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Article

Preparation of Mn-Co-MCM-41 Molecular Sieve with Thermosensitive Template and Its Degradation Performance for Rhodamine B

by
Wenju Peng
1,
Lixia Cai
2,*,
Yani Lu
1 and
Yaoyao Zhang
3,*
1
School of Civil Engineering, Hubei Engineering University, Xiaogan 432000, China
2
College of Technology, Hubei Engineering University, Xiaogan 432000, China
3
School of Chemistry and Materials Science, Hubei Engineering University, Xiaogan 432000, China
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(6), 991; https://doi.org/10.3390/catal13060991
Submission received: 10 May 2023 / Revised: 5 June 2023 / Accepted: 7 June 2023 / Published: 9 June 2023
(This article belongs to the Special Issue Advanced Catalytic Material for Water Treatment)
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Abstract

:
Rhodamine B (RhB) in dyes is widely used in various industries, but it poses a great threat to the natural environment and human health. In this work, a series of thermosensitive polymer materials, PNxDy, with controllable morphology and particle size were prepared by free radical polymerization using N-isopropylacrylamide and N,N-dimethylacrylamide as monomers. Then, by using PNxDy as a template, bimetallic Mn- and Co-doped MCM-41 molecular sieves with good morphology and properties were prepared by the microwave-assisted hydrothermal method. The effects of a series of thermosensitive templates on the morphology and properties of the Mn-Co-MCM-41 molecular sieve were investigated. The results demonstrated that the Mn-Co-MCM-41 by PN100D4 as a templating agent showed the best mesoporous ordering and the most regular material morphology with 2 nm nanoparticles. In addition, the molecular sieve with the best structure was selected for the RhB degradation experiments. The Mn-Co-MCM-41 with PN100D4 as the template showed regular morphology and uniform pore channels. It was applied as a catalyst for the degradation of RhB by potassium monopersulfate (PMS). The degradation rate of RhB could reach 98% with a 20 min reaction by Mn-Co-MCM-41 (PN100D4). Meanwhile, the degradation rate could be maintained at 91% after being reused six times. The bimetallic-doped Mn-Co-MCM-41 molecular sieves prepared using the thermosensitive material PN100D4 as a template have good catalytic performance and can be effectively reused.

