Breakthrough and future: nanoscale controls of compositions,morphologies, and mesochannel orientations toward advanced mesoporous materials

Currently, ordered mesoporous materials prepared through the self‐assembly of surfactants have attracted growing interests owing to their special properties, including uniform mesopores and a high specific surface area. Here we focus on fine controls of compositions, morphologies, mesochannel orientations which are important factors for design of mesoporous materials with new functionalities. This Review describes our recent progress toward advanced mesoporous materials. Mesoporous materials now include a variety of inorganic‐based materials, for example, transition‐metal oxides, carbons, inorganic‐organic hybrid materials, polymers, and even metals. Mesoporous metals with metallic frameworks can be produced by using surfactant‐based synthesis with electrochemical methods. Owing to their metallic frameworks, mesoporous metals with high electroconductivity and high surface areas hold promise for a wide range of potential applications, such as electronic devices, magnetic recording media, and metal catalysts. Fabrication of mesoporous materials with controllable morphologies is also one of the main subjects in this rapidly developing research field. Mesoporous materials in the form of films, spheres, fibers, and tubes have been obtained by various synthetic processes such as evaporation‐mediated direct templating (EDIT), spray‐dried techniques, and collaboration with hard‐templates such as porous anodic alumina and polymer membranes. Furthermore, we have developed several approaches for orientation controls of 1D mesochannels. The macroscopic‐scale controls of mesochannels are important for innovative applications such as molecular‐scale devices and electrodes with enhanced diffusions of guest species. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 321–339; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900022     

A Review of Recent Developments of Mesoporous Materials

This personal account concerns novel recent discoveries in the area of mesoporous materials. Most of the papers discussed have been published within the last two to three years. A major emphasis of most of these papers is the synthesis of unique mesoporous materials by a variety of synthetic methods. Many of these articles focus on the control of the pore sizes and shapes of mesoporous materials. Synthetic methods of various types have been used for such control of porosity including soft templating, hard templating, nano‐casting, electrochemical methods, surface functionalization, and trapping of species in pores. The types of mesoporous materials range from carbon materials, metal oxides, metal sulfides, metal nitrides, carbonitriles, metal organic frameworks (MOFs), and composite materials. The vast majority of recent publications have centered around biological applications with a majority dealing with drug delivery systems. Several other bio‐based articles on mesoporous systems concern biomass conversion and biofuels, magnetic resonance imaging (MRI) studies, ultrasound therapy, enzyme immobilization, antigen targeting, biodegradation of inorganic materials, applications for improved digestion, and antitumor activity. Numerous nonbiological applications of mesoporous materials have been pursued recently. Some specific examples are photocatalysis, photo‐electrocatalysis, lithium ion batteries, heterogeneous catalysis, extraction of metals, extraction of lanthanide and actinide species, chiral separations and catalysis, capturing and the mode of binding of carbon dioxide (CO₂), optical devices, and magneto‐optical devices. Of this latter class of applications, heterogeneous catalysis is predominant. Some of the types of catalytic reactions being pursued include hydrogen generation, selective oxidations, aminolysis, Suzuki coupling and other coupling reactions, oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and bifunctional catalysis. For perspective, there have been over 40,000 articles on mesoporous materials published in the last 4 years and about 1388 reviews. By no means is this personal account thorough or all inclusive. One objective has been to choose a variety of articles of different types to obtain a flavor of the breadth of diversity involved in the area of mesoporous materials.     

