A nano photocatalyst, preparation, application and device

Abstract

A nano photocatalyst, preparation, application and device, belonging to the field of sewage treatment technology, solves the defect that the iron-based MOFs photocatalytic reduction technology for removing nitrate nitrogen usually needs to be doped with other metal elements, which greatly increases the synthesis cost. 2 ‑MIL‑101(Fe)@EPS nanophotocatalyst is an extracellular polymer EPS encapsulated NH 2 ‑MIL‑101(Fe) structure. NH 2 The ‑MIL‑101(Fe)@EPS nanophotocatalyst does not need to be doped with other metal elements, which greatly reduces the synthesis cost and can greatly improve the photocatalytic reduction performance. It is more efficient in degrading nitrate nitrogen, with nitrogen selectivity up to 100%, and ultimately no nitrite nitrogen accumulation, which can reduce the harm to organisms and humans after water discharge. 2 ‑MIL‑101(Fe)@EPS nanophotocatalyst is a green, energy-saving and efficient photocatalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and specifically relates to a nano photocatalyst, preparation, application and device. Background Art

[0002] The nitrogen cycle is an important part of the global biogeochemical cycle, among which nitrate nitrogen (NO3 - ), nitrite nitrogen (NO2 - ) and ammonium nitrogen (NH4 + ) is the main nitrogen-containing species that maintains nitrogen balance in water bodies. However, due to human intervention, the nitrogen cycle in nature has been changed, causing nitrate nitrogen pollution in water bodies. High nitrate levels will not only lead to eutrophication of water bodies and damage the entire aquatic ecosystem, but also cause a decline in the quality of human drinking water. Not only that, nitrates and their metabolites may increase the risk of humans suffering from diseases such as methemoglobinemia and cancer. Nitrates are converted into nitrites in the human body, which may cause various diseases: blue baby syndrome, cancer or hypertension, posing a huge threat to our life and health. In order to protect aquatic life and human health, the World Health Organization (WHO) limits the maximum acceptable concentration of nitrate in drinking water to 10 mg / L. At present, there is an urgent need for environmentally friendly, feasible and low-cost technologies to eliminate nitrate pollution in water.

[0003] Nitrate is a stable and highly soluble ion with a low probability of co-precipitation or adsorption. These properties make it difficult to remove it from water using conventional water treatment technologies. Currently, a series of treatment technologies have been used to try to remove nitrate from water, including biological denitrification, chemical reduction, catalytic hydrogenation, reverse osmosis, ion exchange, membrane technology, etc. However, these traditional methods have their limitations. The biological denitrification and chemical reduction processes have long treatment cycles and complex subsequent treatments, which are not enough to remove nitrate from drinking water; the defect of the catalytic hydrogenation process is the demand for hydrogen, which will lead to safety problems during transportation; reverse osmosis and ion exchange processes require secondary treatment processes to reduce the high nitrate concentration in the wastewater, which is more complicated to handle; ion exchange and membrane technology only separate nitrate from the aqueous solution and will produce waste resin and concentrated nitrate wastewater.

[0004] Photocatalytic reduction is a very promising way to convert solar energy into chemical energy in the form of organic synthesis under relatively mild conditions. However, the existing iron-based MOFs photocatalytic reduction technology for removing nitrate nitrogen usually requires doping with other metal elements, which greatly increases the synthesis cost. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the iron-based MOFs photocatalytic reduction technology for removing nitrate nitrogen in the prior art usually requires doping with other metal elements, which greatly increases the synthesis cost, thereby providing an NH2-MIL-101(Fe)@EPS nanophotocatalyst, preparation, application and device.

[0006] To this end, the present invention provides the following technical solutions.

[0007] In a first aspect, the present invention provides an NH2-MIL-101(Fe)@EPS nano-photocatalyst, which is an extracellular polymer EPS encapsulated NH2-MIL-101(Fe) structure.

[0008] Furthermore, the mass ratio of NH2-MIL-101(Fe) to EPS is 1:0.5 to 1:3.

[0009] In a second aspect, the present invention provides a method for preparing an NH2-MIL-101(Fe)@EPS nano-photocatalyst, comprising: mixing, stirring, and freeze-drying NH2-MIL-101(Fe), EPS, and a chelating agent in water to obtain an NH2-MIL-101(Fe)@EPS nano-photocatalyst.

[0010] Furthermore, the mass ratio of EPS to chelating agent is (10-60):1.

[0011] Furthermore, the EPS is EPS produced by anaerobic ammonium oxidation sludge;

[0012] Optionally, the EPS extraction method comprises:

[0013] Step 1, culturing anaerobic ammonium oxidation sludge at 35° C. and irradiating the anaerobic ammonium oxidation sludge with light; preferably, the lighting condition is to irradiate the anaerobic ammonium oxidation sludge with 500 to 1000 lux for 4 to 8 hours per day for one week;

[0014] Step 2, centrifuging the anaerobic ammonium oxidation sludge, and extracting the supernatant to obtain EPS extract;

[0015] Step 3: freeze-drying the EPS extract to obtain EPS.

