Preparation method and application of modified garden waste biochar adsorption photocatalyst

Abstract

This invention discloses a method for preparing and applying a modified garden waste biochar adsorption photocatalyst, comprising the following steps: preparing garden waste powder; preparing a mixed solution of zirconium oxychloride, Y₂O₃, and ErCl₃•6H₂O; adding the garden waste powder to the mixed solution, adding ammonia water to carry out a precipitation reaction to obtain a coprecipitate product; placing the coprecipitate product in a magnesium chloride solution, shaking the reaction to obtain a precursor; and calcining the precursor under an inert atmosphere to obtain the final product. This invention uses a coprecipitation method to load Y₂O₃ partially stabilized with rare earth element Er onto garden waste biochar to stabilize nano-ZrO₂, and further loads magnesium oxide onto it using an impregnation method. The doped and modified nano-ZrO₂ can act as a photocatalyst to catalyze the degradation of ammonia nitrogen in wastewater. Simultaneously, the surface of the biochar loaded with doped and modified nano-ZrO₂ and magnesium oxide can effectively adsorb phosphates in wastewater, achieving simultaneous nitrogen and phosphorus removal from the wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment materials technology, and in particular to a method for preparing and applying a modified garden waste biochar adsorption photocatalyst. Background Technology

[0002] Excessive nitrogen and phosphorus content is a key factor in water quality deterioration and a major contributor to eutrophication. The discharge of large quantities of nitrogen- and phosphorus-containing wastewater from production and daily life not only causes severe pollution but also poses a significant threat to human health and sustainable development. Currently, wastewater nitrogen and phosphorus removal methods mainly include neutralization sedimentation, biological methods, and adsorption. Neutralization requires the addition of large amounts of lime and coagulants, generating large amounts of difficult-to-treat sludge and easily causing secondary pollution. Biological phosphorus removal processes are complex, have poor operational stability, require strict operating procedures, are greatly affected by wastewater temperature and pH, and are highly dependent on the concentration of organic matter in the wastewater. Adsorption overcomes the aforementioned shortcomings of neutralization and biological methods and is currently one of the most promising wastewater nitrogen and phosphorus removal methods.

[0003] Existing nitrogen and phosphorus removal adsorbents mainly include activated alumina, activated carbon, and zeolite. For example, the Chinese patent document "A method for preparing nano-hydrated zirconium oxide-supported biochar for phosphorus removal," publication number CN111992194A, uses waste nut shells as raw materials. The process involves pretreatment, followed by carbonization and activation to prepare activated biochar; then, zirconium is used as a functionalizing agent to prepare nano-hydrated zirconium oxide-supported biochar. This invention utilizes the prepared nano-hydrated zirconium oxide-supported biochar for phosphorus-containing wastewater treatment, achieving effective utilization of waste biomass and realizing the goal of treating waste with waste.

[0004] However, the adsorbents mentioned above in the existing technology can generally only remove nitrogen or phosphorus at a single time, and cannot remove ammonia nitrogen and phosphorus from water at the same time. In addition, even if nitrogen and phosphorus in wastewater can be adsorbed at the same time, the simultaneous removal effect of nitrogen and phosphorus is not ideal due to the limited adsorption capacity of the adsorbent. Summary of the Invention

[0005] This invention aims to overcome the limitations of existing adsorbents, which typically only remove nitrogen or phosphorus at a time and cannot simultaneously remove ammonia nitrogen and phosphorus from water. Even when nitrogen and phosphorus in wastewater can be adsorbed simultaneously, the limited adsorption capacity of the adsorbent results in less than ideal simultaneous removal of nitrogen and phosphorus. The invention provides a method for preparing and applying a modified garden waste biochar photocatalyst. This involves loading partially stabilized nano-ZrO2, doped with rare earth element Er, onto garden waste biochar using a co-precipitation method, and further loading magnesium oxide using an impregnation method. The modified nano-ZrO2 can act as a photocatalyst to catalyze the degradation of ammonia nitrogen in wastewater. Simultaneously, the loaded modified nano-ZrO2 and magnesium oxide on the biochar surface effectively adsorb phosphates in the wastewater, achieving simultaneous nitrogen and phosphorus removal from the wastewater.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a modified garden waste biochar adsorption photocatalyst includes the following steps:

[0008] (1) The garden waste is washed, dried, crushed and then sieved to obtain garden waste powder;

[0009] (2) Dissolve zirconium oxychloride in deionized water, then add Y2O3 to dissolve, and then add ErCl3·6H2O to dissolve, to obtain a mixed solution;

[0010] (3) Add garden waste powder to the mixed solution, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction, filter, wash and dry the product to obtain the coprecipitated product.

