into carbon quantum dots, avoiding carbon source loss or activity reduction due to over-processing, thus further improving the yield and fluorescence intensity of carbon quantum dots.

Description

Technical Field

[0001] This invention relates to the field of harmless treatment technology for oily sludge, specifically to a method for preparing carbon quantum dots using oily sludge. Background Technology

[0002] Oilfield sludge is one of the main solid wastes generated during the petroleum industry's production process, primarily originating from oilfield extraction, oil and gas gathering and transportation, and wastewater treatment. Its composition is complex, typically including 20%-40% crude oil, 30%-50% inorganic mineral matrix such as clay and silt, 10%-20% aqueous impurities, and small amounts of heavy metal ions, colloids, and asphaltenes. With the rapid development of my country's petroleum industry, the annual production of oilfield sludge is enormous, posing a significant environmental hazard.

[0003] Currently, the main treatment methods for oily sludge both domestically and internationally are harmless disposal, with common methods including landfill, incineration, and solidification / stabilization. However, these traditional methods all have certain limitations and environmental risks. For example, landfill disposal not only occupies a large amount of land resources, but the crude oil and other organic matter may also leak under long-term natural conditions, causing serious secondary pollution to the surrounding soil and groundwater. Incineration can effectively reduce volume and destroy organic matter, but it easily releases volatile organic compounds (VOCs), sulfides, nitrogen oxides, and dioxins, causing air pollution problems, and it also consumes a lot of energy. Solidification / stabilization involves adding solidifying agents to coat or fix the harmful substances in the sludge, but the added value of the treated products is extremely low, usually only suitable for use as low-grade building materials or direct stockpiling, still posing long-term environmental risks and failing to achieve the resource utilization of hazardous waste.

[0004] It is evident that existing oily sludge treatment technologies generally suffer from common problems such as low resource recovery rates, high treatment costs, and significant risks of secondary pollution. Developing a green, efficient method that enables the high-value conversion of oily sludge into valuable resources has become a pressing technical challenge in this field.

[0005] Carbon quantum dots, as a novel zero-dimensional carbon nanomaterial, have shown broad application prospects in fields such as bioimaging, sensing and detection, drug delivery, and optoelectronic devices due to their excellent photoluminescence properties, good biocompatibility, low toxicity, and ease of surface functionalization. Traditional raw materials for carbon quantum dot preparation are mostly small organic molecules, biomass, or polymers, which are relatively expensive. If carbon quantum dots could be prepared using inexpensive and abundant industrial waste such as oily sludge, it would not only enable the resource utilization of hazardous waste, turning waste into treasure, but also provide a new low-cost route for carbon quantum dot preparation, with significant environmental and economic benefits.

[0006] Currently, there are reports on technologies for preparing carbon quantum dots using organic solid waste. For example, Chinese invention patent CN115872393A discloses a method and system for preparing high-value-added carbon quantum dots using organic solid waste as a carbon source. This patent employs a two-step process: first, the organic solid waste undergoes partial oxidative decomposition treatment, breaking down large organic molecules into water-soluble small organic molecules; then, solid residue is removed by filtration; and finally, the filtrate, after adding chemical additives, undergoes a hydrothermal synthesis reaction to ultimately obtain carbon quantum dots. This method provides a feasible technical approach for the resource utilization of organic solid waste, with advantages such as relatively high conversion rate, fewer by-products, and clean and environmentally friendly production.

[0007] However, analysis revealed that the technical solution described in CN115872393A still has the following shortcomings when applied to complex organic solid wastes such as oily sludge: (1) Insufficient raw material adaptability and lack of pretreatment processes tailored to the characteristics of oily sludge. CN115872393A uses grinding and pulverization as the sole pretreatment method, followed by direct partial oxidation and decomposition. Oily sludge contains a large amount of viscous components such as heavy crude oil, colloids, and asphaltenes. These components are difficult to disperse effectively during grinding and will coat inorganic particles, hindering the full contact between the oxidant and organic matter. This patent does not include an extraction and removal step for heavy oil, resulting in reduced efficiency of the subsequent partial oxidation and decomposition reaction, limited conversion rate of organic carbon sources, and ultimately affecting the yield and quality of carbon quantum dots.

