Magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes as well as preparation method and application of magnetic composite photocatalyst

Abstract

The invention relates to the technical field of photocatalytic materials, in particular to a magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes as well as a preparation method and application of the magnetic composite photocatalyst. The preparation method of the magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes comprises the following steps: mixing water, a magnesium source, a zinc source and an iron source to obtain a mixed salt solution; mixing and reacting the mixed salt solution with an alkali solution, and then carrying out solid-liquid separation to obtain a precursor; and freezing the precursor at low temperature, and calcining to obtain the magnetic composite photocatalyst capable of simultaneously removing the antibiotics and the dye. The magnetic composite photocatalyst is synthesized by adopting a one-pot method, the operation is simple, the cost is low, the magnetic composite photocatalyst mainly comprising magnesium-zinc ferrite and ferroferric oxide can be prepared, the magnetic composite photocatalyst can realize simultaneous removal of refractory antibiotics and dyes in a water body, the removal rate is high, and the removal time is short.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalytic materials, and in particular to a magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes, and a preparation method and application thereof. Background Art

[0002] At present, there are four major categories of new pollutants that are widely concerned, including persistent organic dyes, endocrine disruptors, antibiotics and microplastics. Most new pollutants are environmentally persistent and bioaccumulative, difficult to degrade in the environment, and easy to enrich in the ecosystem. They can accumulate in the environment and in organisms for a long time, which is not conducive to green development.

[0003] Tetracycline is a typical broad-spectrum antibiotic that exhibits excellent antibacterial properties against infections caused by Gram-positive and Gram-negative microorganisms, mycoplasmas, chlamydia, rickettsiae and protozoan parasites, and has been widely used in medical and agricultural fields. However, tetracycline has been detected in surface water, groundwater and even drinking water, and efficient removal of antibiotics including tetracycline is of great significance.

[0004] Oxytetracycline, also known as oxytetracycline, is a biosynthetic antibiotic, and the fermentation strain is Streptomyces crassa. The wastewater in the production process is mainly composed of fermentation waste liquor produced in the fermentation tank, acid and alkali wastewater from resin decolorization and fine purification process, and equipment and ground washing wastewater. Among them, the fermentation waste liquor is more harmful, belonging to high-concentration organic wastewater, containing a large amount of fermentation residual nutrients, soluble and colloidal solids, high chroma and high suspended solids, and the wastewater is dark yellow-brown. Oxytetracycline wastewater belongs to fermentation pharmaceutical wastewater. The latest fermentation pharmaceutical industry water pollutant discharge standard (GB 21903-2008) promulgated in 2008 has set more stringent standards for the water quality indicators of discharged wastewater: the discharge wastewater of newly built enterprises requires COD <120mg / L, ammonia nitrogen <35mg / L, and total nitrogen <70mg / L. Therefore, achieving the discharge of various indicators, strengthening the deep treatment of oxytetracycline wastewater, and avoiding problems such as oxytetracycline residue and excessive nitrogen are the key research directions of oxytetracycline wastewater treatment.

[0005] Malachite green is a triphenylmethane organic compound, which is widely used in textile and leather dyeing, aquaculture and other industries due to its low price, easy coloring and good bactericidal effect. However, malachite green has strong biological toxicity, and it will reduce the light transmittance of water, weaken the photosynthesis of aquatic plants, reduce the oxygen content of water, and inhibit the activity of aquatic organisms.

[0006] Congo red is a typical disazo dye and a non-degradable organic substance. It is a brown-red powder under normal conditions and is often used as a laboratory auxiliary to detect free hydrochloric acid in gastric contents, diagnose amyloidosis, as an indicator of pH, and as a histological stain for amyloid protein. Congo red has a high solubility in aqueous media and is widely used in the textile, papermaking, plastic, leather and other fields, but due to its non-degradable nature, it can have an impact on human and animal health.

[0007] At present, wastewater treatment technologies mainly include mixing / flocculation, adsorption, electrochemical, biological, photocatalytic, etc. Among them, photocatalytic technology mainly uses the active species produced by semiconductor photocatalysts under light irradiation to degrade organic pollutants in the environment. It has the advantages of less pollution to the environment, no secondary pollution, thorough degradation, and reaction at normal temperature and pressure. Photocatalytic oxidation technology can convert light energy into chemical energy, so that many reactions that are difficult to achieve can be carried out under relatively mild conditions. When a semiconductor material is exposed to light with energy greater than its own bandgap energy, the semiconductor will be excited to produce photogenerated electrons and holes in its conduction band and valence band. The holes react with OH in water. - It reacts with water molecules to generate hydroxyl free radicals with strong oxidizing properties to oxidatively decompose organic pollutants.