1. Introduction

With the development of the industrial revolution, dyes have been widely used in the food, pharmaceutical, printing, and cosmetic industries. However, dyes also cause environmental pollution, such as water pollution, dramatically threatening human health [1,2]. Rhodamine B (RhB) is a common organic pollutant that is difficult to degrade and accumulates quickly, causing cancer, and has a long half-life [3,4,5]. Several methods have been used to degrade RhB [6,7,8]. Until now, photocatalytic decay of pollutants has been widely studied [9], but dyes are quite stable to radiation, and oxidation and the presence of intermediates make water unsuitable for drinking [10]. Catalytic oxidation, the most used chemical process, has the benefits of non-toxicity, safety, stability, and high catalytic activity [11]. The catalysts used for RhB degradation are carbon-based materials [12], zinc-based materials [13], and molecular sieve titanium-based materials [14]. However, there are disadvantages to the current catalysts, including an inadequate catalytic effect and challenging catalyst reuse.
Since the 1960s, molecular sieves such as MCM-41 molecular sieves [15,16], 4A molecular sieves [17], and SBA-15 molecular sieves [18] have been widely used in separation processes, object chemistry, gas sensors, drug delivery, and optoelectronic devices due to their unique structures and superior properties. MCM-41 molecular sieves are more conducive to the rapid diffusion of organic molecules due to their uniform pore size, large specific surface area, and higher adsorption capacity than other pore channel materials. Therefore, they can be utilized as catalysts or adsorbents [19,20,21]. However, the weak acidity of pure silicon MCM-41 molecular sieves and the homogeneity of the silicon skeleton structure severely limit the application of MCM-41. In particular, the lack of active centers in the pore walls limits its application in catalysis [22,23,24,25]. Subsequent studies have mainly used the introduction of heteroatoms such as Cu, Fe, Sr, Ti, Zn, and V [21,26]. Pradhan et al. [27] used oleic acid and cetyltrimethylammonium bromide (CTAB) as particle size controllers (capping agents) and morphology controllers (surfactant). In the framework structure of mesoporous Al2O3-MCM-41, Co-Fe, Mn-Co, and Fe-Mn bimetallic nanoparticles were prepared. In this system, photo-Fenton and photocatalytic processes effectively degraded the dyes, with 100% degradation within 60 min. However, the metals were highly prone to agglomeration during the doping process [17,28]. They would result in inhomogeneous doping, irregular molecular sieve structure, unstable catalyst activity, and limited catalytic performance. The use of the template is crucial in the preparation method of regularly shaped MCM-41 materials. Thermosensitive materials, as new materials, can achieve structural diversity by controlling the morphology of reactive monomers and have a wide range of applications in templating agents.
In this study, self-prepared thermosensitive nanoparticles were used as templates. In situ filling of manganese (Mn) and cobalt (Co) salts into the pores of molecular sieve MCM-41 took place using the microwave-assisted hydrothermal method. Thus, bimetallic Mn-Co-doped MCM-41 molecular sieve materials with good morphology and properties were prepared, and Co2+/Co3+, Mn2+/Mn3+, and Mn3+/Mn4+ redox pairs could dominate the activation of potassium monopersulfate (PMS) to degrade Rhodamine-B dye [29]. The effects of the doping amounts of bimetallic Mn and Co on the morphology and properties of the MCM-41 molecular sieve were systematically investigated. In addition, the best-structured molecular sieve was screened and applied as a catalyst for the degradation of RhB by PMS. The bimetallic doped MCM-41 catalyst prepared in this work provides a new method for the industrial degradation of RhB.

2. Materials and Methods

2.1. Experimental Reagents and Instruments

Main reagents: N-isopropylacrylamide, N,N-dimethylacrylamide, azodiisobutyronitrile, mercaptoethylamine hydrochloride, ethyl orthosilicate, manganese nitrate, cobalt nitrate, methanol, tetrahydrofuran, PMS, RhB, and deionized water.
Main instruments: an electronic balance, a hydrothermal reactor, a Schlenk reaction tube, a vacuum drying oven, a microwave reactor, an ultrasonic cleaner, a tube furnace, a scanning electron microscope, an elemental analyzer, a UV-Vis spectrophotometer, an infrared spectrometer, and a specific surface area analyzer.

2.2. Synthesis of the Thermosensitive Template PNxDy

Based on the free radical polymerization method, x mmol of N-isopropylacrylamide and y mmol of N,N-dimethylacrylamide were added as reaction monomers to the Schlenk reaction tube. Azo diisobutyronitrile was used as the chain initiator, mercaptoethylamine hydrochloride was used as the chain transfer agent, and methanol was used as the reaction solvent. The reaction was carried out in an oil bath at 60 °C for 24 h. The solvent was removed at the end of the reaction. The solid product was precipitated with ether and dried under vacuum at 30 °C to obtain the thermosensitive polymer PNxDy. x and y denote the degree of polymerization of N-isopropylacrylamide and N, N-dimethylacrylamide, respectively. Three thermosensitive polymers with different hydrophilic ratios were prepared, and their characterization results are shown in Table 1 [30].

