Three-dimensional lignin porous carbon/zinc oxide composite material and its preparation and application in the field of photocatalysis

Abstract

A three-dimensional lignin porous carbon/zinc oxide composite material and its preparation and application in the field of photocatalysis are disclosed. The method includes preparing a lignin/zinc oxide precursor composite by a hydrothermal method from a zinc salt, a weak alkali salt and an industrial lignin, and preparing a three-dimensional lignin porous carbon/zinc oxide composite material by high temperature calcination of the lignin/zinc oxide precursor composite. The composite material has a regular three-dimensional pore structure, with zinc oxide nanoparticles uniformly embedded among the three-dimensional lignin porous carbon nanosheets. Application of the composite material to the field of photocatalysis, especially as a photocatalyst for photocatalytic degradation of organic dye pollutants, can significantly improve the degradation efficiency and rate, and has potential application value in the field of photocatalytic degradation of organic pollutants.

Claims

1. A method for preparing a three-dimensional lignin porous carbon/zinc oxide composite material, comprising (1) preparing a lignin/zinc oxide precursor composite by a hydrothermal method from a zinc salt, a weak alkali salt and an industrial lignin, and (2) preparing a three-dimensional lignin porous carbon/zinc oxide composite material by high temperature calcination of the lignin/zinc oxide precursor composite; wherein step (1) comprises: (1.1) adding a weak alkali salt solution to a zinc salt solution to produce a zinc oxide precursor solution; (1.2) adding industrial lignin to the zinc oxide precursor solution, stirring uniformly, and keeping the temperature at 70 C. to 150 C. for 1-8 hours to produce a lignin/zinc oxide precursor composite.

2. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 1, wherein the amount of each reactant in step (1) is as follows in parts by weight: 10 parts of industrial lignin; 5-30 parts of zinc salt; and 5-30 parts of weak alkali salt.

3. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 2, wherein the mass concentration of the zinc salt solution is from 20% to 40%; and the mass concentration of the weak alkali salt solution is from 20% to 40%.

4. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 2, wherein after adding the industrial lignin to the zinc oxide precursor solution, the solution is stirred for 10-30 min to become uniform; and keeping the temperature is achieved by placing the system in a hydrothermal reactor.

5. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 1, wherein the industrial lignin is at least one of wood pulp alkali lignin, bamboo pulp alkali lignin, wheat straw pulp alkali lignin, reed pulp alkali lignin, bagasse pulp alkali lignin, Chinese alpine rush pulp alkali lignin or biorefinery enzymatic lignin; the zinc salt is at least one of zinc oxalate, zinc acetate, zinc nitrate, zinc chloride, zinc carbonate or zinc sulfate; and the weak alkali salt is at least one of sodium oxalate, sodium carbonate or sodium bicarbonate.

6. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 1, wherein the zinc salt is at least one of zinc oxalate, zinc nitrate or zinc acetate; and the weak alkali salt is sodium bicarbonate.

7. A three-dimensional lignin porous carbon/zinc oxide composite material, obtained by the preparation method according to claim 1.

8. A photocatalyst comprising the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 7.

9. A method for photocatalytic degradation of organic dye pollutants, comprising treating the organic dye pollutants with the photocatalyst according to claim 8.

10. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 1, wherein step (2) comprises: separating and drying the lignin/zinc oxide precursor composite, grinding it into powder, and calcining at 500 C. to 750 C. for 1.5-3 h in an inert gas atmosphere to produce a three-dimensional lignin porous carbon/zinc oxide composite material.

11. The method for preparing the three-dimensional lignin porous carbon/zinc oxide composite material according to claim 10, wherein the separating and drying is carried out by suction filtration of the lignin/zinc oxide precursor composite, and then drying the filter cake.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scanning electron micrograph of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 2.

(2) FIG. 2 is a transmission electron micrograph of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 2.

(3) FIG. 3 is an X-ray diffraction pattern of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Examples 1-5.

(4) FIG. 4 is a Raman spectrum of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 4.

(5) FIG. 5 shows the experimental results of the concentration change of rhodamine B photocatalyzed to degrade by the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 2.

