A cassava dreg derived graphene oxide membrane preparation method

Abstract

The application discloses a cassava residue derived graphene oxide film preparation method and relates to a graphene oxide film preparation method. The application is used to solve the problem of limited natural graphene reserves and environmental influence caused by excessive exploitation. The steps of the application are as follows: step one, drying cassava residue after extracting cassava powder and then crushing the cassava residue by using a crusher; step two, high-temperature pyrolyzing the cassava residue, grinding and sieving the cassava residue to obtain cassava residue biochar; step three, treating the cassava residue biochar by using a two-step oxidation method to obtain cassava residue derived graphene oxide, and recycling the concentrated sulfuric acid mixed solution after the first-stage oxidation; and step four, treating the cassava residue derived graphene oxide by using a vacuum filtration method to obtain a graphene oxide film. The application belongs to the technical field of graphene oxide.

Description

TECHNICAL FIELD

[0001] The application relates to a graphene oxide film preparation method and belongs to the technical field of graphene oxide. BACKGROUND

[0002] At present, water resource pollution has become one of the most severe challenges faced by the world. Textile, printing and dyeing and other industries will produce a large amount of high-toxicity wastewater containing dyes, inorganic salts and other organic pollutants. If the high-toxicity wastewater is directly discharged into the environment without treatment, it will seriously pollute the water body and threaten human health. Therefore, people have developed many physical and chemical treatment methods to purify the wastewater of textile, printing and dyeing and other industries. Among them, the membrane separation technology is considered to be a promising method to solve the problem of water pollution, and has developed rapidly in the past few decades, because it can selectively pass through the required molecules without phase change or addition of other chemicals. In addition, the membrane separation technology can also solve the problem of recycling of powder materials. However, the small molecular size of the pollutants in the wastewater makes it difficult for microfiltration and ultrafiltration membrane materials in the membrane material to play an effective role, and the nanofiltration membrane separation technology with smaller pore size becomes a new solution to remove such pollutants. This treatment technology can effectively remove dyes and inorganic salts in wastewater and recycle them, thereby reducing the cost of the textile industry. Therefore, it is urgent to develop a nanofiltration membrane that can effectively remove dyes and salts.

[0003] Graphene material is a typical two-dimensional material with atomic layer thickness, which is an ideal material for building nanofiltration membranes. However, the mechanical properties and stability of the single graphene film are not ideal, and it is difficult to be applied to the treatment of actual water bodies. The polyvinyl alcohol (PVA) modification can effectively solve the physical and chemical stability of the graphene film, and has excellent mechanical properties, good heat resistance and chemical resistance, and excellent film-forming performance. However, the current mainstream raw material for preparing graphene oxide is still natural graphite, but the reserves of natural graphite are limited, and the exploitation process will damage the ecological environment. Waste cassava residue is rich in cellulose, and high-quality graphene oxide can be easily obtained by exfoliation after carbonization, and because of the renewable characteristics, it is an ideal carbon source substitute for natural graphite. In addition, cassava residue, as a typical waste biomass, is often used in the fermentation industry, but the amount is very limited, and a large amount of cassava residue is still discarded, which causes resource waste and environmental pollution. Therefore, the conversion of cassava residue into graphene oxide film not only realizes the resource utilization of waste, but also provides a practical idea for the treatment of wastewater in textile, printing and dyeing and other industries, and truly realizes the concept of "waste treatment with waste". SUMMARY

[0004] The application is to solve the problem of limited reserves of natural graphene, and excessive exploitation will affect the environment, and further puts forward a preparation method of graphene oxide film derived from cassava residue.

[0005] The technical scheme adopted by the present application to solve the above problems is as follows:

[0006] Step one, drying the cassava residue after extracting cassava powder and then crushing the cassava residue by a crusher;

[0007] Step two, pyrolyzing the cassava residue at high temperature, grinding and sieving to obtain cassava residue biochar;

[0008] Step three, treating the cassava residue biochar by a two-step oxidation method to obtain cassava residue derived graphene oxide, and recycling the concentrated sulfuric acid mixture after the first oxidation;

[0009] Step four, treating the cassava residue derived graphene oxide by vacuum filtration to obtain graphene oxide film.