[0011] (4) The coprecipitated product was placed in a magnesium chloride solution, and after shaking the reaction, the product was filtered and dried to obtain the precursor.

[0012] (5) The precursor was calcined in an inert atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0013] This invention first uses a co-precipitation method to load a co-precipitate product of zirconium and yttrium hydroxide doped with rare earth element Er onto the surface of garden waste powder. Then, magnesium chloride is loaded onto the surface of the co-precipitate product using an impregnation method. After calcination, the garden waste powder forms biochar, and the co-precipitate product loaded on it forms Er-doped Y2O3 partially stabilized nano-ZrO2. The nano-ZrO2 can adsorb and remove phosphate ions from wastewater through the coordination of Zr-OH adsorption sites with phosphate ions. On the other hand, the nano-ZrO2 can also act as a photocatalyst to catalyze the degradation of ammonia nitrogen in wastewater.

[0014] However, nano-ZrO2 has a large band gap and low photocatalytic activity when used as a photocatalyst. Therefore, this invention adds Y2O3 to nano-ZrO2 and does it with the rare earth element Er. The addition of Y2O3 can promote the transformation of ZrO2 crystals from the monoclinic phase to the tetragonal phase, forming a stable non-equilibrium tetragonal phase with good photocatalytic activity; the added Er 3+ Er can enter the ZrO2 lattice, causing lattice distortion, reducing its band gap, and enhancing its photocatalytic activity under visible light. At the same time, Er doping can also inhibit grain growth and improve the sintering resistance of nano ZrO2, which is also beneficial to enhancing its photocatalytic activity.

[0015] This invention also loads magnesium chloride onto the coprecipitate product via impregnation, thereby partially removing Mg during calcination. 2+ Magnesium chloride can enter the zirconium dioxide lattice. Due to the different valence levels of magnesium and zirconium ions, a large number of oxygen vacancies can be generated in the zirconium dioxide crystal, further enhancing its photocatalytic activity. On the other hand, magnesium chloride can generate magnesium oxide after calcination, which is supported on the surface of biochar and is beneficial to improving the adsorption performance of modified biochar on phosphate.

[0016] Therefore, the modified garden waste biochar adsorption photocatalyst in this invention can effectively adsorb phosphate in wastewater while catalyzing the degradation of ammonia nitrogen in wastewater under visible light, thus achieving simultaneous nitrogen and phosphorus removal from wastewater.

[0017] Preferably, the sieving in step (1) is performed through a 200-500 mesh sieve.

[0018] Preferably, in the mixed solution of step (2), the molar ratio of Zr, Y, and Er atoms is 5–7:0.5–1:0.2–0.5. Within this range, the doping amounts of Y and Er can effectively stabilize the crystal structure of nano-ZrO2 and reduce its band gap, thus enabling it to exhibit good photocatalytic activity under visible light.

[0019] Preferably, the concentration of zirconium oxychloride in the mixed solution in step (2) is 0.4–0.6 mol / L. Within this concentration range, the dissolved solution is acidic and can dissolve Y₂O₃.

[0020] Preferably, in step (3), the mass-to-volume ratio of garden waste powder to mixed solution is 8-10 g: 1 L; and the precipitation reaction time is 1-2 h.

[0021] Preferably, in step (3), the washing process involves washing with ammonia and anhydrous ethanol 2 to 3 times in sequence.

[0022] Preferably, the concentration of the magnesium chloride solution in step (4) is 2-3 g / L.

[0023] Preferably, the oscillation reaction time in step (4) is 18 to 24 hours.

[0024] Preferably, the calcination temperature in step (5) is 600-650℃ and the calcination time is 2-3h.

[0025] This invention also provides the application of the modified garden waste biochar adsorption photocatalyst prepared by the above preparation method in the simultaneous denitrification and phosphorus removal of nitrogen and phosphorus wastewater.

[0026] Preferably, the dosage of the modified garden waste biochar adsorption photocatalyst in nitrogen and phosphorus wastewater is 5-10 g / L.

[0027] As a preferred method, the simultaneous denitrification and phosphorus removal is carried out under visible light for 8–12 hours.

