Iron-containing bentonite composite catalytic material, preparation method and application thereof

Abstract

This invention belongs to the field of environmental functional materials and advanced oxidation water treatment technology, and relates to an iron-containing bentonite composite catalytic material, its preparation method, and its application. The composite catalytic material prepared by this invention uses an in-situ co-precipitation method to uniformly load trivalent and divalent iron into the bentonite interlayer, effectively inhibiting the aggregation of iron oxides and significantly improving the dispersion of active sites and the mass transfer efficiency of reactants. Through the synergistic effect of a specific ratio of trivalent and divalent iron and the dual-valent electron transfer mechanism, highly efficient and specific activation of persulfate is achieved, with a degradation rate as high as 95% when degrading pollutants such as pracetamane, far exceeding that of single-valent iron materials, carrier-free materials, and materials prepared by traditional impregnation methods. Furthermore, the preparation method is process-controllable, with a clearly defined optimal iron source volume ratio and drying temperature window, ensuring the stability of the material structure and the consistency of catalytic activity, and possessing excellent industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and advanced oxidation water treatment technology, and relates to an iron-containing bentonite composite catalytic material, its preparation method and application. Background Technology

[0002] In oil-contaminated water and soil, pterostilbene, a typical branched saturated alkane, is difficult to degrade effectively by biological or conventional chemical oxidation methods due to its stable molecular structure and strong hydrophobicity, making it a challenging aspect of remediation of stubborn organic pollution. Advanced persulfate-based oxidation technologies can generate highly oxidizing sulfate radicals, providing a new approach to breaking down these pollutants with high CH bond energies.

[0003] Currently, developing efficient and stable heterogeneous iron-based catalysts for activating persulfate is a research hotspot. However, existing catalysts face significant bottlenecks when treating low-concentration, strongly hydrophobic pollutants such as pterostilbene: on the one hand, the mass transfer efficiency of pollutants from the aqueous phase to the catalyst active sites is low; on the other hand, conventional materials lack specific adsorption capacity for hydrophobic molecules, resulting in "catalytic sites not contacting the target analyte," thus limiting the overall degradation efficiency. Although bentonite has adsorption potential, traditional loading methods often neglect the synergistic effect between its targeted enrichment function for hydrophobic pollutants and its catalytic activity. The prepared materials still have shortcomings in the integrated "adsorption-catalysis" efficiency and cycle stability for pterostilbene.

[0004] Therefore, there is an urgent need to develop a novel composite catalytic material that can simultaneously enhance the enrichment of hydrophobic pollutants and the activation of persulfate. This invention aims to provide an iron-containing bentonite material specifically designed for the efficient degradation of pterostilbene and its preparation method, thereby solving the key problem of the disconnect between the adsorption and catalytic processes mentioned above. Summary of the Invention

[0005] The purpose of this invention is to provide an iron-containing bentonite composite catalytic material for the efficient degradation of squalane, its preparation method and application, in order to solve the problems of insufficient activity, poor stability and low oxidant utilization efficiency of existing heterogeneous iron-based catalysts when activating persulfate to degrade such stubborn saturated alkanes.

[0006] A method for preparing an iron-containing bentonite composite catalytic material includes the following steps: mixing bentonite powder, a ferric salt solution, and a ferrous salt solution to obtain a mixture; adding an alkaline solution to the mixture to initiate a hydrolysis and co-precipitation reaction of iron ions; mixing to fully precipitate and load iron hydroxide and hydroxyl oxides onto the surface and interlayer of the bentonite; filtering, washing, and drying to obtain the iron-containing bentonite composite catalytic material; the volume ratio of the ferric salt solution to the ferrous salt solution is 1:1; in the mixed solution, Fe... 3+ with Fe 2+The molar ratio is 0.5:1 to 1:1; and the total iron ion concentration is 0.75 to 0.85 mol / L.

[0007] Preferably, the trivalent iron salt is ferric nitrate, ferric chloride, or ferric sulfate.

