A nitrogen-enriched carbon hybrid with high selectivity for singlet oxygen system and its construction and application in pollutant degradation

Abstract

The application discloses construction of a high-selectivity singlet oxygen production system and application of the system in pollutant degradation. The steps are as follows: a novel three-dimensional porous carbon layer wrapped Fe2O3-Fe3C nitrogen-rich carbon hybrid is manufactured through a self-sacrifice strategy, the hybrid in-situ combines carbon-wrapped Fe2O3-Fe3C (about 17.7 nm) and has rich oxygen vacancies. The strong coupling effect between Fe2O3-Fe3C and the nitrogen-doped carbon matrix promotes PDS activation. Surface defects and interface charge transfer of the material make the electronic structure of Fe sites rearrange, weaken the positive charge of the Fe sites, and enhance the positive charge of the C-N sites, and these sites synergistically guide PDS oxidation and high-selectivity generation of 1 O2 through a non-radical pathway, thereby realizing efficient degradation of tetracycline. The system of the application improves activation of persulfate and makes it high-selectivity generate 1 O2 for efficient pollutant degradation through engineering architecture and adjustment of local electron density of multiple active sites.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of advanced oxidation Fenton-like catalytic degradation of organic pollutants, and particularly relates to a nitrogen-enriched carbon hybrid with high selectivity for generating singlet oxygen and construction and application of pollutants degradation thereof. BACKGROUND

[0002] Fenton-like oxidation is one of the most promising strategies for generating reactive oxygen species (ROS) to deal with the growing water pollution, leading to the increasing scarcity of freshwater. Fenton-like systems based on persulfate, using peroxymonosulfate (PDS, S2O8 2- ) or persulfate (PMS, HSO5 - ) as oxidant, can efficiently degrade almost all organic pollutants through sulfate radicals (SO4 ·- ), hydroxyl radicals (·OH) and singlet oxygen ( 1 O2). Compared with PMS, PDS is easier to transport and less expensive (PMS is $2.2 / kg, PDS is $0.74 / kg), which makes it a potential choice for degrading recalcitrant pollutants. However, PDS has a symmetric peroxide bond ([SO3-O-O-SO3] 2- ), which is more difficult to activate than PMS. Therefore, it is very urgent to develop advanced catalysts with excellent PDS activation function. Transition metals and their oxides have been used as heterogeneous catalysts for PDS activation. Among them, iron oxides have attracted the attention of researchers due to their low cost and low toxicity. Developing efficient iron-based catalysts is very important for PDS activation and pollutant remediation.

[0003] Although free radicals have high redox potential and extensive reactivity, they are easily, and inevitably, consumed by coexisting inorganic anions and natural organic matter, thereby hindering the degradation of target pollutants. 1 O2 as a highly selective active species has attracted extensive attention in the field of pollutant degradation. It is urgent to explore strategies and catalysts for the generation of 1 O2 with high selectivity. The adsorption structure of PDS on the surface of the catalyst can adjust the activation path of PDS. Therefore, changing the electronic structure of the metal active site through metal-support interaction is to achieve 1An effective strategy for O2 high selectivity generation. Due to the structural and chemical advantages, carbonaceous materials have been widely used in various fields. Recently, the use of nanocarbon as PDS activator or metal component carrier has attracted increasing attention. In order to change and improve the catalytic performance of nanocarbon, heteroatom doping has a unique advantage in improving catalytic activity. Among the doped atoms, N atoms are promising, which can not only achieve high loading due to similar atomic radius, but also change the local charge redistribution generated by different electronegativity. Therefore, the construction of metal oxide / N-doped carbon hybrid materials for efficient PDS activation and 1 O2 generation provides a possibility. SUMMARY

[0004] The purpose of the present application is to solve the problems of low pollutant degradation efficiency, poor stability and anti-interference of advanced oxidation materials in the prior art due to low activation of persulfate and poor selectivity. A three-dimensional nitrogen-doped carbon loaded carbon-coated Fe2O3-Fe3C nanoparticle composite (Fe2O3-Fe3C@NC) with strong interface coupling is synthesized, a high selectivity O2 generation system is constructed, and it is applied to pollutant degradation. The metal sites are wrapped by a carbon layer, effectively inhibiting metal loss and improving catalytic stability. Moreover, as an active species, singlet oxygen shows good anti-interference to inorganic anions and different water environments.

[0005] A nitrogen-rich carbon hybrid for high selectivity O2 generation system, the nitrogen-rich carbon hybrid comprises a carrier and a load carried on the carrier; the carrier comprises a three-dimensional porous nitrogen-doped carbon material; the load comprises metal nanoparticles wrapped by a carbon layer.