[0028] Therefore, the present invention has the following beneficial effects:

[0029] (1) Nano-ZrO2 is loaded and modified on the surface of garden waste biochar; on the one hand, nano-ZrO2 can adsorb and remove phosphate in wastewater through the coordination of Zr-OH adsorption sites with phosphate ions; on the other hand, nano-ZrO2 can act as a photocatalyst to catalyze the degradation of ammonia nitrogen in wastewater; therefore, the adsorption photocatalyst in this invention can effectively adsorb phosphate in wastewater while catalyzing the degradation of ammonia nitrogen in wastewater under visible light, thus achieving simultaneous denitrification and phosphorus removal of wastewater.

[0030] (2) Y₂O₃ was added to nano-ZrO₂, and rare earth element Er was added to dope it; the addition of Y₂O₃ can promote the formation of a stable non-equilibrium tetragonal phase with good photocatalytic activity; the added Er 3+ It can reduce its band gap and improve its photocatalytic activity under visible light; at the same time, Er doping can also inhibit grain growth and improve the sintering resistance of nano ZrO2, which is also conducive to improving its photocatalytic activity.

[0031] (3) Magnesium chloride was loaded onto the coprecipitate product by impregnation, which, on the one hand, partially removed Mg during calcination. 2+ It can enter the zirconium dioxide lattice and generate a large number of oxygen vacancies in the zirconium dioxide crystal, further enhancing its photocatalytic activity; on the other hand, magnesium chloride can generate magnesium oxide after calcination, which is beneficial to improving the adsorption performance of modified biochar on phosphate. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0034] Example 1:

[0035] A method for preparing a modified garden waste biochar adsorption photocatalyst, comprising the following steps:

[0036] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0037] (2) Dissolve zirconium oxychloride in deionized water to obtain a 0.5 mol / L solution; then add Y2O3 to dissolve, and then add ErCl3·6H2O to dissolve to obtain a mixed solution; in the mixed solution, the molar ratio of Zr, Y, and Er atoms is 6:0.6:0.3;

[0038] (3) Add garden waste powder to the mixed solution at a mass-volume ratio of 9g:1L, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction for 2 hours, filter the product, wash it three times with ammonia water and anhydrous ethanol in sequence, and dry it to obtain the coprecipitated product.

[0039] (4) The coprecipitated product was placed in a magnesium chloride solution with a concentration of 2.5 g / L, and the reaction was shaken for 24 h. The product was then filtered and dried to obtain the precursor.

[0040] (5) The precursor was placed in a muffle furnace and calcined at 600°C for 2 hours under N2 atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0041] Example 2:

[0042] A method for preparing a modified garden waste biochar adsorption photocatalyst, comprising the following steps:

[0043] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0044] (2) Dissolve zirconium oxychloride in deionized water to obtain a 0.4 mol / L solution; then add Y2O3 to dissolve, and then add ErCl3·6H2O to dissolve to obtain a mixed solution; in the mixed solution, the molar ratio of Zr, Y, and Er atoms is 5:0.5:0.2;

[0045] (3) Add garden waste powder to the mixed solution at a mass-volume ratio of 8g:1L, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction for 2 hours, filter the product, wash it three times with ammonia water and anhydrous ethanol in sequence, and dry it to obtain the coprecipitated product.

[0046] (4) The coprecipitated product was placed in a magnesium chloride solution with a concentration of 3 g / L, and the reaction was shaken for 24 h. The product was then filtered and dried to obtain the precursor.

[0047] (5) The precursor was placed in a muffle furnace and calcined at 650°C for 2 hours under N2 atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0048] Example 3:

[0049] A method for preparing a modified garden waste biochar adsorption photocatalyst, comprising the following steps:

[0050] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0051] (2) Dissolve zirconium oxychloride in deionized water to obtain a 0.6 mol / L solution; then add Y2O3 to dissolve, and then add ErCl3·6H2O to dissolve to obtain a mixed solution; in the mixed solution, the molar ratio of Zr, Y and Er atoms is 7:1:0.5;

[0052] (3) Add garden waste powder to the mixed solution at a mass-volume ratio of 10g:1L, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction for 2 hours, filter the product, wash it three times with ammonia water and anhydrous ethanol in sequence, and dry it to obtain the coprecipitated product.

[0053] (4) The coprecipitated product was placed in a magnesium chloride solution with a concentration of 2 g / L, and the reaction was shaken for 24 h. The product was then filtered and dried to obtain the precursor.

[0054] (5) The precursor was placed in a muffle furnace and calcined at 600°C for 3 hours under N2 atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0055] Comparative Example 1 (Unloaded modified nano-ZrO2):

[0056] A method for preparing a modified garden waste biochar adsorbent, comprising the following steps:

[0057] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0058] (2) Place garden waste powder in a magnesium chloride solution with a concentration of 2.5 g / L, shake and react for 24 h, then filter and dry the product to obtain the precursor;

[0059] (3) The precursor was placed in a muffle furnace and calcined at 600°C for 2 hours under N2 atmosphere to obtain the modified garden waste biochar adsorbent.