An Electrochemical Sensor Based on Gold Nanoparticles Incorporated in Mesoporous MFI Zeolite for Determination of Purine Bases in DNA

An electrochemical sensor was developed based on gold nanoparticles incorporated in mesoporous MFI zeolite for the determination of purine bases. Au nanoparticles (AuNPs) were incorporated into the mesoporous MFI zeolite (AuNPs/m‐MFI) by post‐grafting reaction. The composite materials were characterized by transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and electrochemical methods. Au nanoparticles with a size of 5‐20 nm are uniformly dispersed in the pores of mesoporous MFI zeolite. And the morphology of MFI zeolite can be perfectly kept after pore expansion and Au nanoparticles incorporation. The electrocatalytic oxidation of purine bases (guanine and adenine in DNA) is investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface‐confined Au nanoparticles provide the good catalytic activity for oxidation of purine bases. The simultaneous detection of guanine and adenine can be achieved at AuNPs/m‐MFI composites modified glassy carbon electrode (GCE). The electrochemical sensor based on AuNPs/m‐MFI exhibits wide linear range of 0.5–500 μM and 0.8–500 μM with detection limit of 0.25 and 0.29 μM for guanine and adenine, respectively. Moreover, the electrochemical sensor is applied to evaluation of guanine and adenine in herring sperm DNA samples with satisfactory results.     

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.     

Voltammetric Detection of Lead(II) Using Amide‐Cyclam‐ Functionalized Silica‐Modified Carbon Paste Electrodes

2‐(4,8,11‐Triscarbamoylmethyl‐1,4,8,11‐tetraazacyclotetradec‐1‐yl)acetamide (TETAM) derivatives bearing 1, 2, or 4 silylated arms have been synthesized and grafted to the surface of silica gel and ordered mesoporous silica samples. The resulting organic‐inorganic hybrids have been incorporated into carbon paste electrodes and applied to the preconcentration electroanalysis of Pb(II). The attractive recognition properties of these cyclam derivatives functionalized with amide pendent groups toward Pb(II) species and the highly porous structure of the adsorbents can be exploited for the selective and sensitive detection of the target analyte. Various parameters affecting the preconcentration and detection steps have been discussed with respect to the composition and pH of both accumulation and detection media, the nature of the adsorbent (number of silylated groups linking the macrocycle to silica, texture of materials), the accumulation time, and the presence of interfering cations. Under optimal conditions and for 2 min accumulation at open‐circuit, the voltammetric response increased linearly with the Pb(II) concentration in a range extending from 2×10^?7 to 10^?5 M, while a longer accumulation time of 15 min afforded a linear calibration curve between 10^?8 and 10^?7 M with a detection limit of 2.7×10^?9 M which is well below the European regulatory limit of lead in consumption water.     

Periodic Mesoporous Silicas and Organosilicas: An Overview Towards Catalysis

Micelle-templated mesoporous and organic–inorganic hybrid mesoporous materials are important in many fields of material research, especially for hosting catalysts in confined space. Among this class, the recent discovery of periodic mesoporous organosilicas (PMOs) represent an exciting new group of organic–inorganic nanocomposites targeted for a broad range of applications ranging from catalysis to microelectronics. Compared to the earlier generation of organic–inorganic hybrid mesoporous samples, obtained by the cocondensation reaction or by the grafting reaction, PMOs represent the right combination of organic and inorganic groups in the frame wall positions. This article reviews the current state of art in organic–inorganic hybrid mesoporous material research with special emphasis over periodic mesoporous organosilica materials having various redox centers (Ti, V, Cr) suitable for oxidation reactions as well as acidic sites (Al, –SO₃H) for the organic transformation of bulky molecules.     

SYNTHESIS AND BIOTECHNOLOGICAL APPLICATIONS OF VINYL POLYMERINORGANIC HYBRID AND MESOPOROUS MATERIALS

We describe the sol-gel synthesis of a new family of organic-inorganic hybrid materials, in which various vinylpolymers are covalently bonded to and uniformly distributed in inorganic oxide matrices. The materials can be tailored tohave both good toughness and hardness while maintaining excellent optical transparency. Doping the sol-gel metal oxideswith optically active compounds such as D-glucose results in new optical rotatory composite materials. Removal of thedopant compounds from the composites affords mesoporous oxide materials, which represents a new, nonsurfactant-templated route to mesoporous molecular sieves. We have successfully immobilized a series of enzymes and other bioactiveagents in mesoporous materials. Catalytical activities of the enzyme encapsulated in mesoporous materials were found to bemuch higher than those encapsulated in microporous materials.     

