Preparation method and application of alga-loaded nano zero-valent iron composite material

Abstract

The application relates to a preparation method and application of an algae-loaded nano zero-valent iron composite material, and the process steps of the method are as follows: taking chlorella as a carrier, adding sodium borohydride and ferric chloride in proportion and in sequence, gently shaking to start a reaction, fully combining nano zero-valent iron and algal cells, and obtaining a suspension; carrying out solid-liquid separation on the suspension, and obtaining the algae-loaded nano zero-valent iron material. The algae-loaded nano zero-valent iron material prepared by the method can fully utilize the dispersibility of algae to reduce the agglomeration of nano zero-valent iron, and has a remarkable effect when treating arsenic-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation for the treatment of heavy metal polluted water bodies, specifically relating to a method for preparing and applying an algae-loaded nano-zero-valent iron composite material. Background Technology

[0002] Nano-zero valent iron has advantages such as low price, large specific surface area, strong reducing power, excellent adsorption and reactivity. It can degrade various environmental pollutants through different mechanisms, such as heavy metals, halogenated organic compounds, radioactive elements, and inorganic anions, and is regarded as a material with broad application prospects.

[0003] However, in actual reaction processes, nano-zero-valent iron is prone to deactivation due to various factors. This is mainly manifested in the following ways: as the reaction pH increases, the corrosion of nano-zero-valent iron is inhibited, and the reaction activity decreases; during the reaction process, the corrosion products of iron continuously generated cover the active sites on the surface of zero-valent iron, leading to the deactivation of nano-zero-valent iron, which greatly restricts the application of nano-zero-valent iron in actual wastewater treatment.

[0004] Currently, various materials are used as carriers to prepare nano-zero-valent iron, such as carboxymethyl cellulose, chitosan, montmorillonite, and biochar, to improve the shortcomings of nano-zero-valent iron, such as easy aggregation and oxidation. However, in the article "Stabilizing interaction of exopolymers with nano-Se and impact on mercury immobilization in soil and groundwater" published in Environmental Science: Nano, selenium nanoparticles were prepared using microbial extracellular polymers as carriers. The study found that microbial extracellular polymers can act as an effective natural dispersant, improving the stability of nanoparticles while reducing their aggregation, thereby improving the removal rate of mercury from wastewater.

[0005] The current technology has several drawbacks: Firstly, supported nano-zero-valent iron often involves depositing iron salts onto a supporting substrate and then reducing them in situ to generate nano-zero-valent iron. This method easily generates significant ion contamination, limiting its application to laboratory settings. Furthermore, the resulting nano-zero-valent iron is still prone to oxidation. Secondly, nano-zero-valent iron prepared using clay minerals as carriers suffers from low remediation efficiency for micro-pollutants in aqueous phases, and desorption can cause secondary pollution. Additionally, the clay is difficult to separate and recover from the solution after adsorption, reducing its use in industrial wastewater treatment. Thirdly, the carrier's own structural limitations, such as small pore size and electrostatic repulsion, result in low loading rates for nano-zero-valent iron. Finally, the high cost of the carrier and the complex preparation process reduce the activity of the nano-zero-valent iron. Summary of the Invention

[0006] To address the shortcomings of the aforementioned nano-zero-valent iron materials, this invention aims to provide a method for preparing and applying an algae-supported nano-zero-valent iron composite material. This invention uses *Chlorella vulgaris* as a carrier to synthesize nano-zero-valent iron, achieving both algal resource utilization and reducing the aggregation of nano-zero-valent iron. The algal surface contains various functional groups, such as hydroxyl, amino, carboxylates, and phosphates, enhancing the algae's biosorption capacity and enabling the removal of various pollutants, such as arsenic, mercury, selenium, and chromium. Furthermore, the algal extracellular polymers act as a natural dispersant, reducing the aggregation of nanoparticles and improving the removal efficiency for various pollutants. This material can be used for the treatment of water bodies polluted by heavy metals.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect is the preparation method of algae-loaded nano-zero-valent iron composite material using Chlorella as a carrier, which includes the following raw material components: Chlorella and nano-zero-valent iron.

[0009] Preferably, the algae-supported nano-zero-valent iron composite material uses Chlorella as a carrier and prepares nano-zero-valent iron using a chemical liquid-phase reduction method. The molar ratio of sodium borohydride to ferric chloride is 2:1.

