CN114377717A - Lignin-based carbon composite graphite phase carbon nitride/Mxene heterojunction photocatalyst and preparation method and application thereof - Google Patents
Lignin-based carbon composite graphite phase carbon nitride/Mxene heterojunction photocatalyst and preparation method and application thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 22
- 239000002131 composite material Substances 0.000 title claims abstract description 13
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 title abstract description 14
- 229910002804 graphite Inorganic materials 0.000 title abstract description 5
- 239000010439 graphite Substances 0.000 title abstract description 5
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 58
- 230000001699 photocatalysis Effects 0.000 claims abstract description 33
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- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims abstract description 14
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- UQZIWOQVLUASCR-UHFFFAOYSA-N alumane;titanium Chemical compound [AlH3].[Ti] UQZIWOQVLUASCR-UHFFFAOYSA-N 0.000 claims abstract description 4
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- 238000003756 stirring Methods 0.000 claims description 12
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 claims description 10
- 239000002243 precursor Substances 0.000 claims description 9
- 239000002244 precipitate Substances 0.000 claims description 8
- 238000001179 sorption measurement Methods 0.000 claims description 7
- 239000001763 2-hydroxyethyl(trimethyl)azanium Substances 0.000 claims description 6
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- SGMZJAMFUVOLNK-UHFFFAOYSA-M choline chloride Chemical compound [Cl-].C[N+](C)(C)CCO SGMZJAMFUVOLNK-UHFFFAOYSA-M 0.000 claims description 6
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- KWIUHFFTVRNATP-UHFFFAOYSA-O N,N,N-trimethylglycinium Chemical compound C[N+](C)(C)CC(O)=O KWIUHFFTVRNATP-UHFFFAOYSA-O 0.000 claims description 2
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- 230000015572 biosynthetic process Effects 0.000 claims description 2
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- 239000000725 suspension Substances 0.000 claims 1
- 229910052724 xenon Inorganic materials 0.000 claims 1
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- B01J35/39—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
- C01B15/01—Hydrogen peroxide
- C01B15/027—Preparation from water
Abstract
The invention provides a heterojunction photocatalyst of lignin-based carbon composite graphite phase carbon nitride/Mxene and a preparation method and application thereof, wherein firstly pulping alkali lignin is taken as a carbon source, and lignin-based nano carbon particles are uniformly dissolved and fired through a eutectic solvent; then, using urea as a raw material, and preparing graphite-phase carbon nitride as a main body part of the photocatalyst by a thermal condensation method; then, preparing a two-dimensional conductive material Mxene by taking titanium aluminum carbide as a raw material and etching the titanium aluminum carbide by hydrofluoric acid; finally, compounding g-C by heat treatment with lignin-based nanocarbon under the protection of inert gas3N4And Mxene, construction of C/g-C3N4the/Mxene ternary heterojunction photocatalysis material. The heterojunction photocatalyst prepared by the invention has the advantages of better illumination absorption, rapid photo-generated electron transfer, higher photo-generated carrier separation efficiency and better photocatalytic reaction activity, and is environment-friendly lightThe catalytic material can be used for preparing hydrogen peroxide by photocatalysis under visible light.
Description
Technical Field
The invention belongs to the technical field of photocatalysts, and particularly relates to lignin-based carbon composite g-C3N4A heterojunction photocatalyst of Mxene and a preparation method and application thereof.
Background
Hydrogen peroxide (H)2O2) The multifunctional oxidant has wide application, and can be applied to the fields of biology, environmental remediation, chemical industry and the like. The hydrogen peroxide is generally weak in oxidizing property, the solution of the hydrogen peroxide can be diluted for sterilization, and the final product after the reaction is mainly water, so that secondary pollution is avoided, and the hydrogen peroxide is an environment-friendly oxidant. The traditional method is not environment-friendly enough, so that the hydrogen peroxide is prepared by photocatalysis. In addition, the photocatalysis method does not need to use hydrogen, and is a safe and green method.
