Carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, preparation method and application thereof

Abstract

The invention discloses a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, a preparation method and an application thereof, wherein the thermosensitive hydrogel is prepared by cross-linking reaction of carbon-doped boron nitride BCN, polyethyleneimine PEI and N-isopropylacrylamide NIPAM; the preparation method comprises mixing and stirring a BCN solution and a PEI solution; placing the mixed and stirred solution under high temperature for reaction to obtain a BCN-PEI solution; adding NIPAM and a cross-linking agent to the BCN-PEI solution for stirring; adding an initiator to the stirred solution for secondary stirring; adding a accelerant to the solution after secondary stirring for three times of stirring, and sealing and standing to obtain a BCN-based thermosensitive hydrogel; the thermosensitive hydrogel is applied to adsorbing and recovering pollutants in water bodies. The thermosensitive hydrogel prepared by the present invention can recover hexavalent chromium in water bodies by adsorption and temperature control, has a large adsorption capacity, and can be recycled, and has good practical application potential.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater resource utilization, and relates to a carbon-doped boron nitride-based temperature-sensitive hydrogel for recovering hexavalent chromium, a preparation method and an application thereof. Background Art

[0002] With the continuous development of industry, more and more pollutants are discharged into water bodies, causing water pollution. Among them, chromium is widely used in electroplating, leather making, chemical industry, pigment, metallurgy, refractory materials and other industries, resulting in an increasing discharge of chromium-containing wastewater. Chromium pollution has gradually become one of the important factors of environmental pollution. The existence of chromium in chromium-containing wastewater is in the form of Cr 3+ and Cr 6+ Two types, Cr 6+ The most toxic is Cr 3+ 100 times of that of heavy metals (Industrial & Engineering Chemistry Research, 2009, 48(4):2113-2117.), which can cause lung cancer, intestinal diseases and anemia. In the ranking of carcinogenic risks of various heavy metal intake exposures, Cr 6+ The risk of cancer is the highest (Scientific African, 2019, 6:197.).

[0003] Common methods for treating chromium-containing wastewater include biological, chemical and physical-chemical methods (Environmental Science and Technology, 2004 (S1): 111-113). Biological methods include biosorption, bioflocculation and plant remediation technology. It has the advantages of low investment, low operating costs, good results and no secondary pollution; but it is difficult to cultivate efficient and toxic bacteria. Chemical methods include reduction precipitation, photocatalysis and electrolytic reduction. The main advantages are simple operation and easy availability of raw materials; but the reagents are required in large quantities, energy consumption is high and the treatment cost is high. Physical-chemical methods include membrane separation, ion exchange and adsorption. The advantages of membrane separation are simple equipment, easy operation and high operating efficiency; but the investment is large, the membrane life is short and the operating cost is high. The advantage of ion exchange is good treatment effect, especially suitable for treating wastewater with low pollutant concentration, small water volume and high effluent requirements; the disadvantage is high material cost and high operating cost. The adsorption method is economical and has good effect on treating low-concentration chromium-containing wastewater (Liaoning Chemical Industry, 2010, 39(02):143-146.).

[0004] Thermosensitive polymer materials are high molecular gels whose swelling degree in solvents changes with temperature. They can undergo structural changes only when the ambient temperature changes, thereby causing changes in the amphiphilicity of the material and achieving the adsorption and release of pollutants under temperature-controlled conditions.

[0005] A preparation method and application of a thermosensitive composite hydrogel utilizing the synergistic effect of photocatalysis and thermosensitivity (application number CN202010034145.9). This patent introduces thermosensitive copolymers and photocatalysts into alginate hydrogels, which can adsorb and degrade dyes under light conditions. The thermosensitive composite hydrogel improves the adsorption capacity of the composite hydrogel for dyes by virtue of the synergistic effect of the porous structure inside the hydrogel caused by the addition of the catalyst and the loose structure formed by the thermosensitive copolymer above the transition temperature. With the help of the photocatalyst embedded inside the hydrogel, the degradation of the adsorbed dyes and the recycling of the composite hydrogel can be achieved, which can be applied to the fields of printing and dyeing wastewater treatment. Although the thermosensitive polymer shows good thermosensitive properties, its own adsorption performance for heavy metal ions is not significant. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, a preparation method and an application thereof. The prepared hydrogel can adsorb and recover hexavalent chromium in water with a large adsorption capacity and can be recycled.

