Mesoporous Silica Layer: Preparation and Opportunity

Periodic mesoporous silicas, which were prepared from silica‐surfactant mesostructured materials, have been investigated for a wide range of application due to their very large surface area, high porosity, pore size uniformity and variation, periodic pore arrangement and possible pore surface modification, after the pioneering papers on the formation of mesoporous silicas (MCM‐41 and FSM‐16). Morphosyntheses from such macroscopic morphologies as bulk monolith and film to nanoscopic ones, nanoparticles and their stable suspension, make mesoporous materials more attractive for applications and detailed characterization. Mesoporous silicas have been studied initially for such applications as adsorbent and catalyst, and more recently, optical, electronic, and bio‐related applications have been investigated. This review summarizes the studies on mesoporous silica film to highlight the present status and future of the preparation, characterization and application of the mesoporous silica film.     

Nanoporous silica films containing aluminum and titanium

By utilizing surfactant aggregates as supramolecular templates, mesoporous and mesostructured silicas with highly ordered structures became available. The resulting mesoporous silicas are promising candidates to host various photo- and electro-active species along with catalytically active species, due to their large and controllable pore sizes, highly ordered pore arrangements with low dimensional geometries, and reactive surfaces. We have developed the rapid solvent evaporation method, which is a modified sol-gel process, for synthesizing the mesostructured silica-surfactant films as well as the mesoporous silica films. Supported thin films, self-standing films and bubbles of mesoporous silicas have been synthesized by the rapid solvent evaporation method. The microstructures of the films have also been successfully controlled by changing the synthetic conditions. Taking advantage of the ease of synthetic operation and the transparency and homogeneity of the resulting materials, we have been interested in the introduction of functional units into the mesostructured materials. This paper reports the synthesis of transparent films of titanium- and aluminum-containing nanoporous silicas to modify the surface properties (such as adsorptive and catalytic) of nanoporous silicas. The incorporation of Al led to the formation of cation exchange or acidic sites on the mesopore surface, as revealed by the cationic dye adsorption experiments. The photocatalytic reactions of the Ti-containing nanoporous silica films were also examined.     

Recent advances in synthesis and applications of transition metal containing mesoporous molecular sieves

Work in mesoporous silica-based materials began in the early 1990s with work by Mobil. These materials had pore sizes from 20-500 A and surface areas of up to 1500 m(2) g(-1) and were synthesized by a novel liquid crystal templating approach. Researchers subsequently extended this strategy to the synthesis of mesoporous transition metal oxides, a class of materials useful in catalysis, electronic, and magnetic applications because of variable oxidation states, and populated d-bands-features not found in silicates. These materials are already showing promise in electronic and optical applications hinging on the semiconducting properties of transition metal oxides and their potential to act as electron acceptors, an important feature in the design of cathodic materials. This is the first general review of non-silicate mesoporous materials and will focus on recent advances in this area, emphasizing materials possessing unique electronic, magnetic, or optical properties. Also covered are advances in the synthesis and applications of mesostructured sulfides as well as a new class of template-synthesized platinum-based materials that show promise in heterogeneous catalysis.     

Ordered mesoporous non-oxide materials

Ordered mesoporous inorganic non-oxide materials attract increasing interest due to their plenty of unique properties and functionalities and potential applications. Lots of achievements have been made on their synthesis and structural characterization, especially in the last five years. In this critical review, the ordered mesoporous non-oxide materials are categorized by compositions, including non-oxide ceramics, metal chalcogenides, metal nitrides, carbides and fluorides, and systematically summarized on the basis of their synthesis approaches and mechanisms, as well as properties. Two synthesis routes such as hard-templating (nanocasting) and soft-templating (surfactant assembly) routes are demonstrated. The principal issues in the nanocasting synthesis including the template composition and mesostructure, pore surface chemistry, precursor selection, processing and template removal are emphatically described. A great number of successful cases from the soft-templating method are focused on the surfactant liquid-crystal mesophases to synthesize mesostructured metal chalcogenide composites and the inorganic-block-organic copolymer self-assembly to obtain non-oxide ceramics (296 references).     

Mesoporous Magnetic Materials Based on Rare Earth Oxides

A novel family of mesoporous oxides of rare earth metals (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized with specific surface areas of 253-348 m(2) g(-1) and pore diameters of 2.5-3.0 nm (see Scheme). The mesoporous solids and their surfactant mesophase precursors are paramagnetic and exhibit a magnetic anomaly due to the mesostructured atomic arrangement.     

