Ozone catalyst as well as preparation method and application thereof in algae removal

Abstract

The invention discloses an ozone catalyst and a preparation method and application thereof, Ni (NO3) 26H2O and Al (NO3) 29H2O are used as raw materials, and NiAl-LDH is prepared through a coprecipitation method; the preparation method comprises the following steps: preparing NiAl-LDH, reacting NiAl-LDH, AgNO3 and a Na2HPO4 solution to prepare Ag3PO4, and finally compounding NiAl-LDH and Ag3PO4 to prepare the ozone catalyst Ag3PO4 / NiAl-LDH composite material. The Ag3PO4 / NiAl-LDH composite material is used as an ozone catalyst to be applied to algae removal through combination of catalytic ozonation and a quorum sensing inhibitor, so that cell walls and internal structures of algae are more efficiently destroyed, and the algae removal effect is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and specifically relates to an ozone catalyst and a preparation method thereof and application in algae removal. Background Art

[0002] Ozone catalytic oxidation algae removal is an efficient and environmentally friendly water treatment method, which is widely used to control algae growth and improve water quality. As a strong oxidant, ozone can quickly oxidize algae cells and metabolites, with high treatment efficiency, and can significantly reduce the concentration of algae in the water in a short period of time. In the algae removal process, ozone directly destroys the cell structure of algae through oxidation reactions, and algae cells lyse and release intracellular substances. The rapid destruction of algae cells may also cause the toxic metabolites inside them (such as microcystins) to be instantly released into the water. These toxins may reach high concentrations in a short period of time, increasing the toxicity risk of the water. In addition, as a strong oxidant, ozone will oxidize other microorganisms, plankton and organic matter in the water while killing algae, destroying the survival of beneficial microorganisms in the water and disrupting the ecological balance.

[0003] Quorum sensing inhibitors (QSI) algae removal is a technology that inhibits the growth and toxin release of algae and other microorganisms by interfering with the quorum sensing mechanism (QS) of algae and other microorganisms. Quorum sensing inhibitors (QSI) specifically interfere with the signal transmission of algae, inhibit the release of toxins without directly killing algae, thereby reducing the impact on non-target microorganisms. Since they do not directly kill algae, resistance develops slowly and is suitable for long-term use. QSIs are generally less toxic, have a small residual risk, and are environmentally friendly. However, compared with chemical methods that directly kill algae, quorum sensing inhibitors (QSIs) are slower to take effect and have a limited range of action, because the quorum sensing mechanisms of different algae are different, and some QSIs are only effective against specific algae. In addition, long-term use may affect the natural quorum sensing in water bodies and lead to ecological imbalance. Some QSIs have poor stability in the natural environment and are easily degraded, affecting their sustained effect. These factors limit the potential application of QSI in large-scale algae removal.

[0004] Using ozone catalytic oxidation or quorum sensing inhibitors alone to remove algae faces problems such as algae removal efficiency, energy consumption, and environmental impact. Therefore, it is necessary to find a more efficient and safe algae removal method. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides an ozone catalyst and a preparation method thereof, and the prepared catalyst is applied to ozone catalytic oxidation and used in series with a quorum sensing inhibitor to produce a synergistic effect, inhibiting algae from a physical and physiological mechanism, and having a stronger killing effect.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a method for preparing an ozone catalyst, comprising the following steps:

[0008] (1) Ni(NO3)2 6H2O and Al(NO3)29H2O were used as raw materials and dissolved in a mixed solution of NaOH and Na2CO3 to prepare NiAl-LDH by coprecipitation;

[0009] (2) dissolving AgNO3 in deionized water as solution A, dissolving Na2HPO4 in deionized water as solution B, slowly dropping solution B into solution A while stirring, and then stirring at room temperature in the dark for at least 4 h to form a light yellow precipitate, collecting and drying the precipitate to obtain Ag3PO4;

[0010] (3) Ultrasonic dispersion of NiAl-LDH and Ag(NO3)3 prepared in step (1) in deionized water, then adding Na2HPO4 solution to the above dispersion, stirring continuously, and then stirring the nanocomposite suspension in secret at room temperature for at least 8 hours to prepare an ozone catalyst Ag3PO4 / NiAl-LDH complex.