[0008] (2) Insufficient removal of inorganic impurities affects the fluorescence performance of carbon quantum dots. Oily sludge is rich in inorganic mineral matrices such as clay and silt (accounting for 30%-50%). CN115872393A removes solid residues through only two-stage filtration (mechanical pressure filtration + membrane filtration), but for inorganic fine particles that are tightly bound to organic matter, it is difficult to achieve complete separation by filtration alone. These residual inorganic impurities may act as impurity nuclei to induce nonradiative recombination during hydrothermal synthesis, or interfere with the ordered nucleation and growth of carbon quantum dots, resulting in increased surface defects and reduced fluorescence quantum yield of the prepared carbon quantum dots.

[0009] (3) Residual heavy metal ions cause fluorescence quenching. Oily sludge commonly contains heavy metal ions such as iron, nickel, vanadium, and copper. These metal ions are paramagnetic or can act as electron acceptors. The technical solution of CN115872393A does not include a dedicated heavy metal removal process. Although partial oxidation and decomposition treatment can allow some metal ions to enter the liquid phase, the residual metal ions are very likely to interact with the functional groups on the surface of carbon quantum dots during the subsequent hydrothermal synthesis process, which will have a significant quenching effect on fluorescence emission and severely restrict the improvement of the fluorescence intensity of carbon quantum dots.

[0010] (4) Insufficient purification of carbon source limits the structural regularity of carbon quantum dots. This patent converts organic solid waste into water-soluble small molecule organic matter through partial oxidation decomposition, but does not further purify the carbon source. The colloids and asphaltenes in oily sludge may produce complex intermediate products after oxidation decomposition. These products are mixed with the target carbon source, resulting in an unsatisfactory nucleation and growth environment for carbon quantum dots during hydrothermal synthesis. The structural regularity of the carbon nucleus and the uniformity of surface functional groups are difficult to guarantee, thus limiting the fluorescence performance of carbon quantum dots.

[0011] In summary, while the technical solution disclosed in CN115872393A provides a valuable exploration for the preparation of carbon quantum dots from organic solid waste, its lack of a specific removal process for characteristic pollutants such as heavy oil, inorganic mineral matrix, and heavy metal ions in oily sludge results in insufficient carbon source purity and significant impurity interference, thus requiring further improvement in the fluorescence intensity of the prepared carbon quantum dots. Therefore, developing a method that can effectively remove multiple impurities from oily sludge, obtain a high-purity refined organic carbon source, and thus prepare high-fluorescence-intensity carbon quantum dots has significant technical value and practical implications.

[0012] Based on this, the present invention provides a method for preparing carbon quantum dots using oily sludge. The method removes complex components such as heavy crude oil, colloids and asphaltenes through ultrasonic extraction, and combines multi-stage purification processes such as water washing, Soxhlet extraction and acidification treatment to effectively remove impurities such as organic pollutants, inorganic mineral matrix and heavy metal ions from oily sludge, thereby obtaining a high-purity refined organic carbon source. Then, carbon quantum dots with excellent fluorescence properties are prepared through hydrothermal reaction. This method overcomes the shortcomings of the prior art and realizes efficient deoiling, purification and high-value-added conversion of oily sludge. Summary of the Invention

[0013] A problem with existing technologies is that the yield and fluorescence intensity of carbon quantum dots prepared from oily sludge using conventional methods need further improvement. To address these issues, this invention provides a method for preparing carbon quantum dots from oily sludge, comprising the following preparation steps: (1) Pretreatment: The oily sludge is mixed with the first organic solvent and ultrasonically extracted. The lower solid phase sediment is collected to remove most of the heavy crude oil, gum and asphalt. (2) Deoiling and purification: The solid phase sediment obtained in step (1) was washed with water, dried and then subjected to Soxhlet extraction with a second organic solvent to obtain deoiled solid phase sediment; (3) Acidification treatment: After grinding the deoiled solid phase deposit obtained in step (2), it is mixed with acid solution to carry out acidification reaction. After the reaction is completed, the solid and liquid are separated, and the obtained solid is washed and dried to obtain a refined organic carbon source. (4) Hydrothermal reaction: The refined organic carbon source obtained in step (3) is mixed with deionized water, dispersed evenly, and placed in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, the mixture is cooled. (5) Separation and purification: Centrifuge and filter the reaction solution obtained in step (4), collect the filtrate, dialyze the filtrate to obtain an aqueous solution of carbon quantum dots; (6) Drying: The aqueous solution of carbon quantum dots obtained in step (5) is dried to obtain carbon quantum dots.