[0008] Preferably, the alkaline solution is an alkali metal hydroxide solution.

[0009] Preferably, the concentration of the alkali metal hydroxide solution is 0.5~0.9 mol / L.

[0010] Preferably, the volume of the added alkali solution is 0.9 to 1.1 times the sum of the volumes of the ferric salt solution and the ferrous salt solution.

[0011] Preferably, the drying temperature is 65~75°C.

[0012] Preferably, the bentonite powder is natural sodium-based bentonite with a montmorillonite content of 75-85%, a cation exchange capacity of 80-100 mmol / 100g, and a particle size greater than 200 mesh.

[0013] An iron-containing bentonite composite catalytic material is prepared by the method described above for preparing iron-containing bentonite composite catalytic materials.

[0014] The application of an iron-containing bentonite composite catalytic material as described above in the catalytic degradation of organic matter by persulfate, wherein the persulfate is an alkali metal persulfate.

[0015] Preferably, the organic compound is pterostilbene.

[0016] The beneficial effects of this invention are as follows: The composite catalytic material prepared by this invention uses an in-situ co-precipitation method to uniformly load trivalent iron and divalent iron between bentonite layers, effectively inhibiting the aggregation of iron oxides and significantly improving the dispersion of active sites and the mass transfer efficiency of reactants; through the synergistic effect of a specific ratio of trivalent iron and divalent iron and the dual-valent electron transfer mechanism, highly efficient and specific activation of persulfate is achieved, with a degradation rate of up to 95% when degrading pollutants such as pracetamane, far exceeding that of single-valent iron materials, carrier-free materials, and materials prepared by traditional impregnation methods; in addition, the preparation method is process-controllable, and the optimal iron source volume ratio and drying temperature window are clearly defined, ensuring the stability of the material structure and the consistency of catalytic activity, and has excellent prospects for industrial application. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments. The scope of protection of the present invention is not limited to the following embodiments. All modifications made based on the technical solutions of the present invention shall fall within the scope of protection of the present invention.

[0018] The bentonite powder used in the following examples and comparative examples is natural sodium bentonite with a montmorillonite content of 85%, a cation exchange capacity (CEC) of 95 mmol / 100g, and a particle size greater than 200 mesh. Example 1

[0019] The preparation method of the iron-containing bentonite composite catalyst in this embodiment includes the following steps: (1) Dissolve 6.35g of anhydrous ferric sulfate in deionized water and make up to 50mL to obtain a ferric salt solution; dissolve 13g of ferrous sulfate heptahydrate in deionized water containing a small amount of dilute sulfuric acid and make up to 50mL to obtain a ferrous salt solution.

[0020] (2) Weigh 5.0g of bentonite powder into a beaker, add 5mL each of the ferric salt solution and ferrous salt solution prepared in step (1), stir thoroughly to obtain a mixture.

[0021] (3) Place the mixture obtained in step (2) on a magnetic stirrer and slowly add 11 mL of 0.78 mol / L sodium hydroxide solution while continuously stirring. Control the dropping rate to slowly increase the pH of the system, initiating the hydrolysis and co-precipitation reaction of iron ions. After the sodium hydroxide solution is added, continue stirring at room temperature for 1 hour to allow the iron hydroxide / hydroxy oxide to fully precipitate and be loaded onto the surface and interlayer of the bentonite. Then filter and wash the filter cake three times with deionized water until the washing liquid is neutral. Place the washed filter cake in an oven and dry it at 71°C for 24 hours. Finally, grind the dried filter cake into powder and pass it through a 100-200 mesh sieve. The resulting powder is the iron-containing bentonite composite catalyst material. Example 2

[0022] The difference between the preparation method of the iron-containing bentonite composite catalytic material in this embodiment and the preparation method of the iron-containing bentonite composite catalytic material in Example 1 is that the amounts of trivalent iron salt solution and divalent iron salt solution used in step (2) of the preparation method of the iron-containing bentonite composite catalytic material in this embodiment are 4.70g and 13.07g, respectively. Example 3

