Periodic Mesoporous Materials Research Articles

A Chemosensor of 1,8-Dihydroxyanthraquinone PMOs Prepared in a Ternary Deep Eutectic Solvent for the Sensitive Detection of Cu2.

A novel type of organic–inorganic hybrid periodic mesoporous materials based on 1,8-dihydroxyanthraquinone (DHAQ-PMOs) was synthesized in a ternary deep eutectic solvent (DES). In the process of the material synthesis, an organosiloxane precursor (DHAQ-Si) and tetraethylorthosilicate (TEOS) were used as the mixed Si source, and cetyltrimethylammonium bromide (CTAB) was used as the structure directing agent. The DES formed by choline chloride (ChCl), urea (U), and ethylene glycol (EG) was used as a green solvent. The water needed for the hydrolysis of DHAQ-Si and TEOS was provided from free water in the sodium hydroxide solution. As characterized by small-angle X-ray scattering, nitrogen adsorption/desorption isotherms, and high-resolution transmission electron microscopy, the obtained mesoporous materials exhibit a two-dimensional hexagonal (P6mm) structure. DHAQ possesses double fluorescence emission peaks at ca. 520 and 580 nm due to the effect of the excited-state intramolecular proton transfer (ESIPT). For DHAQ-PMOs, the silica framework can provide a rigid environment that makes the fluorescence properties more stable and the fluorescence emission peak appears to red-shift obviously. The DHAQ-PMOs have high selectivity and sensitivity in a wide pH range that can be used to detect Cu2+, and the limit of detection (LOD) is as low as 2.39 × 10–9 M. Fluorescence polarization experiments, high-resolution mass spectrometry, and Fourier transform infrared spectroscopy were used to study the coordination interaction between DHAQ and Cu2+. The density functional theory (DFT) was used to further prove the coordination ability and interaction between DHAQ and Cu2+. XPS spectra were also done to prove the coordination of DHAQ and DHAQ-PMO-10 with Cu2+. In addition, confocal fluorescence microscope images exhibit that DHAQ-PMOs can detect Cu2+ in living cells. The results show that DHAQ-PMOs have great application potential as a sensor for the detection of Cu2+.

Chemical sensors based on a Eu(iii)-centered periodic mesoporous organosilica hybrid material using picolinic acid as an efficient secondary ligand.

Through a series of post synthetic modification methods applied to the 100% trans ethenylene-bridged Periodic Mesoporous Organosilica (ePMO), the lanthanide-functionalized hybrid nanomaterial ePMO@Eu_PA (PA = picolinic acid) has been prepared. The pristine and lanthanide-grafted ePMO materials were characterized by powder X-ray diffraction, DRIFTs, TGA, N2 sorption, SEM and TEM. The selected PA ligand could effectively sensitize the Eu3+ ion, leading to the characteristic luminescence of Eu3+ in ePMO@Eu_PA. The luminescence properties of the ePMO@Eu_PA were studied in detail in the solid state and after dispersing in water. The material was investigated for the use as ion sensor and showed a selective monitoring of Fe3+, Co2+ and Cu2+ ions with luminescence quenching. In addition, the material showed a linear relationship between the luminescence intensity and the pH value in the pH range from 7.7 to 10.2. These findings demonstrate that ePMO@Eu_PA possesses potential practical applications in ion sensing as well as in pH sensing.

Controlling Particle Morphology and Pore Size in the Synthesis of Ordered Mesoporous Materials.

Ordered mesoporous materials have attracted considerable attention due to their potential applications in catalysis, adsorption, and separation technologies, as well as biomedical applications. In the present manuscript, we aim at a rational design to obtain the desired surface functionality (Ti and/or hydrophobic groups) while obtaining short channels (short diffusion paths) and large pore size (>10 nm). Santa Barbara Amorphous material SBA-15 and periodic mesoporous organosilica PMO materials are synthesized using Pluronic PE 10400 (P104) surfactant under mild acidic conditions to obtain hexagonal platelet-like particles with very short mesochannels (300–450 nm). The use of expanders, such as 1, 3, 5-trimethylbenzene (TMB) and 1, 3, 5-triisopropylbenzene (TIPB) were tested in order to increase the pore size. TMB yielded in the formation of vesicles in all the syntheses attempted, whereas P104 combined with TIPB resulted both in expanded (E) E-SBA-15 and E-PMO with 12.3 nm pore size short channel particles in both cases. Furthermore, the synthesis method was expanded to the incorporation of small amount of Ti via co-condensation method using titanocene as titanium source. As a result, Ti-E-SBA-15 was obtained with 15.5 nm pore size and isolated Ti-sites maintaining platelet hexagonal morphology. Ti-PMO was obtained with 7.8 nm and short channels, although the pore size under the tried synthesis conditions could not be expanded further without losing the structural ordering.