[0014] Preferably, in step (1), the first organic solvent is toluene, o-xylene, or diesel oil; the ultrasonic extraction is performed 1-3 times, with each extraction lasting 20-40 minutes; the solid-liquid separation is centrifugal separation, with a centrifugation speed of 8000-10000 rpm and a centrifugation time of 15-30 minutes.

[0015] Preferably, in step (2), the water washing is performed by washing with deionized water 2-4 times; the drying is performed by vacuum drying at 50-70℃ for 6-10 hours.

[0016] Preferably, in step (2), the second organic solvent is petroleum ether or n-hexane; the Soxhlet extraction conditions are: extraction at a water bath temperature of 60-80℃ for 10-14h.

[0017] Preferably, in step (3), the grinding is passed through a 60-100 mesh standard sieve; the acid solution is nitric acid or hydrochloric acid with a concentration of 0.5-1 mol / L; in the acidification reaction, the solid-liquid ratio of the deoiled solid phase deposit to the acid solution is 1 g: 20-30 mL, the reaction temperature is 70-85℃, and the reaction time is 1-2 h.

[0018] Preferably, in step (3), the solid-liquid separation is performed by vacuum filtration using a 0.2-0.45 μm filter membrane; the washing is performed by first washing with deionized water until the filtrate is neutral, and then washing with ethanol; the drying is performed by vacuum drying at 50-70°C to constant weight.

[0019] Preferably, in step (4), the ratio of the amount of refined organic carbon source to deionized water is 0.5-1g:50-75mL; the temperature of the hydrothermal reaction is 170-200℃ and the time is 10-15h.

[0020] Preferably, in step (5), the centrifugation speed is 8000-10000 rpm and the centrifugation time is 10-20 min; the filtration is performed using a 0.2-0.45 μm filter membrane; the dialysis bag used for dialysis has a molecular weight cutoff of 1000-4000 Da, the dialysis time is 36-60 h, and the dialysis fluid is replaced 2-4 times during the period.

[0021] Preferably, in step (6), the drying is freeze drying, the freeze drying temperature is -50℃ to -70℃, and the time is 36-60h. Beneficial effects

[0022] (1) This invention addresses the complex composition of oily sludge by designing a multi-stage purification process chain of "ultrasonic extraction—water washing—Soxhlet extraction—acidification treatment." First, ultrasonic extraction utilizes the selective dissolution effect of organic solvents to effectively remove heavy crude oil, colloids, and asphaltenes coated on the surface of inorganic particles in the oily sludge, avoiding interference from these viscous components in subsequent processing. Based on this, water washing is used sequentially to remove water-soluble impurities, Soxhlet extraction further removes residual organic pollutants, and finally, acidification treatment dissolves and removes inorganic mineral matrix and heavy metal ions. Each step works synergistically to purify the sludge step by step, ultimately obtaining a high-purity refined organic carbon source. In contrast, existing technologies (such as CN115872393A) rely solely on grinding and simple filtration, which is insufficient for the efficient removal of complex impurities from oily sludge. The multi-stage purification process of this invention is more targeted and effective.

[0023] (2) Residual inorganic mineral particles and heavy metal ions in oily sludge are key interfering factors affecting the fluorescence performance of carbon quantum dots. Inorganic particles may become non-radiative recombination centers in the hydrothermal reaction, reducing the fluorescence quantum yield; while heavy metal ions such as iron, nickel, and vanadium may quench the fluorescence emission of carbon quantum dots through electron transfer mechanisms. This invention utilizes an acidification treatment step to effectively dissolve and separate these impurities through the chemical reaction between acid and inorganic substances and metal ions, eliminating the adverse effects of these two types of impurities on the fluorescence performance of carbon quantum dots at the source. At the same time, high-purity organic carbon sources can form carbon nuclei with regular structures and few surface defects in the hydrothermal reaction, further ensuring the fluorescence performance of carbon quantum dots.

[0024] (3) In the purification process, this invention does not employ high-temperature carbonization or strong oxidation treatment. Instead, it removes impurities through gentle solvent extraction and acid washing, preserving the chemical activity and structural integrity of the organic carbon source to the greatest extent. These refined organic carbon sources can be effectively converted into carbon quantum dots in hydrothermal reactions, avoiding carbon source loss or activity reduction due to over-treatment. Compared with traditional oily sludge treatment methods (landfill, incineration, solidification and stabilization), this invention transforms low-value or even negative-value hazardous waste into carbon quantum dot functional materials with good fluorescence properties, realizing the transformation of oily sludge from "end-of-life disposal" to "high-value utilization," and significantly improving the added value of resource utilization.

