Silica Walls Research Articles

Synthesis of heterogeneous nanocomposite catalyst ZrO2@SBA-15 for formic acid production from hemicelluloses

Heterogeneous nanocomposite ZrO2@SBA-15 catalysts containing 10 wt. % of zirconium oxide were synthesized by two methods: co-condensation and incipient wetness impregnation. The silica support and catalysts were characterized by X-ray diffraction, gas adsorption, FTIR-spectroscopy and other physicochemical methods. As a result of zirconia introduction into the silica wall, the mesostructured of SBA-15 is preserved, but the specific surface area and pore Volume are reduced. It was established that during one-stage co-condensation synthesis, the particle fibers shorten and stick together. The catalysts were tested in the process of catalytic hydrolysis-oxidation of hemicelluloses of aspen wood. The optimal formic acid synthesis conditions were determined: 150°С, 3 h. The highest formic acid yield obtained over the catalyst obtained by co-condensation under best reaction conditions was 28.4 wt. %.

Dimercaprol-modified mesoporous silica nanoparticles for efficient removal of toxic mercury ions from aqueous solution.

A surface-modified mesoporous silica nanoparticle containing dimercaprol monomers was created utilizing the sol-gel condensation process, using tetraethyl orthosilicate (TEOS) as the silica source and poloxamer as the structure directing agent. To accomplish this synthesis, 3-glycidoxypropyl triethoxysilane (GPTS, 20mol%) was incorporated into the silica walls during the sol-gel condensation process, along with TEOS. Furthermore, dimercaprol (DM) monomers were incorporated onto silica surfaces by a ring-opening reaction between GPTS epoxy groups, and dimercaprol hydroxyl groups. The prepared dimercaprol-modified silica adsorbent (MSN-DT NPs) material has been studied using a variety of instruments, including XRD, FT-IR, N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG) analysis, and zeta potential analysis. The MSN-DT NPs material selectively adsorbs mercury ions, with a high adsorption amount of 125mg/g and a removal capability of roughly ~ 90% from the original metal ion mixture comprising other competing metals such as Pb2+, Ni2+, Fe2+, and Zn2+. The MSN-DT NPs adsorbent shows recyclable qualities for up to five cycles when treated with an acidic aqueous solution (0.1M HCl). As a result, the MSN-DT NPs adsorbent may be regenerated and reused up to five times without losing its adsorption effectiveness. The experimental findings showed that the MSN-DT NPs adsorbent may be employed to selectively remove hazardous Hg2+ ions from an aqueous solution.

Pore analysis of dendritic mesoporous silica nanoparticles by STEM tomography and nitrogen sorption

Dendritic mesoporous silica nanoparticles (DMSN) provide a high diversity and complexity regarding their pore structure. Herein, we present results related to electron tomographic reconstruction and nitrogen sorption analysis of DMSNs with different pore structures obtained through variation of the surfactant concentration in the synthesis. The tomograms revealed that at all DMSNs exhibit a highly porous shell structure and a denser porous core with smaller pores. The shell generally consists of dendritic silica walls forming a disordered pore system of center radially aligned mesopores. At the highest surfactant concentration these mesopores had a roughly conical geometry, providing a highly accessible pore network. Nitrogen sorption revealed a broad pore size distribution, in agreement with this conical mesopore shape. The mesopore dimensions obtained through reconstruction were in good agreement with the pore size distribution obtained by nitrogen sorption. For intermediate and low surfactant concentrations, different pore geometries were observed in the reconstruction with increasing restriction of the pore volume towards the outer surface of the particles by branching of large pores into smaller ones. Nitrogen sorption analyses support these observations by featuring an increasing hysteresis with decreasing surfactant concentration in the synthesis, which indicates that the accessible pore volume is restricted by smaller mesopores towards the rim of the particles.

Fabrication of Rhenium Disulfide/Mesoporous Silica Core-Shell Nanoparticles for a pH-Responsive Drug Release and Combined Chemo-Photothermal Therapy.

