Ordered Mesoporous Materials Research Articles

Synthesis of Coal-Fly-Ash-Based Ordered Mesoporous Materials and Their Adsorption Application.

A feasible approach was developed for the synthesis of ordered mesoporous SBA-15-type materials using coal fly ash (CFA) as raw material. In the proposed approach, CFA was, firstly, activated by subcritical water with the addition of NaOH, which allowed an efficient extraction of silicon species from CFA under strong acidic conditions at near room temperature. Subsequently, in the synthesis system, using silicon extraction solution as the silicon precursor, the introduction of anhydrous ethanol as a co-solvent effectively inhibited the polymerization of silanol species and promoted their collaborative self-assembly with surfactant molecules by enhancing the hydrogen bond interactions. The resultant SBA-15 material had a high purity, high specific surface area (1014 m2/g) and pore volume (1.08 cm3/g), and a highly ordered mesostructure, and, therefore, exhibited an excellent removal efficiency (90.5%) and adsorption capacity (160.8 mg/g) for methylene blue (MB) from simulated wastewater. Additionally, the generation of surface acid sites from the homogenous incorporation of Al atoms onto the mesoporous walls of SBA-15 combined with the perfect retention of the ordered mesostructure endowed the obtained Al-SBA-15 material with a further boost in the removal performance of MB. The MB removal efficiency can reach ~100%, along with a maximum adsorption capacity of 190.1 mg/g.

The Structure of Ordered Mesoporous Materials Synthesized from Aluminum Phyllosilicate Clay (Bentonite).

This paper reports the synthesis and structural analysis of mesoporous silica materials with the use of aluminum phyllosilicate clay (bentonite) as an alternative silica source. In the proposed synthesis, bentonite, as natural aluminosilicate, was used instead of commercially available and quite expensive tetraethyl orthosilicate (TEOS) silica source. The objective of the research study was to determine the effect of aluminum loading in the mesoporous silica body for ordering structure, porosity, and potential sorption capacity to thorium ions. The unique direction developed in this procedure is focused on preparing advanced materials from natural sources with their own desired functionality and general availability. The applied procedure based on the classic, one-step synthesis of SBA-15 silicates was modified by gradually increasing the bentonite amount with simultaneous reduction of the TEOS content. The structural and morphological characterization, as well as evaluation of the porous structure of the obtained materials, was performed using powder wide-angle X-ray diffraction (XRD), small-angle scattering (SAXS), transmission and scanning electron microscopy (TEM, SEM), low-temperature nitrogen adsorption-desorption methods and potentiometric titration. The new, cost-effective composites for the removal of Th(IV) ions are proposed. The synergistic effect of expanding the porous surface using bentonite as a silica precursor and the presence of thorium-binding groups (such as Al2O3) is indicated.

Preparation and characterization of vernolic acid methyl ester functionalized ordered mesoporous materials

ABSTRACT. Vernonia oil is a naturally epoxidized triglyceride oil extracted from the seed of Vernonia galamensis, a native plant in East Africa. After hydrolysis to vernolic acid (VA) and derivatization, vernolic acid methyl ester (VAME) is synthesized and used to functionalize ordered mesoporous materials (OMM). Al-MCM-41 with Si/Al ratio of 15, pure silica SBA-15 and periodic mesoporous organosilica (PMO) are employed as supports exploring the different surface properties. Following optimization of the VAME/OMM ratios, selected samples, i.e. those with 13% VAME, were impregnated with AgNO3 in NaBH4 to obtain Ag-nanoparticles. The final AgVAME-OMM potential catalysts were characterized by transmission electron microscopy, observing an efficient loading of Ag nanoparticles in pure silica SBA-15 with VAME with 500 m2 specific surface area and 6 nm pore size.
 