[0016] Further, the preparation method of NH2-MIL-101(Fe) comprises: mixing 2-aminoterephthalic acid and FeCl3·6H2O in a solvent, reacting at 100-120°C for 22-24h, cooling, separating, washing and drying the precipitate to obtain NH2-MIL-101(Fe);

[0017] Preferably, the molar ratio of 2-aminoterephthalic acid to FeCl3·6H2O is 1:1-1:3.

[0018] In a third aspect, the present invention provides an application of NH2-MIL-101(Fe)@EPS nano-photocatalyst in removing nitrate nitrogen from water.

[0019] Furthermore, the dosage of the NH2-MIL-101(Fe)@EPS nano-photocatalyst in wastewater is 0.1-3 g / L, preferably 0.5 g / L.

[0020] In a fourth aspect, the present invention provides a device for removing nitrate nitrogen from water, comprising a water inlet tank, a peristaltic pump, a nitrate nitrogen degradation reactor and a water outlet tank connected in sequence;

[0021] Also included is a lighting system disposed above the nitrate nitrogen degradation reactor;

[0022] The nitrate nitrogen degradation reactor is provided with NH2-MIL-101(Fe)@EPS nano-photocatalyst.

[0023] In a fifth aspect, the present invention provides an application of NH2-MIL-101(Fe)@EPS nano-photocatalyst in the Anammox process.

[0024] Step 2, centrifuging the anaerobic ammonium oxidation sludge to obtain a supernatant;

[0025] Specifically, step 2 includes: first centrifuging the mud-water mixture, separating the solid and the liquid to obtain a first supernatant and a first precipitate; then adding 50-70°C physiological saline to the first precipitate, fully mixing, heating in a 50-70°C water bath for 20-40 minutes, centrifuging again to separate the solid and the liquid to obtain a second supernatant and a second precipitate. The first supernatant and the second supernatant are mixed to obtain the EPS extract of all layers.

[0026] Anaerobic ammonium-oxidizing bacteria can produce loosely bound extracellular polymers (LB-EPS) and tightly bound extracellular polymers (TB-EPS) under the stimulation of light (e.g. Fig.13 As shown in Figure 2, LB-EPS and TB-EPS are extracted from the outermost layer of extracellular polymers (S-EPS). S-EPS is present in the first supernatant obtained by the first centrifugation; under the stimulation of physiological saline, LB-EPS and TB-EPS are extracted by the second centrifugation.

[0027] The technical solution of the present invention has the following advantages:

[0028] 1. The NH2-MIL-101(Fe)@EPS nanophotocatalyst provided by the present invention is an extracellular polymer EPS encapsulating NH2-MIL-101(Fe) structure.

[0029] (1) NH2-MIL-101(Fe)@EPS nanophotocatalyst does not need to be doped with other metal elements, which greatly reduces the synthesis cost. Extracellular polymeric substances (EPS) are high molecular weight natural polymers secreted by microorganisms into the extracellular environment. They establish the integrity of the biofilm structure and function and usually contain polysaccharides, proteins, lipids and nucleic acids. The reducing ability of EPS will affect the denitrification and reduction of selenite and metals. EPS has effective redox ability and can promote the biological reduction of pollutants. In addition, EPS is widely present in nature and is very convenient to extract and use.

[0030] NH2-MIL-101(Fe) is a metal organic framework material with a hollow cage structure and micropores. Compared with other MOFs materials, it has good framework structure stability, strong adsorption and storage capacity, and huge specific surface area. Its Langmuir specific surface area can reach up to 5900m 2 / g, providing more contact sites for EPS. Compared with bulk photocatalysts, granular NH2-MIL-101(Fe) nanomaterials have a larger surface area, so they contain more active sites and show better photocatalytic activity. Various functional groups such as carboxyl and amino groups in extracellular polymers (EPS) provide abundant binding sites for NH2-MIL-101(Fe).

[0031] The strong chelation between EPS and metal ions and the pore advantage of porous materials enable the NH2-MIL-101(Fe)@EPS nanophotocatalyst of the present invention to greatly improve the photocatalytic reduction performance.

[0032] (2) Efficiently utilize sunlight and avoid ultraviolet light or high-pressure mercury lamps, which is more energy-efficient.

[0033] Some current nitrate degradation catalysts are not photoactive or require high-energy photons from the solar spectrum. Traditional single-component photocatalysts, such as ZnO and La2Ti2O7, can only be activated under ultraviolet light, which easily leads to the recombination of photoinduced carriers. The NH2-MIL-101(Fe)@EPS nanophotocatalyst of the present invention can widely absorb sunlight and obtain energy from it. Compared with other catalysts, it is more energy-saving and environmentally friendly and has better photocatalytic performance.

[0034] (3) The built-in electric field of the NH2-MIL-101(Fe)@EPS nanophotocatalyst of the present invention promotes the separation of photogenerated electron-hole pairs, increases the release rate of photogenerated electrons, and thus improves the photocatalytic activity of nitrate nitrogen reduction.