2.3. Preparation of the Bimetallic (Mn-Co)-Doped MCM-41 Molecular Sieve with PNxDy

Approximately 1 g of PNxDy was dissolved in 100 mL of water and stirred by microwave at 20 °C for 30 min. Approximately 9 mL of ammonia was added to adjust the pH to 11. Magnetic stirring was continued for 30 min. Approximately 50 mmol of ethyl orthosilicate, 1 mmol of manganese nitrate, and 1 mmol of cobalt nitrate were added to the solution, and it was placed in a high-pressure hydrothermal reactor at 140 °C for 10 h to maintain Si:Mn:Co = 50:1:1. Then, when it cooled to room temperature, the sample was removed by centrifugation and dried under vacuum at 50 °C. The bimetallic (Mn-Co)-doped MCM-41 molecular sieve precursors were obtained by grinding to powder. The powder was roasted in the N2 atmosphere in a tube furnace to obtain the final product of the bimetallic (Mn-Co)-doped MCM-41 molecular sieve (named Mn-Co-MCM-41(PNxDy)). The roasting parameters were: 2 °C/min, 1 h at 100 °C, and 3 h at 500 °C [31].

2.4. Characterization of the Molecular Sieve

The PNxDy, Mn-Co-MCM-41 molecular sieve, and Mn-Co-MCM-41(PNxDy) were characterized. Fourier transform infrared spectroscopy (FTIR) was performed using a Vertex 70 FTIR spectrometer (Germany). Sample composition was determined by characteristic peak analysis. The scan number was 32. The scanning range was 400–4000 cm−1 with a 0.1–16 cm−1 resolution. Ultraviolet–visible spectroscopy (UV-Vis) measurements were performed using an ultraviolet spectrometer (Agilent 8453 type) with a 200–900 nm wavelength range. Nuclear magnetic resonance (NMR) characterization of polymers was performed using a Bruker Drx 400 instrument (Bruker Company, Bremen, Germany) with D2O as solvent. The molecular weight of the polymers was measured by gel chromatography (Alltech Instrument Company, Lexington, KY, USA) using tetrahydrofuran as the mobile phase solvent. Transmission electron microscopy (TEM, Tecnai F20) was used to characterize the morphology of the polymer in water and the particle size. The test voltage was 200 kV. The morphology of the Mn-Co-MCM-41 prepared under different template agents was characterized by scanning electron microscopy (SEM, JSM-6510). The X-ray diffraction (XRD) spectra of the samples were collected using an X-ray diffractometer (X’pert MPD Pro, Philips Company, Amsterdam, The Netherlands). A specific surface area analyzer (BSD-660M A6M) was used to determine the specific surface area of the samples.

2.5. Degradation Performance of RhB by the Molecular Sieve

The 5 mg/L RhB solution was prepared, and 60 mL of RhB solution was added to a 100 mL conical flask. Approximately 5 mg (Co amount is 0.5% of Rhodamine-B dye) Mn-Co-MCM-41(PNxDy) was weighed and then mixed into it. Different concentrations of PMS solution (0, 0.1 mmol/L, 0.2 mmol/L, and 0.3 mmol/L) were added and shaken well and then magnetically stirred. Approximately 1 mL samples were taken at 2 min intervals. The reaction was filtered through a 0.22 µL membrane and terminated by adding 100 µL of anhydrous ethanol. The remaining RhB in the solution was then measured using the UV spectrophotometer to determine the degradation rate at each time point [32].

