Pores Of MCM-41 Research Articles

Elucidating the selective adsorption of heavy rare earth by phosphate modified silica: The cooperation of pore confinement and surface structure regulating

Rare earths are considered strategic metals, with heavy rare earth elements of greater importance due to their supply and utilization field. However, efficient separation of heavy rare earth elements is a great challenge as the similar physicochemical properties between light and heavy rare earths. In this study, the highly efficient adsorbents with confinement effect are synthesized by the modification of MCM-41 materials with dimethyl clodronate (NP2) and methylene dichlorophosphate (NDP2). The adsorbents were characterized by XRD, TEM, SEM-EDS, N2 adsorption–desorption, FTIR, TG, 13C NMR, and XPS. It was discovered that the pore size of MCM-41 affected markedly the adsorption selectivity, and the cooperation of the organic adsorption center and pore confinement of MCM-41 support enabled the selective adsorption of heavy rare earth ion. The adsorbent modified by NP2 exhibited high adsorption selectivity toward heavy rare earth ions (Lu3+) with the increase in pore size of MCM-41. In contrast, the expanded pore of MCM-41 enhanced the selectivity of light rare earth ions for the NDP2 modified adsorbents. The distribution coefficient of Lu3+ adsorption over NP2-MCM-41(III) adsorbent reached 20,132 mL g−1 and the separation factor of Lu to La reached 82.17. DFT calculations revealed that a vital driving force for the selective adsorption of Lu was the gap of binding energy between Lu and La complexes with the surface NP2/NDP2 groups. The synergy of pore confinement and organic functional groups in adsorbents in this paper offers a valuable strategy for designing efficient materials in the separation of rare earth elements.

Nanoconfined polyethyleneimine in mesoporous MCM-41 silica for heavy metal ions removal

Water contamination resulting from the presence of the various coexistent pollutants is an urgent environmental challenge, and effective treatment is demanded to remove the toxic substances. The removal of pollutants by adsorption, as an effective, efficient and economic strategy, has been widely used in water treatment. In this work, PEI@MCM-41 was prepared by infiltrating polyethyleneimine (PEI) into the pores of mesoporous MCM-41, and applied for the removal of heavy metal ions. The adsorption kinetics of Cu2+, Ni2+ and Cd2+ by PEI@MCM-41 were supposed to be pseudo-second-ordered, and the adsorption capacities were as high as 39.30, 33.67 and 21.10 mg·g−1, respectively. The influence of temperature, pH, coexistent salt and heavy metal ions concentration on the adsorption performance was studied. Owing to the nanoconfinement effect and hydrogen bond, PEI remained stable during the adsorption and desorption process, and the adsorption capacity for Cu2+ maintained 84.15 % even after four consecutive adsorption–desorption cycles. This work demonstrates that the potential practical applicability of PEI@MCM-41 as promising adsorbent in the removal of heavy metal ions.

Dual role of ‘Al’ impregnated porous MCM-41/ZSM5 composites for the production of biohydrogen and green liquid hydrocarbons

Bio alternative fuels is the most researched concept due to the exhausting fossils and aggregating pollutants. Fuels of liquid and gaseous types are much in demand due to the high expectations from liquid and gas dependent engines. This report is the first of its kind to establish the effectiveness of the synthesized synergistic composite material of micro and mesoporosity for the simultaneous production of biohydrogen and bioliquid organics from kitchen waste. Optimization of temperature, feed:catalyst ratio, and time of study were studied using AlMCM-41 catalyst. Significant yield of products was obtained at 400 0C, 0.5 g of catalyst and at 40 min period. Core -shell type of composites were synthesized using AlMCM-41 and ZSM-5 zeolite with mesopores and micropores as shell and core respectively. The synthesized materials were characterized using XRD, BET, N2 sorption studies, TPD, SEM and TEM techniques. Composite AlMCM-41/ZSM-5 yielded the highest of 70% GLF and maximum of 26.5% of H2. The synergism was well established and also the catalysts showed remarkable reproducibility.

Temperature-Driven Structural Evolution during Preparation of MCM-41 Mesoporous Silica.

