Feoooh / vcn catalyst, feoooh / vcn-coated calcium alginate hydrogel spheres, and methods of making the same

Abstract

The application discloses a FeOOH / VCN catalyst, a FeOOH / VCN coated calcium alginate hydrogel ball and a preparation method thereof. The FeOOH / VCN catalyst is a FeOOH QDs (FeOOH / VCN) type photo-Fenton catalyst supported by carbon vacancy g-C3N4, is prepared by using defect engineering and a wet chemical method, and can realize regulation of the electronic structure and the energy band structure of g-C3N4 at an atomic level, directional promotion of generation and separation of photo-generated carriers, and effective improvement of the performance of FeOOH / VCN in degrading new pollutants in water. The FeOOH / VCN@CA S The hydrogel ball is an organic combination of the FeOOH / VCN powder catalyst with excellent photo-Fenton performance and the calcium alginate hydrogel, ensures the stability of the catalyst, increases the absorption and utilization of light of the catalyst in the composite material, and is favorable for improvement of the photo-Fenton reaction activity.

Description

Technical Field

[0001] The present invention relates to the technical field of organic pollutant treatment, and in particular to a FeOOH / VCN catalyst, FeOOH / VCN-coated calcium alginate hydrogel balls and a preparation method thereof. Background Art

[0002] New pollutants refer to a general term for a class of chemical substances that can be detected in the environment and natural ecosystems and can pose greater risks and hidden dangers to human health and environmental safety even if they enter at low doses. They mainly include persistent organic pollutants, endocrine disruptors, antibiotics, microplastics, etc. that are controlled by international conventions. New pollutants are usually not monitored or regulated in the environment, but they have stable physical and chemical properties, which make them remain in the environment for a long time. After biomagnification and accumulation, they will pose a potential threat to the ecological environment and human health. However, traditional wastewater treatment methods, such as physical technology (filtration, adsorption and membrane separation, etc.) and biological treatment technology (activated sludge method, biological pond method, anaerobic biological treatment method and biofilm method, etc.) have the disadvantages of low efficiency, incomplete removal, and the need to regularly replace filter media or membrane components, and high maintenance costs.

[0003] Advanced oxidation processes (AOPs) have gained widespread attention as green and efficient wastewater treatment technologies. They utilize strong oxidants (such as ozone, hydrogen peroxide, and potassium permanganate) in the presence of catalysts to generate free radicals. These free radicals possess strong oxidizing power and can decompose organic pollutants in water into harmless substances, thereby purifying the water. Among various AOPs, the development of heterogeneous photo-Fenton-like systems based on semiconductor-supported iron catalytic materials for the treatment of new organic pollutants has received increasing attention. However, semiconductor-supported iron catalysts suffer from limited light energy utilization, high recombination probability of photogenerated carriers, low mineralization efficiency, and difficulty in catalyst recovery. Therefore, the development of highly active and stable photo-Fenton-like catalysts and easily recyclable photo-Fenton-like systems can provide technical support for the efficient removal of new pollutants from wastewater. Summary of the Invention

[0004] To solve the above problems, the present invention provides a carbon vacancy graphite phase carbon nitride supported iron oxyhydroxide quantum dot (FeOOH / VCN) catalyst, FeOOH / VCN coated calcium alginate hydrogel spheres and a preparation method thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a FeOOH / VCN catalyst comprises the following steps:

[0007] S1. Preparation of carbon vacancy carbon nitride

[0008] Weigh 80.0 g of urea and place it in a beaker. Heat and stir until the urea is completely melted to form a clear liquid. Then add 20 mL of citric acid solution to the molten urea and stir for 15 min. Pour the liquid from the beaker into a crucible and quickly transfer it to a muffle furnace. Under a N2 atmosphere, heat from 30 °C to 550 °C and continue calcining for 3 h at a heating rate of 5 °C min -1 After cooling to room temperature, the mixture was washed with deionized water three times, dried at 100 °C for 12 h, and ground to obtain carbon vacancy graphitic carbon nitride (VCN).

[0009] S2. Preparation of Carbon Vacancy Graphitic Carbon Nitride-Supported Iron Oxyhydroxide Quantum Dots

[0010] 100 mg of carbon vacancy graphitic carbon nitride (VCN) was weighed and dispersed in 50 mL of anhydrous ethanol. After ultrasonication for 10 min, an appropriate amount of FeCl3·6H2O was added and stirred for 20 min. Then, an appropriate amount of NH4HCO3 solution was added and stirred at room temperature for 9 h. The precipitate obtained after centrifugation at 8000 rpm for 5 min was washed twice with deionized water and once with ethanol. After drying for 5 h, the precipitate was ground to obtain carbon vacancy graphitic carbon nitride-supported iron oxyhydroxide quantum dots FeOOH / VCN.

[0011] Furthermore, in step S1, the amount of citric acid used is 0.005 g to 0.1 g, and can be 0.005 g, 0.01 g, 0.02 g, 0.05 g or 0.1 g. Preferably, the amount of citric acid used is 0.01 g.

[0012] Furthermore, in step S2, a concentration of 0.111 mmol L -1 ~4.499mmol L -1 FeCl3·6H2O, stirred for 20 min, and then added the corresponding concentration of 0.333 mmol L -1 ~13.497 mmol L -1 NH4HCO3 solution. Specifically, FeCl3·6H2O (concentration of 0.111 mmol L -1 、1.124mmol L -1 、2.249mmol L -1 and 4.499 mmol L -1 ), stirred for 20 min, and then added NH4HCO3 solution of corresponding concentration (concentration was 0.333 mmol L -1 、3.372mmol L -1 、6.747mmol L -1 and 13.497 mmol L -1), preferably, 2.249 mmol L -1 of FeCl3·6H2O, and then add 6.747 mmol L -1 NH4HCO3 solution.