[0007] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0008] A method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, comprising:

[0009] The BCN solution and the PEI solution are mixed and stirred;

[0010] The mixed and stirred solution is placed under high temperature for reaction to obtain a BCN-PEI solution;

[0011] Add NIPAM and cross-linking agent to the BCN-PEI solution and stir;

[0012] adding an initiator to the stirred solution and stirring it a second time;

[0013] Add the accelerator to the solution after the second stirring and stir for three times, seal and let stand to obtain the BCN-based thermosensitive hydrogel

[0014] Optionally, prepare BCN, including:

[0015] Adding boron trioxide and melamine into distilled water and stirring;

[0016] The stirred solution is heated until evaporated to dryness;

[0017] Drying the evaporated material to obtain a precursor;

[0018] The precursor is reacted under high temperature conditions, and after the reaction, it is cooled, washed and dried to obtain white carbon-doped boron nitride powder BCN.

[0019] Optionally, the molar ratio of boron trioxide to melamine is 5:3.

[0020] Optionally, the mass ratio of NIPAM to the cross-linking agent is 100:3.

[0021] Optionally, the method further includes: centrifuging the solution after the high-temperature reaction to obtain a BCN-PEI solution; before adding the initiator, filling the solution with nitrogen to remove oxygen from the solution; after obtaining the BCN-based thermosensitive hydrogel, soaking the molded BCN-based thermosensitive hydrogel with deionized water to remove unreacted monomers.

[0022] Optionally, the initiator includes ammonium persulfate; the accelerator includes tetramethylethylenediamine; and the cross-linking agent includes N.N'-methylenebisacrylamide BIS.

[0023] A carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium. The thermosensitive hydrogel is prepared by cross-linking carbon-doped boron nitride BCN, polyethyleneimine PEI and N-isopropylacrylamide NIPAM.

[0024] Optionally, the mass ratio of BCN to PEI is 1:5~8, and the mass of NIPAM is 0.8g

[0025] A carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium is used for adsorbing and recovering pollutants in water bodies.

[0026] Optional: The contaminants include Cr 6+ .

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention uses poly N-isopropylacrylamide PNIPAM as a thermosensitive gel material, and combined with BCN, the composite thermosensitive hydrogel can have higher adsorption;

[0029] By adding PEI hydrophilic monomer, the change process of the thermosensitive hydrogel from hydrophilic to hydrophobic state is delayed, so that the phase change process is delayed and the phase change temperature increases accordingly (32℃~53.53℃). The thermosensitive hydrogel can still be used to treat Cr in wastewater in the summer when the temperature is high. 6+ , which increases the application scope of thermosensitive hydrogel;

[0030] The pollutants can be desorbed after adjusting the temperature and acid soaking, thus realizing the recycling of the thermosensitive hydrogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the composite thermosensitive hydrogel in an embodiment of the present invention;

[0032] Figure 2 The composite thermosensitive hydrogel in the embodiment of the present invention absorbs Cr 6+ Schematic diagram after

[0033] Figure 3 This is a SEM image of the composite thermosensitive hydrogel in an embodiment of the present invention;

[0034] Figure 4 The composite thermosensitive hydrogel in the embodiment of the present invention absorbs Cr 6+ SEM images after

[0035] Figure 5 The composite thermosensitive hydrogel in the embodiment of the present invention is Cr 6+ The adsorption amount changes with the initial pH.

[0036] Figure 6 The composite thermosensitive hydrogel in the embodiment of the present invention is Cr 6+ The adsorption amount varies with the cation concentration.

[0037] Figure 7 The desorption rate of the composite thermosensitive hydrogel in the embodiment of the present invention changes with time.

[0038] Figure 8 This is a schematic diagram of the composite thermosensitive hydrogel after being heated to 55° C. in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0040] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0041] For the purpose of this specification and the appended claims, unless otherwise stated, all numbers expressing amounts, percentages or ratios and other numerical values ​​used in this specification and the appended claims are understood to be modified in all cases by the term "about". In addition, all ranges disclosed herein are inclusive and independently combinable.

[0042] Embodiment 1:

[0043] like Figure 1 As shown, a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium is prepared by cross-linking reaction of carbon-doped boron nitride BCN, polyethyleneimine PEI, and N-isopropylacrylamide NIPAM. The mass ratio of BCN to PEI is 1:7, and the mass of NIPAM is 0.8g. The gel in the figure is a white porous solid, m = 3.51gm.

