MCM-41 Mesoporous Materials Research Articles

Functionalization of ionic liquids for heterogeneous catalysis in CO2 conversion: Cycloaddition of epoxides and hydrogenation

The mitigation of environmental impacts caused by greenhouse gas emissions has become increasingly urgent, and the use of CO2 as a primary carbon source is an alternative in chemical transformations, including the synthesis of organic carbonates, formic acid, or methanol. This work aims to synthesize ionic liquids from the imidazolium cation family to be used in the cycloaddition of CO2 with ILs anchored in SiO2-clay heterostructure, MCM-41 and KIT-6 mesoporous materials, as well as the hydrogenation of CO2 with ILs added to ruthenium complexes, i.e., two catalytic systems. The most satisfactory result for CO2 cycloaddition (TON PC = 226) was obtained using the IL (MeO)3Sipmim.Cl anchored in SiO2-clay heterostructure (0.16 mol%) as the catalyst and ZnBr2 (0.04 mol%) as the co-catalyst. The hydrogenation was conducted with the IL (edaO)3Sipmim.Cl and the ruthenium complex Ru-PNN were not successful, but with co-catalyst PEHA, formic acid/formamide was produced (TON Form = 552). The unique catalytic system that showed activity for forming methanol was the commercial Ru-MACHO, Ru-C29H30ClNOP2, (TON MeOH = 3.3). These results highlight the potential of ruthenium-based complexes and supported ionic liquids as active systems in CO2 conversion.

Comprehensive Study on the Adsorption and Degradation of Dichlorodiphenyltrichloroethane on Bifunctional Adsorption-Photocatalysis Material TiO2/MCM-41 Using Quantum Chemical Methods.

The adsorption and degradation capacities of dichlorodiphenyltrichloroethane (DDT) on a photocatalyst composed of TiO2 supported on the mesoporous material MCM-41 (TiO2/MCM-41) were investigated using density functional theory and real-time density functional theory methods. The van der Waals interactions within the PBE functional were adjusted by using the Grimme approach. The adsorption of DDT was evaluated through analyses involving adsorption energy, Hirshfeld atomic charges, Wiberg bond orders, molecular electrostatic potential, noncovalent interaction analysis, and bond path analysis. The findings reveal that DDT undergoes physical adsorption on pristine MCM-41 or MCM-41 modified with Al or Fe due to the very small bond order (only about 0.15-0.18) as well as the change in total charge of DDT after adsorption is close to 0. However, it chemically adsorbs onto the TiO2/MCM-41 composite through the formation of Ti···Cl coordination bonds because the maximum bond order is very large, about 1.0 (it can be considered as a single bond). The adsorption process is significantly influenced by van der Waals interactions (accounting for approximately 30-40% of the interaction energy), hydrogen bonding, and halogen bonding. MCM-41 is demonstrated to concurrently function as a support for the TiO2 photocatalyst, creating a synergistic effect that enhances the photocatalytic activity of TiO2. Based on the computational results, a novel photocatalytic mechanism for the degradation of DDT on the TiO2/MCM-41 catalyst system was proposed.

Synthesis of sustainable rice husk ash-derived nickel-decorated MCM-41 and SBA-15 mesoporous silica materials for hydrogen storage

To promote sustainability, it is essential to make use of biomass waste to create resources that can be transformed into mesoporous materials like silicates. These materials can be used as effective adsorbents for solid-state H2 storage systems. To meet the requirements of these systems, materials must be inexpensive, possess high specific surface areas, have proper pore arrangements, and exhibit reasonable H2 uptake. In this study, sustainable rice husk ash-derived MCM-41-RHA and SBA-15-RHA mesoporous silica materials were developed. These materials were engineered with different levels of Ni loading (2.5–10 wt%) and are used for H2 storage. The prepared MCM-41-RHA and SBA-15-RHA materials have a high BET-specific surface area of 1092.6 m2/g and 539.2 m2/g, respectively, with a mesopore distribution. The best results were observed for samples with a Ni loading of 5 wt%, such as MCM-41-RHA-Ni5 and SBA-15-RHA-Ni5, which demonstrated the highest H2 uptake of 3.64 wt% and 2.48 wt%, respectively, at 77 K and 1 bar. This was due to the strong interaction between the adsorbent and split over hydrogen despite the decrease in the BET-specific surface area after the incorporation of Ni. The enhanced interaction was evidenced by the increased isosteric heat of adsorption observed for MCM-41-RHA-Ni5 and SBA-15-RHA-Ni5, ranging from 21.1 to 8.1 kJ/mol, in contrast to the range of 6.9 to 4.1 kJ/mol for the pristine MCM-41-RHA and SBA-15-RHA. After five successive H2 uptake/release cycles, more than 92 % of the initial capacity was retained. This study presents a sustainable and cost-effective RHA-derived mesoporous silica material decorated with Ni- nanoparticles for solid-state H2 storage.

