FeN / FeS2 double-active-site modified hydrothermal carbon and application thereof in removal of hexavalent chromium in water

Abstract

The invention relates to the technical field of solid waste recycling and adsorbent preparation, in particular to FeN / FeS2 double-active-site modified hydrothermal carbon and application of the FeN / FeS2 double-active-site modified hydrothermal carbon to removal of hexavalent chromium in water, garden waste is used as raw materials, ferric nitrate and L-cysteine are used as modifiers, three elements of iron (Fe), nitrogen (N) and sulfur (S) are synchronously introduced, and the prepared FeN / FeS2 double-active-site modified hydrothermal carbon is prepared. The modified hydrothermal carbon adsorption material with FeN / FeS2 double active sites is constructed to remove Cr (VI) in wastewater, and the theoretical equilibrium adsorption capacity of hexavalent chromium in water reaches 531.27 mg / g. The FeN / FeS2 modified hydrothermal carbon provided by the invention has the advantages of simple preparation method, wide raw material source, environmental friendliness and low price, and is suitable for industrial scale application. Meanwhile, the hydrothermal carbon can be regenerated, so that secondary pollution is effectively reduced, resource sustainable utilization is realized, the operation cost is reduced, and the method has a wide application prospect in the fields of environmental governance and resource cyclic utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and adsorbent preparation, and particularly relates to FeN / FeS2 double active site modified hydrothermal carbon and application thereof in removal of hexavalent chromium in water. BACKGROUND

[0002] In recent years, due to the rapid development of industrialization and population overpopulation, the harmful substance composition including heavy metals in the environment has increased a lot. Due to the ability of heavy metal pollution to remain, enrich and migrate, heavy metal pollution is changing from point source to large-area, watershed surface source pollution, which threatens ecological safety and human health. Among them, Cr is a common anion heavy metal, which widely exists in the environment in the form of Cr(III) with less toxicity and hexavalent chromium with greater toxicity. Hexavalent chromium has high solubility, mobility, carcinogenicity and teratogenicity, and is classified as a class A carcinogen, which is extremely harmful to the human immune system, nervous system and reproductive system.

[0003] Compared with a large amount of energy required for preparing pyrolytic carbon, hydrothermal carbon is a carbon-rich solid material produced by hydrothermal carbonization of biomass at a lower temperature and self-generated pressure in a relatively mild way, and the hydrothermal carbonization technology is also considered as a sustainable innovative technology. However, the hydrothermal carbon has defects such as small specific surface area and limited active sites, which inhibits its adsorption capacity for hexavalent chromium. Some studies use N and S co-doping to improve the adsorption performance of hydrothermal carbon, but the hexavalent chromium reduction capacity is low, and the removal process is limited at high hexavalent chromium concentration. SUMMARY

[0004] In order to overcome the technical problems pointed out in the background art, the present application uses a simple hydrothermal method to fix FeS2 in the hydrothermal carbon while maintaining and utilizing the advantage of the hydrothermal carbon having rich organic functional groups. In addition, by introducing N atoms and Fe atoms to form Fe-N active sites, a hydrothermal carbon modified with FeS2 and FeN double active sites is prepared for the removal of hexavalent chromium. The removal capacity of the hydrothermal carbon for hexavalent chromium in water is significantly improved, and the problems such as complex functional modification process, high cost and low utilization rate of garden waste resources of the existing hydrothermal carbon are solved.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows: The garden waste raw material used in the present application is mainly willow leaves, and ferric nitrate and L-cysteine are used as modifiers. The hydrothermal carbonization method is used without the need for calcination process. At the same time, FeS2 formed by Fe and S atoms in the hydrothermal process has high efficiency and stability as a functional iron-based material.

