阅读说明：本技术 一种氮、氧、硫共掺杂生物质炭材料及制备方法及应用 (Nitrogen, oxygen and sulfur co-doped biomass charcoal material, and preparation method and application thereof ) 是由 高雯然 张书 林子翔 徐德良 丁宽 张红 于 2021-08-31 设计创作，主要内容包括：本发明提供了一种氮、氧、硫共掺杂生物质炭材料及制备方法及应用,该方法以杨木碎屑和脲醛树脂制备含氮、氧、硫共掺杂生物质炭材料。本发明采用一步法将炭前体杨木和脲醛树脂在氮气保护下进行高温热解,使得氮、氧、硫掺杂剂参与制孔过程,提高了生物质炭的比表面积和孔体积,进而提高了氮、氧、硫共掺杂生物质炭材料的吸附性能。(The invention provides a nitrogen, oxygen and sulfur co-doped biomass carbon material, and a preparation method and application thereof. According to the invention, the carbon precursor poplar and urea-formaldehyde resin are subjected to high-temperature pyrolysis under the protection of nitrogen by adopting a one-step method, so that the nitrogen, oxygen and sulfur doping agents participate in the hole making process, the specific surface area and the pore volume of the biomass carbon are improved, and the adsorption performance of the nitrogen, oxygen and sulfur co-doped biomass carbon material is further improved.)

1. A preparation method of a nitrogen, oxygen and sulfur co-doped biomass charcoal material is characterized by comprising the following steps:

(1) smashing poplar wood chips, sieving the smashed poplar wood chips by 150-250 microns, and grinding urea-formaldehyde resin into powder for later use;

(2) weighing poplar chips, adding urea-formaldehyde resin powder, uniformly mixing, placing in a tubular furnace, setting the heating speed under the protection of nitrogen, heating to 900 ℃, and preserving heat for 1 h;

(3) and (3) taking out the mixture prepared in the step (2), cooling to room temperature, washing with 0.2M hydrochloric acid, washing with deionized water until the filtrate is neutral, and drying the mixture in an oven at 80 ℃ to obtain the nitrogen, oxygen and sulfur co-doped biomass carbon material.

2. The preparation method of the nitrogen, oxygen and sulfur co-doped biomass charcoal material according to claim 1, wherein the mass ratio of the poplar chips to the urea-formaldehyde resin in the step (2) is 1-9: 1.

3. The preparation method of nitrogen, oxygen and sulfur co-doped biomass charcoal material according to claim 1, wherein the temperature rise rate in the step (2) is 10 ℃/min.

4. The preparation method of nitrogen, oxygen and sulfur co-doped biomass charcoal material according to claim 1, wherein the flow rate of the nitrogen in the step (2) is 0.6L/min.

5. The nitrogen, oxygen and sulfur co-doped biomass charcoal material prepared by the preparation method of the nitrogen, oxygen and sulfur co-doped biomass charcoal material according to any one of claims 1 to 4.

6. An application of a nitrogen, oxygen and sulfur co-doped biomass charcoal material in adsorption of tetracycline in water.

Technical Field

The invention belongs to the technical field of preparation of environment application type materials, and particularly relates to a nitrogen, oxygen and sulfur co-doped biomass charcoal material, and a preparation method and application thereof.

Background

Water pollution caused by antibiotics is increasingly harmful to humans and aquatic organisms. Tetracycline (Tetracycline) is a typical tetraphenyl-structured broad-spectrum antibiotic, widely used due to its low price and effective medical use, and is the antibiotic with the largest amount in the world. Tetracycline is relatively inefficient in its metabolism and is mostly excreted into the environment through the feces and urine. Tetracycline is reported to be present in a wide range of water bodies such as surface water, groundwater, and drinking water. To mitigate the contamination caused by tetracycline, appropriate scalable processing techniques are needed. Recent researches show that technologies such as biological digestion, electrochemical oxidation, membrane filtration, chlorination, ultrasonic cavitation, adsorption and the like can treat tetracycline polluted water. The adsorption method has the outstanding characteristics of high cost performance, simple operation, high removal rate, no secondary pollution and the like. Compared with carbon-based adsorbents such as activated carbon and carbon nanotubes, biochar prepared by biomass pyrolysis has attracted much attention because of its environmental protection, low cost, and various structures (such as porous structure, aromatic structure, rich functional groups, etc.).