Mechanistic aspects of n-hexadecane hydroconversion: Impact of di-branched isomers on the cracked products distribution

The mechanism of n-hexadecane (n-C16) hydroisomerization/hydrocracking was studied over bifunctional catalysts employing Pd and Pt as (de)hydrogenation components and large-pore zeolites and (ordered) mesoporous materials as acidic supports. Zeolite Y and Beta supports were compared to amorphous silica-alumina as well as aluminium-containing ordered mesoporous MCM-41, MCM-48 and SBA-15 materials to cover a wide range of pore sizes and topologies. Products were analyzed in terms of mono- and di-branched C16 isomers and cracked products as a function of the n-C16 conversion. All samples followed a similar mechanism in which, at low conversion, di-branched isomers with methyl groups toward the ends of the tetradecane chain were observed. At higher conversion, the products shifted to isomers with methyl groups closer to the center at higher n-C16 conversion. Consistent with these differences, the typical ‘M’ shape distribution of cracked products was obtained at low conversion, which evolved into ideal symmetric cracking patterns at higher conversion. The unusual di-branched isomer distribution at low conversion and the corresponding ‘M’ shaped cracked products distribution have earlier been associated with pore mouth catalysis induced by restricted diffusion in medium-pore zeolites. Here we show that such reaction pathways also occur in catalysts with large enough pores to exclude diffusion restrictions.

Alkyl modified MCM-41 for the sorption of alizarin and limonene from liquid and gas phase

To increase the affinity to hydrophobic molecules, mesoporous hydrophilic material MCM-41 was functionalized by alkyls of various chain lengths, namely ethyl-, isobutyl-, octyl-, and octadecyl-. The performed characterization methods (EA, XRD, DVS, nitrogen sorption, TGA, benzene TPD) demonstrated the successful modification of mesoporous sieve, the preservation of the support´s structure, and especially the increase in its lipophilic character in the modification row: none < ethyl- < isobutyl- < octyl- < octadecyl-. Two hydrophobic molecules, alizarin (from the liquid phase) and limonene (from the liquid and gas phases), were chosen as the model substances for adsorption tests. In the liquid phase, higher amounts of alizarin were adsorbed on the materials with higher lipophilicity, however, the adsorption of limonene displayed distinct behavior. In this case, the specific surface area was more important than lipophilicity. Despite this tendency, a higher amount of the probe was adsorbed in the case of limonene (12.5 mg/gMCM-41) in comparison to alizarin (5.8 mg/goctadecyl modified MCM-41). The opposite trend was seen in the adsorption of limonene from the gas phase because, as would be predicted, the adsorbed amount increased with the increasing lipophilicity. The findings of our study proved that the functionalization of MCM-41 with lipophilic chains can boost its affinity towards lipophilic compounds (alizarin, limonene) demonstrating their potential application, for example, as adsorbents for colorants or terpenes.

Applying MCM-48 mesoporous material, equilibrium, isotherm, and mechanism for the effective adsorption of 4-nitroaniline from wastewater

In this work, the MCM-48 mesoporous material was prepared and characterized to apply it as an active adsorbent for the adsorption of 4-nitroaniline (4-Nitrobenzenamine) from wastewater. The MCM-48 characterizations were specified by implementing various techniques such as; scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, pore size distribution (PSD), and Fourier transform infrared (FTIR). The batch adsorption results showed that the MCM-48 was very active for the 4-nitroaniline adsorption from wastewater. The adsorption equilibrium results were analyzed by applying isotherms like Langmuir, Freundlich, and Temkin. The maximum experimental uptake according to type I Langmuir adsorption was found to be 90 mg g−1 approximately. The Langmuir model with determination coefficient R2 = 0.9965 is superior than the Freundlich model R2 = 0.99628 and Temkin model R2 = 0.9834. The kinetic adsorption was investigated according to pseudo 1st order, pseudo 2nd order, and Intraparticle diffusion model. The kinetic results demonstrated that the regression coefficients are so high R2 = 0.9949, that mean the pseudo 2nd order hypothesis for the adsorption mechanism process appears to be well-supported. The findings of adsorption isotherms and kinetics studies indicate the adsorption mechanism is a chemisorption and physical adsorption process.

