CN107649100B

CN107649100B - Method for preparing water treatment material by using lignin

Info

Publication number: CN107649100B
Application number: CN201711098224.0A
Authority: CN
Inventors: 陈凤贵
Original assignee: Yangtze Normal University
Current assignee: Yangtze Normal University
Priority date: 2017-11-09
Filing date: 2017-11-09
Publication date: 2020-06-02
Anticipated expiration: 2037-11-09
Also published as: CN107649100A

Abstract

The invention discloses a method for preparing a water treatment material by using lignin, which comprises the following steps: preparing lignin into an aqueous solution, freeze-drying to obtain lignin aerogel, placing the obtained lignin aerogel in a tubular furnace, carrying out heat treatment in an argon atmosphere, and cooling to obtain the water treatment material. According to the invention, after the lignin precursor is crosslinked by a heat treatment method, the lignin-based water treatment material with a porous structure is prepared, so that not only can important functional groups in the lignin structure be maintained, but also the diffusion of the lignin in a water body is avoided, and the application of the lignin in water treatment is promoted.

Description

Method for preparing water treatment material by using lignin

Technical Field

The invention belongs to the field of water treatment material preparation, and particularly relates to a method for preparing a water treatment material by using lignin.

Background

The treatment of water environment is an important subject in the world at present, has high-efficiency adsorption capacity to pollutants, and the water treatment material with low price is an important target developed by scientific researchers.

The lignin structure contains a large amount of functional groups such as aromatic groups, alkyl hydroxyl groups, phenolic hydroxyl groups, carboxyl groups and the like, can directly adsorb partial heavy metals and organic pollutants, is rich in lignin in nature, has the content inferior to that of cellulose, is mostly discarded as waste of paper making industry in production and life at present, and causes environmental pollution, so that high-added-value application of the lignin is developed, the waste lignin can be utilized, the environmental pollution is reduced, and the lignin is low in price and unlimited in source, so that the lignin structure is widely concerned in recent years.

However, since lignin contains water-soluble groups such as hydroxyl groups and carboxyl groups in its structure, if the lignin is directly used as an adsorbent to absorb pollutants in water, it is difficult to exert the adsorption effect, and lignin itself is dispersed in the water environment, which is likely to cause secondary pollution.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for preparing a water treatment material by using lignin, which solves the problem that the lignin is easy to disperse in a water environment to cause secondary pollution when the lignin is used for adsorbing pollutants.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for preparing a water treatment material by using lignin comprises the following steps: preparing lignin into an aqueous solution with the concentration of 1-100 mg/L, freezing and drying to obtain lignin aerogel, placing the obtained lignin aerogel in a tubular furnace, carrying out heat treatment at 250-500 ℃ in an argon atmosphere, and cooling to obtain the water treatment material. Wherein the heat treatment temperature is preferably 300 to 350 ℃.

Preferably, the concentration of the lignin aqueous solution is 1-10 mg/L. The lower the concentration of the aqueous lignin solution is, the lower the density of the aerogel is, the larger the specific surface area is, the better the crosslinking effect is during heat treatment, the better the adsorption effect on pollutants is, but the lower the concentration is, the lower the preparation efficiency and the yield are.

Preferably, the heat treatment time is 1 to 2 hours.

Preferably, the lignin is alkali lignin.

The aqueous solution of lignin can be frozen in liquid nitrogen or in a refrigerator. The liquid nitrogen freezing speed is high, the growth time of the ice blocks is short, the lignin is dispersed in the ice blocks in a smaller size, and the strength of the dried lignin aerogel is improved.

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

1. according to the invention, after the lignin precursor is crosslinked through heat treatment, the lignin-based water treatment material with a porous structure is prepared, so that not only can important functional groups in the lignin structure be maintained, but also the diffusion of the lignin in a water body is avoided, and the application of lignin in water treatment is promoted, wherein the contact area among lignin molecules can be increased through freeze drying, and thus the crosslinking effect of heat treatment among lignin molecules is promoted.

2. The lignin-based water treatment material can be prepared by utilizing the waste lignin through freeze drying and heat treatment, the preparation method is simple, and the prepared water treatment material has an aerogel structure and simultaneously retains important functional groups in the lignin structure, so that the water treatment material has a good adsorption effect on pollutants.

3. According to the invention, the lignin aerogel with different densities is prepared by freeze drying, and due to different concentration ranges, the appearance of the freeze-dried lignin is different, the appearance structures of the lignin precursor and the crosslinked product can be regulated and controlled by regulating the concentration of the lignin aqueous solution, and the chemical components of the prepared water treatment material can be controlled by regulating the heat treatment temperature.

4. The method does not need other crosslinking reagents or organic solvents, is environment-friendly, is simple and convenient to operate, and more importantly, the crosslinked lignin prepared by the method has a large specific surface area, so that the adsorption effect on pollutants is better.