[0010] Further, the drying temperature of the cassava residue in step one is 80-120℃, and then the temperature is maintained for 1-3h, and the particle size of the cassava residue is 100-300 mesh.

[0011] Further, the high-temperature pyrolysis process in step two is as follows: heating at a rate of 9-12℃ / min to 800-1000℃, and then maintaining the temperature for 1-3h.

[0012] Further, the two-step oxidation method in step three is as follows: first, using concentrated H2SO4, potassium persulfate and potassium ferrate for first oxidation, and then using a mixed solution of hydrogen peroxide and deionized water for second oxidation.

[0013] Further, the specific process of the first oxidation is as follows: adding concentrated H2SO4 solution into a three-necked flask containing cassava residue biochar, stirring at 400r / min for 30min, then adding stabilizer K2S2O8 and oxidant K2FeO4; after all the chemicals are added, the three-necked flask is heated in a water bath at 75℃ for 6h, and the stirring speed is kept constant during this process; after cooling, the precipitated solid and the mixed acid solution are collected by centrifugation, the precipitated solid is the first oxidation product, and the mixed acid solution is stored for later use; fresh concentrated H2SO4 is used to supplement the mixed acid solution to 80mL after each cycle; the specific process of the second oxidation is as follows: the precipitated solid is transferred into a mixed solution containing deionized water and H2O2, stirred for 30min for second oxidation, and then centrifuged, washed and freeze-dried to obtain cassava residue derived graphene oxide.

[0014] Further, the mass ratio of K2S2O8, K2FeO4 and cassava residue biochar in the primary oxidation process is 1:1:2, the volume of concentrated H2SO4 and the mass of cassava residue biochar is (15-18) m L:1 g, the volume ratio of deionized water and H2O2 in the secondary oxidation process is 2:1, and the mass ratio of H2O2 and the primary oxidation product is (15-18) m L:1 g.

[0015] Further, the specific process of the cassava residue derived graphene oxide film in step four is that the cassava residue graphene oxide and polyvinyl alcohol solution are ultrasonically dispersed into 20 mL of deionized water solution, and the ultrasonic time is set to 20 min; then the mixture is poured into a filter membrane with a pore size of 0.45 μm and vacuum filtered for 5 min; then the cassava residue derived graphene oxide is peeled off from the filter membrane and dried at 80 DEG C for 3 h.

[0016] Further, the volume ratio of the PVA solution and deionized water is 1:4, and the mass ratio of the deionized water and cassava residue graphene oxide is (8-12) mL:1 g.

[0017] The beneficial effects of the present application are:

[0018] 1. The present application uses waste cassava residue as a carbon source for preparing graphene oxide, which reduces the consumption of graphite ore compared with the existing method of using graphite as a carbon source, and embodies the green and sustainable development concept.

[0019] 2. The present application uses green and environmentally friendly K2FeO4 as an oxidizing agent, which avoids the pollution of heavy metal ions Mn 2+ compared with the existing method of using KMnO4 as an oxidizing agent.

[0020] 3. The present application realizes the recycling of concentrated sulfuric acid mixture, which reduces the discharge of high-concentration acidic wastewater and saves costs compared with the existing method of directly discarding the used concentrated H2SO4 mixture.

