CN115779955A

CN115779955A - Lignin carbon-loaded Fe-N single-atom catalyst

Info

Publication number: CN115779955A
Application number: CN202310056535.XA
Authority: CN
Inventors: 马建锋; 代琳心; 刘杏娥; 马千里; 尚莉莉
Original assignee: International Center for Bamboo and Rattan
Current assignee: International Center for Bamboo and Rattan
Priority date: 2023-01-18
Filing date: 2023-01-18
Publication date: 2023-03-14
Anticipated expiration: 2043-01-18
Also published as: CN115779955B

Abstract

The invention relates to a lignin carbon-supported Fe-N monatomic catalyst, wherein a carrier is obtained by carbonizing lignin at high temperature in the presence of a nitrogen source, the carrier has C-N bonds of graphite-nitrogen, pyrrole-N and pyridine-nitrogen, fe is uniformly dispersed on the carrier in a monatomic form, and Fe and N form Fe-N coordination bonds. According to the invention, through nitrogen doping, abundant C-N bonds are formed on the charcoal carrier of lignin, and stable Fe-N is also formed _x And due to coordination bonds, fe is loaded on the carrier in a monatomic form, so that the catalytic activity and stability are improved, and the utilization efficiency of Fe atoms is improved.

Description

Lignin carbon-loaded Fe-N single-atom catalyst

Technical Field

The invention relates to the technical field of composite materials and water treatment, in particular to a lignin carbon-supported Fe-N monatomic catalyst.

Background

With the continuous development of economy, the increase of global population and climate change, the threat of emerging organic pollutants in water bodies to the environment and human health has become a serious problem worldwide. Emerging organic pollutants are artificial organic substances that are present in the environment and cause tremendous damage to the ecosystem due to industrial and human activities. Including endocrine disruptors, herbicides and insecticides, personal care products, pharmaceuticals, and the like. When these large quantities of organic materials in domestic and agricultural sewage, urban runoff and industrial waste are combined, there is worldwide concern due to the toxicity, bioaccumulation tendency and persistence of these materials, and the potential for the fixation and bioaccumulation of pollutants in sediments, or the conversion and activation of pollutants in aquatic systems that pose a great threat to human health and ecological environment. Examples of such organic contaminants include, but are not limited to, bisphenol a, acetaminophen, and the like, which are difficult to treat.

Adsorption is considered to be a potentially promising wastewater treatment process due to its low cost, low energy consumption, no chemicals required and ease of implementation. However, the problems of unsatisfactory adsorption capacity, slow equilibrium rate, unstable adsorption state, incapability of thoroughly removing pollutants and the like of the biomass-based carbon material still remain as bottlenecks restricting the adsorption application of the biomass-based carbon material. Advanced Oxidation Processes (AOPs) using persulfate as an oxidant can degrade organic pollutants into low-toxicity intermediates and even mineralize CO due to high-efficiency active free radicals generated in the reaction ₂ And H ₂ O, and has received a great deal of attention in the field of environmental remediation. For example, nitrogen-doped biochar catalysts prepared by a simple one-step carbonization process can remove organic contaminants such as bisphenol A, acetaminophen and the like in water under the action of Peroxymonosulfate (PMS) or Peroxydisulfate (PDS)And (4) completely degrading. There are various ways of activating persulfate, and heterogeneous activation using a catalyst is the most practical choice. The development of a suitable activator, or catalyst, is critical to find a suitable catalyst support.

The monatomic catalyst is a hotspot of the current metal catalyst research, and the monatomic dispersion has no traditional metal-metal bond, namely no agglomeration of metal active sites, so that the maximum atom utilization rate can be realized. How to uniformly disperse metal atoms with catalytic activity on a carrier in a monoatomic state so as to maximally expose catalytic active sites is a problem to be solved. At present, a common carrier is a nitrogen-doped carbon carrier, but the activation sites of the nitrogen-doped carbon carrier obtained by the conventional method are not uniformly dispersed, so that the defects of poor selection for degrading organic pollutants or poor stability are caused. In order to disperse active metal atoms on a carrier in a monoatomic state, a common method is to introduce organic compounds to anchor individual metal atoms in a precursor through coordination bonds of organic ligands or through Metal Organic Frameworks (MOFs), for example, toxic chemical ligands such as 2-methylimidazole and 1, 10-phenanthroline are used to limit the agglomeration of metal atoms, but these ligands are toxic or expensive and are not suitable for industrial application; therefore, the search for an environmentally friendly, simple to prepare, and efficient biomass charcoal catalyst is an urgent problem to be solved by researchers.