Selective Styrene Oxidation Catalyzed by Phosphate Modified Mesoporous Titanium Silicate

Selective oxidation of organics over an efficient heterogeneous catalyst under mild liquid phase conditions is a very demanding chemical reaction. Herein, we first report the modification of the surface of mesoporous silica MCM-41 material by phosphate for the efficient incorporation of Ti(IV) in the silica framework to obtain highly ordered 2D hexagonal mesoporous material STP-1. STP-1 has been synthesized by using tetraethyl orthosilicate, triethyl phosphate, and titanium isopropoxide as Si, P, and Ti precursors, respectively, in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions. The observed specific surface area and pore volume of STP-1 were 878 m2g−1 and 0.75 ccg−1, respectively. Mesoporous STP-1 has been thoroughly characterized by XRD, FT-IR, Raman spectroscopy, SEM, and TEM analyses. Titanium incorporation (Ti/Si = 0.006) was confirmed from the EDX analysis. This mesoporous STP-1 was used as a heterogeneous catalyst for the selective oxidation of styrene into benzaldehye in the presence of dilute aqueous H2O2 as an oxidizing agent. Various reaction parameters such as the reaction time, the reaction temperature, and the styrene/H2O2 molar ratio were systematically studied in this article. Under optimized reaction conditions, the selectivity of benzaldehyde could reach up to 93.8% from styrene over STP-1. Further, the importance of both titanium and phosphate in the synthesis of STP-1 for selective styrene oxidation was examined by comparing the catalytic result with only a phosphate-modified mesoporous silica material, and it suggests that both titanium and phosphate synergistically play an important role in the high selectivity of benzaldehyde in the liquid phase oxidation of styrene.

Confined phase behavior of ethane in nanoporous media: An experimental investigation probing the effects of pore size and temperature

Ethane is rapidly becoming an efficient and dependable clean energy source for fast-growing and developing countries. It is the second most abundant natural gas after methane. However, it poses a major problem for ozone pollution and plays a significant role in greenhouse warming once released into the atmosphere. Therefore, understanding the mechanisms that govern its behavior during storage in natural and artificial nanoporous materials is essential for numerous industrial and environmental applications. In this work, the confined phase behavior of ethane was investigated in ordered mesoporous silica material MCM-41 at varying nanoscale-pore sizes and temperatures. Adsorption and desorption isotherms were experimentally measured for a wide range of nanopore diameters (7, 10.2, 11.3, and 12.3 nm) and temperatures (varying from −65 to −20 °C) using an automated gravimetric nanocondensation apparatus. This system enabled direct quantification of the mass of ethane adsorbed onto the surfaces of nanopores. We examined the impact of the pore diameter and temperature on the adsorption, capillary condensation, and evaporation of ethane in nanoporous media. The capillary condensation and evaporation pressures were determined using the Lorentzian functions. The accuracy of the measurements was confirmed by comparing the experimental bulk condensation pressures with those reported by the National Institute of Standards and Technology (NIST).The results demonstrate that the capillary condensation pressures increased with ascending pore diameters and temperatures. They also indicate that the degree of suppression of the saturation pressure due to confinement is predominant at low temperatures. The percent reduction in the pressure of vapor-liquid phase change decreased with an increase in temperature. A similar trend was observed with respect to changes in the pore size. The results showed that the effect of confinement was weakened as the nanopores became wider. Furthermore, insights were developed about the effects of pore diameter and temperature on the occurrence of the supercritical-like behavior of ethane in nanopores. A good agreement was evident between our results and the examples available in the literature.To the best of our knowledge, we present the first experimental study that describes the confined phase behavior of ethane using a patented gravimetric apparatus. This work presents a systematic approach to understand the effects of confinement in nanoporous media. Furthermore, it can aid the development of new ethane storage applications, especially the characterization of natural and artificial porous materials for energy and environment-related solutions.