[0006] Preferably, the carbon-coated metal nanoparticles comprise Fe2O3-Fe3C nanoparticles.

[0007] Preferably, the particle size of the carbon-coated iron nanoparticles is 15-25 nm.

[0008] A construction method of the above-mentioned nitrogen-rich carbon hybrid for high selectivity O2 generation system, comprising the following steps:

[0009] A, immerse the chitosan aqueous solution in an acid agent for crosslinking to form a hydrogel;

[0010] B, soak the hydrogel in an iron salt solution for complexation to form a Fe-hydrogel;

[0011] C, dry the Fe-hydrogel to obtain an aerogel precursor;

[0012] D, pyrolyze the aerogel precursor to obtain the nitrogen-rich carbon hybrid.

[0013] A novel three-dimensional porous carbon layer-wrapped Fe2O3-Fe3C nitrogen-rich carbon hybrid is prepared by a self-sacrifice strategy, which in-situ combines carbon-wrapped Fe2O3-Fe3C (≈17.7 nm) and has abundant oxygen vacancies. The strong coupling effect between Fe2O3-Fe3C and the nitrogen-doped carbon matrix promotes PDS activation. Surface defects and interface charge transfer of the material cause the rearrangement of the electronic structure of Fe sites, weakening the positive charge of Fe sites and enhancing the positive charge of C-N sites, which synergistically guide PDS oxidation and selectively generate 1 O2, thereby achieving efficient degradation of tetracycline. The system of the present application improves the activation of persulfate and the high selectivity of 1 O2 for efficient pollutant degradation.

[0014] Preferably, in step A, the acid agent comprises acetic acid; in step B, the iron salt solution comprises an aqueous Fe(CH3COO)2 solution; in step C, the drying comprises low-temperature drying; and in step D, the pyrolysis comprises calcination.

[0015] Preferably, in step A, the concentration of the chitosan aqueous solution comprises 6 wt%; and in step B, the concentration of the iron salt solution comprises 0.1 M.

[0016] Preferably, in step A, the chitosan aqueous solution comprises a carboxymethyl chitosan aqueous solution; the specific operation of step C comprises: washing the Fe-hydrogel and immersing it in an alcohol agent, and then performing the drying to obtain the aerogel precursor; and the specific operation of step D comprises: placing the aerogel precursor in a calcination furnace and performing calcination pyrolysis at 850-1000°C in an inert atmosphere to obtain the nitrogen-rich carbon hybrid.

[0017] In steps A, B, and C, immersion is mainly used, and the amount of the acid agent, the iron salt solution, and the alcohol agent is not particularly limited and can be slightly excessive to accelerate the reaction rate and make the reaction more complete.

[0018] Preferably, in step A, the crosslinking time comprises 15 min; in step B, the complexing time comprises 3 h; in step C, the time for immersing the Fe-hydrogel in the alcohol agent after washing the Fe-hydrogel comprises 24 h; the drying time comprises one day; in step D, the calcination pyrolysis temperature comprises 900°C; and the calcination pyrolysis time comprises 1 h.

[0019] It is found in the experiment that carbon layer wraps Fe2O3-Fe3C nanoparticle structure when the temperature reaches 850-1000 DEG C in the calcination pyrolysis process, and the carbon layer is more uniform when the temperature is controlled at 900 DEG C, and the catalytic effect is the best.

[0020] Preferably, in step C, the Fe-hydrogel is cleaned with deionized water; the alcohol agent comprises tert-butyl alcohol; in step D, the calcination furnace comprises a tube calcination furnace; and the inert atmosphere comprises an argon atmosphere.

[0021] The application of the nitrogen-rich carbon hybrid of the above high-selectivity singlet oxygen production system to pollutant degradation.

[0022] The present application comprises the following contents:

[0023] 1. Preparation of three-dimensional nitrogen-doped carbon loaded carbon-wrapped Fe2O3-Fe3C nanoparticle composite material

[0024] Chitosan is used as a carbon and nitrogen source, and is configured into an aqueous solution with a certain concentration, and is cross-linked by itself under acidic conditions to form a hydrogel. Then the hydrogel is coordinated with Fe ions to form a metal-hydrogel complex, and is dried at low temperature to obtain a metal-chitosan aerogel. The aerogel is calcined at high temperature to obtain a three-dimensional nitrogen-doped carbon loaded carbon-wrapped Fe2O3-Fe3C nanoparticle composite material.

[0025] 2. PDS activation of the composite material and 1 detection and analysis of O2 active species.

[0026] 3. Test of pollutant degradation efficiency, stability and anti-interference ability of the composite material.