[0035] Due to poor interface point matching and the resulting structural defects, the structural stability of the composite material is generally poor, and the photocarrier migration is limited; in addition, the generated IEF (built-in electric field) is only located at the interface, the distribution is quite limited, and the charge separation ability is poor. The structure of the photocatalyst of the present invention maintains the original high crystallinity while establishing a stronger IEF inside the entire material (not just at the heterojunction interface) and accelerating the migration of carriers to the substrate molecules. The resulting photocatalyst will have a higher carrier spatial separation rate and photogenerated charge utilization rate.

[0036] NH2-MIL-101(Fe) is a porous material with pore advantages. Thanks to this unique structure, a built-in electric field is easily formed between NH2-MIL-101(Fe) and EPS. The built-in electric field is the intrinsic driving force for carrier separation, transportation and utilization. Under light, the generated carriers are easy to separate and can radiate radially outward from the surface of the catalyst, which not only improves the separation efficiency of the carriers, but also significantly improves the release efficiency of the carriers, thereby effectively promoting the utilization of photogenerated electrons. In addition, EPS contains a certain amount of quinones, which, as typical electron shuttles, can increase the electron transfer distance.

[0037] (4) The degradation of nitrate nitrogen is more efficient, with nitrogen selectivity as high as 100%, and no nitrite nitrogen accumulation in the end, which can reduce the harm to organisms and humans after discharge into water bodies.

[0038] Nitrate and its metabolites, especially nitrite and ammonia, are toxic. Nitrite is also a highly toxic substance. It will deteriorate the water quality, thus affecting the growth and health of aquaculture and the growth of aquatic animals, causing them to lose weight, grow slowly, and become susceptible to diseases. In addition, nitrite is also extremely harmful to humans. Ingestion of 0.2-0.5 grams by adults can cause poisoning, and 3 grams can be fatal. Therefore, while degrading nitrate, the generation of nitrite byproducts should be avoided. Various photocatalysts such as SrTiO3, ZnO, CdS, and CuCrO2 have been used in the photocatalytic reduction of nitrates, but in these studies, the reduction products of nitrate nitrogen are mainly nitrite nitrogen and ammonia nitrogen, which are still toxic. Under the same experimental conditions, the pure NH2-MIL-101(Fe) nanocatalyst can still produce a small amount of nitrite nitrogen and ammonia nitrogen. After being embedded in EPS, it reacts with photogenerated holes, reducing the recombination rate of holes and electrons. At the same time, the internal electric field formed between NH2-MIL-101(Fe) and EPS further improves the electron utilization rate. In addition, EPS itself has reducing properties and acts as an electron shuttle, which can increase the electron transfer distance and fill the system with electrons. Therefore, nitrite nitrogen and ammonia nitrogen are further reduced to nitrogen gas while being produced. NH2-MIL-101(Fe)@EPS nanophotocatalyst degrades nitrate nitrogen without the accumulation of toxic byproducts, and the nitrogen selectivity is as high as 100%, which is a greener and more efficient photocatalyst.

[0039] 2. The NH2-MIL-101(Fe)@EPS nano-photocatalyst provided by the present invention has a mass ratio of NH2-MIL-101(Fe) to EPS of 1:0.5 to 1:3.

[0040] The present invention accurately controls the ratio of NH2-MIL-101(Fe) and EPS. EPS is sufficient to maximize the excitation of photoelectrons generated by NH2-MIL-101(Fe), thereby improving its performance in degrading nitrate nitrogen. At the same time, it can avoid excessive EPS from inhibiting the transmittance of light, so that EPS can play its maximum role without causing the attenuation of the photocatalytic performance of NH2-MIL-101(Fe).

[0041] 3. The preparation method of the nano photocatalyst provided by the present invention comprises: mixing NH2-MIL-101(Fe), EPS, and a chelating agent in water, stirring, and freeze-drying to obtain NH2-MIL-101(Fe)@EPS nano photocatalyst. The chelating agent can promote the coupling of various functional groups such as amino and carboxyl groups in EPS with Fe-O clusters in NH2-MIL-101(Fe), so that EPS can play the maximum role.

[0042] 4. In the preparation method of the nano photocatalyst provided by the present invention, the EPS is EPS produced by anaerobic ammonia oxidation sludge.

[0043] EPS from various sludges have unique compositions, which may lead to different affinities for NH2-MIL-101(Fe). Differences in EPS properties affect the effectiveness and strength of binding between sludge and NH2-MIL-101(Fe). EPS produced by anaerobic ammonium oxidation sludge can bind well to Fe-O clusters in NH2-MIL-101(Fe), and there are 1.6% sialic acid and 2.4% sulfated aminoglycosides in the extracellular polymers of the anaerobic ammonium oxidation system. These negatively charged components are the main components for binding to holes and are not available in EPS produced by other microorganisms. Therefore, anaerobic ammonium oxidation bacteria were selected as the matrix, and the EPS produced by them was used to bind to NH2-MIL-101(Fe).