Regulating Solvation Structures Enabled by the Mesoporous Material MCM-41 for Rechargeable Lithium Metal Batteries.

For developing the reversible lithium metal anode, constructing an ideal solid electrolyte interphase (SEI) by regulating the Li+ solvation structure is a powerful way to overcome the major obstacles of lithium dendrite and limited Coulombic efficiency (CE). Herein, spherical mesoporous molecular sieve MCM-41 nanoparticles are coated on a commercial PP separator and used to regulate the Li+ solvation structure for lithium metal batteries (LMBs). The regulated solvation structure exhibits an agminated state with more contact ion pairs (CIPs) and ionic aggregates (AGGs), which successfully construct a homogeneous inorganic-rich SEI in the lithium anode. Meanwhile, the regulated solvation structure weakens the interaction between the solvents and Li+, resulting in low Li+ desolvation energy and uniform Li deposition. Thus, a high CE (∼96.76%), dendrite-free Li anode, and stable Li plating/stripping cycling for approximately 1000 h are achieved in the regulated carbonate-based electrolyte without any additives. Therefore, regulating the Li+ solvation structure in the electrolyte by employing a mesoporous material is a forceful way to construct an ideal SEI and harness lithium metal.

Correlation ofo-Ps annihilation properties with catalytic activities of palladium species immobilized on functionalized MCM-41 supports

Design and preparation of highly active and stable supported palladium catalysts have garnered increased attention for their easy separation and reusability. Herein, MCM-41 mesoporous materials functionalized by four different amino functional groups were synthesized by using four commercially available siloxanes and then used to support palladium catalysts. The Fourier transform infrared spectroscopy (FT-IR) was used to analyze the chemical structures of functionalized MCM-41 supports. The thermogravimetric analysis (TGA) and element analysis (EA) were employed to determine the grafting densities of functional groups on MCM-41 supports. The mesoporous structures of functionalized MCM-41 supports and dispersion of palladium species were characterized by high resolution transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD). A study of the materials using positron annihilation lifetime spectroscopy (PALS) reveals the different ortho-positronium (o-Ps) annihilation properties of the supported palladium species on the four supports. Meanwhile, the catalytic activities of supported palladium species on the four supports were evaluated by the Heck reactions of iodobenzene with n-butyl acrylate. At last, the annihilation properties of the supported palladium species on the four supports were successfully correlated with their catalytic activities. The result suggests a facile method to determine and predict the catalytic activities of supported palladium species by using PALS, which may hold great potential in the preparation of rationally designed and highly active supported palladium catalysts.

Base modified organic mesoporous silicas, their characterization and application in the aldol reaction of n-butanal

Representative ordered mesoporous silica materials MCM-41 and SBA-15 were synthesized and modified with nitrogen-containing groups by grafting and co-condensation. The created catalytic centers strongly differ in basicity depending on the degree of substitution of the nitrogen atom. Furthermore, the introduced amount also depends on the structure of the modifier as shown by quantitative liquid phase 1H NMR. This allowed to calculate the turnover number in the aldol condensation of n-butanal which changed in the sequence: secondary > primary >> tertiary >> pyridinic basic centers. Corresponding reaction mechanisms considering the special structural features of the modifier are proposed.

Effect of doped functional bioceramic on in vitro degradation and histocompatibility of poly(l-lactide-trimethylene carbonate-glycolide) terpolymers

The effects of modified calcium carbonate whisker (CCW) and two modified mesoporous silica (SBA-15, MCM-41) bioceramic on the degradation behavior of pure poly(L-lactide-co-trimethylene carbonate-co-glycolide) (PLTG) terpolymer in PBS buffer solution were investigated. Compared with pure PLTG, the addition of inorganic particles can neutralize the acidic products produced during the degradation process and maintain the pH of the system. At the same time, the addition of inorganic particles improves the hydrophilicity of the composite and accelerates the initial degradation rate of the polymer matrix. However, with the prolongation of the degradation time, different inorganic particles show different degradation rate adjustment effects. Because of the barrier effect of the hexagonal phase structure of SBA-15 and MCM-41 mesoporous materials on the diffusion of water molecules and the compatibility with the PLTG matrix is better than that of solid CCW, the addition of mesoporous materials slows down the degradation of the PLTG matrix. The addition of CCW accelerated the autocatalytic degradation of PLTG. It can be seen that the in vitro degradation rate of composite materials can be regulated by adding different inorganic particles, which has important reference value for the artificial regulation of the degradation rate of composite materials. According to the H&E staining appearance, all samples present good histocompatibility. These results suggest that the terpolymer with 5 wt% mesoporous nanoparticles adding is promising for uses as fully biodegradable bone repair scaffold.