[0008] As a new type of semiconductor material, spinel ferrite is highly favored in the field of wastewater treatment due to its abundant oxygen vacancies, stable crystal structure, and excellent ferromagnetism. The abundant oxygen vacancies and large unit cell parameters of spinel ferrite can promote the migration between cations. The metal ions in the structure can be fixed in the lattice to improve the stability of the catalyst. The ferromagnetic properties enable the catalyst to separate water and suspension under the action of an external magnetic field. The abundant oxygen vacancies and surface hydroxyl groups are conducive to the generation of free radicals. The nano-characteristics give spinel ferrite a certain adsorption capacity, which can increase the active sites, thereby promoting the heterogeneous Fenton reaction to degrade organic pollutants in water.

[0009] However, the catalytic activity of pure spinel ferrite has inherent defects such as low conductivity, poor electron mobility, easy accumulation and agglomeration, and limited active sites, which makes it difficult to meet the actual needs of treating organic pollutants. Common methods for improving spinel include selective doping, compounding with other photocatalytic materials, adding hydrogen peroxide to facilitate photo-Fenton reaction, etc.

[0010] For example, the prior art prepares the magnetic material MgFe2O4 / MIL-88A by mechanical ball milling to compound MgFe2O4 and MIL-88A. Under the synergistic action of the catalyst, visible light and H2O2, the catalyst can degrade 99.8% of sulfamethoxazole in 20 minutes. The composite catalyst material improves the degradation efficiency of sulfamethoxazole, but H2O2 needs to be added during the reaction process to form a photo-Fenton system to promote the occurrence of photocatalytic reaction, and H2O2 is easily decomposed, which increases the production cost.

[0011] For example, the existing technology uses the sol-gel method to prepare single-shell NiFe2O4@TiO2-37.5 and double-shell NiFe2O4@SiO2-25@TiO2-37.5 composite materials, and their degradation rates for methyl orange are 98.3% and 95.6%, respectively. However, the multi-component composition of such composite catalysts usually requires multi-step synthesis, and the synthesis process is relatively cumbersome and more expensive.

[0012] In addition, existing photocatalysts often only have obvious effects on a single antibiotic or dye, and there are few catalysts that have degradation effects on multiple targets. Therefore, the preparation of new catalysts that have degradation effects on multiple dyes and antibiotics is of great practical significance.

[0013] In view of this, the present invention is proposed. Summary of the invention

[0014] The first purpose of the present invention is to provide a preparation method of a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes. The magnetic composite photocatalyst is synthesized by a one-pot method, which is simple to operate and low in cost. A magnetic composite photocatalyst whose main components include magnesium zinc ferrite and ferroferric oxide can be obtained. The magnetic composite photocatalyst can achieve the simultaneous removal of difficult-to-degrade antibiotics and dyes in water, and has a high removal rate and a short removal time.

[0015] The second purpose of the present invention is to provide a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes. The magnetic composite photocatalyst has a good degradation effect on organic dyes and antibiotics, a high removal rate, and a short removal time. It can also be recycled and reused multiple times by utilizing its magnetic recyclable characteristics.

[0016] The third object of the present invention is to provide an application of a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes in the removal of antibiotics and dyes.

[0017] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0018] The present invention first provides a preparation method of a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes, comprising the following steps: mixing water, a magnesium source, a zinc source and an iron source to obtain a mixed salt solution; mixing and reacting the mixed salt solution with an alkaline solution, and then performing solid-liquid separation to obtain a precursor; and cryogenically freezing the precursor, and then calcining to obtain the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes.

[0019] Furthermore, the molar ratio of the magnesium element in the magnesium source, the zinc element in the zinc source and the iron element in the iron source is 0.2-0.8:0.2-0.8:1.8-2.4.

[0020] Furthermore, the amount of the alkaline solution added is such that the pH of the mixed system is 7.5 to 12.5.

[0021] Furthermore, the alkaline solution includes at least one of an aqueous solution of sodium hydroxide, an aqueous ammonia solution, and a mixed solution of sodium carbonate and sodium hydroxide.

[0022] Furthermore, the freezing temperature is -5 to -25°C.

[0023] Furthermore, the freezing time is 5 to 30 hours.

[0024] Furthermore, the solid-liquid separation method includes: centrifugation, suction filtration, and water washing.