3. Results and Discussion

3.1. Characterization of the Thermosensitive Polymer PN100D4

The FTIR and lowest critical solution temperature (LCST) characterizations of the prepared thermosensitive polymer PNxDy are shown in Figure 1 and Figure 2, respectively. The characteristic peaks of the thermosensitive polymer PNxDy were at 3310 cm−1 and 3074 cm−1, attributed to -NH- in -CONH-; at 2975 cm−1 and 2932 cm−1, attributed to -CH- in -CH-CH-; at 2876 cm−1, attributed to -CH3 in -CH(CH3)2; and at 1653 cm−1 and 1540 cm−1, attributed to -CH- in -CH(CH3)2 (as shown in Figure 1).
The thermosensitive polymer PNxDy was configured into 0.5 mmol/L aqueous solution. The LCST test was performed by UV characterization, and the absorbance values at λmax = 450 nm were measured (as shown in Figure 2a). The transmittance of PN100D4 decreased abruptly at 33.5 °C. The solution was clear and transparent below 33.5 °C and then became turbid when it increased above 33.5 °C. The LCST of polymer PN120D4 was 34.0 °C and polymer PN80D4 was 33.0 °C. It was repeatedly ramped up and down for the temperature response tests (Figure 2b). The results showed that PN100D4 dissolved at low temperatures and precipitated from the aqueous phase after ramping up, indicating that the thermosensitive polymer PN100D4 has excellent temperature response performance.
Transmission electron microscopy (TEM) and dynamic light scattering (DLS) characterization of PN100D4 were performed. The results are shown in Figure 3. The catalyst was configured in 0.5 mmol/L aqueous solution, and the samples were prepared and characterized by TEM. In Figure 3a–c, with the TEM of PN120D4 (a), PN100D4 (b), and PN80D4 (c), the images show that PN100D4 has formed homogeneous nanoparticles with a diameter of about 2 nm, and PN80D4 showed nanoparticles with a diameter of about 3 nm. Figure 3d is the dynamic light scattering (DLS) of PN120D4, PN100D4, and PN80D4. The hydration kinetic particle size DH of PN100D4 was 39.5 nm, and the PDI value was only 0.227, indicating that the polymer formed a homogeneous spherical structure, while PN80D4 showed a larger DH of 91.3 nm with 0.382 PDI. The comprehensive analysis showed that the polymer could form nanoparticles with regular shapes and uniform size in water, which can be used as an excellent templating agent to prepare bimetal-doped MCM-41 materials.

3.2. Characterization of the Bimetallic Mn-Co Doped MCM-41 Molecular Sieve

3.2.1. FTIR

The FTIR test results of Mn-Co-MCM-41 are shown in Figure 4.
Curve A is the FTIR spectrum of MCM-41/PN100D4 with unloaded metal. Its characteristic peaks correspond to the 1080 cm−1 peak being attributed to the asymmetric stretching vibration of the Si-O tetrahedra; the 965 cm−1 peak being attributed to the stretching vibration of the Si-O bond; the 809 cm−1 peak being attributed to the symmetric stretching vibration of the Si-O tetrahedra; and the 463 cm−1 peak being attributed to the bending vibration of the Si-O bond. The comprehensive analysis showed that MCM-41 had a unique skeleton of molecular sieves.
Curve B is the FTIR spectrum of MCM-41 after metal loading. Characteristic peaks of thermosensitive materials appeared in both B and A at 2932 cm−1 due to the use of the templating agent. Curve B is similar to curve A, indicating that Mn-Co doping did not destroy the skeletal structure of MCM-41. Curves B-PN100D4, B-PN120D4, and B-PN80D4 exhibited similar infrared characteristic peaks. The adsorption of the molecular sieve after doping with Mn-Co was stronger than that of pure silicon MCM-41. The absorption peak of Mn-Co-MCM-41(PNxDy) at 3400~3800 cm−1 was stronger than that of the pure silicon MCM-41 molecular sieve. With Mn-Co doping, the characteristic peak near 965 cm−1 was enhanced because the introduction of the metal increased the asymmetry of the molecular sieve skeleton structure. It was indirectly proven that manganese and cobalt ions had penetrated the molecular sieve skeleton [33].
Curve C is the FTIR spectrum of Mn-Co-MCM-41(PNxDy) after calcination in the N2 atmosphere. Compared with curve B, the uncalcined Mn-Co-MCM-41(PNxDy) had three peaks at 2920 cm−1, 2850 cm−1, and 1650 cm−1, which were attributed to the characteristic peaks of the templating agent contained before calcination. After calcination, the disappearance of the three peaks proved that the thermosensitive template agent was completely removed. The other characteristic peaks of curve C were consistent with curve B, indicating that calcination did not destroy the pore structure of Mn-Co-MCM-41 [34].

