Multifunctional catalyst based on space confinement effect as well as preparation method and application of multifunctional catalyst

Abstract

The invention discloses a multifunctional catalyst based on a space confinement effect as well as a preparation method and application thereof, and belongs to the technical field of water treatment. The multifunctional catalyst comprises a modified carbon nano tube, iron and variable valence metal, the modified carbon nano tube is prepared by carrying out ball milling treatment on a carbon nano tube and adding an oxidizing agent for oxidation; the molar ratio of iron to variable valence metal ions is 4: (1-4); the sum of the loading capacities of the iron and the variable-valence metal is 1-12wt.%. The catalyst is simple in preparation method and low in cost, can be used as a catalyst in heterogeneous Fenton and electro-Fenton reactions, and has the advantages of high catalytic efficiency, good stability, less active component dissolution and high application value.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a multifunctional catalyst based on spatial confinement effect, a preparation method and application thereof. Background Art

[0002] The acceleration of the global industrialization process has led to the generation of a large amount of industrial wastewater. A wide variety of difficult-to-biodegrade organic matter is the main pollutant in industrial wastewater, and its large presence is one of the uncontrollable factors leading to safe water supply. Therefore, the efficient degradation and treatment of organic matter in industrial wastewater is of great significance.

[0003] The essence of Fenton oxidation technology is the chain reaction between divalent iron ions and hydrogen peroxide to generate hydroxyl radicals. Hydroxyl radicals have strong oxidizing ability, and their oxidation potential is second only to fluorine, up to 2.80V. In addition, hydroxyl radicals have high electronegativity or electrophilicity, and their electron affinity is as high as 569.3kJ. They have strong addition reaction characteristics. Therefore, Fenton reagent can non-selectively oxidize most organic matter in water, and is particularly suitable for the oxidation treatment of organic wastewater that is difficult to biodegrade or difficult to be oxidized by general chemical oxidation. However, a large amount of iron mud after the reaction is a hazardous solid waste, which leads to secondary pollution and additional disposal costs, which greatly limits the application of Fenton oxidation. Therefore, the heterogeneous Fenton oxidation technology based on heterogeneous Fenton catalysts can circumvent the above shortcomings in principle, but the actual application faces certain challenges, and there are not many successful applications in the industry. The core problem is the activity and stability of the catalyst, especially the difficulty of taking both into account.

[0004] In practical applications, the leaching of metal ions is the main reason for the decrease in stability of heterogeneous Fenton catalysts. The leaching of metal ions not only reduces the activity of the catalyst, but also produces a certain degree of secondary pollution. However, the activity of the catalyst is often positively correlated with the amount of metal ion leaching. Therefore, inhibiting leaching and improving the stability of heterogeneous Fenton catalysts, while minimizing the inhibitory effect on the active sites of the catalyst, and seeking the best balance between activity and stability are important research directions in this field.

[0005] Chinese patent CN117205925A discloses a method for preparing a confined catalyst and its application in water treatment, wherein the preparation method first modifies multi-walled carbon nanotubes with acid and then loads transition metals, then ultrasonicates and dries. The catalyst can quickly and efficiently catalyze and activate oxidants such as peracetic acid, persulfate, periodate, and hydrogen peroxide to produce active components such as free radicals and singlet oxygen, thereby achieving selective degradation of organic pollutants in water and killing pathogens in water. However, it does not study catalyst stability and cycle performance.

[0006] Chinese patent CN111807350A discloses a method for preparing short carbon nanotubes with open ends, wherein the preparation method comprises using a mixed solution of concentrated nitric acid and concentrated sulfuric acid to create defects on the surface of the carbon nanotubes; then using a planetary ball mill to shorten the carbon nanotubes; and then using concentrated nitric acid and concentrated sulfuric acid to treat the shortened carbon nanotubes again to achieve the purpose of opening. The carbon nanotubes prepared by the method have a high degree of carboxylation and good opening in aqueous solution, but the effect of using the method to degrade organic pollutants in water is poor. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a multifunctional catalyst based on the spatial confinement effect, a preparation method thereof and an application thereof. The catalyst preparation method is simple to operate, can achieve efficient degradation of difficult-to-degrade organic matter, has both adsorption and degradation functions, and has high catalytic efficiency, good stability, less dissolution of active components, and has high application value.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] On the one hand, the present invention provides a multifunctional catalyst based on spatial confinement effect, comprising modified carbon nanotubes, iron and variable valence metals; the modified carbon nanotubes are obtained by ball milling carbon nanotubes and adding an oxidant for oxidation; the molar ratio of the iron to the variable valence metal ions is 4:(1-4); the sum of the loading amounts of the iron and the variable valence metals is 1wt.%-12wt.%.