Dissolution–Recrystallization Formation of Huge Thin 2D Silicalite Lamella for Promoted Sorption

AbstractAn all silica MEL‐type silicalite‐2 nanocrystal is hydrothermally treated in coexistence with cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) at ordinary and elevated temperatures. From monitoring its structural transition process by various physico‐chemical methodologies, it is found that, instead of simple delamination, silicalite‐2 nanocrystal changes with a dissolution and recrystallization mechanism by treatment at an elevated temperature and for a long time, that is, it is first dissolved and then reorganized to huge 2D platelets via an intermediate step forming periodic mesoporous material. The newly formed nanoplatelets (h‐nanoplatelets) from in‐plane growth along a (or b)‐, c‐directions (normal to b (or a)‐axis) are of silicalite (either MEL or MEL/MFI intergrowth)‐type framework topology with a thickness of 3.3 nm (the equivalent of ≈1.6 unit cell) and interspersed with a minor part of small square‐like MFI‐type nanoplatelets (s‐nanoplatelets). The h‐nanoplatelets have expanded lattice parameters and a larger micropore size compared to the parent silicalite‐2 nanocrystal and s‐nanoplatelets, whose micropore structure are modified so as to benefit from both equilibrium adsorption and desorption‐recovering ability of organic contaminants particularly at a low vapor pressure range. This is the first report regarding the dissolution–recrystallization formation of 2D lamella‐type silicalites mediated by popular types of surfactant and base species.

Chemical sensors based on nano-sized lanthanide-grafted periodic mesoporous organosilica hybrid materials

Nano-sized PMOs grafted with lanthanides show selective ion sensing for Pb2+ and Cr3+ and strong solvatochromism allowing their use as protic and aprotic solvent sensors.

Selectivity for CO2 over CH4 on a functionalized periodic mesoporous phenylene-silica explained by transition state theory

Efficient separation of CO2/CH4 is critical in biogas upgrading, requiring highly selective adsorbents. Based on the adsorption energies of −0.30 and −0.14eV, previously calculated by dispersion corrected density functional theory for adsorption/desorption of CO2 and CH4 on the functionalized periodic mesoporous phenylene-silica material APTMS@Ph-PMO, respectively, transition state theory rates were derived and used to simulate the adsorption/desorption rates of these two gases on APTMS@Ph-PMO. The latter yielded an estimation of initial CO2/CH4 selectivity at various temperatures. At T=298K, selectivity of 32.2 agrees to an experimental value of 26.1, which validates the method used for evaluating CO2/CH4 adsorption selectivities.

Novel photoactive lanthanide hybrids covalently grafted on functionalized periodic mesoporous organosilicons (PMOs) by Schiff-base derivative

Novel functionalized periodic mesoporous organosilicons (Salen-PMOs) were synthesized by co-condensation of 1,2-bis(triethoxysilyl)ethane (BTEE) and the modified Salen-type Schiff-base compound N,N′-bis(salicylidene)ethylenediamine (Salen-Si) in the presence of Pluronic P123 surfactant as a template. N,N′-bis(salicylidene)ethylenediamine (Salen) grafted on the coupling agent 3-(triethoxysilyl)-propy-lisocyanate (TEPIC) was used as the precursor for the preparation of periodic mesoporous materials. The two kinds of resulting materials(denoted as Ln(Salen-PMOs)2 and Ln(Salen-PMOs)2phen, respectively Ln = Eu, Tb) were characterized in detail by Fourier-transform infrared spectra, ultraviolet–visible absorption spectra, small-angle X-ray diffraction, nitrogen adsorption/desorption isotherms, photoluminescence spectroscopy and luminescence decay time measurements. The results reveal that luminescent periodic mesoporous materials have high surface area, uniformity in the mesoporous structure and good crystallinity. Furthermore, the efficient intramolecular energy transfer in mesoporos material Ln(Salen-PMOs)2phen mainly occurs between the modified ligand Salen-Si and the central Eu3+ ion. In addition, the luminescent mesoporous hybrid containing terbium ions, designated as Tb(Salen-PMOs)2 and Tb(Salen-PMOs)2phen were also prepared, and were found to emit green photoluminescence characteristic of terbium ions.