3.2.2. Small-Angle XRD

Figure 5 shows the small-angle XRD spectra of Mn-Co-MCM-41(PNxDy) prepared from different thermosensitive polymers as surfactants. All samples showed distinct characteristic diffraction peaks around 2θ = 2.2°, attributed to the (100) crystal plane in the two-dimensional hexagonal material structure. Without the templating agent, the characteristic peak of Mn-Co-MCM-41 was not obvious, and there was no sharp (100) crystallographic plane. With the addition of PNxDy, the characteristic peaks of the molecular sieve gradually appeared, and the characteristic peaks intensity of the (100) crystallographic plane increased. When the hydrophilic ratio of the polymer was at the maximum, the characteristic peak intensity of the two-dimensional hexagonal (110) crystallographic plane was enhanced under the action of PN120D4 compared to the one without the template. With the increasing hydrophobic ratio, the (100) crystallographic plane of the Mn-Co-MCM-41 structure formed by PN100D4 was the strongest. New characteristic peaks corresponding to the (110) and (200) crystallographic planes appeared at 4.0° and 4.7°, respectively. This demonstrated that the Mn-Co-MCM-41 had good mesoporous ordering and the most regular material morphology when using PN100D4 as a templating agent.
With the increasing hydrophobicity, the characteristic peak intensity of the two-dimensional hexagonal (110) crystal plane was significantly reduced under the action of PN80D4. Meanwhile, the characteristic peaks attributed to (110) and (200) disappeared, and the orderliness of the Mn-Co-MCM-41 material was reduced.

3.2.3. SEM

SEM characterization was performed to investigate the effect of the thermosensitive templating agent PNxDy on the morphology of Mn-Co-MCM-41. Figure 6a shows the Mn-Co-MCM-41 prepared without the addition of a thermosensitive templating agent. The Mn-Co-MCM-41 samples showed a random state with uneven dimensions when the thermosensitive templating agent was not added. After adding the templating agent, Mn-Co-MCM-41(PNxDy) (Figure 6b–d) had a more regular shape and started to appear cubic. Among them, when PN120D4 and PN80D4 were added, the samples both contained a few uniform spherical particles under the action of the templating agent. However, most of them showed irregular states. After adding PN100D4, Mn-Co-MCM-41(PN100D4) showed a regular shape, and the cubic-shaped molecular sieve had a large specific surface area and a uniform size (Figure 6d). Therefore, the addition of the PN100D4 template agent was beneficial to the formation of regular morphology. The EDS elemental scan of the sample in Figure 7 showed that Mn and Co elements were successfully doped into the molecular sieve MCM-41, and the weight ratio Si:Mn:Co in Mn-Co-MCM-41(PN100D4) was 50:1:1.

3.2.4. N2 Adsorption–Desorption

The N2 adsorption–desorption isotherm test results of Mn-Co-MCM-41 prepared with the PN100D4 thermosensitive material as a templating agent are shown in Figure 8. Mn-Co-MCM-41(PN100D4) exhibited a type IV adsorption isotherm, indicating that the sample had a typical and uniform structure. The adsorption amount increased rapidly in the interval of relative pressure from 0.2 to 0.4, indicating the uniform pore size distribution of the sample. In addition, there was no obvious hysteresis loop in the graph, indicating that the obtained Mn-Co-MCM-41(PN100D4) had a good pore structure when the PN100D4 thermosensitive material was used as the templating agent.