Graphite phase carbon nitride (g-C)3N4) As a new nonmetal two-dimensional material, the material has the advantages of easily obtained raw materials, simple and convenient synthesis, stable physicochemical property, no toxicity, adjustable visible light response and electronic property and the like, and becomes one of popular materials in the field of photocatalysis in recent ten years. Despite the original g-C3N4Has relatively ideal energy band structure, theoretical forbidden band width of about 2.7eV, visible light response and strong coulomb restraint effect, and makes g-C3N4The defects of serious carrier recombination, poor conductivity and the like are inevitably generated. Albeit g-C3N4The photocatalyst has larger theoretical specific surface area, but because two-dimensional sheets are easy to agglomerate and stack in the actual preparation process, the actual specific surface area is often not up to the theoretical value, so that the lack of active sites is caused, and the photocatalytic performance is damaged.
Mxene proved to be a promising class of co-catalyst, but with poor stability. In thatIn the research of this chapter, we succeeded in constructing a robust heterojunction photocatalyst in which a few layers of Mxene are wrapped in g-C3N4In the process, self-oxidation is prevented. The catalyst shows stable and efficient photocatalytic performance in hydrogen peroxide production.
Disclosure of Invention
Aiming at the problems, the invention provides lignin-based carbon composite g-C3N4The prepared heterojunction photocatalyst has the advantages of good illumination absorption, rapid photo-generated electron transfer, high photo-generated carrier separation efficiency and excellent photocatalytic reaction activity, is an environment-friendly photocatalytic material, and can be used for preparing hydrogen peroxide under visible light photocatalysis.
In order to achieve the purpose, the technical scheme of the invention is as follows:
(1) alkali lignin treatment: putting 10-20 g of alkali lignin extracted from pulping black liquor into a beaker, pouring 250-500 mL of dilute hydrochloric acid (0.1-0.5 mol/L), standing for 12-24 h, filtering, and finally putting into an air drying oven for drying at 60-80 ℃ to obtain the lignin.
(2) Preparing lignin-based nanocarbon: firstly, preparing a eutectic solvent, putting choline chloride serving as a hydrogen bond acceptor and thiourea (urea or betaine) serving as a hydrogen bond donor into a three-neck flask in a molar ratio (1: 1-1: 5), reacting for 15-90 min in an oil bath pot (80-90 ℃), and after a clear and transparent solution is formed, mixing the materials in a mass ratio of 1: 3-1: 10 (the sum of the mass of the lignin and the mass of the hydrogen bond acceptor and the hydrogen bond donor) is added into the lignin obtained in the step (1) and continuously stirred, after reaction for 12-24 h, a proper amount of liquid is taken and put into a freezing bottle for freezing for 12-24 h, and the lignin freeze-dried powder is obtained after grinding.
（3）g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10-20 g of melamine, putting the melamine into a tubular furnace at 450-550 ℃, heating at 1-2 ℃/min, and preparing g-C3N4。
(4) Mxene: under continuous stirring (to prevent the solution from heat release and splash), 0.5-1 g of commercially available titanium aluminum carbide Ti is weighed3AlC2Slowly adding the powder into the container to be filled with the powder for 40 to80mL of 40wt% hydrofluoric acid solution is stirred in a centrifuge tube under the water bath heating condition of 25-50 ℃ for 24-48 h. And then washing the precipitate by using deionized water for centrifugation (rotating speed of 6000-9000 r/min) until the pH value of the supernatant is close to 7. Vacuum drying the obtained precipitate at 40-60 ℃ overnight to obtain etched-phase Ti3C2Black powder, noted Mxene.
（5）C/g-C3N4Preparation of a/Mxene ternary heterojunction photocatalytic material: putting 5-10mg of lignin freeze-dried powder into 5-20 mL of deionized water, performing ultrasonic treatment for 15-30 min, adding 5-10mg of Mxene, performing ultrasonic treatment for 15-30 min, and finally adding 1g g-C3N4 Performing ultrasonic treatment for 15-30 min, pouring the mixture into a crucible after the ultrasonic treatment is finished, drying the mixture in a blast drying oven at the temperature of 60-80 ℃ for 12-24 h, putting the sample into a tube furnace at the temperature of 450-550 ℃ and at the temperature of 1-2 ℃/min after the drying is finished, preserving the heat for 0.5-1 h, and obtaining the lignin-based carbon composite g-C under the protection of inert gas3N4A heterojunction photocatalyst of/Mxene.
Mixing C/g-C3N4Taking a/Mxene ternary heterojunction photocatalytic material as a photocatalyst, putting 50mg of the novel photocatalyst into 50mL of aqueous solution, introducing oxygen, preparing hydrogen peroxide under the condition of visible light illumination, and testing the content of the hydrogen peroxide by using a POD/DPD method.