Drawings

FIG. 1 is a scanning electron micrograph of the water-treating material prepared in examples 1 to 4;

FIG. 2 is an infrared spectrum of the water-treating material prepared in examples 4 to 7.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

The lignins used in the following examples were all alkali lignins, and were prepared into an aqueous solution according to a conventional method.

Example 1

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 100mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 300 ℃, cooling, and preparing the microcosmic flaky cross-linked lignin aerogel, wherein the chemical components comprise free lignin, and the lignin is partially cross-linked.

Wherein the product can be analyzed by infrared spectroscopy and dispersed in water, and the uv spectrum of the dispersed water is measured, and if uv absorption occurs, it indicates free lignin, as in the following examples.

Example 2

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 10mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 300 ℃, cooling, and preparing the microcosmic flaky cross-linked lignin aerogel, wherein the chemical components comprise free lignin, and the lignin is partially cross-linked.

Example 3

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 5 mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 300 ℃, and cooling to prepare the microscopically flaky crosslinked lignin aerogel, wherein the lignin is basically crosslinked.

Example 4

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 1 mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 300 ℃, and cooling to prepare the microcosmic fibrous cross-linked lignin aerogel, wherein most of lignin is cross-linked.

Example 5

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 1 mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 350 ℃, and cooling to prepare the microcosmic fibrous cross-linked lignin aerogel, wherein most of lignin is cross-linked.

Example 6

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 1 mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the conditions of argon atmosphere and 400 ℃, and cooling to prepare the microcosmic fibrous cross-linked lignin aerogel, wherein the lignin is carbonized in a small amount.

Example 7

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 1 mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 500 ℃, cooling, and preparing the micro-fibrous cross-linked lignin aerogel, wherein the lignin is partially carbonized.

Example 8

Dissolving lignin in water, preparing a lignin aqueous solution with the concentration of 1 mg/L, quickly freezing the lignin solution in liquid nitrogen, and freeze-drying to prepare the lignin aerogel. Putting the lignin aerogel into a tubular furnace, carrying out heat treatment for 1 hour under the condition of argon atmosphere and 250 ℃, and cooling to prepare the microscopically flaky crosslinked lignin aerogel, wherein the chemical components contain free lignin, and the lignin is not completely crosslinked.

In FIG. 1, (1), (2), (3) and (4) are scanning electron micrographs of the water-treatment materials prepared in examples 1, 2, 3 and 4, respectively, and it can be seen from FIG. 1 that the morphology of lignin changes from a very thick large sheet to a thin small sheet with decreasing concentration of freeze-dried lignin, and when the concentration of lignin is less than 5mg/mL, the distribution of lignin in ice cubes cannot be supported to form a continuous sheet structure and changes from a sheet assembly to a fiber shape because of too low concentration of lignin.

FIG. 2 is an infrared spectrum of the carbon material prepared in examples 4 to 7, which shows that when the temperature of lignin is relatively low, such as 300 ℃ and 350 ℃, the chemical functional groups, such as phenolic hydroxyl groups, can be well preserved, and when the temperature is further increased, the effective functional groups are gradually reduced due to carbonization of the lignin material.

Application test

Rhodamine B solution and copper ion solution with initial concentrations of 10mg/L and 30mg/L respectively are prepared and used for testing the adsorption performance of the cross-linked lignin aerogels prepared in the examples 4 and 5.

The test method comprises the following steps: uniformly dispersing the prepared cross-linked lignin aerogel in a solution to be treated, placing the solution on an oscillator to shake and adsorb for 12 hours, then recovering the cross-linked lignin aerogel, and determining the concentration of rhodamine B or copper ions in the solution.

The test result shows that: the adsorption capacity of the cross-linked lignin aerogel prepared in the embodiment 4 on rhodamine B can reach 157mg/g, and the adsorption capacity on a copper ion solution can reach 290 mg/g; the adsorption capacity of the cross-linked lignin aerogel prepared in example 5 on rhodamine B solution and copper ion solution can reach 47mg/g and 340mg/g respectively.

The above examples of the present invention are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Variations and modifications in other variations will occur to those skilled in the art upon reading the foregoing description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.

Claims

1. A method for preparing a water treatment material by using lignin is characterized in that the lignin is prepared into an aqueous solution with the concentration of 1-10 mg/L, the aqueous solution is subjected to freeze drying to obtain lignin aerogel, the obtained lignin aerogel is placed in a tubular furnace to be subjected to heat treatment for 1-2 hours at the temperature of 250-500 ℃ in an argon atmosphere, and the water treatment material is obtained after cooling.

2. The method of producing a water-treating material using lignin according to claim 1, wherein the lignin is an alkali lignin.