3.3. Performance of Catalyst-Activated PMS for RhB Degradation

3.3.1. Influence of Catalyst Type

A comparative reaction test was used to investigate the effect of different thermosensitive templating agents on the efficiency of Mn-Co-MCM-41 (PNxDy) for the degradation of RhB. The results are shown in Figure 9.
RhB was not degraded even with the catalyst when PMS was not added (Figure 9a). The reaction system degraded RhB by 20% with PMS and without Mn-Co-MCM-41 (Figure 9b). This showed that PMS had oxidative properties. However, it could not generate free radicals with strong catalytic activity without a catalyst [35], resulting in poor degradation of RhB. The catalytic effects were all enhanced by adding thermosensitive template agents (Figure 9c–e). The performance of Mn-Co-MCM-41 was slightly enhanced when PN80D4 was used as the templating agent. The catalytic material’s performance was further improved when the hydrophilic ratio increased to PN120D4. However, the material’s performance was poor due to the inappropriate hydrophilicity ratio of the templating agent. Until the thermosensitive material PN100D4 was used, the RhB degradation efficiency was close to 100% with the catalytic reaction within 20 min (Figure 9e), while the Co-Fe-MCM-41-type catalyst could reach 100% degradation for a longer time with 60 min [17]. This exciting result is significantly better than that reported in the existing literature [36,37,38]. It showed that the pore material Mn-Co-MCM-41 (PN100D4) with uniform morphology and size acted as a catalyst in the degradation of RhB. Its catalytic mechanism was that Mn-Co-MCM-41 activated the PMS to the more oxidizing SO4−·, facilitating the degradation reaction of RhB easier. Thus, the degradation efficiency was improved [39].

3.3.2. Influence of PMS Concentration

The effect of the catalytic reaction on RhB degradation at different PMS concentrations (0, 0.1 mmol/L, 0.2 mmol/L, and 0.3 mmol/L) is shown in Figure 10.
When using Mn-Co-MCM-41 (PN100D4) as the catalyst, RhB was not degraded even when the catalyst was added without PMS. The degree of RhB degradation increased gradually with increasing PMS concentration. In the system with different concentrations of PMS, the degree of RhB degradation increased by 78%, 100%, and 100%, compared with the system without PMS. It showed that RhB degradation was better when the content of strong oxidizing SO4−· in the reaction system was higher. This was due to the increase in the active HSO5− in the reaction system by increasing the concentration of PMS, which catalyzed the formation of the strong oxidizing SO4−· on the active site of the Mn-Co-MCM-41 (PN100D4) surface. Thus, the degradation efficiency was significantly improved. In this study, a 0.20 mmol/L PMS concentration was finally selected as the optimal PMS dosage for the degradation of RhB. Just as the literature report, with the increase in PMS concentration (0.02–0.06 mM), the degradation of RhB gradually increased. However, when the PMS concentration was further increased, the degradation did not significantly increase [40,41].

3.3.3. Reaction Mechanism of Mn-Co-MCM-41(PN100D4)-Activated PMS for RhB Degradation

It has been reported that ethanol can trap ·OH and SO4−· in solution and that isopropanol can trap ·OH in solution [42,43,44]. Therefore, experiments were designed to verify whether ·OH and SO4−· were produced during the reaction. The degradation efficiency of Mn-Co-MCM-41(PN100D4) decreased when isopropanol was added to the reaction system. In addition, the inhibition was more significant when ethanol was added (Figure 11). The results demonstrated that SO4−· played an essential role in activating Mn-Co-MCM-41(PN100D4) in the degradation of RhB by PMS. In addition, -OH was also involved in the degradation process.
Comparative experiments were designed to verify whether oxygen is necessary for the reaction process. Mn-Co-MCM-41(PN100D4) was selected as the catalyst for the RhB degradation experiments by PMS under air and nitrogen atmosphere. The results are shown in Figure 12. It can be seen that the degradation effect under the air atmosphere was significantly higher than that of the nitrogen atmosphere. This was due to the participation of oxygen in the degradation reaction whereby O2 was reduced to O2−·. Thus, PMS was activated to produce more SO4−·, which increased the RhB degradation efficiency [45]. The results showed that SO4−· could improve the reaction efficiency, and O2−· also played a crucial role in the Mn-Co-MCM-41(PN100D4)-activated PMS degradation RhB reaction system.
Based on the above analysis, the reaction mechanism of this experiment was described in Figure 13. The bimetallic Mn-Co-MCM-41(PN100D4) catalyst first reacted with PMS in solution to produce the active species SO4−· and Co2+. The SO4−· came into contact with H2O/OH− to further produce -OH and also reacted with molecular oxygen adsorbed on the surface of Mn-Co-MCM-41(PN100D4) to release O2−·. In addition, the three reactive groups simultaneously degraded RhB. As the reaction progressed, Co2+ in the solution reacted with PMS to produce SO4−· and Co3+. Then, Co3+ reacted with Mn-Co-MCM-41(PN100D4) to produce Co2+. Finally, the generated Co2+ reacted further with PMS to achieve a cyclic process to achieve the catalytic effect.