[0027] A certain amount of pollutant solution is taken in a beaker, and a catalyst and potassium peroxodisulfate (PDS) are added to test the PDS activation and pollutant degradation effect. Through capture experiments and electron paramagnetic resonance (EPR) tests 1 O2 and contribution. 1 Possible generation path of O2:

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[0033]

[0034] Compared with the prior art, implementing the present invention has the following beneficial effects:

[0035] (1) A composite catalyst was prepared by loading carbon-encapsulated Fe2O3-Fe3C nanoparticles onto a three-dimensional porous nitrogen-doped carbon material as a support. The large surface area of ​​the support can both disperse and expose active sites and act as an electron transport framework. At the same time, Fe3C can serve as PDS adsorption sites, synergistically promoting the activation efficiency of PDS on the catalyst surface. Moreover, the metal sites are encapsulated by the carbon layer, effectively inhibiting metal loss. This catalyst exhibits good PDS catalytic activity and stability.

[0036] (2) Through the interaction of the material interface, the charge density between the support and the metal active sites is rearranged, which changes the PDS activation pathway, making the reactive oxygen species generated by the activation of PDS in the composite material mainly... 1 O2 promotes efficient degradation of pollutants and exhibits strong resistance to inorganic anions and aquatic environments. Attached Figure Description

[0037] Figure 1 Here is a structural characterization diagram of the catalyst, where, Figure 1 a is the XRD pattern of Fe2O3-Fe3C@NC. Figure 1 b is a TEM image of Fe2O3-Fe3C@NC. Figure 1 c shows the N2 adsorption-desorption isotherms and pore size distribution for different samples. Figure 1 d is a graph showing the performance of Fe2O3-Fe3C@NC and CoOx-Co@NC catalysts in activating PDS to degrade tetracycline;

[0038] Figure 2 Comparison of the N1s fine XPS spectra of NC and Fe2O3-Fe3C@NC;

[0039] Figure 3 XRD pattern and TEM image of CoOx-Co@NC;

[0040] Figure 4 PDS activation and 1 Detection and analysis chart of O2 active species; among which, Figure 4 a is a comparison chart of PDS consumption for different catalysts. Figure 4 b is 1 EPR test chart for O2 Figure 4 c represents the capture experiment diagram;

[0041] Figure 5 The graphs show the pollutant degradation activity, stability, and anti-interference test results; among them, Figure 5 Figure a shows a comparative experiment using different catalysts. Figure 5 b is the cyclic stability test plot.Figure 5 c is a comparison chart of the influence of different inorganic ions, Figure 5 d is a comparison chart of the influence of different aqueous environments. DETAILED DESCRIPTION

[0042] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings.

[0043] Example 1

[0044] Step 1: Preparation of the catalyst:

[0045] a. Preparation of metal-chitosan aerogel: At room temperature, 6wt% chitosan aqueous solution (5g) was placed in a petri dish, and was immersed in acetic acid for 15min to form a hydrogel. Then it was immersed in Fe(CH3COO)2 aqueous solution (0.1M) for complexation for 3h, washed with deionized water, and soaked in t-butyl alcohol for 24h. The Fe- hydrogel was dried at low temperature for one day to obtain Fe(II)-chitosan complexation aerogel.

[0046] b. Preparation of three-dimensional nitrogen-doped carbon supported carbon-coated Fe2O3-Fe3C nanoparticle composite: The above aerogel precursor was placed in a tube furnace and calcined at 900℃ for 1h under argon atmosphere. The Fe(II)-chitosan complexation aerogel was in-situ converted into a three-dimensional nitrogen-doped carbon supported carbon-coated Fe2O3-Fe3C nanoparticle composite. The structure of the catalyst was characterized as shown in Figure 1 The XRD pattern shows that the iron species exists in the form of Fe2O3 and Fe3C, and these nanoparticles are wrapped by a carbon layer and uniformly supported in the three-dimensional network carbon material framework. Figure 1 b). Figure 1 The specific surface area of the obtained NC catalyst is 107.96m 2 / g, and after loading of the metal Fe, the specific surface area of the catalyst Fe2O3-Fe3C@NC increases to 348.11m 2 / g. The strong coupling effect of the metal oxide and the carbon substrate makes the specific surface area greatly improved. Figure 2 The XPS N 1s fine spectrum comparison chart of NC and Fe2O3-Fe3C@NC. Compared with the original NC, the binding energy of the Fe2O3-Fe3C@NC peak is obviously shifted to a higher binding energy, which indicates that Fe2O3-Fe3C causes changes in the electronic environment of the N-doped C matrix. This phenomenon also indicates that there is a strong interaction between Fe2O3-Fe3C and NC, which induces the rearrangement of electrons.

