An α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material and its preparation method and application

Abstract

The present invention discloses an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material and its preparation method and application, belonging to the field of materials science and technology. The mpg-C3N4 material is modified in terms of morphology control, element doping, and heterostructure construction, and a Z-type heterojunction photocatalyst with a solid electron mediator is synthesized based on the mpg-C3N4. By controlling the synthesis conditions, a large specific surface area, visible light response, non-toxic and environmentally friendly α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material is prepared. This nanocomposite material overcomes the inherent shortcomings of single semiconductors g-C3N4 and α-Fe2O3, such as small specific surface area, low charge carrier separation efficiency, and limited visible light absorption capacity. The structure and properties of the nanocomposite material are characterized by XPS, XRD, SEM, TEM, FT-IR, BET, UV-vis DRS, and Zeta potential analysis, proving the successful preparation of the material. It was used to photocatalytically degrade the explosive 2,4,6-trinitrotoluene. A series of exploratory experiments showed that under 12 hours of illumination, the photodegradation rate of TNT by 10wt% α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material can reach 99.57%, which is better than other materials and methods.

Description

Technical Field

[0001] The present invention belongs to the field of material science and technology, and specifically relates to an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material and a preparation method and application thereof. Background Art

[0002] Nitroaromatic compounds, a class of compounds containing both aromatic rings and nitro functional groups, are widely used in military and civilian applications, including dyes, explosives, insecticides, and pesticides. During the production and use of chemical products, large quantities of nitroaromatic compounds are released into environmental water bodies and soils. Through bioaccumulation and transport through the food chain, they pose serious risks to microorganisms, plants, animals, and the surrounding ecosystem. 2,4,6-Trinitrotoluene (TNT), the most widely used nitroaromatic explosive, offers advantages such as low impact sensitivity, good detonation performance, and low cost. However, it is also highly toxic and carcinogenic. Conventional treatment technologies for TNT in wastewater, typically based on biological systems (aerated or non-aerated biofilters) and physicochemical systems (flocculation, sedimentation / filtration), perform poorly in this wastewater treatment process. Alternative methods, such as membrane separation, can reduce pollutant concentrations but do not disrupt the pollutant's structure. Photocatalytic oxidation technology can treat wastewater containing nitroaromatic compounds in a cheap, green and environmentally friendly way, and will be one of the most effective methods for treating TNT wastewater.

[0003] Photocatalytic oxidation technology, using semiconductors as catalysts, can convert abundant solar energy into chemical energy and is used to degrade a variety of pollutants in water and air. In recent years, in response to the energy crisis and the increasing utilization of solar energy, the development of photocatalytic materials with narrow band gaps and visible light responsiveness has become a research hotspot. Among these narrow-bandgap, visible-light-responsive semiconductors, research on graphite-like carbon nitride (g-C3N4) has been extremely popular in recent years due to its numerous advantages over other materials, such as non-toxicity, stable photochemical properties, metal-free nature, and ease of preparation. While its application in the field of photocatalysis has been extensively reported, its application in the degradation of TNT has not been reported. While other catalysts, such as TiO2, have been extensively studied for the photodegradation of TNT, the results have been suboptimal, particularly when used as single photocatalysts, which cannot completely degrade or remove TNT.

[0004] After extensive research, it was found that g-C3N4 and α-Fe2O3 themselves have some shortcomings that limit their application, mainly manifested in small specific surface area, limited absorption range, high electron and hole recombination rate, etc., and they need to be modified to improve their performance in photocatalytic degradation of TNT wastewater. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material and its preparation method and application, so as to solve the technical problems of low visible light photocatalytic performance and low TNT wastewater treatment capacity due to the shortcomings of single semiconductors g-C3N4 and α-Fe2O3, such as small specific surface area, low charge carrier separation efficiency and limited visible light absorption capacity.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The invention discloses an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material, wherein mpg-C3N4 and α-Fe2O3 nanoparticles are attached to RGO sheets to form a Z-type heterojunction nanocomposite material; the mass percentage of the α-Fe2O3 nanoparticles is 5%-15%.

[0008] Preferably, the α-Fe2O3 nanoparticles are connected to the RGO sheets via Fe-OC bonds.

[0009] Preferably, the surface of mpg-C3N4 has irregular pores with a diameter of 48-52 nm; the diameter of α-Fe2O3 nanoparticles is 20-50 nm.

[0010] The present invention also discloses a method for preparing the above-mentioned α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material, comprising the following steps:

[0011] 1) calcining urea, cooling, and grinding to obtain mpg-C3N4, adding the obtained mpg-C3N4 to a dilute hydrochloric acid solution, ultrasonically homogenizing, stirring to react, filtering, washing to neutrality, and drying to obtain protonated mpg-C3N4;

[0012] 2) dispersing α-Fe2O3 nanoparticles, RGO powder, sodium dodecylbenzenesulfonate and the protonated mpg-C3N4 prepared in step 1) in deionized water, ultrasonically treating, hydrothermally reacting, washing, filtering and freeze-drying to obtain an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material.

[0013] Preferably, in step 1), the concentration of dilute hydrochloric acid is 0.1-0.7 mol / L, and the usage ratio of mpg-C3N4: dilute hydrochloric acid is (1-5) g: (200-1000) mL.