A stimuli-responsive drug delivery nanocarrier with a core-shell structure combining photothermal therapy and chemotherapy for killing cancer cells was constructed in this study. The multifunctional nanocarrier ReS2@mSiO2-RhB entails an ReS2 hierarchical nanosphere coated with a fluorescent mesoporous silica shell. The three-dimensional hierarchical ReS2 nanostructure is capable of effectively absorbing near-infrared (NIR) light and converting it into heat. These ReS2 nanospheres were generated by a hydrothermal synthesis process leading to the self-assembly of few-layered ReS2 nanosheets. The mesoporous silica shell was further coated on the surface of the ReS2 nanospheres through a surfactant-templating sol-gel approach to provide accessible mesopores for drug uploading. A fluorescent dye (Rhodamine B) was covalently attached to silica precursors and incorporated during synthesis in the mesoporous silica walls toward conferring imaging capability to the nanocarrier. Doxorubicin (DOX), a known cancer drug, was used in a proof-of-concept study to assess the material's ability to function as a drug delivery carrier. While the silica pores are not capped, the drug molecule loading and release take advantage of the pH-governed electrostatic interactions between the drug and silica wall. The ReS2@mSiO2-RhB enabled a drug loading content as high as 19.83 mg/g doxorubicin. The ReS2@mSiO2-RhB-DOX nanocarrier's cumulative drug release rate at pH values that simulate physiological conditions showed significant pH responsiveness, reaching 59.8% at pH 6.8 and 98.5% and pH 5.5. The in vitro testing using HeLa cervical cancer cells proved that ReS2@mSiO2-RhB-DOX has a strong cancer eradication ability upon irradiation with an NIR laser owing to the combined drug delivery and photothermal effect. The results highlight the potential of ReS2@mSiO2-RhB nanoparticles for combined cancer therapy in the future.

Construction of Nickel Single Atoms by Using the Inherent Confined Space in Template-Occupied Mesoporous Silica.

Due to their maximum atomic use of metal sites, single-atom catalysts (SACs) exhibit excellent catalytic activity in a variety of reactions. Although many techniques have been reported for the production of SACs, the construction of single atoms through a convenient strategy is still challenging. Here, we provide a facile method to prepare nickel SACs by utilizing the inherent confined space between the template and silica walls in template-occupied mesoporous silica KIT-6 (TOK). After the introduction of nickel-containing precursors into the inherent confined space of the TOK by solid-phase grinding, Ni SACs can be produced promptly during calcination. Single Ni atoms create a covalent Ni-O-Si structure in the TOK, as indicated by density functional theory (DFT) calculations and experimental data. This synthetic approach is easy to scale up, and 10 g of sample can be effortlessly synthesized using ball milling. The resultant Ni SACs were applied to the oxygen evolution reaction and exhibited higher catalytic activity and stability than the comparative sample synthesized in the absence of confined space.

Facile fabrication of confined spaces with molybdenum atoms for fast oxidative desulfurization of fuel oil

Molybdenum-based heterogeneous catalysts are promising for oxidative desulfurization (ODS) of fuel oil. However, the catalytic activity is linked with the dispersibility of Mo atoms on appropriate carriers. Here, Mo-based mesoporous silica was constructed by using confined spaces of as-synthesized SBA-15 (AS), where Mo atoms are homogeneously dispersed. By utilizing facile solid phase grinding followed by calcination, the Mo precursor was introduced into the confined spaces between template and silica walls to form Mo-O-Si structure during which the template P123 was also released. Characterization results revealed that up to 5 wt% of Mo can be well dispersed while sever aggregation takes place in the catalysts derived from template free SBA-15(CS) at similar loading. Confined spaces and abundant hydroxyl groups played a significant role for Mo dispersion. The catalysts derived from AS showed superior ODS activity to their counterparts derived from CS and converted 100 % of DBT in 25 min at T = 30 °C, O/S = 5 and a catalyst dose of 0.1 g. The kinetic studies revealed that the DBT oxidation follow pseudo-first-order kinetic and the activation energy of DBT calculated via Arrhenius equation is 36.97 kJ/mol and 33.88 kJ/mol over Mo-AS and Mo-CS, respectively. The thermodynamic studies demonstrated that DBT oxidation is endothermic with positive Gibbs free energy, suggesting the non-spontaneity of ODS of DBT over Mo based catalysts. Furthermore, the stability and regeneration capability of Mo-AS made it promising for ODS technology for fuel oil.