[0013] The present invention also provides an FeOOH / VCN catalyst, which is a carbon vacancy g-C3N4 solidified iron oxyhydroxide quantum dot catalyst yFeOOH / VCNx, wherein x represents the dosage of citric acid, and y represents the mass percentage of the FeOOH QDs loading amount to FeOOH / VCN, and is prepared by the above-mentioned preparation method.

[0014] The present invention also provides a FeOOH / VCN coated calcium alginate hydrogel sphere (FeOOH / VCN@CA S ), the hydrogel sphere (FeOOH / VCN@CA S ) comprising a calcium alginate core and a FeOOH / VCN film wrapped around the calcium alginate core; prepared by the following steps:

[0015] S1. Preparation of sodium alginate (SA) core

[0016] 1 g of sodium alginate (SA) was weighed with an electronic balance and dispersed into 20 mL of deionized water. After stirring evenly, it was squeezed into a spherical membrane with a diameter of 0.65 cm using a syringe and frozen for 3 h to form a sodium alginate spherical template (SA). S );

[0017] S2. Preparation of FeOOH / VCN / SAs suspension

[0018] 20 mg of FeOOH / VCN was weighed and dispersed into 6 mL of deionized water using an electronic balance. The mixture was ultrasonicated for 5 min, and 180 mg of sodium alginate (SA) was added. The mixture was stirred for 30 min until homogeneous. Finally, a FeOOH / VCN / SAs suspension with appropriate viscosity was obtained.

[0019] S3. Preparation of FeOOH / VCN@CAs hydrogel spheres by impregnation-extraction method

[0020] Sodium alginate spherical template (SA S ) was immersed in the FeOOH / VCN / SAs suspension, then slowly pulled out and immediately placed in the CaCl2 solution and allowed to stand overnight to obtain the FeOOH / VCN@CAs hydrogel spheres.

[0021] The FeOOH / VCN@CAs hydrogel spheres provided by the present invention can stably and efficiently degrade organic pollutants in water under natural light.

[0022] In the above scheme, defect engineering combined with wet chemical methods are used to prepare carbon vacancy g-C3N4 immobilized FeOOH QDs (FeOOH / VCN)-type photo-Fenton catalysts, so as to achieve the regulation of the electronic structure and band structure of g-C3N4 at the atomic level, directionally promote the generation and separation of photogenerated carriers, thereby increasing the Fe(Ⅱ) / Fe(Ⅲ) conversion rate, and effectively improving the performance of FeOOH / VCN in degrading new pollutants in water by increasing the type and number of reactive oxygen species (ROS) generated in the system.

[0023] In the above scheme, FeOOH / VCN@CA S The hydrogel spheres are an organic combination of FeOOH / VCN powder catalyst with excellent photo-Fenton-like performance and calcium alginate hydrogel. Sodium alginate is pre-frozen to form solid spheres, and then the FeOOH / VCN film-coated sodium alginate spheres are placed in a CaCl2 solution. The Ca in the aqueous solution 2+ Will gradually replace the Na in the alginate grid + , converting water-soluble sodium alginate into water-insoluble calcium alginate, thereby enabling the catalyst to be loaded into the outer reticular shell structure of the calcium alginate hydrogel spheres. The outer shell and inner core of the calcium alginate are tightly connected by hydrogen bonds. This not only ensures the stability of the catalyst, allowing the FeOOH / VCN catalyst film to firmly coat the calcium alginate spheres and resist detachment, but also increases the catalyst's absorption and utilization of light in the composite material, which is beneficial for improving the activity of the photo-Fenton reaction. Under clean sunlight, the FeOOH / VCN@CAs hydrogel spheres were placed in a continuous flow tubular photo-Fenton reaction device, which can sustainably and efficiently treat wastewater containing organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is (a) CN, (b) 1.19% FeOOH / CN, (d) VCN 0.01 and (e) 1.60% FeOOH / VCN 0.01 TEM images of (c) 1.19% FeOOH / CN and (f) 1.60% FeOOH / VCN. 0.01 TEM images and corresponding element distribution diagrams.

[0025] Figure 2 (a) VCN and (b) FeOOH / VCN 0.01 XRD spectrum of .

[0026] Figure 3 FeOOH, CN, VCN 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 FT-IR spectrum of .

[0027] Figure 4 FeOOH, CN, VCN 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 ESR spectrum of .

[0028] Figure 5 FeOOH, and 1.60% FeOOH / VCN 0.01 and 2.54%FeOOH / VCN 0.01 Roman picture.

[0029] Figure 6 CN, VCN 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 X-ray electron spectroscopy (XPS) analysis results;

[0030] In the figure: (a) High-resolution XPS spectra: (b) C 1s, (c) N 1s and (d) Fe 2p.

[0031] Figure 7 The light absorption characteristics and energy band structure test results of the catalyst in the embodiment of the present invention;

[0032] In the figure: (a) FeOOH, CN, VCN 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 UV-vis / DRS spectra of CN and VCN; (b) 0.01 (c) valence band spectrum, (d) energy band structure diagram.

[0033] Figure 8 (a; d; g) degradation activity and (b and c; e and f; h and i) kinetic analysis of various g-C3N4 materials for SMX in different systems; λ>420nm, H2O2=40mmol L -1 , C SMX =5mg L -1 , solution volume = 50 mL, catalyst = 0.5 g L -1 .

[0034] Figure 9 1.60% FeOOH / VCN 0.01 (ae) Conditions and (f) kinetic constants for the photo-Fenton-like degradation of APAP, PNP, TEN, LEVO, and NOR; where λ>420 nm, H2O2=40 mmol L -1, solution volume = 50 mL, catalyst = 0.5 g L -1 .