[0014] Preferably, in step 1), the calcination conditions are: heating to 600-700° C. at a heating rate of 10° C. / min and calcining for 4-6 hours.

[0015] Preferably, in step 1), the ultrasonication time is 0.5-1.5 h; the stirring reaction time is 4-6 h; and the drying time is 12-24 h.

[0016] Preferably, in step 2), the usage ratio of protonated mpg-C3N4:α-Fe2O3 nanoparticles:RGO powder:sodium dodecylbenzenesulfonate is (100-1000) mg:(15-150) mg:(50-500) mg:(100-500) mg.

[0017] Preferably, in step 2), the hydrothermal reaction is carried out at 160-200° C. for 6-8 h; and the freeze-drying time is 12 h.

[0018] The present invention also discloses the application of the above-mentioned α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material in treating wastewater containing nitroaromatic compounds. When the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material is used to treat 2,4,6-trinitrotoluene wastewater, the optimal adsorption capacity is 31.22 mg / g and the optimal photodegradation rate is 99.57%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention discloses an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material, wherein mpg-C3N4 and α-Fe2O3 nanoparticles are attached to RGO sheets to form a Z-type heterojunction nanocomposite material. The Z-type heterojunction nanocomposite material based on mpg-C3N4 and having a solid electron mediator has the advantages of large specific surface area, visible light response, and being non-toxic and environmentally friendly. The highly dispersed α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material effectively overcomes some inherent shortcomings of single semiconductors g-C3N4 and α-Fe2O3, such as small specific surface area, low charge carrier separation efficiency, and limited visible light absorption capacity. The material exhibits excellent photocatalytic activity under visible light irradiation, thereby greatly improving the ability to treat TNT wastewater.

[0021] The present invention also discloses a method for preparing the above-mentioned α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material. By controlling the synthesis conditions, the g-C3N4 material is modified in terms of morphology control, element doping, and heterostructure construction, thereby preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material with a large specific surface area, visible light response, and non-toxic and environmentally friendly. Compared with existing physical, chemical, and microbiological methods for treating TNT in wastewater, photocatalytic oxidation technology can efficiently and environmentally treat wastewater containing nitroaromatic compounds. The highly dispersed Z-type heterojunction α-Fe2O3 / RGO / mpg-C3N4 nanocomposite prepared by the present invention effectively overcomes some inherent shortcomings of single semiconductors g-C3N4 and α-Fe2O3, such as small specific surface area, low charge carrier separation efficiency, and limited visible light absorption capacity. Therefore, it exhibits excellent photocatalytic activity under visible light irradiation, thereby greatly improving the ability to treat TNT wastewater.

[0022] The present invention also discloses the application of the above-mentioned α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material in the treatment of wastewater containing nitro aromatic compounds, which can efficiently treat wastewater containing nitro aromatic compounds in an inexpensive, green and environmentally friendly manner. Compared with traditional physical, chemical and microbial treatment methods, it can completely degrade nitro aromatic compounds and is more efficient and environmentally friendly.

[0023] Furthermore, when the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite was used to treat 2,4,6-trinitrotoluene wastewater, the adsorption of TNT by mpg-C3N4, RGO / mpg-C3N4, α-Fe2O3 / mpg-C3N4, and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites was enhanced compared to pure g-C3N4. The strongest adsorption was achieved by the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite, indicating that the preparation of mesoporous g-C3N4 and its combination with α-Fe2O3 nanoparticles and graphene can enhance the adsorption of TNT by g-C3N4. Through a large number of practical examples, the effects of different conditions on the adsorption and photodegradation properties of the nanocomposites were investigated, and the optimal conditions for the photocatalytic degradation of TNT using the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite were identified. When the conditions are pH = 7.0, C0 = 20 mg / L, C adsorbent = 0.2 g / L, and constant temperature adsorption in the dark for 24 hours, the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material has the strongest adsorption effect on TNT, and the adsorption capacity Qmax is 31.22 mg / g. The adsorption of TNT by α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material can be attributed to three aspects: first, the material itself has a large porous structure, which gives it a large specific surface area and allows physical adsorption; second, mpg-C3N4 and RGO have a large conjugated π bond system, which can interact with the conjugated structure of TNT; third, the amino group on the surface of mpg-C3N4 can form NH···π hydrogen bonds with the π electron cloud of TNT and NH···O hydrogen bonds with the O atom of the nitrosyl group in the TNT molecule, and the carbonyl π bond of the carboxyl group on the RGO surface can form a π hydrogen bond CH···O=C with the methyl group in the TNT molecule. When the conditions are pH = 7.0, C0 = 20 mg / L, C photocatalyst = 0.2 g / L, adsorption in the dark for 1 hour, and illumination for 12 hours, the 10wt% α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material has the strongest photocatalytic degradation performance for TNT, and the photodegradation rate can reach 99.57%, which is better than other materials and methods.Compared with g-C3N4, under the same illumination time, the degradation rates of TNT by mpg-C3N4, RGO / mpg-C3N4, α-Fe2O3 / mpg-C3N4 and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites were all improved. The α-Fe2O3 / RGO / mpg-C3N4 nanocomposite had the strongest photocatalytic degradation performance. This is because the mpg-C3N4 and graphene introduced first have a large specific surface area and rich pore structure, which greatly increases the physical adsorption of TNT by the material; secondly, mpg-C3N4 and RGO will form hydrogen bonds and π-π conjugation with TNT in the solution, and the chemical adsorption is enhanced; finally, the Z-type heterojunction α-Fe2O3 / RGO / mpg-C3N4 formed can reduce the recombination of photogenerated electron and hole pairs while having strong redox ability, which can degrade more TNT. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the preparation of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material of the present invention;