[0011] Furthermore, in step S1, the metal molar ratio of the raw materials Ni(NO3)2 6H2O and Al(NO3)29H2O is 2:1.

[0012] Furthermore, the pH of the mixed solution in step S1 is 10-10.2.

[0013] The present invention also provides an ozone catalyst prepared according to the preparation method.

[0014] The present invention also provides the application of ozone catalyst in algae removal by combining ozone catalytic oxidation with a quorum sensing inhibitor.

[0015] Furthermore, the quorum sensing inhibitor is 2(5H)-furanone.

[0016] The present invention also provides a method for algae removal by combining ozone catalytic oxidation with a quorum sensing inhibitor, wherein the ozone catalyst and the quorum sensing inhibitor are added to a water body to be treated, the water body to be treated is stirred, and then ozone is discharged from an ozone generator in a gaseous form, and the algae removal is achieved by continuous reaction.

[0017] Furthermore, the quorum sensing inhibitor is 2(5H)-furanone.

[0018] Furthermore, the pH of the water to be treated is controlled at 7.0-7.5.

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

[0020] 1. The Ag3PO4 / NiAl-LDH catalyst prepared by the present invention can effectively promote the decomposition of ozone and generate highly active oxygen species (such as OH free radicals). These active oxygen species have stronger oxidizing ability than ozone itself, thereby more efficiently destroying the cell wall and internal structure of algae and improving the algae removal effect.

[0021] 2. The present invention uses Ag3PO4 / NiAl-LDH complex as an ozone catalyst, and applies it to the combination of ozone catalytic oxidation and quorum sensing inhibitors in algae removal. Ozone directly destroys the algae cell wall, cell membrane and internal structure through its strong oxidizing property, causing algae cell lysis and death. The quorum sensing inhibitor inhibits the aggregation and reproduction of algae by interfering with the signal transduction between algae cells. The series use can inhibit algae from both physical and physiological mechanisms, with a stronger killing effect, and maintain the inhibitory effect for a long time, reducing the possibility of algae recurrence.

[0022] 3. Ozone will produce oxidation by-products (such as bromate and microcystin) in water, causing secondary pollution to the water body. The present invention provides the serial use of ozone catalytic oxidation and quorum sensing inhibitors, which can reduce the dosage of ozone, thereby reducing the generation of by-products, and can also reduce the toxin production of algae before lysis, reduce the toxin load in the water body, and reduce the impact on the ecology and safety of the water body.

[0023] 4. The combined use method of ozone catalytic oxidation and quorum sensing inhibitor provided by the present invention can combine the advantages of the two methods, cover a wider spectrum of algae types, and enhance the algae removal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD test diagrams of NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composite materials in Example 1;

[0025] Figure 2 FTIR test graphs of NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composite materials in Example 1;

[0026] Figure 3 It is the BET test graph of NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composite material in Example 1;

[0027] Figure 4 The algae removal performance diagram of ozone alone in Example 2, NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composite material added as catalyst;

[0028] Figure 5The effects of different factors in Example 3 on the removal of chlorophyll a by ozone catalytic oxidation using Ag3PO4 / NiAl-LDH composite material as catalyst: a) pH, b) algae density, c) catalyst dosage, d) humic acid dosage;

[0029] Figure 6 This is the algae removal performance diagram of the ozone catalytic oxidation and quorum sensing inhibitor used in series in Example 4; DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments.

[0031] In the following examples, Microcystis aeruginosa was used as the research object. The Microcystis aeruginosa (FACHB 905) algae species were purchased from the freshwater algae species bank of the Chinese Academy of Sciences, and BG-1 medium was used for culture; the incubator temperature was set at 25° C., the light intensity was 2000 Lux, the light duration was 14 h, and the dark duration was 10 h; after the Microcystis aeruginosa cells were cultured to the logarithmic growth phase, subsequent experiments were started.

