阅读说明：本技术 一种锌铝氧化物修饰生物炭负载磷酸盐复合材料及其制备方法和应用 (Zinc-aluminum oxide modified charcoal-loaded phosphate composite material and preparation method and application thereof ) 是由 姜传佳 刘松林 张煜 陈再豪 张彤 陈威 于 2021-09-17 设计创作，主要内容包括：本发明公开了一种锌铝氧化物修饰生物炭负载磷酸盐复合材料及其制备方法和应用一种,包括锌铝氧化物修饰的生物炭和负载于所述锌铝氧化物上的磷酸盐纳米矿物,所述锌铝氧化物修饰的生物炭包括生物炭和沉积在所述生物炭表面的锌铝氧化物,所述锌铝氧化物包括锌铝层状双金属氢氧化物和氧化锌两种物相,所述磷酸盐纳米矿物中包括四水合磷酸锌复合纳米片。锌铝氧化物-四水合磷酸锌复合纳米片使其在环境条件下表现出磷酸盐缓释性质,可用于磷肥缓释应用。(The invention discloses a zinc-aluminum oxide modified biochar loaded phosphate composite material and a preparation method and application thereof. The zinc-aluminum oxide-zinc tetrahydrate composite nanosheet enables the zinc-aluminum oxide-zinc tetrahydrate composite nanosheet to show phosphate slow release property under environmental conditions, and can be used for slow release application of phosphate fertilizer.)

1. The zinc-aluminum oxide modified biochar loaded phosphate composite material is characterized by comprising zinc-aluminum oxide modified biochar and phosphate nano minerals loaded on the zinc-aluminum oxide, wherein the zinc-aluminum oxide modified biochar comprises biochar and zinc-aluminum oxide deposited on the surface of the biochar, the zinc-aluminum oxide comprises two phases of zinc-aluminum layered double hydroxide and zinc oxide, and the phosphate nano minerals comprise zinc phosphate tetrahydrate composite nanosheets.

2. The zinc-aluminum oxide modified biochar-loaded phosphate composite material of claim 1, wherein the mass of phosphorus in the phosphate nano mineral accounts for 4-10% of the total mass of the composite material;

the zinc-aluminum oxide is in a porous nano structure, and the specific surface area of the biological carbon modified by the zinc-aluminum oxide is 50-60 m²/g。

3. The zinc aluminum oxide modified biochar-supported phosphate composite material according to claim 1, wherein the zinc aluminum oxide is supported on the biochar by a forced hydrolysis method to obtain the zinc aluminum oxide modified biochar, preferably, the forced hydrolysis method comprises the following steps:

step 1, preparing a zinc and aluminum precursor solution: dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until solutes are completely dissolved, wherein the mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step 2, dipping the biochar in the zinc and aluminum precursor solution, gradually adding a sodium hydroxide solution in the stirring process, and continuously stirring for reaction, wherein the mass ratio of the biochar to the zinc and aluminum precursor solution is 1: (28-36); after the sodium hydroxide is added, the pH value of the solution is adjusted to 9.5-10.5, and the continuous stirring time is 1-3 hours;

and 3, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar, preferably, the centrifuging speed is 3000-4000 rpm, the centrifuging time is 5-8 minutes, the deionized water cleaning times are 4-6, and the drying temperature is 60-70 ℃.

4. The zinc aluminum oxide modified biochar supported phosphate composite material according to claim 1, wherein the phosphate nanomineral is supported on the zinc aluminum oxide modified biochar by an impregnation precipitation method, preferably comprising the following steps: adding the zinc-aluminum oxide modified biochar into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar loaded phosphate composite material, wherein preferably, the mass ratio of the zinc-aluminum oxide modified biochar to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

5. A preparation method of a zinc-aluminum oxide modified biochar loaded phosphate composite material comprises the following steps:

step 1, preparing a zinc and aluminum precursor solution: dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until solutes are completely dissolved, wherein the preferred mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step 2, dipping the biochar in the zinc and aluminum precursor solution, gradually adding a sodium hydroxide solution in the stirring process, and continuously stirring for reaction, wherein preferably, the mass ratio of the biochar to the zinc and aluminum precursor solution is 1: (28-36); after the sodium hydroxide is added, the pH value of the solution is adjusted to 9.5-10.5, and the continuous stirring time is 1-3 hours;

step 3, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar, preferably, the centrifuging speed is 3000-4000 rpm, the centrifuging time is 5-8 minutes, the deionized water cleaning times are 4-6 times, and the drying temperature is 60-70 ℃;

and 4, adding the biochar modified by the zinc-aluminum oxide into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar loaded phosphate composite material, wherein preferably, the mass ratio of the biochar modified by the zinc-aluminum oxide to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

6. The zinc-aluminum oxide nanosheet loaded phosphate composite material is characterized by comprising a zinc-aluminum oxide nanosheet and a phosphate nano mineral loaded on the zinc-aluminum oxide nanosheet, wherein the zinc-aluminum oxide nanosheet comprises two phases of zinc-aluminum layered double metal hydroxide and zinc oxide, and the phosphate nano mineral comprises a zinc phosphate tetrahydrate composite nanosheet.