[0025] Figure 2 X-ray diffraction patterns of various samples prepared in Example 1 of the present invention; wherein (a) is graphite, (b) is GO, (c) is g-C3N4, (d) is mpg-C3N4, (e) is RGO / mpg-C3N4, and (f) is α-Fe2O3 / RGO / mpg-C3N4;

[0026] Figure 3 The XPS spectra of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material prepared in Example 1 of the present invention and the peak fitting spectra of C, N, O, and Fe; wherein (a) is the full spectrum, (b) is the C1s spectrum, (c) is the N1s spectrum, (d) is the O1s spectrum, and (e) is the Fe2p spectrum;

[0027] Figure 4 These are SEM images of various samples prepared in Example 2 of the present invention; among them, (a) is mpg-C3N4, (b) is RGO / mpg-C3N4 composite material, (c) is α-Fe2O3 nanoparticles, and (d) is α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material;

[0028] Figure 5TEM images of various samples prepared in Example 3 of the present invention; wherein, (a) is g-C3N4, (b) is mpg-C3N4 at low magnification, (c) is mpg-C3N4 at high magnification, (d) is GO, (e) is α-Fe2O3 nanoparticles, (f) is α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material, (g) is a high-resolution TEM image of the dotted portion in (f), and (h) is an electron diffraction pattern;

[0029] Figure 6 The following are Fourier transform infrared spectra of various samples prepared in Example 4 of the present invention; wherein, (a) is g-C3N4, (b) is mpg-C3N4, (c) is RGO / mpg-C3N4, and (d) is α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material;

[0030] Figure 7 Adsorption performance test of g-C3N4, mpg-C3N4 and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites prepared in Example 5 of the present invention; wherein (a) is the nitrogen adsorption-desorption isotherm, and (b) is the pore size distribution diagram;

[0031] Figure 8 The UV-visible diffuse reflectance spectra of different materials prepared in Example 4 of the present invention are shown;

[0032] Figure 9 This is the Zeta potential diagram of the material prepared in Example 1 of the present invention;

[0033] Figure 10 The effect of different solution pH on TNT adsorption;

[0034] Figure 11 The effect of different adsorbent concentrations on TNT adsorption;

[0035] Figure 12 The effect of different initial TNT concentrations on TNT adsorption;

[0036] Figure 13 The effect of different adsorbent types on TNT adsorption;

[0037] Figure 14 The effect of different solution pH on TNT degradation rate;

[0038] Figure 15 The effect of different solution initial concentrations on TNT degradation rate;

[0039] Figure 16 The effect of different photocatalyst concentrations on TNT degradation rate;

[0040] Figure 17The effects of different photocatalyst types on TNT degradation rate; (a) is g-C3N4, (b) is mpg-C3N4, (c) is RGO / mpg-C3N4, (d) is α-Fe2O3 / mpg-C3N4, and (e) is α-Fe2O3 / RGO / mpg-C3N4;

[0041] Figure 18 The effect of α-Fe2O3 content in α-Fe2O3 / RGO / mpg-C3N4 nanocomposite materials on TNT degradation rate; among them, (a) is 0% α-Fe2O3, (b) is 5wt% α-Fe2O3, (c) is 10wt% α-Fe2O3, and (d) is 15wt% α-Fe2O3. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] Existing methods for treating TNT in wastewater include physical and chemical techniques (such as activated carbon adsorption) and microbial treatment. However, these methods have numerous drawbacks, including high cost, complex processes, incomplete degradation, difficulty in adsorbent regeneration, and secondary pollution. Furthermore, conventional microbial methods struggle to completely treat this type of wastewater, resulting in far less than ideal treatment results. Photocatalytic oxidation technology offers the potential for efficient and environmentally friendly treatment of wastewater containing nitroaromatic compounds.

[0045] The present invention uses a template-free method to prepare mpg-C3N4 with a large specific surface area. In order to make it easier to composite with negatively charged graphene, the mpg-C3N4 is protonated with dilute hydrochloric acid. The α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material can be controllably prepared by a hydrothermal method.

[0046] In addition, the nanocomposite's structure and properties were characterized using various instruments, including XPS, XRD, SEM, TEM, FT-IR, BET, UV-vis DRS, and zeta potential analysis. The photocatalyst's performance in adsorbing and photocatalytically degrading the organic pollutant TNT was then investigated. Factors influencing adsorption and photocatalytic degradation were analyzed to determine optimal conditions for TNT adsorption and photocatalytic degradation, which will be applied to treat TNT-containing wastewater.