[0032] In the following examples, the chlorophyll a removal rate is used as an indicator of the degree of algal cell inactivation. The extraction and determination of chlorophyll a mainly refer to the water conservancy industry standard of the People's Republic of China "Spectrophotometric Method for Determination of Chlorophyll in Water Quality", which will not be repeated here.

[0033] Example 1

[0034] This embodiment provides a method for preparing an ozone catalyst, comprising the following steps:

[0035] (1) 11.6 g Ni(NO3)2 6H2O and 7.5 g Al(NO3)29H2O were used as raw materials and dissolved in 100 mL deionized water as solution A, 3.8 g NaOH and 4.2 g Na2CO3 were dissolved in 100 mL deionized water as solution B, and then solution B was dripped into solution A dropwise at room temperature while vigorously stirring and controlling the pH of the solution at 10 to prepare NiAl-LDH;

[0036] (2) 0.254 g of AgNO3 was dissolved in 50 mL of deionized water as solution A, and 0.071 g of Na2HPO4 was dissolved in 50 mL of deionized water as solution B. Solution B was slowly added dropwise to solution A while stirring, and then stirred at room temperature in the dark for at least 4 h to form a light yellow precipitate. The precipitate was collected and dried at 80°C for 12 h to obtain Ag3PO4;

[0037] (3) 2.1 g NiAl-LDH and 0.25 g Ag(NO3)3 prepared in step (1) were ultrasonically dispersed in 80 mL deionized water for 30 min, and then 10 mL of Na2HPO4 solution was added to the above dispersion, and the mixture was stirred for 2 h. The nanocomposite suspension was then stirred in secret at room temperature for at least 8 h to obtain an Ag3PO4 / NiAl-LDH complex.

[0038] The NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composite materials prepared by the above steps were subjected to XRD, FTIR and adsorption performance tests. The specific test results are as follows:

[0039] The composition and crystal structure of NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composites were determined by XRD. Figure 1 As shown, it corresponds to hexagonal Ni-Al LDH (JCPDS No. 22-0452) and cubic Ag3PO4 (JCPDS No. 06-0505). These half-peak widths are small and the peaks are sharp, indicating that the materials are well crystallized.

[0040] like Figure 2 FTIR test results show that at 3500 and 1630 cm -1 The broad bands near 1370 cm correspond to the stretching and bending vibrations of interlayer and surface (OH) water molecules; -1 The band at 800 cm represents the stretching vibration of the interlayer anionic carbonate group; -1 The following peaks represent the MO (Ni-O and Al-O) and MOM (Ni-O-Al) bond stretching, confirming the successful synthesis of Ag3PO4 / NiAl-LDH composites.

[0041] like Figure 3 As shown in the figure, the synthesized NiAl-LDH, Ag3PO4 and Ag3PO4 / NiAl-LDH composite materials all exhibit type IV adsorption isotherms, where Figure (a) is NiAl-LDH, Figure (b) is Ag3PO4, and Figure (c) is Ag3PO4 / NiAl-LDH composite materials, indicating that the above materials have typical porosity, and the appearance of H2 hysteresis loops indicates a complex pore structure. The larger the surface area of ​​the catalyst, the more active sites can effectively assist the interfacial reaction, such as the adsorption, mass diffusion and reactivity of key adsorbates. Therefore, the prepared materials can be expected to exhibit enhanced catalytic ozonation performance.