[0025] (4) The operating conditions of each step in this invention have been optimized, such as the number and time of ultrasonic extraction, the solvent and temperature of Soxhlet extraction, and the concentration and solid-liquid ratio of the acid solution for acidification, all of which are controlled within a suitable range. The overall process does not involve harsh conditions such as high temperature and high pressure (except for hydrothermal reaction, but this step is a necessary step in the synthesis of carbon quantum dots), and the operation is safe and controllable, making it easy to achieve industrial scale-up. At the same time, the organic solvents used (toluene, petroleum ether, etc.) can be recovered and recycled through distillation, and the amount of acid discharged after neutralization is small, making the overall process environmentally friendly.

[0026] (5) In summary, the present invention effectively solves the technical problem of interference from multiple impurities such as heavy oil, inorganic minerals and heavy metal ions in oily sludge through a multi-stage purification process. The carbon quantum dots prepared have high purity and excellent fluorescence performance, providing a practical new way for the high-value resource utilization of oily sludge. Attached Figure Description

[0027] Figure 1 SEM image of the carbon quantum dots obtained in Example 1.

[0028] Figure 2 Fluorescence emission spectrum of carbon quantum dots obtained in Example 1.

[0029] Figure 3 Fluorescence emission spectrum of carbon quantum dots obtained in Example 2.

[0030] Figure 4 Fluorescence emission spectrum of carbon quantum dots obtained in Example 3.

[0031] Figure 5 Fluorescence emission spectrum of carbon quantum dots obtained in Comparative Example 4.

[0032] Figure 6 Fluorescence emission spectrum of carbon quantum dots obtained in Comparative Example 5.

[0033] Figure 7 Fluorescence emission spectrum of carbon quantum dots obtained in Comparative Example 6. Detailed Implementation

[0034] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0035] The dialysis bags used in this invention have all been activated, and the activation method is as follows: Immerse the dialysis bag in 0.5 mol / L hydrochloric acid and heat in a water bath at 50°C for 30 minutes. After removing it, rinse it thoroughly inside and out three times with plenty of deionized water, and then soak it in deionized water for 20 minutes. Example

[0036] (1) Oily sludge pretreatment system: Take 10g of oily sludge from the oilfield, add 150mL of toluene, and extract by ultrasonication for 30min, repeating twice. Then, put the extract into a centrifuge tube and centrifuge at 9000 rpm and room temperature for 20min. Discard the upper toluene-crude oil organic phase (removing most of the heavy crude oil) and collect the lower solid phase sediment. (2) Wash the obtained solid phase sediment three times with deionized water to remove residual toluene. Then, place the washed solid phase sediment under vacuum drying at 60°C for 8 hours. Subsequently, transfer the dried solid phase sediment into the filter paper tube of a Soxhlet extractor, add 200 mL of petroleum ether, and extract by Soxhlet extraction at 60°C under slight boiling conditions for 12 hours to completely remove residual light oil and trace amounts of toluene from the solid phase sediment. (3) Take out the solid sediment after Soxhlet extraction, grind it and pass it through an 80-mesh standard sieve to obtain fine powder; add 1 mol / L nitric acid at a solid-liquid ratio of 1 g: 25 mL, and acidify it by magnetic stirring in a water bath at 75 °C for 1.5 h to obtain an acidified solution; then use a 0.22 μm filter membrane to vacuum filter the acidified solution to obtain a filter cake, wash the filter cake repeatedly with deionized water until the filtrate is neutral, continue to wash the filter cake with ethanol, and then vacuum dry it at 60 °C to constant weight to obtain a refined organic carbon source; (4) Accurately weigh 1g of refined organic carbon source, transfer it to the lining of the hydrothermal reactor, add 75mL of deionized water, ultrasonically disperse to form a uniform and stable suspension, seal and load into the high-pressure reactor. (5) Place the high-pressure reactor into a forced-air drying oven and perform a constant-temperature hydrothermal reaction at 185°C for 13 hours. After the reaction is completed, allow it to cool naturally to room temperature. (6) Take out the reaction solution in the vessel, transfer it to a centrifuge tube, centrifuge at 9000 rpm for 15 min, and collect the supernatant; filter the supernatant through a 0.22 μm filter membrane and collect the filtrate; put the filtrate into a 1500 Da dialysis bag, immerse it in 500 mL of deionized water and dialyze for 48 h, changing the external dialysis solution (deionized water) every 12 h. After dialysis, carbon quantum dot aqueous solution is obtained. (7) Freeze-dry the aqueous solution of carbon quantum dots (temperature -60℃, time 48h), collect the solid powder after freeze-drying, and obtain carbon quantum dots (SEM image as shown in the instruction manual). Figure 1 As shown, the fluorescence emission spectrum is as per the attached instruction manual. Figure 2 (As shown). Example