 KEY WORDS: Vernolic acid methyl ester, Vernonia oil, Functionalization, Ordered mesoporous materials, Catalysis
 
 Bull. Chem. Soc. Ethiop. 2023, 37(3), 689-702. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i3.12

Non‐siliceous ordered mesoporous materials via nanocasting for small molecule conversion electrocatalysis

AbstractSince the pioneering work of Ryoo and co‐workers in 1999 on the synthesis of ordered mesoporous carbons via nanocasting, the nanocasting pathway has endured the test of time and has established itself as a robust and versatile method for preparing ordered mesoporous materials (OMMs). This method enables the generation of a remarkably wide range of non‐siliceous OMMs, some of which are otherwise inaccessible. In this account, we present our decade‐long efforts toward the function‐oriented design of non‐siliceous OMM‐based electrocatalysts for promoting small molecule conversion reactions relevant to renewable energy conversion and commodity chemical production, including hydrogen evolution reaction, oxygen evolution reaction, and selective oxygen reduction reaction. We also discuss the extension of the nanocasting concept to a silica‐coating‐mediated synthesis for preparing new catalytic materials. We conclude the account by suggesting the remaining challenges and outlook for the future development of advanced OMMs.

From Al-SBA-15 to Ga-SBA-15: Morphology and acidity evolution in the acid-free synthesis

Tuning the morphological and acidic properties of mesoporous molecular sieve materials is highly valuable for catalyst design towards the reactions involving large molecules. In this work, a series of Ga-containing SBA-15 ordered mesoporous materials (OMMs) were synthesized following the acid-free strategy. Ga-SBA-15 exhibits an acid amount of 0.48 mmol/g, comparable to the Al-SBA-15 (0.45 mmol/g). In addition, it is found that the straight short stick particles of Al-SBA-15 integrally bended upon a replacement of Al with Ga and the tendency continuous with the incremental addition of gallium, until fully transforms into the highly dispersed isolated bending particles of Ga-SBA-15. Owing to the improved interparticle-type mesoporosity derived from the dispersed bending particles, the active sites on external surface are highly accessible for large molecules. As for the acidic property, the Brönsted-type acidic property of Al-SBA-15 changed to the Lewis-type acidity with the replacement of gallium. In the Ga-SBA-15 case, more than 93% of strong acid sites were confirmed as Lewis characteristic. On the other hand, Low Density Polyethylene (LDPE) exhibits a faster decomposition rate over Ga-SBA-15 than Al-SBA-15 and Al–Ga bimetallic doped SBA-15 (galloaluminosilicate) catalysts. • Ga-containing SBA-15 mesoporous materials were synthesized following the acid-free strategy. • Replacement of Al with Ga induces a morphological evolution from the straight short stick to a bending shape. • Ga-SBA-15 exhibits strong Lewis acidity and hierarchical pore structure solely composed of interparticle-type mesopores.

Pushing the Limit of Ordered Mesoporous Materials via 2D Self‐Assembly for Energy Conversion and Storage

AbstractMaterial and energy efficiencies are two key parameters that benchmark the electrochemical energy conversion and storage devices (EECSDs). Maximizing both requires researchers to grasp the limits of the physiochemical properties of core electrode materials. Ordered mesoporous materials (OMMs) have been regarded as promising electrode materials; however, their intrinsic deficiencies (e.g., plugs, inaccessible pores, and surfaces) impose limits for wide applications. 2D ordered mesoporous materials (2DOMMs) featured with an extended lateral dimension and a nanometer thickness not only inherit the structure advantages of mesoporous materials, but also have a unique 2D ultrathin feature that can fully address the imperfections of conventional OMMs. Herein, recent achievements on the preparation of 2DOMMs by combining single micelle assembly strategy with 2D bottom‐up patterning techniques including the molecular/space confined, interfacial orientated, and surface limited assembly are focused. Special focus is devoted to the newly developed synthetic strategies and their fundamental mechanisms for accurate control of some key structural parameters. Recent advances of 2DOMMs in EECSDs are also highlighted, which suggest that 2DOMMs are excellent material platforms for developing new battery chemistry as well as targeting performance optimization and cost reduction. Finally, the challenges and prospects are proposed based on current development.

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.