[0021] 4. The biomass graphene oxide obtained by the present application can be used as an excellent raw material for nanofiltration membranes without other treatment, and has excellent separation effect on dyes and salt-containing wastewater; this is not possessed by other biomass graphene oxides; and the preparation method of each stage of the present application has the technical advantages of green environmental protection, simple operation and strong popularization. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 TEM image of the cassava residue graphene oxide material prepared in Example 1;

[0023] Figure 2TEM image of cassava dreg-derived graphene oxide material prepared for Comparative Example 2;

[0024] Figure 3 TEM image of cassava dreg-derived graphene oxide material prepared for Comparative Example 3;

[0025] Figure 4 TEM image of cassava dreg-derived graphene oxide material prepared for Comparative Example 4;

[0026] Figure 5 TEM image of commercial graphene oxide material purchased for Comparative Example 5;

[0027] Figure 6 Schematic diagram of the rejection effect of different graphene oxide membranes prepared in the application on anionic dye methyl orange;

[0028] Figure 7 Schematic diagram of the rejection effect of different graphene oxide membranes prepared in the application on cationic dye rhodamine B;

[0029] Figure 8 Schematic diagram of the rejection effect of different graphene oxide membranes prepared in the application on Na + ;

[0030] Figure 9 Schematic diagram of the rejection effect of different graphene oxide membranes prepared in the application on Mg 2+ ; DETAILED DESCRIPTION

[0031] Specific embodiment one: in combination Figures 6-9 To illustrate the present embodiment, the preparation method of the cassava dreg-derived graphene oxide membrane described in the present embodiment is realized through the following steps:

[0032] Step one, drying the cassava dregs after extracting cassava powder and then crushing them with a crusher;

[0033] Step two, high-temperature pyrolysis of the cassava dregs, grinding and sieving to obtain cassava dreg biochar;

[0034] Step three, treating the cassava dreg biochar with a two-step oxidation method to obtain cassava dreg-derived graphene oxide, and recycling the concentrated sulfuric acid mixture after the first-stage oxidation;

[0035] Step four, treating the cassava dreg-derived graphene oxide with vacuum filtration to obtain a graphene oxide membrane.

[0036] The cassava dreg-derived graphene oxide membrane prepared in the application is used for separating dyes and high-concentration salt-containing wastewater; the concentration of the dyes and salts is 25-75 mg / L and 100-300 mg / L, respectively.

[0037] Specific implementation method two: combination Figures 6-9 In this embodiment, the drying temperature of the cassava dregs in step one of the preparation method of the cassava dregs derived graphene oxide film is 80-120°C, and then the temperature is kept for 1-3h. The particle size of the cassava dregs is 100-300 mesh.

[0038] Specific implementation method three: combination Figures 6-9 In this embodiment, the high-temperature pyrolysis process in step two of the preparation method of the cassava dregs derived graphene oxide film is as follows: the temperature is raised to 800-1000°C at a rate of 9-12°C / min, and then the temperature is kept for 1-3h.

[0039] Specific implementation method four: combination Figures 6-9 In this embodiment, the secondary oxidation method in step three of the preparation method of the cassava dregs derived graphene oxide film is as follows: first, primary oxidation is carried out using concentrated H2SO4, potassium persulfate and potassium ferrate, and then secondary oxidation is carried out using a mixed solution of hydrogen peroxide and deionized water.

[0040] Specific implementation method five: combination Figures 6-9 In this embodiment, the specific process of the primary oxidation in the preparation method of the cassava dregs derived graphene oxide film is as follows: concentrated H2SO4 solution is added to a three-necked flask containing cassava dregs biochar, stirred at 400r / min for 30min, and then stabilizer K2S2O8 and oxidant K2FeO4 are added; after all the chemicals are added, the three-necked flask is heated in a water bath at 75°C for 6h, and the speed is kept constant during this process; after static cooling, the precipitated solid and the mixed acid solution are collected by centrifugation, the precipitated solid is the primary oxidation product, and the mixed acid solution is stored for later use; fresh concentrated H2SO4 is used to supplement the mixed acid solution to 80mL after each cycle; the specific process of the secondary oxidation is as follows: the precipitated solid is transferred to a mixed solution containing deionized water and H2O2, stirred for 30min for secondary oxidation, and then centrifuged, washed and freeze-dried to obtain cassava dregs derived graphene oxide.

