Preparation method of natural lignin-based photocatalytic material
Technical Field
The invention belongs to the technical field of catalyst material preparation, and discloses a preparation method of a natural polymer lignin-based catalytic material. Can be applied to the field of photocatalysis, and particularly has potential application value in the field of photocatalytic degradation of difficultly-treated volatile organic compounds and degradation of nitrogen-containing organic pollutants.
Background
In recent years, with the development of society, organic wastewater discharged in the production process of textiles and fine chemicals causes serious environmental pollution, and has been paid high attention by global researchers. The photocatalysis technology is a novel effective green technology and has important application prospect in the fields of environment and energy. As an excellent semiconductor material, the nano titanium dioxide has the advantages of stable chemical property, corrosion resistance, acid and alkali resistance, low price and the like, is widely used as a photocatalyst and can be used for degrading organic pollutants in water. Lignin, one of the most widely occurring resources in nature, is a polyphenol polymer in the second largest amorphous state, second only to cellulose, in content in the plant world. It is a renewable, green and environment-friendly natural polymer material. Commercial lignin, which is a by-product of the paper industry, is present in black liquor and is rarely further processed and utilized, resulting in waste of resources and even environmental problems. The lignin contains abundant phenolic hydroxyl groups, so the lignin has certain reduction performance, and the heterogeneous catalyst taking the lignin as a carrier has attracted the attention of researchers,
however, the photocatalytic activity of titanium dioxide is limited by its forbidden bandwidth (the forbidden bandwidth of rutile phase is 3.0eV, and the forbidden bandwidth of anatase phase is 3.2eV), and it can only be excited by ultraviolet light having a wavelength of less than 380nm, and the solar light utilization rate is low. On the other hand, when the TiO2 photocatalyst is irradiated by sunlight, electrons and holes generated by excitation easily recombine on the surface and in the body, resulting in low photocatalytic efficiency. The carbon material has good electron transport capacity and a certain sensitization effect on the semiconductor material, and the defects can be overcome to a certain extent by compounding the semiconductor material and the carbon material together. A large number of researches show that the photocatalytic performance of the composite material can be obviously improved by compounding a carbon material (graphene, carbon fiber, carbon nanotube and the like) and TiO 2. The literature (ACS Applied Materials & Interfaces,2013,5(3): 1156-1164) discloses a method for preparing TiO 2/carbon (GR, CNT and C60) nanocomposites with different carbon material addition ratios through sol-gel method and hydrothermal method treatment, the photocatalytic performance of the synthesized TiO 2/carbon composites is researched through photocatalytic degradation of benzyl alcohol, the addition of GR, CNT and C60 can induce the increase of light absorption intensity in the visible light region, effectively promote the visible light response of Ti O2/GR, Ti O2/CNT and Ti O2/C60 nanocomposites, and promote the effective separation of photoexcited electron-hole pairs, thereby improving the photocatalytic efficiency. Chinese patent CN 107308929a discloses "a graphene-nano titanium dioxide composite photocatalyst" which is prepared by synthesizing graphene oxide with graphite powder, adding deionized water to prepare a graphene oxide solution, adding a cetyl ammonium bromide solution and a titanium trichloride solution, reacting in a high-pressure reaction kettle, precipitating, and washing to obtain the product. However, the preparation process of the carbon-based material (graphene, carbon nanotube, fullerene, etc.) of the carbon-based/Ti O2 composite photocatalyst is complex and expensive, strong acid and strong base are required in the preparation process, and the environmental pollution is serious; the prepared carbon-based material with a certain morphology is compounded with TiO2, so that the bonding force between the two materials is weak; meanwhile, carbon-based materials such as graphene are easy to agglomerate, so that the carbon-based materials and titanium dioxide in the prepared composite photocatalyst are not uniformly distributed. These problems greatly limit the photocatalytic performance and hinder the commercial application prospect.