[0044] Embodiment 2:

[0045] Based on the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium described in Example 1, this embodiment provides a method for preparing the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, comprising the following steps:

[0046] S1, grind 6.7g of boron trioxide and 7.6g of melamine for 10min to mix them evenly, then add them into a beaker containing 100mL of distilled water and stir for 3h;

[0047] S2, placing the prepared solution in a water bath and heating it to 90°C until evaporated;

[0048] S3, drying the evaporated material at 80°C and keeping the temperature for 8 hours to obtain a precursor;

[0049] S4, after the precursor is fully ground, it is placed in a graphite crucible for calcination, the crucible is covered, the temperature is increased at a rate of 10°C / min, the temperature is increased to 1100°C and kept at this temperature for 3 hours, and then the temperature is cooled to room temperature to obtain white BCN powder;

[0050] S5, 0.3 g BCN and 1.5 g PEI were added into a beaker containing 40 mL pure water, and stirred on a magnetic stirrer at 200 rpm for 4 h to obtain a mixed solution;

[0051] S6, then the mixed solution was placed in a 50 mL stainless steel autoclave, reacted at 180 °C for 4 h, and then naturally cooled to room temperature;

[0052] S7, centrifuging the mixture cooled to room temperature at 5000 r / min for 15 min to obtain a BCN-PEI solution;

[0053] S8, take 6 mL of the above BCN-PEI solution, add 0.8 g NIPAM and 24 mg cross-linking agent BIS;

[0054] S9, after the substances in S8 are completely dissolved and the solution is transparent, fill with high-purity N 2 Bubble for 30 min to remove oxygen from the solution;

[0055] S10, add 12 mg of initiator ammonium persulfate to the solution after deoxygenation and stir

[0056] S11, add 100 μL of the initiator tetramethylethylenediamine TEMED to the solution stirred evenly in S10, stir rapidly for 30 seconds, seal and let stand for 24 hours to allow the gel to fully polymerize and form;

[0057] S12, after the gel is fully polymerized and formed, the formed gel is soaked in deionized water for 3 times, each time for 30 minutes, to remove unreacted monomers;

[0058] S13, placing the soaked gel in a low-temperature refrigerator for 12 hours, and then placing it in a freeze dryer for 24 hours to obtain a dry gel.

[0059] Embodiment three:

[0060] Based on the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium described in Example 1, this embodiment provides a method for preparing the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, comprising the following steps:

[0061] S1, grind 6.7g of boron trioxide and 7.6g of melamine for 10min to mix them evenly, then add them into a beaker containing 100mL of distilled water and stir for 3h;

[0062] S2, placing the prepared solution in a water bath and heating it to 90°C until evaporated;

[0063] S3, drying the evaporated material at 80°C and keeping the temperature for 8 hours to obtain a precursor;

[0064] S4, after the precursor is fully ground, it is placed in a graphite crucible for calcination, the crucible is covered, the temperature is increased at a rate of 10°C / min, the temperature is increased to 1100°C and kept at this temperature for 3 hours, and then the temperature is cooled to room temperature to obtain white BCN powder;

[0065] S5, 0.3 g BCN and 2.1 g PEI were added into a beaker containing 40 mL pure water, and stirred on a magnetic stirrer at 200 rpm for 4 h to obtain a mixed solution;

[0066] S6, then the mixed solution was placed in a 50 mL stainless steel autoclave, reacted at 180 °C for 4 h, and then naturally cooled to room temperature;

[0067] S7, centrifuging the mixture cooled to room temperature at 5000 r / min for 15 min to obtain a BCN-PEI solution;

[0068] S8, take 6 mL of the above BCN-PEI solution, add 0.8 g NIPAM and 24 mg cross-linking agent BIS;

[0069] S9, after the substances in S8 are completely dissolved and the solution is transparent, fill with high-purity N 2 Bubble for 30 min to remove oxygen from the solution;

[0070] S10, add 12 mg of initiator ammonium persulfate to the solution after deoxygenation and stir

[0071] S11, add 100 μL of the initiator tetramethylethylenediamine TEMED to the solution stirred evenly in S10, stir rapidly for 30 seconds, seal and let stand for 24 hours to allow the gel to fully polymerize and form;

[0072] S12, after the gel is fully polymerized and formed, the formed gel is soaked in deionized water for 3 times, each time for 30 minutes, to remove unreacted monomers;

[0073] S13, placing the soaked gel in a low-temperature refrigerator for 12 hours, and then placing it in a freeze dryer for 24 hours to obtain a dry gel.