Unprecedented superoleophobicity achieved with fluorinated wrinkle mesoporous silica

Superoleophobic surfaces can be facilely fabricated by utilizing fluoroalkyl-modified wrinkled mesoporous silica (F-WMS). Initially, a hydrophilic wrinkled mesoporous silica (WMS) (average particle size ∼400 nm) with radial pores and narrow silica walls was prepared, and subsequently modified with a fluoroalkylsilane, specifically 1H,1H,2H,2H-heptadecafluorodecyl trimethoxysilane (FAS-17), to impart low surface energy. Preservation of the WMS pore structure was observed even at a 20 mol% FAS-17 feeding ratio; thus, the resulting F-WMS was designated as F20-WMS. An aluminum substrate was coated with an epoxy resin (EP) for adhesion, followed by spray-coating the F20-WMS suspension onto the EP layer. The resulting EP/F20-WMS coating displayed a notably high static water contact angle (CA) of 172.3° and a low roll-off angle (RA) of 1° Notably, the coating exhibited exceptional oil repellency, showcasing a hexadecane CA of 165.1° and an RA of 4.3°, surpassing the performance of most reported superoleophobic coatings. Plotting cos (CAs on EP/F20-WMS) against (CAs on a flat surface coated with FAS-17), utilizing CA data with various liquids (water – dodecane, 72.1 – 25.3 mN/m, respectively), indicated that the liquids were consistently in Cassie states with a contacting fraction of approximately 0.03 between the liquid droplets and the surface. The unprecedented superoleophobicity of EP/F20-WMS was attributed to the extremely low contact fraction and the presence of a re-entrant texture. Moreover, the coatings exhibited exceptional mechanical durability in tape-peeling tests (50 cycles) and achieved the highest adhesion rating (5 B) in cross-cut tests. This superior oleophobicity, coupled with high durability, opens up opportunities for real-life applications necessitating liquid-free surfaces.

Mesoporous organosilicas with highly-content tyrosine framework as extractive phases for non-steroidal anti-inflammatory drugs in aquatic media

BackgroundAttentions regarding ordered mesoporous silica materials (OMSs), with large specific surface areas and narrow pore size distribution, which are prepared via self-assembly techniques, have been raised in sorption, separation, and sample preparation. However, in order to extend and improve their applications, a functionalization step is required. Organic units can be anchored on the inner or outer surface as well as in the silica wall framework by co-condensation-, grafting-, and periodic mesoporous organosilica (PMO) preparation approaches. Apparently, by synthesizing PMO with extensive and flexible organic bridging groups within the mesoporous wall, an efficient extractive phase can be achieved. ResultsWe employed tyrosine amino acid to synthesize a PMO-based extractive phase. The FT-IR, 1H NMR, HR-ESI-MS, Low angle-XRD, TEM, FESEM, BET, and EDX-MAP analyses confirmed the successful synthesis of PMO within the salt-assisted templating method. A comprehensive study on sorption behavior of PMO was performed and its efficiency was evaluated against the grafting and co-condensation methods. Then, it was implemented to the pipette tip-micro solid phase extraction (PT-μ-SPE) of widely used non-steroidal anti-inflammatory drugs (NSAIDs) in water/wastewaters. Limits of detection and quantification were obtained in the range of 0.1–1.5 and 0.3–5 μg L−1, respectively. The calibration plots are linear in the 1–1000, 3–1000, 10–750, and 3–750 μg L−1, respectively. The intra-and inter-day precision at 50 and 200 μg L−1 levels are 2.9–7.1 % and 3.5–8%, while recoveries are between 84 and 111 %. SignificanceHigh-capacity tyrosine functionalized PMO with 2D hexagonal symmetry silica mesoporous structures found to be highly efficient extractive media. Despite the bulkiness and flexibility of the bridging group within the mesoporous wall, the synthesis condition was optimized in order to load more organic content in the PMO structure. The PMO performance was superior over organically modified ordered mesoporous silica materials prepared by the grafting and co-condensation methods.

PH responsive curcumin released from urea-amine group functionalized mesoporous organosilica nanoparticles.

