Periodic Mesoporous Organosilica Materials Research Articles

Highly ordered Periodic Mesoporous Organosilica material containing the ionic 4,4-bipyridinium group and decorated with palladium nanoparticles: A proposal for nanoreactor

A Periodic Mesoporous Organosilica (PMO) containing the cationic 4,4-bipyridinium group, presenting 0.25 mmol g−1 that corresponds to 11.5 w/w%, was successfully prepared. This material was designed to have the ionic group acting as anchoring agent of PdCl42- anion complex, in a much lower amount than the available cationic sites (3 and 15 molar%). Subsequently, the palladium complex was in situ reduced to obtain stabilized palladium nanoparticles (PdNP). The ensemble of characterization results showed that the PMO material walls have a cylindrical morphology with hexagonal packing, generating well-ordered pores with a narrow size distribution and high surface area, even after being decorated with PdNP. This material is a candidate to be an efficient nanoreactor considering that it contains spatial uniformity in its chemical sites and confined environment. Aiming to evaluate the availability of palladium sites, the material was used as a catalyst in the reduction of p-nitrophenol model reaction. Although the catalyst of the present study has a comparable activity with other already reported systems, it presents the impressive lowest molar palladium/p-nitrophenol ratio found in literature.

Enhanced adsorption of short-chain perfluorobutanoic acid by functionalized periodic mesoporous organosilica: Performance and mechanisms

Removal of short-chain per- and polyfluoroalkyl substances (PFAS) represents a unique challenge in comparison to the long-chain homologs. In this study, a series of functionalized periodic mesoporous organosilica (PMO) materials with tunable molar ratio of fluoroalkyl to amine functional groups were developed and used as platform adsorbents to investigate the adsorption behavior of short-chain PFAS, with a focus on perfluorobutanoic acid (PFBA). Modification with fluoroalkyl group substantially enhanced the adsorption affinity of PFBA with the functionalized PMO materials. Adsorption free energy analysis suggested that although electrostatic interactions were more predominant in PFBA adsorption, modification of PMOs with increased fluoroalkyl group loadings increased the non-electrostatic interactions with PFBA, resulting in more favorable PFBA adsorption. The optimal functionalized PMO showed fast PFBA adsorption kinetics, excellent PFBA removal efficiency in various water chemistry conditions, and can be regenerated and reused for numerous cycles with methanol/water mixture containing 500-mM NH3·H2O as regenerant. Furthermore, the optimal functionalized PMO showed robust performance for the removal of PFAS mixtures under complex natural water matrix. Results of this study suggested the important role of non-electrostatic interactions in enhancing the removal of short-chain PFAS and can provide mechanistic insights into guiding the design of improved adsorbents for PFAS removal.

Artificial metalloenzyme with peroxidase-like activity based on periodic mesoporous organosilica with ionic-liquid framework

Artificial enzymes were developed as alternatives to natural enzymes. Considering the unique characteristics of periodic mesoporous organosilica (PMO) materials, a rational design approach was investigated to simulate the coordination sphere around the iron active center in natural horseradish peroxidase (HRP) and fabricate a new peroxidase-like nanozyme. Well-ordered mesoscopic structure, high surface area, tunable pore size, high thermal-hydrothermal stability, and facile surface functionalization are unique properties of PMOs which allow them be potential candidate for enzyme mimic catalysis. In the present study, a monofunctional PMO with ionic-liquid framework (PMO-IL) was prepared as a support to incorporate the iron protoporphyrin IX hemin. The interior surface of mesochannels were also modified by imidazole functional groups. The synthetic peroxidase-like nanomaterial was fully characterized using several techniques such as N2 adsorption-desorption analysis, Thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) spectroscopy, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray analysis (EDAX). Peroxidase-like activity of the current nanomaterial was evaluated using 2,2′-Azinobis [3-ethylbenzothiazoline-6-sulfonic acid]-diammonium salt (ABTS) in the presence of hydrogen peroxide in neutral pH condition. Michaelis-Menten kinetic parameters indicated enhanced affinity toward substrate. Results imply that the biomimetic pathways can be developed to achieve a new generation of nanozymes with excellent thermal stability and long-term storage stability which are promising as peroxidase mimics for various applications.