[0023] The difference between the preparation method of the iron-containing bentonite composite catalytic material in this embodiment and the preparation method of the iron-containing bentonite composite catalytic material in Example 1 is that the amounts of trivalent iron salt solution and divalent iron salt solution used in step (2) of the preparation method of the iron-containing bentonite composite catalytic material in this embodiment are 9.42g and 8.73g, respectively. Example 4

[0024] The difference between the preparation method of the iron-containing bentonite composite catalyst in this embodiment and the preparation method of the iron-containing bentonite composite catalyst in Example 1 is that the drying temperature in step (3) of the preparation method of the iron-containing bentonite composite catalyst in this embodiment is adjusted from 71°C to 105°C. Example 5

[0025] The difference between the preparation method of the iron-containing bentonite composite catalyst in this embodiment and the preparation method of the iron-containing bentonite composite catalyst in Example 1 is that the drying temperature in step (3) of the preparation method of the iron-containing bentonite composite catalyst in this embodiment is adjusted from 71°C to 40°C.

[0026] Comparative Example 1 The difference between the preparation method of the iron-containing bentonite composite catalyst in this comparative example and the preparation method of the iron-containing bentonite composite catalyst in Example 1 is that the amounts of ferric salt solution and ferrous salt solution used in step (2) of the preparation method of the iron-containing bentonite composite catalyst in this comparative example are 0 mL and 8.39 mL, respectively (the total iron content is equal to the total iron content in Example 1).

[0027] Comparative Example 2 The difference between the preparation method of the iron-containing bentonite composite catalytic material in this comparative example and the preparation method of the iron-containing bentonite composite catalytic material in Example 1 is that the amounts of ferric salt solution and ferrous salt solution used in step (2) of the preparation method of the iron-containing bentonite composite catalytic material in this comparative example are 12.36 mL and 0 mL, respectively (the total iron content is equal to the total iron content in Example 1).

[0028] Comparative Example 3 The difference between the preparation method of the iron-containing bentonite composite catalyst in this comparative example and the preparation method of the iron-containing bentonite composite catalyst in Example 1 is that in step (2) of the preparation method of the iron-containing bentonite composite catalyst in this comparative example, the trivalent iron salt solution and the divalent iron salt solution are replaced with deionized water.

[0029] Comparative Example 4 The difference between the preparation method of the catalytic material in this comparative example and the preparation method of the iron-containing bentonite composite catalytic material in Example 1 is that the amount of bentonite powder used in step (2) of the preparation method of the catalytic material in this comparative example is 0.

[0030] Comparative Example 5 The preparation method of the iron-containing bentonite composite catalytic material of this comparative example includes the following steps: 5.0 g of bentonite powder is added to 200 mL of ferric nitrate solution with a concentration of 10 g / L, stirred at room temperature for 2 h, allowed to stand for 24 h, filtered, and the filter cake is collected. The filter cake is washed three times with 50 mL of deionized water to remove unbound free iron ions on the surface until the filtrate is colorless. The washed filter cake is dried at 105 °C for 12 h. The dried filter cake is taken out, ground into powder in an agate mortar, passed through a 200-mesh standard sieve, and the sieve-passing material is collected, which is the iron-containing bentonite composite catalytic material.