[0044] 5. In the EPS extraction method, the anaerobic ammonium oxidizing sludge is illuminated for 4 to 8 hours every day at an intensity of 500-1000 lux for one week. More EPS can be produced on the sludge surface while ensuring the activity of the sludge, and algae formation can be inhibited. Under the stimulation of the lighting conditions of the present invention, anaerobic ammonium oxidizing bacteria can produce higher "densities" of loosely bound extracellular polymers (LB-EPS) and tightly bound extracellular polymers (TB-EPS).

[0045] 6. Application of NH2-MIL-101(Fe)@EPS nanophotocatalyst in Anammox process (i.e. anaerobic ammonia oxidation process).

[0046] Compared with the traditional denitrification process, the anaerobic ammonium oxidation process has become a very promising wastewater denitrification process because it saves 62.5% of the aeration volume, has a short denitrification pathway, does not require an external carbon source, and has low greenhouse gas production. However, its limitation is that it will produce nitrate byproducts, causing secondary pollution to the water environment. The present invention denitrifies by coupling the Anammox process with NH2-MIL-101(Fe)@EPS nanophotocatalyst, and uses NH2-MIL-101(Fe)@EPS nanophotocatalyst to degrade the nitrate nitrogen generated in situ in the Anammox process, which can not only eliminate the hazards of byproducts, but also further improve the total nitrogen removal efficiency. Therefore, coupling photocatalytic materials with microbial processes has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 is the X-ray diffraction pattern (XRD) of the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in Example 1;

[0049] Figure 2 is a scanning electron microscope image (SEM) of pure NH2-MIL-101(Fe) obtained in step (1) of Example 1;

[0050] Figure 3 is a scanning electron microscope image (SEM) of the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in Example 1;

[0051] Figure 4 TEM image of pure NH2-MIL-101(Fe) prepared in step (1) of Example 1;

[0052] Figure 5 is a transmission electron microscopy (TEM) image of the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in Example 1;

[0053] Figure 6 It is a nitrate nitrogen degradation effect diagram of Example 2 and Comparative Examples 1 to Comparative Examples 3;

[0054] Figure 7 It is the nitrate nitrogen degradation effect diagram of Example 2-Example 4;

[0055] Figure 8 is a schematic diagram of the selectivity for N2 during nitrate nitrogen degradation in Example 2;

[0056] Fig. 9 Schematic diagram of selectivity to N2 during nitrate nitrogen degradation in Comparative Example 2;

[0057] Fig.10 is the electrochemical impedance spectroscopy (EIS) of NH2-MIL-101(Fe)@EPS and pure NH2-MIL-101(Fe) prepared in Example 1;

[0058] Fig.11 Schematic diagram of the device for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst in Example 1;

[0059] Fig.12The device for removing nitrate from water in Example 5;

[0060] Fig.13 This is a schematic diagram of EPS produced by oxygen-ammonia-oxidizing bacteria under the stimulation of light.

[0061] Reference numerals:

[0062] 1-high temperature integrated synthesis device, 2-lamp tube, 3-UASB reactor, 4-vortex flow meter, 5-centrifuge, 6-freeze dryer, 7-NH2-MIL-101(Fe)@EPS material synthesis device, 8-water inlet tank, 9-peristaltic pump, 10-nitrate nitrogen degradation reactor, 11-lighting system, 12-water outlet tank. DETAILED DESCRIPTION

[0063] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0064] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0065] Example 1

[0066] This embodiment provides a method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst, using Fig.11 The device shown comprises the following steps:

[0067] (1) Preparation of NH2-MIL-101(Fe):

[0068] NH2-MIL-101(Fe) was synthesized using a high-temperature integrated synthesis device 1. The specific steps are as follows: 1.08 g of 2-aminoterephthalic acid (NH2-BDC, 0.006 mol) and 3.22 g of FeCl3·6H2O (0.012 mol) were added to 144 mL of N, N-dimethylformamide (DMF), and the stirring paddle in the device was started to mix them evenly. Then, the heating switch was turned on, and the temperature was raised to 110°C. After 24 hours, the heating switch was turned off and the device door was opened for cooling. After the sample was cooled to room temperature, the precipitate was separated from the reaction mixture by centrifugation (4000 r / min), and was thoroughly washed three times with DMF and ethanol respectively to remove unreacted raw materials. Finally, the obtained solid was placed in a high-temperature integrated synthesis device 1 and dried at 80°C for 12 hours to obtain NH2-MIL-101(Fe).

[0069] (2) Extraction of EPS:

[0070] Anaerobic ammonium oxidation sludge was cultured at 35°C using a 1.5L UASB reactor 3. The UASB reactor 3 was illuminated for 6 hours every day using a T828W lamp 2 (light intensity 500lux), and the illumination lasted for one week. Then, the EPS of the anaerobic ammonium oxidation sludge was extracted. All layers of EPS were extracted using a one-step extraction method: 1000ml of the mud-water mixture was taken from the UASB reactor 3, and centrifuged at 4000rpm for 15min using a centrifuge 5 to extract the supernatant. In order to ensure that the protein components in the sludge would not be inactivated, 60°C physiological saline was added to the sludge to make it up to 1000ml, and the sludge was placed in a vortex instrument 4 for thorough mixing and then heated in a 60°C water bath for 30min, and then centrifuged at 4000rpm for 15min. The supernatant was taken and filtered through a 0.45μm membrane. The supernatants obtained from the two centrifugations were mixed to obtain all layers of EPS extract.