Engineering biodegradable periodic mesoporous functionalized-organosilica nanocarriers for efficient paclitaxel delivery

Periodic mesoporous organosilica (PMO) materials have attracted considerable attention as promising nanocarriers to improve the therapeutic efficacy of anticancer drugs. Herein, a new type of biodegradable disulfide-based PMO was synthesized by incorporating disulfide linkers into the silica framework of nanoparticles (NPs). The homogeneous spherical morphology with an average size of 50 nm is observed by scanning electron microscope, transmission electron microscopy. Furthermore, the physicochemical characterizations were also performed by using Fourier transform infrared spectra and X-ray photoelectron spectroscopy confirmed the presence of disulfide in the structure of NPs. It is notable that the disulfide moieties incorporated into the structure of NPs lead to fast degradation, within 5 days to complete degradation. Paclitaxel (PTX), a hydrophobic anticancer drug, was loaded into the porous particles with a high loading capacity up to 602 mg.g−1. A large amount of PTX was released at the early stage of the release process in the phosphate buffer saline solution containing reduced glutathione and then released slowly at a steady rate. The effective cellular uptake of NPs into malignant cells and normal cells also demonstrated. PTX-loaded NPs exhibited higher anticancer activity against cancer cells as compared to free PTX, indicating the potential nanocarrier for cancer therapy.

Ethane-bridge periodic mesoporous organosilica materials as a novel fiber coating in headspace solid-phase microextraction of phthalate esters from saliva and PET container samples.

The current study presents a periodic mesoporous organosilica (PMO) with a high surface area and uniform-porosity material. The PMO materials were successfully synthesized and modified. The resultant material was characterized by different characterization techniques. The prepared PMO was immobilized on a stainless steel wire surface and was evaluated for headspace solid-phase microextraction of the ultra-trace amount of phthalate esters from saliva and polyethylene terephthalate containers which were in contact with hot and cold water. Separation and determination of the phthalate esters (PEs) were performed by the GC-FID and GC-MS instruments. The key parameters affecting the extraction efficiencies, including extraction temperature, extraction time, ionic strength, and desorption temperature and time, were investigated and optimized. Under optimum conditions, the repeatability for one fiber (n = 7) was 4.8-8.7%, and fiber-to-fiber reproducibility (n = 3) was 7.5-10.6% for the extracted compounds. The limits of detection of the developed method for the studied compounds were between 0.01 and 1μg L-1. The results showed suitable coefficients of determination (R2 ≥ 0.99) for all of the analytes in the 0.05-300μg L-1 calibration range. Acceptable recovery values of 91-107%, 82-110%, and 98-104% were obtained in saliva, polyethylene terephthalate containers hot water, and cold water, respectively.

Janus bifunctional periodic mesoporous organosilica.

Synthesis of a Janus periodic mesoporous organosilica material (JPMO) is presented here. In this strategy, the surface of the hollow silica material was selectively functionalized with two different bridged organic-inorganic hybrid groups. It was found that the resulting bifunctional material is able to form a stable Pickering emulsion. This new type of PMO material may be suitable for widespread applications in various fields related to material science and catalysis.

The synthetic approaches, properties, classification and heavy metal adsorption applications of periodic mesoporous organosilicas

Periodic Mesoporous Organosilica (nano)materials (bulk PMO and PMO NPs), one of the most advanced organic–inorganic hybrid silica materials, are increasingly studied in recent years. Compared with other hybrid silica materials, PMOs have some unique advantages, such as robust porous channels, organic–inorganic framework, tunable pore size arrangement, biocompatibility, high organic contents and easy functionalization. They have attracted growing interest of study in some newly emerged fields including biology, biomedicine and catalysis. On the other hand, heavy metals in wastewaters severely pollute the environment and thus do harm to the aquatic ecosystems as well as human health, which is considered an urgent issue to be solved in modern society. It is very meaningful to use PMO materials to realize the effective detection of heavy metal ions and to solve their recovery. Herein, this review focuses on the synthetic strategies of PMO adsorbents as well as their performance and mechanism of adsorption for the heavy metals.

Ti-PMO materials as selective catalysts for the epoxidation of cyclohexene and vernonia oil

The aim of this study is to obtain Ti-containing Periodic Mesoporous Organosilica (PMO) materials with catalytic activity in epoxidation reactions. Characterization of the PMO materials using X ray diffraction, N2 sorption isotherms, chemical analysis (ICP-OES) and UV–vis spectroscopy reveals that the Ti-PMO materials possess ordered 2-dimensional hexagonal mesostructures, high surface areas (593–944 m2/g), uniform pore sizes (4.5–11 nm), large pore volumes (0.59–1.62 cm3/g), and tetrahedrally incorporated Ti(IV) species on the surface of the pore walls. The PMO materials with fiber-like particle morphology, which may hinder the diffusion of substrates, have been compared with those of plate-like morphology in which diffusion problems may be avoided. The catalytic activities of these materials were tested in epoxidation of cyclohexene with an optimum conversion rate of 30.5% and good epoxide selectivity (93.8%). Selected Ti-PMO materials were also effective for the epoxidation of vernonia oil, a naturally expoxidized triglyceride oil, using tert-butyl hydroperoxide as an oxidant.