Studies on natural products with anticancer properties have gained more importance in recent years in order to not damage healthy tissues during cancer treatments or to perform the treatment causing the least damage. Curcumin is a common natural product with anticancer properties, but its low solubility, instability, and bioavailability have limited its use in clinical applications in cancer research. As a proposed solution to this problem, a new mesoporous organosilica nanocarrier (MON-A) functionalized with a 1,2-diphenylethane-1,2-diamine structure capable of pH-controlled release was prepared in this study. MON-A was characterized by TGA, BET, XRD, FT-IR, and SEM-EDS analyses. Dispersion of MON-A into curcumin stock solution in ethanol afforded a curcumin-loaded MON-A-Cur system. Elevated loading capacity and pH-controlled release were provided by the Schiff base reaction that occurred during loading of curcumin with 1,2-diphenylethane-1,2-diamine placed on the silica wall of the nanocarrier system. The encapsulation efficiency was 25% for MON-A-Cur. In in vitro release experiments, curcumin release from the MON-A-Cur system was 0.5% at physiological and endosomal pH values. The resulting low release percentage indicates the presence of very strong interactions between the nanocarrier MON-A and curcumin. This strong interaction showed that MON-A nanocarrier could carry 99.5% of the curcumin without leakage under physiological and endosomal pH conditions without using pore capping agents. At a lower acidic pH value (pH 4.5), 26.3% curcumin release was obtained. These findings showed that the cumulative release of curcumin from the MON-A-Cur system can be achieved in a long-term and pH-controlled manner.

Interfacial nanolayer effect on thermophysical properties of silica-paraffin phase change material - A molecular dynamics simulation

Thermophysical properties of composite phase change materials (PCMs) are influenced by the interfacial nanolayer. Molecular dynamics (MD) method is used to study the effect of interfacial nanolayer on thermophysical properties of silica-paraffin composite PCM. The simulation results show that the melting enthalpy is reduced from 197.9 J·g−1 to 29.1 J·g−1, and the thermal conductivity is enhanced from 0.142 W·m−1·K−1 to 0.268 W·m−1·K−1, when the silica thickness is increased from 0 to 15.0 Å. The interfacial nanolayer is observed in composite PCM, and its thickness increases with the increase of silica wall thickness. In the composite PCM with 7.0 Å silica wall, a loss of 62.9% in the melting enthalpy is observed, with 32.6% attributed to the silica mass and 30.3% attributed to the nanolayer. Based on that, a modified model is proposed to predict the melting enthalpy of composite PCMs by considering the effects of both silica mass fraction and nanolayer. To reveal the thermal conductivity enhancement mechanism, the total heat flux is decomposed into three terms (namely, kinetic energy term, potential energy term and interaction energy term). It is found that the interaction energy term has the largest contribution to the total heat flux. The presence of nanolayer strengths the interactions, leading to the thermal conductivity enhancement.

Amine-bridged periodic mesoporous organosilica adsorbents for CO2 capture

Novel periodic mesoporous organosilica (PMOs) were synthesized using different commercial non-aminated and aminated bisilanes in order to incorporate aminated sites within the silica walls. Three different commercial bisilanes were employed: i)without amine groups, ii)with one amine group, and iii)with two amine groups. Moreover, materials were prepared with different molar ratios of non-aminated and aminated bisilanes. P123 was used as structure directing agent for the mesoporosity. The amino functional groups of the PMOs so prepared were incorporated within the silica walls of the obtained solid particles. Moreover, for comparative purposes, BEBA-0, that is a non-aminated PMO, was functionalized via grafting with N1-(3-trimethoxysilylpropyl)diethylenetriamine (DT) and impregnation with polyethyleneimine (PEI) to produce amino functionalized materials. All these materials were tested for CO2 capture through CO2 adsorption/desorption isotherms and TGA studies. It was observed that increasing the concentration of amine containing bisilane increased the CO2 capture capacity significantly from 21.4 mg/g to 47.3 mg/g. The PMO synthesized with the bisilane containing two amine groups had higher CO2 uptake than the one containing one amine group from 47.3 to 62.6 mg/g due to the presence of more functional groups in the final material (6.0 versus 9.4% wt N, respectively). The cyclic capacity of the adsorbents via a series of adsorption/desorption tests has also been determined, the results showing the low reactivity decay (less than 3%) of the novel PMOs and materials prepared by grafting during the first 10 cycles, when compared with the 13% of PEI-impregnated material.