The invention has the following advantages:
1. lignin-based carbon composite g-C of the present invention3N4The heterojunction photocatalyst of/Mxene takes industrial alkali lignin as a carbon precursor, and realizes the maximum utilization of resources.
2. The dissolved lignin adopts the eutectic solvent, so that the cost is low, the environment is protected, and the dissolving effect is good.
3. The Mxene is introduced, so that the conductive capability of the carbon nitride is enhanced.
4. The composite photocatalyst provided by the invention not only has excellent photocatalytic property, but also has good visible light response performance; at the same time, C/g-C3N4The Mxene heterojunction photocatalytic material can endow the advantages of continuous surface electron transmission, and further improves the catalytic performance of the composite photocatalyst.
Drawings
FIG. 1 is a drawing of Mxene, g-C prepared in example 1 of the present invention3N4And Mxene/g-C3N4SEM picture of (1);
FIG. 2 shows g-C prepared in example 1 of the present invention3N4And Mxene/g-C3N4XRD pattern of (a).
Detailed Description
The following further describes the embodiments of the present invention. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto.
Example 1
Alkali lignin treatment: and (3) putting 20g of industrial alkali lignin into a beaker, pouring 500mL of dilute hydrochloric acid, standing for 24h, filtering, and finally putting into an air-blast drying oven for drying at 80 ℃.
Preparing lignin-based nano carbon: firstly, preparing a eutectic solvent, taking choline chloride as a hydrogen bond acceptor and thiourea as a hydrogen bond donor according to a molar ratio of 1: 2, putting the mixture into a three-neck flask, carrying out reaction in an oil bath kettle at 90 ℃ for 90min, and reacting in a mass ratio of 1:3 (the sum of the mass of the lignin and the mass of the hydrogen bond acceptor and the hydrogen bond donor) adding the lignin and continuously stirring, reacting for 24 hours, taking a proper amount of liquid, putting the liquid into a freezing bottle, freeze-drying for 24 hours, and grinding to obtain the lignin freeze-dried powder.
③g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10g of melamine, putting the melamine into a tube furnace at 500 ℃, heating at 2 ℃/min, and preparing g-C3N4。
Mxene: 1g of commercially available Ti-aluminum-carbon (Ti) was weighed with constant stirring (to prevent exothermic splashing of the solution)3AlC2The powder was slowly added to a centrifuge tube containing 80mL of 40% hydrofluoric acid solution and stirred under heating in a water bath at 50 ℃ for 48 hours. The pellet was then washed by centrifugation with deionized water (9000 r/min) until the supernatant pH was close to 7. Vacuum drying the obtained precipitate at 60 ℃ overnight to obtain etching phase Ti3C2Black powder, noted Mxene.
⑤C/g-C3N4Ternary heterojunction photocatalysis material for MxeneMaterial preparation: putting 5mg of lyophilized powder into 10mL of deionized water, performing ultrasonic treatment for 30min, adding 5mg of Mxene, performing ultrasonic treatment for 30min, and adding 1gg-C3N4 Performing ultrasonic treatment for 30min, pouring into a crucible after the ultrasonic treatment, drying in a forced air drying oven at 80 deg.C for 24h, placing the sample in a tubular furnace at 500 deg.C for 2 deg.C/min, maintaining for 1h, and protecting with inert gas to obtain C/g-C3N4the/Mxene ternary heterojunction photocatalysis material.
And (3) photocatalytic reaction: taking 50mg of C/g-C3N4Putting the Mxene ternary heterojunction photocatalytic material into a photocatalytic reaction device, adding 50mL of water, reacting for 30min in a dark condition, sampling after dark adsorption, starting a visible light to irradiate the solution after sampling, taking samples every 1h, immediately filtering all the sampled solutions by using a filter membrane after sampling, putting the filtered solutions into a 5 mL centrifuge tube for shading and sealing, finally testing the content of hydrogen peroxide by using a POD/DPD method, and measuring the absorbance of a hydrogen peroxide solution by using an ultraviolet visible absorption light detector to obtain the hydrogen peroxide concentration of 1.2 mmol/L.