[0025] Furthermore, after the low-temperature freezing and before the calcination, a grinding step is also included.

[0026] Furthermore, the calcination temperature is 300-650°C.

[0027] The present invention further provides a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes, which is mainly prepared by the preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes. The main components of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes include magnesium zinc ferrite and ferrosoferric oxide.

[0028] The invention also provides application of the magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes in removing antibiotics and dyes.

[0029] Furthermore, the antibiotics include tetracycline and oxytetracycline.

[0030] Furthermore, the dye includes malachite green and Congo red.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention provides a method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes. The method adopts a one-pot method to synthesize the magnetic composite photocatalyst, which is simple to operate and low in cost. The magnetic composite photocatalyst whose main components include magnesium zinc ferrite and ferroferric oxide can be prepared. The magnetic composite photocatalyst can simultaneously remove difficult-to-degrade antibiotics and dyes in water, and has a high removal rate and a short removal time.

[0033] (2) The present invention provides a method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes. The prepared magnetic composite photocatalyst has magnetism, is easy to recycle, and still has a high removal effect on antibiotics and dyes even after repeated use. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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.

[0035] Figure 1 This is the XRD pattern of the magnetic composite photocatalyst prepared in Example 2 provided by the present invention;

[0036] Figure 2 The curve showing the change of the removal rate of the tetracycline solution by the magnetic composite photocatalyst prepared in Example 2 provided by the present invention as a function of the treatment time;

[0037] Figure 3 The curve showing the change of the removal rate of oxytetracycline solution by the magnetic composite photocatalyst prepared in Example 4 provided by the present invention as a function of the treatment time;

[0038] Figure 4 The curve showing the change of the removal rate of the malachite green solution by the magnetic composite photocatalyst prepared in Example 3 provided by the present invention as a function of the treatment time;

[0039] Figure 5 The curve showing the variation of the removal rate of the Congo red solution by the magnetic composite photocatalyst prepared in Example 1 provided by the present invention as a function of the treatment time;

[0040] Figure 6 A comparison chart of the removal rates of tetracycline solution by photocatalysis after four cycles of using the magnetic composite photocatalyst prepared in Example 2 of the present invention;

[0041] Figure 7 This is a comparison chart of the removal rates of malachite green solution after four cycles of photocatalysis of the magnetic composite photocatalyst prepared in Example 3 of the present invention;

[0042] Figure 8 A comparison chart of the removal rates of Congo red solution by photocatalysis after four cycles of use of the magnetic composite photocatalyst prepared in Example 1 of the present invention;

[0043] Fig. 9 A comparison chart of the removal rates of oxytetracycline solution by photocatalysis after four cycles of using the magnetic composite photocatalyst prepared in Example 4 of the present invention;

[0044] Fig.10 This is a comparison chart of the removal rate of tetracycline solution by the catalyst prepared in Comparative Example 3 provided by the present invention under conditions of illumination and no illumination. DETAILED DESCRIPTION

[0045] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0046] If there is no special explanation, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0047] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0048] If there is no special explanation, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0049] In a first aspect, the present invention provides a method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes, comprising the following steps:

[0050] Water, a magnesium source, a zinc source and an iron source are mixed to obtain a mixed salt solution.

[0051] The mixed salt solution is mixed with an alkaline solution and reacted, followed by solid-liquid separation to obtain a precursor.

[0052] The precursor is cryogenically frozen, then calcined, and cooled to obtain the magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes.

[0053] The invention provides a method for preparing a magnetic composite photocatalyst capable of simultaneously removing antibiotics and dyes. The method adopts a one-pot method to synthesize the magnetic composite photocatalyst, which is easy to operate, has a short process flow, low raw material and production costs, and is suitable for large-scale production. In addition, the magnetic composite photocatalyst whose main components include magnesium zinc ferrite and ferroferric oxide can be prepared. The magnetic composite photocatalyst has a good degradation effect on antibiotics and dyes that are difficult to degrade, a high removal rate, and a short removal time.

[0054] In addition, the magnetic composite photocatalyst is magnetic and has low recycling difficulty. It can be recovered and reused many times through an external magnetic field. Even if it is reused, the removal rate is still high. It is environmentally friendly and energy-saving, has high added value, and reduces wastewater treatment costs.

[0055] This magnetic composite photocatalyst can achieve a high degradation rate without forming a photo-Fenton system with H2O2.