SBA-15 with short channels for laccase immobilization

Ordered Mesoporous Materials offer wide application areas in chemistry and biotechnology. SBA-15 displays hexagonal arrangement of parallel unidirectional channels, where pore size and particle morphology are the controlling parameters when used as enzyme support to favour the diffusion of the protein molecules. The synthesis conditions can be controlled to yield the desired structural and morphological features of the material, as well as the functionalization of its surface to improve chemical affinity with the enzyme. Functionalization with amine groups has been performed to immobilize laccase on SBA-15. Particles of SBA-15 with short channels (300–500 nm length) and large pore diameter (10–14 nm) have been obtained. The experimental parameters varied to control the structural features were surfactant, micelle expander and silica source. Upon functionalization with amine groups, laccase was immobilized at a pH in the range between the isoelectric point of the enzyme (pI = 4.2) and the pKa value of the amino groups (~10) via non-covalent (electrostatic) interaction between carboxylate groups of the enzyme and the protonated amino groups. The enzyme was successfully immobilized on all the supports tested (loading from 18 to 57 mg/g) with fair catalytic activity and observing enzyme desorption (leaching) below 9% after 48 h in all cases.

On the Universality of Capillary Condensation and Adsorption Hysteresis Phenomena in Ordered and Crystalline Mesoporous Materials

AbstractUsing adsorption experiments for argon over a wide range of temperatures from above the triple point (i.e., 87 K) down to 65 K, coupled with advanced molecular simulation studies, the underlying mechanism of capillary condensation and hysteresis in a mesoporous metal‐organic framework (MOF), MIL‐101(Cr) is explored. The results obtained on the mesoporous MOFs are compared with the experimental and molecular simulation studies of argon adsorption and phase behavior in mesoporous molecular sieves (e.g., MCM‐41 silica) of similar pore size and over the same temperature range (65–87 K). The studies provide insights into the nature of confinement effects on the adsorption and phase behavior of fluids in mesoporous MOFs. The obtained results suggest that certain features of adsorption, capillary condensation, and associated hysteresis phenomena in mesoporous MOFs and in mesoporous molecular sieves are governed by the same underlying physics, despite the striking differences in pore structure and chemical composition. Hence, the findings are of importance for advancing characterization methodologies based on gas adsorption, but also for predicting the behavior of mesoporous MOFs in various potential applications.

Ethanol conversion into 1,3-butadiene over Zn[sbnd]Zr mixed oxide catalysts supported on ordered mesoporous materials

In order to increase 1,3-BD yield, ordered mesoporous materials (OMMs) was synthesized and used as supporting materials of heterogeneous catalysts for ethanol conversion into 1,3-BD. To make acidic and basic sites acting as active sites on the surface of catalysts, a moderate (5 wt%) amount of zinc oxide (ZnO) and zirconium oxide (ZrO2) were impregnated on as-prepared various supporting materials at a time. Prepared catalysts showed different acid-base properties according to used supporting materials. The ordered mesoporous silicas (OMSs) based catalysts were proven to exhibit higher ethanol conversions and 1,3-BD selectivities because they have not only adequate number and strength of acidic sites and basic sites but also very regular mesoporous structure. Especially ZnO-ZrO2/KIT-6 revealed a higher 1,3-BD selectivity above 54.0% at ethanol conversion of 82.5% at 400 °C. On the other hand, the selectivity of diethylether (DEE) was grown to over 68% in the case of ordered mesoporous alumina (OMA) based catalyst for example ZnO-ZrO2/OMA catalyst with a higher ethanol conversion above 80% at the same temperature. A similar type of catalyst with the ZnO-ZrO2/KIT-6, ZnO-ZrO2/a-SiO2 exhibited relatively low ethanol conversion and selectivity toward 1,3-BD. Through these results, it was confirmed that adequate number and strength of strong acidic and basic sites are key factors for full conversion of ethanol to 1,3-BD with well-developed ordered mesoporous structure.

Major advances in the development of ordered mesoporous materials.

In this feature article we focus on the main developments in the area of ordered mesoporous materials (OMMs) since their discovery in 1992, which is considered one of the milestones in the history of porous materials. Nowadays, there are almost unlimited opportunities in the synthesis of composite- or modified OMMs by using soft- and hard-templating strategies and related methods. Nevertheless, there is still a great challenge to obtain diverse OMMs with well-developed porosity and desired morphology, crystallinity and surface properties. The evolution of the leading OMM members: silicas, organosilicas, metal oxides, carbons, metal-organic frameworks and zeolites, including the main factors affecting their development, is briefly summarized with special emphasis on the authors' accomplishments in this area. Additionally, recent advancements, challenges and prospects in the field of OMMs are presented.