FIG. 1 shows Mxene and Mxene/g-C prepared in example 13N4As can be seen from fig. 1, Mxene has a layered structure, and g-C of carbon nitride precursor melamine after one-step heat treatment3N4The total is a block structure, and g-C after Mxene and lignin-based carbon are loaded3N4After heat treatment, part of lignin is carbonized into small particles (shown by white circles) loaded on the surface of the Mxene or entering gaps of the Mxene, and carbon nitride is well combined with the Mxene and lignin-based carbon. FIG. 2 shows g-C prepared in example 13N4And C/g-C3N4XRD pattern of/Mxene, as can be seen from FIG. 2, there appear two characteristic peaks 12.9 typical of graphite phase carbon nitrideoAnd 27.6oCorresponding to the (100) and (002) crystal planes, respectively; and C/g-C3N4The ternary heterojunction of/Mxene appears 33.9o、38.9o、41.7o、60.1o、70.3o 、73.9oThe new diffraction peaks are all characteristic peaks from Mxene, and in addition, a small amount of lignin-based diffraction carbon is introduced into the ternary heterojunction, so that g-C3N4The (100) and (002) crystal face strengths of the (A) and (B) are weakened without affecting g-C3N4As a characteristic peak of the main catalyst.
Example 2
Alkali lignin treatment: and (3) putting 20g of industrial alkali lignin into a beaker, pouring 500mL of dilute hydrochloric acid, standing for 24h, filtering, and finally putting into an air-blast drying oven for drying at 80 ℃.
Preparing lignin-based nano carbon: firstly, preparing a eutectic solvent, taking choline chloride as a hydrogen bond acceptor and thiourea as a hydrogen bond donor according to a molar ratio of 1: 2, putting the mixture into a three-neck flask, carrying out reaction in an oil bath kettle at 90 ℃ for 90min, and reacting in a mass ratio of 1: and 5 (the mass of the lignin is the sum of the mass of the hydrogen bond acceptor and the mass of the hydrogen bond donor), adding the lignin, continuously stirring, reacting for 24 hours, taking a proper amount of liquid, putting the liquid into a freezing bottle, freeze-drying for 24 hours, and grinding to obtain the lignin freeze-dried powder.
③g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10g of melamine, putting the melamine into a tube furnace at 500 ℃, heating at 2 ℃/min, and preparing g-C3N4。
Mxene: 1g of commercially available Ti-aluminum-carbon (Ti) was weighed with constant stirring (to prevent exothermic splashing of the solution)3AlC2The powder was slowly added to a centrifuge tube containing 80mL of 40% hydrofluoric acid solution and stirred under heating in a water bath at 50 ℃ for 48 hours. The pellet was then washed by centrifugation with deionized water (9000 r/min) until the supernatant pH was close to 7. Vacuum drying the obtained precipitate at 60 ℃ overnight to obtain etching phase Ti3C2Black powder, noted Mxene.
⑤C/g-C3N4Preparation of a/Mxene ternary heterojunction photocatalytic material: putting 10mg lyophilized powder into 10mL deionized water, performing ultrasonic treatment for 30min, adding 5mg Mxene, performing ultrasonic treatment for 30min, and adding 1g g-C3N4 Performing ultrasonic treatment for 30min, pouring into a crucible after the ultrasonic treatment, drying in a forced air drying oven at 80 deg.C for 24h, placing the sample in a tubular furnace at 500 deg.C for 2 deg.C/min, maintaining for 1h, and protecting with inert gas to obtain C/g-C3N4the/Mxene ternary heterojunction photocatalysis material.
And (3) photocatalytic reaction: taking 50mg of C/g-C3N4Putting the Mxene ternary heterojunction photocatalytic material into a photocatalytic reaction device, adding 50mL of water, reacting for 30min in a dark condition, sampling after dark adsorption, starting a visible light to irradiate the solution after sampling, taking samples every 1h, immediately filtering all the sampled solutions by using a filter membrane after sampling, putting the filtered solutions into a 5 mL centrifuge tube for shading and sealing, finally testing the content of hydrogen peroxide by using a POD/DPD method, and measuring the absorbance of a hydrogen peroxide solution by using an ultraviolet visible absorption light detector to obtain the hydrogen peroxide concentration of 0.75 mmol/L.
Example 3
Alkali lignin treatment: and (3) putting 20g of industrial alkali lignin into a beaker, pouring 500mL of dilute hydrochloric acid, standing for 24h, filtering, and finally putting into an air-blast drying oven for drying at 80 ℃.