[0010] Preferably, the total amount of iron and variable valence metal loading is 1 wt.%-8 wt.%.

[0011] More preferably, the sum of the total loading of iron and variable valence metal is 8 wt.%.

[0012] Furthermore, the ball milling is one of dry ball milling and wet ball milling.

[0013] Furthermore, the oxidant is nitric acid, sulfuric acid and hydrochloric acid.

[0014] Furthermore, the molar concentration of the oxidant is 3-6M.

[0015] Preferably, the molar concentration of the oxidant is 5M.

[0016] Preferably, the oxidant is nitric acid, sulfuric acid and hydrochloric acid in a molar ratio of 3:1:1.

[0017] Furthermore, the mass ratio of the oxidant to the carbon nanotubes is 1:10.

[0018] Furthermore, the variable-valence metal salt is at least one of a copper salt, a cobalt salt, a cerium salt, a manganese salt, a nickel salt and a molybdenum salt.

[0019] In another aspect, the present invention provides a method for preparing a multifunctional catalyst based on spatial confinement effect, comprising the following steps:

[0020] (1) firstly subjecting the carbon nanotubes to ball milling treatment, and then adding an oxidant to oxidize the carbon nanotubes to obtain modified carbon nanotubes;

[0021] (2) mixing the iron salt and the variable valence metal salt with water, heating until dissolved, and cooling to room temperature to obtain a precursor solution;

[0022] (3) Adding the modified carbon nanotubes obtained in step (1) to the precursor solution obtained in step (2), dispersing, standing, drying, and calcining to obtain a multifunctional catalyst.

[0023] Preferably, in step (2), the iron salt is a soluble trivalent iron salt.

[0024] More preferably, in step (2), the iron salt is selected from at least one of ferric sulfate, ferric chloride, ferric nitrate or a hydrate thereof.

[0025] As an example of the present invention, in step (2), the iron salt is ferric nitrate nonahydrate.

[0026] Preferably, in step (2), the variable valence metal salt is a soluble variable valence metal salt.

[0027] More preferably, in step (2), the variable-valence metal salt is at least one of a copper salt, a cobalt salt, a cerium salt, a manganese salt, a nickel salt and a molybdenum salt.

[0028] Preferably, the volume of the precursor solution in step (2) is equal to the saturated water absorption capacity of the carbon nanotubes used.

[0029] Preferably, in step (3), the dispersion is performed by ultrasonication for 20-60 minutes followed by stirring for 1-8 hours.

[0030] Preferably, in step (3), the calcination temperature is 110-180°C.

[0031] More preferably, in step (3), the calcination temperature is 120-150°C.

[0032] Preferably, in step (3), the heating rate of the calcination is 1-3°C / min.

[0033] Preferably, in step (3), the calcination time is 8-12 hours.

[0034] Preferably, step (3) further comprises naturally cooling to room temperature after the roasting is completed.

[0035] In another aspect, the present invention provides the use of the multifunctional catalyst in wastewater treatment, comprising the following steps:

[0036] The multifunctional catalyst is placed in wastewater and continuously stirred to adsorb organic pollutants. After reaching adsorption equilibrium, an oxidant is added or applied to an electro-Fenton reaction to oxidatively degrade the organic pollutants.

[0037] Preferably, the organic pollutants include at least one of phenol, p-nitrophenol, p-chlorophenol, pyridine, sodium dodecylbenzene sulfonate and antibiotics.