[0006] The material for preparing the FeN / FeS2 double active site modified hydrothermal carbon includes willow leaves, ferric nitrate and L-cysteine, and is prepared by the following steps: S1, the willow leaves as raw material washing, through the oven 105 DEG C drying, pulverizer crushing, then 80 mesh sieve, get raw material powder; S2, take raw material powder and a certain amount of ferric nitrate and L-cysteine in a beaker, add deionized water, use magnetic stirring dispersion. Stirring time is not less than 4h, to ensure that the ferric nitrate and L-cysteine are dispersed and absorbed by the raw material powder. Then the suspension is transferred to the hydrothermal reactor, and the hydrothermal reaction is carried out at a hydrothermal temperature of 180-240 DEG C for 6-12h. After the reaction is completed, it is naturally cooled to room temperature. After cooling, suction filtration, deionized water, anhydrous ethanol are used for washing 3 times respectively, 105 DEG C oven drying, grinding and then 100 mesh sieve, get FeN / FeS2 double active site modified hydrothermal carbon (Fe-NSHC).

[0007] Preferably, in the process of preparing FeN / FeS2 double active site modified hydrothermal carbon, the temperature of the hydrothermal carbonization reaction in S2 is 220 DEG C; the time is 8h.

[0008] In some embodiments, in the process of preparing the FeN / FeS2 double active site modified hydrothermal carbon, the solid-liquid ratio in S2 is 7-13g:60ml, for example, it can be 7g:60ml, 8g:60ml, 9g:60ml, 10g:60ml, 11g:60ml, 12g:60ml, 13g:60ml or other values in the range; the mass ratio of ferric nitrate and L-cysteine is 1-4:1-4, for example, it can be 1:2, 2:2, 3:2, 4:2, 3:1, 3:3, 3:4 or other values in the range.

[0009] Preferably, in the process of preparing the FeN / FeS2 double active site modified hydrothermal carbon, the solid-liquid ratio in S2 is 10g:60ml; the mass ratio of ferric nitrate and L-cysteine is 3:2.

[0010] Preferably, in the process of preparing the FeN / FeS2 double active site modified hydrothermal carbon, the suction filtration in S2 is vacuum suction filtration, and deionized water and anhydrous ethanol are used for washing 3-4 times during the suction filtration process; the sieving is 100 mesh sieve.

[0011] The application also provides the application of the hydrothermal carbon modified with FeS2 and FeN double active sites in removing heavy metal pollutants in water, and the FeN / FeS2 double active site modified hydrothermal carbon is used as an adsorbent to remove hexavalent chromium in water. The technical scheme is carried out according to the following steps: To further study the adsorption behavior of FeN / FeS2 double active site modified hydrothermal carbon, under the condition of initial concentration of 200 mg / L and pH of 3, the adsorption kinetics experiment was carried out with the adsorbent concentration of 0.4 g / L. The FeN / FeS2 double active site modified hydrothermal carbon with a concentration of 0.4 g / L was added to the water containing 200 mg / L of Cr(Ⅵ), and the pH of the solution was adjusted to 3 by using 0.5 M of HCl and NaOH. The solution was stirred at a speed of 160 rpm / min at room temperature (293 K). The reaction time was set to 96 h, and the solution was sampled at different times (0.25, 0.5, 1, 2, 4, 8, 12, 24, 36 h) to determine the concentration of Cr(Ⅵ) in the solution.

[0012] Preferably, the FeN / FeS2 double active site modified hydrothermal carbon has magnetic recovery performance.

[0013] Beneficial effects: The present application uses garden waste as raw material to prepare a new type of hydrothermal carbon containing FeS2 and FeN double active sites by one-step hydrothermal method to enhance the synergistic adsorption and reduction of Cr(Ⅵ).

[0014] (1) The synergistic effect of FeS2 (high reducibility) and FeN (enhanced electron conduction) breaks through the limitations of traditional doped carbon relying on adsorption or single catalytic mechanism. During the co-doping of Fe, N and S atoms, the hydrothermal carbon retains rich organic functional group structures. Unlike the direct action of N and S on the carbon skeleton, the electronegative N and S atoms have the ability to anchor Fe atoms, forming active sites mainly composed of FeN and FeS2, which improves the chemical activity of the hydrothermal carbon.