[0071] The EPS extract is placed in a refrigerator to freeze, and then the bottle mouth is sealed with a sealing film, holes are pierced with a needle (to allow water molecules to pass through), and the EPS extract is placed in a freeze dryer 6 for freeze drying to obtain EPS powder.

[0072] (3) Preparation of NH2-MIL-101(Fe)@EPS nanophotocatalyst

[0073] The NH2-MIL-101(Fe)@EPS nanophotocatalyst was synthesized using the NH2-MIL-101(Fe)@EPS material synthesis device 7. The specific steps are as follows: 0.5 g NH2-MIL-101(Fe) was dispersed into 500 mL of ultrapure water by ultrasonic dispersion. After complete dispersion, 0.5 g EPS and 0.05 g ethylenediaminetetraacetic acid (EDTA) were respectively added to the NH2-MIL-101(Fe) nanoparticle dispersion. The mixture was stirred and incubated in an ice bath for 6 hours. The formed brown suspension was then frozen and freeze-dried for 72 hours to obtain a brown powder NH2-MIL-101(Fe)@EPS nanophotocatalyst.

[0074] Figure 1 is the X-ray diffraction pattern (XRD) of the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in Example 1. Figure 1 It can be seen that the main XRD peaks of NH2-MIL-101(Fe)@EPS are basically consistent with those of pure NH2-MIL-101(Fe), and similar characteristic peaks are observed at 8.36°, 8.96°, 16.38°, 24.52° and 32.78°, indicating that the phase composition and crystallinity of MOFs did not change significantly after loading EPS, and under the induction of EPS, NH2-MIL-101(Fe)@EPS showed a new peak at 31.6°, which was also detected in EPS, indicating that EPS was successfully attached to NH2-MIL-101(Fe)@EPS and NH2-MIL-101(Fe)@EPS nanophotocatalyst was successfully synthesized. In addition, a peak at 45.4° was found in NH2-MIL-101(Fe)@EPS, corresponding to (110) of α-Fe (Pow-der Diffraction File#06-0696), but there was no corresponding crystal in pure NH2-MIL-101(Fe). It is reasonable to speculate that the embedding of EPS promoted the formation of Fe in NH2-MIL-101(Fe).

[0075] Figure 2 , Figure 3 The following are the scanning electron microscopy (SEM) images of pure NH2-MIL-101(Fe) and NH2-MIL-101(Fe)@EPS nanophotocatalysts. Figure 2 It can be seen that pure NH2-MIL-101(Fe) presents uniformly distributed, well-shaped octahedral nanoparticles with a particle size of about 600nm and a large number of nanopores evenly distributed on the surface, similar to the morphology of a sponge. Figure 3It can be seen that since EPS is evenly wrapped on the outer surface of NH2-MIL-101(Fe), its particle size increases to about 1 μm. NH2-MIL-101(Fe)@EPS is an octahedron with a smooth surface and sharp edges, which proves that EPS is successfully embedded in the nanopores of NH2-MIL-101(Fe), and the two are evenly combined, which can better play the role of EPS as a hole scavenger and enhance the performance of the photocatalyst.

[0076] Figure 4 , Figure 5 TEM images of pure NH2-MIL-101(Fe) and NH2-MIL-101(Fe)@EPS nanophotocatalysts. Figure 4 , Figure 5 It can be seen more clearly that EPS is evenly wrapped around the outside of NH2-MIL-101(Fe), making NH2-MIL-101(Fe)@EPS present a more regular octahedral shape.

[0077] Fig.10 The electrochemical impedance spectra (EIS) of NH2-MIL-101(Fe)@EPS and pure NH2-MIL-101(Fe) prepared in Example 1 show that NH2-MIL-101(Fe)@EPS shows a smaller arc radius than pure NH2-MIL-101(Fe), indicating that the NH2-MIL-101(Fe)@EPS photocatalyst has a smaller charge transfer resistance. This phenomenon is related to the formation of the NH2-MIL-101(Fe)@EPS heterojunction and the formation of the internal electric field in the NH2-MIL-101(Fe)@EPS photocatalyst. Pure NH2-MIL-101(Fe) generates less photogenerated charge under the same conditions and has a greater charge transfer resistance. The heterojunction and built-in electric field of the NH2-MIL-101(Fe)@EPS photocatalyst of the present invention can reduce the charge transfer resistance and promote the separation of photogenerated charges, indicating that the separation efficiency of photogenerated electrons and holes is higher. This confirms that the NH2-MIL-101(Fe)@EPS nanophotocatalyst of the present invention shows better application prospects in photocatalysis.

[0078] Example 2

[0079] Prepare a solution containing 50 mg / L NO3 using deionized water —The simulated wastewater containing N was stirred in the dark before the experiment to achieve adsorption-dissociation equilibrium, and the dissolved oxygen (DO) was maintained at an extremely low level (<0.2 mg / L) by inert gas (N2). The simulated wastewater was added to a 150 ml serum bottle for the photocatalytic degradation of nitrate nitrogen. 0.5 g / L of NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in Example 1 was added to the serum bottle. The adsorption loss of nitrate by the catalyst was extremely small and could be ignored. The reaction was carried out under sunlight for 180 min.