3.4. Catalyst Recycling Performance

The used catalysts were centrifuged, washed, and dried for the subsequent catalytic reaction. The results showed that the Mn-Co-MCM-41(PN100D4) catalyst was still more than 90% efficient in degrading RhB after six cycles (Figure 14), indicating that the catalyst structure was stable and there was no significant metal loss from the bimetallic loading. To date, many kinds of catalysts can be reused. However, they usually required complex recycling procedures with lower degradation rates [46,47,48]. In this work, the new Mn-Co-MCM-41(PNxDy) catalyst can easily be recycled and run more than six times.

4. Conclusions

Bi-metallically Mn and Co doped MCM-41 materials with excellent morphology and properties were prepared by the microwave-assisted hydrothermal method using self-made thermosensitive PNxDy as a templating agent. The morphology, structural composition, and thermal stability of the bimetallic-doped MCM-41 molecular sieve were investigated by FTIR, small-angle XRD, SEM, and N2 adsorption–desorption characterization. We systematically investigated the effects of each condition on the structure and properties of the Mn-Co-MCM-41 molecular sieve. The results showed that:
  • The Mn-Co-MCM-41 molecular sieves obtained by bimetallic doping with the 12 hermos-sensitive templating PN100D4 had uniform pore channels and regular morphology.
  • Bimetallic (Mn-Co) doping did not destroy the skeletal structure of MCM-41.
  • The MCM-41 molecular sieve was loaded with bimetallic (Mn-Co) doping using the thermosensitive polymer material PN100D4 as a templating agent to better activate PMS for RhB degradation. The degradation rate of RhB could reach 98% with a 20 min reaction by Mn-Co-MCM-41 (PN100D4).
  • This type of catalyst can be conveniently recycled and recovered for efficient reuse, which is expected to realize industrial applications.