[0047] The present invention is described in further detail below with reference to the accompanying drawings:

[0048] 1. Preparation of α-Fe2O3 / RGO / mpg-C3N4 nanocomposites

[0049] Preparation of protonated mpg-C3N4(pCN): Weigh 10-50g of urea into a covered ceramic crucible, heat to 600-700°C at a heating rate of 10°C / min, heat for 4-6 hours, cool to room temperature, remove, and grind to obtain mpg-C3N4. Prepare a 0.3-0.7mol / L dilute hydrochloric acid solution, take 200-1000mL of dilute hydrochloric acid solution, add 1-5g of the prepared mpg-C3N4, ultrasonicate for 0.5-1.5h, and then vigorously stir the mixed solution with a constant speed stirrer for 4-6h. Remove and filter the mixed solution, wash with deionized water until neutral, and dry in a 70°C oven for 12-24h to obtain protonated mpg-C3N4(pCN).

[0050] α-Fe2O3 / RGO / mpg-C3N4 (FGN) nanocomposites were prepared by hydrothermal method: 100-1000 mg of protonated mpg-C3N4, 15-150 mg of α-Fe2O3 nanoparticles, 50-500 mg of RGO powder and 0.1-0.5 g of sodium dodecylbenzenesulfonate (SDBS) were weighed and dispersed in 20-80 mL of deionized water and ultrasonically treated for 30 min; the mixture was transferred to a high-pressure reactor and reacted at 160-200°C for 6-8 h; the product was washed with deionized water and anhydrous ethanol respectively, filtered and freeze-dried for 12 h; by controlling the mass of RGO and α-Fe2O3 nanoparticles added, α-Fe2O3 / RGO / mpg-C3N4 nanocomposites with different α-Fe2O3 ratios (5%-15%) were finally prepared.

[0051] Example 1

[0052] A method for preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material comprises the following steps:

[0053] Step 1: Preparation of protonated mpg-C3N4(pCN)

[0054] Weigh 10g of urea into a covered ceramic crucible, heat to 600℃ at a heating rate of 10℃ / min, heat for 4h, cool to room temperature, remove, and grind to obtain mpg-C3N4. Prepare a 0.3mol / L dilute hydrochloric acid solution, take 200mL of dilute hydrochloric acid, add 1g of the prepared mpg-C3N4, ultrasonicate for 0.5h, and then vigorously stir the mixed solution with a constant speed stirrer for 4h; remove and filter the mixed solution, wash with deionized water until neutral, and dry in a 70℃ oven for 12h to obtain protonated mpg-C3N4 (pCN);

[0055] Step 2: Preparation of α-Fe2O3 / RGO / mpg-C3N4 (FGN) nanocomposites by hydrothermal method

[0056] 100 mg of protonated mpg-C3N4, 15 mg of α-Fe2O3 nanoparticles, 50 mg of rGO powder, and 0.1 g of sodium dodecylbenzenesulfonate (SDBS) were dispersed in 20 mL of deionized water and sonicated for 30 minutes. The mixture was transferred to an autoclave and reacted at 180°C for 6 hours. The product was washed with deionized water and anhydrous ethanol, filtered, and freeze-dried for 12 hours. By controlling the amount of rGO and α-Fe2O3 nanoparticles added, an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite with a mass percentage of 10% α-Fe2O3 was prepared.

[0057] See also Figure 2 These are the X-ray diffraction patterns of various samples prepared in Example 1 of the present invention. It can be seen from the figure that the interlayer spacing of graphene oxide prepared from graphite is greatly increased, and then GO is reduced to RGO in the hydrothermal reaction. g-C3N4 has two characteristic crystal plane peaks. The composite of the prepared mesoporous g-C3N4 with graphene and α-Fe2O3 nanoparticles will only increase the interlayer spacing of g-C3N4, and will not change the crystal structure of g-C3N4.

[0058] See also Figure 3 The XPS spectrum of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material prepared in Example 1 of the present invention and the peak fitting spectrum of C, N, O, and Fe can be seen from the figure. It can be seen that the α-Fe2O3 nanoparticles are successfully composited and connected to the graphene sheets in the form of Fe-OC bonds.

[0059] See also Figure 9 This is the Zeta potential diagram of the material prepared in Example 1 of the present invention; it can be seen from the figure that mpg-C3N4, GO, and α-Fe2O3 are all negatively charged, and the surface of mpg-C3N4 is positively charged after protonation modification with HCl, which is conducive to the composite with graphene sheets during the hydrothermal reaction.

[0060] Example 2

[0061] A method for preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material comprises the following steps:

[0062] Step 1: Preparation of protonated mpg-C3N4(pCN)

[0063] 20g of urea was weighed into a covered ceramic crucible and heated to 600°C at a rate of 10°C / min. After heating for 4.5 hours, the mixture was cooled to room temperature and ground to obtain mpg-C3N4. A 0.5mol / L concentrated hydrochloric acid solution was prepared. 2g of the prepared mpg-C3N4 was added to 200mL of dilute hydrochloric acid. The mixture was ultrasonically treated for 1 hour, and then vigorously stirred for 4 hours using a constant-speed stirrer. The mixed solution was removed and filtered, washed with deionized water until neutral, and dried in a 70°C oven for 16 hours to obtain protonated mpg-C3N4 (pCN).