[0037] (1) Oily sludge pretreatment system: Take 10g of oily sludge from the oilfield, add 100mL of o-xylene, and extract by ultrasonication for 30min, repeating twice. Then, put the extract into a centrifuge tube and centrifuge at 8000 rpm and room temperature for 20min. Discard the upper o-xylene-crude oil organic phase (removing most of the heavy crude oil) and collect the lower solid phase sediment. (2) Wash the obtained solid phase sediment three times with deionized water to remove residual toluene. Then, place the washed solid phase sediment under vacuum drying at 60°C for 6 hours. Subsequently, transfer the dried solid phase sediment into the filter paper tube of a Soxhlet extractor, add 200 mL of n-hexane, and extract it under Soxhlet extraction at 70°C water bath under slight boiling conditions for 10 hours to completely remove residual light oil and trace amounts of o-xylene from the solid phase sediment. (3) Take out the solid sediment after Soxhlet extraction, grind it and pass it through an 80-mesh standard sieve to obtain fine powder; add hydrochloric acid with a concentration of 1 mol / L at a solid-liquid ratio of 1 g: 20 mL, and acidify it by magnetic stirring in a water bath at 80 °C for 1.5 h to obtain an acidified solution; then use a 0.22 μm filter membrane to vacuum filter the acidified solution to obtain a filter cake, wash the filter cake repeatedly with deionized water until the filtrate is neutral, continue to wash the filter cake with ethanol, and then vacuum dry it at 60 °C to constant weight to obtain a refined organic carbon source; (4) Accurately weigh 0.5g of refined organic carbon source, transfer it to the lining of the hydrothermal reactor, add 60mL of deionized water, ultrasonically disperse to form a uniform and stable suspension, seal and load into the high-pressure reactor. (5) Place the high-pressure reactor into a forced-air drying oven and perform a constant-temperature hydrothermal reaction at 185°C for 13 hours. After the reaction is completed, allow it to cool naturally to room temperature. (6) Take out the reaction solution in the vessel, transfer it to a centrifuge tube, centrifuge at 9000 rpm for 15 min, and collect the supernatant; filter the supernatant through a 0.22 μm filter membrane and collect the filtrate; put the filtrate into a pretreated 3500 Da dialysis bag, immerse it in 500 mL of deionized water and dialyze for 48 h, changing the external dialysis solution (deionized water) every 12 h. After dialysis, carbon quantum dot aqueous solution is obtained. (7) Freeze-dry the aqueous solution of carbon quantum dots (temperature -60℃, time 48h), collect the solid powder after freeze-drying, and obtain carbon quantum dots. The fluorescence emission spectrum is shown in the attached instruction manual. Figure 3 As shown. Example