CN114733523A reports a preparation method of an iron monatomic catalyst, in which an iron nitrate solution is added dropwise to an activated carbon black suspension to obtain an iron precursor, the iron precursor is mixed with urea, and the mixture is heated and carbonized under an argon atmosphere to obtain the iron monatomic catalyst. However, the technology of the patent needs to use concentrated nitric acid to activate the raw material carbon black, which increases the production cost. Meanwhile, the catalyst has low degradation efficiency, and the treatment effect on the acesulfame potassium reaches nearly 100% at 60min under the condition of high-concentration PMS (2.4 g/L).

CN114177927A discloses a preparation method of a two-dimensional carbon nitride iron monatomic catalyst, which is obtained by respectively dissolving melamine and cyanuric acid in water to assemble a supramolecular assembly, mixing the supramolecular assembly with an iron-containing precursor, inserting the iron precursor into the layers of the supramolecular assembly through ball milling, and calcining in an inert atmosphere. However, this catalyst consumes a large amount of chemical reagents to anchor the iron atoms. And is seriously affected by anions in water in the process of removing the sulfamethoxazole.

The prior art reports that nitrogen-coordinated cobalt monoatomic catalysts prepared by using bamboo lignin as a carbon source show good catalytic activity (Applied Catalysis B: environmental 286 (2021) 119910). The preparation method comprises the steps of measuring cobalt acetate and zinc nitrate into a lignin solution through a one-pot pyrolysis method, aging to form a Co/Zn-lignin compound, physically separating Co atoms by Zn atoms, mixing a certain amount of nitrogen source with a solid, carrying out pyrolysis, evaporating and removing the Zn atoms in the pyrolysis process, and leaving nitrogen-doped carbon as a carrier to load the composite material of monoatomic Co. However, the method needs high temperature (more than 1000 ℃) to evaporate and remove Zn atoms, and has large energy consumption; and Zn atoms are not easy to recycle in the preparation process, which violates the principle of atom utilization efficiency of the monoatomic technology to be the maximum. The materials still have the problems of low catalytic degradation efficiency, complex leaching and preparation process of toxic metal ions (Co ions have high toxicity) and the like.

Disclosure of Invention

Aiming at the problems that the catalytic efficiency of the biomass charcoal catalyst is to be improved, the preparation process of the catalyst is complex and the like, the invention provides an N-coordinated Fe ultrahigh-dispersion lignin charcoal catalyst material. The preparation method not only makes full use of the advantages of wide sources, low price, rich functional groups and the like of the industrial bamboo pulp lignin, but also has the performance of efficiently activating persulfate to degrade organic pollutants in water, and provides a new idea for the development of the industrial bamboo pulp lignin.

In order to solve the technical problems, the invention provides the following technical scheme:

a lignin carbon-supported Fe-N monatomic catalyst is characterized in that a carrier is obtained by carbonizing lignin at high temperature in the presence of a nitrogen source, the lignin carbon-supported Fe-N monatomic catalyst has C-N bonds of graphite-nitrogen, pyrrole-N and pyridine-nitrogen, fe is uniformly dispersed on the carrier in a monatomic form, and Fe and N form Fe-N coordination bonds.

Preferably, the lignin is a bamboo lignin.

Further, the loading of the monoatomic iron in the catalyst is 1 to 3wt%, preferably 1.53 to 2.87wt%. The loading was obtained by ICP test.

Further, the XPS N1s spectrum of the ligno-carbon supported Fe-N monatomic catalyst has the following characteristic peaks: 402.4 + -0.1eV, 401.1 + -0.1eV, 399.7 + -0.1eV, 398.4 + -0.1 eV. Wherein the characteristic peak near 402.4eV is graphite-N bond, the characteristic peak near 401.1eV is Fe-Nx bond, the characteristic peak near 399.7eV is pyrrole-N bond, and the characteristic peak near 398.4eV is pyridine-N bond.