[0035] Figure 10 1.60% FeOOH / VCN 0.01 Photo-Fenton-like degradation of SMX by cycling experiments; where λ>420nm, H2O2=40mmol / L -1 , C SMX =5mg L -1 , solution volume = 50 mL, catalyst = 0.5 g L -1 ; After five cycles, 1.60% FeOOH / VCN 0.01 (a) XRD spectrum, (c) FT-IR spectrum and (d) ESR spectrum of the samples.

[0036] Figure 11 1.60% FeOOH / VCN 0.01 Changes in (a) fatty acids and (b) TOC values ​​during the photo-Fenton-like degradation of SMX; where λ>420nm, H2O2=40mmol L -1 , C SMX =20mg L -1 , solution volume = 100 mL, catalyst = 1 g L -1 .

[0037] Figure 12 1.60% FeOOH / VCN 0.01 Photo-Fenton-like degradation activity of SMX under sunlight; where λ>420nm, H2O2=40mmol L -1 , C SMX =5mg L -1 , solution volume = 50 mL, catalyst = 0.5 g L -1 .

[0038] Figure 13 (a) Photograph of FeOOH / VCN@CAs hydrogel catalytic spheres, (b) cross-sectional photographs before use, and (c) cross-sectional photographs after use.

[0039] Figure 14 Schematic diagram of a continuous flow tubular photofen-like reaction device.

[0040] Figure 15 The degradation activity of SMX by FeOOH / VCN@CAs hydrogel spheres for 4 h; reaction conditions: catalyst = 120 mg; H2O2 = 10 mmol L -1 , C SMX =5mg L -1 ; The solution residence time is 72min. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0042] Example 1

[0043] Preparation of carbon vacancy carbon nitride (VCN):

[0044] 80.0 g of urea was weighed using an electronic balance and placed in a beaker. The mixture was placed in a silicone oil pan and heated to 150 °C. The mixture was stirred until the urea was completely melted and a clear liquid was formed. 20 mL of citric acid solution was then added to the molten urea and stirred for 15 min. The liquid was poured from the beaker into a crucible and quickly transferred to a muffle furnace. Under a N2 atmosphere, the temperature was raised from 30 °C to 550 °C and calcined for 3 h at a heating rate of 5 °C min -1 After programmed cooling, the mixture was washed three times with deionized water and dried at 100°C for 12 h. After grinding, g-C3N4(VCNx) containing different amounts of carbon vacancy defects was obtained. Here, x represents the amount of citric acid added, which is 0.005 g, 0.01 g, 0.02 g, 0.05 g, and 0.1 g, respectively.

[0045] Preparation of carbon vacancy g-C3N4 supported iron oxyhydroxide quantum dots (FeOOH / VCN):

[0046] 100 mg of VCNx was weighed using an electronic balance and dispersed in 50 mL of anhydrous ethanol. Ultrasonication was performed for 10 min. Subsequently, a certain amount of FeCl3·6H2O (concentration of 0.111 mmol L -1 、1.124mmo lL -1 、2.249mmol L -1 and 4.499 mmol L -1 ), stirred for 20 min, and then added the corresponding amount of NH4HCO3 solution (concentration of 0.333 mmol L -1 、3.372mmol L -1 、6.747mmol L -1 and 13.497 mmol L -1) and stirred at room temperature for 9 hours. The prepared material was washed twice with deionized water and once with ethanol, dried at 60°C for 5 hours, and then ground to obtain yFeOOH / VCNx, where y represents the mass percentage of FeOOH QDs loaded on FeOOH / VCN, which were 0.21%, 0.53%, 1.60%, and 2.54%, respectively.

[0047] Photo-Fenton-like degradation experiment

[0048] Sulfamethoxazole (SMX), acetaminophen (APAP), levofloxacin (LEVO), norfloxacin (NOR), atenolol (TEN) and p-nitrophenol (PNP) were selected as target pollutants to investigate the photo-Fenton degradation performance of FeOOH / VCN. The initial concentration of SMX solution was 5 mg L -1 The initial concentrations of APAP, NOR, TEN, and PNP were 10 mg L -1 The initial concentration of LEVO was 20 mg L -1 , the solution volume was 50 mL, and the catalyst concentration was 0.5 g L -1 , the catalyst was added to the above pollutant aqueous solution, ultrasonically dispersed for 5 min, then adsorbed in the dark for 60 min, and 40 mmol L -1 H2O2 was added to the reaction system. A PLS-SXE300 xenon lamp equipped with a 420nm filter was used for illumination. At the corresponding reaction intervals, 1 mL of the suspension was removed and filtered through a 0.22μm filter. Photocatalytic and Fenton-like degradation experiments were conducted in the same manner as the photo-Fenton-like catalytic process. In the former, H2O2 was not added to the reaction system, while in the latter, no illumination was provided. The resulting clear liquid was analyzed by HPLC using a C18 column and UV detector. The HPLC test conditions are shown in Table 1.

[0049] Table 1. Liquid chromatography detection conditions

[0050]

[0051] result

[0052] Sample morphology and porosity properties

[0053] The microstructure of the prepared samples can be observed through transmission electron microscopy (TEM) images. Figure 1 As shown in Figure 2, all four catalysts exhibit stacked and curled porous sheet-like nanostructures. Figure 1 As shown in c, obvious FeOOH QDs clusters were observed in the Fe element distribution map of 1.19% FeOOH / CN. Figure 1 f shows that at 1.60% FeOOH / VCN 0.01No FeOOH QDs nanoparticles or clusters were found on the surface, which is speculated to be due to VCN 0.01 The carbon vacancy defect structure in VCN is conducive to the fixation of FeOOH QDs and enhances its dispersion. It is speculated that FeOOH exists in the form of quantum dots. 0.01 In. With CN and VCN 0.01 In contrast, after the FeOOH QDs were immobilized, the size of the catalyst nanosheets became smaller and the number of pores decreased, which is presumably due to the fact that the immobilization of FeOOH QDs covered the CN and VCN. 0.01 The hole on the .