Investigations of the Mechanical and Hydrothermal Stabilities of SBA-15 and Al-SBA-15 Mesoporous Materials

Periodic mesoporous materials possess high surface to volume ratio and nano-scale sized pores, making them potential candidates for heterogeneous catalysis, ion exchange, gas sensing and other applications. In this study, we use in situ small angle x-ray scattering (SAXS) and molecular dynamics (MD) simulations to investigate the mechanical and hydrothermal stability properties of periodic mesoporous SBA-15 silica and SBA-15 type aluminosilica (Al-SBA-15) to extreme conditions. The mesoporous SBA-15 silica and Al-SBA-15 aluminosilica possess amorphous frameworks and have similar pore size distribution (pore size ∼9-10 nm). The in situ SAXS measurements were made at the B1 beamline, at the Cornell High Energy Synchrotron Source (CHESS). The mesoporous SBA-15 silica and Al-SBA-15 aluminosilica specimens were loaded in a diamond anvil cell (DAC) for pressure measurements, and, separately, with water in the DAC for hydrothermal measurements to high P-T conditions (to 255 °C and ∼ 114 MPa). Analyses of the pressure-dependent SAXS data show that the mesoporous Al-SBA-15 aluminosilica is substantially more mechanically stable than the SBA-15 silica. Hydrothermal measurements show a small net swelling of the framework at elevated P-T conditions, due to dissolution of water into the pore walls. Under elevated P-T conditions, the Al-SBA-15 aluminosilica shows significantly greater hydrothermal stability than the SBA-15 silica. Our MD simulations show that the bulk modulus value of periodic mesoporous SBA-15 silica varies exponentially with percentage porosity. Molecular dynamics simulations are being made in order to better understand how the pore architecture and the chemical composition of the host structure govern the stability properties of the mesoporous materials.

Mesoporous Silica Coating on Rf-Sputtered Apatite/Titanium Substrate

The preparation of mesoporous silica coated rf-sputterd apatite / titanium substrate and protein adsorptive property is reported. Hydroxyapatite coated titanium implant has been used, and the adsorption of proteins onto implant is very important for bond formation between bone and implant. Mesoporous silica (MPS) materials have been extensively studied as carriers of bio-molecules due to their potential practical applications in medical materials. Pore diameters of 1.5 – 30 nm of the periodic mesoporous materials are close to the diameters of target molecules and high adsorbed amount of proteins onto MPS has been reported, and also enclosure of the protein in a well-defined space may help to prevent denaturation. Previously, we reported the MPS coating on the porous hydroxyapatite (HAp) ceramics obtained by dip-coating method, and by the vapor phase synthesis. Protein adsorption on the porous HAp with the MPS coatings was evaluated using UV-VIS spectrometry, and the quantity of adsorbed amount of protein was remarkably improved. In this study, the HAp deposition on Ti substrate (HAp/Ti) was carried out by rf magnetron sputtering and hydrothermal treatment, and MPS coating on HAp/Ti using LB deposition apparatus to improve the protein adsorptive property of HAp/Ti. The quantity of adsorbed protein onto the HAp /Ti was around 12 times high, and that onto the MPS/HAp/Ti was 18 times high compared to that on Ti substrate.

Evaporation-induced Self-assembly Process Controlled for Obtaining Highly Ordered Mesoporous Materials with Demanded Morphologies.

A large number of periodic mesoporous materials have been reported using amphiphilic organic molecules with increasing development of synthetic methods for mesostructural, morphological, and compositional designs. The evaporation-induced self-assembly (ESIA) process to fabricate ordered mesoporous films is one of the most essential synthetic methods, which has extensively been applied for obtaining a wide variety of samples (e.g., films and monoliths, including powders). It contains complicated physical variations and chemical reactions, but has been simply explained by several research groups. However, a current, exact understanding of such complicated systems should be given with respect to all the variations and reactions. In this article, I have mainly surveyed the exact EISA process by considering the difference between simple and controlled EISA processes on the basis of my own experiments. I believe that the insights are consequently helpful for obtaining highly ordered mesoporous materials with demanded morphologies.

A high-pressure synthesis of hydrothermally stable periodic mesoporous crystalline aluminosilica materials

We report a synthetic route to mesoporous crystalline aluminosilica materials using high pressure and temperature.