7. The zinc-aluminum oxide nanosheet supported phosphate composite of claim 6, wherein the phosphate nanomineral comprises 3-8% by mass of the phosphorus element based on the total mass of the composite;

the specific surface area of the zinc-aluminum oxide nanosheet is 50-60 m²/g。

8. The zinc aluminum oxide nanoplate-supported phosphate composite of claim 6, wherein the zinc aluminum oxide nanoplate-supported phosphate composite is prepared by a method comprising:

step s1, preparing a zinc and aluminum precursor solution, preferably, dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until the solute is completely dissolved, preferably, the mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step s2, preparing a carrier zinc-aluminum oxide nanosheet, preferably, adding a sodium hydroxide solution into the zinc and aluminum precursor solution prepared according to the step s1 by using a dropper while stirring until the pH value is 9.5-10.5, continuously stirring for 1-3 hours, centrifuging, washing and drying;

step s3, adding the carrier zinc-aluminum oxide nanosheets obtained in the step s2 into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide nanosheet-supported phosphate composite material, wherein the preferable mass ratio of the carrier zinc-aluminum oxide nanosheets to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

9. A preparation method of a zinc-aluminum oxide nanosheet loaded phosphate composite material is characterized by comprising the following steps:

step s1, preparing a zinc and aluminum precursor solution, preferably, dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until the solute is completely dissolved, preferably, the mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step s2, preparing a carrier zinc-aluminum oxide nanosheet, preferably, adding a sodium hydroxide solution into the zinc and aluminum precursor solution prepared according to the step s1 by using a dropper while stirring until the pH value is 9.5-10.5, continuously stirring for 1-3 hours, centrifuging, washing and drying;

step s3, adding the carrier zinc-aluminum oxide nanosheets obtained in the step s2 into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide nanosheet-supported phosphate composite material, wherein the preferable mass ratio of the carrier zinc-aluminum oxide nanosheets to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

10. Use of the zinc aluminium oxide modified biochar-supported phosphate composite of any one of claims 1 to 4 or the zinc aluminium oxide nanoplate-supported phosphate composite of any one of claims 6 to 8 as a soil slow release fertilizer.

Technical Field

The invention relates to the technical field of soil conditioning materials, in particular to a zinc-aluminum oxide modified charcoal-loaded phosphate composite material, and a preparation method and application thereof.

Background

The food safety is an important foundation of national safety and also an important guarantee for peace and development of the world. According to the annual report of world food safety and nutrition conditions released in 2020 of the United nations, one fourth of the world population faces moderate or severe food deficiency, and nearly 6.9 hundred million people face hunger globally in 2019, accounting for 8.9 percent of the world population. In order to meet the challenge of new changes in new vigor on global grain safety, the green development of agriculture must be greatly promoted, the yield and the quality of grains can be continuously improved, the ever-increasing demand of society on grains can be met, the grain safety can be guaranteed, and the negative influence of agricultural production activities on the ecological environment can be reduced.

At present, agricultural production activities in the global scope still mainly adopt extensive operation modes depending on resource consumption, and have a plurality of inherent limitations, wherein the most important limitation factor is the low utilization efficiency of agricultural chemicals such as chemical fertilizers, pesticides and the like. For example, the average utilization of nitrogen, phosphorus and potassium, which are main nutrients of conventional fertilizers, is 30-35%, 18-20% and 35-40%. To improve the yield and quality of agricultural products, agricultural chemicals such as fertilizers are applied in large areas for a long time. On the one hand, the high dependence of modern agriculture on resources such as fresh water, energy and the like is caused; on the other hand, agricultural production activities cause ecological environmental problems such as degradation of farmland soil, eutrophication of water bodies, and the like. Therefore, new agricultural technologies must be developed to improve the utilization efficiency of agricultural chemicals such as chemical fertilizers, thereby realizing reduction in application and improvement in efficiency and promoting green development of agriculture.