[0038] (1) Oily sludge pretreatment system: Take 10g of oily sludge from the oilfield, add 100mL of diesel oil, and extract by ultrasonication for 30min. Repeat twice. Then, put the extract into a centrifuge tube and centrifuge at 9000 rpm and room temperature for 30min. Discard the upper diesel-crude oil organic phase (removing most of the heavy crude oil) and collect the lower solid phase sediment. (2) Wash the obtained solid phase sediment three times with deionized water to remove residual diesel oil. Then, place the washed solid phase sediment under vacuum drying at 60°C for 8 hours. Subsequently, transfer the dried solid phase sediment into the filter paper tube of a Soxhlet extractor, add 200 mL of n-hexane, and extract it under Soxhlet extraction at 70°C water bath under slight boiling conditions for 12 hours to completely remove residual light oil and trace amounts of diesel oil from the solid phase sediment. (3) Take out the solid sediment after Soxhlet extraction, grind it and pass it through an 80-mesh standard sieve to obtain fine powder; add hydrochloric acid with a concentration of 1 mol / L at a solid-liquid ratio of 1 g: 30 mL, and acidify it by magnetic stirring in a water bath at 80 °C for 1.5 h to obtain an acidified solution; then use a 0.22 μm filter membrane to vacuum filter the acidified solution to obtain a filter cake, wash the filter cake repeatedly with deionized water until the filtrate is neutral, continue to wash the filter cake with ethanol, and then vacuum dry it at 60 °C to constant weight to obtain a refined organic carbon source; (4) Accurately weigh 0.5g of refined organic carbon source, transfer it to the lining of the hydrothermal reactor, add 50mL of deionized water, ultrasonically disperse to form a uniform and stable suspension, seal and load into the high-pressure reactor. (5) Place the high-pressure reactor into a forced-air drying oven and perform a constant-temperature hydrothermal reaction at 185°C for 13 hours. After the reaction is completed, allow it to cool naturally to room temperature. (6) Take out the reaction solution in the vessel, transfer it to a centrifuge tube, centrifuge at 9000 rpm for 15 min, and collect the supernatant; filter the supernatant through a 0.22 μm filter membrane and collect the filtrate; put the filtrate into a pretreated 3500 Da dialysis bag, immerse it in 500 mL of deionized water and dialyze for 48 h, changing the external dialysis solution (deionized water) every 12 h. After dialysis, carbon quantum dot aqueous solution is obtained. (7) Freeze-dry the aqueous solution of carbon quantum dots (temperature -60℃, time 48h), collect the solid powder after freeze-drying, and obtain carbon quantum dots. The fluorescence emission spectrum is shown in the attached instruction manual. Figure 4 As shown.

[0039] Comparative Example 1 is the same as Example 1, except that Comparative Example 1 did not remove heavy crude oil from the oily sludge, but directly performed Soxhlet extraction. The specific steps are as follows: (1) Take 10g of oily sludge from the oilfield and transfer it to the filter paper tube of the Soxhlet extractor. Add 200mL of petroleum ether and extract it in a Soxhlet extractor at 60℃ under a gentle boiling condition for 12h. (2) Take out the solid sediment after Soxhlet extraction, grind it and pass it through an 80-mesh standard sieve to obtain fine powder; add 1 mol / L nitric acid at a solid-liquid ratio of 1 g: 25 mL, and acidify it by magnetic stirring in a water bath at 75 °C for 1.5 h to obtain an acidified solution; then use a 0.22 μm filter membrane to vacuum filter the acidified solution to obtain a filter cake, wash the filter cake repeatedly with deionized water until the filtrate is neutral, continue to wash the filter cake with ethanol, and then vacuum dry it at 60 °C to constant weight to obtain a refined organic carbon source; (3) Accurately weigh 1g of refined organic carbon source, transfer it to the lining of the hydrothermal reactor, add 75mL of deionized water, ultrasonically disperse to form a uniform and stable suspension, seal and load into the high-pressure reactor. (4) Place the high-pressure reactor into a forced-air drying oven and perform a constant-temperature hydrothermal reaction at 185°C for 13 hours. After the reaction is completed, allow it to cool naturally to room temperature. (5) Take out the reaction solution in the vessel, transfer it to a centrifuge tube, centrifuge at 9000 rpm for 15 min, and collect the supernatant; filter the supernatant through a 0.22 μm filter membrane and collect the filtrate; put the filtrate into a 1500 Da dialysis bag, immerse it in 500 mL of deionized water and dialyze for 48 h, changing the external dialysis solution (deionized water) every 12 h. After dialysis, carbon quantum dot aqueous solution is obtained. (6) The aqueous solution of carbon quantum dots was freeze-dried (temperature -60℃, time 48h), and the solid powder was collected after freeze-drying to obtain carbon quantum dots.