Preparing lignin-based nano carbon: firstly, preparing a eutectic solvent, taking choline chloride as a hydrogen bond acceptor and urea as a hydrogen bond donor, and mixing the two materials in a molar ratio of 1:3, putting the mixture into a three-neck flask, carrying out reaction in an oil bath kettle at 90 ℃ for 60min, and carrying out reaction in a mass ratio of 1:3 (the sum of the mass of the lignin and the mass of the hydrogen bond acceptor and the hydrogen bond donor) adding the lignin and continuously stirring, reacting for 24 hours, taking a proper amount of liquid, putting the liquid into a freezing bottle, freeze-drying for 24 hours, and grinding to obtain the lignin freeze-dried powder.
③g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10g of melamine, putting the melamine into a tube furnace at 500 ℃, heating at 2 ℃/min, and preparing g-C3N4。
Mxene: 1g of commercially available Ti-aluminum-carbon (Ti) was weighed with constant stirring (to prevent exothermic splashing of the solution)3AlC2The powder was slowly added to a centrifuge tube containing 80mL of 40% hydrofluoric acid solution and stirred under heating in a water bath at 50 ℃ for 48 hours. The pellet was then washed by centrifugation with deionized water (9000 r/min) until the supernatant pH was close to 7. Vacuum drying the obtained precipitate at 60 ℃ overnight to obtain etching phase Ti3C2Black powder, noted Mxene.
⑤C/g-C3N4Preparation of a/Mxene ternary heterojunction photocatalytic material: taking 10mg of jellyPutting the dry powder into 10mL deionized water, performing ultrasonic treatment for 30min, adding 10mg Mxene, performing ultrasonic treatment for 30min, and finally adding 1gg-C3N4 Performing ultrasonic treatment for 30min, pouring into a crucible after the ultrasonic treatment, drying in a forced air drying oven at 80 deg.C for 24h, placing the sample in a tubular furnace at 500 deg.C for 2 deg.C/min, maintaining for 1h, and protecting with inert gas to obtain C/g-C3N4the/Mxene ternary heterojunction photocatalysis material.
And (3) photocatalytic reaction: taking 50mg of C/g-C3N4Putting the Mxene ternary heterojunction photocatalytic material into a photocatalytic reaction device, adding 50mL of water, reacting for 30min in a dark condition, sampling after dark adsorption, starting a visible light to irradiate the solution after sampling, taking samples every 1h, immediately filtering all the sampled solutions by using a filter membrane after sampling, putting the filtered solutions into a 5 mL centrifuge tube for shading and sealing, finally testing the content of hydrogen peroxide by using a POD/DPD method, and measuring the absorbance of a hydrogen peroxide solution by using an ultraviolet visible absorption light detector to obtain the hydrogen peroxide concentration of 0.45 mmol/L.
Comparative example 1
Alkali lignin treatment: and (3) putting 20g of industrial alkali lignin into a beaker, pouring 500mL of dilute hydrochloric acid, standing for 24h, filtering, and finally putting into an air-blast drying oven for drying at 80 ℃.
Preparing lignin-based nano carbon: firstly, preparing a eutectic solvent, taking choline chloride as a hydrogen bond acceptor and thiourea as a hydrogen bond donor according to a molar ratio of 1: 2, putting the mixture into a three-neck flask, carrying out reaction in an oil bath kettle at 90 ℃ for 90min, and reacting in a mass ratio of 1:3 (the sum of the mass of the lignin and the mass of the hydrogen bond acceptor and the hydrogen bond donor) adding the lignin and continuously stirring, reacting for 24 hours, taking a proper amount of liquid, putting the liquid into a freezing bottle, freezing for 24 hours, and grinding to obtain the nano carbon freeze-dried powder.
③g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10g of melamine, putting the melamine into a tube furnace at 500 ℃, heating at 2 ℃/min, and preparing g-C3N4。
④C/g-C3N4Preparing a binary heterojunction photocatalytic material: putting 5mg of lyophilized powder into 10mL of deionized water, performing ultrasonic treatment for 30min, and adding 1gg-C3N4 Ultrasonic 30min, pouring the mixture into a crucible after the ultrasonic treatment is finished, drying the mixture for 24 hours at the temperature of 80 ℃ in a blast drying oven, putting the sample into a tubular furnace after the drying is finished, keeping the temperature for 1 hour at the temperature of 500 ℃ at the speed of 2 ℃/min, and obtaining C/g-C under the protection of inert gas3N4A binary heterojunction photocatalytic material.