At present, one of the most effective ways to improve the utilization efficiency of agrochemicals such as chemical fertilizers is to develop a slow/controlled release fertilizer with high efficiency and low cost. By loading plant nutrient elements such as nitrogen and phosphorus in a carrier material with a porous structure, a core-shell structure or a layered structure, the release rate of the nutrient elements to soil pore water can be slowed down, so that the rapid and excessive release of the nutrient elements is avoided, and the utilization efficiency of nutrients is improved. However, most of the currently reported slow/controlled release fertilizers use inorganic nanomaterials and polymer nanomaterials as carriers (Guha et al, J.Agric.food chem.2020,68, 3691-. The invention selects cheap, easily-obtained and environment-friendly agricultural soil conditioner biochar as a carrier material, can efficiently load inorganic phosphate after being modified by zinc-aluminum oxide, and realizes the slow release of phosphorus nutrient elements under environmental conditions. The preparation process is simple, the preparation process is easy to regulate and control, and the requirements of actual production and application are hopefully met.

Disclosure of Invention

The invention aims to provide a zinc-aluminum oxide modified charcoal-loaded phosphate composite material aiming at the technical defects of agricultural soil conditioners in the prior art.

Another object of the invention is to provide a zinc-aluminum oxide nanosheet supported phosphate composite.

Another object of the present invention is to provide a method for preparing said composite material.

Another object of the present invention is to provide the use of said composite material as a soil slow release fertilizer.

The technical scheme adopted for realizing the purpose of the invention is as follows:

a zinc-aluminum oxide modified biochar loaded phosphate composite material comprises zinc-aluminum oxide modified biochar and a phosphate nano mineral loaded on the zinc-aluminum oxide, wherein the zinc-aluminum oxide modified biochar comprises biochar and zinc-aluminum oxide deposited on the surface of the biochar, the zinc-aluminum oxide comprises two phases of zinc-aluminum layered double metal hydroxide and zinc oxide, and the phosphate nano mineral comprises zinc phosphate tetrahydrate composite nanosheets.

In the technical scheme, the mass of the phosphorus element in the phosphate nano mineral accounts for 4-10% of the total mass of the composite material.

In the technical scheme, the zinc-aluminum oxide is in a porous nano structure, and the specific surface area of the biochar modified by the zinc-aluminum oxide is 50-60 m²/g。

In the above technical solution, the biochar is prepared by pyrolyzing corn stalks, preferably, the biochar is prepared by the following steps:

step 1, cutting corn straws into pieces;

step 2, pyrolyzing the corn straws obtained in the step 1 in a nitrogen atmosphere, and naturally cooling to room temperature; more preferably, the pyrolysis temperature is 300-400 ℃, the pyrolysis time is 3-5 hours, and the temperature rise speed is 5 ℃/min;

and 3, grinding the biochar obtained in the step 2, and sieving for later use, wherein the sieve mesh number is preferably 100 meshes.

In the above technical solution, the zinc-aluminum oxide is loaded on the biochar by a forced hydrolysis method to obtain the biochar modified by the zinc-aluminum oxide, preferably, the forced hydrolysis method comprises the following steps:

step 1, preparing a zinc and aluminum precursor solution: dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until solutes are completely dissolved, wherein the mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step 2, dipping the biochar in the zinc and aluminum precursor solution, gradually adding a sodium hydroxide solution in the stirring process, and continuously stirring for reaction, wherein the mass ratio of the biochar to the zinc and aluminum precursor solution is 1: (28-36); after the sodium hydroxide is added, the pH value of the solution is adjusted to 9.5-10.5, and the continuous stirring time is 1-3 hours;

and 3, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar, preferably, the centrifuging speed is 3000-4000 rpm, the centrifuging time is 5-8 minutes, the deionized water cleaning times are 4-6, and the drying temperature is 60-70 ℃.

In the above technical solution, the phosphate nanomineral is loaded on the charcoal modified by zinc aluminum oxide by an impregnation precipitation method, and preferably, the method comprises the following steps: adding the zinc-aluminum oxide modified biochar into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar loaded phosphate composite material, wherein preferably, the mass ratio of the zinc-aluminum oxide modified biochar to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

In another aspect of the invention, a preparation method of a zinc-aluminum oxide modified biochar loaded phosphate composite material comprises the following steps:

step 1, preparing a zinc and aluminum precursor solution: dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until solutes are completely dissolved, wherein the preferred mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step 2, dipping the biochar in the zinc and aluminum precursor solution, gradually adding a sodium hydroxide solution in the stirring process, and continuously stirring for reaction, wherein preferably, the mass ratio of the biochar to the zinc and aluminum precursor solution is 1: (28-36); after the sodium hydroxide is added, the pH value of the solution is adjusted to 9.5-10.5, and the continuous stirring time is 1-3 hours;

and 3, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar, preferably, the centrifuging speed is 3000-4000 rpm, the centrifuging time is 5-8 minutes, the deionized water cleaning times are 4-6, and the drying temperature is 60-70 ℃.