[0056] Specifically, the preparation method of the magnetic composite photocatalyst for removing antibiotics and dyes provided by the present invention is a chemical coprecipitation method, wherein the coprecipitation method refers to a solution containing two or more cations, which are homogeneously present in the solution, and a precipitate with uniform components can be obtained after a precipitation reaction by adding a precipitant. It is also an important method for preparing ultrafine powders of composite oxides containing two or more metal elements, and a complex with a relatively ideal structure and surface charge is synthesized by controlling the concentration of the precipitation solution, the synthesis temperature, the precipitant, and the method and speed of adding the precipitant. The coprecipitation method has simple synthesis conditions and has broad application prospects.

[0057] The preparation method of the magnetic composite photocatalyst for removing antibiotics and dyes provided by the present invention can increase the brittleness of the material and the strain between particles through low-temperature freezing, accelerate the solid-phase reaction rate during calcination, reduce the particle size of the magnetic composite photocatalyst, and increase the specific surface area of ​​the magnetic composite photocatalyst, thereby increasing the diffusion rate of the magnetic composite photocatalyst in the photocatalytic reaction. Specifically, during the low-temperature freezing process, the solution between the particles is sublimated and removed in the form of ice, avoiding the phenomenon of hard agglomeration between particles caused by solid-liquid and liquid-gas interfacial tension, thereby preserving the organizational structure and pore distribution of the precursor to the maximum extent, laying a foundation for obtaining a sample with a large specific surface area and good dispersibility during calcination.

[0058] Compared with the unfrozen material, the catalyst prepared after freezing has a significant photocatalytic effect. In addition, low-temperature freezing can also enhance the stability of the magnetic composite photocatalyst, reduce the agglomeration of particles, and improve the particle uniformity of the material.

[0059] In addition, the present invention uses water as a solvent, which is low in cost.

[0060] In order to further improve the degradation effect of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes on antibiotics and dyes and improve the removal rate, the present invention optimizes the reaction parameters such as pH value, freezing temperature, freezing time, etc. as follows.

[0061] In some specific embodiments, the molar ratio of the magnesium element in the magnesium source, the zinc element in the zinc source and the iron element in the iron source is 0.2-0.8:0.2-0.8:1.8-2.4, including but not limited to 0.2:0.2:2, 0.3:0.2:2, 0.4:0.2:2, 0.5:0.2:2, 0.6:0.2:2, 0.7:0.2:2, 0.8:0.2:2, 0.2:0.3:2, 0.2:0.4:2, 0.2:0.5:2, 0.2:0.6: 2, 0.2:0.7:2, 0.2:0.8:2, 0.3:0.3:2, 0.4:0.4:2, 0.5:0.5:2, 0.6:0.6:2, 0.7:0.7:2, 0.8:0.8:2, 0.2:0.2:1.8, 0.3:0.3:1.9, 0.4:0.5:2, 0.5:0.5:2.1, 0.6:0.6:2.2, 0.7:0.7:2.3, 0.8:0.8:2.4, or the range value between any two of them.

[0062] In some specific embodiments, the magnesium source includes but is not limited to soluble magnesium salts such as magnesium nitrate and magnesium chloride.

[0063] In some specific embodiments, the zinc source includes but is not limited to soluble zinc salts such as zinc nitrate and zinc chloride.

[0064] In some specific embodiments, the iron source includes but is not limited to soluble iron salts such as ferric nitrate and ferric chloride.

[0065] In some specific embodiments, the amount of the alkaline solution added is such that the pH of the mixed system is 7.5 to 12.5, and then the reaction is carried out, wherein the pH includes but is not limited to any point value of 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or a range value between any two of them.

[0066] In some specific embodiments, the alkaline solution includes at least one of an aqueous solution of sodium hydroxide, an aqueous ammonia solution, and a mixed solution of sodium carbonate and sodium hydroxide.

[0067] In some specific embodiments, the method of mixing the mixed salt solution with the alkaline solution comprises: adding the alkaline solution dropwise to the mixed salt solution under stirring, and adjusting the pH of the mixed system.

[0068] In some specific embodiments, the reaction temperature is 35-65°C, including but not limited to any point value of 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or a range between any two of them.

[0069] In some specific embodiments, the reaction time is 30 to 180 min, including but not limited to any one of 30 min, 45 min, 60 min, 90 min, 120 min, 150 min, 180 min or any range between two thereof. In some specific embodiments, the freezing temperature is -5 to -25°C, including but not limited to any one of -5°C, -10°C, -15°C, -20°C, -25°C or any range between two thereof.

[0070] In some specific embodiments, the freezing time is 5 to 30 hours, including but not limited to any one of 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, and 30 hours, or a range between any two of them.