This study explores the influence of micelles on the evolution of MCM-41's pore structure via 24 h hydrothermal treatments in a range of temperatures from 100 °C to 200 °C. MCM-41 was characterized using BET, SAXD, FTIR, TEM, and TG-DSC. The findings demonstrate that with temperature elevation from 100 °C to 160 °C, the micelles undergo expansion, leading to an enhanced lattice constant from 4.50 nm to 4.96 nm and an increase in pore diameter from 3.17 nm to 3.45 nm, while maintaining the structural orderliness of the pore channels. Upon cooling, the reversible contraction of micelles and the strategic addition of water glass contribute to a reduction in pore size. However, at a threshold of 180 °C, the SAXD (100) peak's half-peak width surges by approximately 40% relative to that at 160 °C, illustrating a progressive disruption of the hexagonal configuration of MCM-41. Coupled with elevated silica dissolution at higher temperatures in an alkaline solution, a total disintegration of the ordered pore structure at 200 °C results in a drastic reduction in the specific surface area to 307 m2/g. These results are beneficial to developing structural transformation mechanisms of MCM-41 materials and designing mesoporous materials via temperature modulation innovatively.

Thermodynamical characterization of confined indomethacin in MCM-41 pores

Thermodynamical characterization of confined indomethacin in MCM-41 pores

Experimental Investigation and Proposal of Artificial Neural Network Models of Lead and Cadmium Heavy Metal Ion Removal from Water Using Porous Nanomaterials

This study used porous nanomaterials MCM-41 and SBA-15, as well as their modified species, to remove lead and cadmium ions from water. We used X-ray diffraction (XRD), a scanning electron microscope (SEM), the Brunauer–Emmett–Teller (BET), and the Fourier transform infrared (FT-IR) method to investigate the characteristics of porous nanomaterials. Additionally, atomic absorption spectroscopy (AAS) measured the concentration of lead and cadmium ions. The stratigraphic analysis showed the samples’ isothermal shape to be type IV. This study investigated the amount, absorbent, pH changes, and adsorption time parameters. We observed that the adsorption efficiency of lead by the synthesized samples was higher than that of the adsorption of cadmium. Mesoporous structures also displayed increased adsorption efficiency due to the amino group. Four testing stages were conducted to determine the reproducibility of the adsorption by the synthesized samples, with the results showing no significant changes. As a result of the adsorption process, the structure of the recycled sample NH2-MCM-41 was preserved. We also used artificial neural networks (ANN) to propose predictive models based on the experimental results. The ANN models were very accurate, such that the mean absolute error (MAE) was less than 2% and the R2 was higher than 0.98.

Distribution and Transport of CO2 in Hyperbranched Poly(ethylenimine)-Loaded MCM-41: A Molecular Dynamics Simulation Approach.

Fossil fuel use is accelerating climate change, driving the need for efficient CO2 capture technologies. Solid adsorption-based direct air capture (DAC) of CO2 has emerged as a promising mode for CO2 removal from the atmosphere due to its potential for scalability. Sorbents based on porous supports incorporating oligomeric amines in their pore spaces are widely studied. In this study, we investigate the intermolecular interactions and adsorption of CO2 and H2O molecules in hyperbranched poly(ethylenimine) (HB-PEI) functionalized MCM-41 systems to understand the distribution and transport of CO2 and H2O molecules. Density Functional Theory (DFT) is employed to compute the binding energies of CO2 and H2O molecules with HB-PEI and MCM-41 and to develop force field parameters for molecular dynamics (MD) simulations. The MD simulations are performed to examine the distribution and transport of CO2 and H2O molecules as a function of the HB-PEI content. The study finds that an HB-PEI content of approximately 34 wt % is thermodynamically favorable, with an upper limit of HB-PEI loading between 45 and 50 wt %. The distribution of CO2 and H2O molecules is primarily determined by their adsorptive binding energies, for which H2O molecules dominate the occupation of binding sites due to their strong affinity with silanol groups on MCM-41 and amine groups of HB-PEI. The HB-PEI content has a considerable impact on the diffusion of CO2 and H2O molecules. Furthermore, a larger number of water molecules (higher relative humidity) reduces the correlation of CO2 with the MCM-41 pore surface while enhancing the correlation of CO2 with the amine groups of the HB-PEI. Overall, the presence of H2O molecules increases the CO2 correlation with the amine groups and also the CO2 transport within HB-PEI-loaded MCM-41, meaning that the presence of H2O enhances the CO2 capture in the HB-PEI-loaded MCM-41. These findings are consistent with experimental observations of the impact of increasing humidity on CO2 capture while providing new, molecular-level explanations for the macroscopic experimental findings.

