One-step method for preparing magnetic magnesium-iron layered double hydroxide (LDH)-biochar composite material and use thereof

Abstract

A one-step method for preparing a magnetic magnesium-iron layered double hydroxide (LDH)-biochar composite material and use thereof provided. Biomass, as a substrate, is placed in a ferric salt solution, magnesium hydroxide is added, the materials are fully stirred and aged for a certain time, the aged materials are dried to obtain a magnesium-iron LDH-biomass, and the magnetic magnesium-iron LDH-biochar composite material is obtained after pyrolysis. The method solves problems of uncontrollable reaction and low crystallinity of products in preparing LDH using a coprecipitation method, reduces the amount of drugs, omits a step of adjusting a pH with an alkaline solution, improves yield and reduces a cost. The obtained magnetic magnesium-iron LDH-biochar composite material exhibits an excellent performance in adsorbing phosphate in water and can be recovered by an external magnetic field. Thus, an important method is provided for preparing LDH and the composite thereof.

Claims

1. A method for preparing a magnetic magnesium-iron layered double hydroxide (LDH)-biochar composite material, wherein magnesium hydroxide is added into a ferric salt solution containing biomass to prepare a magnesium-iron LDH-biomass precursor material, the magnetic magnesium-iron LDH-biochar composite material is obtained after pyrolysis, and the method comprises the following steps: 1) drying and pulverizing the biomass as a base material for loading LDH; 2) preparing the ferric salt solution at a concentration of a ferric salt of 0.2 M1 M; and adding the biomass obtained in step 1), ultrasonically treating the ferric salt solution containing the biomass, adding the magnesium hydroxide and stirring continuously during the adding until an obtained mixture has a uniform color and is in the form of a slurry, and putting the slurry into an oven for standing and aging to obtain an aged slurry; 3) Centrifuging the aged slurry obtained in step 2) and drying a solid matter after the centrifugation to prepare the magnesium-iron LDH-biomass precursor material; and 4) pyrolyzing the magnesium-iron LDH-biomass precursor material obtained in step 3) in an inert gas atmosphere to obtain the magnetic magnesium-iron LDH-biochar composite material, wherein in step 2), the magnesium hydroxide and the ferric salt have a molar ratio of (2-4):1.

2. The method for preparing a magnetic magnesium-iron LDH-biochar composite material according to claim 1, wherein the biomass is selected from corn stalk and the corn stalk is dried to a dried corn stalk with a moisture content 5%; and the dried corn stalk is crushed to be capable of passing through a 20-40 mesh sieve.

3. The method for preparing a magnetic magnesium-iron LDH-biochar composite material according to claim 1, wherein in step 2), the ferric salt is one or more of FeCl.sub.3, Fe(NO.sub.3).sub.3, and Fe.sub.2(SO.sub.4).sub.3.

4. The method for preparing a magnetic magnesium-iron LDH-biochar composite material according to claim 1, wherein in step 2), the aging is performed at 6010 C. for 2-4 h.

5. The method for preparing a magnetic magnesium-iron LDH-biochar composite material according to claim 1, wherein in step 2), an adding amount of the biomass and the ferric salt solution is that 5-10 g of the biomass is added into every 100 ml of the ferric salt solution.

6. The method for preparing a magnetic magnesium-iron LDH-biochar composite material according to claim 1, wherein in step 3), the drying is performed in an oven at a temperature of 505 C.

7. The method for preparing a magnetic magnesium-iron LDH-biochar composite material according to claim 1, wherein in step 4), the pyrolyzing is performed in the inert gas of nitrogen and at a temperature of 500200 C. for 20.5 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a comparison of technology roadmaps of a preparation method of the present invention and a preparation of traditional magnesium-iron LDH-biomass composite material;

(2) FIG. 2 shows a separation of a magnetic magnesium-iron LDH-biochar composite material after adsorption using a magnet;

(3) FIG. 3 is a scanning electron microscope image of the magnetic magnesium-iron LDH-biochar composite material prepared in example 1;

(4) FIG. 4 is an FT-IR spectrogram of the magnetic magnesium-iron LDH-biochar composite material prepared in example 1; and

(5) FIG. 5 is an XRD pattern of the magnetic magnesium-iron LDH-biochar composite material prepared in example 1.