Controllable synthesis of yolk–shell nickel phyllosilicate for CO2 methanation: Identifying effect of pore structure of silica sacrificial template

A group of yolk-shell nickel phyllosilicate catalysts were synthesized via the hydrothermal reaction of fibrous silica (KCC-1) and nickel nitrate for CO2 methanation. For the sake of revealing the effect of the pore structure of silica material on the Ni-phyllosilicate morphology, a mesoporous MCM-41 material with a smooth outer surface was used as a sacrificial template for comparison. After the hydrothermal reaction at 180 °C for 36 h, the KCC-1-dervied Ni-phyllosilicate (Ni/K-36) displayed a typical yolk-shell nanosphere morphology covered by nanosheets, while MCM-41-derived Ni-phyllosilicate (Ni/M-36) obtained nanosheets-wrapped sphere morphology with core-shell structure. This result showed that the pore structure of silica material played an important role in the formation of Ni-phyllosilicate with different structures. The fibrous, drive-through channels of KCC-1 enhanced pore accessibility and mass transfer for the simultaneous growth of Ni-phyllosilicate on its external and internal section, and the rapid accumulation of Ni-phyllosilicate outside as “shell” could slow down the further hydrothermal reaction of internal KCC-1, resulting in the shell of Ni-phyllosilicate and yolk of unreacted KCC-1. The chamber between yolk and shell could be expanded by increasing hydrothermal time; however, too long hydrothermal time was adverse for the catalytic activity because of the increased Ni particle size. On the other hand, the gradual etching of MCM-41 sphere from the outer surface resulted in the external accumulation of Ni-phyllosilicate as “shell” and internally unreacted MCM-41 as “core”. The yolk-shell Ni/K-36 exhibited higher catalytic activity than the core-shell structural Ni/M-36 for CO2 methanation owing to high Ni content and similar Ni particle size. In situ DRIFTS analysis showed that the existence of more active formate and absorbed CO intermediates resulted in the high activity of Ni/K-36 for CO2 methanation.

Curcumin Loaded onto Magnetic Mesoporous Material MCM-41 for Controlled and Released in Drug Delivery System

In this work, the mesoporous silica nanoparticles (MSNs) of type MCM-41 were manufactured and modified with Fe3O4 to load curcumin (CUR) CUR@Fe3O4/MCM-41 as an efficient carrier in drug delivery systems. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR), and nitrogen adsorption-desorption isotherms were used to characterize the three samples: pure MCM-41, Fe3O4/MCM-41, & CUR@Fe3O4/MCM-41. Adsorption processes tests were carried out to determine the impact of various variables on the CUR load efficiency. These variables were the carrier dosage, pH, contact time, and initial CUR concentration. The maximal drug loading efficiencies (DL %) were 15.78 % and 22.98 %, respectively. According to the data, The Freundlich isotherm had a stronger correlation coefficient R2= 0.999 for MCM-41, while the Langmuir isotherm had a greater R2 of 0.9666 for Fe3O4/MCM-41. A pseudo-second-order kinetic model fits well with R2=0.9827 for MCM-41 and 0.9994 for Fe3O4/MCM-41. Phosphate Buffer Solution (PBS) with a pH of 7.4 was utilized to study CUR release behavior. According to the research, the maximum release for MCM-41 and Fe3O4/MCM-41 might be 74.1 % and 25.19 % after 72 h, respectively. Various kinetic release models were used, including First-order, Korsmeyer-Peppas, Hixson and Crowell, Higuchi, and Weibull. After 72h, the drug release data were fit using a Weibull kinetic model with an R2 of 0.944 and 0.764 for MCM-41 and Fe3O4/MCM-41, respectively.

Adsorption and Catalytic Activity of Gold Nanoparticles in Mesoporous Silica: Effect of Pore Size and Dispersion Salinity.