According to the invention, rich C-N bonds are formed on the charcoal carrier of lignin by nitrogen doping, so that the activity of a catalytic site can be improved, and graphite-N can activate PMS to generate PMS through a non-free radical way ¹ O ₂ (singlet oxygen). pyridine-N and/or pyrrole-N with lone pair electrons can promote the generation of sp from biochar ² Transfer of free-flowing pi electrons of carbon to activate PMS and generate SO ₄ ^•− And ^• OH; on the other hand, stable Fe-N is formed _x And the coordination bond anchors Fe atoms on the carrier to improve the stability of catalytic active sites, and nitrogen doping enables Fe to be loaded on the carrier in a monoatomic form, so that the catalytic activity and stability are improved, and the utilization efficiency of the Fe atoms is improved.

The second purpose of the invention is to provide a preparation method of the lignin carbon-supported Fe-N single-atom catalyst, which comprises the following steps:

(S1) dispersing lignin in an alcohol solvent, adding an iron source, and uniformly mixing;

(S2) stirring the material obtained in the step (S1) at the temperature of 30-40 ℃ until the material is dried to obtain a dry matter I;

(S3) dispersing the dried substance I obtained in the step (S2) and a nitrogen source in water to obtain a mixed solution, and freeze-drying to obtain a dried substance II;

(S4) calcining the dried product II obtained in the step (S3) in an inert atmosphere for carbonization, and cooling to room temperature;

and (S5) putting the carbonized material into inorganic acid, heating, washing to be neutral, and drying to obtain the lignin carbon-supported Fe-N single-atom catalyst.

Further, the lignin in the step (S1) is not particularly limited, and may be a common industrial lignin. Washing lignin before use, specifically, mixing lignin and 0.3-1M hydrochloric acid uniformly, treating for 1-5h under stirring, washing with water until pH is 6-7, drying, and grinding to obtain the final product. Preferably, the milled material is passed through a 60-80 mesh screen. The alcohol solvent is selected from at least one of methanol and ethanol.

Further, in the step (S1), the iron source is a water-soluble salt of trivalent iron and/or a hydrate thereof, such as FeCl ₃ And/or Fe (NO) ₃ ) ₃ Their hydrates are each FeCl ₃ ·6H ₂ O and Fe (NO) ₃ ) ₃ ·9H ₂ O。

Further, in the step (S1), the amount of the alcohol solvent is not particularly limited in terms of 1 to 5mmol of the iron source (in terms of iron) per g of the lignin charged, and in one embodiment of the present invention, the amount of the alcohol solvent is such that the molar concentration of Fe in the system is 5 to 20mM, preferably 8 to 16mM.

Further, in the step (S3), the nitrogen source is at least one selected from dicyandiamide, urea and melamine; preferably, the mass ratio of the dry matter I and the nitrogen source is 1. The nitrogen source is excessive because nitrogen is lost much by pyrolysis at high temperature, and nitrogen with more than 10 times of mass is added mainly for fully forming Fe-N bond and C-N bond.

Further, in the step (S3), the amount of water used is not particularly limited, and in one embodiment of the present invention, the amount of water used satisfies the following conditions in a solid-liquid mass ratio of 1:10-15.

Further, in the step (S3), the freeze-drying is performed in a freeze-dryer at-70 to-90 ℃ for 60 to 72 hours.

Further, in the step (S4), the inert atmosphere is nitrogen and/or argon; the calcination is carried out at the temperature rise rate of 5-30 ℃/min, the temperature is raised to 700-800 ℃, and the calcination is carried out for 1-2h under the condition of heat preservation.

Further, in the step (S5), the inorganic acid is at least one of 0.5 to 2M hydrochloric acid, sulfuric acid and nitric acid, and is heated to 60 to 80 ℃. The purpose of the acid washing is to wash away the excess nano-iron formed. In the process, the monatomic iron cannot be washed away because the monatomic Fe forms a chemical bond with N or C, which is equivalently stably anchored on the carrier, and cannot be removed by acid washing.