Supported phosphine free bis-NHC palladium pincer complex: An efficient reusable nanocatalyst for Suzuki-Miyaura coupling reaction

A periodic mesoporous organosilica material functionalized with a bis-NHC palladium pincer complex was synthesized by sol-gel process. The resulting organic-inorganic hybrid nano material was characterized by XRD, TEM, SEM, TGA analysis, and BET measurements. The hybrid nanomaterial act as highly active catalysts for the Suzuki–Miyaura cross-coupling between deactivated aryl chlorides and phenylboronic acid under heterogeneous and aerobic conditions. The supported catalyst exhibited excellent activity and stability and it could be reused at least ten times without any significant loss of activity. Furthermore, the SEM image revealed that high order mesostructure of the recycled nanocatalyst. After ninth run, catalyst showed almost similar structure as compared to the fresh catalyst. ICP-AES detected no Pd contamination in the products, and leaching tests verified that the reaction was truly heterogeneous.

Exploring periodic mesoporous organosilicas for ethane–ethylene adsorption–separation

Ethylene is a core building block in the chemical industry and its separation from ethane is very challenging due to high energy requirements. Adsorption-based processes can be an alternative to current processes based on cryogenic distillation. In this work, we explore for the first time the application of periodic mesoporous organosilica (PMO) materials, whose surface properties can be tuned with different functional groups. With the aim of correlating the PMO structure with ethane and ethylene adsorption, eight different PMO materials have been prepared, viz. the phenylene-bridged PMO, PMO aminated at the organic bridges, and PMO functionalized by silylation of free silanol (inorganic) moieties. High pressure adsorption isotherms were measured, and the separation selectivity and phase diagrams of a binary mixture of ethane and ethylene were estimated. Results have shown that, overall, the PMO studied tend to be more selective towards ethylene than ethane probably due to the interactions between the quadrupole moment of ethylene and the free silanols in the samples. After silylation, the novel materials presented surfaces with higher affinity towards ethane than those of the pristine material. For the aminated samples, functionalization with primary amines originated materials displaying better selectivity towards ethylene than those functionalized with secondary or tertiary amines.

CO2 and CH4 adsorption on periodic mesoporous organosilica: A DFT study

Periodic mesoporous organosilicas (PMO) were proposed as potential adsorbents for CO2/CH4 adsorption-separation due to their strong interactions with CO2 and low affinity for CH4. Herewith, we present a comprehensive density functional theory (DFT) study about the binding properties of CO2 and CH4 with the pore walls of different PMO materials. The calculations considered the M06−2X DFT exchange-correlation functional, and cluster models of the walls of the PMO materials with organic bridges based on phenylene (Ph-), biphenylene (Bph-), pyridine (Py-) and bipyridine (Bpy-) fragments or on mixtures of Ph/Py- and Bph/Bpy- moieties. All materials showed stronger interactions with CO2 than with CH4, which suggests they are potentially selective for CO2 over CH4. From the calculated data it is demonstrated that the PMO materials with phenylene moieties establish more favorable contacts with CO2 than those found in their counterparts with bridges based on the homologous heteroaromatic nitrogen compounds, viz. pyridine. Independently of the size of the organic bridge, both phenylene- and biphenylene- PMO materials showed similar CO2 adsorption behavior. The presence of bipyridine-bridges improved the CO2 adsorption behavior only when mixed with biphenylene moieties. The adsorption behavior of CO2 gas can be directly related to the SiOH···OCO distance, i.e., the adsorption strength increases with the decrease of this distance. In the case of the CH4 adsorption, the least favorable adsorptions were determined for PMO materials with pyridine and phenylene/pyridine bridges.

Rational design of lanthanide nano periodic mesoporous organosilicas (Ln-nano-PMOs) for near-infrared emission.