And 4, adding the biochar modified by the zinc-aluminum oxide into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide modified biochar loaded phosphate composite material, wherein preferably, the mass ratio of the biochar modified by the zinc-aluminum oxide to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

In another aspect of the invention, a zinc-aluminum oxide nanosheet-supported phosphate composite material comprises zinc-aluminum oxide nanosheets and a phosphate nanominer supported on the zinc-aluminum oxide nanosheets, wherein the zinc-aluminum oxide nanosheets comprise two phases of zinc-aluminum layered double hydroxide and zinc oxide, and the phosphate nanominer comprises zinc phosphate tetrahydrate composite nanosheets.

In the technical scheme, the mass percentage of the phosphorus element in the phosphate nano mineral to the total mass of the composite material is 3-8%.

In the technical scheme, the specific surface area of the zinc-aluminum oxide nanosheet is 50-60 m²/g。

In the technical scheme, the zinc-aluminum oxide nanosheet loaded phosphate composite material is prepared by the following method:

step s1, preparing a zinc and aluminum precursor solution, preferably, dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until the solute is completely dissolved, preferably, the mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step s2, preparing a carrier zinc-aluminum oxide nanosheet, preferably, adding a sodium hydroxide solution into the zinc and aluminum precursor solution prepared according to the step s1 by using a dropper while stirring until the pH value is 9.5-10.5, continuously stirring for 1-3 hours, centrifuging, washing and drying;

step s3, adding the carrier zinc-aluminum oxide nanosheets obtained in the step s2 into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide nanosheet-supported phosphate composite material, wherein the preferable mass ratio of the carrier zinc-aluminum oxide nanosheets to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

In another aspect of the invention, a preparation method of a zinc-aluminum oxide nanosheet loaded phosphate composite material comprises the following steps:

step s1, preparing a zinc and aluminum precursor solution, preferably, dissolving zinc chloride and aluminum chloride hexahydrate in deionized water, and stirring at room temperature until the solute is completely dissolved, preferably, the mass ratio of the zinc chloride to the aluminum chloride hexahydrate to the water is (1.5-1.8): 1: (8-10); stirring for 20-40 minutes;

step s2, preparing a carrier zinc-aluminum oxide nanosheet, preferably, adding a sodium hydroxide solution into the zinc and aluminum precursor solution prepared according to the step s1 by using a dropper while stirring until the pH value is 9.5-10.5, continuously stirring for 1-3 hours, centrifuging, washing and drying;

step s3, adding the carrier zinc-aluminum oxide nanosheets obtained in the step s2 into a potassium dihydrogen phosphate solution, mixing and oscillating at room temperature, centrifuging, cleaning and drying to obtain the zinc-aluminum oxide nanosheet-supported phosphate composite material, wherein the preferable mass ratio of the carrier zinc-aluminum oxide nanosheets to potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is (0.5-2.5): 1, the mass concentration of the potassium dihydrogen phosphate solution is 0.2-1.0 g/L; the mixing oscillation time is 24-30 hours, the mixing oscillation speed is 100-200 revolutions per minute, deionized water is used for cleaning, the cleaning frequency is 4-6 times, and the drying temperature is 50-60 ℃.

In another aspect of the invention, the zinc-aluminum oxide modified biochar loaded phosphate composite material or zinc-aluminum oxide nanosheet loaded phosphate composite material is applied as a soil slow release fertilizer.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention adopts common soil conditioner biochar as a substrate material, is cheap and easily available, and is environment-friendly. The specific surface area and the phosphate loading capacity of the biochar modified by the zinc-aluminum oxide are far larger than those of the biochar.

2. The method for preparing the zinc-aluminum oxide modified charcoal-loaded phosphate composite material and the prepared zinc-aluminum oxide nanosheet-loaded phosphate composite material has the characteristics of simple preparation process, easy regulation and control of the preparation process, low production cost and the like.

3. The zinc-aluminum oxide modified biochar loaded phosphate composite material prepared by the invention has the advantages that zinc-aluminum oxide-zinc tetrahydrate zinc phosphate composite nanosheets on the surfaces of biochar and the zinc-aluminum oxide nanosheet loaded phosphate composite material enable the biochar to show phosphate slow release property under environmental conditions, and can be used for phosphate slow release application.

Drawings

Fig. 1 is a scanning electron microscope image of a bulk material under different magnifications, wherein (a) and (b) are biochar, (c) and (d) are zinc aluminum oxide nanoplatelets, (e) and (f) are zinc aluminum oxide modified biochar.