[0080] Comparative Example 1

[0081] This comparative example is substantially the same as Example 2, except that no photocatalyst is added to the serum bottle.

[0082] Comparative Example 2

[0083] This comparative example is substantially the same as Example 2, except that 0.5 g / L of NH2-MIL-101(Fe) was added to the serum bottle.

[0084] Comparative Example 3

[0085] This comparative example is basically the same as Example 2, except that 0.5 g / L NH2-MIL-101(Fe)+0.5 g / L EPS is added into the serum bottle.

[0086] The nitrate nitrogen degradation effects of Example 2 and Comparative Examples 1 to 3 are as follows: Figure 6 As shown by Figure 6 It can be seen that NH2-MIL-101(Fe) modified with EPS showed the strongest photocatalytic activity in terms of nitrate nitrogen conversion rate, and the nitrate removal rate reached 95.5%. The degradation efficiency of nitrate nitrogen with the addition of NH2-MIL-101(Fe) alone or with the addition of free EPS on the basis of NH2-MIL-101(Fe) was lower than 95.5%, which were 42.08% and 74.74% respectively.

[0087] Example 2 Nitrate nitrogen degradation during the selectivity of N2 Figure 8 As shown, the selectivity of nitrogen is as high as 100%, and no toxic byproducts, nitrite nitrogen and ammonia nitrogen, are generated. Fig. 9 As shown, pure NH2-MIL-101(Fe) obviously produces nitrite nitrogen and ammonia nitrogen during the photocatalytic reaction, and the selectivity for nitrogen is only 60.3%.

[0088] From the above experimental results, it can be seen that NH2-MIL-101(Fe)@EPS nanophotocatalyst is the best photocatalyst for photocatalytic degradation of nitrate nitrogen.

[0089] Example 3

[0090] This comparative example is basically the same as Example 2, except that 0.1 g / L of NH2-MIL-101(Fe)@EPS nanophotocatalyst is added into the serum bottle.

[0091] Example 4

[0092] This comparative example is basically the same as Example 2, except that 1 g / L of NH2-MIL-101(Fe)@EPS nanophotocatalyst is added into the serum bottle.

[0093] The nitrate nitrogen degradation effects of Examples 2 to 4 are as follows: Figure 7 ,Depend on Figure 7 It can be seen that the removal efficiency of different photocatalyst dosages is 0.5g / L NH2-MIL-101(Fe)@EPS>1.0g / LNH2-MIL-101(Fe)@EPS>0.1g / L NH2-MIL-101(Fe)@EPS, and from the slope, the nitrate degradation rate is 0.5g / L NH2-MIL-101(Fe)@EPS>1.0g / LNH2-MIL-101(Fe)@EPS>0.1g / L NH2-MIL-101(Fe)@EPS.

[0094] From the above experimental results, it can be seen that the optimal dosage of NH2-MIL-101(Fe)@EPS nanophotocatalyst is 0.5g / L.

[0095] Example 5

[0096] This embodiment provides a device for removing nitrate from water, such as Fig.12 As shown, including:

[0097] 50 mg / L potassium nitrate was added to tap water to obtain simulated wastewater, and the simulated wastewater was stored in the water inlet tank 8. The peristaltic pump 9 rotated at a speed of 3.5 rpm to pump the simulated wastewater in the water inlet tank 8 into the nitrate nitrogen degradation reactor 10, and the nitrate nitrogen degradation reactor 10 contained the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in Example 1. A full-spectrum quantum plate was used to illuminate 6-8 cm above the nitrate nitrogen degradation reactor 10. In order to simulate real illumination, illumination was performed from 6 am every day, and the illumination intensity was gradually increased. The light intensity reached a peak at 2 pm, and then the light intensity was gradually reduced until the light was turned off at 7 pm. The experiment was carried out continuously for half a month.

[0098] In this embodiment, the nitrate nitrogen degradation reactor 10 is made of polymethyl methacrylate (PMMA), has a diameter of 10-30 cm, and an effective surface area of ​​300-500 m 2 / m 3 . Ensure the light transmittance, actual utilization rate of light source and firmness of materials under the condition of cost saving.

[0099] Example 6

[0100] In order to demonstrate the degradation of nitrate nitrogen generated in situ during the Anammox process by the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared in the present invention and the improvement of total nitrogen removal efficiency, 0.5 g / L of NH2-MIL-101(Fe)@EPS photocatalyst was added to the continuous flow reactor of the Anammox process for experiments. The experiment lasted for half a month. During this period, the NO3 - -N and total nitrogen removal efficiency were tested and calculated, and the results are shown in Table 1.

[0101] Table 1

[0102]

[0103] Comparative Example 4

[0104] This comparative example is basically the same as Example 6, except that no NH2-MIL-101(Fe)@EPS nanophotocatalyst was added. - -N and total nitrogen removal efficiency were tested and calculated, and the results are shown in Table 2.