We present three Periodic Mesoporous Organosilica (PMO) materials: a PMO material functionalized with pyridine dicarboxamide (DPA-PMO) and two amine functionalized PMO materials (Am-PMO and Am-ePMO). The pyridine dicarboxamide ligands in the DPA-PMO material provide the tethering sites for Ln3+-coordination. A Schiff base reaction was carried out on the amine functionalized PMOs to introduce similar lanthanide coordination sites. The Nd and Yb modified nano-PMOs are evaluated as near-infrared (NIR) emitting luminescent materials. The DPA-PMO and Am-ePMO materials can act as good platforms for NIR luminescence. A significant enhancement in the decay time can be observed upon grafting an Yb(hfa)3 complex to the PMO materials instead of YbCl3. All of the DPA-PMO@Ln(hfa)3 and Am-ePMO@Ln(hfa)3 materials show characteristic NIR emission performance both in the solid state and in aqueous suspension.

Trends in Degradable Mesoporous Organosilica-Based Nanomaterials for Controlling Drug Delivery: A Mini Review.

The last few years of enhancing the design of hybrid mesoporous organosilica nanoparticles has allowed their degradation under specific pathologic conditions, which finally is showing a light in their potential use as drug delivery systems towards clinical trials. Nevertheless, the issue of controlling the degradation on-demand at cellular level still remains a major challenge, even if it has lately been addressed through the incorporation of degradable organo-bridged alkoxysilanes into the silica framework. On this basis, this mini review covers some of the most recent examples of different degradable organosilica nanomaterials with potential application in nanomedicine, from degradable non-porous to mesoporous organosilica nanoparticles (MONs), functionalized with responsive molecular gates, and also the very promising degradable periodic mesoporous organosilica materials (PMOs) only consisting of organosilica bridges.

Mesoscale model of the synthesis of periodic mesoporous benzene-silica

A coarse-grained (CG) model is developed to reproduce the early stages of the templated synthesis of periodic mesoporous organosilicas (PMO), focusing on benzene as the organic linker. Molecular dynamics simulations of hexadecyltrimethylammonium bromide (CTAB) surfactant in aqueous organosilicate solutions were performed to analyze the micelle formation, growth and aggregation during the synthesis of surfactant-templated PMOs. The CG model parameters were calibrated to reproduce radial density profiles of all-atom CTAB spherical micelles in a solution with benzenesilicates (BZS). Our simulations, with over a thousand surfactants, reproduced the experimental micelle aggregation, promoted and driven by the BZS moieties. The micelle sphere-to-rod transition and the subsequent formation of a hexagonally ordered mesophase were observed and characterized, displaying rod diameters (in the range 38–41 Å) very close to experimental estimates (38 Å). Furthermore, the addition of BZS to a CTAB aqueous solution with spherical micelles at equilibrium promoted the formation of prolate-shaped rods, in accordance with experiments. Subsequent removal of the BZS from the final PMO structure caused the system to revert to the original spherical micelles. In our simulations, the CTAB rods were formed above a 1:5 BZS/CTAB ratio while a ratio of 1:2 was found to be required to induce the hexagonal arrangement of the rods. Overall, this work reinforces the active and cooperative role of organosilicates in the formation of PMO materials.

Probing Functionalities and Acidity of Calcined Phenylene-Bridged Periodic Mesoporous Organosilicates Using Dynamic Nuclear Polarization NMR, Diffuse Reflectance Infrared Fourier Transform Spectroscopy, and X-ray Photoelectron Spectroscopy

Owing to their high surface area, their high stability, and their hydrophobicity, periodic mesoporous organosilica (PMO) materials represent promising catalytic support for environmentally friendly chemical processes in water. We investigate here how the calcination of PMO material with benzene linkers (PMOB) allows its functionalization. Conventional and dynamic nuclear polarization (DNP)-enhanced NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy prove that calcination at 450 {\deg}C results in the oxidation of phenylene bridges into (poly)phenols but also into carboxylic acids. Ketone, aldehyde, as well as allyl and aliphatic alcohol functionalities are also observed, but their amount is much lower than that of carboxylic acids. The calcination also cleaves the Si-C bonds. Nevertheless, N2 adsorption desorption measurements, powder X-ray diffraction, and transmission electron microscopy indicate that the PMOB materials calcined up to 600 {\deg}C still exhibit ordered mesopores. We show that the phenol and carboxylic acid functionalities of PMOB calcined at 450 {\deg}C protonate the NH2 group of 1-(3-aminopropyl)imidazole (API) in water at room temperature, but no formation of a covalent bond between API and the calcined PMOB functionalities has been detected.

Light-Emitting Lanthanide Periodic Mesoporous Organosilica (PMO) Hybrid Materials.