Hybrid mesoporous silica materials templated with surfactant polyion complex (SPIC) micelles for pH-triggered drug release

New Surfactant PolyIon Complex (SPIC) micelles were assembled by electrostatic complexation of an antibacterial cationic surfactant, cetylpyridinium chloride (CPC), and a double hydrophilic block copolymer (DHBC) containing a neutral comb block of poly(oligo(ethylene glycol)) methyl ether acrylate (PEOGA) and a weak polyacid block of poly(acrylic acid) (PAA). The corresponding SPIC micelles, with a CPC/PAA core and a PEOGA corona, were successfully used as structure directing and functionalizing agents in a soft and sustainable sol-gel strategy, yielding hybrid mesoporous silica (MS) materials with a monomodal pore size distribution centred at 2.8 nm. The influence of synthesis parameters, including the pH, concentrations and ratios of components, was systematically investigated. The obtained hybrid MS materials were intrinsically functional, with PEOGA blocks anchored in silica walls via H-bonding, while weak polyacid blocks, complexed with CPC, were confined within the mesopores. The response of the materials to pH changes (pH 7.4, 4.2 and 3) indicated remarkable stability of the anchored DHBC, while CPC was selectively released under the acidic conditions typical of orodental biofilm microenvironments. This result is noteworthy, since the release of encapsulated amphiphilic drugs into water is less favorable than that of hydrophilic drugs. Owing to the control of their pore and functionality properties, ordered hybrid silica materials templated and functionalized with SPIC systems will be materials of choice for developing pH-responsive biomedical devices using wet processing techniques.

Fabrication of nanoconfined spaces of KIT-6 with small-sized SnO2 for enhanced oxidative desulfurization of fuel: Kinetics and thermodynamics

SnO2 functionalized catalysts have great potential in oxidative desulfurization (ODS) of fuels. However, a facile strategy is required to enhance its catalytic performance. In this contribution, solid phase grinding (SPG) strategy is proposed to functionalize as-synthesized KIT-6 (AK-6) with SnO2 NPs. The SnCl2·2H2O was directly incorporated into the confined spaces between silica walls and template of AK-6 and the subsequent calcination not only remove template (P123) but also convert SnCl2·2H2O to SnO2, which saves much time and energy. Confined spaces and silanols of AK-6 regulated the size and dispersion of SnO2 NPs up to loading of 10 wt% SnO2 (Sn10AK-6). In contrast, larger SnO2 NPs were observed in Sn10CK-6 derived from calcined KIT-6 (CK-6). The activity of Sn10AK-6 is also higher than Sn10CK-6 and converts 96.5 % DBT to sulfones at 303 K in 40 min with 0.1 g of catalyst using O/S = 4 M ratio of NaOCl. The DBT conversion over Sn10AK-6/NaOCl followed pseudo first order kinetics. Moreover, the calculated activation energy of 46.08 kJ/mol and thermodynamic parameters like ΔH = 49.70 kJ/mol, ΔS = −437 J/mol K and ΔG = 180.30 kJ/mol evinced that the ODS over Sn10AK-6 is endergonic, non-spontaneous and practicable under ambient conditions.

Electropolymerization of Polydopamine at Electrode-Supported Insulating Mesoporous Films.

Bioinspired, stimuli-responsive, polymer-functionalized mesoporous films are promising platforms for precisely regulating nanopore transport toward applications in water management, iontronics, catalysis, sensing, drug delivery, or energy conversion. Nanopore technologies still require new, facile, and effective nanopore functionalization with multi- and stimuli-responsive polymers to reach these complicated application targets. In recent years, zwitterionic and multifunctional polydopamine (PDA) films deposited on planar surfaces by electropolymerization have helped surfaces respond to various external stimuli such as light, temperature, moisture, and pH. However, PDA has not been used to functionalize nanoporous films, where the PDA-coating could locally regulate the ionic nanopore transport. This study investigates the electropolymerization of homogeneous thin PDA films to functionalize nanopores of mesoporous silica films. We investigate the effect of different mesoporous film structures and the number of electropolymerization cycles on the presence of PDA at mesopores and mesoporous film surfaces. Our spectroscopic, microscopic, and electrochemical analysis reveals that the amount and location (pores and surface) of deposited PDA at mesoporous films is related to the combination of the number of electropolymerization cycles and the mesoporous film thickness and pore size. In view of the application of the proposed PDA-functionalized mesoporous films in areas requiring ion transport control, we studied the ion nanopore transport of the films by cyclic voltammetry. We realized that the amount of PDA in the nanopores helps to limit the overall ionic transport, while the pH-dependent transport mechanism of pristine silica films remains unchanged. It was found that (i) the pH-dependent deprotonation of PDA and silica walls and (ii) the insulation of the indium-tin oxide (ITO) surface by increasing the amount of PDA within the mesoporous silica film affect the ionic nanopore transport.