[0064] Step 2: Preparation of α-Fe2O3 / RGO / mpg-C3N4 (FGN) nanocomposites by hydrothermal method

[0065] 400 mg of protonated mpg-C3N4, 60 mg of α-Fe2O3 nanoparticles, 200 mg of rGO powder, and 0.2 g of sodium dodecylbenzenesulfonate (SDBS) were dispersed in 30 mL of deionized water and sonicated for 40 minutes. The mixture was transferred to an autoclave and reacted at 180°C for 6 hours. The product was washed with deionized water and anhydrous ethanol, filtered, and freeze-dried for 16 hours. By controlling the amount of rGO and α-Fe2O3 nanoparticles added, an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite with a mass percentage of 10% α-Fe2O3 was prepared.

[0066] Example 3

[0067] A method for preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material comprises the following steps:

[0068] Step 1: Preparation of protonated mpg-C3N4(pCN)

[0069] Weigh 30g of urea into a covered ceramic crucible, heat to 650℃ at a heating rate of 10℃ / min, heat for 5h, cool to room temperature, remove, and grind to obtain mpg-C3N4. Prepare 0.5mol / L concentrated hydrochloric acid solution, take 300mL of dilute hydrochloric acid, add 3g of prepared mpg-C3N4, ultrasonicate for 1h, and then vigorously stir the mixed solution with a constant speed stirrer for 4h; remove and filter the mixed solution, wash with deionized water until neutral, and dry in a 70℃ oven for 18h to obtain protonated mpg-C3N4 (pCN);

[0070] Step 2: Preparation of α-Fe2O3 / RGO / mpg-C3N4 (FGN) nanocomposites by hydrothermal method

[0071] 300 mg of protonated mpg-C3N4, 30 mg of α-Fe2O3 nanoparticles, 300 mg of rGO powder, and 0.3 g of sodium dodecylbenzenesulfonate (SDBS) were dispersed in 40 mL of deionized water and sonicated for 40 minutes. The mixture was transferred to an autoclave and reacted at 160°C for 8 hours. The product was washed with deionized water and anhydrous ethanol, filtered, and freeze-dried for 12 hours. By controlling the amount of rGO and α-Fe2O3 nanoparticles added, an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite with a mass percentage of 5% α-Fe2O3 was prepared.

[0072] See also Figure 4 These are SEM images of various samples prepared in Example 2 of the present invention; Figure 5 TEM images of various samples prepared in Example 3 of the present invention; it can be seen from the figure that the prepared g-C3N4 has a typical lamellar structure, some irregular holes with a diameter of about 50nm appear on the surface of mpg-C3N4, and the mesoporous structure greatly improves the specific surface area of ​​the photocatalyst; GO is a thin and transparent two-dimensional planar structure sheet with a certain degree of curling at the edge; α-Fe2O3 nanoparticles are spheres with a diameter of 20-50nm; after hydrothermal reaction, mpg-C3N4 and α-Fe2O3 nanoparticles adhere to RGO to form α-Fe2O3 / RGO / mpg-C3N4 heterojunction nanocomposite material, and high-resolution TEM images and electron diffraction patterns prove that mpg-C3N4 has an amorphous structure.

[0073] See also Figure 8 The UV-visible diffuse reflectance spectra of different materials prepared in Example 3 of the present invention are as follows. It can be seen from the figure that, compared with g-C3N4, the band gap of the prepared mesoporous g-C3N4 after being compounded with RGO and α-Fe2O3 is reduced, and the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material has a wider absorption range for visible light.

[0074] Example 4

[0075] A method for preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material comprises the following steps:

[0076] Step 1: Preparation of protonated mpg-C3N4(pCN)

[0077] 40g of urea was weighed into a covered ceramic crucible and heated to 650°C at a rate of 10°C / min. After heating for 4 hours, the mixture was cooled to room temperature and ground to obtain mpg-C3N4. A 0.5mol / L concentrated hydrochloric acid solution was prepared. 400mL of dilute hydrochloric acid was added to 4g of the prepared mpg-C3N4. The mixture was ultrasonically treated for 1.5 hours, and then vigorously stirred for 4 hours using a constant-speed stirrer. The mixed solution was removed and filtered, washed with deionized water until neutral, and dried in a 70°C oven for 18 hours to obtain protonated mpg-C3N4 (pCN).

[0078] Step 2: Preparation of α-Fe2O3 / RGO / mpg-C3N4 (FGN) nanocomposites by hydrothermal method

[0079] 400 mg of protonated mpg-C3N4, 30 mg of α-Fe2O3 nanoparticles, 200 mg of rGO powder, and 0.4 g of sodium dodecylbenzenesulfonate (SDBS) were dispersed in 60 mL of deionized water and sonicated for 30 minutes. The mixture was transferred to an autoclave and reacted at 180°C for 6 hours. The product was washed with deionized water and anhydrous ethanol, filtered, and freeze-dried for 12 hours. By controlling the amount of rGO and α-Fe2O3 nanoparticles added, an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite with a mass percentage of 5% α-Fe2O3 was prepared.

[0080] See also Figure 6 The Fourier transform infrared spectra of various samples prepared in Example 4 of the present invention can be seen from the figure. It can be seen that the composite of the prepared mesoporous g-C3N4 and RGO does not destroy the basic structural unit of g-C3N4. At the same time, it shows that the α-Fe2O3 nanoparticles are successfully composited, and the α-Fe2O3 nanoparticles will not change the structure of g-C3N4.