Periodic mesoporous organosilicas (PMOs) have a well ordered mesoporous structure, a high thermal and mechanical stability and a uniform distribution of organic functionalities in the pore walls. The organic groups allow PMOs to be modified and functionalized by using a wide range of organic reactions. Since their first report in 1999, PMOs have found a vast range of applications, such as for catalysis, adsorbents, low-k films, biomedical supports and also for optical applications. Optical applications are very interesting as PMOs offer the possibility of designing advanced luminescent hybrid materials comprising of organic components, yet with much higher stability and very good processability. Despite their promising possibilities, the optical properties of pristine PMOs and PMOs grafted with d-metal or f-metal ions and complexes have been explored less frequently. In this review, we aimed to overview the exciting light emitting properties of various reported lanthanide PMO hybrid materials and interest the reader in this promising application for lanthanide PMO materials.

Thiadiazole containing N- and S-rich highly ordered periodic mesoporous organosilica for efficient removal of Hg(ii) from polluted water.

A new N- and S-rich highly ordered periodic mesoporous organosilica material DMTZ-PMO bearing thiadiazole and thiol moieties inside the pore-wall of a 2D-hexagonal nanomaterial has been synthesized. DMTZ-PMO shows a very high surface area (971 m2 g-1), and can be used for efficient and fast removal of Hg2+ from polluted water with a very high Hg2+ uptake capacity of 2081 mg g-1.

Amine-containing (nano-) Periodic Mesoporous Organosilica and its application in catalysis, sorption and luminescence

Abstract In this work we introduce a novel Periodic Mesoporous Organosilica (PMO) material, where the walls of the PMO are constructed of a long linear amine precursor (3-trimethoxysilylpropyl)diethylenetriamine at 5% or 10% and 1,2-bis(triethoxysilyl)ethane. This AM-PMO is very simple to synthesize and we show that it can be used for a wide range of applications. After synthesis of the PMO, the dangling amine groups can be grafted with an aldehyde/ketone to form Schiff base ligand functionalized PMOs. Such PMOs can subsequently be reacted with lanthanide salts or lanthanide complexes yielding luminescent hybrid PMO materials. A potential application of such materials is heavy metal sensing. The AM-PMO2_nano@o-van@Eu material (o-van = o-vanilin) shows significant “turn on” fluorescence in the presence of Hg2+ ions. The obtained AM-PMO material was also evaluated as a heterogeneous catalyst in Knoevenagel condensation reaction. The reactions between various aldehydes and malononitrile, could proceed smoothly in the presence of AM-PMO2 presenting high conversions of 85–99% with great selectivity (>99%). The AM-PMO additionally showed good CO2 adsorption behavior, similar to other previously reported PMOs with amine groups. However, the advantage of this material is its simplicity in preparation. In addition, the amine PMO can also be prepared in the form of nano-sized particles by altering the reaction parameters.

Highly selective luminescent sensing of Cu2+ in aqueous solution based on a Eu(III)-centered periodic mesoporous organosilicas hybrid

Using Pluronic P123 surfactant as template, a periodic mesoporous organosilica (PMO) functionalized with 4′-(4-carboxy-methyleneoxy phenyl)-2,2′:6′,2″-terpyridine (L-COOH) was successfully prepared via co-condensation using 1,2-bis(triethoxysilyl)ethane (BTESE) and the modified L-COOH (L-COOH-NH2). This terpyridine moiety forms interesting chelates to europium ions and enhances the luminescence of Eu3+ ions. Thus, a novel luminescent hybrid material was developed via linking Eu3+ complex Eu(NTA)3(H2O)2 to L-COOH-functionalized PMO material (L-COOH-PMO) using ligand exchange reactions. Investigation of photoluminescent properties shows that the prepared mesoporous hybrid Eu(NTA)3L-COOH-PMO exhibited red emission, long lifetime and high absolute quantum efficiency Φ in solid-state and aqueous solution. More interestingly, it demonstrates greatly sensitive and selective detection of Cu2+ ions in aqueous medium among test ions. The sensing mechanism was also discussed in this report.

Atomistic Model of Realistic Crystalline Mesoporous Organosilica Materials Including Nanochannels

The new class of periodic mesoporous organosilica materials (PMOs), due to the peculiar features, has attracted growing interest from several research areas. We present an atomistic model of a p-phenylenesilica crystalline mesoporous structure with a hexagonal framework, explicitly including channels on nanoscale. OPLS-AA force-field optimization, to get a suitable PMO structure compared with the experimental one, is described. In particular, DFT calculations have been performed to calculate torsional energy barrier of phenyl rings connected to the silicon atoms belonging to inorganic layers and to improve the OPLS-AA force field performances for these materials. Finally, inclusion of small molecules and their interactions with PMO walls have been investigated for CO2 and H2O.