[0038] Preferably, the oxidant includes but is not limited to at least one of hydrogen peroxide, persulfate and peroxymonosulfate.

[0039] The beneficial effects of the present invention are:

[0040] (1) The multifunctional catalyst provided by the present invention is based on an iron base, which reacts with an oxidant or generates free radicals in an electro-Fenton reaction to achieve oxidative degradation of organic pollutants. A variable-valence metal salt is added to form a bimetallic oxide active center. The synergistic effect of the two can increase the degradation rate of organic matter.

[0041] (2) The present invention fills the lumen of carbon nanotubes with bimetallic oxides to form a composite material. Carbon nanotubes can adsorb organic matter due to their own structure. This spatial confinement effect is beneficial to the catalytic reaction, inhibits the agglomeration of active components, improves the catalyst's resistance to deactivation, and greatly reduces the generation of iron sludge.

[0042] (3) The multifunctional catalyst provided by the present invention has good electrical conductivity, simple reaction conditions, simple preparation method, and low raw material cost, which can effectively reduce the cost of wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the removal of para-chlorophenol after 10 cycles of application in Example 2.

[0044] Figure 2 This is the removal of para-chlorophenol in Comparative Example 4 after 10 cycles of application example 2.

[0045] Figure 1 , Figure 2 The dashed lines in the figure represent, from left to right: 0, 30, 60, 90 and 120 min. DETAILED DESCRIPTION

[0046] In order to make the technical means, creative features, purpose and efficacy of the present invention easy to understand, the present invention is further explained in conjunction with specific embodiments below, but the following embodiments are only preferred embodiments of the present invention, not all. Based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present invention. The technical and scientific terms used in the embodiments have the meanings commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0047] Definition of terms

[0048] Unless otherwise indicated, the following terms and phrases as used herein have the following meanings:

[0049] In the present invention, "normal temperature" refers to normal ambient temperature, which is from 10°C to 40°C. In some embodiments, "normal temperature" refers to a temperature from 20°C to 30°C; in other embodiments, "normal temperature" refers to a temperature from 25°C to 30°C; in still other embodiments, "normal temperature" refers to 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, etc.

[0050] It is worth noting that the raw materials used in the present invention are all common commercially available products, and their sources are not specifically limited. The following is an exemplary description.

[0051] Carbon nanotubes: MWCNT (carbon basis ≥ 98%) were purchased from Sigma Aldrich.

[0052] The material table of Examples 1-8 and Comparative Examples 1-4 is shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] Note: The molar ratio of nitric acid, sulfuric acid and hydrochloric acid is (3:1:1). Preparation methods of Examples 1-7 and Comparative Examples 2 and 4:

[0057] (1) Firstly, the carbon nanotubes (comparative example 4 is silicon dioxide) are dry-milled at a speed of 500 rpm, a time of 1 h, and a temperature of room temperature; then, an oxidant is added for oxidation at a time of 6 h and a temperature of room temperature to obtain modified carbon nanotubes;

[0058] (2) mixing the iron salt and the variable valence metal salt with water, heating until dissolved, and cooling to room temperature to obtain a precursor solution;

[0059] (3) Add the modified carbon nanotubes (comparative example 4 is treated silica) to the precursor solution, ultrasonicate for 30 minutes and then stir for 2 hours to disperse the precursor salt and introduce it into the carbon nanotube channel under the action of capillary force. After natural drying, calcine at 150°C for 10 hours with a heating rate of 2°C / min. Cool naturally to room temperature.

[0060] The iron salt is Fe(NO3)2·9H2O, the cobalt salt is Co(NO3)2·2H2O, and the cerium salt is

[0061] Ce(NO3)3·6H2O, copper salt is Cu(NO3)2·3H2O.