[0047] In the previous experiment, cobalt was used as the metal precursor, the calcination temperature was increased to 900℃, and other operations were unchanged. Through XRD, TEM Figure 3)The characterization found that the existence form of cobalt was CoOx and Co single element, and these nanoparticles were directly embedded in the three-dimensional carbon network, and no obvious carbon layer wrapping structure was found on the surface. Using different metal elements, the catalyst structures obtained by the same preparation method showed obvious differences. The iron-based catalyst obtained 3D nitrogen-doped carbon loaded carbon-wrapped Fe2O3-Fe3C nanoparticle composite material, and the carbon layer wrapping could effectively inhibit the metal loss, maintain the catalytic stability and be friendly to the environment. At the same time, Fe3C can be used as an adsorption site for PDS, thereby improving the activity of the catalyst. Through performance testing, it was found that the effect of the iron-based catalyst (Fe2O3-Fe3C@NC) on the activation of PDS for degrading tetracycline was better than that of the cobalt-based catalyst (CoOx-Co@NC).

[0048] Step 2: PDS activation and 1 Detection and analysis of O2active species

[0049] PDS activation detection: high concentration iodine quantity method was used to detect the concentration of PDS, and the operation was as follows: 2.5 mL of the suspension was taken at a set time interval, and the catalyst was immediately removed by filtration. 0.1 mL of the sample was mixed with NaHCO3(0.02 g), KI(0.415 g) and 4.9 mL of deionized water, and then reacted for 20 min. The residual concentration of PDS was determined at 400 nm by ultraviolet-visible spectrophotometer.

[0050] 1 O2active species capture experiment test: 0.2 g / L of catalyst and 0.2 g / L of PDS were weighed, and a 20 mg / L tetracycline (TC) solution was configured. 40 mL of 20 mg / L TC solution was taken in a 150 mL beaker, a certain concentration of capture agent was added and stirred uniformly, and then the catalyst and persulfate (PDS) were added for catalytic degradation test. 2.5 mL of the suspension was taken at a set time interval, and the catalyst was immediately removed by filtration. The residual concentration of the pollutant was determined at 357 nm by ultraviolet-visible spectrophotometer. EPR test: 2,2,6,6-tetramethyl-4-piperidinol (TEMP 100 mM) was used as the capture agent, and the test results are listed in Figure 4

[0051] Figure 4 aIn the figure, it was found that the activation performance of the Fe2O3-Fe3C@NC catalyst was higher than that of NC and pure Fe2O3-Fe3C, and it had higher PDS activation ability. Figure 4 bThe EPR test confirmed the existence of 1 O2. Figure 4 cIn the figure, methanol (MA) quenched SO4 ·- ,·OH, and p-benzoquinone (BQ) quenched O2 ·- ​, tert-butyl alcohol (TBA) quenching ·OH; L-histidine (L-his) quenching 1 O2; benzyl sulfone (PMSO) quenching high valence iron, by comparison found that the main role is 1 O2, followed by O2 ·- .

[0052] Step 3: Contaminant degradation activity, stability and anti-interference test

[0053] Performance test: weigh 0.2g / L catalyst, 0.2g / L PDS, configure 20mg / L tetracycline (TC) solution, take 40mL 20mg / L TC solution in 150mL beaker, add catalyst and potassium persulfate (PDS) at the same time for catalytic degradation test. In the set time interval, 2.5mL of suspension is taken and immediately filtered to remove the catalyst; the residual concentration of pollutants is measured at 357nm by UV-visible spectrophotometer. Test its performance;

[0054] Stability test: filter the catalyst after the reaction, while the parallel experiment supplements the catalyst, and wash several times with distilled water, then dry completely in the oven at 60℃, after 300℃ annealing for 30min, continue to carry out the next experiment, repeat four times; by digestion for ICP test, calculate the metal leaching rate of catalyst.

[0055] Anti-interference test: first dissolve different anion reagents in deionized water, mix evenly, add catalyst and PDS for catalyst degradation test; take tap water, reservoir and lake water to configure 20mg / L tetracycline solution, then add catalyst and PDS for catalytic degradation test, then the steps are the same as performance test.

[0056] The above results are listed in Figure 5 [conditions: Fe2O3-Fe3C@NC = 0.2g / L, PDS = 0.2g / L, TC = 20mg / L, pH = 6].

[0057] Figure 5 The comparative experiment of a found that PDS and Fe2O3-Fe3C alone basically have no ability to activate PDS, the performance of Fe2O3-Fe3C@NC catalyst obtained by combining the substrate NC with metal Fe is greatly improved, the degradation effect reaches 92%, which shows that Fe2O3-Fe3C@NC catalyst has good catalytic activity.