[0042] Example 2

[0043] In this example, NiAl-LDH, Ag3PO4, and Ag3PO4 / NiAl-LDH composite materials prepared in Example 1 were used as catalysts, respectively, and the algae removal efficiency of ozone catalytic oxidation with ozone alone and the three catalysts was compared;

[0044] 400mL of algae liquid (OD680≈0.314) was measured and placed in a reaction container. NiAl-LDH, Ag3PO4, and Ag3PO4 / NiAl-LDH were selected as catalysts, respectively. The catalyst dosage was 0.2g / L. The algae liquid was continuously stirred and the pH of the algae liquid was controlled to be about 7.2. After reaching the adsorption / desorption equilibrium, ozone flowed out of the ozone generator in gaseous form with a gas flow rate of 0.8L / min. After 1h, the ozone concentration in the dissolved water was 1.5mg / L. The change of chlorophyll a during the reaction process indicated the degree of inactivation of Microcystis aeruginosa.

[0045] like Figure 4 The results show that compared with ozone alone and ozone catalytic oxidation, the algae removal effect of ozone catalytic oxidation with the addition of catalyst is improved. The ozone catalytic oxidation performance of Ag3PO4 / NiAl-LDH composite material is better than that of single material. The presence of the composite material catalyzes ozone to produce more active substances with stronger oxidizing properties, thereby improving the algae removal performance.

[0046] Example 4

[0047] The pH value of the solution will affect the adsorption potential of the catalyst and the surface charge of the algae cells. Therefore, in this embodiment, algae removal is performed at different pH values, and the specific operation is as follows:

[0048] 400mL of algae liquid (OD680≈0.314) was measured and placed in a reaction container. Ag3PO4 / NiAl-LDH was used as a catalyst with a dosage of 0.2g / L. The algae liquid was continuously stirred and the pH of the algae liquid was controlled to be about 7.2. After reaching the adsorption / desorption equilibrium, ozone flowed out of the ozone generator in gaseous form with a gas flow rate of 0.8L / min. After 1h, the ozone concentration in the dissolved water was 1.5mg / L. The change of chlorophyll a during the reaction process indicated the degree of inactivation of Microcystis aeruginosa.

[0049] The results are as follows Figure 5 As shown in (a), the algae removal effect of the catalyst is different at different pH values. After 1 hour of reaction, the chlorophyll a removal effect is from high to low: pH = 8 > pH = 9 > pH = 7 > pH = 6. No significant difference was observed under different pH values. The reason for the large-scale inactivation of algae may be that the active substances produced by the catalyst continuously attack the algae cells.

[0050] In this embodiment, the initial algae density is set to be about 5×10 6 , 6×10 6,7×10 6 , 8×10 6 ,9×10 6 , 10×10 6 cells / mL to explore the effect of algae density on algae removal performance. Figure 5 (b) It can be seen that for different algae densities (5×10 6 , 6×10 6 ,7×10 6 , 8×10 6 ,9×10 6 , 10×10 6 cells / mL) were 99.4%, 67.7%, 53.9%, 41.2%, 32.9% and 4.1% respectively. With the increase of algae density, the removal efficiency gradually decreased. It may be that too many algae cells adsorbed on the catalyst surface, resulting in a decrease in active sites; it may also be that the substrate concentration increased the number of oxidative decomposition products, thereby accelerating the consumption of O3 and ROS to resist further oxidation. For actual water bodies, when the algae cell density exceeds 10 5 When the concentration of Ag3PO4 / NiAl-LDH is less than 100 cells / mL, it means that the blue algae bloom has occurred. It can be seen that the Ag3PO4 / NiAl-LDH composite material has an excellent ability to inactivate algae.

[0051] like Figure 5 As shown in (c), when the dosage of Ag3PO4 / NiAl-LDH composite material as a catalyst increases, the chlorophyll a removal rate shows a trend of first increasing and then decreasing. As the dosage increases from 0.1g / L to 0.2g / L, the reaction rate increases. However, when the dosage is further increased to 0.3g / L and 0.5g / L, the chlorophyll a removal rate decreases. There are two possibilities for the performance degradation caused by excessive catalyst. One is the reduction in the number of available active sites on the stacked and agglomerated materials, and the other is the competition between the catalyst and the organic compound. The optimal catalyst dosage with the highest chlorophyll a degradation rate constant is 0.2g / L.