[0010] Secondly, the present invention provides a method for preparing algae-supported nano-zero-valent iron composite material, comprising the following steps:

[0011] S1: For the cultivation of Chlorella, first add sodium nitrate, dipotassium hydrogen phosphate, magnesium sulfate heptahydrate, disodium EDTA, sodium carbonate, and A5 solution to a volumetric flask and bring the volume to a final volume. Adjust the pH to 7.1 with 1 M NaOH or HCl. Then sterilize in an autoclave at 120°C for 2 hours. Next, add citric acid, ferric ammonium citrate, and calcium chloride dihydrate solution to the volumetric flask. Finally, inoculate approximately 5% of the liquid culture medium volume into the culture medium and place it in a light / dark incubator with a light / dark ratio of 12:12 for cultivation.

[0012] S2: Add 7.56 mg of sodium borohydride and 27.05 mg of ferric chloride to 10 mL of Chlorella suspension in sequence, gently shake to start the reaction, and allow the nano-zero valent iron to fully combine with the algal cells.

[0013] S3: Centrifuge the obtained suspension, discard the supernatant, collect the precipitate in the centrifuge tube, and freeze-dry under vacuum for 24 h to obtain algae-loaded nano-zero-valent iron composite material.

[0014] Preferably, in S1: the culture medium for Chlorella is BG11 medium, comprising 10 mL sodium nitrate; 10 mL dipotassium hydrogen phosphate; 10 mL magnesium sulfate heptahydrate; 10 mL calcium chloride dihydrate; 10 mL citric acid; 10 mL ferric ammonium citrate; 10 mL disodium ethylenediaminetetraacetate; 10 mL sodium carbonate; and 1 mL A5 solution. A5 (trace metal solution) comprises: boric acid 2.86 g / L dH2O; manganese chloride tetrahydrate 1.86 g / L dH2O; zinc sulfate heptahydrate 0.22 g / L dH2O; sodium molybdate dihydrate 0.39 g / L dH2O; copper sulfate pentahydrate 0.08 g / L dH2O; and cobalt nitrate hexahydrate 0.05 g / L dH2O.

[0015] Preferably, in S1: the temperature of the high-pressure steam sterilizer is set to 120°C and the time is 30 min.

[0016] Preferably, in S2: sodium borohydride is added first, followed by ferric chloride.

[0017] Preferably, in S2: nano-zero valent iron reacts with Chlorella for 2-3 minutes.

[0018] Preferably, in S3: the centrifugation conditions are 6000 r / min and the time is 6 min.

[0019] Algae-loaded nano-zero-valent iron composite material was prepared using the above method.

[0020] Thirdly, the algae-loaded nano-zero-valent iron composite material provided by this invention can be used to treat arsenic-polluted water. Its mechanism of action is that *Chlorella* primarily removes arsenic through adsorption, while also reducing the aggregation of nano-zero-valent iron, thus increasing the solution pH. As the pH increases, the nano-zero-valent iron undergoes a classic corrosion reaction in the water, oxidizing to Fe(II). Fe(II) can be further oxidized to Fe(III), forming iron (hydroxy) oxides such as magnetite and goethite. During their formation, these iron (hydroxy) oxides can co-precipitate arsenic from the water, fixing it within their structure to form Fe-As (hydroxy) oxides, thereby achieving the purpose of removing arsenic from the water.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a scanning electron microscope (SEM) image of algae-loaded nano-zero valent iron prepared in this embodiment.

[0024] Figure 2 This is the energy dispersive spectroscopy (EDS) spectrum of the algae-loaded nano-zero valent iron prepared in this embodiment.

[0025] Figure 3 This is the X-ray diffraction (XRD) pattern of the algae-loaded nano-zero-valent iron prepared in this embodiment.

[0026] Figure 4 The graph shows the removal rates of arsenic-containing wastewater treated with different amounts of algae-loaded nano-zero-valent iron.

[0027] Figure 5 The removal rate of arsenic-containing wastewater at different pH values ​​is shown in the figure. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described implementations are only a part of the embodiments of the invention, and not all of them. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of the same element in the process, method, article, or apparatus that includes said element.