(6) FIG. 6 shows the experimental results of the concentration change of methyl orange photocatalyzed to degrade by the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) The present invention will be further described in detail with reference to examples, but the embodiments of the present invention are not limited thereto.

(8) The materials used in the following examples are commercially available.

Example 1

(9) 5 g of zinc nitrate and 5 g of sodium bicarbonate were respectively dissolved in water to prepare a solution having a mass concentration of 20%, and then the sodium bicarbonate solution was added to the zinc nitrate solution, followed by stirring at room temperature. Then 10 g of wood pulp alkali lignin solid powder was added, and the resulted solution was stirred for 10 min and transferred to a hydrothermal reactor and kept at 70 C. for 8 h to produce a lignin/zinc oxide precursor composite, which was subjected to suction filtration to produce a filter cake. The filter cake was dried in a low temperature oven at a drying temperature of 40 C. for a drying time of 3 h. The obtained solid was ground into a powder, and calcined at 500 C. under the protection of N.sub.2 for 3 h, and then cooled to room temperature to produce a three-dimensional lignin porous carbon/zinc oxide composite material.

Example 2

(10) 30 g of zinc chloride and 30 g of sodium carbonate were respectively dissolved in water to prepare a solution having a mass concentration of 40%, and then the sodium carbonate solution was added to the zinc chloride solution, followed by stirring at room temperature. Then 10 g of bamboo pulp alkali lignin solid powder was added, and the resulted solution was stirred for 30 min and transferred to a hydrothermal reactor and kept at 90 C. for 8 h to produce a lignin/zinc oxide precursor composite, which was subjected to suction filtration to produce a filter cake. The filter cake was dried in a low temperature oven at a drying temperature of 60 C. for a drying time of 4 h. The obtained solid was ground into a powder, and calcined at 750 C. under the protection of N.sub.2 for 1.5 h, and then cooled to room temperature to produce a three-dimensional lignin porous carbon/zinc oxide composite material.

Example 3

(11) 15 g of zinc oxalate and 15 g of sodium bicarbonate were respectively dissolved in water to prepare a solution having a mass concentration of 30%, and then the sodium bicarbonate solution was added to the zinc oxalate solution, followed by stirring at room temperature. Then 10 g of wheat straw pulp alkali lignin solid powder was added, and the resulted solution was stirred for 20 min and transferred to a hydrothermal reactor and kept at 120 C. for 2 h to produce a lignin/zinc oxide precursor composite, which was subjected to suction filtration to produce a filter cake. The filter cake was dried in a low temperature oven at a drying temperature of 40 C. for a drying time of 5 h. The obtained solid was ground into a powder, and calcined at 650 C. under the protection of N.sub.2 for 2 h, and then cooled to room temperature to produce a three-dimensional lignin porous carbon/zinc oxide composite material.

Example 4

(12) 10 g of zinc carbonate and 10 g of sodium oxalate were respectively dissolved in water to prepare a solution having a mass concentration of 30%, and then the sodium oxalate solution was added to the zinc carbonate solution, followed by stirring at room temperature. Then 10 g of reed pulp alkali lignin solid powder was added, and the resulted solution was stirred for 20 min and transferred to a hydrothermal reactor and kept at 130 C. for 5 h to produce a lignin/zinc oxide precursor composite, which was subjected to suction filtration to produce a filter cake. The filter cake was dried in a low temperature oven at a drying temperature of 50 C. for a drying time of 3 h. The obtained solid was ground into a powder, and calcined at 750 C. under the protection of N.sub.2 for 2 h, and then cooled to room temperature to produce a three-dimensional lignin porous carbon/zinc oxide composite material.

Example 5

(13) 20 g of zinc nitrate and 20 g of sodium bicarbonate were respectively dissolved in water to prepare a solution having a concentration of 25%, and then the sodium bicarbonate solution was added to the zinc nitrate solution, followed by stirring at room temperature. Then 10 g of enzymatic lignin solid powder was added, and the resulted solution was stirred for 20 min and transferred to a hydrothermal reactor and kept at 150 C. for 3 h, and then cooled to room temperature to produce a lignin/zinc oxide precursor composite, which was subjected to suction filtration to produce a filter cake. The filter cake was dried in a low temperature oven at a drying temperature of 50 C. for a drying time of 4 h. The obtained solid was ground into a powder, and calcined at 750 C. under the protection of N.sub.2 for 1.5 h, and then cooled to room temperature to produce a three-dimensional lignin porous carbon/zinc oxide composite material.