[0052] Natural Organic Matter (NOM), including humic acid (HA) and fulvic acid (FA), is widely distributed in water environments. During the oxidation process, NOM will compete with the active sites of Microcystis aeruginosa cells, thereby affecting the efficiency of inactivating Microcystis aeruginosa. Therefore, in this example, HA is taken as an example, and the results are as follows: Figure 5(d) In the catalytic oxidation system, when the HA dosage was 5 mg / L, the degradation rate of chlorophyll a after 60 minutes of reaction decreased from 99.4% when no HA was added to 98.8%. At this time, the effect of HA on algae removal was weak. When the HA dosage was 10 mg / L, the removal rate of chlorophyll a decreased to 86.08%. Although the removal rate decreased, it still maintained a high removal rate. When the HA dosage was 20 mg / L, the removal rate of chlorophyll a decreased to 44.79%. The algae removal performance decreased significantly. This may be because HA competed with Microcystis aeruginosa for active sites and consumed some active oxygen substances, thereby reducing the removal rate of chlorophyll a.

[0053] Example 4

[0054] In this embodiment, the ozone catalyst is applied to the algae removal by combining ozone catalytic oxidation with a quorum sensing inhibitor, and the specific operation is as follows:

[0055] Ag3PO4 / NiAl-LDH composite material is an ozone catalyst, and 2(5H)-furanone is a quorum sensing inhibitor. The ozone catalyst and the quorum sensing inhibitor are added to the water body to be treated, and the water body to be treated is stirred. Then ozone is discharged from the ozone generator in gaseous form, and the algae are removed by continuous reaction. A good inactivation effect is achieved in about 40 minutes.

[0056] At the same time, in this embodiment, the algae removal effects of single ozone, ozone catalytic oxidation, and quorum sensing inhibitor are also used for comparison. Figure 6 The results showed that quorum sensing inhibitors had a certain synergistic effect with ozone catalytic oxidation and had certain potential in algae removal.

[0057] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing an ozone catalyst, characterized in that: The following steps are involved: (1) Ni(NO3)2 6H2O and Al(NO3)29H2O were used as raw materials and dissolved in a mixed solution of NaOH and Na2CO3 to prepare NiAl-LDH by coprecipitation; (2) dissolving AgNO3 in deionized water as solution A, dissolving Na2HPO4 in deionized water as solution B, slowly dropping solution B into solution A while stirring, and then stirring at room temperature in the dark for at least 4 h to form a light yellow precipitate, collecting and drying the precipitate to obtain Ag3PO4; (3) Ultrasonic dispersion of NiAl-LDH and Ag(NO3)3 prepared in step (1) in deionized water, then adding Na2HPO4 solution to the above dispersion, stirring continuously, and then stirring the nanocomposite suspension in secret at room temperature for at least 8 hours to prepare an ozone catalyst Ag3PO4 / NiAl-LDH complex.

2. The preparation method according to claim 1, characterized in that: The metal molar ratio of the raw materials Ni(NO3)26H2O and Al(NO3)29H2O in step S1 is 2:

1.

3. The preparation method according to claim 1, characterized in that: The pH of the mixed solution in step S1 is 10-10.

2.

4. An ozone catalyst prepared according to the preparation method according to any one of claims 1 to 3.

5. The ozone catalyst according to claim 4 is used in algae removal by combining ozone catalytic oxidation with a quorum sensing inhibitor.

6. The use according to claim 5, characterized in that: The quorum sensing inhibitor is 2(5H)-furanone.

7. A method for removing algae by combining ozone catalytic oxidation with a quorum sensing inhibitor, characterized in that: The ozone catalyst and quorum sensing inhibitor as described in claim 4 are added to the water body to be treated, the water body to be treated is stirred, and then ozone is discharged from the ozone generator in gaseous form, and the algae are removed by continuous reaction.

8. The method according to claim 7, characterized in that: The quorum sensing inhibitor is 2(5H)-furanone.

9. The method according to claim 7, characterized in that: The pH of the water to be treated is controlled at 7.0-7.5.

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