Nanocasting of Periodic Mesoporous Materials as an Effective Strategy to Prepare Mixed Phases of Titania

Mesoporous titanium dioxide materials were prepared using a nanocasting technique involving silica SBA-15 as the hard-template. At an optimal loading of titanium precursor, the hexagonal periodic array of pores in SBA-15 was retained. The phases of titanium dioxide could be easily varied by the number of impregnation cycles and the nature of titanium alkoxide employed. Low number of impregnation cycles produced mixed phases of anatase and TiO2(B). The mesoporous TiO2 materials were tested for solar hydrogen production, and the material consisting of 98% anatase and 2% TiO2(B) exhibited the highest yield of hydrogen from the photocatalytic splitting of water. The periodicity of the pores was an important factor that influenced the photocatalytic activity. This study indicates that mixed phases of titania containing ordered array of pores can be prepared by using the nanocasting strategy.

Highly sensitive and selective fluorescent detection of rare earth metal Sn(II) ion by organic fluorine Schiff base functionalized periodic mesoporous material in aqueous solution

Abstract A Schiff base 3-((4-aminophenyl)imino)-5-fluoroindolin-2-one (APIFI) functionalized mesoporous material (APIFI-SBA) has been first developed by covalent binding with epoxypropoxyl groups on the inner surface of siliceous wall. The obtained material has been characterized by small angle X-ray diffraction, nitrogen adsorption–desorption and Fourier transform infrared spectroscopy. The results indicate that the Schiff base molecule APIFI is successfully immobilized within the channels of mesoporous material with linked ligand. Moreover, the ordered porous structure of mesoporous host is still retained on the Schiff base functionalized mesoprous material. The material APIFI-SBA shows high sensitivity and selectivity of detecting Sn2+ ions in aqueous media. A good linearity between the fluorescence intensity of the material and the concentration of Sn2+ ion is constructed, which enables it as a fluorescent chemosensor for detecting Sn2+ ion in aqueous solution. In future, it is potential to be used as a novel chemosensor for a lot of practical applications in chemical, environmental and biological systems.

A Brief Overview of Periodic Mesoporous Materials as Robust Supports for Photocatalytic Splitting of Water

The growing demand to power the World has prompted intense research into the pursuit of developing sustainable and renewable sources that are carbon neutral. In this respect, the photocatalytic splitting of water to generate hydrogen and oxygen as fuel seems to be an attractive option. The rapid advances in the field of nanostructured materials has made it possible to design materials with novel properties, high reactivity, and catalytic efficiency. In recent years, mesoporous materials have proven to be popular choice for dispersion of photocatalytically active semiconductors. Their relatively high surface areas, large pore volumes, and tunable pore sizes allows for good dispersion of spatially isolated semiconductors. Such spatially isolated semiconductors and single-site containing mesoporous photocatalysts offer fresh perspective towards the realization of overall water splitting photocatalysts.

An insight into the adsorption and photocatalytic degradation of rhodamine B in periodic mesoporous materials

The present study explores the different modes of adsorption of rhodamine B dye over two different siliceous (Si-MCM-48 and Si-MCM-41) and titania loaded siliceous (Ti-MCM-48 and Ti-MCM-41) mesoporous materials. The equilibrium adsorption studies indicate that siliceous as well as Ti-loaded mesoporous materials are good adsorbents for the removal of rhodamine B dye from aqueous solutions, and an enhanced uptake was obtained with siliceous than the titania loaded mesoporous materials. The adsorption data were fitted with different isotherms, and it was observed in general that the dye molecules obeyed Langmuir type of adsorption. The presence of rhodamine B dimer was evident from DRS analysis, and the J-dimer formation of rhodamine B molecules was proved by photoluminescence (PL) studies. In addition, the degradation of rhodamine B dye over titania loaded and siliceous mesoporous materials indicate that Ti-MCM-41 is more effective than Ti-MCM-48, whereas only decoloration of the dye was observed in both of the siliceous materials. Furthermore, Ti4+ in tetrahedral coordination plays a vital role in enhancing the degradation efficiency, and the degraded products were identified by using electrospray ionization-mass spectrometry (ESI-MS) studies.