[0054] The comparative area of ​​the sample to be tested can be obtained from the nitrogen adsorption-desorption isotherm curve. 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 It shows porosity characteristics related to its morphology. The specific surface area of ​​CN is 68.3m 2 g -1 After modification with carbon vacancy defects, VCN 0.01 The specific surface area is 70.9m 2 g -1 After loading 1.19% of FeOOH QDs, the specific surface area of ​​CN decreased slightly to 66.5 m 2 g -1 VCN 0.1 After loading 1.60% of FeOOH QDs, the specific surface area decreased to 67.7 m 2 g -1 .

[0055] Sample structure and composition

[0056] In order to explore the crystal structure of FeOOH QDs supported on g-C3N4 with carbon vacancy defects, the catalyst was characterized by X-ray diffraction (XRD) test. Figure 2 As can be seen in b, FeOOH QDs have no XRD diffraction characteristic peaks, indicating that FeOOH exists in the form of amorphous quantum dots. Figure 2 As shown in ab, CN, VCN, FeOOH / CN and FeOOH / VCN all have two characteristic diffraction peaks, located at 12.9° and 27.6°, respectively, corresponding to the (001) crystal plane of the heptazine structural unit stacking in the plane of g-C3N4 and the (002) crystal plane of the CN conjugated heterocyclic layer stacking. The above results show that the prepared catalysts all have the basic skeleton structure of g-C3N4. Figure 2As shown in a, with the increase of citric acid dosage, the two characteristic diffraction peaks of VCN gradually weakened, and the order and layered structure of the g-C3N4 plane structure were destroyed, proving that the ordered structure of g-C3N4 can be regulated by the dosage of citric acid. Figure 2 As shown in b, with the increase of FeOOH QDs loading, FeOOH / VCN 0.01 The two characteristic diffraction peaks gradually weakened, indicating that the order and layered structure of the g-C3N4 in-plane structure gradually weakened, proving that FeOOH QD weakened the interlayer stacking effect of g-C3N4 and caused perturbation of the ordered structure.

[0057] The molecular structure of the prepared catalyst was studied by Fourier transform infrared spectroscopy (FT-IR). Figure 3 As shown, all catalysts have a -1 1200~1600cm -1 and 300~3500cm -1 Characteristic peaks within the g-C3N4 catalyst range are attributed to the bending vibration of the heptazine ring, the stretching vibration of the CN heterocycle, and the stretching vibration of the -NH / NH2 groups, respectively. This indicates that the prepared catalysts all possess the basic structural unit of g-C3N4. Compared with CN, the characteristic peaks of the modified catalysts do not change significantly, indicating that g-C3N4 retains its original basic structure after the immobilization of FeOOH QDs and the introduction of carbon vacancy defects.

[0058] Electron paramagnetic resonance spectroscopy (ESR) analysis can be used to measure the resonance response signal of unbonded electrons in atoms. The changes in the resonance signal can be used to analyze the electronic structure changes of the g-C3N4 skeleton after immobilized FeOOH QDs and the introduction of carbon vacancies. Figure 4 As shown, CN and 1.19% FeOOH / CN have no obvious characteristic ESR signal. 0.01 and 1.60% FeOOH / VCN 0.01 A characteristic signal appears at g = 2.004, which is derived from the non-bonding electrons carried by the N atoms around the carbon vacancies in the g-C3N4 skeleton. 0.01 , 1.60%FeOOH / VCN 0.01 The characteristic ESR signal of VCN is significantly weakened, which is due to the coordination of the N atoms containing unbonded electrons around the carbon vacancies in the FeOOH QDs and g-C3N4 skeleton on the catalyst, which consumes some of the unbonded electrons. The above results further prove that VCN 0.01 and 1.60% FeOOH / VCN 0.01 The existence of carbon vacancies also shows that the presence of carbon vacancies is beneficial to the immobilization of FeOOH QDs.

[0059] Figure 5 FeOOH QDs, 1.60% FeOOH / VCN 0.01 and 2.54%FeOOH / VCN 0.01 In the Raman spectrum of FeOOH QDs, a wavelength of 214 cm -1 and 273cm -1 The two Raman bands can be attributed to the asymmetric stretching of the metal and hydroxide groups. Compared with FeOOH QDs, 1.60%FeOOH / VCN 0.01 and 2.54%FeOOH / VCN 0.01 Located at 214cm -1 and 273cm -1 The two Raman peaks of FeOOH QDs are shifted to the right. It is speculated that this is due to the interaction between Fe atoms in FeOOH QDs and VCN. 0.01 The interaction between the N atoms in the cations leads to bending and stretching of the functional groups.

[0060] The actual loading amount of FeOOH QDs in the catalyst was studied by ICP test. When the carrier was CN, the FeCl3·6H2O addition concentration was 2.249 mmol L -1 The corresponding FeOOH QDs loading is 1.19%. The carrier is VCN 0.01 When the FeCl3·6H2O addition concentrations were 0.111, 1.124, 2.249 and 4.499 mmol lL -1 The corresponding FeOOH QDs loadings were 0.21%, 0.53%, 1.60% and 2.54%, respectively. When the FeCl3·6H2O addition concentration was 2.249 mmol L -1 When VCN 0.005 、VCN 0.02 、VCN 0.05 and VCN 0.1 The FeOOH QDs loading amounts corresponding to the supports were 1.82%, 1.51%, 1.23% and 1.12%, respectively.