[0074] Embodiment 4:

[0075] Based on the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium described in Example 1, this embodiment provides a method for preparing the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, comprising the following steps:

[0076] S1, grind 6.7g of boron trioxide and 7.6g of melamine for 10min to mix them evenly, then add them into a beaker containing 100mL of distilled water and stir for 3h;

[0077] S2, placing the prepared solution in a water bath and heating it to 90°C until evaporated;

[0078] S3, drying the evaporated material at 80°C and keeping the temperature for 8 hours to obtain a precursor;

[0079] S4, after the precursor is fully ground, it is placed in a graphite crucible for calcination, the crucible is covered, the temperature is increased at a rate of 10°C / min, the temperature is increased to 1100°C and kept at this temperature for 3 hours, and then the temperature is cooled to room temperature to obtain white BCN powder;

[0080] S5, 0.1 g BCN was added into a beaker containing 10 mL pure water, and the mixture was stirred on a magnetic stirrer at 200 rpm for 4 h to obtain a BCN solution;

[0081] S6, take 6 mL of the above BCN solution, add 0.8 g NIPAM and 24 mg crosslinker BIS;

[0082] S7, after the substances in S6 are completely dissolved and the solution is transparent, high-purity N 2 Bubble for 30 min to remove oxygen from the solution;

[0083] S8, add 12 mg of initiator ammonium persulfate to the solution after deoxygenation and stir

[0084] S9, add 100 μL of the initiator tetramethylethylenediamine TEMED to the solution stirred evenly in S8, stir rapidly for 30 seconds, seal and let stand for 24 hours to allow the gel to fully polymerize and form;

[0085] S10, after the gel is fully polymerized and formed, the formed gel is soaked in deionized water for 3 times, each time for 30 minutes, to remove unreacted monomers;

[0086] S11, placing the soaked gel in a low-temperature refrigerator for 12 hours, and then placing it in a freeze dryer for 24 hours to obtain a dry gel.

[0087] Embodiment five:

[0088] Based on the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium described in Example 1, this embodiment provides a method for preparing the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, comprising the following steps:

[0089] S1, add 2.1 g PEI into a beaker containing 40 mL pure water and stir on a magnetic stirrer at 200 rpm for 4 h to obtain a PEI solution;

[0090] S2, take 6 mL of the above PEI solution, add 0.8 g NIPAM and 24 mg cross-linker BIS;

[0091] S3, after the substances in S2 are completely dissolved and the solution is transparent, high-purity N 2 Bubble for 30 min to remove oxygen from the solution;

[0092] S4, add 12 mg of initiator ammonium persulfate to the solution after deoxygenation and stir

[0093] S5, add 100 μL of the initiator tetramethylethylenediamine TEMED to the solution stirred evenly in S4, stir rapidly for 30 seconds, seal and let stand for 24 hours to allow the gel to fully polymerize and form;

[0094] S6, after the gel is fully polymerized, the formed gel is soaked in deionized water for 3 times, each time for 30 min, to remove unreacted monomers;

[0095] S7, placing the soaked gel in a low-temperature refrigerator for 12 hours, and then placing it in a freeze dryer for 24 hours to obtain a dry gel.

[0096] Embodiment six:

[0097] Based on the preparation method of the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium described in Example 1 and the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium described in Examples 2 to 5, this embodiment provides an application of the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium in adsorbing and recovering pollutants in water, wherein the pollutants include Cr 6+ .

[0098] like Figure 2 As shown, the composite thermosensitive hydrogel adsorbs Cr 6+ After reaching saturation, the gel swells and increases in volume, and its color turns noticeably yellow.

[0099] like Figure 3 As shown, the gel has a porous structure, and the cross-sectional shape of its mesh is approximately oblate and irregularly distributed; Figure 4 As shown in the figure, the gel network structure has undergone certain changes. Although it is still a porous structure, the mesh has no obvious circular shape, and has undergone certain collapse and shrinkage, and the overall structure is denser.