[0062] The preparation method of embodiment 8:

[0063] (1) firstly wet-mill the carbon nanotubes, add the medium: deionized water, the volume ratio of the carbon nanotubes is 0.8:1, the speed is 500 rpm, the time is 1 h, the temperature is room temperature; add the oxidant for oxidation, the oxidation time is 6 h, the temperature is room temperature, and the modified carbon nanotubes are obtained;

[0064] (2) mixing the iron salt and the variable valence metal salt with water, heating until dissolved, and cooling to room temperature to obtain a precursor solution;

[0065] (3) Add the modified carbon nanotubes to the precursor solution, ultrasonicate for 30 minutes, and stir for 2 hours to disperse the solution and introduce the precursor salt into the carbon nanotube channel under the action of capillary force. After natural drying, calcine at 150°C for 10 hours with a heating rate of 2°C / min. Cool naturally to room temperature.

[0066] The iron salt is Fe(NO3)2·9H2O, the cobalt salt is Co(NO3)2·2H2O, and the cerium salt is

[0067] Ce(NO3)3·6H2O.

[0068] Preparation method of comparative example 1:

[0069] (1) Firstly, the carbon nanotubes are ball-milled at a speed of 500 rpm, a time of 1 h, and a temperature of room temperature to obtain modified carbon nanotubes;

[0070] (2) mixing the iron salt and the variable valence metal salt with water, heating until dissolved, and cooling to room temperature to obtain a precursor solution;

[0071] (3) Add the modified carbon nanotubes to the precursor solution, ultrasonicate for 30 minutes, and stir for 2 hours to disperse the solution and introduce the precursor salt into the carbon nanotube channel under the action of capillary force. After natural drying, calcine at 150°C for 10 hours with a heating rate of 2°C / min. Cool naturally to room temperature.

[0072] The iron salt is Fe(NO3)2·9H2O and the cobalt salt is Co(NO3)2·2H2O.

[0073] Preparation method of comparative example 3:

[0074] (1) firstly adding an oxidant to the carbon nanotubes for oxidation for 6 hours at room temperature to obtain modified carbon nanotubes;

[0075] (2) mixing the iron salt and the variable valence metal salt with water, heating until dissolved, and cooling to room temperature to obtain a precursor solution;

[0076] (3) Add the modified carbon nanotubes to the precursor solution, ultrasonicate for 30 minutes, and stir for 2 hours to disperse the solution and introduce the precursor salt into the carbon nanotube channel under the action of capillary force. After natural drying, calcine at 150°C for 10 hours with a heating rate of 2°C / min. Cool naturally to room temperature.

[0077] The iron salt is Fe(NO3)2·9H2O and the cobalt salt is Co(NO3)2·2H2O.

[0078] Application Example 1

[0079] 180 mg of the multifunctional catalysts prepared in Examples 1-8 and Comparative Examples 1-4 were weighed and added to 300 mL of phenol wastewater with a pH of 3, and the phenol concentration was 100 mg / L. After stirring for 30 min to allow the multifunctional catalyst to adsorb phenol to reach adsorption equilibrium, 200 ml of 54 mmol / L hydrogen peroxide was added as an oxidant to degrade the phenol.

[0080] The quantitative method of phenol is: sampling test, HPLC, ultraviolet detector, wavelength 280nm. The initial phenol content, 30min phenol content and 120min phenol content are tested respectively.

[0081] 30 min adsorption rate = (initial phenol content - 30 min phenol content) / initial phenol content × 100%.

[0082] 120 min removal rate = (initial phenol content - 120 min phenol content) / initial phenol content × 100%.

[0083] The iron dissolution concentration was determined by the 1,1-phenanthroline spectrophotometric method (HJ / T 345-2007).

[0084] The experimental results are shown in Table 2.

[0085] Table 2

[0086]

[0087]

[0088] Application Example 2

[0089] A platinum sheet was used as the anode, and a graphite felt loaded with 350 mg of the multifunctional catalyst prepared in Example 2 and Comparative Example 4 was used as the cathode. The distance between the cathode and the anode was 3 cm, pH = 3, and the aeration rate was 0.3 L / min. 350 mL of wastewater with a sodium sulfate concentration of 6500 mg / L and a para-chlorophenol concentration of 200 mg / L was degraded. Stir for 30 minutes to allow the multifunctional catalyst to adsorb para-chlorophenol. Subsequently, para-chlorophenol was degraded under a voltage of 3 V. The experimental results are shown in Table 3.