And (3) photocatalytic reaction: taking 50mg of C/g-C3N4Putting the binary heterojunction photocatalytic material into a photocatalytic reaction device, adding 50mL of water, reacting for 30min in the dark, sampling after dark adsorption, starting a visible light to irradiate the solution after sampling, taking samples every 1h, immediately filtering all the sampled solutions by using a filter membrane after sampling, putting the filtered solutions into a 5 mL centrifuge tube for shading and sealing, finally testing the content of hydrogen peroxide by using a POD/DPD method, and measuring the absorbance of the hydrogen peroxide solution by using an ultraviolet visible absorption light detector to obtain the hydrogen peroxide concentration of 0.2 mmol/L.
Comparative example 2
①g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10g of melamine, putting the melamine into a tube furnace at 500 ℃, heating at 2 ℃/min, and preparing g-C3N4。
Mxene: 1g of commercially available Ti-aluminum-carbon (Ti) was weighed with constant stirring (to prevent exothermic splashing of the solution)3AlC2The powder was slowly added to a centrifuge tube containing 80mL of 40% hydrofluoric acid solution and stirred under heating in a water bath at 50 ℃ for 48 hours. The pellet was then washed by centrifugation with deionized water (9000 r/min) until the supernatant pH was close to 7. Vacuum drying the obtained precipitate at 60 ℃ overnight to obtain etching phase Ti3C2Black powder, noted Mxene.
③g-C3N4Preparation of/Mxene binary heterojunction photocatalytic material: 5mgMxene is put into 10mL deionized water for 30min by ultrasonic treatment, and then 1gg-C is added3N4 Performing ultrasonic treatment for 30min, pouring into a crucible after the ultrasonic treatment, drying in a forced air drying oven at 80 deg.C for 24h, placing the sample in a tubular furnace at 500 deg.C for 2 deg.C/min, maintaining for 1h, and protecting with inert gas to obtain g-C3N4the/Mxene binary heterojunction photocatalytic material.
And (3) photocatalytic reaction: taking 50mg g-C3N4Putting the Mxene binary heterojunction photocatalytic material into a photocatalytic reaction device, adding 50mL of water, reacting for 30min in a dark condition, sampling after dark adsorption, starting a visible light to irradiate the solution after sampling, taking samples every 1h, immediately filtering all the sampled solutions by using a filter membrane after sampling, putting the filtered solutions into a 5 mL centrifuge tube for shading and sealing, finally testing the content of hydrogen peroxide by using a POD/DPD method, and measuring the absorbance of a hydrogen peroxide solution by using an ultraviolet visible absorption light detector to obtain the hydrogen peroxide concentration of 0.3 mmol/L.
Comparative example 3
g-C3N4The preparation of (1): taking melamine as a precursor, weighing 10g of melamine, putting the melamine into a tube furnace at 500 ℃, heating at 2 ℃/min, and preparing g-C3N4。
And (3) photocatalytic reaction: taking 50mg g-C3N4Placing a photocatalytic material into a photocatalytic reaction device, adding 50mL of water, reacting for 30min in the dark, sampling after dark adsorption, starting a visible light to irradiate the solution after sampling, taking samples every 1h, immediately filtering all the sampled solutions by using a filter membrane after sampling, placing the filtered solutions into a 5 mL centrifuge tube for shading and sealing, finally testing the content of hydrogen peroxide by using a POD/DPD method, and measuring the absorbance of the hydrogen peroxide solution by using an ultraviolet visible absorption light detector to obtain the hydrogen peroxide concentration of 0.1 mmol/L.
According to the invention, carbon nitride is a main catalyst and is responsible for exciting out photo-generated electrons and holes after illumination, and Mxene and lignin-based carbon are cocatalyst, so that the electrons generated by the carbon nitride are promoted to be rapidly transferred, the separation and transfer of photo-generated carriers are improved, and the effect of photosynthesizing the hydrogen peroxide is improved. After lignin-based carbon is added into the system, the electron transfer effect of Mxene can be further improved, and the Mxene needs to be stripped to form gaps, so that the filling of the lignin-based nano carbon is facilitated. In the invention, photo-generated electrons excited by the carbon nitride conduction band can be combined with oxygen molecules to form superoxide radicals; and the valence band oxidizes water molecules to form protons, which are then combined with superoxide radicals to form hydrogen peroxide. And a part of Mxene is introduced into the carbon nitride system, so that the specific surface area and the electron transfer effect can be improved.