[0071] In some specific embodiments, the solid-liquid separation method includes: centrifuging the material obtained after the reaction, then filtering it, and washing it with deionized water, wherein the water washing cost is low.

[0072] In some specific embodiments, after the low-temperature freezing and before the calcination, a grinding step is also included. By grinding, large particles are dispersed into small particles, which can ensure the increase of the solid phase reaction rate during the calcination process and the fineness of the product particles, thereby increasing the specific surface area of ​​the prepared magnetic composite photocatalyst and increasing the contact area between the magnetic composite photocatalyst and the antibiotic and the dye.

[0073] In some specific embodiments, the calcination temperature is 300-650°C, including but not limited to any point value of 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or a range between any two of them.

[0074] In some specific embodiments, the calcination time is ≥30 min, including but not limited to any one of 30 min, 1 h, 2 h, 3 h, 4 h, 6 h, 8 h, 10 h, 12 h, 15 h, 20 h, 24 h or a range between any two of them.

[0075] In some specific embodiments, the calcination further includes the steps of washing and drying. Among them, drying can reduce the probability of agglomeration or agglomeration of the material during the subsequent calcination process. It is understandable that although the precursor is dried, some water still exists therein, and the remaining water sublimates in the form of ice during the subsequent low-temperature freezing process.

[0076] In some specific implementations, the drying temperature may be 65 to 85° C., and the drying time may be 30 to 300 min, but is not limited thereto.

[0077] In some specific embodiments, the preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes specifically includes: mixing water, a magnesium source, a zinc source and an iron source to obtain a mixed salt solution A; mixing sodium hydroxide with water to obtain a mixed alkaline solution B; under stirring, adding the mixed alkaline solution B dropwise to the mixed salt solution A to adjust the pH of the mixture, and continuously stirring at a constant temperature to obtain a muddy precipitate, centrifuging the muddy precipitate, filtering, and washing with deionized water to obtain a filter cake; drying the filter cake to obtain a precursor; low-temperature freezing the precursor and then grinding it; and calcining the ground precursor to obtain a magnetic composite photocatalyst.

[0078] In the second aspect, the present invention provides a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes, which is mainly prepared by the preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes. The main components of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes include magnesium zinc ferrite and ferrosoferric oxide.

[0079] The magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided by the present invention is a new type of efficient magnetic composite visible light photocatalyst, which improves the utilization rate of light energy and utilizes its magnetic recyclable characteristics to recycle and reuse it multiple times. The magnetic composite photocatalyst has a good removal effect on organic dyes and antibiotics, a high removal rate, and a short removal time.

[0080] In a third aspect, the present invention provides the use of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes in removing antibiotics and dyes.

[0081] The magnetic composite photocatalyst for removing antibiotics and dyes at the same time provided by the invention can be widely used in antibiotic and dye water treatment.

[0082] The interaction between the components of the magnetic composite photocatalyst provided by the present invention may cause the bandwidth between the conduction band and the valence band to become narrower, thereby increasing the probability of generating photogenerated carriers (photogenerated electrons and holes) during illumination and broadening the spectral response range of the composite photocatalyst in the visible light region. As a result, the dye or antibiotic adsorbed on the surface of the magnetic composite photocatalyst during illumination can contact with more photogenerated carriers, thereby improving the photocatalytic degradation efficiency of the magnetic composite photocatalyst for the dye or antibiotic.

[0083] In some specific embodiments, the antibiotics include tetracycline and oxytetracycline.

[0084] In some specific embodiments, the dye comprises malachite green and Congo red.

[0085] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0086] Example 1

[0087] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment comprises the following steps:

[0088] A magnesium source, a zinc source and an iron source are mixed with 100 mL of deionized water in a molar ratio of 0.3:0.7:2 to prepare a mixed salt solution. Sodium hydroxide is mixed with water to obtain a 3 mol / L alkaline solution. Under stirring, the alkaline solution is added dropwise to the mixed salt solution, and the pH of the mixed system is adjusted to 10. Then, the mixture is continuously stirred at a constant temperature of 45°C to react, and a muddy precipitate is obtained after 90 minutes of reaction.

[0089] The muddy precipitate is centrifuged, filtered, and washed with deionized water to obtain a filter cake; the filter cake is dried to obtain a precursor.

[0090] The precursor was frozen at -5°C for 10 hours and then ground. The ground precursor was calcined at 600°C for 2 hours. After cooling, it was washed with water and dried to obtain a magnetic composite photocatalyst that can remove antibiotics and dyes at the same time.