Design of Nanostraws in Amine-Functionalized MCM-41 for Improved Adsorption Capacity in Carbon Capture.

Polymeric amine encapsulation in high surface area MCM-41 particles for CO2 capture is well established but has the drawback of leaching out the water-soluble polymer upon exposure to aqueous environments. Alternatively, chemical (covalent) grafting amine functional groups from an alkoxysilane such as 3-aminopropyltriethoxysilane (APTES) on MCM-41 offer better stability against this drawback. However, the diffusional restriction exhibited by the narrow uniform MCM-41 pores (2-4 nm) may impede amine functionalization of the available silanol groups within the inner mesoporous core. This leads to incomplete amine functionalization and could reduce the CO2 adsorption capacity in such materials. Our concept to improve access to the MCM-41 interior is based on the incorporation of nanostraws with larger inner diameter (15-30 nm) to create a hierarchical porosity and enhance the molecular transport of APTES. Halloysite nanotubes (HNT) are used as tubular straws that are integrated into the MCM-41 matrix using an aerosol-assisted synthesis method. Characterization results show that the intrinsic structure of MCM-41 remains unaltered after the incorporation of the nanostraws and amine functionalization. At an optimal APTES loading of 0.5 g (X = 2.0), the amine-functionalized composite of MCM-41 with straws (APTES/M40H) has a 20% higher adsorption capacity than the amine-modified MCM-41 (APTES/MCM-41) adsorbent. Furthermore, the CO2 adsorption capacity APTES/M40H doubles that of APTES/MCM-41 when normalized based on the composition of MCM-41 in the composite particle with straws. The facile integration of nanostraws in MCM-41 leading to hierarchical porosities could be effective toward the mitigation of diffusional restriction in porous materials with potential for other catalytic and adsorption technologies.

Development of date seed extract encapsulated MCM-41: Characterization, release kinetics, antioxidant and antibacterial studies

The encapsulation of natural bioactive compounds in porous support can lead to a sustained release of antioxidants and antimicrobial substances. In this study, the natural antioxidant of date seed extract (DSE) was encapsulated into the mesoporous silica matrix (MCM-41) through the physical vacuum impregnation method. Various characterization studies confirmed the successful encapsulation of DSE into MCM-41 with an encapsulation efficiency of 91%. Date seed extract encapsulated MCM-41(DSE@MCM-41) exhibited rougher morphology, lower specific surface area (1.2 m2 g−1), and lower pore volume (0.023 g cm−3) than MCM-41, indicating higher loading of DSE into the MCM-41 pore channels. The in vitro release profile and bioactive DSE@MCM-41 release kinetics were determined using phosphate buffer solution at pH 5.2 and 7.4. Studies showed that DSE release from DSE@MCM-41 followed first-order kinetics with a sustained release rate, preferably in an acidic medium. The results of radical scavenging activity also showed that the release of antioxidants from DSE@MCM-41 was more sustained than that of free DSE when stored at 4 °C for 3 months. Furthermore, antibacterial studies of DSE@MCM-41 against Escherichia coli and Staphylococcus aureus showed a significant and sustained bactericidal effect at a concentration of 10 mg/mL. These results suggest that DSE-encapsulated MCM-41 could be used as a sustainable-release nanocarrier to extend the shelf-life of food in food packaging applications.

Unexpected Factors Affecting the Kinetics of Guest Molecule Release from Investigation of Binary Chemical Systems Trapped in a Single Void of Mesoporous Silica Particles.