[0040] Comparative Example 2 is the same as Example 2, except that Comparative Example 2 did not remove heavy crude oil from the oily sludge, but directly performed Soxhlet extraction. The specific steps are as follows: (1) Take 10g of oily sludge from the oilfield and transfer it to the filter paper tube of the Soxhlet extractor. Add 200mL of n-hexane and extract it in a Soxhlet extractor at 70℃ under a gentle boiling condition for 10h. (2) Take out the solid sediment after Soxhlet extraction, grind it and pass it through an 80-mesh standard sieve to obtain fine powder; add hydrochloric acid with a concentration of 1 mol / L at a solid-liquid ratio of 1 g: 20 mL, and acidify it by magnetic stirring in a water bath at 80 °C for 1.5 h to obtain an acidified solution; then use a 0.22 μm filter membrane to vacuum filter the acidified solution to obtain a filter cake, wash the filter cake repeatedly with deionized water until the filtrate is neutral, continue to wash the filter cake with ethanol, and then vacuum dry it at 60 °C to constant weight to obtain a refined organic carbon source; (3) Accurately weigh 0.5g of refined organic carbon source, transfer it to the lining of the hydrothermal reactor, add 60mL of deionized water, ultrasonically disperse to form a uniform and stable suspension, seal and load into the high-pressure reactor; (4) Place the high-pressure reactor into a forced-air drying oven and perform a constant-temperature hydrothermal reaction at 185°C for 13 hours. After the reaction is completed, allow it to cool naturally to room temperature. (5) Take out the reaction solution in the vessel, transfer it to a centrifuge tube, centrifuge at 9000 rpm for 15 min, and collect the supernatant; filter the supernatant through a 0.22 μm filter membrane and collect the filtrate; put the filtrate into a pretreated 3500 Da dialysis bag, immerse it in 500 mL of deionized water and dialyze for 48 h, changing the external dialysis solution (deionized water) every 12 h. After dialysis, carbon quantum dot aqueous solution is obtained. (6) The aqueous solution of carbon quantum dots was freeze-dried (temperature -60℃, time 48h), and the solid powder was collected after freeze-drying to obtain carbon quantum dots.

[0041] Comparative Example 3 is the same as Example 3, except that Comparative Example 3 did not remove heavy crude oil from the oily sludge, but directly performed Soxhlet extraction. The specific steps are as follows: (1) Take 10g of oily sludge from the oilfield and transfer it to the filter paper tube of the Soxhlet extractor. Add 200mL of n-hexane and extract it in a Soxhlet extractor at 70℃ under a gentle boiling condition for 12h. (2) Take out the solid sediment after Soxhlet extraction, grind it and pass it through an 80-mesh standard sieve to obtain fine powder; add hydrochloric acid with a concentration of 1 mol / L at a solid-liquid ratio of 1 g: 30 mL, and acidify it by magnetic stirring in a water bath at 80 °C for 1.5 h to obtain an acidified solution; then use a 0.22 μm filter membrane to vacuum filter the acidified solution to obtain a filter cake, wash the filter cake repeatedly with deionized water until the filtrate is neutral, continue to wash the filter cake with ethanol, and then vacuum dry it at 60 °C to constant weight to obtain a refined organic carbon source; (3) Accurately weigh 0.5g of refined organic carbon source, transfer it to the lining of the hydrothermal reactor, add 50mL of deionized water, ultrasonically disperse to form a uniform and stable suspension, seal and load into the high-pressure reactor; (4) Place the high-pressure reactor into a forced-air drying oven and perform a constant-temperature hydrothermal reaction at 185°C for 13 hours. After the reaction is completed, allow it to cool naturally to room temperature. (5) Take out the reaction solution in the vessel, transfer it to a centrifuge tube, centrifuge at 9000 rpm for 15 min, and collect the supernatant; filter the supernatant through a 0.22 μm filter membrane and collect the filtrate; put the filtrate into a pretreated 3500 Da dialysis bag, immerse it in 500 mL of deionized water and dialyze for 48 h, changing the external dialysis solution (deionized water) every 12 h. After dialysis, carbon quantum dot aqueous solution is obtained. (6) The aqueous solution of carbon quantum dots was freeze-dried (temperature -60℃, time 48h), and the solid powder was collected after freeze-drying to obtain carbon quantum dots.

[0042] Comparative Example 4 is the same as Example 1, except that a mixed solution of citric acid and hydrogen peroxide is used in Comparative Example 4 instead of the 1 mol / L nitric acid in Example 1. The mixed solution of citric acid and hydrogen peroxide is prepared as follows: 1 g of citric acid was added to 3 mL of a 30% hydrogen peroxide solution. Deionized water was then added to the mixture to increase the volume of the solution to 100 mL. The fluorescence emission spectrum of the carbon quantum dots obtained in Comparative Example 4 is shown in the attached instruction manual. Figure 5 As shown.

[0043] Comparative Example 5 is the same as Example 2, except that a mixed solution of citric acid and hydrogen peroxide is used in Comparative Example 5 instead of the 1 mol / L nitric acid in Example 2. The mixed solution of citric acid and hydrogen peroxide is prepared as follows: 1 g of citric acid was added to 3 mL of a 30% hydrogen peroxide solution. Then, deionized water was added to the mixed solution to increase the volume of the solution to 100 mL. The fluorescence emission spectrum of the carbon quantum dots obtained in Comparative Example 5 is shown in the attached instruction manual. Figure 6 As shown.