The assembled state of nanoparticles (NPs) within porous matrices plays a governing role in directing their biological, electronic, and catalytic properties. However, the effects of the spatial confinement and environmental factors, such as salinity, on the NP assemblies within the pores are poorly understood. In this study, we use adsorption isotherms, spectrophotometry, and small-angle neutron scattering to develop a better understanding of the effect of spatial confinement on the assembled state and catalytic performance of gold (Au) NPs in propylamine-functionalized SBA-15 and MCM-41 mesoporous silica materials (mSiO2). We carry out a detailed investigation of the effect of pore diameter and ionic strength on the packing and spatial distribution of AuNPs within mSiO2 to get a comprehensive insight into the structure, functioning, and activity of these NPs. We demonstrate the ability of the adsorbed AuNPs to withstand aggregation under high salinity conditions. We attribute the observed preservation of the adsorbed state of AuNPs to the strong electrostatic attraction between oppositely charged pore walls and AuNPs. The preservation of the structure allows the AuNPs to retain their catalytic activity for a model reaction in high salinity aqueous solution, here, the reduction of p-nitrophenol to p-aminophenol, which otherwise is significantly diminished due to bulk aggregation of the AuNPs. This fundamental study demonstrates the critical role of confinement and dispersion salinity on the adsorption and catalytic performance of NPs.

Catalytic acetylene hydration over the Zn/Zr-MCM catalyst: Effect of preparation methods for doping zirconia on catalytic performance

The ordered mesoporous Zr-modified MCM-41 materials were synthesized by using four different preparation methods including impregnation method, precipitation method, ultrasound method and trituration method, respectively; active zinc species were immobilized on the modified materials with different methods for introducing zirconia species as effective catalysts for the acetylene hydration. All the synthesized materials were characterized by various techniques including BET, FTIR, XRD, TGA, TEM, XPS, NH3-TPD, H2-TPR, and solid-stated UV–vis. The correlation between structural properties of zirconia modified support and catalytic performance of the Zn catalysts was evaluated in detailed in the acetylene hydration. It is demonstrate that the Zr-modified materials showed the excellent thermostability, and zirconia species addition could enhance the interactions between active metal and support, as well as control the metal particles size with better dispersion. In addition, the substantial enhancement of acid sites and total acid quantity for the modified materials were contributed to the zirconia species addition. Besides, activity evaluation confirms that the Zn/ZM-P catalyst showed more optimistic catalytic performance above 92% C2H2 conversion and 85% selectivity to acetaldehyde in the acetylene hydration due to the stronger metal-support interactions and more acid sites. The study would provide scientific basis for the design of metal catalysts.

One-Pot Green Synthesis of Pyridine-2-carbaldehyde based Chalcones under Solvent-Free Condition using Mesoporous MCM-41 Materials and their Antimicrobial Activities

A simplistic one-pot synthetic protocol was performed using aromatic ketones (1a-e) and substituted pyridine-2-carbaldehydes (2a-e) to obtain various substituted chalcones (3a-e). The synthesis was catalyzed by various metal incorporated (Mn, Al) and acid functionalized (H2SO4, H3PW12O40) mesoporous MCM-41 materials, under solvent free conditions. Using pyridine-2-carbaldehyde (2a), its analogs viz., 4-methoxy (2b), 4-chloro (2c), 4-hydroxy (2d) and 4-nitro (2e) pyridine-2-carbaldehydes were synthesized separately, in order to use these precursors for the formation of the organic derivatives 3b to 3e. Their structural features were characterized by using 1H NMR, 13C NMR and mass spectral techniques. Both the acid functionalized MCM-41 were almost equal in their catalytic performance, whereas among the Mn+-MCM-41 [Mn+ = Mn/Al], the Al incorporated material has shown slightly higher catalytic performance. The antimicrobial activities of the derivatives (3a-e), was investigated on the selected microorganisms, using standard procedures. In these studies, except the compound 3e, remaining compounds have displayed superior biological activity.

Recent progress in magnetic nanoparticles and mesoporous materials for enzyme immobilization: an update.

Enzymes immobilized onto substrates with excellent selectivity and activity show a high stability and can withstand extreme experimental conditions, and their performance has been shown to be retained after repeated uses. Applications of immobilized enzymes in various fields benefit from their unique characteristics. Common methods, including adsorption, encapsulation, covalent attachment and crosslinking, and other emerging approaches (e.g., MOFs) of enzyme immobilization have been developed mostly in recent years. In accordance with these immobilization methods, the present review elaborates the application of magnetic separable nanoparticles and functionalized SBA-15 and MCM-41 mesoporous materials used in the immobilization of enzymes.