Biochar is chemically highly aromatic and contains randomly stacked graphitic layers, generally evaluated with an elemental concentration of C, H, O, N and ratios of H/C and O/C, and determines the degree of aromatisation and maturation. The surface chemistry of biochar is very diverse, where hydrophilicity, hydrophobicity and acid-base determine the action activity of the biochar, which properties are influenced by the biomass feedstock, the pyrolysis process and the various functional groups, charges and pi-electrons on the surface of the biochar. The structure of the biochar is formed by irregularly stacking highly twisted aromatic rings, and the biochar is strong in stability and has decomposition resistance. However, a large amount of tar-like substances and amorphous carbon are generated in the carbonization process, and the formed pore structure is blocked, so that the specific surface area is greatly reduced, and the requirement of large-capacity adsorption on the pore structure cannot be met, so that the activation medium is required to be used for activating the biochar. Secondly, the biochar has the defects of low hydrophilicity, few surface active sites and the like, so that the applicability of the biochar is reduced, and the contribution of O, N, S co-doped biochar to tetracycline adsorption is not clear at present.

Disclosure of Invention

The invention mainly aims to overcome the defects in the prior art and provide a nitrogen, oxygen and sulfur co-doped biomass charcoal material, a preparation method and application thereof.

The invention provides a preparation method of a nitrogen, oxygen and sulfur co-doped biomass charcoal material, which comprises the following steps:

(1) smashing poplar wood chips, sieving the smashed poplar wood chips by 150-250 microns, and grinding urea-formaldehyde resin into powder for later use;

(2) weighing poplar chips, adding urea-formaldehyde resin powder, uniformly mixing, placing in a tubular furnace, setting the heating speed under the protection of nitrogen, heating to 900 ℃, and preserving heat for 1 h;

(3) and (3) taking out the mixture prepared in the step (2), cooling to room temperature, washing with 0.2M hydrochloric acid, washing with deionized water until the filtrate is neutral, and drying the mixture in an oven at 80 ℃ to obtain the nitrogen, oxygen and sulfur co-doped biomass carbon material.

Preferably, the mass ratio of the poplar chips to the urea-formaldehyde resin in the step (2) is 1-9: 1.

Preferably, the temperature increase rate in the step (2) is 10 ℃/min.

Preferably, the flow rate of the nitrogen gas in the step (2) is 0.6L/min.

The invention also provides the nitrogen, oxygen and sulfur co-doped biomass charcoal material prepared by the preparation method of the nitrogen, oxygen and sulfur co-doped biomass charcoal material.

The invention also provides application of the nitrogen, oxygen and sulfur co-doped biomass carbon material in adsorption of tetracycline in water.

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

1. according to the invention, the carbon precursor poplar and urea-formaldehyde resin are subjected to high-temperature pyrolysis under the protection of nitrogen by adopting a one-step method, so that the nitrogen, oxygen and sulfur dopants participate in the pore-making process, the specific surface area and pore volume of the biomass carbon are improved, and the adsorption performance of the nitrogen, oxygen and sulfur co-doped biomass carbon material is further improved;

2. the method has the advantages of simple process, short flow, improved preparation efficiency, low requirement on equipment and easy realization;

3. the nitrogen, oxygen and sulfur co-doped biomass carbon material has rich nitrogen, oxygen and sulfur functional groups, nitrogen elements in the carbon material mainly exist in the forms of pyridine nitrogen, pyrrole nitrogen and graphite nitrogen, and simultaneously contain a certain amount of sulfur functional groups and oxygen functional groups, and the nitrogen group and the hydrogen acceptor are used for providing the adsorption performance of tetracycline, so that the carbon material has the advantages of high adsorption capacity, high adsorption rate, strong stability and great superiority.

The foregoing is only an overview of the technical solutions of the present invention, and in order to more clearly understand the technical solutions of the present invention, the present invention is further described below with reference to the accompanying drawings.