[0100] like Figure 5 As shown in Figure 5, the composite thermosensitive hydrogel has the best adsorption performance when pH is 5. The specific experimental steps are as follows: 100 mL, 20 mg / L Cr 6+ The solution was added to 5 beakers, and the pH values ​​were adjusted to 3 and 5 by adding deionized water and 0.1 mol / L HCl. The pH values ​​were adjusted to 7, 9 and 11 by adding 0.1 mol / L HCl and NaOH. 0.1 g of the dry gel sample of Example 3 was weighed and placed in the above beakers. The sample was adsorbed by shaking at room temperature for 6 h until adsorption equilibrium was reached. After filtering, the filtrate was taken and the Cr content was determined by diphenylcarbazide spectrophotometry. 6+ Concentration, calculate the Cr 6+ The adsorption amount.

[0101] like Figure 6 As shown in Figure 2, as the cation concentration increases, the inhibitory effect becomes more significant; Ca 2+ The inhibitory effect is stronger than that of Na + .

[0102] like Figure 7 As shown in the figure, the desorption equilibrium is basically reached in 150 min, and Cr 6+ The desorption rate is 92.02%.

[0103] like Figure 8 As shown, m = 0.51 g, the gel can release 85.56% of its own mass of water, while almost no Cr is discharged 6+ , can be used to recover and enrich Cr from water 6+ .

[0104] In summary, the composite thermosensitive hydrogel of the present invention has a good 6+ The thermosensitive hydrogel of the present invention has certain adsorption performance. Changing the mass ratio of BCN to PEI will affect the adsorption performance and low critical phase transition temperature of the composite thermosensitive hydrogel. The thermosensitive hydrogel of the present invention can discharge more than 85% of its own mass of water without discharging hexavalent chromium by adjusting the temperature, thereby recovering and enriching Cr from water. 6+ Purpose: After shrinking, the gel can be soaked in HCl to desorb 92% of Cr 6+ After being reused three times, it still has good adsorption performance, is easy to separate and remove, and will not cause secondary pollution to the environment

[0105] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium, characterized in that: The following steps are involved: The carbon-doped boron nitride BCN solution and the PEI solution are mixed and stirred; The mixed and stirred solution is placed under high temperature for reaction to obtain a BCN-PEI solution; Add NIPAM and cross-linking agent to the BCN-PEI solution and stir; adding an initiator to the stirred solution and stirring it a second time; A catalyzer was added to the solution after the second stirring and stirred for three times, and the solution was sealed and allowed to stand to obtain a BCN-based thermosensitive hydrogel.

2. The method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 1, characterized in that: Also included is the step of preparing BCN, comprising: Adding boron trioxide and melamine into distilled water and stirring; The stirred solution is heated until evaporated to dryness; Drying the evaporated material to obtain a precursor; The precursor is reacted under high temperature conditions, and after the reaction, it is cooled, washed and dried to obtain white carbon-doped boron nitride powder BCN.

3. The method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 2, characterized in that: The molar ratio of boron trioxide to melamine is 5:

3.

4. The method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 2, characterized in that: The mass ratio of NIPAM to cross-linking agent was 100:

3.

5. The method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 1, characterized in that: Also includes: The solution after the high temperature reaction is centrifuged to obtain a BCN-PEI solution; nitrogen is filled into the solution before the initiator is added; after the BCN-based thermosensitive hydrogel is obtained, the molded BCN-based thermosensitive hydrogel is soaked in deionized water.

6. The method for preparing a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 1, characterized in that: The initiator includes ammonium persulfate; the accelerator includes tetramethylethylenediamine; and the crosslinking agent includes N,N'-methylenebisacrylamide BIS.

7. A carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium prepared according to the preparation method according to any one of claims 2 to 6, characterized in that: The thermosensitive hydrogel is prepared by cross-linking reaction of carbon-doped boron nitride (BCN), polyethyleneimine (PEI), and N-isopropylacrylamide (NIPAM).

8. The carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 7, characterized in that: The mass ratio of BCN to PEI is 1:5~8, and the mass of NIPAM is 0.8g.

9. Use of the carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 8 in adsorbing and recovering pollutants in water.

10. The use of a carbon-doped boron nitride-based thermosensitive hydrogel for recovering hexavalent chromium according to claim 9, characterized in that: The pollutants include Cr 6+ .

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