The lignin is a high molecular polymer with a three-dimensional space network structure, has high carbon content and a plurality of active functional groups, is second to cellulose in the natural reserve, and is an excellent precursor for preparing carbon materials. Industrial lignin is mainly derived from by-products of the pulp and paper industry: most of the lignosulfonate in the red liquor of the sulfite pulping and the alkali lignin in the black liquor of the alkali pulping are treated and discharged as waste liquor. The effective utilization of the industrial lignin not only can save resources, but also is beneficial to reducing the environmental burden. For example, in the literature (forest engineering, 2015(3): 54-56), alkali lignin is used as a raw material, and a lignin amine salt obtained through a mannich reaction is added into a hydrochloric acid solution of butyl titanate to perform a hydrothermal reaction at 80-130 ℃ for 72 hours, and then the mixture is sintered at 500 ℃ for 10 hours to obtain titanium dioxide nanoparticles. Chinese patent CN106824151A discloses a lignin-based mesoporous titanium dioxide photocatalytic material, a preparation method and application, wherein titanium tetrachloride is added into an alkali lignin solution, the pH value is adjusted to 1-5, heating is carried out for a period of time at 60-100 ℃, ammonia water is added, centrifugal separation is carried out, after ball milling, calcination is carried out for 5 hours at 400-600 ℃, and the titanium dioxide is obtained after lignin is removed. Although the method for preparing titanium dioxide by using lignin as a template can obtain titanium dioxide with good performance, the preparation process is complex, the processes of hydrothermal, ball milling and the like are required, and in order to remove the template, long-time calcination is generally required, so that the cost is increased, and the lignin is not fully utilized
In the existing preparation of the lignin carbon/titanium dioxide composite photocatalyst, because titanium alkoxide serving as a titanium dioxide precursor is very easy to hydrolyze and cannot be well dispersed in a lignin solution, the titanium dioxide precursor can only be slowly added into the lignin aqueous solution, so that the obtained titanium dioxide particles are large, strong acting force does not exist between the titanium dioxide and the lignin, and the coating amount of the lignin is small. These factors have greatly limited the development of lignin-based nano-metal oxide photocatalysts prepared using lignin as a carbon source.
Disclosure of Invention
In order to solve the problem of the defect of limiting lignin as a raw material to prepare the photocatalyst, the preparation method of the natural lignin-based photocatalytic material is provided.
The technical scheme adopted by the invention for solving the problems is as follows: a method for preparing a natural lignin-based photocatalytic material comprises the following specific processes,
modification of S1: firstly, natural lignin separated from plants is modified;
s2 mixing: adding dry ice and nano metal oxide into the modified natural lignin, and placing the mixture into a ball mill for ball milling to prepare a lignin-nano metal oxide mixture;
s3, drying: heating the mixture at the temperature of 100-900 ℃ for 1-24 hours to prepare the nano-particle catalytic material.
Further, the S1 modification: lignin modification includes, but is not limited to, amine cationization, sulfomethylation, multi-monomer graft copolymerization, and the like.
Further, the S2 compounding: the amount of the added dry ice is 0.01 to 10 times of the mass amount of the lignin, and the amount of the added metal oxide is 0.01 to 1 time of the mass amount of the lignin.
Further, the S2 compounding: nano metal oxides include, but are not limited to, semiconductor catalytic materials such as ZnO, SeO and Cu2O, etc.; magnetic catalytic material, Fe2O3,Fe3O4NiO, CoO, etc.
Further, the step S3 is drying: the lignin-based nano metal oxide compound is heated to 400-800 ℃ in an inert atmosphere and calcined for 1-4 hours to obtain the lignin-based nano metal oxide composite photocatalyst, and the catalytic material can be directly applied to photocatalytic degradation of VOCs or high-concentration organic wastewater.