Facile Synthesis of Ordered Mesoporous Zirconia for Electrochemical Enrichment and Detection of Organophosphorus Pesticides

Highly crystallized mesoporous ZrO₂ nanomaterials were synthesized by solvent evaporation induced self‐assembly approach. Ordered mesoporous ZrO₂ nanomaterials were characterized by TEM, SEM, BET, XRD and UV‐Vis spectroscopy. The obtained nanomaterials exhibit the close‐packing mesopores with average pore size of 7 nm and a highly crystallized framework with tetragonal phase. A non‐enzyme electrochemical sensor based on ordered mesoporous ZrO₂ is established for selective detection of methyl parathion (MP). The online extraction of MP is firstly achieved by ZrO₂ modified electrode at open‐circuit potential for 5 min., and the sensitive detection of MP is performed by differential pulse voltammetry (DPV) method. By comparison, DPV responses of mesoporous ZrO₂ are 40 times and 25 times larger than that of mesoporous silica and mesoporous carbon with the similar pore structure, implying the specific affinity advantage of zirconia to phosphoric group. The quantitative analysis result shows that the voltammetric currents are linear with concentrations of MP ranging from 1 ng/ml to 2 μg/ml with a detection limit of 0.53 ng/ml. The sensor also exhibits good stability and high selectivity against interfering species. The excellent analytical performances are owed to the accessible and uniform mesoporous structures, highly crystallized frameworks of ZrO₂ and its specific affinity to phosphate groups.     

Carbon Paste Electrode Modified with Carbamoylphosphonic Acid Functionalized Mesoporous Silica: A New Mercury‐Free Sensor for Uranium Detection

This study reports a new approach for developing a uranium electrochemical sensor that is mercury‐free, solid‐state, and has less chance for ligand depletion than existing sensors. A carbon‐paste electrode modified with carbamoylphosphonic acid self‐assembled monolayer on mesoporous silica was developed for uranium detection based on an adsorptive square‐wave stripping votammetry technique. Voltammetric responses for uranium detection are reported as a function of pH, preconcentration time, and aqueous phase uranium concentration. The uranium detection limit is 25 ppb after 5 minutes preconcentration and improved to 1 ppb after 20 minutes preconcentration. The relative standard deviations are normally less than 5%.     

Electrochemical Sensor Platforms Based on Nanostructured Metal Oxides,and Zeolite‐Based Materials

Electrochemical sensors have drawn significant attention over the last couple of decades because of their ability to improve detection of organic and inorganic analytes found in the field of biotechnology, environmental sciences, medicine, and food quality control. This personal account summarizes the state‐of‐art research carried out in the construction and evaluation of nanostructured metal oxides and zeolite based electrochemical sensors. Metal oxides and zeolite‐based nanomaterials have many unique and extraordinary properties such as tunable redox activity, surface functionalization ability, optimum conductivity, large surface area, biocompatibility and so forth. In this personal account, the current advances in electrochemical sensor applications of metal oxides, zeolite‐based nanomaterials, and their nanocomposites are described for the single and simultaneous determination of organic & inorganic contaminants present in water bodies, physiological bio‐molecules present in human blood & urine samples, and organic contaminants present in food materials.Moreover, concluding section focuses discussion on the future developments and applications of these materials in various emerging technologies.     

Electroanalytical Applications of Microporous Zeolites and Mesoporous (Organo)Silicas: Recent Trends

Microporous zeolites and ordered mesoporous (organo)silicas have been widely used as electrode modifiers because of their attractive properties (ion exchange and size selectivity of zeolites, well ordered nanoreactors containing a high number of widely accessible active centers in mesoporous (organo)silicas). These properties have been intelligently combined to selected redox processes to improve the response of the resulting modified electrodes or to design novel electrochemical detection schemes. This up‐to‐date review provides the recent advances made in the electroanalytical applications of zeolite modified electrodes and discusses the interest of ordered mesoporous (organo)silica materials in electroanalysis.     