[0061] The elemental composition and chemical state of the prepared catalyst were studied by X-ray electron spectroscopy (XPS) analysis. Figure 6 In b, there are two characteristic peaks in the C1s high-resolution XPS spectrum of CN. The characteristic peaks at 284.80 and 288.37 eV correspond to the external sp 3 Hybridized carbon and sp in NC=N in g-C3N4 skeleton 2 Hybridized carbon. Compared with CN, VCN 0.01The binding energy of the NC=N characteristic peak in the C1s spectrum of NC=N shifts to the low binding energy region (288.35eV), which indicates that due to the VCN 0.01 The presence of carbon vacancies in the carbon matrix increases the electron density around the adjacent nitrogen atoms. After immobilizing FeOOH QDs, the binding energy of the characteristic peak of 1.19% FeOOH / CN shifts slightly to the high binding energy region (288.43 eV) compared with CN, indicating that the Fe atoms in FeOOH QDs can interact with the N atoms in NC=N, causing a decrease in the electron density of the C atoms in NC=N. 0.01 The binding energy of the NC=N characteristic peak is 288.45eV, which is similar to that of VCN 0.01 Compared with 1.60% FeOOH / VCN, it shifted 0.1eV toward higher binding energy. 0.01 The presence of carbon vacancies in the FeOOH QDs makes them more inclined to coordinate with the N atoms adjacent to the carbon vacancies, which results in a decrease in the electron density of the C atoms in NC=N. This result is consistent with the ESR results.

[0062] exist Figure 6 In c, it can be seen from the N1s high-resolution XPS spectrum that CN and VCN 0.01 , three characteristic peaks appeared at 398.8, 400.0 and 401.2 eV, corresponding to the sp 2 Hybridized nitrogen atoms (CN=C), nitrogen atoms of N-(C)3 groups and -NH x Nitrogen atoms in (x=1,2). With CN and VCN 0.01 In comparison, 1.19%FeOOH / CN (399.0 eV) and 1.60%FeOOH / VCN 0.01 The binding energy of the CN=C characteristic peak at (398.9 eV) shifts slightly to the high binding energy region, and the electron density of nitrogen atoms in CN=C decreases, indicating that FeOOH QDs are coordinated with nitrogen atoms.

[0063] exist Figure 6 In d, the high-resolution XPS spectrum of Fe 2p shows that the two characteristic peaks at 711.7 and 725.3 eV belong to Fe 2p 3 / 2 and Fe 2p 1 / 2 orbitals, indicating the formation of FeOOH. Fe 2p 3 / 2 and Fe 2p 1 / 2 The two satellite peaks at 719.5 eV and 733.7 eV are the result of charge transfer screening of Fe atoms, which can be attributed to the Fe 3+ The presence of FeOOH quantum dots in amorphous FeOOH. 1.19% FeOOH / CN and 1.60% FeOOH / VCN0.01 No characteristic peaks of Fe 2p orbitals were detected, presumably because the Fe atomic content was too low to be detected.

[0064] Light absorption properties and band structure

[0065] The light absorption properties of the catalyst were studied by ultraviolet-visible diffuse reflectance (UV-Vis / DRS) test. Figure 7 As shown in a, CN has a strong intrinsic absorption at 250-450nm, which is caused by the π-π* electronic transition of the CN heterocycle. 0.01 The absorption band edge of the FeOOH QDs is slightly red-shifted, and a new absorption band appears in the range of 450-800 nm, which is due to the generation of intermediate energy states induced by carbon vacancies. Amorphous FeOOH QDs show strong light absorption in the entire UV-Vis range. 0.01 The carrier phase ratio is 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 The visible light absorption region is significantly expanded along 450-600 nm, which is attributed to the enhanced light absorption of the catalyst by FeOOH QDs immobilized on g-C3N4.

[0066] According to the converted Kubel ka-Munk function and photon energy diagram, CN and VCN are obtained 0.01 Band gap value (Eg). Compared with CN (2.71eV), VCN 0.01 The band gap value of (2.66eV) is reduced. In addition, VCN 0.01 The intermediate state energy level induced by carbon vacancies is 1.82eV. Figure 7 As shown in c, for CN and VCN 0.01 The XPS valence band spectrum was measured, and then the valence band edge potential of the sample was determined from the spectrum. According to the determined valence band edge potential and Eg value, CN and VCN can be obtained. 0.01 The band structure of Figure 7 As shown in d, compared with CN, VCN 0.01 The band gap value of VCN decreased from 2.71eV to 2.66eV, the valence band edge potential increased from 1.71eV to 1.89eV, and the conduction band edge potential decreased from -1.00eV to -0.77eV, which indicates that VCN 0.01 The visible light absorption ability and the oxidation ability of valence band holes are enhanced, but at the same time the reduction ability of conduction band electrons is slightly decreased.