Generalized variables for both porous and ordered mesoporous materials

This work is a continuation of our previously published work (Titelman in J Porous Mater 19:1–13, 2012), where generalized variables for the synthesis of porous materials were proposed: processing X and structural Y. X represents the route of the entire production process and covers the complete set of individual variables, both quantitative and qualitative. This paper proposes a concept of equivalent X-s, that is, routes leading to equal values of the property of interest. Examples of equivalent X are given. The most economical route can be chosen. Y = Vw/Vp (the ratio of the apparent volume of the walls to the total volume of open pores) is the structural parameter of the ordered mesoporous materials (OMMs), more sensitive than the wall thickness. For OMMs a formula is proposed for estimating Vw; this is the product of the total surface area SBET and the wall thickness t. Now the Y covers all parameters of OMM. Excluding the volume Vsk of the skeleton from Vw, we obtain the volume Viw of inaccessible intrawall pores; the size effect (Vradman et al. in Microporous Mesoporous Mater 93:313–317, 2006) on Viw was discovered. The specific length of the adsorbate body Lv proposed in Titelman (2012) is supplemented by the length of the surface area of the adsorbent Ls and the equation relating the hydraulic diameter Dh to the average pore diameter Dp is obtained. The known Dh = 4Vp/SBET is equal to Dp, only if Lv = Ls. Dh is considered as a diameter of pores with smooth walls, and Ls/Lv—as a roughness factor. Application of the proposed parameters gives a new insight of many published results. Presentation of equivalent processing variables (routs); roughness factor as result of new derivation of hydraulic pore diameter and size effect on intrawall void space.

The State of Research Regarding Ordered Mesoporous Materials in Batteries.

Ordered mesoporous materials, porous materials with a pore size of 2-50 nm which are prepared via the sol-gel process using surfactant molecular aggregates as a template to assemble channels through the interfacial action of organic and inorganic substances, have recently triggered a heated debate. In addition to applications in the catalytic cracking of heavy oils and residues, the manufacturing of graft materials, the purification of water, the conversion of automobile exhaust, biochips, and the treatment of environmental pollutants via photocatalysts, ordered mesoporous materials have drawn substantial attention in the field of electrochemical energy storage due to advantages such as large specific surface area, uniform and continuously adjustable pore size, and orderly arrangement. Here, a general summary and appraisal of the study of ordered mesoporous materials for batteries in recent years is given, including the synthesis methods, meso/nanostructural features, and electrochemical capabilities of such materials.

Recent Advances in the Separation of Rare Earth Elements Using Mesoporous Hybrid Materials.

Over the past decades, the need for rare earth elements (REEs) has increased substantially, mostly because these elements are used as valuable additives in advanced technologies. However, the difference in ionic radius between neighboring REEs is small, which renders an efficient sized‐based separation extremely challenging. Among different types of extraction methods, solid‐phase extraction (SPE) is a promising candidate, featuring high enrichment factor, rapid adsorption kinetics, reduced solvent consumption and minimized waste generation. The great challenge remains yet to develop highly efficient and selective adsorbents for this process. In this regard, ordered mesoporous materials (OMMs) possess high specific surface area, tunable pore size, large pore volume, as well as stable and interconnected frameworks with active pore surfaces for functionalization. Such features meet the requirements for enhanced adsorbents, not only providing huge reactional interface and large surface capable of accommodating guest species, but also enabling the possibility of ion‐specific binding for enrichment and separation purposes. This short personal account summarizes some of the recent advances in the use of porous hybrid materials as selective sorbents for REE separation and purification, with particular attention devoted to ordered mesoporous silica and carbon‐based sorbents.

Hyperpolarized 129Xe NMR as an Alternative Approach for Investigating Structure and Transport in Ordered Mesoporous Materials Prepared via Pseudomorphic Transformation

The stepwise pseudomorphic transformation of silica gel and porous glass into MCM-41 (Mobil Composition of Matter No. 41) has been investigated for the first time with hyperpolarized 129Xe NMR. The changes in structure were followed by changes in the line shape and chemical shift of the 129Xe NMR signals, whereby variable temperature (VT)-NMR and selective 1D exchange spectroscopy (EXSY) experiments revealed differences in the mechanism of the transformation, depending on the starting material.

New Insight into the Synthesis of Large-Pore Ordered Mesoporous Materials.