Description of Example Effects

(14) The crystal structure of the prepared three-dimensional lignin porous carbon/zinc oxide composite material was measured by a Brooke D8 Advance X-ray powder diffractometer according to the method described in the specification thereof; the carbonization effect of the lignin in the prepared three-dimensional lignin porous carbon/zinc oxide composite material was measured by a LabRAMAramis micro-Raman spectrometer according to the method described in the specification thereof; the microstructure of the prepared three-dimensional lignin porous carbon/zinc oxide composite material was characterized by a scanning electron microscope (SEM, Merlin, Zeiss) and a transmission electron microscope (TEM, JEM-2100F, JEOL); and the carbonization effect was characterized by a Raman spectrometer (LabRAMAramis, France).

(15) It can be seen from the scanning electron micrograph of FIG. 1 that the zinc oxide nanoparticles and the three-dimensional lignin porous carbon obtained by high-temperature carbonization were very closely combined to form a three-dimensional lignin porous carbon/zinc oxide nanocomposite structure. It is apparent from FIG. 2 that the zinc oxide nanoparticles were combined with the three-dimensional lignin porous carbon.

(16) FIG. 3 shows an XRD pattern of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Examples 1-5. It can be seen from the figure that zinc oxide in the prepared composite material had a typical hexagonal wurtzite structure, which indicates that the addition of the industrial lignin did not alter the nanostructured crystal form of zinc oxide during the preparation of the hybrid structure.

(17) FIG. 4 shows a Raman spectrum of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 4. The characteristic peaks of zinc oxide at 200-400 cm.sup.1 and the characteristic peaks D and G of the carbon material can be seen from FIG. 4, which indicates that the three-dimensional lignin porous carbon/zinc oxide composite material had been successfully obtained.

(18) FIG. 5 shows the experimental results of the concentration change of rhodamine B photocatalyzed to degrade by the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 2.

(19) FIG. 6 shows the experimental results of the concentration change of methyl orange photocatalyzed to degrade by the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 3.

(20) 60 mg of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 2 were weighed for each of six groups, respectively, and 60 mg of pure zinc oxide were weighed for each of six groups, respectively. These groups of the three-dimensional lignin porous carbon/zinc oxide composite material and pure zinc oxide were respectively added to 100 mL of a rhodamine B solution having a mass concentration of 15 mg/L, and irradiated by simulated sunlight (a 500 W xenon lamp). A group of solutions was taken at intervals for determination of the concentration thereof, and a group of blank contrast experiment without any catalyst was provided. The experimental results show that the obtained three-dimensional lignin porous carbon/zinc oxide composite material had the excellent property of photocatalytic degradation of rhodamine B, and its photocatalytic degradation rate was about 2.7 times higher than that of the pure zinc oxide.

(21) 60 mg of the three-dimensional lignin porous carbon/zinc oxide composite material prepared in Example 3 were weighed for each of six groups, respectively, and 60 mg of pure zinc oxide were weighed for each of six groups, respectively. These groups of the three-dimensional lignin porous carbon/zinc oxide composite material and pure zinc oxide were respectively added to 100 mL of a methyl orange solution having a mass concentration of 15 mg/L, and irradiated by simulated sunlight (a 500 W xenon lamp). A group of solutions was taken at intervals for determination of the concentration thereof, and a group of blank contrast experiment without any catalyst was provided. The experimental results show that the obtained three-dimensional lignin porous carbon/zinc oxide composite material had the excellent property of photocatalytic degradation of methyl orange, and its photocatalytic degradation rate was about 5.1 times higher than that of the pure zinc oxide.

(22) The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited thereto, and any other alterations, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention should all be equivalent replacements and included in the scope of protection of the present invention.