[0067] Study on the performance of photo-Fenton-like catalytic oxidation

[0068] Photo-Fenton-like catalytic degradation performance

[0069] Figure 8 The activity of different catalysts in the visible light photocatalytic degradation of SMX and the corresponding kinetic experimental data were tested. In the absence of a catalyst, SMX was basically not degraded after 60 minutes of visible light irradiation. In addition, the catalyst and SMX solution can reach adsorption-desorption equilibrium under light-proof conditions for 1 hour. At this time, CN, VCN 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 The adsorption amount of the catalyst was 1.3%, 3.8%, 2.9% and 9.3% respectively. When the suspension formed by the catalyst powder and SMX aqueous solution was irradiated with visible light, the SMX concentration decreased significantly with the extension of the irradiation time. When the CN, VCN 0.01 , 1.19%FeOOH / CN and 1.60%FeOOH / VCN 0.01 After 60 min, the removal rates of SMX were 26.9%, 86.2%, 24.4% and 76.7% respectively. The pseudo-first-order kinetic model was used to analyze the photocatalytic degradation of SMX by the above catalysts, and the reaction process followed the first-order kinetics. 0.01 It exhibits the best photocatalytic degradation activity of SMX, and its apparent first-order reaction rate constant k app The value is 0.0327min -1 , respectively CN(0.0044min -1 )、1.19%FeOOH / CN(0.0040min -1 ), 1.60%FeOOH / VCN 0.01 (0.0224min -1 ) 7.5, 8.2 and 1.5 times.

[0070] Figure 8 df is the difference between different catalysts after adding 40mmol L -1 Fenton degradation and kinetics after H2O2. After 60 min of reaction, CN and VCN 0.01 ,1.19%FeOOH / CN, 1.60%FeOOH / VCN 0.01 The Fenton removal rates of SMX were 6.2%, 9.2%, 16.5% and 24.4% respectively. 0.01 It exhibits the best Fenton degradation activity for SMX, with an apparent first-order reaction rate constant k app 0.0031min -1 , is CN(0.005min -1 )、1.19%FeOOH / CN(0.0024min -1 ) and VCN 0.01(0.008min -1 In the Fenton reaction, the degradation performance of the catalyst is mainly determined by the 1.60% FeOOH / VCN 0.01 This is achieved by decomposing H2O2 to produce ·OH by FeOOH QDs immobilized in 1.19% FeOOH / CN. The former has 0.41% more FeOOH QDs loading than the latter, and has better catalytic performance.

[0071] Figure 8 gi provides the activity and corresponding kinetic experimental data of photo-Fenton degradation of SMX by different catalysts. In the absence of catalyst, visible light irradiation of 40 mmol L -1 After 60 minutes of SMX solution in H2O2, SMX was basically not degraded. Under the conditions of H2O2 and light, after 40 minutes of catalytic reaction, the removal rates of SMX were 21.8 (CN), 56.1 (VCN) and 1.3 (V) respectively. 0.01 ), 43.4 (1.19% FeOOH / CN) and 95% (1.60% FeOOH / VCN 0.01 After 60 min of catalytic reaction, 1.60% FeOOH / VCN 0.01 The removal rate of SMX reached 100%. In order to further evaluate the photo-Fenton activity of the prepared catalyst, the pseudo-first-order kinetic model was used to describe the degradation kinetics of SMX. t The fitting of the degradation time (t) and the degradation rate (c0) showed a good linear relationship, indicating that the degradation reaction of SMX by photo-Fenton-like reaction conforms to the apparent first-order kinetics. 0.01 It exhibits the best photo-Fenton-like degradation activity for SMX, with an apparent first-order reaction rate constant k app 0.0727min -1 , respectively CN(0.0055min -1 ), VCN 0.01 (0.0241min -1 )、1.19%FeOOH / CN(0.0146min -1 ) are 13.2, 3.01 and 5.0 times of those in the previous report.

[0072] To evaluate 1.60% FeOOH / VCN 0.01 The catalyst has a universal applicability. We selected a variety of common organic pollutants in wastewater, including levofloxacin (LEV), norfloxacin (NOR), atenolol (ATN), acetaminophen (APAP) and p-nitrophenol (PNP) as target pollutants, and further investigated the activity of its photo-Fenton system in degrading other organic pollutants in water. Figure 9As shown, 1.60% FeOOH / VCN 0.01 LEVO, NOR, TEN, APAP and PNP can be completely degraded within 8min, 20min, 20min, 20min and 40min. 1.60% FeOOH / VCN 0.01 Apparent first-order reaction rate constant k for degradation of SMX, PNP, APAP, TEN, NOR and LEVO app 0.0727min respectively -1 、0.0755min -1 、0.2383min -1 、0.3194min -1 、0.3647min -1 and 0.5632min -1 The degradation of the above six target pollutants showed that the prepared 1.60% FeOOH / VCN 0.01 It has good universal applicability and can degrade a variety of pollutants.

[0073] In order to investigate 1.60%FeOOH / VCN 0.01 Cyclic stability of 1.60%FeOOH / VCN 0.01 The photo-Fenton-like degradation of SMX was carried out for five cycles. After each catalytic cycle, the catalyst was separated by filtration, washed three times with deionized water, dried at 60°C, and ground. The recovered catalyst was used for the next cycle. Figure 10 As shown in a, after five consecutive photo-Fenton degradation experiments, 1.60% FeOOH / VCN 0.01 Still has high SMX removal efficiency. In the presence of 40mmol L -1 H2O2, and after irradiation with visible light with a wavelength greater than 420nm for 60min, 1.60% FeOOH / VCN 0.01 Each time, SMX was still completely degraded, and its catalytic activity did not decrease significantly, showing excellent photo-Fenton-like catalytic stability for the degradation of SMX. The suspension after the cycle was centrifuged and filtered, and the solution was tested by ICP. It was found that after each cycle, Fe 3+ To further prove that 1.60%FeOOH / VCN 0.01 The stability of the photo-Fenton cycle was tested by XRD, FT-IR and ESR on the 1.60% FeOOH / VCN after use. 0.01 The crystal structure, fine chemical structure and carbon vacancy defects of the Figure 10 As shown in bd, after five consecutive cycles of catalysis, 1.60% FeOOH / VCN 0.01Still maintains the ideal g-C3N4 graphite crystal structure, and the chemical structure and carbon vacancy defect structure are still intact. Therefore, 1.60% FeOOH / VCN 0.01 It exhibits excellent stability in the photo-Fenton-like catalytic degradation of SMX.