[0031] A preferred embodiment of the present invention provides a method for preparing algae-supported nano-zero-valent iron composite material, comprising the following steps:

[0032] S1: For the cultivation of Chlorella, first add sodium nitrate, dipotassium hydrogen phosphate, magnesium sulfate heptahydrate, disodium EDTA, sodium carbonate, and A5 solution to a volumetric flask and bring the volume to a final volume. Adjust the pH to 7.1 with 1 M NaOH or HCl. Then sterilize in an autoclave at 120°C for 2 hours. Next, add citric acid, ferric ammonium citrate, and calcium chloride dihydrate solution to the volumetric flask. Finally, inoculate approximately 5% of the liquid culture medium volume into the culture medium and place it in a light / dark incubator with a light / dark ratio of 12:12 for cultivation.

[0033] S2: Add 7.56 mg of sodium borohydride and 27.05 mg of ferric chloride to 10 mL of Chlorella suspension in sequence, gently shake to start the reaction, and allow the nano-zero valent iron to fully combine with the algal cells.

[0034] S3: Centrifuge the obtained suspension, discard the supernatant, collect the precipitate in the centrifuge tube, and freeze-dry under vacuum for 24 h to obtain algae-loaded nano-zero-valent iron composite material.

[0035] In the examples, sodium borohydride (NaBH4) and ferric chloride (FeCl3) produced by Sinopharm Chemical Reagent Co., Ltd. were used, and Chlorella was obtained from the Key Laboratory of Solid Waste Treatment and Resource Utilization of Southwest University of Science and Technology, Ministry of Education, Mianyang, Sichuan.

[0036] Centrifugation was performed using a centrifuge manufactured by Eppendorf GmbH, Germany. Drying was carried out using a LABCONCO vacuum freeze dryer. The morphology of algal-loaded zero-valent iron nanoparticles was observed using a Carl Zeiss EVO18 scanning electron microscope, Germany. The phase composition of algal-loaded zero-valent iron nanoparticles was characterized using X-ray diffraction, manufactured by Japan Co., Ltd. The arsenic content was determined using an inductively coupled plasma mass spectrometer (ICP-AES, Optima 8300DV) manufactured by PerkinElmer Instruments Ltd., USA.

[0037] Example 1

[0038] Preparation of algae-supported nano-zero valent iron:

[0039] S1: For the cultivation of Chlorella, first add sodium nitrate, dipotassium hydrogen phosphate, magnesium sulfate heptahydrate, disodium EDTA, sodium carbonate, and A5 solution to a volumetric flask and bring the volume to a final volume. Adjust the pH to 7.1 with 1 M NaOH or HCl. Then sterilize in an autoclave at 120°C for 2 hours. Next, add citric acid, ferric ammonium citrate, and calcium chloride dihydrate solution to the volumetric flask. Finally, inoculate approximately 5% of the liquid culture medium volume into the culture medium and place it in a light / dark incubator with a light / dark ratio of 12:12 for cultivation.

[0040] S2: Add 7.56 mg of sodium borohydride and 27.05 mg of ferric chloride to 10 mL of Chlorella suspension in sequence, gently shake to start the reaction, and allow the nano-zero valent iron to fully combine with the algal cells.

[0041] S3: Centrifuge the obtained suspension, discard the supernatant, collect the precipitate in the centrifuge tube, and freeze-dry under vacuum for 24 h to obtain algae-loaded nano-zero-valent iron composite material.

[0042] The characteristics of the final product obtained by this method are as follows:

[0043] Please see Figure 1 As shown in the figure, the nano-zero valent iron is spherical and uniformly dispersed on the surface of Chlorella.

[0044] Please see Figure 2 As shown in the figure, the scanning electron microscope energy dispersive spectroscopy (SEM) spectrum shows that the surface of algae-loaded nano-zero valent iron contains zero valent iron.

[0045] Please see Figure 3 As shown in the figure, the iron in the prepared algae-loaded nano-zero-valent iron is zero-valent iron.

[0046] Arsenic removal test

[0047] The wastewater contains various pollutants, among which arsenic is carcinogenic and has a serious impact on natural ecosystems and human health, and is listed as a priority heavy metal pollutant for treatment. To simulate the arsenic content in the wastewater, a 10 mg / L As(III) solution was first prepared.