Drawings

FIG. 1 is a flow chart of a preparation process of a nitrogen, oxygen and sulfur co-doped biomass charcoal material of the invention;

FIG. 2 is a scanning electron microscope image of the nitrogen, oxygen and sulfur co-doped biomass charcoal material prepared in example 3;

FIG. 3 shows N of nitrogen, oxygen and sulfur co-doped biomass charcoal material prepared in example 3₂Adsorption-desorption isotherm diagram;

FIG. 4 comparison of N of undoped Biomass charcoal material prepared in comparative example 2₂Adsorption-desorption isotherm diagram;

FIG. 5 is a graph showing the influence of adsorption performance of biomass charcoal materials prepared in examples 1 to 3 of the present invention and comparative examples 1 to 2.

Detailed Description

In order to understand the present invention, the following examples are given to further illustrate the present invention.

Example 1

The invention provides a preparation method of a nitrogen, oxygen and sulfur co-doped biomass charcoal material, which comprises the following steps:

(1) smashing poplar wood chips, sieving the smashed poplar wood chips by 150-250 microns, and grinding urea-formaldehyde resin into powder for later use;

(2) weighing 13.5g of poplar chips, adding 1.5g of urea-formaldehyde resin powder, uniformly mixing, placing in a tubular furnace, setting the flow rate of nitrogen at 0.6L/min and the heating rate at 10 ℃/min, heating to 900 ℃, and preserving heat for 1 h;

(3) and (3) taking out the mixture prepared in the step (2), cooling to room temperature, washing with 0.2M hydrochloric acid, washing with deionized water until the filtrate is neutral, and drying the mixture in an oven at 80 ℃ to obtain the nitrogen, oxygen and sulfur co-doped biomass carbon material, wherein the label is PUF-10%.

Example 2

The method is the same as example 1, except that 10.5g of poplar chips and 4.5g of urea-formaldehyde resin powder are weighed to obtain the nitrogen, oxygen and sulfur co-doped biomass carbon material which is marked as PUF-30%.

Example 3

The method is the same as example 1, except that 7.5g of poplar chips and 7.5g of urea-formaldehyde resin powder are weighed to obtain the nitrogen, oxygen and sulfur co-doped biomass carbon material which is marked as PUF-50%.

Comparative example 1

In order to further study the contribution of nitrogen-containing functional groups, a biomass charcoal material using poplar and urea as raw materials was prepared, the method was the same as example 1 except that 13.5g of poplar chips and 1.5g of urea were weighed to obtain a nitrogen-doped biomass charcoal material, which was labeled as PU-10%.

Comparative example 2

The method is the same as example 1 except that 15g of poplar chips were weighed to obtain an undoped biomass charcoal material, which was marked as PBC.

The biomass charcoal materials obtained in examples 1 to 3, comparative example 1 and comparative example 2 were tested by a fully automatic specific surface area and micropore analyzer (BSD-PM4) to obtain a pore structure, and the results are shown in table 1:

TABLE 1

As can be seen from Table 1, the biomass charcoal material has a specific surface area when 10% urea-formaldehyde resin or 10% urea is addedThe product is reduced from 477.1m²The/g is reduced to 431.4m²G and 459.8m²Per g, possibly due to the introduction of nitrogen or sulfur atoms into the biochar framework, may cause collapse of the micropores, which also results in a reduction in the total pore volume. When the doping ratio of the urea resin is increased to 30% and 50%, the specific surface area and the pore volume are increased. This is probably due to the pore-forming effect of urea formaldehyde on biochar, since its pyrolysis products are mainly isocyanates and NH₃And the nitrogen-containing compound can be used as an activating agent in the pyrolysis process so as to realize pore-forming of the biomass carbon material.

The results of the elemental analysis of the biomass charcoal materials obtained in examples 1 to 3, comparative example 1 and comparative example 2 are shown in Table 2:

TABLE 2

As can be seen from table 2, as the doping ratio of the urea-formaldehyde resin increases, the carbon content of the biomass charcoal material decreases from 97.65% to 83.24%, the oxygen content gradually increases from 1.09% to 5.56%, and the sulfur is successfully doped, and the content thereof significantly increases from 0.01% to 4.98%, respectively. The nitrogen content in the biochar carbon material is also greatly increased from 0.26% to 4.92%, which indicates that nitrogen is successfully doped into the biochar.