[0015] (2) Using biomass waste as raw material, it is green and sustainable, in line with the concept of resource recycling. At the same time, the material has magnetic recovery performance, reducing secondary pollution. The hydrothermal method has lower energy consumption than pyrolysis, is efficient at low temperature and can retain more surface functional groups (such as -OH, -COOH), enhancing the adsorption capacity. The process is simplified, and one-step hydrothermal synthesis avoids high-temperature pyrolysis or complex post-treatment, making it suitable for large-scale application.

[0016] (3) High Cr(Ⅵ) removal efficiency: the theoretical equilibrium adsorption capacity reaches 531.27 mg / g, which is significantly higher than that of most literature reported N / S co-doped carbon or single iron-based materials. BRIEF DESCRIPTION OF DRAWINGS

[0017] For ease of illustration, the present application is described in detail by the following specific embodiments and drawings.

[0018] Figure 1 The yield of hydrothermal carbon prepared for Example 1 to Example 13, Comparative Example 1 and Comparative Example 2 and its adsorption capacity for Cr(Ⅵ) in water with a concentration of 200 mg / L are shown in the figure.

[0019] Figure 2 The present invention provides a graph showing the number of cycles of regeneration of FeN / FeS2 dual-active-site modified hydrothermal carbon prepared in Example 9 and its removal rate of hexavalent chromium in water.

[0020] Figure 3 The FeN / FeS2 dual-active-site modified hydrothermal carbon prepared in Example 9 of this invention (Figure c), and the NS2HC prepared in Comparative Example 1 8-220 (Figure a) and Fe3HC prepared in Comparative Example 2 8-220 (Figure b) SEM image.

[0021] Figure 4 The FeN / FeS2 dual-active-site modified hydrothermal carbon prepared in Example 9 of this invention and the NS2HC prepared in Comparative Example 1 are examples of the present invention. 8-220 Fe3HC prepared in Comparative Example 2 8-220 XRD pattern.

[0022] Figure 5 The FeN / FeS2 dual-active-site modified hydrothermal carbon prepared in Example 9 of this invention and the NS2HC prepared in Comparative Example 1 are examples of the present invention. 8-220 Fe3HC prepared in Comparative Example 2 8-220 FTIR plot.

[0023] Figure 6 This is a technical roadmap for the FeN / FeS2 dual-active-site modified hydrothermal carbon prepared according to the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. In this invention, willow leaves are used as raw material, washed, dried in an oven at 105°C, pulverized, and then sieved through an 80-mesh sieve to obtain raw material powder. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. All raw materials and reagents used without specified manufacturers are commercially available conventional products.

[0025] Example 1: 5 g of raw material powder, 1 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 6 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe1-NS2HC 6-180 .

[0026] Example 2: 5 g of raw material powder, 2 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 6 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe2-NS2HC 6-180 .

[0027] Example 3: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 6 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe3-NS2HC 6-180 .

[0028] Example 4: 5 g of raw material powder, 4 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 6 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe4-NS2HC 6-180 .

[0029] Example 5: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named Fe3-NS2HC 8-180 .

[0030] Example 6: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 10 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named Fe3-NS2HC 10-180 .

[0031] Example 7: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 180°C for 12 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named Fe3-NS2HC 12-180 .

[0032] Example 8: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 200°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named Fe3-NS2HC 8-200 .

[0033] Example 9: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 220°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe3-NS2HC 8-220 .

[0034] Example 10: 5 g of raw material powder, 3 g of ferric nitrate, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 240°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe3-NS2HC 8-240 .

[0035] Example 11: 5 g of raw material powder, 3 g of ferric nitrate, 1 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 220°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe3-NS1HC 8-220 .

[0036] Example 12: 5 g of raw material powder, 3 g of ferric nitrate, 3 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 220°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, washed with deionized water, anhydrous ethanol each 3 times, placed in an oven with a temperature of 105°C for drying 12 h, after constant weight, ground through a 100 mesh sieve, the black powder obtained is the modified hydrothermal carbon, named as Fe3-NS3HC 8-220 .

[0037] Example 13: 5 g of raw material powder, 3 g of ferric nitrate, 4 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 220°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, and then washed with deionized water, anhydrous ethanol each for 3 times, placed in a drying oven with a temperature of 105°C for drying for 12 h, after constant weight, the black powder obtained after grinding through a 100 mesh sieve was the modified hydrothermal carbon, named Fe3-NS4HC 8-220 .