The invention utilizes the adsorption action force of the inherent abundant functional groups of lignin to realize the uniform dispersion of the transition metal iron atoms at the single atom level in the volatilization drying process of alcohol solvents such as methanol, and the subsequent high-temperature carbonization achieves the effect of nitrogen doping modification. On one hand, C-N bonds of graphite nitrogen, pyrrole-azapyrine and pyridine-nitrogen are formed in a carbon structure of the original lignin and are used as the activation sites of persulfate, so that the yield of active free radicals is increased; on the other hand, the introduced Fe atoms and N form Fe-N under the action of high temperature _x A bond, also has the effect of activating the persulfate. The introduction of Fe increases the electric charge of an adjacent structure, promotes the adsorption of persulfate, and enhances the catalytic degradation performance of the catalyst material on organic pollutants in water.

The lignin is uniformly dispersed in the alcohol solvent and fully contacted with iron ions in the solution. At low temperature (40 deg.C), alcohol is gradually evaporated, and lignin can fully adsorb iron ions. And (3) after the mixture is completely dried, adding a nitrogen source and deionized water in a corresponding proportion, freeze-drying and then using a freeze-dryer. By adding the nitrogen source, the sample is fluffy like cotton in the freeze-drying process, and the uniform distribution of iron ions can be further promoted.

The third purpose of the invention is to provide the application of the lignin carbon-supported Fe-N single-atom catalyst in persulfate oxidation removal of organic pollutants in water.

Further, the use comprises the steps of: and adding the lignin carbon-supported Fe-N monatomic catalyst and persulfuric acid into sewage to be treated to degrade organic pollutants.

The persulfate is selected from at least one of sodium persulfate, potassium persulfate and ammonium persulfate; the ratio of catalyst to persulfate is 0.05-0.2g:0.5-5mmol; the adding amount of the catalyst is 0.05-0.02g of catalyst per L of wastewater.

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

1. the method takes the industrial lignin as a production raw material, the industrial lignin is used as a byproduct of the papermaking black liquor, the method is environment-friendly, cheap and easy to obtain, the whole preparation process is simple to operate, the used chemical reagent is safe, does not contain any harmful substance to human bodies, has low equipment requirement and no secondary pollution, and is suitable for industrial production. Meanwhile, the catalyst material contains iron element, has magnetism, can be recycled, and has high catalytic degradation efficiency and stable performance.

2. According to the invention, N is adopted to modify lignin, then iron is unloaded, iron is loaded on nitrogen-doped lignin carbon in a monatomic manner, the excellent structural characteristics of the original lignin are utilized, and a two-stage process of firstly volatilizing and drying alcohol solvent and then freeze-drying is adopted, so that Fe atoms are uniformly dispersed in a monatomic manner, and the maximum utilization of the Fe atoms is realized. Simultaneously adding nitrogen source and then carbonizing at high temperature to form more stable Fe-N _x The bond obviously improves the performance of catalyzing persulfate by the biomass charcoal to degrade organic pollutants. Furthermore, the resulting catalyst is not sensitive to anions and no adverse effect on the catalytic activity is obtained in the presence of various anions.

3. The catalyst prepared by the invention is used for treating organic pollutants by persulfate oxidation in wastewater, has high catalytic activity, stable catalytic performance and long service life, and is expected to be industrialized.

Drawings

FIG. 1 is an XPS N1s spectrum of a catalyst material prepared in example 1;

FIG. 2 is a spherical aberration corrected high angle toroidal dark field scanning transmission electron micrograph (HADDF-STEM) of the catalyst material prepared in example 1;

FIG. 3 is an XRD diffraction pattern of the resulting catalyst;

FIG. 4 is an SEM photograph of catalysts obtained in example 1 and comparative example 4;

FIG. 5 is a TEM image of catalysts prepared in example 1 and comparative example 4;

FIG. 6 is a graph of the catalytic activity data for the catalyst of example 1;

FIG. 7 is a graph of the effect of the catalyst of example 1 on the degradation of BPA in the presence of different anions.