The biomass charcoal materials obtained in examples 1 to 3, comparative example 1 and comparative example 2 were analyzed by XPS for the elemental composition, oxygen-containing functional group, nitrogen-containing functional group and sulfur-containing functional group on the product surface, as shown in table 3:

TABLE 3

As can be seen from Table 3, C1s, O1s, N1s andthe C content of 4 main peaks of S2p decreased with increasing doping ratio, and N, O, S content increased, which is consistent with the rules of elemental analysis. In the PUF-50% with the highest nitrogen doping proportion, the contents of N and S atoms are the highest and can reach 3.3% and 1.3% respectively. The peak fit data for C1S, O1S, N1S are shown in Table 3, with N1S for PBC, and S2p for PU-10% not analyzed because the corresponding amounts were lower than the values detected. The high-resolution S2p peak of the biochar can obtain three peaks of sulfur oxide species (168.5eV, -C-SO 4-C-or-C-SO 3) and S2p_1/2(165.2eV) and S2p_3/2(164.0 eV). As the doping ratio increases, the content of oxidized S increases as the urea formaldehyde ratio increases. This is probably due to the higher doping ratio resulting in an enhanced reaction between sulphur-containing groups and oxygen-containing groups on the biochar surface. The N1s peak of the biomass charcoal material can be divided into four peaks corresponding to pyridine N (N-6), pyrrole N (N-5), graphite N and nitrogen oxide (N-O). The relative content of N-5 decreases significantly as the doping ratio increases, while the relative content of N-6, N-Q and N-O increases significantly. As mentioned above, this may be due to the enhanced reaction between nitrogen-containing and oxygen-containing groups on the surface of the biochar that is led by the doping with more nitrogen. It is reported that the introduction of nitrogen-and sulfur-containing functional groups can reduce the electronegativity of the carbon layer to improve its adsorption capacity by increasing the ability to accept pi electrons, and further by pi-pi interaction with TC molecules and lewis acid-base interaction.

As shown in fig. 2, the nitrogen, oxygen and sulfur co-doped biomass charcoal material prepared in example 3 has very dense pores, quite abundant pore structure and obvious pore structure on the surface.

As can be seen from FIG. 3, N of the nitrogen, oxygen and sulfur co-doped biomass charcoal material₂The adsorption-desorption isotherm diagram is obvious I-type curve adsorption, the adsorption capacity is increased sharply in a relatively low pressure region (P/P0 is 0-0.1), the gas adsorption capacity of the nitrogen, oxygen and sulfur co-doped biomass carbon material is increased linearly and reaches a higher adsorption platform, the adsorption effect of a large number of microporous structures in the nitrogen, oxygen and sulfur co-doped biomass carbon material is illustrated, and the nitrogen, oxygen and sulfur co-doped biomass carbon material is under the relatively high pressure region (P/P0 is 0.02-0.99)The adsorption amount of the gas is still increased but the acceleration rate is slower, and a remarkable hysteresis loop appears, and the hysteresis loop is usually generated by a stacked layered structure, which indicates that the nitrogen, oxygen and sulfur co-doped biomass carbon material has a large amount of micropores and a small amount of mesopores.

As can be seen from FIG. 4, N of the undoped biomass charcoal material₂The adsorption-desorption isotherm diagram is obvious I-shaped curve adsorption, which shows that micropores exist in the poplar-based biomass charcoal material; meanwhile, the adsorption capacity is increased sharply in a relatively low pressure area (P/P0 is 0-0.1), the gas adsorption capacity of the undoped biomass charcoal material is increased linearly and reaches a higher adsorption platform, which shows that the poplar-based biomass charcoal material has adsorption of a large number of microporous structures, and the gas adsorption capacity of the poplar-based biomass charcoal material is still increased but is accelerated slowly in a relatively high pressure area (P/P0 is 0.02-0.99), which shows that the poplar-based biomass charcoal material only has micropores.