[0090] The quantitative method of p-chlorophenol is: sampling test, HPLC, ultraviolet detector, wavelength 280nm. The initial p-chlorophenol content, the p-chlorophenol content at 30min and the p-chlorophenol content at 120min are tested respectively.

[0091] 30 min adsorption rate = (initial p-chlorophenol content - 30 min p-chlorophenol content) / initial p-chlorophenol content × 100%.

[0092] 120 min removal rate = (initial p-chlorophenol content - 120 min p-chlorophenol content) / initial p-chlorophenol content × 100%.

[0093] The iron dissolution concentration was determined by the 1,1-phenanthroline spectrophotometric method (HJ / T 345-2007).

[0094] Table 3

[0095] serial number 30min adsorption rate (%) 120min removal rate (%) Iron dissolution concentration (mg / L) Example 2 45.1 99.9％ 1.53 Comparative Example 4 12.2 57.2％ 33.5

[0096] Further, the graphite felt loaded with 350 mg of the multifunctional catalyst prepared in Example 2 and Comparative Example 4 was repeatedly used as the cathode to carry out the above-mentioned degradation experiment of p-chlorophenol (120 min each time). The experimental results are as follows: Figure 1 and 2 After the experimental system corresponding to Example 2 was cycled 10 times, the removal rate of p-chlorophenol could still reach 98.63%, indicating that the cathode material has strong stability and can be reused. Compared with Comparative Example 4, the performance is significantly improved.

[0097] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A multifunctional catalyst based on spatial confinement effect, characterized in that: Includes modified carbon nanotubes, iron and variable valence metals; The modified carbon nanotubes are prepared by ball-milling the carbon nanotubes and then adding an oxidant to oxidize them. The molar ratio of iron to variable-valence metal ions is 4:(1-4); The total loading amount of the iron and the variable valence metal is 1 wt.%-12 wt.%.

2. The multifunctional catalyst according to claim 1, characterized in that The oxidizing agent is nitric acid, sulfuric acid and hydrochloric acid; The molar concentration of the oxidant is 3-6M.

3. The multifunctional catalyst according to claim 1, characterized in that The mass ratio of the oxidant to the carbon nanotubes is 1:

10.

4. The multifunctional catalyst according to claim 1, characterized in that The variable valence metal salt is at least one of copper salt, cobalt salt, cerium salt, manganese salt, nickel salt and molybdenum salt.

5. A method for preparing the multifunctional catalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) ball-milling the carbon nanotubes, adding an oxidant to oxidize them, and obtaining modified carbon nanotubes; (2) mixing the iron salt and the variable valence metal salt with water, heating until dissolved, and cooling to room temperature to obtain a precursor solution; (3) Adding the modified carbon nanotubes obtained in step (1) to the precursor solution obtained in step (2), dispersing, standing, drying, and calcining to obtain a multifunctional catalyst.

6. The preparation method according to claim 5, characterized in that: In step (3), the dispersion is performed by ultrasonication for 20-60 minutes and then stirring for 1-8 hours.

7. The preparation method according to claim 5, characterized in that: In step (3), the calcination temperature is 110-180°C, the heating rate is 1-3°C / min, and the calcination time is 8-12h.

8. Use of the multifunctional catalyst according to claims 1 to 4 or the multifunctional catalyst prepared by the preparation method according to any one of claims 5 to 7 in wastewater treatment.

9. The use according to claim 8, comprising the following steps: The multifunctional catalyst is placed in wastewater and continuously stirred to adsorb organic pollutants. After reaching adsorption equilibrium, an oxidant is added or applied to an electro-Fenton reaction to oxidatively degrade the organic pollutants.

10. The use according to claim 9, characterized in that: The organic pollutants include at least one of phenol, p-nitrophenol, p-chlorophenol, pyridine, sodium dodecylbenzene sulfonate and antibiotics; The oxidant includes at least one of hydrogen peroxide, persulfate and peroxymonosulfate.

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