Ultrasensitive multiwall carbon nanotube-mesoporous MCM-41 hybrid-based platform for the electrochemical detection of ascorbic acid.

This work presents for the first time the systematic preparation of a novel carbon nanotube-MCM-41 hybrid employing the mesoporous material MCM-41 as a successful dispersant for multiwall carbon nanotubes (MWCNTs). Relevant dispersion variables such as the amount of MWCNTs, MCM-41 concentration, and sonication time were optimized through a central composite design (CDD)/response surface methodology (RSM). Several solvents were evaluated and N,N-dimethylformamide (DMF) was selected because it allowed reaching stable dispersions with very good electrochemical response. The electrochemical performance of glassy carbon electrodes (GCE) modified with different hybrids was evaluated by cyclic voltammetry (CV) using ascorbic acid (AA) as redox marker, while their surface morphology was characterized by SEM microscopy. The optimal MWCNT-MCM-41 dispersion condition was 0.75 mg mL-1 MWCNTs, 0.25 mg mL-1 MCM-41, and 30 min sonication. Both, electrochemical results and SEM images correlate with a percolation behavior from MWCNT-MCM-41 hybrid. Electrooxidation of AA at GCE modified with the optimal hybrid occurred under diffusion control and exhibited an enhanced current response (65 μA) and a lower overvoltage (-0.005 V) compared to bare GCE (ip = 22 μA, Ep = 0.255 V). The amperometric response of AA at GCE/MWCNT-MCM-41 exhibited remarkable figures of merit, including an ultralow detection limit (1.5 nM), high sensitivity (45.4 × 103 μA M-1), excellent short- and long-term stability, and very good anti-interference ability for AA detection. The analytical applicability of the developed electrochemical sensor was evaluated by sensing AA in several real samples, showing excellent correlation with the values reported by manufacturers in both pharmaceutical and food samples.

Ag modification of SBA-15 and MCM-41 mesoporous materials as sorbents of thiophene

Zeolites and some mesoporous materials modified by Ag possess excellent desulfurization performances toward the adsorption of thiophenic compounds. However, Ag in Ag-based sorbents has different forms, and the interactions between different forms of silver and thiophene still require further studies. In this paper, pure silica SBA-15 and MCM-41 mesoporous materials with weak acidity were loaded with Ag from the silver ammonia solution to form Ag/SBA-15 and Ag/MCM-41 sorbents. By comparing the desulfurization efficiencies of the sorbents in the simulated solution of thiophene-cyclohexane, thiophene-benzene, tetrahydrothiophene-cyclohexane and tetrahydrothiophene-benzene, it is found that the adsorption of sorbent for thiophene was accompanied by S-Ag and π complexation, and the adsorption performances of thiophene by the sorbents were greatly affected by benzene. The XPS results show that most Ag in Ag/SBA-15 and Ag/MCM-41 sorbents was metallic Ag, and some Ag strongly interacting with the carrier led to the formation of Ag-O-Si bonds as the main active center of thiophenic compounds. In addition, the sulfur atomic mulliken charges (e-) of different thiopheic compounds (thiophene, tetrahydrothiophene, methylthiophene) will affect the interactions between active components Ag and thiophene sulfur compounds. The desulfurization efficiencies of the sorbents in thiophene-cyclohexane, 2-methylthiophene-cyclohexane, and 3-methylthiophene-cyclohexane showed that the decrease in mulliken charges (e-) of sulfur atoms facilitated the S-Ag bond interaction between the sulfur atom of thiophenic compounds and active component in the sorbent. In conclusion, to obtain the Ag-based sorbent with good adsorption performance for thiophenic compounds, the carrier should contain a certain content of silicon hydroxyl and the suitable pore structure. During the preparation of SBA-15 and MCM-41 mesoporous materials modified by Ag, the Ag-O-Si bonds are more easily formed when silver ammonia interacts with the silicon hydroxyl group on the surface of the carrier. The suitable pore size can inhibit agglomerate to form metallic Ag during the calcination process. These conclusions will provide theoretical guidance for the preparation of silver-based sorbents for thiophene.