[0074] The intermediate products produced during the photo-Fenton-like degradation of organic pollutants may cause potential secondary pollution. The complete mineralization of pollutants into non-toxic and harmless carbon dioxide (CO2) and water (H2O) is of great practical significance for the removal of water pollution.

[0075] Taking SMX as the target pollutant, the degradation of 1.60% FeOOH / VCN was evaluated by monitoring the changes in the concentrations of two major fatty acids (acetic acid and formic acid) produced during the degradation of SMX. 0.01 Photo-Fenton-like mineralization ability. Figure 11 As shown in a, 1.60% FeOOH / VCN under H2O2 and visible light conditions 0.01 In the degradation system of SMX, the concentrations of acetic acid and formic acid increased rapidly in the initial reaction stage and then decreased slowly. The above results show that SMX underwent continuous mineralization and was completely mineralized after 10 hours. By monitoring the changes in the total organic carbon (TOC) value during the photo-Fenton degradation of SMX, it was 1.60% FeOOH / VCN. 0.01 The mineralization ability of Figure 11 As shown in b, with the extension of illumination time, TOC removal rate continues to increase. Under the conditions of H2O2 and visible light, after 10h of catalytic reaction, 1.60% FeOOH / VCN 0.01 The TOC removal rate of SMX reached 100%. The above results show that 1.60% FeOOH / VCN 0.01 It can not only completely degrade organic pollutants in water, but also realize the mineralization of organic matter, which proves its extremely strong visible light photo-Fenton catalytic oxidation ability.

[0076] In order to investigate 1.60%FeOOH / VCN 0.01 The practical application of the catalytic system is to place it under natural light for degradation. The photo-Fenton degradation system under natural light gets rid of the dependence on lighting equipment and directly utilizes green and environmentally friendly natural light. Figure 12 As shown in the figure, after 60 minutes of natural light exposure to the SMX aqueous solution, SMX was basically not degraded. After 60 minutes of natural light exposure to the SMX aqueous solution with H2O2 added, the SMX removal rate was 38%. -1 H2O2, at 125°25′42.9″E, 43°49′39.7″N, the average optical power density is 39.58 mW cm -2When natural light irradiates 1.60%FeOOH / VCN 0.01 After 40 minutes of suspension formed by powder and SMX aqueous solution, 1.60% FeOOH / VCN 0.01 The removal rate of SMX reached 92%, and SMX was completely removed after 60 minutes of reaction.

[0077] Example 2

[0078] Preparation of FeOOH / VCN@CAs hydrogel spheres:

[0079] First, prepare a 5% sodium alginate (SA) core. Using an electronic balance, weigh 1g of SA and disperse it in 20mL of deionized water. Stir thoroughly, squeeze the mixture into a 0.65cm diameter spherical mold using a syringe, and freeze for 3 hours to form a solid 5% sodium alginate spherical template (5% SAs).

[0080] Then 1.60% FeOOH / VCN with appropriate viscosity was prepared 0.01 / SA suspension. Weigh 20 mg of 1.60% FeOOH / VCN using an electronic balance. 0.01 Disperse into 6 mL of ionized water, ultrasonicate for 5 min, add 180 mg of SA, stir for 30 min until homogeneous, and finally obtain 1.60% FeOOH / VCN with appropriate viscosity. 0.01 / SA suspension.

[0081] Finally, FeOOH / VCN@CAs hydrogel spheres were prepared by the dip-coating method. 0.01 The FeOOH / VCN film-coated calcium alginate hydrogel spheres were obtained after being completely immersed in the FeOOH / VCN suspension, then slowly pulled out and immediately placed in a 5% CaCl2 solution. After standing overnight, the FeOOH / VCN film-coated calcium alginate hydrogel spheres were obtained, which were abbreviated as FeOOH / VCN@CA. S Then use secondary water to fully wash to remove Ca 2+ and Cl - .

[0082] FeOOH / VCN@CA S Hydrogel spheres such as Figure 13 As shown, the core of the catalyst is 5% CAs with a diameter of 6.3 mm and the shell is 1.60% FeOOH / VCN. 0.01The catalyst is supported within a 0.6mm thick, 0.6mm thick, calcium alginate hydrogel spheres in a reticular shell structure. The outer shell and inner core of the calcium alginate are tightly connected by hydrogen bonds, ensuring catalyst stability while increasing the composite's absorption and utilization of light, promoting the photo-Fenton-like reaction. As wastewater flows over the catalyst on the carrier surface, pollutants come into contact with the catalyst and undergo oxidation.

[0083] Example 3

[0084] Under actual sunlight, the FeOOH / VCN@CA obtained in Example 2 was S The hydrogel balls are used to degrade organic pollutants in water, including the following steps:

[0085] Figure 14 This is a homemade continuous flow tube-type photo-Fenton reaction device, which mainly consists of a composite parabolic reflector, a reaction tube, and a peristaltic pump. The composite parabolic reflector consists of a base and a reflective film. By pasting a 0.06mm thick vacuum aluminum reflective film (reflectivity >90%) on the resin base with the composite parabola, all incident light within the receiving angle range is reflected onto the reaction tube. A reaction tube is installed above the composite parabolic reflector with a concentration ratio of 1 to form a catalytic unit. The reaction tube uses a quartz tube with high transmittance to solar radiation. The tube is 200mm long, with an inner diameter of 10mm and an outer diameter of 12mm. The interior of the reaction tube is filled with FeOOH / VCN@CA. S Hydrogel spheres containing 20 mg of FeOOH / VCN powder. Two adjacent catalytic units are connected by a rubber hose, and the solution is pumped into the reaction tube via a peristaltic pump. When operating the continuous tubular photo-Fenton reactor, the composite parabolic reflector faces the direction of solar incidence, at a 45° angle to the ground.