[0091] Example 2

[0092] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment is basically the same as that in Example 1, except that the molar ratio of magnesium, zinc and iron is replaced with 0.4:0.6:2, and the ground precursor is calcined at 500°C for 5h.

[0093] like Figure 1 The figure shows the XRD pattern of the magnetic composite photocatalyst prepared in Example 2 of the present invention. It can be seen that the magnetic composite photocatalyst is composed of magnesium zinc ferrite and ferrosoferric oxide.

[0094] Example 3

[0095] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment is basically the same as that in Example 1, except that the pH of the mixed system is adjusted to 11.

[0096] Example 4

[0097] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment is basically the same as that in Example 1, except that the precursor is frozen at -15°C for 5 hours.

[0098] Example 5

[0099] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment is basically the same as that in Example 1, except that the precursor is frozen at -20°C for 25 hours.

[0100] Example 6

[0101] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment is basically the same as that in Example 1, except that the ground precursor is calcined at 550° C. for 6 hours.

[0102] Example 7

[0103] The preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided in this embodiment is basically the same as that in Example 1, except that the molar ratio of magnesium, zinc and iron is replaced with 0.8:0.8:2.2.

[0104] Comparative Example 1

[0105] The photocatalyst provided in this comparative example is magnesium zinc ferrite.

[0106] Comparative Example 2

[0107] The photocatalyst provided in this comparative example is ferrosoferric oxide.

[0108] Comparative Example 3

[0109] The preparation method of the catalyst provided in this comparative example is basically the same as that of Example 1, except that low-temperature freezing is not performed, but drying is performed at 80°C.

[0110] Comparative Example 4

[0111] The preparation method of the photocatalyst provided in this comparative example is basically the same as that of Example 1, except that the precursor is frozen at -5°C for 1 hour.

[0112] Comparative Example 5

[0113] The preparation method of the photocatalyst provided in this comparative example is basically the same as that of Example 1, except that the water in the raw material is replaced with an equal mass of ethanol.

[0114] Experimental example

[0115] The magnetic composite photocatalysts prepared in the above embodiments and the photocatalysts and catalysts prepared in the comparative examples were respectively used to carry out antibiotic and dye degradation tests. After the antibiotic and dye degradation tests were completed, the magnetic composite photocatalysts were recovered, and the removal rates of antibiotics (tetracycline and oxytetracycline) and dyes (malachite green and Congo red) by each group of photocatalysts were calculated. The results are shown in Table 1.

[0116] The test method of tetracycline degradation test is as follows: 100 ml of 10 mg / L tetracycline solution is transferred to the reactor, the initial concentration of the tetracycline solution is measured, the weighed photocatalyst (100 mg) is added to the tetracycline solution, the illumination (40 W visible light) is started, the stirring treatment is started, and the timing is started; the tetracycline solution (5 ml) is taken every 30 minutes, and after centrifugation and magnetic separation, the concentration of the supernatant is measured to examine its change law over time; when the concentration of the supernatant does not change with time, it means that the reaction has reached equilibrium, the removal rate of the tetracycline solution by the photocatalyst is calculated, and the magnetic composite photocatalyst is separated by a magnet, and then washed alternately with anhydrous ethanol and distilled water, and then placed in an oven for drying. The dried magnetic composite photocatalyst is repeatedly used in the photocatalytic degradation of tetracycline experiment, and the antibiotic removal rate of each photocatalytic experiment is calculated. The degradation time of the tetracycline degradation test is 300 minutes.

[0117] The test method of oxytetracycline degradation test is as follows: 100 ml of 10 mg / L oxytetracycline solution is transferred to the reactor, the initial concentration of the oxytetracycline solution is measured, the weighed photocatalyst (100 mg) is added to the oxytetracycline solution, the illumination (40 W visible light) is started, the stirring treatment is started, and the timing is started; the oxytetracycline solution (5 ml) is taken every 30 minutes, and after centrifugation and magnetic separation, the concentration of the supernatant is measured to examine its change law over time; when the concentration of the supernatant does not change with time, it means that the reaction has reached equilibrium, and the removal rate of each photocatalyst on the oxytetracycline solution is calculated, and the magnetic composite photocatalyst is separated by a magnet, and then washed alternately with anhydrous ethanol and distilled water, and then placed in an oven for drying. The dried magnetic composite photocatalyst is repeatedly used for the photocatalytic degradation of oxytetracycline experiment, and the antibiotic removal rate of each photocatalytic experiment is calculated. The degradation time of the oxytetracycline degradation test is 75 minutes.