Detailed Description

The preparation and performance of the lignocellulosic carbon-supported Fe-N monatomic catalyst according to the present invention is further illustrated by the following specific examples.

Example 1

S1: adding 15g of industrial lignin into 150mL of 0.1M hydrochloric acid solution, magnetically stirring at room temperature for 3h, performing suction filtration, leaching with deionized water until the pH is 6-7, drying in a 105 ℃ oven until grinding, and sieving with a 60-mesh sieve to obtain pure lignin; to 50mL of methanol solution were added 0.4g of lignin and 0.108g of FeCl ₃ ·6H ₂ O (Fe concentration in methanol solution 8mM, i.e. 1mmol of Fe dosed per g of lignin).

S2: putting the mixture solution obtained in the step S1 into a water bath kettle at 40 ℃ until the mixture solution is completely dried to obtain a dry substance;

s3: adding 0.4g of the dried substance and 4g of melamine into 50m of water, fully stirring until the melamine is completely dissolved to obtain a dispersion liquid, and putting a dispersion liquid sample into a freeze dryer at the temperature of 84 ℃ below zero for drying for 72 hours to obtain a freeze-dried substance;

s4: pouring the freeze-dried substance into a crucible, placing the crucible into a tube furnace, and performing reaction in a reaction environment with N ₂ Heating to 800 ℃ at a heating rate of 5 ℃/min under the condition that the blowing flow rate is 0.2mL/min, preserving heat for 2h for carbonization, naturally cooling to room temperature after the reaction is finished, and taking out;

s5: pouring the carbonized lignin carbon material into 150mL of 4M sulfuric acid solution, heating and stirring at 80 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value is 6-7, drying at 105 ℃ to constant weight to obtain the lignin carbon catalyst material with iron monoatomic dispersion, and marking as Fe ₁ -N ₁₀ -BC ₂ . Wherein, fe ₁ "1" in (A) means 1mmol Fe, N per g lignin charge ₁₀ "10" of (a) indicates that the mass ratio of the nitrogen source to the lignin is 10 ₂ The "2" of (1) indicates that the lignin and Fe source are subjected to primary dispersion and drying of the methanol dispersion liquid for the first time, and the lignin and Fe source are subjected to secondary drying after adding the nitrogen source and waterAnd (4) freeze-drying.

The amount of Fe supported by ICP test in example 1 was 1.53%.

FIG. 1 is an XPS N1s spectrum of a catalyst material prepared in example 1. The Fe-N monatomic catalyst has the following characteristic peaks of XPS N1s spectrum: characteristic peaks of 402.4eV,401.1eV,399.7eV, 398.4eV. Wherein the characteristic peak near 402.4eV is graphite-N bond, the characteristic peak near 401.1eV is Fe-Nx bond, the characteristic peak near 399.7eV is pyrrole-N bond, and the characteristic peak near 398.4eV is pyridine-N bond.

FIG. 2 is a high angle annular dark field scanning transmission electron microscopy characterization (HADDF-STEM) with spherical aberration correction of the catalyst obtained in example 1 to further reveal the spatial position of the metal atoms. Atomic dispersion of Fe throughout the structure was confirmed.

Example 2

The other operations are the same as in example 1, except that in step S3, 0.4g of lyophilizate and 3g of melamine are added to 50ml of ultrapure water. The final catalyst obtained is reported as Fe ₁ -N ₁₅ -BC ₂ 。

Example 3

The other operations are the same as in example 1, except that in step S3, 0.4g of lyophilizate and 2g of melamine are added to 50ml of ultrapure water. The catalyst finally obtained is recorded as Fe ₁ -N ₅ -BC ₂ 。

Example 4

The other operation was the same as in example 1 except that in step S1, 0.4g of lignin and 0.216g of FeCl were added to 50mL of ultrapure water ₃ ·6H ₂ O (i.e. 2mmol Fe per g lignin charge). The catalyst finally obtained is recorded as Fe ₂ -N ₁₀ -BC ₂ . The amount of Fe supported by ICP test was 2.87% in example 4.