Example 5

The biomass charcoal materials obtained in examples 1-3, comparative example 1 and comparative example 2 are added into an aqueous solution containing tetracycline for oscillation adsorption, and the adsorption capacity of the biomass charcoal materials on the tetracycline is tested, and the method specifically comprises the following steps:

(1) preparing a tetracycline solution: weighing 40mg of tetracycline sample, adding deionized water to a constant volume of 1L, and preparing a tetracycline solution with the concentration of 40 mg/L;

(2) respectively taking 100mg of the biomass charcoal materials obtained in the examples 1-3, the comparison example 1 and the comparison example 2, respectively placing the biomass charcoal materials in 100ml of tetracycline solution, oscillating at the constant temperature of 150r/min at 27 ℃, filtering the mixed solution through a 0.22 mu m filter head to obtain filtrate, measuring the concentration of tetracycline in the filtrate at 360nm by adopting an ultraviolet spectrophotometer, and further calculating the adsorption capacity Q_t(mg/g) in terms of adsorption capacity Q_t(mg/g) is plotted on the ordinate, and the results are shown in FIG. 5.

Wherein, η removal efficiency, C₀And C_eInitial concentration of tetracycline (mg/L) and averageAnd (5) balancing the concentration.

Adsorption capacity q_eCalculated according to the following formula:

wherein, C₀And C_eIs the initial and equilibrium concentration of tetracycline (mg/L), V is the volume of tetracycline solution (L), m is the weight of biochar (g), and q_eAs the adsorption capacity (mg/g).

As can be seen from FIG. 5, the removal efficiency of the nitrogen, oxygen and sulfur co-doped biomass charcoal material is higher than that of PBC (29.45%), wherein the PUF-50% removal efficiency is the highest and is 71.84%.

Based on the above discussion of the characterization of the biochar sample, there are three reasons for the improved adsorption performance: 1) the BET surface area is increased, providing more adsorption sites; 2) the content of O is increased, more oxygen functional groups are provided, and the tetracycline molecules can interact through hydrogen bonds; 3) nitrogen or functional groups are introduced to enhance pi-pi interaction and lewis acid-base interaction. Whereas the PUF-10% has a BET surface area of 459.8m²Slightly lower than PBC (477.1 m)/g²G) while the PUF-10% (31.0%) removal efficiency is slightly higher than PBC (29.5%). This indicates that higher levels of O, N and/or S are the primary reason for the improved adsorption efficiency.

As can be seen from FIG. 5, the BET surface area and S content (431 m) of PU-10%²Per g and 0.53%), high oxygen, nitrogen content (3.99% and 2.45%). But PU-10% (41.7%) has a much higher removal efficiency than PUF-10%. This indicates that the incorporation of N and O into the biochar is more important than the doping of the sulfur functionality.

It is currently known that adsorption occurs on the surface of biochar, and it is therefore necessary to analyze the elemental composition and functional groups of the biochar surface. As can be seen from Table 2, the surface O, N, S content was slightly higher for PUF-10% than for PU-10% and the surface S content was lower. This also means that oxygen and nitrogen containing functional groups play a dominant role in tetracycline adsorption of biochar compared to sulfur containing functional groups. However, this does not explain that PUF-50% has a better adsorption performance than PUF-30%. Thus, we analyzed the composition of different types of nitrogen-containing functional groups. As can be seen from Table 3, the proportion of N-5 and N-6 in PUF-30% is higher than that of PUF-50%, while the proportion of N-Q and N-O is lower. The N-Q and N-O content of PU-10% is higher than that of PUF-10%. This shows that N-Q and N-O play an important role in tetracycline adsorption of nitrogen-doped biochar among the four nitrogen-containing functional groups, so that the adsorption efficiency of PUF-50% is higher than that of PUF-30%. It is reasonable to consider the structure of N-Q, where the N atom is located in the middle of three aromatic rings, resulting in a decrease in the electronegativity of the C layer, increasing the ability to accept pi electrons. Therefore, as mentioned above, the biological carbon and the tetracycline molecules have pi-pi interaction and Lewis acid-base interaction in the adsorption process, thereby improving the adsorption capacity. And N-O can enhance the interaction between the tetracycline and the biochar through hydrogen bonds. This study shows that the mixed doping is successfully enriched with O-N, O-S functional groups and N-Q groups, which are responsible for the improved adsorption performance. In conclusion, the research proposes that the nitrogen, oxygen and sulfur co-doped biomass carbon material is utilized to remove the antibiotics in the aqueous solution, a new method is provided for the synergistic effect of mixed doping, and the performance of the material is greatly improved compared with the performance of the conventional common poplar-based carbon material.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.