Synthesis, thermal evolution and magnetic investigations of SBA-15 silica functionalized with anchored iron phosphonate molecules.

In the current work, we report on the synthesizing of a series of novel nanocomposite materials obtained by functionalizing the SBA-15 silica matrix with anchored iron phosphonate molecules and the following thermal treatment. The obtained results reveal the formation of a unique amorphic layer of Fe-based compounds on the surface of silica walls of SBA-15 channels as a result of the organic groups' decomposition after moderate thermal treatment. Due to their unique structure, represented in an active Fe-containing amorphous coating spread over a large surface area, these materials are of great interest for their potential applications in fields such as catalysis, adsorption, and non-linear optics. The obtained materials remain amorphous, preserving the SBA-15 mesoporous structure up to temperatures of approximately 800 °C, after which the partial melting of the silica backbone is observed with the simultaneous formation of nanocrystals inside the newly-formed glassy mass. All obtained materials were characterized using such techniques as thermogravimetry, transmission and scanning electron microscopy combined with energy dispersive x-ray spectroscopy mapping, Raman spectroscopy, N2sorption analysis, x-ray diffraction, x-ray photoelectron spectroscopy, Mössbauer spectroscopy, and SQUID measurements.

Sub-THz Vibrational Dynamics in Ordered Mesoporous Silica Nanoparticles.

The vibrational dynamics in the sub-THz range of mesoporous silica nanoparticles (MSNs) having ordered cylindrical mesopores was investigated. MCM-41 and SBA-15 particles were synthesized, and their structure was determined using scanning electron microscopy (SEM), low-angle X-ray diffraction (XRD), N2 physisorption analyses, and Raman scattering. Brillouin scattering measurements are reported and enabled determining the stiffness of the silica walls (speed of sound) using finite element calculations for the ordered mesoporous structure. The relevance of this approach is discussed based on the comparison between the numerical and experimental results and previous works reported in the literature.

Evaluations of atomic-resolution strain fields using molecular dynamics simulations combined with corrected smoothed particle hydrodynamics

Deformation analyses of polymeric materials using molecular dynamics (MD) simulations are very useful in evaluating the physical properties based on the atomic features. Generally, the average responses of a system, such as the stress–strain response, are evaluated, but a molecular chain around a solid should deform in an unusual manner in a composite system, such as a solid/polymer system. This may lead to damage and a microscopic inelastic deformation, ultimately affecting the macroscopic behavior of the material. In this study, we propose a technique for use in evaluating the local pseudo-continuum deformation quantities, such as strain and stretch, during MD simulations by introducing deformation analysis via corrected smoothed particle hydrodynamics in a total Lagrangian formulation. Three different types of systems (uniform deformation of an Au crystal, cured resin sandwiched between silica walls, and cured resin containing a nanofiller) are considered, and the unique local deformations in the composite systems are quantitatively evaluated. In particular, local constitutive behavior can be evaluated using this technique, and in the sandwiched system, a high correlation is observed between the local stiffness inhomogeneity and the cohesive failure point. In the filler-containing system, a highly rigid epoxy resin layer is observed around the filler, and local deformation at the poles of the filler is confirmed owing to elongation. The observed trends are consistent with the experimental results. The insights obtained should contribute to the evaluation and understanding of microscopic deformation and damage, which is the beginning of macroscopic failure in a composite material.