Multifunctional hybrids by combining ordered mesoporous materials and macromolecular building blocks

This critical review presents and discusses the recent advances in complex hybrid materials that result from the combination of polymers and mesoporous matrices. Ordered mesoporous materials derived from supramolecular templating present high surface area and tailored pore sizes; pore surfaces can be further modified by organic, organometallic or even biologically active functional groups. This permits the creation of hybrid systems with distinct physical properties or chemical functions located in the framework walls, the pore surface, and the pore interior. Bringing polymeric building blocks into the game opens a new dimension: the possibility to create phase separated regions (functional domains) within the pores that can behave as "reactive pockets" of nanoscale size, with highly controlled chemistry and interactions within restricted volumes. The possibilities of combining "hard" and "soft" building blocks to yield these novel nanocomposite materials with tuneable functional domains ordered in space are potentially infinite. New properties are bound to arise from the synergy of both kinds of components, and their spatial location. The main object of this review is to report on new approaches towards functional polymer-inorganic mesostructured hybrids, as well as to discuss the present challenges in this flourishing research field. Indeed, the powerful concepts resulting from the synergy of sol-gel processing, supramolecular templating and polymer chemistry open new opportunities in the design of advanced functional materials: the tailored production of complex matter displaying spatially-addressed chemistry based on the control of chemical topology. Breakthrough applications are expected in the fields of sustainable energy, environment sensing and remediation, biomaterials, pharmaceutical industry and catalysis, among others (221 references).     

Preparation and characterization of novel mesoporous ceria-titania

Synthesis of a novel thermally stable mesoporous ceria-titania phase using a neutral templating route is reported. The as-made inorganic-template hybrid mesostructured matrix showed a broad low-angle XRD peak characteristic of mesoporous materials. Careful thermal treatment of the matrix allowed the subsequent densification (of the pore walls) of the inorganic component and removal of the organic component so that a high-quality mesoporous ceria-titania was formed as observed by TEM analysis. The calcined material showed the formation of fluorite type structure of CeO(2) but no crystalline titania phase was observed. The mesoporous structure remained even after high-temperature treatment. The material had high surface area after calcination up to the temperature of 973 K, with well-dispersed ceria and titania components and negligible bulk oxide formation (from XRD, UV-vis, and XPS analysis). These novel mesoporous ceria-titania materials showed high performance for the removal of volatile organic compound (toluene). The toluene removal performance was further enhanced for Pt impregnated mesoporous ceria-titania.     

Block copolymer-templated mesoporous oxides

Block copolymers (BC) are indeed suitable and versatile templates for the creation of mesostructured and mesoporous materials. Great advances have been achieved in the last 3 years. Nowadays, it is possible to obtain highly controlled large-pore and highly stable mesostructured and mesoporous materials (silica, non-silica oxides, carbons,…) shaped as powders, films, monoliths or aerosols. This paper reviews mainly the synthesis of BC-templated mesostructured oxides, stressing in the physical, chemical and processing parameters, which have to be thoroughly controlled to reproducibly obtain mesoporous materials.     

Two-dimensional mesoporous materials：From fragile coatings to flexible membranes

This paper reviews the progress of two-dimensional mesoporous materials including their synthesis strategy,mesostructure,composition,surface property,flexibility,and potential applications.During the past two decades,research on two-dimensional mesoporous materials has experienced an evolution from fragile coatings to flexible membranes.Aiming at practical applications,it is significant to support mesoporous materials with proper matrices for example porous membranes especially flexible ones to form mesoporous composite membranes with designed pore size and chemistry.     

由沸石纳米粒子自组装制备具有高催化活性中心和水热稳定的新型介孔分子筛材料

 人们合成了一系列介孔分子筛材料，并发现它们在催化、吸附与分离以及化学组装制备先进材料和分子器件等方面具有很大的潜在应用价值．但是，介孔分子筛材料相对于微孔沸石分子筛存在着两个致命弱点：较低的水热稳定性和较不活泼的催化活性中心．这两个弱点大大地影响了介孔分子筛在催化反应中的广泛应用．本文系统地综述了最近几年利用沸石纳米粒子自组装制备具有高催化活性中心和水热稳定的介孔分子筛材料的研究进展．这包括利用硅铝沸石纳米粒子自组装制备具有强酸性和水热稳定的新型介孔硅铝分子筛材料，利用钛硅沸石纳米粒子自组装制备具有高催化氧化活性中心和水热稳定的新型钛硅介孔分子筛材料，以及利用含有不同杂原子的沸石纳米粒子自组装制备一系列水热稳定的新型介孔分子筛催化材料．     