[0031] Experimental Example 1 To investigate the catalytic degradation effect of the catalysts prepared in the various examples and comparative examples on ptarchosane, a 50 mL stoppered conical flask was used. 1.00 mL of ptarchosane stock solution with a concentration of 100 mg / L and hexane as the solvent was accurately added using a microsyringe. The stopper was opened, and the flask was left to stand in a fume hood to allow the hexane to completely evaporate and the ptarchosane to adhere evenly to the bottom. Then, 10.00 mL of ultrapure water was added to the flask, the mouth was sealed, and the flask was placed in an ultrasonic cleaner and ultrasonically vibrated for 30 minutes to fully disperse the ptarchosane in the water, forming a simulated polluted water sample with an initial concentration of approximately 5 mg / L. 10.00 mL of a 4 mM peroxide solution was accurately added to the prepared simulated polluted water sample and gently shaken. Then, a certain amount of the catalyst to be tested was quickly added to bring the concentration of the catalyst in the entire reaction system (20 mL) to 2 g / L (i.e., 40.0 mg). Immediately seal the conical flask and place it in a constant-temperature shaking incubator at 25±1℃ and 150 rpm, avoiding light, for 1 hour. After the predetermined reaction time (1 hour), immediately remove the conical flask and add excess methanol to the reaction solution to quench residual free radicals and terminate the reaction. Then, extract with 10 mL of n-hexane by sonication for 30 minutes. After standing until complete separation, take the upper organic phase and filter it through a 0.22 μm organic phase filter membrane. Using adamantane as an internal standard, determine the concentration of residual pterostilbene in the filtrate by gas chromatography-mass spectrometry. The degradation rate (η) is calculated according to the following formula: η(%)=(C0-C e ) / C0×100% Where C0 is the initial concentration, C e This represents the concentration at the end of the reaction.

[0032] The catalytic degradation effects of the catalysts prepared in each embodiment and comparative example on pterostilbene are shown in Table 1.

[0033] Table 1. Catalytic degradation effect of catalyst materials on pterostilbene

[0034] As shown in Table 1, the catalytic material prepared using the method described in Example 1 of this invention (co-precipitation and loading of ferric and ferrous iron at a specific drying temperature) achieved a degradation rate as high as 95% when activated potassium persulfate degraded pracetamane. Compared with Comparative Example 3 (bentonite only, degradation rate 33%) and Comparative Example 4 (no bentonite support, degradation rate 49%), the material of this invention exhibits a significant synergistic effect. This indicates that loading iron species in a specific form onto the bentonite support not only effectively prevents the aggregation of iron oxides and improves the dispersion of active sites, but also utilizes the interlayer structure of bentonite to promote the enrichment and mass transfer of reactants, thereby achieving highly efficient catalytic oxidation.

[0035] Comparing the data from Examples 1, 2, and 3 with Comparative Examples 1 and 2, it can be seen that the valence state composition and ratio of iron ions have a decisive influence on catalytic performance: when both ferric and ferrous iron are present in the system (Examples 1-3), the degradation rate (73%-95%) is significantly higher than that of Comparative Examples 1 and 2, which contain only iron in a single valence state. This demonstrates that there is a significant synergistic electron transfer mechanism between ferric and ferrous iron in the catalytic cycle, and a single valence state cannot form an efficient redox cycle. At a volume ratio of ferric salt solution to ferrous iron solution of 1:1 (5 mL each, Example 1), the degradation rate reaches a peak of 95%. When the ratio deviates to 3:7 (Example 2, 79%) or 7:3 (Example 3, 73%), the catalytic activity decreases by 16% and 22%, respectively. This indicates that only under specific stoichiometric ratios can an active phase structure with the fewest lattice defects and the best redox potential matching be formed on the bentonite surface; any deviation in the ratio will lead to a reduction in the number of active sites or hindered electron transfer.

[0036] Comparing Examples 1, 4, and 5, it is evident that drying temperature is a sensitive parameter affecting the final morphology and activity of the catalyst: when the drying temperature increases to 105°C (Example 4), the degradation rate decreases to 75%. Analysis suggests that excessively high temperatures may cause over-crystallization or phase transformation of the supported iron hydroxide / hydroxyl oxide (e.g., conversion to low-activity hematite or magnetite), resulting in a decrease in specific surface area and loss of surface-active hydroxyl groups. When the drying temperature decreases to 40°C (Example 5), the degradation rate drops significantly to 65%. Analysis suggests that excessively low temperatures lead to incomplete dehydration of the precursor, failing to form a specific crystal structure with catalytic activity, and residual moisture may clog pores, hindering reactant diffusion.