[0118] The test method of malachite green degradation test is as follows: 100ml of 25mg / L malachite green solution is transferred to the reactor, the initial concentration of the malachite green solution is measured, the weighed photocatalyst (50mg) is added to the malachite green solution, the illumination (40W visible light) is started, the stirring treatment is started, and the timing is started; the malachite green solution (5ml) is taken every 30min, and after centrifugation and magnetic separation, the concentration of the supernatant is measured to examine its change law over time; when the concentration of the supernatant does not change with time, it means that the reaction has reached equilibrium, and the removal rate of the malachite green solution by each photocatalyst is calculated, and the magnetic composite photocatalyst is separated by a magnet, and then washed alternately with anhydrous ethanol and distilled water, and then placed in an oven for drying. The dried magnetic composite photocatalyst is repeatedly used for the photocatalytic degradation of malachite green experiment, and the dye removal rate of each photocatalytic experiment is calculated. The degradation time of the malachite green degradation test is 180min.

[0119] The test method of Congo red degradation test is as follows: 100ml of 150mg / L Congo red solution is transferred to the reactor, the initial concentration of Congo red solution is measured, the weighed photocatalyst (50mg) is added to the Congo red solution, the illumination (40W visible light) is started, the stirring treatment is started, and the timing is started; Congo red solution (5ml) is taken every 30min, and after centrifugation and magnetic separation, the concentration of the supernatant is measured to examine its change law over time; when the concentration of the supernatant does not change with time, it means that the reaction has reached equilibrium, and the removal rate of each photocatalyst on the Congo red solution is calculated, and the magnetic composite photocatalyst is separated by a magnet, and then washed alternately with anhydrous ethanol and distilled water, and then placed in an oven for drying. The dried magnetic composite photocatalyst is repeatedly used for the photocatalytic degradation of Congo red experiment, and the dye removal rate of each photocatalytic experiment is calculated. The degradation time of the Congo red degradation test is 60min.

[0120] Table 1 Removal rate of antibiotics and dyes by various photocatalysts

[0121] Group tetracycline / % Oxytetracycline / % Malachite green / % Congo Red / % Example 1 75.2 79.4 92.5 99.8 Example 2 85.0 73.2 95.2 97.3 Example 3 82.7 85.4 98.3 92.4 Example 4 83.1 91.5 87.4 88.3 Example 5 79.4 76.4 94.1 90.1 Example 6 78.5 80.1 90.2 92.2 Example 7 78.4 75.9 91.8 94.3 Comparative Example 1 23.2 18.1 30.8 18.2 Comparative Example 2 19.6 33.7 24.3 23.4 Comparative Example 3 65.2 49.3 58.9 65.4 Comparative Example 4 56.8 65.2 59.7 61.9 Comparative Example 5 53.2 43.6 60.2 45.8

[0122] It can be seen from Table 1 that the magnetic composite photocatalysts prepared in the examples have a high removal rate for dyes and antibiotics; while the photocatalysts in the comparative examples have a low removal rate for dyes and antibiotics.

[0123] Among them, the removal rate of the magnetic composite photocatalyst prepared in Example 2 for tetracycline solution is as high as 85.0%; the removal rate of the magnetic composite photocatalyst prepared in Example 3 for malachite green solution is as high as 98.3%; the removal rate of the magnetic composite photocatalyst prepared in Example 1 for Congo red solution is as high as 99.8%; the removal rate of the magnetic composite photocatalyst prepared in Example 4 for oxytetracycline solution is as high as 91.5%.

[0124] Figure 2 The removal rate of the magnetic composite photocatalyst prepared in Example 2 for tetracycline solution changes with the treatment time; Figure 3 The curve showing the change of the removal rate of oxytetracycline solution by the magnetic composite photocatalyst prepared in Example 4 as a function of the treatment time; Figure 4 The removal rate of the malachite green solution by the magnetic composite photocatalyst prepared in Example 3 changes with the treatment time; Figure 5 The figure is a curve showing the variation of the removal rate of the Congo red solution by the magnetic composite photocatalyst prepared in Example 1 as a function of the treatment time.

[0125] However, in Comparative Example 1, a single magnesium zinc ferrite is used, and in Comparative Example 2, a single ferroferric oxide is used, and the removal rates of dyes and antibiotics are significantly reduced. This indicates that the preparation method of the magnetic composite photocatalyst for removing antibiotics and dyes provided by the present invention has a synergistic effect between the components in the prepared magnetic composite photocatalyst.