The heterojunction photocatalyst prepared by the method has the advantages of better illumination absorption, rapid photo-generated electron transfer, higher photo-generated carrier separation efficiency and better photocatalytic reaction activity, is an environment-friendly photocatalytic material, and can be used for preparing hydrogen peroxide under visible light photocatalysis.
Although specific embodiments of the invention have been described above, it will be understood by those skilled in the art that the specific embodiments described are illustrative only and are not limiting upon the scope of the invention, and that equivalent modifications and variations can be made by those skilled in the art without departing from the spirit of the invention, which is to be limited only by the appended claims.
Claims (9)
1. Lignin-based carbon composite g-C3N4The preparation method of the Mxene heterojunction photocatalyst is characterized in that: the preparation method comprises the following steps:
(1) alkali lignin treatment: taking alkali lignin and dilute sulfuric acid extracted from the pulping black liquor, magnetically stirring and mixing for 12-24 hours at room temperature, filtering, and drying to obtain lignin;
(2) preparing lignin-based nanocarbon: preparing a eutectic solvent, taking choline chloride as a hydrogen bond receptor and thiourea or urea or betaine as a hydrogen bond donor, reacting for 15-90 min at 80-90 ℃, adding the lignin treated in the step (1) after forming a clear and transparent solution, continuously stirring, reacting for 12-24 h, freeze-drying for 12-24 h, and grinding to obtain lignin freeze-dried powder;
（3）g-C3N4the preparation of (1): taking urea as a precursor, heating to 450-550 ℃ at a heating rate of 1-2 ℃/min in a tubular furnace, and preserving heat for 0.5-1 h to obtain g-C3N4；
(4) Preparation of Mxene: slowly adding aluminum titanium carbide powder into hydrofluoric acid solution, stirring for 24-72 h under the water bath heating condition of 25-50 ℃, centrifuging by using deionized water, washing the precipitate until the pH of the supernatant is 7, and drying the obtained precipitate to obtain etched Ti3C2Black powder, noted Mxene;
（5）C/g-C3N4preparation of the/Mxene ternary heterojunction photocatalytic material: putting the lignin freeze-dried powder prepared in the step (2) into deionized water for uniform ultrasonic dispersion, adding the Mxene prepared in the step (4), continuing to perform uniform ultrasonic dispersion, and adding the g-C prepared in the step (3)3N4 Then performing ultrasonic dispersion uniformly, drying at 60-80 ℃ for 12-24 h after the ultrasonic treatment is finished, and performing heat treatment after the drying is finished to obtain the lignin-based carbon composite g-C3N4A heterojunction photocatalyst of/Mxene.
2. The method of claim 1, wherein: the concentration of the dilute sulfuric acid in the step (1) is 0.1-0.5 mol/L.
3. The method of claim 1, wherein: the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor in the step (2) is 1: 1-1: 5.
4. the method of claim 1, wherein: in the step (2), the ratio of the mass of the lignin to the sum of the mass of the hydrogen bond acceptor and the mass of the hydrogen bond donor is 1: 3-1: 10.
5. the method of claim 1, wherein: in the step (5), the mass of the lignin freeze-dried powder is 5-10mg, the mass of Mxene is 5-10mg, and g-C3N4The mass of (2) is 1 g.
6. The method of claim 1, wherein: the heat treatment in the step (5) is specifically as follows: under the protection of inert gas, the temperature is raised to 450-550 ℃ in a tubular furnace at the heating rate of 1-2 ℃/min, and the temperature is preserved for 0.5-1 h.
7. A lignin-based carbon composite g-C prepared by the method of any one of claims 1 to 63N4A heterojunction photocatalyst of/Mxene.
8. The lignin-based carbon composite g-C of claim 73N4Application of a/Mxene heterojunction photocatalyst in photocatalytic synthesis of hydrogen peroxide.
9. Use according to claim 8, characterized in that: and (3) photocatalytic reaction: compounding lignin-based carbon with g-C3N4The heterojunction photocatalyst of/Mxene is mixed with deionized water, and reacts under the condition of keeping out of the sun, and after dark adsorption is balanced, a visible light xenon lamp is started to irradiate the suspension.
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