[0048] Add 20 mL of prepared As(III) solution to six 50 mL Erlenmeyer flasks, adjust the pH of the As(III) solution to 7.0, and add 1 mg, 2 mg, 10 mg, 20 mg, 50 mg, and 100 mg of algae-supported nano-zero-valent iron prepared in Example 1, respectively. Seal the Erlenmeyer flasks and place them in a constant-temperature shaking incubator at 25 °C and 170 rpm. Samples were taken at 10 min, 30 min, 60 min, 120 min, 180 min, 240 min, and 480 min, and the arsenic content in the solution was determined by ICP-AES.

[0049] Please see Figure 4 As shown in the figure, the horizontal axis represents the reaction time and the vertical axis represents the arsenic removal rate. The reaction rate is the highest in the first 10 minutes, and then tends to level off. The removal effect is better as the amount of algae-loaded nano-zero valent iron increases. After 8 hours of reaction, 20-100 mg of algae-loaded nano-zero valent iron material can remove more than 95% of the arsenic.

[0050] To further investigate the effect of pH on arsenic removal, 20 mL of prepared As(III) solution was added to five 50 mL Erlenmeyer flasks, and the pH of the As(III) solution was adjusted to 3.0, 5.0, 7.0, 9.0, and 11.0, respectively. 20 mg of algae-supported nano-zero-valent iron prepared in Example 1 was added to each flask. The flasks were sealed and placed in a constant-temperature shaking incubator at 25°C and 170 rpm. Samples were taken at 10 min, 30 min, 60 min, 120 min, 180 min, 240 min, and 480 min, and the arsenic content in the solution was determined by ICP-AES.

[0051] Please see Figure 5 As shown in the figure, within the experimental pH range, over 93% of arsenic could be removed within 8 hours, and at pH 7.0, a removal rate of over 95% could be achieved within 30 minutes. The figure also shows that algae-loaded nano-zero-valent iron exhibits good arsenic removal effects within the pH range of 3-11.

[0052] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art. Unless otherwise specifically stated, the relative steps, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. In all examples shown and described herein, unless otherwise specified, any value should be interpreted as merely exemplary and not as a limitation; therefore, other examples of exemplary embodiments may have different values.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the protection scope of the present invention.

Claims

1. Application of algae-loaded nano zero-valent iron composite material in treatment of arsenic-containing wastewater, characterized in that: the components of the algae-loaded nano zero-valent iron composite material include Chlorella vulgaris and nano zero-valent iron, the algae-loaded nano zero-valent iron composite material uses Chlorella vulgaris as a carrier, and the nano zero-valent iron is prepared by using a chemical liquid-phase reduction method. The method comprises the following steps:

2. The use of the algal supported nano zero-valent iron composite material according to claim 1 in treating arsenic-containing wastewater, characterized in that, S1: Cultivation of Chlorella vulgaris, sodium nitrate, dipotassium hydrogen phosphate, magnesium sulfate heptahydrate, EDTA, sodium carbonate and A5 solution are first added into a volumetric flask, sterilized by using a high-pressure steam sterilization pot, then citric acid, ammonium iron citrate and calcium chloride dihydrate solution are added into the volumetric flask, finally, 5% of algae liquid is inoculated into the culture medium, and the medium is placed in a light incubator with a light / dark ratio of 12:12 for cultivation; S2: Preparation of algae-loaded nano zero-valent iron, 7.56 mg of sodium borohydride and 27.05 mg of ferric chloride are sequentially added into 10 mL of Chlorella vulgaris suspension, the reaction is started by gently shaking, and the nano zero-valent iron is fully combined with the algae cells; S3: The obtained suspension is centrifuged, the supernatant is discarded, the algae-loaded nano zero-valent iron particles in the centrifuge tube are collected, vacuum freeze-drying is performed for 24 h, and the algae-loaded nano zero-valent iron composite material is obtained. In the step S1, the high-pressure steam sterilization pot is sterilized at a temperature of 120°C for 30 min.

3. The use of the algal supported nano zero-valent iron composite material according to claim 2 in treating arsenic-containing wastewater, characterized in that: In the step S2, the volume of the Chlorella vulgaris suspension is 10 mL, and the nano zero-valent iron reacts with the Chlorella vulgaris for 2-3 min.

4. The use of the algal supported nano zero-valent iron composite material according to claim 2 in treating arsenic-containing wastewater, characterized in that: In the step S3, the number of revolutions of the centrifuge is set to 6000, and the time is 6 min.

5. The use of the algal supported nano zero-valent iron composite material according to claim 2 in the treatment of arsenic-containing wastewater, characterized in that: ​

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