General Formation of Macro-/Mesoporous Nanoshells from Interfacial Assembly of Irregular Mesostructured Nanounits

Mesoporous core–shell nanostructures with controllable ultra-large open channels in their nanoshells are of great interest. However, soft template-directed cooperative assembly to mesoporous nanoshells with highly accessible pores larger than 30 nm, or even above 50 nm into macroporous range, remains a significant challenge. Herein we report a general approach for precisely tailored coating of hierarchically macro-/mesoporous polymer and carbon shells, possessing highly accessible radial channels with extremely wide pore size distribution from ca. 10 nm to ca. 200 nm, on diverse functional materials. This strategy creates opportunities to tailor the interfacial assembly of irregular mesostructured nanounits on core materials and generate various core–shell nanomaterials with controllable pore architectures. The obtained Fe,N-doped macro-/mesoporous carbon nanoshells show enhanced electrochemical performance for the oxygen reduction reaction in alkaline condition.     

Deposition of thin mesoporous silica films on glass substrates from basic solution

Transparent thin (ca. 100 nm) films of silica-surfactant mesostructured materials were deposited on borosilicate glass plates and soda-lime glass tubes from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, ammonia, and methanol. By calcination in air, the films became mesoporous (BET surface area of 700-900 m2 g-1) with pore diameter 2.0-2.8 nm.     

Materials with Nanoscale Porosity: Energy and Environmental Applications

In this personal account, several key inventions on designing novel microporous and mesoporous materials, and their applications in energy and environmental research are reviewed. Although, crystalline materials with sub‐nanometer pore size regime like zeolites, AlPOs, MOFs, ZIFs etc. are known over the years, silicious and non‐silicious mesoporous materials have revolutionized the research on the materials with nanoscale porosity in last two and half decades. A wide range of inorganic, organic‐inorganic hybrid as well as purely organic mesoporous materials with either periodic or disordered mesopores are known. Apart from conventional hydrothermal syntheses involving soft templating route, hard templating, evaporation induced self‐assembly (EISA), electrochemical or solvothermal (using hydrophilic solvents) synthetic routes are often employed in designing a large spectrum of mesoporous materials. Ease of synthesis using available cheap raw chemicals and versatility in the framework compositions together with the unique surface properties like exceptionally high surface area, pore volume and tunability in pore dimensions have made these materials very exciting to a wide range of researchers working on materials chemistry. Nanoscale porosity in the semiconductor nanomaterials is highly beneficial for the photocatalytic, optoelectronic and related light‐harvesting applications. Their high chemical stability has been explored intensively in designing novel heterogeneous catalysts for the synthesis of biofuels from biomass or CO₂ fixation to reactive organic molecules for the synthesis of fine chemicals and fuels, which has a large impact on energy and environmental research for the years to come. Diversity in mesoporous frameworks and their potential applications related to light harvesting, generation of renewable energy and synthesis of value added fine chemicals and fuels through environment friendly routes are mostly focused in this review.     

功能模板导向的自组装合成介孔结构有机／无机复合材料

回顾了近年来硅基介孔材料有机功能化的基本方法和研究进展．基于作者的相关研究工作,着重介绍一种新型的介孔氧化硅有机功能化的方法——功能模板导向的自组装法,阐述了该方法在自组装合成新型有机／无机复合材料方面的应用．     

Functionalization of mesostructured inorganic–organic and porous inorganic materials

The capability to functionalize the interior channels and/or high internal surface areas of mesostructured inorganic–organic or porous inorganic solids with specific organic or inorganic moieties has dramatically expanded the potential applications for these versatile materials in catalysis, separations, optical and opto-electronic devices, drug delivery, sensors, and energy conversion. Key to the widespread application of these materials are the various synthetic schemes that have been developed to provide control over the types of species incorporated and, more importantly, their distributions within the mesostructured hosts. Furthermore, multiple active species can often be independently incorporated and collectively optimized to yield multifunctional properties that widen application prospects. Several recent developments and examples in this rapidly growing field of materials chemistry and engineering are highlighted and discussed.     