[0105] Table 2

[0106]

[0107] From the experimental results of Example 6 and Comparative Example 4, it can be seen that the NH2-MIL-101(Fe)@EPS nanophotocatalyst can degrade the nitrate nitrogen generated in situ by Anammox, eliminate the byproducts generated during the Anammox process, and increase the total nitrogen removal efficiency to maintain it between 96% and 99%. The NH2-MIL-101(Fe)@EPS nanophotocatalyst of the present invention can improve the total nitrogen removal rate of Anammox while continuously and efficiently strengthening the degradation of nitrate nitrogen in water, thereby avoiding further harm to the environment by nitrate byproducts.

[0108] Example 7

[0109] This embodiment provides a method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst, comprising the following steps:

[0110] (1) Preparation of NH2-MIL-101(Fe):

[0111] NH2-MIL-101(Fe) was synthesized using a high-temperature integrated synthesis device 1. The specific steps are as follows: 1.08 g of 2-aminoterephthalic acid (NH2-BDC, 0.006 mol) and 1.61 g of FeCl3·6H2O (0.006 mol) were added to 144 mL of N, N-dimethylformamide (DMF), and the stirring paddle in the device was started to mix them evenly. Then, the heating switch was turned on, and the temperature was raised to 120°C. After 22 hours, the heating switch was turned off and the device door was opened for cooling. After the sample was cooled to room temperature, the precipitate was separated from the reaction mixture by centrifugation (4000 r / min), and was thoroughly washed three times with DMF and ethanol respectively to remove unreacted raw materials. Finally, the obtained solid was placed in a high-temperature integrated synthesis device 1 and dried at 80°C for 12 hours to obtain NH2-MIL-101(Fe).

[0112] (2) Extraction of EPS:

[0113] Anaerobic ammonium oxidation sludge was cultured at 30°C using a 1.5L UASB reactor 3, and 700lux light was used to illuminate the UASB reactor 3 for 8 hours every day for one week, and then the EPS of the anaerobic ammonium oxidation sludge was extracted. A one-step extraction method was used to extract all layers of EPS: 1000ml of the mud-water mixture was taken from the UASB reactor 3, and centrifuged at 4000rpm for 15min using a centrifuge 5 to extract the supernatant. In order to ensure that the protein components in the sludge would not be inactivated, 70°C physiological saline was added to the sludge to make it up to 1000ml, and then placed in a vortex instrument 4 for full mixing and then heated in a 50°C water bath for 30min, and then centrifuged at 4000rpm for 15min, and the supernatant was taken and filtered through a 0.45μm membrane, and the supernatants obtained from the two centrifugations were mixed to obtain all layers of EPS extract.

[0114] The EPS extract is placed in a refrigerator to freeze, and then the bottle mouth is sealed with a sealing film, holes are pierced with a needle (to allow water molecules to pass through), and the EPS extract is placed in a freeze dryer 6 for freeze drying to obtain EPS powder.

[0115] (3) Preparation of NH2-MIL-101(Fe)@EPS nanophotocatalyst

[0116] The NH2-MIL-101(Fe)@EPS nanophotocatalyst was synthesized using the NH2-MIL-101(Fe)@EPS material synthesis device 7. The specific steps are as follows: 1.0 g NH2-MIL-101(Fe) was dispersed into 500 mL of ultrapure water by ultrasonic dispersion. After complete dispersion, 0.5 g EPS and 0.05 g ethylenediaminetetraacetic acid (EDTA) were added to the NH2-MIL-101(Fe) nanoparticle dispersion respectively. The mixture was stirred and incubated in an ice bath for 6 hours. The formed brown suspension was then frozen and freeze-dried for 72 hours to obtain a brown powder NH2-MIL-101(Fe)@EPS nanophotocatalyst.

[0117] Example 8

[0118] This embodiment provides a method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst, comprising the following steps:

[0119] (1) Preparation of NH2-MIL-101(Fe):

[0120] NH2-MIL-101(Fe) was synthesized using a high-temperature integrated synthesis device 1. The specific steps are as follows: 1.08 g of 2-aminoterephthalic acid (NH2-BDC, 0.006 mol) and 4.83 g of FeCl3·6H2O (0.018 mol) were added to 144 mL of N, N-dimethylformamide (DMF), and the stirring paddle in the device was started to mix them evenly. Then, the heating switch was turned on, and the temperature was raised to 100°C. After 23 hours, the heating switch was turned off and the device door was opened for cooling. After the sample was cooled to room temperature, the precipitate was separated from the reaction mixture by centrifugation (4000 r / min), and was thoroughly washed three times with DMF and ethanol respectively to remove unreacted raw materials. Finally, the obtained solid was placed in a high-temperature integrated synthesis device 1 and dried at 80°C for 12 hours to obtain NH2-MIL-101(Fe).