Fig. 2 is an X-ray diffraction pattern of a zinc aluminum oxide modified biochar (sample 2) and a control support zinc aluminum oxide nanosheet (sample 5). Standard spectra of zinc oxide (ZnO) and zinc aluminium layered double hydroxide (Zn-Al LDH) are given and diffraction peaks of different phases in the sample are indicated by different symbols (filled squares or circular patterns).

Fig. 3(a) scanning electron microscope images of biochar-supported phosphate composite (sample 4), (b) zinc aluminum oxide nanosheet-supported phosphate composite (sample 6), (c) zinc aluminum oxide modified biochar-supported phosphate composite (sample 3), and (d) biochar-one-step-supported zinc phosphate composite (sample 7).

FIG. 4 shows that zinc-aluminum oxide modified biochar-supported phosphate composite (sample 3), biochar-supported phosphate composite (sample 4), and zinc-aluminum oxide nanosheet-supported phosphate compositeXRD spectra of the composite material (sample 6) and the biochar one-step method loaded zinc phosphate composite material (sample 7). The graph shows ZnO, Zn-Al LDH and zinc phosphate tetrahydrate (Zn)₃(PO₄)₂·4H₂O) and the diffraction peaks of the different phases in the sample are indicated with different symbols (filled squares, circles, triangular patterns).

Fig. 5 shows the phosphate release kinetics curves of the zinc-aluminum oxide modified biochar-supported phosphate composite material (sample 3) and the zinc-aluminum oxide nanosheet-supported phosphate composite material (sample 6), the comparative biochar-supported zinc phosphate composite material by the one-step method (sample 7), the commercial zinc phosphate and the commercial zinc tetrahydrate phosphate in deionized water.

Detailed Description

The present invention will be described in further detail with reference to specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

The zinc-aluminum oxide modified biochar loaded phosphate composite material comprises zinc-aluminum oxide modified biochar and a phosphate nano mineral loaded on the zinc-aluminum oxide, wherein the zinc-aluminum oxide modified biochar comprises biochar and zinc-aluminum oxide deposited on the surface of the biochar, the zinc-aluminum oxide comprises two phases of zinc-aluminum layered double metal hydroxide and zinc oxide, and the phosphate nano mineral comprises zinc phosphate tetrahydrate composite nanosheets.

The zinc-aluminum oxide modified charcoal-loaded phosphate composite material is prepared by the following steps:

step (1), preparation of biochar (sample 1): taking corn straws as a raw material, pyrolyzing the corn straws for 4 hours at 300 ℃ in a nitrogen atmosphere at the heating speed of 5 ℃/min, naturally cooling the corn straws to room temperature, grinding the corn straws, and sieving the corn straws with a 100-mesh sieve;

step (2), preparation of zinc and aluminum precursor solution: dissolving a certain amount of zinc chloride (6.13g) and aluminum chloride hexahydrate (3.62g) in a certain amount (30mL) of deionized water, and stirring at room temperature for 30 minutes until the solute is completely dissolved;

step (3), preparation of zinc aluminum oxide modified biochar (sample 2): 1.0g of the biochar prepared according to the step 1 (sample 1) was immersed in the zinc and aluminum precursor solution prepared according to the step 2, and then a sodium hydroxide solution (3mol/L) was added with a dropper while stirring until the pH was 10, and stirring was continued for 2 hours. Centrifuging at 3000rpm for 5min, discarding supernatant, adding deionized water, repeating the centrifuging-water changing step for 5 times, and drying the collected solid sample in an oven at 60 deg.C;

step (4), preparation of zinc-aluminum oxide modified biochar-supported phosphate composite (sample 3): 0.1g of the zinc aluminum oxide-modified biochar (sample 2) prepared in step (3) was added to 200mL of a solution of 219.7mg/L potassium dihydrogen phosphate (the solution had a phosphorus element concentration of 50mg/L by mass), mixed and shaken at 150rpm at room temperature (25. + -. 1 ℃) for 24 hours, and the sample was centrifuged, washed with deionized water, and dried at 60 ℃. The concentration of phosphate remaining in the solution was measured and the phosphorus loading was calculated.

Example 2

A zinc-aluminum oxide nanosheet-supported phosphate composite (sample 6) comprising zinc-aluminum oxide nanosheets and a phosphate nanominer supported on the zinc-aluminum oxide nanosheets, wherein the zinc-aluminum oxide nanosheets comprise two phases of zinc-aluminum layered double hydroxides and zinc oxide, and the phosphate nanominer comprises zinc phosphate tetrahydrate composite nanosheets.