[0081] Example 5

[0082] A method for preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material comprises the following steps:

[0083] Step 1: Preparation of protonated mpg-C3N4(pCN)

[0084] Weigh 50g of urea into a ceramic crucible with a lid, heat to 700℃ at a heating rate of 10℃ / min, heat for 6h, cool to room temperature, remove, and grind to obtain mpg-C3N4. Prepare 0.7mol / L concentrated hydrochloric acid solution, take 1000mL of dilute hydrochloric acid, add 5g of prepared mpg-C3N4, ultrasonicate for 1.5h, and then vigorously stir the mixed solution with a constant speed stirrer for 4h; remove and filter the mixed solution, wash with deionized water until neutral, and dry in a 70℃ oven for 24h to obtain protonated mpg-C3N4 (pCN);

[0085] Step 2: Preparation of α-Fe2O3 / RGO / mpg-C3N4 (FGN) nanocomposites by hydrothermal method

[0086] 1000mg of protonated mpg-C3N4, 150mg of α-Fe2O3 nanoparticles, 500mg of rGO powder, and 0.5g of sodium dodecylbenzenesulfonate (SDBS) were dispersed in 80mL of deionized water and sonicated for 30 minutes. The mixture was transferred to an autoclave and reacted at 200°C for 6 hours. The product was washed with deionized water and anhydrous ethanol, filtered, and freeze-dried for 12 hours. By controlling the amount of rGO and α-Fe2O3 nanoparticles added, an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite with a mass percentage of 10% α-Fe2O3 was prepared.

[0087] See also Figure 7 The adsorption performance test of g-C3N4, mpg-C3N4 and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites prepared in Example 5 of the present invention; wherein, (a) is the nitrogen adsorption-desorption isotherm, and (b) is the pore size distribution diagram; it can be seen from the figure that the spectra of g-C3N4, mpg-C3N4 and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites are typical type IV N2 adsorption-desorption isotherms, and have H3 type hysteresis loops, indicating that the materials contain mesoporous structures.

[0088] Table 1: BET test results

[0089]

[0090] See Table 1 for the BET test results of each material. It can be seen from the table that the specific surface area of ​​mpg-C3N4 is 93.1969m 2 / g, and the specific surface area of ​​g-C3N4 is 9.5637m 2 / g increased by 8.74 times, which will enhance the adsorption and photocatalytic properties of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite. The total pore volumes of g-C3N4, mpg-C3N4, and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites were 0.0512mL / g, 0.4823mL / g, and 0.3801mL / g, respectively. The maximum possible pore sizes were 2.63nm, 2.46nm, and 3.83nm, respectively, and the average pore diameters were 21.41nm, 20.70nm, and 28.76nm, respectively. It can be concluded from this comparison that the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite has a pore size distribution similar to that of mpg-C3N4. The preparation of the mesoporous mpg-C3N4 significantly increased the number of pores on the g-C3N4 surface, while the pore size did not change much.

[0091] 2. Adsorption of TNT by α-Fe2O3 / RGO / mpg-C3N4 nanocomposites

[0092] The prepared 50 mg / L TNT solution was diluted to the required concentration for the test, 50 mL was taken into a 75 mL conical flask, the pH of the solution was adjusted with 1 mol / L HCl and NaOH solutions, a certain amount of the prepared α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material was added, and the conical flask was placed in a constant temperature oscillator at 25°C for light adsorption for a certain period of time. The supernatant was taken and the concentration of 2,4,6-trinitrotoluene after adsorption for a period of time was determined by high performance liquid chromatography. The adsorption effect of α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material on 2,4,6-trinitrotoluene was evaluated by the removal rate p and the adsorption amount Q.

[0093] See also Figure 10Figure 1 shows the effect of different solution pH values ​​on TNT adsorption. As shown in the figure, at pH 7, the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite exhibits the best TNT adsorption, with a maximum adsorption capacity of 31.22 mg / g and a TNT removal rate of 62.45%. The TNT adsorption behavior of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite can be attributed to three factors: first, the material's inherent porous structure and large specific surface area allow for physical adsorption; second, mpg-C3N4 and RGO possess a large conjugated π-bond system, which allows for π-π interactions with the conjugated structure of TNT. Finally, the amino groups on the mpg-C3N4 surface form NH···π hydrogen bonds with the π electron cloud of TNT and NH···O hydrogen bonds with the O atoms of the nitrosyl groups in the TNT molecule. Furthermore, the carbonyl π bonds of the carboxyl groups on the RGO surface form π hydrogen bonds with the methyl groups in the TNT molecule, forming CH···O=C π bonds. When the pH of the mixed solution is low, the amino groups on the surface of mpg-C3N4 will be protonated, destroying the formation of hydrogen bonds. In addition, α-Fe2O3 will be decomposed into ions by the acid, which will destroy the stability of the material and reduce the adsorption amount. When the pH of the solution gradually increases to a strong alkaline solution, the negatively charged TNT molecules and the similarly negatively charged mpg-C3N4 and RGO will produce electrostatic repulsion, which is not conducive to the adsorption. Therefore, this experiment was carried out under neutral conditions of pH = 7.