Example 5

The other operation was the same as in example 1 except that in step S1, 0.4g of lignin and 0.324g of FeCl were added to 50mL of ultrapure water ₃ ·6H ₂ O (i.e. 3mmol Fe charged per g lignin). The final catalyst obtained is reported as Fe ₃ -N ₁₀ -BC ₂ . The amount of Fe supported in example 5 was 3.94% by ICP testing. The excessive addition of the iron source causes poor iron dispersibility in the obtained catalyst, part of iron atoms are agglomerated, and the degradation efficiency is reduced. The adding amount of the iron is not easy to be excessive.

Comparative example 1

In contrast to example 1, no modifying material was added. The method specifically comprises the following steps: and (3) adding no iron source and nitrogen source, and performing freeze-drying, carbonization and acid washing to obtain the lignin carbon catalyst, which is marked as BC.

Comparative example 2

S1: adding 15g of industrial lignin into 150mL of 0.1M hydrochloric acid solution, magnetically stirring at room temperature for 3h, performing suction filtration, leaching with deionized water until the pH is 6-7, drying in a 105 ℃ oven until grinding, and sieving with a 60-mesh sieve to obtain pure lignin; to 50mL of methanol was added 0.4g of lignin, 0.106g of FeCl ₃ ·6H ₂ O and 4g of dicyandiamide, fully stirring for 1h, and stirring the mixture solution at 40 ℃ until the mixture solution is dried;

s2: pouring the dried substance into a crucible, placing the crucible into a tube furnace, and reacting in a reaction vessel N ₂ Heating to 800 ℃ at a heating rate of 5 ℃/min under the condition that the blowing flow rate is 0.2mL/min, preserving heat for 2h for carbonization, naturally cooling to room temperature after the reaction is finished, and taking out;

s3: pouring the carbonized lignin carbon material into 150mL of 2M hydrochloric acid solution, heating and stirring at 80 ℃, performing suction filtration, repeatedly washing with deionized water until the pH is 6-7, drying at 105 ℃ to constant weight to obtain the lignin carbon catalyst material with iron monoatomic dispersion, and recording as Fe ₁ -N ₁₀ -BC。

That is, in comparison with example 1, comparative example 2 was obtained by mixing lignin, an iron source, and a nitrogen source together, dispersing the mixture in methanol, and drying the mixture.

Comparative example 3

S1: adding 15g of industrial lignin into 150mL of 0.1M hydrochloric acid solution, magnetically stirring at room temperature for 3h, performing suction filtration, leaching with deionized water until the pH is 6-7, drying in a 105 ℃ oven until grinding, and sieving with a 60-mesh sieve to obtain pure lignin; to 50mL of methanol solution were added 0.4g of lignin and 0.108g of FeCl ₃ ·6H ₂ O。

S2: putting the mixture solution obtained in the step S1 into a water bath kettle at 40 ℃ until the mixture solution is completely dried to obtain a dried substance;

s3: adding 0.4g of the dried substance and 4g of melamine into 50m of methanol, fully stirring until the melamine is completely dissolved to obtain a dispersion liquid, placing the methanol dispersion liquid in a water bath kettle at 40 ℃, and stirring until the mixture is dried;

s4: pouring the dried substance obtained in the step (S3) into a crucible, placing the crucible into a tube furnace, and reacting in N ₂ Heating to 800 ℃ at a heating rate of 5 ℃/min under the condition that the blowing flow rate is 0.2mL/min, preserving heat for 2h for carbonization, naturally cooling to room temperature after the reaction is finished, and taking out;

s5: and pouring the carbonized lignin carbon material into 150mL of 4M sulfuric acid solution, heating and stirring at 80 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value is 6-7, and drying at 105 ℃ to constant weight to obtain the lignin carbon catalyst material with dispersed iron monoatomic atoms.

That is, in comparative example 3, both drying were carried out by adding methanol, and the resulting dispersion was dried at 40 ℃.

Comparative example 4

S1: adding 15g of industrial lignin into 150mL of 0.1M hydrochloric acid solution, magnetically stirring at room temperature for 3h, performing suction filtration, leaching with deionized water until the pH is 6-7, drying in a 105 ℃ oven until grinding, and sieving with a 60-mesh sieve to obtain pure lignin; to 50mL of deionized water was added 0.4g of lignin and 0.108g of FeCl ₃ ·6H ₂ And O, obtaining a dispersion.