The preparation method of the zinc-aluminum oxide nanosheet loaded phosphate composite material comprises the following steps:

step (1), preparing zinc and aluminum precursor solution: dissolving a certain amount of zinc chloride (6.13g) and aluminum chloride hexahydrate (3.62g) in a certain amount (30mL) of deionized water, and stirring at room temperature for 30 minutes until the solute is completely dissolved;

step (2), preparation of support zinc aluminum oxide nanosheets (sample 5): adding a sodium hydroxide solution (3mol/L) into the zinc and aluminum precursor solution prepared in the step (1) by using a dropper while stirring until the pH value is 10, and continuing stirring for 2 hours. The subsequent centrifugation, washing, drying steps and operating parameters were in accordance with step (3) in example 1;

and 3) adding 0.1g of the carrier zinc-aluminum oxide nanosheet material prepared in the step (2) into 200mL of 219.7mg/L potassium dihydrogen phosphate solution (the mass concentration of phosphorus in the solution is 50mg/L), measuring the concentration of phosphate remained in the solution after mixing and oscillating at the speed of 150 revolutions per minute at room temperature (25 +/-1 ℃) for 24 hours, calculating the phosphorus loading amount, centrifuging the sample, washing with deionized water, and drying at 60 ℃.

Comparative example 1.1

A control sample biochar-supported phosphate composite (sample 4) was prepared, comprising biochar and phosphate nanominer supported on the biochar.

The biochar loaded phosphate composite material is prepared by the following steps:

0.1g of the biochar (sample 1) prepared in the step (1) was added to 200mL of a solution of 219.7mg/L potassium dihydrogen phosphate (the concentration of phosphorus in the solution was 50mg/L by mass), mixed and shaken at 150rpm at room temperature (25. + -. 1 ℃ C.) for 24 hours, and the sample was centrifuged, washed with deionized water, and dried at 60 ℃. The concentration of phosphate remaining in the solution was measured and the phosphorus loading was calculated.

Comparative example 1.2

Control sample zinc aluminum oxide nanoplates (sample 5) were prepared.

The zinc-aluminum oxide nanosheet loaded phosphate composite material is prepared by the following steps:

step a1, preparation of control sample support zinc aluminum oxide nanoplates (sample 5): adding a sodium hydroxide solution (3mol/L) into the zinc and aluminum precursor solution prepared in the step (2) by using a dropper while stirring until the pH value is 10, and continuing stirring for 2 hours. Subsequent centrifugation, washing and drying steps and operation parameters are consistent with those in the step (3);

comparative example 1.3

Preparation of control sample biochar one-step loaded zinc phosphate composite (sample 7): 1.0g of biochar is immersed in 200mL of 2.197g/L potassium dihydrogen phosphate solution (the mass concentration of phosphorus in the solution is 500mg/L), and stirred for 1 hour at room temperature; while stirring, a solution of 306g/L zinc chloride (prepared by completely dissolving 6.13g of zinc chloride in 20mL of deionized water) was slowly added dropwise to the above-obtained suspension of biochar using a pipette, and then the mixture was put into an incubator at room temperature and 150rpm with shaking for 24 hours, and the sample was centrifuged, washed with deionized water, and dried at 60 ℃. The concentration of phosphate remaining in the solution was measured and the phosphorus loading was calculated.

Example 3

Physicochemical property characterization was performed on the biochar (sample 1), the zinc-aluminum oxide modified biochar (sample 2), the control group carrier zinc-aluminum oxide nanosheet (sample 5) and the composite material (samples 3, 4 and 6) obtained after loading phosphate thereof, which were obtained in the examples and comparative examples.

The microscopic morphologies of 3 carrier materials, such as biochar (sample 1), zinc-aluminum oxide nanosheet (sample 5), and zinc-aluminum oxide modified biochar (sample 2), are shown in fig. 1. The surface of the biochar is relatively flat (fig. 1a, b); the thickness of the zinc-aluminum oxide nanosheet is 15-20 nanometers, and the transverse dimension is 100-200 nanometers (figure 1c, d); the surface micro-morphology (figure 1e, f) of the biochar modified by the zinc-aluminum oxide is close to that of the zinc-aluminum oxide nanosheet material, a nanosheet structure with the transverse dimension of 100-200 nm can be observed, but irregular granular nanoparticles also exist.

The X-ray diffraction (XRD) patterns of the zinc-aluminum oxide-modified biochar (sample 2) and the zinc-aluminum oxide nanosheet (sample 5) are shown in fig. 2. As can be seen from the figure, both materials contain two phases of zinc-aluminum layered double hydroxide (Zn-Al LDH) and zinc oxide (ZnO); the relative peak intensity of the ZnO characteristic peak in the biochar modified by the zinc-aluminum oxide is higher, which qualitatively shows that the content of ZnO in the biochar is higher than that of ZnO in the zinc-aluminum oxide nanosheet. The composition of the metal elements in the biochar modified by the zinc-aluminum oxide according to the atomic emission spectroscopy of the conductance-coupled plasma is determined, the mass fractions of zinc and aluminum are respectively 43.7 percent and 3.2 percent, the mass ratio of the zinc to the aluminum (Zn: Al ratio) is 5.7:1 and is larger than the theoretical Zn: Al ratio range of Zn-Al LDH (about 2:1 to 4.9:1), and the conclusion that the material contains ZnO is further proved.