[0094] See also Figure 11 The figure shows the effect of different adsorbent concentrations on TNT adsorption. As can be seen, the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite exhibits the best TNT adsorption performance at a concentration of 0.2 g / L. Because mpg-C3N4 and RGO possess a large conjugated π-bond system, they can interact with the conjugated structure of TNT through π-π interactions. When a low concentration of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite is added, the material reaches maximum adsorption, with some TNT remaining. When a high concentration of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite is added, the TNT is completely adsorbed, leaving some adsorbent redundancy. Considering both adsorption efficiency and material utilization, the optimal photocatalyst concentration is 0.2 g / L.

[0095] See also Figure 12Figure 1 shows the effect of different initial TNT concentrations on TNT adsorption. The figure shows that when the same mass of α-Fe₂O₃ / RGO / mpg-C₃N₄ nanocomposite was used to adsorb TNT solutions of varying concentrations, the adsorption capacity gradually increased in each group, gradually approaching complete adsorption, reaching a maximum adsorption capacity of 39.85 mg / g. The adsorption removal rate initially decreased rapidly, then gradually decreased. Considering both adsorption efficiency and material utilization, the optimal initial TNT concentration for subsequent adsorption experiments was 20 mg / L.

[0096] See also Figure 13 Figure 2 shows the effect of different adsorbent types on TNT adsorption. Compared to pure g-C3N4, the adsorption of TNT by mpg-C3N4, RGO / mpg-C3N4, α-Fe2O3 / mpg-C3N4, and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites is enhanced, with the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite exhibiting the strongest adsorption. This suggests that preparing mesoporous g-C3N4 and combining it with α-Fe2O3 nanoparticles and graphene can enhance g-C3N4's adsorption of TNT.

[0097] Figures 10 to 13 The results show that solution pH, adsorbent concentration, initial concentration of TNT solution and type of adsorbent all affect the adsorption of TNT. Under the same conditions, α-Fe2O3 / RGO / mpg-C3N4 nanocomposite has the strongest adsorption effect on TNT. The optimal adsorption conditions are pH = 7.0, C0 = 20 mg / L, C adsorbent = 0.2 g / L, and constant temperature adsorption in the dark for 24 hours. At this time, the adsorption capacity Q of α-Fe2O3 / RGO / mpg-C3N4 nanocomposite for TNT is max It is 31.22 mg / g.

[0098] 3. Photodegradation of TNT by α-Fe2O3 / RGO / mpg-C3N4 nanocomposites

[0099] Dilute the prepared TNT solution to the desired concentration and transfer an appropriate amount to a 75mL thin-walled cell culture flask. Adjust the pH of the TNT solution with a specific concentration of HCl and NaOH solutions, and add a specific mass of α-Fe2O3 / RGO / mpg-C3N4 nanocomposite. Adsorb the solution under magnetic stirring for 1 hour in a dark place. After reaching adsorption-desorption equilibrium, collect the supernatant and analyze the concentration using liquid chromatography. Determine the initial concentration of the photodegradation reaction using the standard curve formula. Irradiate the reaction system with light, and after a period of time, take another sample to calculate the TNT concentration. The photocatalytic degradation rate of TNT can be calculated using the following formula.

[0100]

[0101] Where: DR represents the photodegradation rate of TNT, %; C'0 represents the concentration of TNT when adsorption in the dark for 1 hour reaches the adsorption-desorption equilibrium, mg / L; C t Represents the concentration of TNT at time t, mg / L.

[0102] See also Figure 14 Figure 2 shows the effect of different solution pH values ​​on the degradation rate of TNT. As can be seen from the figure, the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite exhibits the highest TNT degradation rate of 99.26% at pH 7. Previous adsorption experiments have shown that the adsorption of TNT by the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite relies primarily on hydrogen bonding and π-π conjugation. At lower pH values, the amino groups on the mpg-C3N4 surface are protonated, disrupting hydrogen bonding. Furthermore, the α-Fe2O3 is decomposed into ions by the acid, destabilizing the material and reducing its photocatalytic degradation performance. At strongly alkaline solution pH, electrostatic repulsion between the negatively charged TNT molecules and the similarly negatively charged mpg-C3N4 and RGO hinders adsorption. Photocatalytic degradation is optimal under neutral conditions.

[0103] See also Figure 15 Figure 2 shows the effect of different initial solution concentrations on TNT degradation. As can be seen from the figure, the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite can completely degrade TNT at initial solution concentrations of 10 mg / L and 20 mg / L. Subsequently, as the initial solution concentration increases, the TNT degradation rate gradually decreases because the photocatalyst has reached its photocatalytic limit and can no longer degrade TNT. Therefore, the initial TNT concentration for subsequent photodegradation in this experiment was set at 20 mg / L.

[0104] See also Figure 16 Figure 2 shows the effect of different photocatalyst concentrations on TNT degradation. As can be seen from the figure, when the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite concentration is 0.1g / L, the TNT in the solution is not completely degraded, with some excess degradation. When the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite concentration is higher, the material blocks incident visible light, significantly reducing the TNT photocatalytic degradation rate. At a photocatalyst concentration of 0.2g / L, the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite achieves the highest TNT degradation rate, reaching 99.48%.