According to the method, a natural lignin polymer separated from plants is modified, amination modification, grafting modification and the like are carried out according to the property of an adsorbed substance when the natural lignin polymer is used as an adsorbing material according to the application requirement of a product, dry ice and nano metal oxide are mixed, and the mixture is placed into a ball mill for ball milling to prepare a lignin-metal oxide mixture, wherein the lignin-metal oxide mixture aims at removing branch chains on lignin, converting phenolic hydroxyl into carboxyl and embedding the metal oxide into the gaps of the lignin. And then the mixture is made into a granular catalytic material. The adopted preparation method comprises but is not limited to adding a binder for extrusion forming and electrostatic spraying granulation, or the obtained lignin-metal oxide mixture is subjected to pyrolysis carbonization and activation to prepare the porous adsorption-catalysis composite material.
The lignin-based nano metal oxide composite photocatalyst prepared by the method has small metal oxide particle size, uniform distribution and obviously improved photocatalytic efficiency, has strong catalytic degradation effect on volatile organic compounds and high-concentration organic wastewater, can be applied to the field of photocatalysis, and particularly has potential application value in the field of photocatalytic degradation of difficultly-treated volatile organic compounds and nitrogen-containing organic pollutants.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto. The materials referred to in the following examples are commercially available.
Example 1
A preparation method of a natural lignin-based photocatalytic material comprises the following specific steps:
modification of S1: taking 100g of lignin, adding 200g of water and 120mL of 1.5% (mass concentration) NaOH aqueous solution, stirring for 20 minutes, adding 10g of formaldehyde, continuing stirring for 20 minutes, adding 20mL of ethylenediamine while stirring, heating in a water bath at 100 ℃, and refluxing and stirring for 3 hours to obtain an aminated modified lignin sample;
s2, mixing: drying the sample obtained in S1 in an oven at a constant temperature of 105 ℃ for 24 hours, taking out, adding 10g of nano TiO2 (particle size 10nm) and 10g of dry ice, putting into a ball milling tank, and simultaneously adding 300g of Al with the diameter of 3mm2O3Grinding balls, placing in a planetary ball mill, setting the rotating speed at 500RPM, and ball-milling for 3 hours to obtain a lignin-based nano titanium dioxide mixture;
s3, drying: and (3) placing the nano titanium dioxide mixture obtained in the step (S2) in an atmosphere furnace, reacting for 3h at 700 ℃ in the atmosphere of N2, continuously introducing a small amount of water vapor, fully reacting for 1h at 900 ℃, and stopping heating until the temperature in the furnace is reduced to room temperature to obtain the lignin carbon-based nano metal oxide composite photocatalyst.
Example 2
A preparation method of a natural lignin-based photocatalytic material comprises the steps of taking natural high-molecular lignin, carrying out amination modification, adding nano TiO2 and dry ice according to the mass ratio, placing the mixture into a planetary ball mill, and carrying out ball milling on the mixture to obtain powder, wherein the powder is prepared into the nano composite matrix catalytic material by adopting an electrostatic spraying method.
The method comprises the following specific steps:
modification of S1: modifying lignin by amination in the same way as in example 1;
s2 mixing: drying the sample obtained in S1 in an oven at a constant temperature of 105 ℃ for 24 hours, taking out, adding 10g of nano TiO2 (particle size 10nm) and 10g of dry ice, putting into a ball milling tank, and simultaneously adding 300g of Al with the diameter of 3mm2O3Grinding balls, namely, setting the rotation speed of a planetary ball mill to be 500RPM, and carrying out ball milling for 3 hours to obtain a lignin-based nano titanium dioxide mixture;
s3, drying: and (3) placing the nano titanium dioxide mixture obtained in the step (S2) in an atmosphere furnace, reacting for 3h at 700 ℃ in the atmosphere of N2, continuously introducing a small amount of water vapor, fully reacting for 1h at 900 ℃, stopping heating, reducing the temperature in the furnace to room temperature, and removing the sample to obtain the lignin carbon-based nano metal oxide composite photocatalyst.