[0060] Comparative Example 2 (without adding Y2O3):

[0061] A method for preparing a modified garden waste biochar adsorption photocatalyst, comprising the following steps:

[0062] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0063] (2) Dissolve zirconium oxychloride in deionized water to obtain a 0.5 mol / L solution; then add ErCl3·6H2O to dissolve and obtain a mixed solution; in the mixed solution, the molar ratio of Zr to Er atoms is 6:0.3;

[0064] (3) Add garden waste powder to the mixed solution at a mass-volume ratio of 9g:1L, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction for 2 hours, filter the product, wash it three times with ammonia water and anhydrous ethanol in sequence, and dry it to obtain the coprecipitated product.

[0065] (4) The coprecipitated product was placed in a magnesium chloride solution with a concentration of 2.5 g / L, and the reaction was shaken for 24 h. The product was then filtered and dried to obtain the precursor.

[0066] (5) The precursor was placed in a muffle furnace and calcined at 600°C for 2 hours under N2 atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0067] Comparative Example 3 (without Er doping):

[0068] A method for preparing a modified garden waste biochar adsorption photocatalyst, comprising the following steps:

[0069] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0070] (2) Dissolve zirconium oxychloride in deionized water to obtain a 0.5 mol / L solution; then add Y2O3 to dissolve and obtain a mixed solution; in the mixed solution, the molar ratio of Zr to Y atoms is 6:0.6;

[0071] (3) Add garden waste powder to the mixed solution at a mass-volume ratio of 9g:1L, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction for 2 hours, filter the product, wash it three times with ammonia water and anhydrous ethanol in sequence, and dry it to obtain the coprecipitated product.

[0072] (4) The coprecipitated product was placed in a magnesium chloride solution with a concentration of 2.5 g / L, and the reaction was shaken for 24 h. The product was then filtered and dried to obtain the precursor.

[0073] (5) The precursor was placed in a muffle furnace and calcined at 600°C for 2 hours under N2 atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0074] Comparative Example 4 (without magnesium oxide loading):

[0075] A method for preparing a modified garden waste biochar adsorption photocatalyst, comprising the following steps:

[0076] (1) After washing, drying and crushing the garden waste, pass it through a 200-mesh sieve and retain the material passing through the sieve to obtain garden waste powder;

[0077] (2) Dissolve zirconium oxychloride in deionized water to obtain a 0.5 mol / L solution; then add Y2O3 to dissolve, and then add ErCl3·6H2O to dissolve to obtain a mixed solution; in the mixed solution, the molar ratio of Zr, Y, and Er atoms is 6:0.6:0.3;

[0078] (3) Add garden waste powder to the mixed solution at a mass-volume ratio of 9g:1L, stir and disperse evenly, then add excess ammonia water to the solution. After precipitation reaction for 2 hours, filter the product, wash it three times with ammonia water and anhydrous ethanol in sequence, and dry it to obtain the coprecipitated product.

[0079] (4) The coprecipitated product was placed in a muffle furnace and calcined at 600°C for 2 hours under N2 atmosphere to obtain the modified garden waste biochar adsorption photocatalyst.

[0080] The simultaneous nitrogen and phosphorus removal effects of the modified garden waste biochar adsorption photocatalysts prepared in the above embodiments and comparative examples were tested using the following methods:

[0081] (1) Weigh 0.4 g of each of the modified garden waste biochar adsorption photocatalysts prepared in each example and comparative example into a 100 mL conical flask, add 50 mL of simulated wastewater with a phosphate concentration of 50 mg / L and an ammonium ion concentration of 50 mg / L, and adjust the pH of the solution to 8.0; wrap the outer wall of the conical flask with tin foil to prevent stray light from entering and affecting the reaction;

[0082] (2) Place the conical flasks from step (1) into a constant temperature shaker (200 r·min). -1 The reactor was oscillated at 29℃, and irradiated with visible light (10cm away from the reactor) for 10h. Meanwhile, an oscillation reaction without visible light irradiation was set up as a control group. Samples were taken and tested at 30, 60, 90, 120, 180, 240, 480 and 600 min respectively.