[0038] Comparative Example 1: 5 g of raw material powder, 2 g of L-cysteine were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 220°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, and then washed with deionized water, anhydrous ethanol each for 3 times, placed in a drying oven with a temperature of 105°C for drying for 12 h, after constant weight, the black powder obtained after grinding through a 100 mesh sieve was the modified hydrothermal carbon, named NS2HC 8-220 .

[0039] Comparative Example 2: 5 g of raw material powder, 3 g of ferric nitrate were mixed with 60 ml of deionized water, and after stirring for 4 h, a uniformly mixed solution was obtained; the uniformly mixed solution was transferred to a hydrothermal reaction kettle, and hydrothermal carbonization was carried out at 220°C for 8 h, after the reaction was completed, it was naturally cooled to room temperature, suction filtration, and then washed with deionized water, anhydrous ethanol each for 3 times, placed in a drying oven with a temperature of 105°C for drying for 12 h, after constant weight, the black powder obtained after grinding through a 100 mesh sieve was the modified hydrothermal carbon, named Fe3HC 8-220 .

[0040] Experimental Example

[0041] In order to further study the adsorption behavior of FeN / FeS2 double active site modified hydrothermal carbon, the adsorption kinetics experiment was carried out under the condition of initial concentration of 200 mg / L and pH of 3 with the adsorbent concentration of 0.4 g / L. 0.4 g / L of FeN / FeS2 double active site modified hydrothermal carbon (prepared by using Example 1~Example 13, Comparative Example 1, Comparative Example 2) was added to the water with the concentration of 200 mg / L of hexavalent chromium, and the pH of the solution was adjusted to 3 by using 0.5 M of HCl and NaOH, and the solution was stirred at a speed of 160 rpm / min at room temperature (293 K). The reaction time was set to 96 h, and the solution was sampled at different times (0.25, 0.5, 1, 2, 4, 8, 12, 24, 36 h) to determine the concentration of hexavalent chromium in the solution.

[0042] Preferably, Fe3-NS2HC 8-220The theoretical equilibrium adsorption capacity at pH = 3 can reach 531.27 mg / g, and it has a good removal effect on hexavalent chromium. Fe3-NS2HC 8-220 The correlation coefficient R 2 (R 2 = 0.94) of pseudo-second-order kinetics is more significant than the correlation coefficient R 2 (R 2 = 0.90) of pseudo-first-order kinetics, indicating that chemical adsorption dominated by valence force and electron transfer are the main factors affecting the removal efficiency of Fe3-NS2HC 8-220 on hexavalent chromium.

[0043] Table 1 Kinetic model parameters of Fe3-NS2HC 8-220 for removing hexavalent chromium in water

[0044] The specific surface area and pore structure distribution results of the FeN / FeS2 bireactive site modified hydrothermal carbon prepared in Example 9 and the hydrothermal carbon prepared in Comparative Example 1 and Comparative Example 2 are shown in Table 1.

[0045] Table 2 Specific surface area and pore structure distribution of samples before and after modification

[0046] Table 3 Element content of samples before and after modification

[0047] Regarding the preparation conditions of Fe3-NS2HC 8-220 , it can be seen in the examples that the use of 3 g of Fe(NO3)3·9H2O has the best hexavalent chromium removal performance. This is because during the hydrothermal carbonization process, when the content of Fe is too high, L-cysteine cannot completely convert the excess gray iron ore into pyrite. However, when the amount of Fe added is reduced, the excess L-cysteine will inhibit the growth of pyrite crystals.

[0048] Synthesis temperature is another key factor in the hydrothermal carbonization process, and the results show that when the hydrothermal temperature is 240°C, the material has the best hexavalent chromium removal performance. At this time, the hydrothermal temperature greatly promotes the hydrolysis process of biomass, which is beneficial to the rapid degradation and depolymerization of polymers, thereby providing higher activity for the hydrothermal carbon, which is most conducive to improving the adsorption and reduction capacity of Fe3-NS2HC 8-220 .