[0105] See also Figure 17The effect of different photocatalyst types on the degradation rate of TNT; (a) is g-C3N4, (b) is mpg-C3N4, (c) is RGO / mpg-C3N4, (d) is α-Fe2O3 / mpg-C3N4, and (e) is α-Fe2O3 / RGO / mpg-C3N4; it can be seen from the figure that compared with g-C3N4, under the same illumination time, the degradation rates of TNT by mpg-C3N4, RGO / mpg-C3N4, α-Fe2O3 / mpg-C3N4 and α-Fe2O3 / RGO / mpg-C3N4 nanocomposites are all improved. The α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material has the strongest photocatalytic degradation performance, and the photocatalytic degradation rate can reach 99.57% after 12 hours of illumination. This is because the mpg-C3N4 and graphene introduced first have a large specific surface area and rich pore structure, which greatly increases the physical adsorption of the material to TNT; secondly, mpg-C3N4 and RGO will form hydrogen bonds and π-π conjugation effects with TNT in the solution, and the chemical adsorption is enhanced; finally, the Z-type heterojunction α-Fe2O3 / RGO / mpg-C3N4 formed can reduce the recombination of photogenerated electron and hole pairs while having strong redox ability, which can degrade more TNT.

[0106] See also Figure 18 The effect of α-Fe2O3 content in α-Fe2O3 / RGO / mpg-C3N4 nanocomposite materials on the TNT degradation rate, where (a) is 0% α-Fe2O3, (b) is 5wt% α-Fe2O3, (c) is 10wt% α-Fe2O3, and (d) is 15wt% α-Fe2O3. It can be seen from the figure that compared with RGO / mpg-C3N4, under the condition of the same illumination time, the degradation rate of TNT by α-Fe2O3 / RGO / mpg-C3N4 nanocomposites containing different mass fractions of α-Fe2O3 is improved, and the 10wt% α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material has the strongest photocatalytic degradation performance, and the photocatalytic degradation rate can reach 99.57% after 12 hours of illumination.

[0107] Figures 14 to 18Results show that the solution pH, initial TNT solution concentration, photocatalyst concentration and type, and the mass fraction of α-Fe2O3 nanoparticles in the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite all affect the photodegradation of TNT. Under the optimal photocatalytic conditions of pH = 7.0, C0 = 20 mg / L, C photocatalyst = 0.2 g / L, dark adsorption for 1 hour, and illumination for 12 hours, the 10 wt% α-Fe2O3 / RGO / mpg-C3N4 nanocomposite exhibited the strongest photocatalytic performance for TNT degradation, achieving a photodegradation rate of 99.57%.

[0108] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material, characterized in that: The following steps are involved: 1) calcining urea, cooling, and grinding to obtain mpg-C3N4, adding the obtained mpg-C3N4 to a dilute hydrochloric acid solution, ultrasonically homogenizing, stirring to react, filtering, washing to neutrality, and drying to obtain protonated mpg-C3N4; 2) dispersing α-Fe2O3 nanoparticles, RGO powder, sodium dodecylbenzenesulfonate and the protonated mpg-C3N4 prepared in step 1) in deionized water, ultrasonically treating, hydrothermally reacting, washing, filtering, and freeze-drying to obtain an α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material; The α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material is a Z-type heterojunction nanocomposite material formed by attaching mpg-C3N4 and α-Fe2O3 nanoparticles to RGO sheets. The mass percentage of the α-Fe2O3 nanoparticles is 5%-15%. The α-Fe2O3 nanoparticles are connected to the RGO sheets via Fe-OC bonds. The surface of the mpg-C3N4 has irregular pores with a diameter of 48-52nm. The diameter of the α-Fe2O3 nanoparticles is 20-50nm.

2. The method for preparing the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material according to claim 1, characterized in that: In step 1), the concentration of dilute hydrochloric acid is 0.1-0.7 mol / L, and the usage ratio of mpg-C3N4: dilute hydrochloric acid is (1-5) g: (200-1000) mL.

3. The method for preparing the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material according to claim 1, characterized in that: In step 1), the calcination conditions are: heating to 600-700° C. at a heating rate of 10° C. / min and calcining for 4-6 hours.

4. The method for preparing the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material according to claim 1, characterized in that: In step 1), the ultrasonication time is 0.5-1.5 h; the stirring reaction time is 4-6 h; and the drying time is 12-24 h.

5. The method for preparing the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material according to claim 1, characterized in that: In step 2), the usage ratio of protonated mpg-C3N4:α-Fe2O3 nanoparticles:RGO powder:sodium dodecylbenzenesulfonate is (100-1000) mg:(15-150) mg:(50-500) mg:(100-500) mg.

6. The method for preparing the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material according to claim 1, characterized in that: In step 2), the hydrothermal reaction is carried out at 160-200° C. for 6-8 h; and the freeze-drying time is 12 h.

7. Use of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material prepared by the preparation method of the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material according to claim 1 in treating 2,4,6-trinitrotoluene wastewater, characterized in that: When the α-Fe2O3 / RGO / mpg-C3N4 nanocomposite material was used to treat 2,4,6-trinitrotoluene wastewater, the optimal adsorption capacity was 31.22 mg / g and the optimal photodegradation rate was 99.57%.

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