[0041] Specific implementation method six: combination Figures 6-9 In this embodiment, the mass ratio of K2S2O8, K2FeO4 and cassava dregs biochar in the primary oxidation process of the preparation method of the cassava dregs derived graphene oxide film is 1:1:2, the volume ratio of concentrated H2SO4 to the mass of cassava dregs biochar is (15-18)mL:1g, the volume ratio of deionized water to H2O2 in the secondary oxidation process is 2:1, and the mass ratio of H2O2 to the primary oxidation product is (15-18)mL:1g.

[0042] Specific implementation seven: combination Figures 6-9 To illustrate the present embodiment, the specific process of the cassava dreg-derived graphene oxide film in step four of the preparation method of the cassava dreg-derived graphene oxide film according to the present embodiment is as follows: the cassava dreg-derived graphene oxide and the polyvinyl alcohol solution are ultrasonically dispersed in 20 mL of deionized water solution, and the ultrasonic time is set to 20 min; then the mixture is vacuum filtered through a filter membrane with a pore size of 0.45 μm for 5 min; subsequently, the cassava dreg-derived graphene oxide is peeled off from the filter membrane and dried at 80℃ for 3 h.

[0043] Specific implementation eight: combination Figures 6-9 To illustrate the present embodiment, the volume ratio of the PVA solution to the deionized water in the preparation method of the cassava dreg-derived graphene oxide film according to the present embodiment is 1:4, and the mass ratio of the deionized water to the cassava dreg-derived graphene oxide is (8-12) mL: 1 g.

[0044] Example

[0045] Example 1

[0046] The present embodiment provides a preparation method of cassava dreg-derived graphene oxide, which comprises the following steps:

[0047] (1) The raw material of the cassava dreg-derived graphene oxide is the cassava dregs remaining after the extraction of cassava powder. Since the cassava dregs after the extraction of cassava powder contain a large amount of water, they need to be dried at 105℃ before use, and then crushed by a crusher to obtain 200-mesh cassava dreg particles.

[0048] (2) The obtained cassava dreg particles are placed in a high-temperature tube furnace for pyrolysis, and the temperature is raised to 900℃ at a rate of 10℃ / min under N2 atmosphere, and the pyrolysis time is set to 2 h, and then ground and sieved to obtain cassava dreg biochar.

[0049] (3) Put 5.0 g of cassava dreg biochar prepared in step (2) into a three-necked flask for primary oxidation, slowly drop 80 mL of concentrated H2SO4 solution with volume fraction of 98%, and after 30 min of magnetic stirring, slowly add 10 g of K2S2O8 and K2FeO4 into the above suspension. Then, heat the three-necked flask in a water bath at 75 °C for 6 h. Collect the precipitated solid and mixed acid solution by centrifugation. Note that the mixed acid solution needs to be supplemented to 80 mL using fresh concentrated H2SO4 after each cycle. After drying, the obtained precipitated solid is transferred into a mixed solution composed of 150 mL of deionized water and 75 mL of H2O2, and stirred for 30 min for secondary oxidation. After centrifugation, washing, and freeze-drying, cassava dreg-derived graphene oxide is obtained, which is denoted as graphene oxide 1. The obtained mixed acid solution needs to be stored in a tightly closed glass bottle in the dark and reused as needed.

[0050] Comparative Example 2: The difference between this example and Example 1 is that the concentrated H2SO4 solution used in step (3) is the mixed acid solution obtained after Example 1, and other conditions are exactly the same as Example 1, which is denoted as graphene oxide 2.

[0051] Comparative Example 3: The difference between this example and Example 1 is that the concentrated H2SO4 solution used in step (3) is the mixed acid solution obtained after Comparative Example 2, and other conditions are exactly the same as Example 1, which is denoted as graphene oxide 3.

[0052] Comparative Example 4: The difference between this example and Example 1 is that the concentrated H2SO4 solution used in step (3) is the mixed acid solution obtained after Comparative Example 3, and other conditions are exactly the same as Example 1, which is denoted as graphene oxide 4.

[0053] Comparative Example 5: Commercial graphene oxide purchased directly is denoted as graphene oxide 5.