The specific surface area and pore structure parameters of biochar (sample 1), zinc aluminum oxide nanosheets (sample 5) and zinc aluminum oxide modified biochar (sample 2) are shown in table 1. The BET specific surface area of the zinc-aluminum oxide nanosheet is far larger than that of the biochar, and the BET specific surface area, the pore volume and the average pore diameter of the biochar modified by the zinc-aluminum oxide are closer to those of the zinc-aluminum oxide nanosheet and also far larger than that of the biochar.

TABLE 1 specific surface area and pore Structure parameters of the support materials

The phosphorus loadings of the composites (samples 3, 4, 6, and 7) obtained by loading the above three materials with phosphate are shown in table 2. The phosphorus loading of the zinc-aluminum oxide modified biochar-loaded phosphate composite (sample 3) is much higher than that of the comparative biochar-loaded phosphate composite (sample 4) and also higher than that of the comparative zinc-aluminum oxide nanosheet-loaded phosphate composite (sample 6). Moreover, the forest loading of sample 3 was higher than the sum of the phosphorus loadings of samples 4 and 6, indicating that the composite structure of sample 3 was more favorable for phosphate loading than the zinc aluminum oxide nanosheets alone. On the other hand, as can be seen from Table 2, the phosphorus loading of the biochar one-step zinc phosphate composite (sample 7) is higher than that of sample 3, mainly due to the tendency of the formation of hydrated zinc phosphate precipitates due to the large amount of phosphate ions and zinc ions in the solution.

TABLE 2 phosphorus loading of different phosphorus-loaded composites

Sample numbering	Name of Material	Phosphorus loading (mg/g)
			Sample 3	Zinc-aluminum oxide modified charcoal-loaded phosphate composite material	48.9
Sample No. 4	Biochar loaded phosphate composite material	0.9
			Sample No. 6	Zinc-aluminum oxide nanosheet loaded phosphate composite material	39.0
Sample 7	Biochar one-step method loaded zinc phosphate composite material	71.7

The micro-topography of the three phosphorus-loaded composites (samples 3, 4, 6) is shown in FIG. 3. After the biological carbon is loaded with the potassium dihydrogen phosphate, the surface is still relatively flat, the zinc-aluminum oxide nanosheet loaded phosphate composite material (sample 6) and the zinc-aluminum oxide modified biological carbon loaded phosphate composite material (sample 3) both keep a nanosheet structure, but the transverse size of the zinc-aluminum oxide modified biological carbon loaded phosphate composite material is increased, the thickness of the zinc-aluminum oxide modified biological carbon loaded phosphate composite material is increased, and the transverse size of part of the nanosheets reaches more than 1 micrometer. According to the scanning electron microscope image of the biochar one-step method loaded zinc phosphate composite material (sample 7), the surface of the biochar is loaded with a micron sheet structure with the thickness of more than 100 nanometers and the transverse dimension of more than 1 micron. From the above results, it can be seen that the zinc-aluminum oxide nanosheets obtained in the first step of the two-step loading method disclosed in the present patent function as templates in the process of loading phosphate in the second step, and are beneficial to finally forming phosphate minerals with nanometer dimensions.

The XRD patterns of the three phosphorus-loaded composite materials (samples 3, 4, 6 and 7) are shown in FIG. 4. After the biochar is loaded with the phosphate (sample 4), the XRD spectrogram only has the characteristic broad peak of the carbon material, and no characteristic diffraction peak of the phosphorus-containing mineral is observed, so that the phosphate monolayer is adsorbed on the surface of the biochar material, and no new phase is formed. After the phosphate is loaded on the biochar by the zinc-aluminum oxide nanosheets and the zinc-aluminum oxide modified biochar, XRD spectrograms of the obtained composite materials (sample 6 and sample 3) are observed for zinc phosphate tetrahydrate (Zn), besides characteristic peaks of Zn-Al LDH and ZnO₃(PO₄)₂·4H₂O), indicating that the main component of the phosphate nanominer in the composite is zinc phosphate tetrahydrate. The XRD spectrum of the biochar one-step method loaded zinc phosphate composite material (sample 7) is highly consistent with the standard spectrum of zinc phosphate tetrahydrate, which shows that the phosphate mineral in sample 7 is zinc phosphate tetrahydrate with higher purity.