Acid–Base Bifunctional Periodic Mesoporous Metal Phosphonates for Synergistically and Heterogeneously Catalyzing CO2 Conversion

Integrating multiple functions into one host for improved catalytic performance is challenging and promising for both catalysis and material science. Herein a new acid–base bifunctional periodic mesoporous titanium phosphonate hybrid material is synthesized by a facile one-pot hydrothermal method, using alendronate sodium trihydrate as a coupling molecule. The new material possesses highly periodic mesopores with a large specific surface area of 540 m2 g–1 and pore volume of 0.43 cm3 g–1, favoring the smooth mass transport of reactants and products during the catalytic reaction. It also has an organic–inorganic hybrid framework with homogeneously incorporated phosphonate groups, in which a large number of accessible acidic P–OH and basic −NH2 sites can, respectively, activate aziridine and CO2, synergistically leading to the high conversion (>99%), yield (98%), and regioselectivity (98:2) for the CO2 cycloaddition reaction. The catalytic activity is better than that of the scarcely reported heterogeneous ...

Periodic Mesoporous Materials for Overall Water Splitting: Design of an Artificial Leaf

The overall splitting of water to produce hydrogen and oxygen using visible light photocatalysts is considered to be a holy grail in chemistry. Several semiconductors have been developed towards this purpose, however despite intense research, they suffer from poor quantum efficiencies. Furthermore, the development of stable and robust visible light absorbing photocatalysts seems to pose greater challenges.In recent years, periodic mesoporous have attracted attention as support materials for catalytic reactions. Among the various classes of M41S series of materials, the cubic form called MCM-48 is an attractive material compared because it’s three-dimensional interpenetrating network of pores that provides efficient diffusion of reactants and products to the photocatalytically active sites. In addition, MCM-48 mesoporous materials also have high surface areas, tunable pore sizes, and large pore volumes that facilitate good dispersion of catalytically active sites. Our results show that the cubic MCM-48 materials containing spatially isolated titania clusters are efficient photocatalysts compared to titania incorporated into one-dimensional mesoporous supports such as MCM-41. Our research has demonstrated that titanium dioxide and CdS quantum dots can be well-dispersed within the MCM-48 mesoporous matrix. By deposition of RuO2 onto the CdS-Ti-MCM-48 photocatalyst, photocorrosion can be completely suppressed. The photocatalyst, RuO2-CdS-Ti-MCM-48 is the first known visible light photocatalyst capable of overall water splitting.

Mechanical and hydrothermal stability of mesoporous materials at extreme conditions

In situ SAXS measurements were made on periodic mesoporous carbon and silica-based materials as a function of pressure and temperature and in water to supercritical conditions. Our data show that periodic mesoporous silica-based materials exhibit substantial mechanical strength. The pore structure, size and related mesoscale properties appear to directly impact the mechanical response of silica-based materials to high pressures and temperatures. Our results indicate that hydrolysis does not seem to be responsible for the mechanical collapse of the pore structure of silica-based mesoporous materials under high pressure conditions. SBA-15 type mesoporous carbon exhibits excellent hydrothermal stability under extreme conditions. The mesostructure of FDU-12 silica is irreversibly disordered after extreme hydrothermal exposure in a manner consistent with H2O dissociation reactions causing topological alteration of the silicate network.

Effective One-Step Synthesis of Silica Supported 1,3-Dibutylimidazolium Acetate for Carbon Dioxide Capture

A new methodology has been developed to immobilize 1,3-dibutylimidazolium acetate on the surface of amino-propyl functionalized periodic mesoporous silica materials via an efficient one-pot synthesis. FTIR and solid state 13C NMR analysis confirmed the presence of the supported 1,3-dibutylimidazolium acetate compared to the separately prepared pure ionic liquid 1,3-dibutylimidazolium acetate. The resulting materials were investigated for use as possible capture reagents for carbon dioxide.

Synthesis of mesostructured stishovite from FDU-12/carbon composite

Nanocasting at high pressure has been recently proposed as a novel strategy for the synthesis of periodic mesoporous materials with crystalline walls. In this study we present results on the synthesis of mesostructured stishovite from mesostructured FDU-12/carbon composite precursor using the multi-anvil press. Results from quenched experiments performed at a pressure of 14GPa indicate that a minimum temperature of 500°C is needed to crystallize stishovite from the amorphous silica precursor with a preserved mesostructure. Transmission electron microscopy combined with small angle X-ray scattering measurements confirmed the mesostructure of synthetic stishovite having carbon-filled pores with a diameter of ∼19nm similar to the pore size of the FDU-12 precursor. Calcination of the stishovite/carbon composite at 450°C in air at ambient condition leads to amorphization of the stishovite. Our results show that mesostructure materials can be synthesized at very high pressures without loss or critical modification of the mesostructure.