[0054] Example 2

[0055] The present embodiment also provides a preparation method of cassava dreg-derived graphene oxide, which comprises the following steps:

[0056] (1) Cassava dreg-derived graphene oxide film is synthesized by simple vacuum filtration. 0.2 g of graphene oxide synthesized in Example 1, 5 mL of PVA (0.5 wt%) solution is ultrasonically dispersed into 20 mL of deionized water solution, and the ultrasonic time is set to 20 min.

[0057] (2) The mixture is vacuum filtered through a filter membrane with a pore size of 0.45 μm for 5 min. Then, the cassava dreg-derived graphene oxide is peeled off from the filter membrane and dried at 80 °C for 3 h, which is denoted as graphene oxide film 1.

[0058] Comparative Example 6: This example is different from Example 2 in that the graphene oxide used in step (1) is prepared under the conditions of Comparative Example 6, and other steps and parameters are the same as Example 2, denoted as graphene oxide film 6.

[0059] Comparative Example 7: This example is different from Example 2 in that the graphene oxide used in step (1) is prepared under the conditions of Comparative Example 7, and other steps and parameters are the same as Example 2, denoted as graphene oxide film 7.

[0060] Comparative Example 8: This example is different from Example 2 in that the graphene oxide used in step (1) is prepared under the conditions of Comparative Example 8, and other steps and parameters are the same as Example 2, denoted as graphene oxide film 8.

[0061] Comparative Example 9: This example is different from Example 2 in that the graphene oxide used in step (1) is a commercially purchased graphene oxide, and other steps and parameters are the same as Example 2, denoted as graphene oxide film 9.

[0062] Effect Example 1: The cassava dreg graphene oxides of Example 1 and Comparative Examples 2-4 and the commercial graphene oxide of Comparative Example 5 were respectively placed under a transmission electron microscope (TEM) for observation, and the TEM images obtained are shown in FIG. 1. Figures 1-5 As can be observed from the figure, the cassava dreg graphene oxide of Example 1 exhibits a "thin gauze" like ultra-thin structure, and even shows a single-layer graphene structure at the edge position. The sheet layer structures of the cassava dreg graphene oxides of Comparative Examples 2-4 generally show that as the number of times of using the mixed acid increases, the sheet layer structure also thickens accordingly. It is worth noting that the sheet layer structure of the cassava dreg graphene oxide of Comparative Example 4 is the most serious stacking, which indicates that when the number of times of using the mixed acid reaches 3 times, it may have reached its limit of use. In addition, the commercial graphene in Comparative Example 5 also shows a relatively stacked layered structure.

[0063] Effect Example 2: Dye and salt separation experiment, the specific process is as follows:

[0064] (1) Select typical anion (methyl orange) and cation (rhodamine B) dyes to be dissolved in water to prepare a solution with a concentration of 50 mg / L as a test sample. The separation experiment of salt is similar to that of dye. Sodium chloride, magnesium chloride are prepared into an aqueous solution with a concentration of 200 mg / L for standby.

[0065] (2) The graphene oxide film is fixed in a special filtration device, then the dye and salt solution is added to the device and the solution is separated by the film after applying pressure. After filtration is completed, the filtrate is collected and its concentration is measured.

[0066] (3) The separation efficiency of dye and salt is calculated according to the following formula:

[0067] R=(1-C p / C f )×100%, where R represents the removal rate of dye or salt, C p and C f The concentrations of dyes and inorganic salts were measured by UV-visible spectrophotometer and ion chromatography, respectively.

[0068] (4) Results:

[0069] ① The separation ability of graphene oxide membrane was tested using two typical anionic and cationic dyes, methyl orange and rhodamine B. The experimental results are as follows Figures 6-7 As shown, graphene oxide membrane 1 achieved a retention efficiency of over 99% for both typical dyes. Furthermore, the retention efficiency of graphene oxide membranes 2-3 prepared using the recycled mixed acid solution decreased slightly, but was still higher than that of the commercial graphene oxide membrane (graphene oxide membrane 5). However, the retention efficiency of graphene oxide membrane 4 was lower than that of graphene oxide membrane 5, indicating that after the mixed acid solution was used for the third time, it was no longer suitable for preparing graphene oxide.