S2: putting the dispersion liquid obtained in the step S1 into a freeze dryer at the temperature of-84 ℃ for drying for 72h to obtain a freeze-dried substance I;

s3: adding 0.4g of the freeze-dried substance I and 4g of melamine into 50mL of deionized water, fully stirring to obtain a dispersion liquid, and drying the dispersion liquid in a freeze dryer at the temperature of-84 ℃ for 72 hours to obtain a freeze-dried substance II;

s4: pouring the freeze-dried substance II obtained in the step (S3) into a crucible, placing the crucible into a tube furnace, and performing reaction on the crucible in N ₂ Heating to 800 ℃ at a heating rate of 5 ℃/min under the condition that the blowing flow rate is 0.2mL/min, preserving heat for 2h for carbonization, naturally cooling to room temperature after the reaction is finished, and taking out;

s5: and pouring the carbonized lignin carbon material into 150mL of 4M sulfuric acid solution, heating and stirring at 80 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value is 6-7, and drying at 105 ℃ to constant weight to obtain the lignin carbon catalyst material with dispersed iron monoatomic atoms. That is, in comparative example 4, both drying were carried out by adding deionized water and then freeze-drying.

FIG. 3 is an XRD diffraction pattern of the catalyst prepared in accordance with the present invention, and it can be seen that the catalyst Fe obtained in example 1 ₁ -N ₁₀ -BC ₂ No peak position of nano Fe is found, which indicates that transition metal Fe atoms in the material are uniformly distributed and are in monoatomic dispersion. In contrast, in the XRD patterns of the sample 5 and the comparative sample 4, obvious iron phase peaks appear. For example, characteristic diffraction peaks at 35.6, 49.2, 53.7 and 57.2 ° with Fe ₂ O ₃ Crystal planes (JCPDS No. 33-0644) (110), (024), (116), (122) and (300) are matched, and 30.3, 43.7 and 62.7 degrees are matched with Fe ₂ O ₃ The (206), (0012) and (4012) crystal planes of (JCPDS No. 25-1402) are well matched.

FIG. 4 is an SEM image of catalysts prepared in example 1 (FIG. 4 left) and comparative example 4 (FIG. 4 left); fig. 5 is a TEM image of the catalysts prepared in example 1 (fig. 5 left) and comparative example 4 (fig. 5 left), and it can be seen that in example 1, the surface of the sample was smooth and almost no Fe particles were observed. While the surface of comparative example 4 forms some bright spot particles, the presence of nano-iron particles in the sample is clearly seen in the TEM image.

Comparative example 5

The other operations are the same as those in example 1, except that in step S5, the carbonized lignin-carbon material is repeatedly washed with deionized water until the pH is 6-7, and dried at 105 ℃ to constant weight, so as to obtain the lignin-carbon catalyst material with dispersed iron monoatomic atoms. I.e. not subjected to pickling.

Application example

The bisphenol A catalytic degradation experiments were carried out on the catalysts of the examples and comparative examples in the following specific manner: under the condition of room temperature, selecting ultrapure water to prepare 100mg/L bisphenol A stock solution, taking 5mL of the stock solution, adding ultrapure water to dilute the stock solution to 50mL, and obtaining 10mg/L bisphenol A solution. The lignin-char catalysts obtained in examples and comparative examples were added with PMS (potassium hydrogen persulfate), wherein the lignin-char catalyst concentration was 0.1g/L and PMS was 1mM. Shake the reaction for 30min in the dark. Sampling 1mL at regular intervals, adding 0.5mL of methanol for quenching, selecting a 0.22 mu m PTFE needle filter head, and detecting bisphenol A under the conditions of methanol: water =70:30, the ultraviolet detection wavelength is 278nm, the injection volume is 10 mu L, and the flow rate of the mobile phase is 1mL/min. The degradation performance of the catalyst obtained by the invention at 10min is shown in the following table 1:

TABLE 1 catalyst Properties

。

The results show that: the lignin-charcoal catalyst prepared by the modification method provided by the invention has high-efficiency bisphenol A catalytic degradation performance. In which the catalyst obtained in example 1 was Fe ₁ -N ₁₀ -BC ₂ The catalyst has the best catalytic activity, and can effectively degrade bisphenol A in a shorter time.