Example 4

As can be seen from table 2 in example 2, the zinc-aluminum oxide modified biochar can achieve higher phosphorus loading under the same conditions (e.g., the same initial concentration of monopotassium phosphate) than the pure biochar and the zinc-aluminum oxide nanosheets, but the phosphorus loading of sample 3 is lower than that of sample 7 prepared by one-step method, mainly because: in the step of preparing sample 7 (step (8) in example 1), the initial concentration of potassium dihydrogen phosphate in the solution (corresponding to a phosphorus element mass concentration of 500mg/L) was much higher than the initial concentration of potassium dihydrogen phosphate (corresponding to a phosphorus element mass concentration of 50mg/L) in the step of preparing sample 3 (step (4) in example 1).

In order to obtain a zinc aluminum oxide modified biochar-supported phosphate composite material with higher phosphorus loading, this example examines the influence of the initial concentration of potassium dihydrogen phosphate solution on the phosphorus loading of the material in the process of preparing the zinc aluminum oxide modified biochar-supported phosphate composite material according to the step (4) in the example 1: the initial phosphorus concentration of the potassium dihydrogen phosphate solution was varied within a range of 5.0 to 200.0mg/L, and the phosphorus loading amount (mass fraction of phosphorus element) of the obtained material was measured, and the results are shown in Table 3. As can be seen from the data in Table 3, the phosphorus loading of the material increases with the increase of the initial concentration of the potassium dihydrogen phosphate solution in the preparation process, and when the mass concentration of the initial phosphorus element in the solution is 100.0mg/L, the phosphorus loading of the prepared material is 74.0mg/g, which is equivalent to the phosphorus loading of the sample 7; and when the initial phosphorus element mass concentration in the solution is 200.0mg/L, the phosphorus loading capacity of the prepared material is higher and is 97.0 mg/g.

TABLE 3 Effect of potassium dihydrogen phosphate solution concentration on phosphorus loading of zinc aluminum oxide modified biochar loaded phosphate composite

Initial phosphorus concentration of solution (mg/L)	Phosphorus loading of materials (mg/g)
		5.0	8.0
10.0	15.4
		25.0	41.4
100.0	74.0
		200.0	97.0

Example 5

In this example, phosphate slow release performance of zinc-aluminum oxide modified biochar loaded phosphate composite (sample 3), zinc-aluminum oxide nanosheet loaded phosphate composite (sample 6) and 3 control samples biochar loaded zinc phosphate composite by one-step method (sample 7), commercial zinc phosphate (Ron, analytical grade), commercial zinc tetrahydrate (Meclin, analytical grade) in deionized water (pH 6) was examined.

The amounts of the respective materials used in the experiment and the amounts of the respective phosphorus elements added are shown in Table 4, and the results of the experiment are shown in FIG. 5. The phosphate can be slowly released from the sample 3 in the deionized water, and the concentration of the phosphorus element released into the water is 3.55mg/L and accounts for about 14% of the total phosphorus loading after 96 hours of the experiment; the material can release phosphate in water for 30 days. The sustained release performance of sample 6 was similar to that of sample 3. In contrast, the concentration of elemental phosphorus released into deionized water during the first 2 to 96 hours of the experiment increased only slightly from 0.85mg/L to 1.20mg/L for sample 7, with the corresponding percentage release remaining between 2.4% and 3.4%, much lower than for sample 3.

The other two control samples (commercial zinc phosphate and commercial zinc tetrahydrate) also did not exhibit sustained release, but the phosphate release capacity of the zinc tetrahydrate was slightly higher than that of the zinc phosphate, with the percent phosphorus release during the experiment being between 1.6% and 2.4% and 2.1% and 2.8%, respectively.

The results show that the zinc-aluminum oxide modified biochar loaded phosphate composite material shows the characteristic of sustained and slow release of phosphorus element under the environmental pH. Mainly due to the synergy of the 3 aspects: (1) the porous structure of the biochar carrier is beneficial to uniform dispersion of the nano phosphate minerals; (2) the large specific surface area of the zinc-aluminum oxide and zinc phosphate tetrahydrate composite nanosheets provides rich sites for the release of phosphate; (3) the low temperature drying of the resulting zinc tetrahydrate phase further enhances phosphate release. The composite material can be used for slowly releasing phosphate fertilizer.

TABLE 4 amount of material and corresponding total phosphorus added in phosphate release experiments

The zinc-aluminum oxide modified biochar-supported phosphate composite/zinc-aluminum oxide nanosheet-supported phosphate composite of the present invention can be prepared with process parameter adjustments made in accordance with the present disclosure, and exhibits substantially the same performance as the samples of example 1 or example 2.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.