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.

Incorporation of organic photochromic molecules in mesoporous silica materials: Synthesis and applications

Abstract The ability to control the function and structure of some promising nanosystems using an external stimulus is attractive research to develop programmable and reconfigurable intelligent nanomaterials. The focal point of this review is the silicon-based nanoporous materials, and particularly the mesoporous silica materials (MSMs) class (pore size: 2–50 nm), due to their important intrinsic properties, such as high surface area, highly ordered nanostructure, narrow pore size distribution, various dimensions (one-dimensional, two-dimensional, and three-dimensional), and easily functionable. One of the most essential organic components that can be incorporated in MSMs is organic photochromic molecules (OPMs), such as azobenzene, stilbene, dithienylethenes, and spiropyrans. OPMs can be incorporated into MSMs, to form photochromic mesoporous organosilica materials (PMOMs), in two different ways: physical (non-covalent immobilization) or chemical (covalent immobilization) binding. PMOMs are considered smart nanomaterials because they have the ability to undergo reversible changes in the solid state when exposed to an external electromagnetic radiation. PMOMs have been the subject of many research studies during the last decade due to their potential applications, especially as chemosensors. This review discusses the main families of OPMs, their incorporation into MSMs using different methods, and the applications of some PMOMs as chemosensors.

Tailoring pore size of mesoporous silica and organosilica using biodegradable pentablock copolymer templates via EISA process

In this work, we have designed unique poly(lactic acid-co-glycolic acid)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(lactic acid-co-glycolic acid) pentablock copolymers using Pluronic F68 and F108 triblock copolymers as macroinitiators. The poly(lactic acid-co-glycolic acid) (PLGA) blocks were attached as glycolide and lactide monomers at the both ends of each F68 and F108 triblock copolymer. The molecular weights and the block fractions were confirmed by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) for the four kinds of pentablock copolymers. Using these pentablock copolymers as templates, we synthesized mesoporous ethane-silicas as well as silicas by the evaporation-induced self-assembly (EISA) method. 1,2-bis(triethoxysily)ethane (BTEE) were used as an organosilica precursor. The mesoporous ethane-silica samples were characterized using synchrotron small angle X-ray scattering (SAXS), nitrogen sorption experiments, transmission electron microscopy (TEM), and solid-state 29Si CP-MAS NMR. Based on the experimental results, it was confirmed that the porosity and pore diameter can be varied with the PLGA weight fraction of the pentablock copolymer. It is due to the PLGA block in polymer forming the hydrophobic domain in micelles, which leads to the formation of increased pore size over 20 nm without any additive pore expander. In addition, it seems that as the organosilica precursor increases, the association number of block copolymers forming one micelle decreases, resulting in a decrease in pore size. In summary, the polymer template plays a vital part in tuning the structure of the mesoporous ethane-silica samples. Thus, the development of synthetic method of mesoporous organosilica materials using polymer templates with different topology is still challenging and can endow the unique structure and property for mesoporous organosilica for future applications.

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.

Trans-stilbene based spherical mesoporous organosilica material for loading and release of hydrophobic curcumin

In this study, a new mesoporous organosilica carrier system was synthesized in which hydrophobic trans-stilbene is placed on the walls of the drug delivery system. In this way, it is aimed to increase the interaction between hydrophobic curcumin and the silica surface and to load more curcumin into the drug delivery system. Trans-stilbene based mesoporous organosilica (TSMON) material was prepared in the reaction of (E)-1,2-bis(4-(3-(triethoxysilyl)propyl)phenyl)ethylene (1) with tetraethyl orthosilicate in the presence of triblock copolymer cetyltrimethylammonium bromide as a template in NaOH solution. Characterization of synthesized TSMON was done by FT-IR, XRD, BET, SEM and TGA analyses. Curcumin loading into the drug delivery system TSMON was carried out by mixing curcumin and TSMON in the dark for 24 hours. After the measurements made in the UV-Vis spectrophotometer, entrapment efficiency and loading capacity for TSMON were calculated as 22% and 18.2%, respectively. Next, the time dependent release of curcumin from Cur@TSMON at physiological and endosomal pH was studied. After 5 days of UV-Vis measurements, the percentage of curcumin release from Cur@TSMON was around 1% at pH = 5 and 7.4. The low release percentage obtained indicates a strong interaction between TSMON and curcumin penetrating the pores of the TSMON. This strong interaction allowed the drug delivery system TSMON to carry 99% of the payload without leaking at pH = 5 and 7.4 without pore capping agents.

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.

Enzymatic Production of Ecodiesel by Using a Commercial Lipase CALB, Immobilized by Physical Adsorption on Mesoporous Organosilica Materials

The synthesis of two biocatalysts based on a commercial Candida antarctica lipase B, CALB enzyme (E), physically immobilized on two silica supports, was carried out. The first support was a periodic mesoporous organosilica (PMO) and the second one was a commercial silica modified with octyl groups (octyl-MS3030). The maximum enzyme load was 122 mg enzyme/g support on PMO and 288 mg enzyme/g support on octyl-MS3030. In addition, the biocatalytic efficiency was corroborated by two reaction tests based on the hydrolysis of p-nitrophenylacetate (p-NPA) and tributyrin (TB). The transesterification of sunflower oil with ethanol was carried out over the biocatalysts synthesized at the following reaction conditions: 6 mL sunflower oil, 1.75 mL EtOH, 30 °C, 25 μL NaOH 10 N and 300 rpm, attaining conversion values over 80% after 3 h of reaction time. According to the results obtained, we can confirm that these biocatalytic systems are viable candidates to develop, optimize and improve a new methodology to achieve the integration of glycerol in different monoacylglycerol molecules together with fatty acid ethyl esters (FAEE) molecules to obtain Ecodiesel.

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.

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.

New bi-functionalized ordered mesoporous material as heterogeneous catalyst for production of 5-hydroxymethylfurfural

Newly designed ordered two dimensional hexagonal bi-functionalized mesoporous organosilica material (b-MPOS) has been synthesized through the step-by-step post-grafting synthetic pathway. The pure calcined SBA-15 was subjected for functionalization using chloro-substituted organo-silica ligand to get MPCFOS, denoted by mesoporous chloro-functionalized organosilica material. This material undergoes through the substitution reaction (SN2) between the pore wall attached chloro-functional group and the organic bi-functionalized ligand i.e. 3-Amino-1,2,4-triazole-5-carboxylic acid containing amine group in the presence of potassium carbonate which was used as a mild base under the refluxing conditions. The as-synthesized bi-functionalized material displays the high specific surface area as well as pore diameter of 537 m2 g−1 and 9.4 nm, respectively. Since, as-synthesized material contains both acid and basic functional groups, temperature programmed desorption (TPD) of NH3 and CO2 analysis, have been performed to determine the total amount of surface acidic and basic sites of this material which are estimated to be 1.87 and 2.07 mmol g−1, respectively. Due to the presence of Brønsted acid and base groups together with the bi-functionalized material, it has been investigated as a heterogeneous catalyst for carbohydrates transformation to synthesize the valuable chemical like 5-hydroxymethylfurfural (HMF) from fructose with the high product yield of 86 mol% by using microwave irradiated heating conditions.

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.

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.

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.