[0058] Figure 5bIt can be seen that the removal efficiency of TC by the catalyst is still 87% after 5 cycles, which indicates that Fe2O3-Fe3C@NC has excellent stability. Moreover, the metal leaching rate of the catalyst is 13% after 5 cycles, while the leaching rate of cobalt-based catalyst (CoOx-Co@NC) is as high as 79.3% after 3 cycles. The conclusion shows that the carbon layer wrapping structure can significantly inhibit the metal loss.

[0059] Figure 5 c、dIt can be seen that different anions and different water systems have little effect on the degradation of tetracycline by Fe2O3-Fe3C@NC / PDS system, wherein 1 O2plays a major role, and the free radical 1 O2is not easily affected by inorganic ions and natural organic matter, which indicates that the Fe2O3-Fe3C@NC / PDS system has strong anti-interference and wide application range.

[0060] The above only discloses the preferred embodiments of the present application, and of course cannot limit the scope of the rights of the present application, so the equivalent changes made according to the claims of the present application still belong to the scope covered by the present application.

Claims

1. A nitrogen-enriched carbon hybrid for a highly selective singlet oxygen production system, characterized in that, The nitrogen-enriched carbon hybrid includes a support and a loaded material on the support; the support includes a three-dimensional porous nitrogen-doped carbon material; the loaded material includes metal nanoparticles encapsulated by a carbon layer; the metal nanoparticles encapsulated by the carbon layer are Fe2O3-Fe3C nanoparticles. The construction of nitrogen-enriched carbon hybrids in the highly selective singlet oxygen production system includes the following steps: A. Crosslinking is achieved by immersing an aqueous solution of chitosan in an acidic agent to form a hydrogel; B. The hydrogel is immersed in an iron salt solution to form a complex, thereby forming an Fe-hydrogel; C. Dry the Fe-hydrogel to obtain an aerogel precursor; D. Pyrolyze the aerogel precursor to obtain the nitrogen-enriched carbon hybrid.

2. The nitrogen-enriched carbon hybrid of the highly selective singlet oxygen production system according to claim 1, characterized in that, The iron nanoparticles encased in the carbon layer have a particle size of 15-25 nm.

3. A method for constructing a nitrogen-enriched carbon hybrid in a highly selective singlet oxygen production system according to claim 1, characterized in that, Includes the following steps: A. Crosslinking is achieved by immersing an aqueous solution of chitosan in an acidic agent to form a hydrogel; B. The hydrogel is immersed in an iron salt solution to form a complex, thereby forming an Fe-hydrogel; C. Dry the Fe-hydrogel to obtain an aerogel precursor; D. Pyrolyze the aerogel precursor to obtain the nitrogen-enriched carbon hybrid.

4. The construction method according to claim 3, characterized in that, In step A, the acid agent includes acetic acid; in step B, the iron salt solution includes an aqueous solution of Fe(CH3COO)2; in step C, the drying includes low-temperature drying; and in step D, the pyrolysis includes calcination.

5. The construction method according to claim 3, characterized in that, In step A, the concentration of the chitosan aqueous solution is 6 wt%; in step B, the concentration of the iron salt solution is 0.1 M; in step C, the drying includes vacuum freeze drying at a temperature of -55°C.

6. The construction method according to claim 3, characterized in that, In step A, the chitosan aqueous solution includes a carboxymethyl chitosan aqueous solution; the specific operation of step C includes: washing the Fe-hydrogel, immersing it in an alcohol, and then drying it to obtain the aerogel precursor; the specific operation of step D includes: placing the aerogel precursor in a calcination furnace and calcining and pyrolyzing it at 850~1000℃ in an inert atmosphere to obtain the nitrogen-enriched carbon hybrid.

7. The construction method according to claim 6, characterized in that, In step A, the crosslinking time includes 15 min; in step B, the complexation time includes 3 h; in step C, the Fe-hydrogel is soaked in alcohol after washing for 24 h; the drying time includes one day; in step D, the calcination pyrolysis temperature includes 900 ℃; the calcination pyrolysis time includes 1 h.

8. The construction method according to claim 6, characterized in that, In step C, the Fe-hydrogel is cleaned with deionized water; the alcohol agent includes tert-butanol; in step D, the calcination furnace includes a tubular calcination furnace; the inert atmosphere includes an argon atmosphere.

9. An application of nitrogen-enriched carbon hybrids in a highly selective singlet oxygen production system according to claim 1, characterized in that, Used for pollutant degradation.

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