In this work, we present results for loading of well-defined binary systems (cocrystal, solid solution) and untreated materials (physical mixtures) into the voids of MCM-41 mesoporous silica particles employing three different filling methods. The applied techniques belong to the group of "wet methods" (diffusion supported loading - DiSupLo) and "solvent-free methods" (mechanical ball-mill loading - MeLo, thermal solvent free - TSF). As probes for testing the guest1-guest2 interactions inside the MCM-41 pores we employed the benzoic acid (BA), perfluorobenzoic acid (PFBA), and 4-fluorobenzoic acid (4-FBA). The guests intermolecular contacts and phase changes were monitored employing magic angle spinning (MAS) NMR Spectroscopy techniques and powder X-ray diffraction (PXRD). Since mesoporous silica materials are commonly used in drug delivery system research, special attention has been paid to factors affecting guest release kinetics. It has been proven that not only the content and composition of binary systems, but also the loading technique have a strong impact on the rate of guests release. Innovative methods of visualizing differences in release kinetics are presented.

Experimental and simulation investigation of water vapor adsorption on mesoporous MCM-41 derived from natural Opoka

Highly ordered hexagonal mesoporous silica was successfully synthesized from natural Opoka minerals, and an all-atom model of MCM-41 was constructed by simulation. The samples were characterized by XRD, N2 adsorption, FE-SEM, TEM and FT-IR, and its water vapor adsorption/desorption performance were also evaluated. The structural rationality of MCM-41 model was verified by XRD, Connolly volume, and radial distribution function. The adsorption behavior of water molecules on MCM-41 model was simulated by Monte Carlo method, and the adsorption mechanism was discussed at the micro level. Results showed that the synthesized MCM-41 possessed a large surface area of 988 m2/g and pore volume of 1.02 cm3/g, and an average pore diameter of 4.1 nm. The moisture adsorption/desorption content of MCM-41 can be as high as 82 % and 67 %, respectively, with a high adsorption/desorption rate. The simulation results show that the adsorption sites of water molecules on MCM-41 are mainly concentrated on the silanol groups and skeleton defects of the pore surface. With the increase of pressure, the adsorption of water molecules on the surface of MCM-41 pores changes from mono-layer to multi-layer. Meanwhile, microdroplets are formed due to hydrogen bonding, and further capillary condensation occurs in the pores.

Enhanced adsorption-oxidation performance of PMo12 immobilized onto porous MCM-41 derived from rice husk for H2S at room temperature

In this study, a novel adsorbent (PMo12@RH-MCM-41) was synthesized through impregnation method using waste rice husk and phosphomolybdic acid (PMo12) as the silica source and active center, respectively. The regular fibrous-like structure of RH-MCM-41 with hierarchical pores provides a high percentage of exposed PMo12 sites, enhancing the desulfurization activity of PMo12. PMo12@RH-MCM-41 exhibited excellent desulfurization ability in comparison with PMo12 and RH-MCM-41, demonstrating the synergistic effect between PMo12 and RH-MCM-41. The efficient transformation of H2S to elemental S with a yield of 61.3 % was achieved at room temperature. The PMo12@RH-MCM-41 regenerated by hot air purging can maintain the stable desulfurization ability for more than 8 cycles. The mechanism analysis demonstrated the redox ability of PMo12 in the heterogeneous desulfurization system. This work provides important insights for the application of polyoxometalates in solid-phase desulfurization, and broadens high-value utilization patterns of agricultural waste biomass.

Enhancement of photoactivity and cellular uptake of (Bu4N)2[Mo6I8(CH3COO)6] complex by loading on porous MCM-41 support. Photodynamic studies as an anticancer agent

The incorporation by ionic assembly of the hexanuclear molybdenum cluster (Bu 4 N) 2 [Mo 6 I 8 (CH 3 CO 2 ) 6 ] ( 1 ) in amino-decorated mesoporous silica nanoparticles MCM-41 , has yielded the new molybdenum-based hybrid photosensitizer 1@MCM-41 . The new photoactive material presents a high porosity, due to the intrinsic high specific surface area of MCM-41 nanoparticles (989 m 2 g −1 ) which is responsible for the good dispersion of the hexamolybdenum clusters on the nanoparticles surface, as observed by STEM analysis. The hybrid photosensitizer can generate efficiently singlet oxygen, which was demonstrated by using the benchmark photooxygenation reaction of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) in water. The photodynamic therapy activity has been tested using LED light as an irradiation source (λ irr ~ 400–700 nm; 15.6 mW/cm 2 ). The results show a good activity of the hybrid photosensitizer against human cervical cancer (HeLa) cells, reducing up to 70 % their viability after 20 min of irradiation, whereas low cytotoxicity is detected in the darkness. The main finding of this research is that the incorporation of molybdenum complexes at porous MCM-41 supports enhances their photoactivity and improves cellular uptake, compared to free clusters. Incorporation of photoactive molybdenum complexes at porous MCM-41 supports enhance their photoactivity and improves cellular uptake. • A hexanuclear molybdenum cluster has been incorporated in amino-decorated mesoporous silica nanoparticles. • The new photoactive material can generate efficiently singlet oxygen upon illumination with white light. • The photodynamic therapy activity has been tested with HeLa cells, reducing up to 70 % their viability. • The incorporation of molybdenum complexes at porous supports enhances their photoactivity and improves cellular uptake.