[0121] (2) Extraction of EPS:

[0122] Anaerobic ammonium oxidation sludge was cultured at 33°C using a 1.5L UASB reactor 3, and 1000lux light was used to illuminate the UASB reactor 3 for 7 hours every day for one week, and then the EPS of the anaerobic ammonium oxidation sludge was extracted. A one-step extraction method was used to extract all layers of EPS: 1000ml of the mud-water mixture was taken from the UASB reactor 3, and centrifuged at 4000rpm for 15min using a centrifuge 5 to extract the supernatant. In order to ensure that the protein components in the sludge would not be inactivated, 70°C physiological saline was added to the sludge to make it up to 1000ml, and then placed in a vortex instrument 4 for full mixing and then heated in a 70°C water bath for 40min, and then centrifuged at 4000rpm for 15min, and the supernatant was taken and filtered through a 0.45μm membrane, and the supernatants obtained from the two centrifugations were mixed to obtain all layers of EPS extract.

[0123] The EPS extract is placed in a refrigerator to freeze, and then the bottle mouth is sealed with a sealing film, holes are pierced with a needle (to allow water molecules to pass through), and the EPS extract is placed in a freeze dryer 6 for freeze drying to obtain EPS powder.

[0124] (3) Preparation of NH2-MIL-101(Fe)@EPS nanophotocatalyst

[0125] NH2-MIL-101(Fe)@EPS nanophotocatalyst was synthesized using NH2-MIL-101(Fe)@EPS material synthesis device 7. The specific steps are as follows: 1.0g NH2-MIL-101(Fe) was dispersed into 500mL of ultrapure water by ultrasonication. After complete dispersion, 3.0g EPS and 0.05g ethylenediaminetetraacetic acid (EDTA) were added to the NH2-MIL-101(Fe) nanoparticle dispersion respectively. The mixture was stirred and incubated in an ice bath for 6 hours. The formed brown suspension was then frozen and freeze-dried for 72 hours to obtain a brown powder NH2-MIL-101(Fe)@EPS nanophotocatalyst.

[0126] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A NH2-MIL-101(Fe)@EPS nanophotocatalyst, characterized in that: The extracellular polymer EPS encapsulates the NH2-MIL-101(Fe) structure; The mass ratio of the NH2-MIL-101 (Fe) to EPS is 1:0.5 to 1:

3.

2. A method for preparing the NH2-MIL-101(Fe)@EPS nanophotocatalyst according to claim 1, characterized in that: include: NH2-MIL-101(Fe), EPS and a chelating agent were mixed in water, stirred and freeze-dried to prepare NH2-MIL-101(Fe)@EPS nanophotocatalyst.

3. The method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst according to claim 2, characterized in that: The mass ratio of EPS to chelating agent is (10-60):

1.

4. The method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst according to claim 2, characterized in that: The EPS is EPS produced by anaerobic ammonium oxidation sludge.

5. The method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst according to claim 4, characterized in that: The EPS extraction method comprises: Step 1, culturing anaerobic ammonium oxidation sludge at 35° C. and irradiating the anaerobic ammonium oxidation sludge with light; Step 2, centrifuging the anaerobic ammonium oxidation sludge, and extracting the supernatant to obtain EPS extract; Step 3: freeze-drying the EPS extract to obtain EPS.

6. The method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst according to claim 5, characterized in that: The lighting condition is to use 500-1000 lux light to irradiate the anaerobic ammonium oxidation sludge for 4-8 hours every day, and continue the lighting for one week.

7. The method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst according to claim 2, characterized in that: The preparation method of NH2-MIL-101(Fe) comprises: mixing 2-aminoterephthalic acid and FeCl3·6H2O in a solvent, reacting at 100-120°C for 22-24h, cooling, separating, washing and drying the precipitate to obtain NH2-MIL-101(Fe).

8. The method for preparing NH2-MIL-101(Fe)@EPS nano-photocatalyst according to claim 7, characterized in that: The molar ratio of the 2-aminoterephthalic acid to FeCl3·6H2O is 1:1-1:

3.

9. Use of the NH2-MIL-101(Fe)@EPS nanophotocatalyst described in claim 1 or the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared according to the preparation method according to any one of claims 2 to 8 in removing nitrate nitrogen from water.

10. The use according to claim 9, characterized in that: The dosage of the NH2-MIL-101(Fe)@EPS nano photocatalyst in wastewater is 0.1-3 g / L.

11. The use according to claim 10, characterized in that: The dosage of the NH2-MIL-101(Fe)@EPS nano-photocatalyst in wastewater is 0.5 g / L.

12. A device for removing nitrate nitrogen from water, characterized in that: It includes a water inlet tank, a peristaltic pump, a nitrate nitrogen degradation reactor and a water outlet tank which are connected in sequence; Also included is a lighting system disposed above the nitrate nitrogen degradation reactor; The nitrate nitrogen degradation reactor contains the NH2-MIL-101(Fe)@EPS nanophotocatalyst described in claim 1 or the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared according to the preparation method described in any one of claims 2-8.

13. Use of the NH2-MIL-101(Fe)@EPS nanophotocatalyst described in claim 1 or the NH2-MIL-101(Fe)@EPS nanophotocatalyst prepared by the preparation method according to any one of claims 2 to 8 in the Anammox process.

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