[0037] Comparing Example 1 (coprecipitation method, 95%) with Comparative Example 5 (conventional impregnation method, 69%), it is evident that although both used bentonite and an iron source, the difference in preparation processes led to a significant performance gap. In the impregnation method used in Comparative Example 5, iron ions were mainly physically adsorbed or simply exchanged on the bentonite surface, easily leading to aggregation and low utilization of active sites. The in-situ coprecipitation method (steps 2-3) used in this invention allows iron ions to directly nucleate and grow on the bentonite surface and between layers under alkaline conditions, forming a nanoscale iron oxide / hydroxy oxide composite with strong binding force and extremely high dispersion.

[0038] Comparative Example 1 and different peroxide complex systems show that the catalytic material prepared in this invention exhibits extremely high specific activation ability (95%) for potassium persulfate, while the activation effect on sodium persulfate (85%), urea peroxide (46%), and potassium peroxymonosulfate (31%) is significantly lower. This indicates that there is a special matching mechanism between this material and persulfate, enabling more efficient generation of sulfate radicals. Simultaneously, this result demonstrates that potassium ions may play a unique co-catalytic role at the reaction interface (such as stabilizing the transition state or regulating the double-layer structure), or that sodium ions may have an inhibitory effect on the active site.

Claims

1. A method for preparing an iron-containing bentonite composite catalytic material, characterized in that, Includes the following steps: Bentonite powder, ferric salt solution, and ferrous salt solution were mixed to obtain a mixture. Alkali solution was added to the mixture to initiate the hydrolysis and co-precipitation reaction of iron ions. Mixing allowed iron hydroxide and hydroxyl oxides to fully precipitate and be loaded onto the surface and interlayer of the bentonite. After filtration, washing, and drying, an iron-containing bentonite composite catalytic material was obtained. The volume ratio of the ferric salt solution to the ferrous salt solution was 1:

1. In the mixed solution, the molar ratio of ferric ions to ferrous ions was 0.5:1 to 1.0:1, and the total iron ion concentration was 0.75 to 0.85 mol / L.

2. The preparation method of the iron-containing bentonite composite catalytic material as described in claim 1, characterized in that, The ferric salts mentioned are ferric nitrate, ferric chloride, and ferric sulfate.

3. The preparation method of the iron-containing bentonite composite catalytic material as described in claim 1, characterized in that, The alkaline solution is an alkali metal hydroxide solution.

4. The preparation method of the iron-containing bentonite composite catalytic material as described in claim 3, characterized in that, The concentration of the alkali metal hydroxide solution is 0.5~0.9 mol / L.

5. The preparation method of the iron-containing bentonite composite catalytic material as described in claim 3, characterized in that, The volume of the added alkali solution is 0.9 to 1.1 times the sum of the volumes of the ferric salt solution and the ferrous salt solution.

6. The preparation method of the iron-containing bentonite composite catalytic material as described in claim 1, characterized in that, The drying temperature is 65~75℃.

7. The preparation method of the iron-containing bentonite composite catalytic material as described in claim 1, characterized in that, The bentonite powder is natural sodium-based bentonite with a montmorillonite content of 75-85%, a cation exchange capacity of 80-100 mmol / 100g, and a particle size greater than 200 mesh.

8. An iron-containing bentonite composite catalytic material, characterized in that, It is prepared by the method for preparing iron-containing bentonite composite catalytic materials as described in any one of claims 1-7.

9. The application of the iron-containing bentonite composite catalytic material as described in claim 8 in the catalytic degradation of organic matter by persulfate, characterized in that, The persulfate is an alkali metal perdisulfate.

10. The application as described in claim 9, characterized in that, The organic compound is pterosaccharane.

Images