Author Contributions

Conceptualization and funding acquisition, Y.Z.; methodology, data curation and writing, W.P.; formal analysis, Y.L.; writing—review and editing, L.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (22278118; 22108065) and the Postgraduate Scientific Research Innovation Project of Hunan Province (QL20220189).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Infrared spectrum of PN120D4 (a), PN100D4 (b), and PN80D4 (c).
Figure 1. Infrared spectrum of PN120D4 (a), PN100D4 (b), and PN80D4 (c).
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Figure 2. Testing of PNxDy: (a) LCST; (b) temperature responsiveness test.
Figure 2. Testing of PNxDy: (a) LCST; (b) temperature responsiveness test.
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Figure 3. TEM of PN120D4 (a), PN100D4 (b), and PN80D4 (c). (d) Dynamic light scattering (DLS).
Figure 3. TEM of PN120D4 (a), PN100D4 (b), and PN80D4 (c). (d) Dynamic light scattering (DLS).
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Figure 4. Infrared spectra of the MCM-41(PN100D4) and Mn-Co-MCM-41(PNxDy) molecular sieves.
Figure 4. Infrared spectra of the MCM-41(PN100D4) and Mn-Co-MCM-41(PNxDy) molecular sieves.
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Figure 5. Small-angle XRD characterization of Mn-Co-MCM-41.
Figure 5. Small-angle XRD characterization of Mn-Co-MCM-41.
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Figure 6. SEM of Mn-Co-MCM-41: (a) Mn-Co-MCM-41 prepared without a thermosensitive template; (b) Mn-Co-MCM-41 prepared with PN120D4; (c) Mn-Co-MCM-41 prepared with PN80D4; and (d) Mn-Co-MCM-41 prepared with PN100D4.
Figure 6. SEM of Mn-Co-MCM-41: (a) Mn-Co-MCM-41 prepared without a thermosensitive template; (b) Mn-Co-MCM-41 prepared with PN120D4; (c) Mn-Co-MCM-41 prepared with PN80D4; and (d) Mn-Co-MCM-41 prepared with PN100D4.
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Figure 7. EDS of Mn-Co-MCM-41 prepared with PN100D4.
Figure 7. EDS of Mn-Co-MCM-41 prepared with PN100D4.
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Figure 8. N2 adsorption–desorption isotherm of Mn-Co-MCM-41 prepared with PN100D4.
Figure 8. N2 adsorption–desorption isotherm of Mn-Co-MCM-41 prepared with PN100D4.
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Figure 9. Effect comparison of different catalysts activating PMS to degrade RhB.
Figure 9. Effect comparison of different catalysts activating PMS to degrade RhB.
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Figure 10. Effect of RhB degradation by PMS at different PMS concentrations.
Figure 10. Effect of RhB degradation by PMS at different PMS concentrations.
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Figure 11. Free radical quenching experiments of the activated PMS degradation RhB reaction system.
Figure 11. Free radical quenching experiments of the activated PMS degradation RhB reaction system.
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Figure 12. Effect of Mn-Co-MCM-41 (PN100D4) activation of PMS for RhB degradation under different atmospheres.
Figure 12. Effect of Mn-Co-MCM-41 (PN100D4) activation of PMS for RhB degradation under different atmospheres.
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Figure 13. Possible reaction mechanism for the degradation of rhodamine B by Mn-Co-MCM-41.
Figure 13. Possible reaction mechanism for the degradation of rhodamine B by Mn-Co-MCM-41.
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Figure 14. Recycling efficiency of Mn-Co-MCM-41.
Figure 14. Recycling efficiency of Mn-Co-MCM-41.
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Table
Table 1. Characterization of three polymers with different hydrophobic ratios.
Table 1. Characterization of three polymers with different hydrophobic ratios.
PolymersHydrophilic/Hydrophobic RatioGPCLCST(°C)MorphologyParticle Size
PN120D430:117,62434.0Random/
PN100D425:116,12133.5Nanoparticles2 nm
PN80D420:114,57333.0Nanoparticles3 nm
GPC: Gel permeation chromatography; LCST: lowest critical solution temperature.
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Peng, W.; Cai, L.; Lu, Y.; Zhang, Y. Preparation of Mn-Co-MCM-41 Molecular Sieve with Thermosensitive Template and Its Degradation Performance for Rhodamine B. Catalysts 2023, 13, 991. https://doi.org/10.3390/catal13060991

AMA Style

Peng W, Cai L, Lu Y, Zhang Y. Preparation of Mn-Co-MCM-41 Molecular Sieve with Thermosensitive Template and Its Degradation Performance for Rhodamine B. Catalysts. 2023; 13(6):991. https://doi.org/10.3390/catal13060991

Chicago/Turabian Style

Peng, Wenju, Lixia Cai, Yani Lu, and Yaoyao Zhang. 2023. "Preparation of Mn-Co-MCM-41 Molecular Sieve with Thermosensitive Template and Its Degradation Performance for Rhodamine B" Catalysts 13, no. 6: 991. https://doi.org/10.3390/catal13060991

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