Application example 2

We also performed other organic matter degradation experiments on the lignin-char catalyst of the preferred embodiment 1 of the present invention, and the results are shown in fig. 6. The lignin carbon catalyst of the invention is shown to be used for treating other organic pollutants such as carbamazepine, benzotriazole, sulfamethoxazole, acyclovir and bentazone besides bisphenol A.

The effect of the presence of anions when the lignin-charcoal catalyst of the present invention degrades organic matter was also tested. Presence of anions, e.g. Cl ^-1 、HCO ₃ ^- 、SO ₄ ^2- And HA may participate in the competition of active sites on the surface of the catalyst, and influence the degradation performance of organic pollutants. The invention tests the degradation efficiency of the lignin carbon catalyst in example 1 on BPA (bisphenol A) in the presence of different anions and organic matters (the anion concentration is 5mM, and the HA concentration is 5 mg/L), and as shown in FIG. 7, it can be seen that the presence of various anions and organic matters has no influence on the catalytic activity of the lignin carbon catalyst.

Claims

1. A lignin carbon-supported Fe-N monatomic catalyst is characterized in that a carrier is obtained by carbonizing lignin at high temperature in the presence of a nitrogen source, the lignin carbon-supported Fe-N monatomic catalyst has C-N bonds of graphite-nitrogen, pyrrole-N and pyridine-nitrogen, fe is uniformly dispersed on the carrier in a monatomic form, and Fe and N form Fe-N coordination bonds.

2. The lignocellulosic carbon-supported Fe-N monatomic catalyst as claimed in claim 1, wherein the loading of monatomic iron in the catalyst is 1-3wt%.

3. The lignocellulosic carbon-supported Fe-N monatomic catalyst as claimed in claim 1, wherein the loading of monatomic iron in the catalyst is 1.53-2.87wt%.

4. The lignocellulosic carbon supported Fe-N monatomic catalyst of claim 1, wherein said lignocellulosic carbon supported Fe-N monatomic catalyst has an XPS N1s spectrum with characteristic peaks as follows: 402.4 + -0.1eV, 401.1 + -0.1eV, 399.7 + -0.1eV, 398.4 + -0.1 eV.

5. A method of preparing a lignocellulosic carbon-supported Fe-N monatin catalyst as claimed in any one of claims 1 to 4, which comprises the steps of:

(S3) dispersing the dried substance I obtained in the step (S2) and a nitrogen source in water to obtain a mixed solution, and performing freeze drying to obtain a dried substance II;

6. The method according to claim 5, wherein in the step (S1), the alcohol solvent is at least one selected from methanol and ethanol; the iron source is a water-soluble salt of ferric iron and/or a hydrate thereof; feeding 1-5mmol of iron source per g of lignin, wherein the iron source is calculated by iron.

7. The process according to claim 5, wherein in step (S3), the nitrogen source is at least one selected from dicyandiamide, urea and melamine; the mass ratio of the dried substance I to the nitrogen source is 1.

8. The method for preparing a pharmaceutical composition according to claim 5, wherein the freeze-drying in the step (S3) is carried out in a freeze-dryer at-70 to-90 ℃ for 60 to 72 hours.

9. The method according to claim 5, wherein in the step (S4), the inert atmosphere is nitrogen and/or argon; the calcination is carried out at the temperature rise rate of 5-30 ℃/min, the temperature is raised to 700-800 ℃, and the calcination is carried out for 1-2h under the condition of heat preservation; and/or

In the step (S5), the inorganic acid is at least one of 0.5-2M hydrochloric acid, sulfuric acid and nitric acid, and is heated to 60-80 ℃.

10. Use of the lignin carbon supported Fe-N monatomic catalyst according to any one of claims 1 to 4 or the lignin carbon supported Fe-N monatomic catalyst produced by the production method according to any one of claims 5 to 9 for persulfate oxidation removal of organic contaminants in water.