DESCRIPTION OF THE EMBODIMENTS

Example 1

(6) A magnetic magnesium-iron LDH-biochar composite material was prepared in one step: a specific preparation route was compared with a traditional preparation route shown in FIG. 1: 1) corn stalk is dried to a moisture content 5% and the dried corn stalk is crushed to be capable of passing through a 20 mesh sieve as a biomass; 2) 27.05 g (0.25 mol) of FeCl.sub.3.Math.6H.sub.2O was weighed into a 250-ml beaker, 100 ml of deionized water was added, ultrasonic treatment was performed to completely dissolve the FeCl.sub.3.Math.6H.sub.2O, a completely dissolved ferric salt solution was added into a 500-ml volumetric flask with water to a constant volume, and thus a 0.5 mol/L ferric salt solution was prepared; 3) the ferric salt solution prepared in step 2) was added into a 1-L beaker containing 50 g of the biomass, stirring was performed continuously during the adding, the solution was ultrasonically treated for 30 min, 29 g (0.5 mol) of Mg(OH).sub.2 was finally slowly added with a molar ratio of magnesium to iron being 2:1, stirring was performed continuously during the adding until the whole solution was a slurry with a uniform color, and the beaker containing the solution was placed in an oven at 60 C. for aging for 2 h; and 4) a product obtained in step 3) was centrifuged and dries in an oven at 50 C. for 12 h to obtain a dried solid; and

(7) the dried solid was pyrolyzed at 500 C. for 2 h under a nitrogen atmosphere to obtain an LDH biochar-loaded composite material.

(8) A scanning electron microscope image of the magnetic magnesium-iron LDH-biochar composite material prepared in the example was shown in FIG. 3, an FT-IR spectrogram was shown in FIG. 4 and an XRD pattern was shown in FIG. 5.

(9) The LDH-biochar composite material was proved to be magnetic by using a strong magnet for recovery in an aqueous solution. A recovery effect was shown in FIG. 2.

(10) An adsorption test of removing phosphate radicals in water using the magnetic magnesium-iron LDH-biochar composite material prepared by the method of the present example was specifically as follows:

(11) Preparation of stock solution: 1,000 mg/L of a PO.sub.4.sup.3 solution: 1.4315 g of KH.sub.2PO.sub.4 was weighed and dissolved in 1 L of deionized water to prepare the solution.

(12) Preparation of adsorption solution: the PO.sub.4.sup.3 stock solution was diluted with deionized water to prepare an adsorption solution of a corresponding concentration.

(13) 0.04 g of the magnetic magnesium-iron LDH-biochar composite material was weighed and placed in a 50-ml centrifuge tube, 40 ml of the PO.sub.4.sup.3 solution with concentrations of 50/100/200 mg/L was separately added, shaking and adsorption were performed at 25 C. and 200 rpm for 24 h, a supernatant was extracted and filtered with a 45-m microporous membrane, a concentration of phosphate radicals in the supernatant was determined by ultraviolet spectrophotometry, and the adsorption capacity and a removal rate were calculated.

(14) The concentration of phosphate radicals in the solution was determined by a national standard method of ascorbic acid-molybdenum blue colorimetry, and ascorbic acid-molybdate was used as a color developer to generate a blue compound which was determined by an ultraviolet spectrophotometer at a wavelength of 700 nm.

Example 2

(15) 67.625 g (0.25 mol) FeCl.sub.3.Math.6H.sub.2O was weighed and 29 g (0.5 mol) of Mg(OH).sub.2 was finally slowly added in step 2) of example 1, and pyrolyzed at 500 C. for 2 h under a nitrogen atmosphere in step 4) were separately modified to observe an effect of different modifications on removing phosphorus from the magnetic magnesium-iron LDH-biochar composite material. The modifications were shown in Table 1.