[0126] In contrast, in Comparative Example 3, the removal rate of dyes and antibiotics by the obtained catalyst was significantly reduced without low-temperature freezing. This indicates that the present invention can improve the photocatalytic efficiency of the magnetic composite photocatalyst by low-temperature freezing.

[0127] The low-temperature freezing time of Comparative Example 4 is insufficient, and an inappropriate solvent is used in Comparative Example 5. The removal rate of dyes and antibiotics by the obtained photocatalyst is also reduced. This shows that the present invention can also improve the photocatalytic efficiency of the magnetic composite photocatalyst by adjusting the preparation parameters.

[0128] It can be seen that the preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided by the present invention adopts a one-pot method to synthesize the magnetic composite photocatalyst, which is simple to operate and low in cost. The magnetic composite photocatalyst whose main components include magnesium zinc ferrite and ferroferric oxide can be prepared. The magnetic composite photocatalyst can achieve the simultaneous removal of difficult-to-degrade antibiotics and dyes in water bodies, and has a high removal rate and a short removal time.

[0129] Further, Figure 6 This is a comparison chart of the removal rates of tetracycline solution by photocatalysis after the magnetic composite photocatalyst prepared in Example 2 was recycled four times (first photocatalysis and repeated recycling three times for photocatalysis); Figure 7 This is a comparison chart of the removal rates of malachite green solution when the magnetic composite photocatalyst prepared in Example 3 is recycled four times (photocatalysis for the first time and repeated recycling for photocatalysis three times); Figure 8 This is a comparison chart of the removal rates of Congo red and green solutions after the magnetic composite photocatalyst prepared in Example 1 was recycled four times (first photocatalysis and repeated recycling three times for photocatalysis); Fig. 9 This is a comparison chart of the removal rates of oxytetracycline solution by photocatalysis when the magnetic composite photocatalyst prepared in Example 4 was recycled four times (first photocatalysis and repeated recycling three times for photocatalysis).

[0130] It can be seen that the magnetic composite photocatalyst prepared by the preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes provided by the present invention has magnetism, is easy to recycle, can be reused many times, and still has a high removal effect on antibiotics and dyes after repeated reuse.

[0131] In addition, the comparison of the removal rate of the catalyst prepared in Comparative Example 3 for tetracycline solution under light (unfrozen-light) and no light (unfrozen-dark) conditions is shown in Fig.10 As shown, it can be seen that the curve with illumination and the curve without illumination almost overlap, which shows that the photocatalyst obtained by conventional drying only has an adsorption effect and is an adsorbent rather than a photocatalyst.

[0132] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes, characterized in that: The steps include: Mixing water, a magnesium source, a zinc source and an iron source to obtain a mixed salt solution; mixing the mixed salt solution with an alkaline solution and reacting them, and then performing solid-liquid separation to obtain a precursor; The precursor is cryogenically frozen and then calcined to obtain the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes.

2. The method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 1, characterized in that: The molar ratio of the magnesium element in the magnesium source, the zinc element in the zinc source, and the iron element in the iron source is 0.2-0.8:0.2-0.8:1.8-2.

4.

3. The method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 1, characterized in that: The amount of the alkaline solution added is such that the pH of the mixed system is 7.5 to 12.

5.

4. The method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 1, characterized in that: The alkaline solution includes at least one of an aqueous solution of sodium hydroxide, an aqueous ammonia solution, and a mixed solution of sodium carbonate and sodium hydroxide.

5. The method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 1, characterized in that: The freezing temperature is -5 to -25°C, and / or the freezing time is 5 to 30 hours.

6. The method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 1, characterized in that: The solid-liquid separation method includes: centrifugation, suction filtration, and water washing; And / or, after the low-temperature freezing and before the calcination, a grinding step is also included.

7. The method for preparing a magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 1, characterized in that: The calcination temperature is 300-650°C.

8. A magnetic composite photocatalyst for simultaneously removing antibiotics and dyes, characterized in that: The invention is mainly prepared by the preparation method of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes as claimed in any one of claims 1 to 7, wherein the main components of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes include magnesium zinc ferrite and ferrosoferric oxide.

9. Use of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes as claimed in any one of claims 7 to 8 in removing antibiotics and dyes.

10. Use of the magnetic composite photocatalyst for simultaneously removing antibiotics and dyes according to claim 9 in removing antibiotics and dyes, characterized in that: The antibiotics include tetracycline and oxytetracycline, and the dyes include malachite green and Congo red.

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