[0044] Comparative Example 6 is the same as Example 3, except that a mixed solution of citric acid and hydrogen peroxide is used in Comparative Example 6 instead of the 1 mol / L nitric acid in Example 3. The mixed solution of citric acid and hydrogen peroxide is prepared as follows: 1 g of citric acid was added to 3 mL of a 30% hydrogen peroxide solution. Deionized water was then added to the mixture to increase the volume of the solution to 100 mL. The fluorescence emission spectrum of the carbon quantum dots obtained in Comparative Example 6 is shown in the attached instruction manual. Figure 7 As shown.

[0045] Performance testing The carbon quantum dots obtained in Examples 1-3 and Comparative Examples 1-6 of this invention were subjected to relevant performance tests, and the test results are shown in Table 1.

[0046] Table 1 .

[0047] In Table 1, "-" indicates that no fluorescence effect was detected.

[0048] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing carbon quantum dots using oily sludge, characterized in that, The preparation steps include the following: (1) Pretreatment: The oily sludge is mixed with the first organic solvent and ultrasonically extracted. The lower solid phase sediment is collected to remove most of the heavy crude oil, gum and asphalt. (2) Deoiling and purification: The solid phase sediment obtained in step (1) was washed with water, dried and then subjected to Soxhlet extraction with a second organic solvent to obtain deoiled solid phase sediment; (3) Acidification treatment: After grinding the deoiled solid phase deposit obtained in step (2), it is mixed with acid solution to carry out acidification reaction. After the reaction is completed, the solid and liquid are separated, and the obtained solid is washed and dried to obtain a refined organic carbon source. (4) Hydrothermal reaction: The refined organic carbon source obtained in step (3) is mixed with deionized water, dispersed evenly, and placed in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, the mixture is cooled. (5) Separation and purification: Centrifuge and filter the reaction solution obtained in step (4), collect the filtrate, dialyze the filtrate to obtain an aqueous solution of carbon quantum dots; (6) Drying: The aqueous solution of carbon quantum dots obtained in step (5) is dried to obtain carbon quantum dots.

2. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (1), the first organic solvent is toluene, o-xylene or diesel; the ultrasonic extraction is performed 1-3 times, with each extraction lasting 20-40 minutes; the solid-liquid separation is centrifugal separation, with a centrifugation speed of 8000-10000 rpm and a centrifugation time of 15-30 minutes.

3. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (2), the water washing is washing with deionized water 2-4 times; the drying is vacuum drying at 50-70℃ for 6-10 hours.

4. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (2), the second organic solvent is petroleum ether or n-hexane; the conditions for Soxhlet extraction are: extraction at a water bath temperature of 60-80℃ for 10-14h.

5. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (3), the grinding is passed through a 60-100 mesh standard sieve; the acid solution is nitric acid or hydrochloric acid with a concentration of 0.5-1 mol / L; in the acidification reaction, the solid-liquid ratio of the deoiled solid phase deposit to the acid solution is 1 g: 20-30 mL, the reaction temperature is 70-85℃, and the reaction time is 1-2 h.

6. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (3), the solid-liquid separation is performed by vacuum filtration using a 0.2-0.45 μm filter membrane; the washing is performed by first washing with deionized water until the filtrate is neutral, and then washing with ethanol; the drying is performed by vacuum drying at 50-70℃ to constant weight.

7. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (4), the ratio of the amount of refined organic carbon source to deionized water is 0.5-1g:50-75mL; the temperature of the hydrothermal reaction is 170-200℃ and the time is 10-15h.

8. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (5), the centrifugation speed is 8000-10000 rpm and the centrifugation time is 10-20 min; the filtration is performed using a 0.2-0.45 μm filter membrane; the dialysis bag used for dialysis has a molecular weight cutoff of 1000-4000 Da and the dialysis time is 36-60 h, during which the external dialysis fluid is replaced 2-4 times.

9. The method for preparing carbon quantum dots using oily sludge according to claim 1, characterized in that, In step (6), the drying is freeze drying, the freeze drying temperature is -50℃ to -70℃, and the time is 36-60h.

10. A carbon quantum dot, characterized in that, It is prepared by any one of the methods for preparing carbon quantum dots using oily sludge as described in claims 1-9.

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