Observation of a solid phase under measuring the 3He diffusion coefficient in the nanopores of the MCM-41 adsorbent

Using nuclear magnetic resonance, the stimulated spin-echo method was applied to measure the diffusion coefficient in a 3He monolayer adsorbed inside cylindrical pores (channel diameter 25 Å) of a new-generation nanostructured adsorbent MCM-41. Helium was let into the sample in small portions, which made it possible to change in a controlled way the coverage of the walls of the cavities in the adsorbent. It is found that the measured dependence of the stimulated spin-echo amplitude on the square of the magnetic field gradient is exponential. The nature of this dependence made it possible to determine the diffusion coefficient in the adsorbed monolayer. The value of this coefficient turned out to be close to the diffusion coefficient in solid helium, which indicates that the first 3He monolayer on the inner surface of the cylindrical cavity is solid. This conclusion was confirmed when calculating the pressure acting on the helium monolayer due to the van der Waals forces from the adsorbent substance.

Utilization of e-wastes as a sustainable silica source in synthesis of ordered mesostructured titania nanocomposites with high adsorption and photoactivity

The production of electronic waste (e-waste) is rapidly increasing globally. This waste is not effectively used at present. Moreover, few studies have investigated the synthesis of photocatalytic materials using materials recovered from e-waste. This paper reports the synthesis of a nanosized TiO2 catalyst supported on mesoporous Mobil Composition of Matter No. 41 (MCM-41). Sodium silicate precursor extracted from e-waste was used as a silicon source for the synthesis of an MCM-41 support. Transmission electron microscopy images revealed that TiO2 was successfully embedded in the pores of MCM-41. The particle size and crystalline structure of TiO2 was controlled by the mesostructured MCM-41 support. Nitrogen adsorption isotherms confirmed that TiO2/MCM-41 had uniform pore size (2.83 nm), a large pore volume (0.757 cm3/g), and high surface area (947 m2/g). The purity of TiO2/PRA-MCM-41 was as high as 99.90 wt%. The influences of TiO2 ratio, calcination temperature, and catalyst weight on the efficiency of methylene blue photodegradation were investigated. Different proportions of titanium species deposited on the MCM-41 surface resulted in the formation of differently sized TiO2 particles and strongly influenced the adsorption and photocatalytic activity. The TiO2/MCM-41 composite synthesized from e-waste had higher photocatalytic performance than TiO2/silica gel and pure TiO2. The composite catalyst had a combination of features that ensured high photocatalytic activity: small TiO2 particles, effective dispersion of TiO2 on the mesoporous silica, and high adsorptive efficiency. The proposed method, using an environmentally friendly approach, can reduce the accumulation of e-waste and produce highly valuable photocatalyst composites for environmental uses.

MAL: High performance method for loading hydrophobic molecular materials into MCM-41 mesoporous silica – analysis of confined L-tryptophan by Raman spectroscopy

The capabilities of the recent MAL (Milling-Assisted Loading) method were analyzed for the geometric confinement of amino acids within mesoporous silica matrices. The present study has shown a high filling degree (45 wt%) of L-tryptophan into unmodified MCM-41 pores. It was shown that the low-frequency Raman spectroscopy is a suited technique to determine that molecular materials are actually confined into silica-based ordered mesoporous materials from the analysis of lattice mode region, and to probe the molecular conformation of confined materials and their interaction with the pore surface from the analysis of internal vibrations.