Ordered mesoporous materials (OMMs) have received increasing interest due to their uniform pore size, high surface area, various compositions and wide applications in energy conversion and storage, biomedicine and environmental remediation, etc. The soft templating synthesis using surfactants or amphiphilic block copolymers is the most efficient method to produce OMMs with tailorable pore structure and surface property. However, due to the limited choice of commercially available soft templates, the common OMMs usually show small pore size and amorphous (or semicrystalline) frameworks. Tailor-made amphiphilic block copolymers with controllable molecular weights and compositions have recently emerged as alternative soft templates for synthesis of new OMMs with many unique features including adjustable mesostructures and framework compositions, ultralarge pores, thick pore walls, high thermal stability and crystalline frameworks. In this Perspective, recent progresses and some new insights into the coassembly process about the synthesis of OMMs based on these tailor-made copolymers as templates are summarized, and typical newly developed synthesis methods and strategies are discussed in depth, including solvent evaporation induced aggregation, ligand-assisted coassembly, solvent evaporation induced micelle fusion-aggregation assembly, homopolymer assisted pore expanding and carbon-supported crystallization strategy. Then, the applications of the obtained large-pore OMMs in catalysis, sensor, energy conversion and storage, and biomedicine by loading large-size guest molecules (e.g., protein and RNA), precious metal nanoparticles and quantum dots, are discussed. At last, the outlook on the prospects and challenges of future research about the synthesis of large-pore OMMs by using tailor-made amphiphilic block copolymers are included.

Progress on the Fabrication of Ordered Mesoporous Materials with Large Pores by Using Novel Amphiphilic Block Copolymers as Templates

Progress on the Fabrication of Ordered Mesoporous Materials with Large Pores by Using Novel Amphiphilic Block Copolymers as Templates

Fischer-Trospch Synthesis on Ordered Mesoporous Cobalt-Based Catalysts with Compact Multichannel Fixed-Bed Reactor Application: A Review

CO hydrogenation to hydrocarbons through Fischer–Tropsch synthesis (FTS) reaction is one of the promising chemical processes, which can convert alternative feedstocks such as natural gas or biomass into synthetic fuels. The FTS reaction has received many attentions due to a limited petroleum resource with an increased demand for using alternative carbon sources such as stranded gas or shale gas. Some proper synthetic methods of an effective FTS catalyst having a larger active metal surface area and a lower deactivation rate are the most important issues for a long-term operation. Therefore, some ordered mesoporous materials (OMM) have been widely investigated in the field of CO hydrogenation using some heterogeneous catalysts. The present brief review paper summarized the various preparation methods of the ordered mesoporous materials for the possible applications of FTS reaction with a lower deactivation rate and a higher catalytic performance. The applications of the ordered mesoporous cobalt oxides for FTS reaction are briefly introduced and the ways to improve a structural stability even under reductive CO hydrogenation conditions by using efficient pillaring materials as well as by preparing mixed metal oxides. A higher catalytic activity of the ordered mesoporous cobalt oxide was also verified in a multi-channel fixed-bed compact reactor having the intersected interlayers of micro-channel heat exchanger. The thermal stability of ordered mesoporous cobalt-based catalysts was mainly affected by a structural stability which can easily remove the heavy hydrocarbons from the inner surfaces.

Ordered Mesoporous Materials as Supports for Stable Iron Catalysts in the Fischer–Tropsch Synthesis of Lower Olefins

AbstractThe Fe‐catalyzed Fischer–Tropsch to olefins (FTO) synthesis is a non‐oil‐based route for the production of C2–C4 olefins. The understanding of the interplay between the catalytically active species, promoters, and support materials has improved over the last years, but the nanostructures of the various supports used are often not comparable. Several ordered mesoporous materials with a comparable pore size and pore symmetry are used as model supports for Fe‐based FTO catalysts. Ammonium iron citrate is used as the Fe source for all supports, and Na and S are added as promoters. The formation of catalytically active iron carbide species is suppressed within the strongly interacting mesoporous silica support, but the weakly interacting carbon and silicon carbide supports yield highly active FTO catalysts. Carbon‐supported catalysts show a high selectivity towards lower olefins, low methane production, and stable operation for up to 140 h under industrially relevant FTO conditions.

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.