Example 3
Modification of S1: adding 1500g of deionized water into 100g of lignin, adding the lignin into a flask with a stirring rod and reflux condensation, heating to 40 ℃, slowly adding dilute hydrochloric acid to adjust the pH value to 2, adding 50g of 30% aqueous hydrogen peroxide, stirring and heating at 50 ℃ for 2 hours, then heating to 80 ℃, adding 40g of sodium bisulfite and 30g of 30% aqueous formaldehyde, reacting at constant temperature for 12 hours, and then cooling to room temperature to obtain a crude product. The anion resin was then soaked with 2M aqueous sodium hydroxide overnight and the cation resin was soaked with 2M aqueous hydrochloric acid overnight. Sequentially flowing the obtained crude product through anion exchange resin and cation exchange resin, washing the anion and cation exchange resin by using distilled water until the pH of the cleaning solution is nearly neutral to obtain an extracting solution, and performing rotary evaporation and vacuum drying on the extracting solution to obtain sulfomethylated modified lignin;
s2 mixing: the same as example 1;
s3, drying: the same as in example 1.
Example 4
Modification of S1: adding 200g of water into 100g of lignin, simultaneously adding 20g of phenol and 50g of 30-concentration formaldehyde aqueous solution, adding the lignin into a flask with a stirring rod and reflux condensation, heating to 100 ℃, reacting for 12 hours, stopping the reaction, cooling, removing water in reaction liquid by using a rotary evaporator, drying for 12 hours in a constant-temperature drying oven at 100 ℃, and drying to obtain a lignin molecular monomer graft copolymerization product;
s2 mixing: the same as example 1;
s3, drying: the same as in example 1.
Example 5
Modification of S1: performing sulfomethylation modification on lignin in the same way as in example 3;
s2 mixing: the same as example 2;
s3, drying: the same as example 2;
example 6
Modification of S1: grafting, copolymerizing and modifying the lignin multi-monomer in the same way as in example 4;
s2 mixing: the same as example 2;
s3, drying: the same as in example 2.
The use function of the invention is verified by UV photocatalytic degradation experiments on high-concentration organic wastewater.
Comparative example 1: no photocatalyst is added;
example 1: the catalyst is an amination modified nano composite particle photocatalytic material;
example 2: the catalyst is an amination modified nano composite photocatalytic material;
example 3: the catalyst is a lignin sulfomethylation modified nano composite base photocatalytic material;
example 4: the catalyst is a lignin multi-monomer graft copolymerization nano composite base photocatalysis material;
example 5: the catalyst is a lignin sulfomethylation modified carbon-based nano metal oxide composite photocatalyst;
example 6: the catalyst is a lignin multi-monomer graft copolymerization modified carbon-based nano metal oxide composite photocatalyst;
the TOC (total organic carbon) value of the high-concentration organic wastewater adopted in the experiment is 20000mg/L, and the dosage of the catalyst is 10g/1000g of wastewater
Detecting items
|
TOC after 5min
|
TOC after 10min
|
TOC after 15min
|
TOC after 20min
|
Comparative example 1
|
19200
|
19100
|
18600
|
18500
|
Example 1
|
14200
|
8900
|
5900
|
2800
|
Example 2
|
14010
|
12140
|
8750
|
6800
|
Example 3
|
10250
|
9800
|
7850
|
4850
|
Example 4
|
8750
|
6500
|
3800
|
2950
|
Example 5
|
6900
|
5500
|
2800
|
1800
|
Example 6
|
5800
|
4500
|
2900
|
2200 |
The use function of the invention is verified by the experiment of UV photocatalytic degradation of VOCs.
Comparative example 2: no photocatalyst is added;
example 1: the photocatalyst is a particle catalytic material;
example 2: a nano metal oxide composite photocatalyst;
the total non-methane hydrocarbons in the waste gas VOCs adopted in the experiment are 1000mg/L, and the space velocity of the catalyst is 300--1。
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.