Porphyrin-doped mesoporous silica films for rapid TNT detection

Two kinds of porphyrin-doped silica films with mesoporous structures were fabricated using evaporation-introduced self-assembly approach and examined for chemosensor applications to detect explosive compounds such as 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), and nitrobenzene (NB). All synthesized silica films showed high fluorescence quenching sensitivity toward the vapors of TNT, DNT, and NB but is strongly dependent on pore structure. The silica film with three dimensional pore structure exhibits the highest quenching efficiency close to the quenching efficiency reported for emissive conjugated polymers, indicating these kinds of mesostructured composites are potentially useful chemosensory materials for rapidly detecting trace explosives. The preparation conditions, the structures of the resulting films, their sensing performances, and the fluorescence quenching mechanism were discussed in this paper.     

Enzyme-functionalized mesoporous silica for bioanalytical applications

The unique properties of mesoporous silica materials (MPs) have attracted substantial interest for use as enzyme-immobilization matrices. These features include high surface area, chemical, thermal, and mechanical stability, highly uniform pore distribution and tunable pore size, high adsorption capacity, and an ordered porous network for free diffusion of substrates and reaction products. Research demonstrated that enzymes encapsulated or entrapped in MPs retain their biocatalytic activity and are more stable than enzymes in solution. This review discusses recent advances in the study and use of mesoporous silica for enzyme immobilization and application in biosensor technology. Different types of MPs, their morphological and structural characteristics, and strategies used for their functionalization with enzymes are discussed. Finally, prospective and potential benefits of these materials for bioanalytical applications and biosensor technology are also presented. Figure Enzyme-functionalized mesoporous silica fibers and their integration in a biosensor design. The immobilization process takes place essentially in the silica micropores.     

Mesoporous metal-organic framework materials

Metal-organic frameworks (MOFs) have emerged as a new type of porous materials for diverse applications. Most open MOFs reported to date are microporous (pore sizes <2 nm), and only a small fraction of MOFs with ordered mesoscale domains (2-50 nm) is reported. This tutorial review covers recent advances in the field of mesoporous MOFs (mesoMOFs), including their design and synthesis, porosity activation and surface modification, and potential applications in storage and separation, catalysis, drug delivery and imaging. Their specificities are dependent on the pore shape, size, and chemical environments of the cages or channels. The relationship between the structures and functions is discussed. The future outlook for the field is discussed in the context of current challenges in applications of mesoporous materials.     

有序介孔材料: 历史、 现状与发展趋势

有序介孔材料是指孔径在2~50 nm之间的多孔材料, 是一类具有均匀孔径、 高有序度纳米孔道和高比表面积的新材料. 在过去30年里, 有序介孔材料的研究取得了长足的进步, 在可控合成、 结构设计和调控及功能化等方面形成了系统的理论. 同时, 其应用领域也不断被拓展, 包括能源存储与转化、 催化、 生物医药和传感等方面. 本文首先回顾了有序介孔材料的发展历史, 简要介绍发展过程中“里程碑式”的研究工作; 然后根据构效关系总结了其在不同领域应用的最新进展; 最后讨论了有序介孔材料领域进一步发展所面临的挑战与机遇, 并对未来前景进行了展望.     

Characterization of the hydrophobicity of mesoporous silicas and clays with silica pillars by water adsorption and DRIFT

The hydrophobic-hydrophilic properties of a solid are related to the material chemistry and, often, these properties are relevant to the applications of a particular material. Contrarily to what happens with other properties, such as specific surface areas or pore volumes, the methodologies to ascertain on the hydrophilicity of a porous material are not well defined. In this work, we discuss and relate the information on the hydrophobicity degree obtained from water adsorption isotherms and from diffuse reflectance infrared Fourier transform (DRIFT), in a set of porous materials. The studied materials were mainly mesoporous solids, namely of MCM-41 and SBA-15 types, two xerogels and also different porous clays heterostructures. Both techniques were informative on the hydrophobic-hydrophilic properties of the studied samples, but the correlation between the information obtained by each technique was not straightforward. Water adsorption isotherms are much more sensitive to the differences of the studied materials than the DRIFT spectra. For silica-based mesoporous materials with similar surface chemistry, the water adsorption process and hence, the hydrophobic-hydrophilic properties, is mainly dependent on the pore diameters. However, water adsorption is much more sensitive to changes in the nature of the adsorbent surface than to changes in the pore diameter.