Direct and Indirect DNP NMR Uncovers the Interplay of Surfactants with Their Mesoporous Host Material

Two different mesoporous silica materials (SBA-15 and MCM 41) were impregnated with four different, commercially available surfactants, namely, E5, PEG 200, C10E6, and Triton X-100. Differential scanning calorimetry was employed to confirm the confinement of the surfactants in the pores of their host materials. Dynamic nuclear polarization enhanced solid state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were recorded for these materials, showing that both the direct as well as the indirect polarization transfer pathways are active for the carbons of the polyethylene glycol moieties of the surfactants. The presence of the indirect polarization pathway implies the presence of molecular motion with correlation times faster than the inverse Larmor frequency of the observed signals. The intensities of the signals were determined, and an approach based on relative intensities was employed to ensure comparability throughout the samples. From these data, the interactions of the surfactants with the pore walls could be determined. Additionally, a model describing the surfactants’ arrangement in the pores was developed. It was concluded that all carbons of the hydrophilic surfactants, E5 and PEG 200, interact with the silica walls in a similar fashion, leading to similar polarization transfer pathway patterns for all observed signals. For the amphiphilic surfactants C10E6 and Triton X-100, the terminal hydroxyl group mediates the majority of the interactions with the pore walls and the polarizing agent.

Conformation features and interaction of pyrrolidinium-based ionic liquids immobilized with silicon dioxide: Infrared spectroscopy

Ionic liquids (ILs) based on pyrrolidinium cation, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrrTFSI) and 1-butyl-1-methylpirrolidinium dicyanamide (BMPyrrN(CN)2), were incorporated into the silica matrix (SiO2, particle size about 80 nm) by a simple mixing procedure. Semitransparent phase-stable ionogels with an IL content of more than 90 wt% have been obtained and studied by FTIR spectroscopy. The analysis of microscopic mechanisms of interaction, in particular, hydrogen bonding, was carried out using the procedure of fitting the characteristic bands of pure and confined ILs. The observed changes in the position and intensity of some characteristic frequencies were interpreted in terms of the interaction of SiO2 with IL. Under confined condition, the cis–trans equilibrium of both the TFSI− anion and BMPyrr+ cation changes in favor of the trans population due to the predominant interaction of cis conformers with silica walls. This data for confined BMPyrr-based ionic liquids were obtained in our study for the first time and will be useful for designing of a new nanostructured hybrid materials with promising properties.

Sn-doped nanoconfinements of SBA-15 for oxidative desulfurization: Kinetics and thermodynamics

SnO2-containing catalysts are highly active in oxidative desulfurization (ODS) of fuels, and their activity depends on the size and dispersion extent of SnO2 NPs. Herein, we report a facile but efficient strategy for dispersing SnO2 NPs by utilizing the nanoconfined spaces formed between silica walls and template of as-synthesized SBA-15 (AS-15). The Sn precursor is introduced directly into the nanoconfined spaces of AS-15 by solid phase dispersive (SPD) strategy and converted to SnO2 via calcination, during which template P123 was also eliminated. Characterization results demonstrated that up to 10 wt% SnO2 (Sn10AS) can be highly dispersed with smaller size; however, severe aggregation of SnO2 NPs occur in the catalyst obtained from calcined SBA-15 (Sn10CS) with similar loading. Nanoconfined spaces in AS-15 and stronger SnO2 interactions with AS-15 caused by abundant hydroxyl groups are responsible for high dispersion of SnO2 NPs. Moreover, Sn10AS exhibited superior catalytic activity in ODS of fuel and convert 94.5% of DBT within 20 min under ambient conditions with O/S molar ratio of 5 and a catalyst dose of 0.09 g, which is much better than its analogue Sn10CS in terms of DBT conversion rate and time. The ODS process followed pseudo first- order kinetics and activation energy (Ea = 32.38 kJ/mol), enthalpy (ΔH = 35.02 kJ/mol), entropy (ΔS = −376.8 J/mol.K) and Gibbs free energy (ΔG = 149.21 kJ/mol) indicates that the ODS over Sn10AS catalyst is endothermic, non-spontaneous and favorable under ambient conditions. In addition, the regeneration ability and stability of the Sn10AS catalyst made it cost-effectivefor the ODS of fuel.