[0049] The crystal structures of NS2HC 8-220 , Fe3HC 8-220 and Fe3-NS2HC 8-220 were determined by XRD, and the results showed that NS2HC 8-220The structure similar to cellulose was reserved, and the diffraction peaks of Fe3O4 appeared in Fe3HC 8-220 . However, Fe3O4 was not detected in Fe3-NS2HC 8-220 , which indicated that the introduction of N and S atoms during hydrothermal carbonization changed the structure of the material. The NH3 released by L-cysteine during hydrothermal carbonization promoted the formation of FeN, and S atoms anchored Fe atoms to form FeS2 with a higher reduction potential.

[0050] FT-IR spectra revealed the differences between the main functional groups of NS2HC 8-220 , Fe3HC 8-220 , and Fe3-NS2HC 8-220 . Among them, NS2HC 8-220 had many organic functional groups on the surface, including C-H bonds, C=C / C=O bonds, C-N bonds, S=O=S bonds, and S-O bonds, due to the presence of N and S atoms. In addition, Fe-O oscillation peaks were observed in the spectrum of Fe3HC 8-220 , indicating the presence of Fe3O4 in FeHC. Compared with NS2HC 8-220 and Fe3HC 8-220 , the peak at 1120 cm 8-220 in the spectrum of Fe3-NS2HC -1 was related to the Fe=S bond in FeS2, which was consistent with the XRD spectrum results. In addition, no S-containing functional groups were observed in the spectrum of Fe3-NS2HC 8-220 , which indicated that S atoms formed coordination bonds with Fe atoms, rather than being introduced into the carbon skeleton in a simple atomic doping manner to break down oxygen-containing functional groups.

[0051] The above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto. The technical solutions described in the foregoing embodiments can still be modified.

Claims

1. A FeN / FeS2 bi-active site modified hydrothermal carbon, characterized in that, The double active site modified hydrothermal carbon is a FeN / FeS2 double active site modified hydrothermal carbon prepared by taking garden waste as raw material and taking iron nitrate and L-cysteine as modifiers through a hydrothermal carbonization reaction.

2. The FeN / FeS2 bi-active site modified hydrothermal carbon according to claim 1, characterized in that, The preparation method of the FeN / FeS2 double active site modified hydrothermal carbon is as follows: the garden waste after washing, drying, crushing, and sieving is uniformly mixed with iron nitrate and L-cysteine, and then deionized water is added and stirred to obtain a mixed solution; the mixed solution is subjected to a hydrothermal carbonization reaction, and then the FeN / FeS2 double active site modified hydrothermal carbon is obtained after cooling, suction filtration, washing, drying, grinding, and sieving.

3. The FeN / FeS2 bi-active site modified hydrothermal carbon according to claim 2, characterized in that, In the preparation process, the solid-liquid ratio of the reaction is 7-13 g:60 ml, and the mass ratio of iron nitrate to L-cysteine is 1-4:1-4.

4. The FeN / FeS2 bi-active site modified hydrothermal carbon of claim 2, wherein, The temperature of the hydrothermal carbonization reaction is 180-240 DEG C, and the time is 6-12; the suction filtration is vacuum suction filtration, and the mixed solution is washed with deionized water and anhydrous ethanol for 3-4 times during the suction filtration; the sieving is sieving through a 100-mesh sieve.

5. The use of the FeN / FeS2 bi-active site modified hydrothermal carbon according to claim 1, characterized in that, The double active site modified hydrothermal carbon is used for removing heavy metal pollutants in water.

6. The use of the FeN / FeS2 bi-active site modified hydrothermal carbon according to claim 5, characterized in that, The method for removing hexavalent chromium in water by using the double active site modified hydrothermal carbon as an adsorbent is as follows: the modified hydrothermal carbon with a concentration of 0.4 g / L is added into water with a hexavalent chromium concentration of 200 mg / L, the pH of the solution is adjusted to 3 by using 0.5 M HCl and NaOH, the solution is stirred at a speed of 160 rpm / min at room temperature, and the reaction is performed for 96 h.

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