[0083] (3) The residual phosphate content in the sample was determined by the ammonium molybdate spectrophotometer method (GB11893-89), and the residual ammonia nitrogen content in the sample was determined by the Nessler's reagent spectrophotometer method (HJ535-2009). The removal rates of phosphate and ammonia nitrogen by different modified garden waste biochar adsorption photocatalysts were calculated. The results are shown in Table 1 and Table 2.

[0084] Table 1: Results of phosphate adsorption test.

[0085]

[0086] Table 2: Ammonia nitrogen degradation rate test results.

[0087]

[0088] As can be seen from the data in Tables 1 and 2, the modified garden waste biochar adsorption photocatalysts prepared in Examples 1-3 using the method of this invention can effectively remove nitrogen and phosphorus from wastewater simultaneously under visible light, with removal rates of phosphate and ammonia nitrogen both exceeding 90%. Under light-free conditions, the phosphate removal rate showed no significant change, while the ammonia nitrogen removal rate decreased significantly compared to the light-bearing conditions, reaching only about 40%. This indicates that the adsorption photocatalysts prepared in this invention primarily remove phosphate through adsorption, while the removal of ammonia nitrogen is achieved through a combination of adsorption and photocatalytic degradation.

[0089] In Comparative Example 1, no modified nano-ZrO2 was loaded onto the biochar surface; only magnesium oxide was loaded. The removal efficiency of nitrogen and phosphorus by the modified biochar was lower than that in Example 1, especially the ammonia nitrogen removal rate under light irradiation. This indicates that without the catalytic effect of modified nano-ZrO2, ammonia nitrogen in wastewater cannot be photocatalytically degraded and can only be removed through adsorption. However, the adsorption effect is limited, making it difficult to achieve simultaneous removal of nitrogen and phosphorus.

[0090] The nano-ZrO2 in Comparative Example 2 was not doped with Y2O3, and the nano-ZrO2 in Comparative Example 3 was not doped with rare earth element Er. The nitrogen and phosphorus removal efficiency of the modified biochar was also reduced compared with that in Example 1. This indicates that the crystal form and structure of nano-ZrO2 have a significant impact on its photocatalytic activity and adsorption performance.

[0091] In Comparative Example 4, without magnesium oxide loading on the modified biochar surface, the removal efficiency of phosphate in wastewater was significantly lower compared to Example 1, and the photocatalytic degradation performance of ammonia nitrogen also decreased. This indicates that magnesium oxide loading is beneficial for the adsorption of phosphate by the modified biochar and can enhance the photocatalytic activity of nano-ZrO2.

Claims

1. A method for preparing a modified garden waste biochar adsorption photocatalyst, characterized in that, Includes the following steps: (1) The garden waste is washed, dried, crushed and then screened to obtain garden waste powder; (2) Dissolve zirconium oxychloride in deionized water, then add Y2O3 to dissolve, and then add ErCl3•6H2O to dissolve to obtain a mixed solution; the molar ratio of Zr, Y, and Er atoms is 5~7:0.5~1:0.2~0.5; (3) Add garden waste powder to the mixed solution, stir and disperse evenly, then add excess ammonia water to the solution, and after precipitation reaction, filter, wash and dry the product to obtain coprecipitated product; (4) The coprecipitated product was placed in a magnesium chloride solution, and after shaking the reaction, the product was filtered and dried to obtain the precursor; (5) The precursor is calcined in an inert atmosphere to obtain the modified garden waste biochar adsorption photocatalyst; the calcination temperature is 600~650℃.

2. The preparation method according to claim 1, characterized in that, In step (1), the material is sieved through a 200-500 mesh sieve.

3. The preparation method according to claim 1, characterized in that, In the mixed solution in step (2), the concentration of zirconium oxychloride is 0.4~0.6 mol / L.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass-to-volume ratio of garden waste powder to mixed solution is 8-10 g: 1 L; the precipitation reaction time is 1-2 h.

5. The preparation method according to claim 1, characterized in that, In step (4), the concentration of magnesium chloride solution is 2~3 g / L; the shaking reaction time is 18~24 h.

6. The preparation method according to claim 1, characterized in that, The calcination time in step (5) is 2-3 hours.

7. The application of a modified garden waste biochar adsorption photocatalyst prepared by any one of the preparation methods described in claims 1 to 6 in the simultaneous denitrification and phosphorus removal of nitrogen and phosphorus wastewater.

8. The application according to claim 7, characterized in that, The dosage of the modified garden waste biochar adsorption photocatalyst in nitrogen and phosphorus wastewater is 5~10g / L.

9. The application according to claim 7 or 8, characterized in that, During simultaneous nitrogen and phosphorus removal, the reaction is carried out under visible light for 8-12 hours.

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