[0070] ② Salt-containing wastewater is extremely harmful to the environment, so it is necessary to remove inorganic salts from the wastewater. + and Mg 2+ ions were used to simulate inorganic salts in wastewater (concentration was 200 mg / L). Figures 8-9 It shows that graphene oxide film 1 has a great + and Mg 2+ The retention efficiencies of the ions can reach 64.5% and 85.7% respectively. The different retention efficiencies may be due to the differences in ionic charge and ionic radius. + and Mg 2+ The ion retention efficiency showed a downward trend. Except for graphene oxide membrane 4, the retention efficiency of the other two membranes was better than that of graphene oxide membrane 5. The above analysis shows that the biomass graphene oxide membrane prepared by the present invention can effectively remove dyes and salt-containing wastewater.

[0071] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a graphene oxide film derived from cassava residue, characterized in that: The method for preparing a cassava residue-derived graphene oxide film is achieved by the following steps: Step 1: drying the cassava residue after extracting cassava flour and then crushing it with a crusher; The drying temperature of the cassava residue is 80-120°C, and then the temperature is maintained for 1-3 hours, and the particle size of the cassava residue is 100-300 mesh; Step 2: pyrolyzing the cassava residue at high temperature, grinding and screening to obtain cassava residue biochar; The high-temperature pyrolysis process is as follows: heating to 800-1000 °C at a rate of 9-12 °C / min, and then keeping at this temperature for 1-3 h; Step 3: treating the cassava residue biochar with a two-step oxidation method to obtain cassava residue-derived graphene oxide, and recycling the concentrated sulfuric acid mixture after the primary oxidation; The secondary oxidation method specifically comprises the following steps: firstly using concentrated H2SO4, potassium persulfate and potassium ferrate for primary oxidation, and then using a mixed solution of hydrogen peroxide and deionized water for secondary oxidation; Step 4: Treat the cassava residue-derived graphene oxide by vacuum filtration to obtain a graphene oxide membrane. The specific process of the cassava residue-derived graphene oxide membrane is as follows: ultrasonically disperse the cassava residue-derived graphene oxide and polyvinyl alcohol solution in 20 mL of deionized water solution, and the ultrasonic time is set to 20 minutes; then pour the mixture into a filter membrane with a pore size of 0.45 μm and vacuum filter for 5 minutes; then, the product of the reaction between the cassava residue-derived graphene oxide and the polyvinyl alcohol solution is peeled off from the filter membrane and dried at 80 ºC for 3 hours; The specific process of the primary oxidation is as follows: adding concentrated H2SO4 solution to a three-necked flask containing cassava residue biochar, stirring at 400 r / min for 30 minutes, and then adding stabilizer K2S2O8 and oxidant K2FeO4; after all the drugs are added, heating the three-necked flask in a water bath at 75°C for 6 hours, keeping the speed unchanged during this process; after static cooling, centrifugation is performed to collect the precipitated solid and the mixed acid solution, and the obtained precipitated solid is the primary oxidation product; the obtained mixed acid solution is stored for future use; after each cycle, the mixed acid solution is replenished to 80 mL with fresh concentrated H2SO4; the specific process of the secondary oxidation is as follows: transferring the obtained precipitated solid to a mixed solution containing deionized water and H2O2, stirring for 30 minutes for secondary oxidation, and obtaining cassava residue-derived graphene oxide through centrifugation, washing and freeze-drying; During the primary oxidation process, the mass ratio of K2S2O8, K2FeO4 and cassava residue biochar is 1:1:2, the volume ratio of concentrated H2SO4 to the mass of cassava residue biochar is (15-18) mL:1g, and during the secondary oxidation process, the volume ratio of deionized water and H2O2 is 2:1, and the mass ratio of H2O2 to the primary oxidation product is (15-18) mL:1g; The volume ratio of the polyvinyl alcohol solution to deionized water is 1:4.

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