[0086] SMX was selected as the target pollutant to evaluate the FeOOH / VCN@CA S The continuous flow tube-type photo-Fenton reaction device of the hydrogel ball has the ability to remove organic pollutants under sunlight. The prepared SMX solution (5 mg L -1 ) and H2O2 solution was pumped into the quartz reaction tube. After the quartz reaction tube was filled with the pollutant solution and H2O2 solution, the reaction device was moved under sunlight to conduct a photo-Fenton degradation experiment. The peristaltic pump speed was 4.5radmin -1 The residence time of the solution in the reactor was 72 min. 1 mL of the mixed solution was taken at each point in the reaction time and filtered through a 0.22 μm filter. The pollutant determination conditions were the same as in Example 1.

[0087] Fill the reaction tube with FeOOH / VCN@CA SAfter the hydrogel ball, the time of degradation of the reaction device is 8:55-12:55 on the morning of November 8, 2024, with a total reaction time of 4 hours, and the location is 125°25′42.9″ east longitude and 43°49′39.7″ north latitude. Figure 15 As shown, the real-time optical power density of the actual sunlight during the catalytic reaction is 25-65 mW / cm 2 , there is 10mmo l L - 1 Under H2O2 conditions, the filling rate of FeOOH / VCN@CA in 6 reaction tubes was 20%. S Hydrogel spheres (containing 120 mg FeOOH / VCN) for SMX (5 mg L -1 ) reached a removal rate of 90% at 120 min and remained stable in the subsequent degradation, with a removal rate of 90±3%. S It has high practical application value in removing organic pollutants using sunlight.

[0088] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing calcium alginate hydrogel spheres coated with FeOOH / VCN-based photo-Fenton composite materials, characterized by: The photo-Fenton-like composite material FeOOH / VCN-coated calcium alginate hydrogel sphere comprises a calcium alginate core and FeOOH / VCN wrapped outside the calcium alginate core, and the preparation method comprises the following steps: S1. Preparation of sodium alginate core Weigh 1 g of sodium alginate and disperse it in 20 mL of deionized water. Stir well and squeeze it into a spherical membrane mold with a diameter of 0.65 cm using a syringe. Freeze for 3 h to form a sodium alginate spherical template. S2. Preparation of FeOOH / VCN / SAs suspension Weigh 20 mg of FeOOH / VCN and disperse it in 6 mL of deionized water. Ultrasonicate for 5 min, add 180 mg of sodium alginate, and stir for 30 min until uniform. Finally, a FeOOH / VCN / SAs suspension with appropriate viscosity is obtained. S3. Preparation of FeOOH / VCN@CAs hydrogel spheres by impregnation-extraction method The sodium alginate spherical template was immersed in the FeOOH / VCN / SAs suspension, then slowly pulled out and immediately placed in a CaCl2 solution, and allowed to stand overnight to obtain FeOOH / VCN@CAs hydrogel spheres, i.e., FeOOH / VCN-coated calcium alginate hydrogel spheres. The FeOOH / VCN is a carbon vacancy graphite phase carbon nitride-supported iron oxyhydroxide quantum dot catalyst FeOOH / VCN, which is prepared by the following steps: S (1) Preparation of carbon vacancy graphite phase carbon nitride 80.0 g of urea was weighed and placed in a beaker. The urea was heated and stirred until it was completely melted and a clear liquid was formed. Then, 20 mL of citric acid solution was added to the molten urea and stirred for 15 min. The liquid was poured from the beaker into a crucible and quickly transferred to a muffle furnace. Under a N2 atmosphere, the temperature was raised from 30 °C to 550 °C and calcined for 3 h at a heating rate of 5 °C min −1 After the temperature was lowered to room temperature, the mixture was washed with deionized water, dried, and ground to obtain carbon vacancy graphite phase carbon nitride; wherein the amount of citric acid used was 0.005 g to 0.1 g; S (2) Preparation of carbon vacancy graphite phase carbon nitride supported iron oxyhydroxide quantum dots Weigh 100 mg of carbon vacancy graphite phase carbon nitride and disperse it in 50 mL of anhydrous ethanol. After ultrasonication for 10 min, add an appropriate amount of FeCl3•6H2O and stir for 20 min. Then add an appropriate amount of NH4HCO3 solution and stir at room temperature for 9 h. After centrifugation at 8000 rpm for 5 min, the obtained precipitate was washed with deionized water and ethanol respectively, dried, and ground to obtain carbon vacancy graphite phase carbon nitride-supported iron oxyhydroxide quantum dots FeOOH / VCN.

2. The method for preparing a calcium alginate hydrogel sphere coated with FeOOH / VCN as claimed in claim 1, characterized in that: In the step S (1), after programmed cooling, the product is washed with deionized water three times, dried at 100°C for 12 hours, and then ground.

3. The method for preparing a calcium alginate hydrogel sphere coated with FeOOH / VCN as claimed in claim 1, characterized in that: In the step S (2), a concentration of 0.111 mmol L −1 ~4.499 mmol L −1 FeCl3•6H2O, stirred for 20 min, and then added the corresponding concentration of 0.333 mmol L −1 ~13.497 mmol L −1 NH4HCO3 solution.

4. The method for preparing a calcium alginate hydrogel sphere coated with FeOOH / VCN as claimed in claim 1, characterized in that: In the step S(2), the obtained precipitate is washed twice with deionized water, once with ethanol, dried at 60°C for 5 h, and then ground.

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