(16) TABLE-US-00001 TABLE 1 Adding amount of Adding amount Pyrolysis Modifications FeCl.sub.36H.sub.2O of Mg(OH).sub.2 temperature Examples 2-1 67.63 g (0.25 mol) 29 g (0.5 mol) 400 C. Examples 2-2 27.05 g (0.1 mol) 11.6 g (0.2 mol) 500 C. Examples 2-3 108.2 g (0.4 mol) 46.4 g (0.8 mol) 500 C. Examples 2-4 67.63 g (0.25 mol) 43.5 g (0.75 mol) 500 C. Examples 2-5 67.63 g (0.25 mol) 58 g (1 mol) 500 C.

(17) An experiment was carried out under the method and conditions in example 1, and the adsorption test was carried out on the PO.sub.4.sup.3 solution of 50-200 mg/L. The obtained results were shown in Table 2.

(18) TABLE-US-00002 TABLE 2 Concentrations Removal rate Adsorption capacity Example 1 50 mg/L 97.36% 48.68 mg/g 100 mg/L 91.32% 91.32 mg/g 200 mg/L 75.36% 150.72 mg/g Examples 2-1 50 mg/L 97.32% 48.66 mg/g 100 mg/L 81.29% 81.29 mg/g 200 mg/L 52.42% 104.84 mg/g Examples 2-2 50 mg/L 99.67% 49.84 mg/g 100 mg/L 64.51% 64.51 mg/g 200 mg/L 47.22% 94.44 mg/g Examples 2-3 50 mg/L 99.26% 49.63 mg/g 100 mg/L 94.27% 94.27 mg/g 200 mg/L 89.23% 178.46 mg/g Examples 2-4 50 mg/L 98.68% 49.34 mg/g 100 mg/L 87.11% 87.11 mg/g 200 mg/L 65.85% 131.70 mg/g Examples 2-5 50 mg/L 95.84% 47.92 mg/g 100 mg/L 99.23% 99.23 mg/g 200 mg/L 84.72% 169.44 mg/g

Comparative Example 1

(19) The magnesium hydroxide in step 2) of example 1 was replaced with magnesium chloride, and the remaining was the same as in example 1.

Comparative Example 2

(20) Magnesium-aluminum LDH-biochar composite material Preparation method: sodium hydroxide (NaOH) was added into magnesium nitrate hexahydrate (Mg(NO.sub.3).sub.2.Math.6H.sub.2O) and aluminum nitrate nonahydrate (Al(NO.sub.3).sub.3.Math.9H.sub.2O) at a molar ratio of 2:1, magnesium-aluminum LDH was generated on a surface of rice hull powder by coprecipitation and co-pyrolysis was performed at 500 C. for 2 h.

(21) 0.1 g of the magnesium-aluminum LDH-biochar composite material was placed in a 100-ml conical flask, and 80 ml of a phosphate solution with a concentration of 50-100 mg/L was added to conduct an adsorption test.

Comparative Example 3

(22) Iron-magnesium LDH material Preparation method: the iron-magnesium LDH material was prepared by adding sodium hydroxide (NaOH) to a solution of magnesium chloride hexahydrate (MgCl.sub.2.Math.6H.sub.2O) and ferric chloride (FeCl.sub.3) at a molar ratio of 2:1 for precipitation.

(23) 0.025 g of the material obtained in example 1 and 0.025 g of the material obtained in comparative examples 1-3 were separately taken and placed in a 50-ml conical tube, 25 ml of a phosphate solution (pH=7.4) with a concentration of 50 mg/L was added into each conical tube, and an adsorption test was performed under the same condition. The test results were shown in Table 3.

(24) TABLE-US-00003 TABLE 3 Concentrations Removal rate Adsorption capacity Example 1 50 mg/L 97.36% 48.68 mg/g Comparative 50 mg/L 88.06% 44.03 mg/g example 1 Comparative 50 mg/L 67.18% 26.87 mg/g example 2 Comparative 50 mg/L 73.00% 36.50 mg/g example 3

(25) It can be seen from Table 3 that the magnetic magnesium-iron LDH-biochar composite material prepared by the innovative synthesis method of the present disclosure had the highest removal rate and adsorption capacity of phosphorus in a phosphate solution with a concentration of 50 mg/L.