Confinement in Extruded Nanocomposites Based on PCL and Mesoporous Silicas: Effect of Pore Sizes and Their Influence in Ultimate Mechanical Response

In this study, nanocomposites based on polycaprolactone (PCL) and two types of mesoporous silicas, MCM-41 and SBA-15, were attained by melt extrusion. The effect of the silica incorporated within the PCL matrix was observed, firstly, in the morphological characteristics and degradation behavior of the resultant composites. DSC experiments provided information on the existence of confinement in the PCL–SBA-15 materials through the appearance of an additional small endotherm, located at about 25–50 °C, and attributed to the melting of constrained crystallites. Displacement to a slightly lower temperature of this endothermic event was observed in the first heating run of PCL–MCM-41 composites, attributed to the inferior pore size in the MCM-41 particles. Thus, this indicates variations in the inclusion of PCL chains within these two mesostructures with different pore sizes. Real-time variable-temperature small-angle X-ray scattering (SAXS) experiments with synchrotron radiation were crucial to confirm the presence of PCL within MCM-41 and SBA-15 pores. Accurate information was also deduced from these measurements regarding the influence of these two mesoporous MCM-41 and SBA-15 silicas on PCL long spacing. The differences found in these morphological and structural features were responsible for the ultimate mechanical response exhibited by the two sets of PCL nanocomposites, with a considerably higher increase of mechanical parameters in the SBA-15 family.

Behavior of mesoporous silica under 2 MeV electron beam irradiation

This work deals with the evolution of the mesoporous structure of two silicas MCM-41 and SBA-15 under a 2 MeV electron beam as a function of the dose (0–5 GGy). For a dose of 2 GGy, the pore volume of the two materials decreases significantly by 40–45%. The irradiation-induced porosity closure is significantly more effective on smaller pores, resulting in a loss of the mesoporous network concerning MCM-41 (pore diameter ∼ 3.8 nm) and the conservation of the SBA-15 one (pore diameter ∼ 7.0 nm). The mechanism of silica porosity closure/collapse has not been fully identified, but it might result from damage effects as “Knock-on” processes. From a technological point of view, this phenomenon could be exploited for RadioNuclides (RN) encapsulation in a self-evolving porous material.

A novel strategy for stabilization of sub-nanometric Pd colloids on kryptofix functionalized MCM-41: nanoengineered material for Stille coupling transformation

The stabilization of sub-nanometric metal particles (< 1 nm) with suitable distribution remained challenging in the catalytic arena. Herein, an intelligent strategy was described to anchoring and stabilizing sub-nanometric Pd colloids with an average size of 0.88 nm onto Kryptofix 23 functionalized MCM-41. Then, the catalytic activity of Pd@Kryf/MCM-41 was developed in Stille coupling reaction with a turnover frequency (TOF) value of 247 h−1. The findings demonstrate that porous MCM-41 structure and high-affinity Kryptofix 23 ligand toward adsorption of Pd colloids has a vital role in stabilizing the sub-nanometric particles and subsequent catalytic activity. Overall, these results suggest that Pd@Kryf/MCM-41 is a greener, more suitable option for large-scale applications and provides new insights into the stabilization of sub-nanometric metal particles.

Anchoring of palladium onto the surface of porous MCM-41 modified with DL-pyroglutamic acid as a novel heterogeneous catalyst for Suzuki–Miyaura coupling reactions

An environmentally friendly solid catalyst was synthesized by palladium (II) anchored to the silica MCM-41 after synthetic modification with DL-pyroglutamic acid (PCA). Palladium particles were immobilized on the surface of an acid-functionalized MCM-41 (MCM-41@PCA/Pd) and was identified using several analytical methods. In this method, the surface of MCM-41 was moderated by DL-pyroglutamic acid functional molecule, which assist the steady distribution of Pd particles. By electron donation from the acid molecule, the electron density of Pd particles increases. This extended catalyst displays excellent catalytic performance toward the Suzuki coupling reaction under mild reaction conditions with a large range of substrates for the reaction. The MCM-41@PCA/Pd catalyst offers eight reuse cycles without the loss of its activity. The immobilized complex did not leach or decompose through the catalytic reactions, indicating practical benefits over the homogeneous catalysis.