Synthesis of morphology-controllable mesoporous Co3O4 and CeO2

Recently, extensive works have been devoted to the morphology control of mesoporous materials with respect to their use in various applications. In this paper, we used two kinds of mesoporous silica, SBA-15 rods and spheres as hard templates to synthesize morphology-controllable mesoporous metal oxides. By carefully controlling the loading of metal precursors in the mesopores of the hard template, mesoporous Co₃O₄ and CeO₂ with different morphologies, such as micrometer-sized rod, hollow sphere, saucer-like sphere, and solid sphere were conveniently obtained. The structural properties of these materials were characterized by XRD, BET, SEM and TEM. In addition, it is found that the differences observed in the textural properties of the two mesoporous metal oxides nanocasted from the same template can be attributed to the properties of metal precursors and the interaction between metal oxide and SiO₂. Thus-obtained mesoporous metal oxides with such special morphologies may have a potential application in the field of environmental catalytic oxidation.     

Silica‐modified Electrodes for Electrochemical Detection of Malachite Green

New silica‐modified glassy carbon electrodes prepared with three different sorts of ordered mesoporous silica (OMS) were characterized and tested for the electrochemical detection of Malachite Green (MG). The electrodes were prepared by drop casting using silica suspensions and, for stability sake, a Nafion coating was deposited on the electrode top by the same technique. Square wave anodic stripping voltammetry was used to investigate the effect of various experimental parameters (deposition time, solution pH, silica type and concentration) on the performance of the modified electrodes. The best electrode (GC/MCM‐41‐NH₂/Nafion) with detection limit 0.36 μM, sensitivity 0.164±0.003 A/M; linear domain 1–6 μM was applied to detect MG in a commercial product commonly used as biocide in aquaria for ornamental fish.     

介孔分子筛的酸性和水热稳定性

介孔分子筛材料在催化、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潜在的应用价值.但是,由于介孔分子筛材料较低的水热稳定性和较弱的酸性,极大地影响了其在催化研究中的广泛应用.本文系统地综述了最近几年在提高介孔分子筛酸性和水热稳定性的研究工作.其中包括:(1)将超酸组份负载于介孔分子筛的孔道中以达到提高介孔分子筛材料的酸强度的目的;(2)通过在合成介孔分子筛的过程中加入无机盐和有机胺等助剂或采用合适的后处理方法以提高介孔分子筛的水热稳定性;(3)通过新型模板剂来合成具有较高水热稳定性的介孔分子筛材料;(4)利用具有沸石分子筛基本结构单元的沸石分子筛导向剂与表面活性剂自组装来合成具有强酸中心和高温水热稳定的介孔分子筛材料.     

Polymer Nanoassembly as Delivery Systems and Anti‐Bacterial Toolbox: From PGMAs to MSN@PGMAs

Researches on cargo delivery systems have received burgeoning attention and advanced rapidly. For synthetic nanodevices, polymer nanoassemblies and their inorganic‐organic hybrid materials, especially smart mesoporous silica nanoparticle (MSN)‐polymer hybrids (e. g., MSN@PGMAs), have attracted increasing attention in recent years. Their superior characteristics and unique features such as dynamic transition of morphology endow them the ability to efficiently entrap cargo molecules and undergo smart cargo delivery and release in response to various external stimuli. In this Personal Account, we present our recent research progress in the construction of cargo delivery systems based on polymers, poly(glycidyl methacrylate) (PGMA) and its derivatives in particular, ranging from polymer nanoparticles, reverse micelles, to vesicles and reverse vesicles, and their performance in the delivery and controlled release of model molecules and therapeutic agents. Significantly, MSN‐PGMA hybrid nanoassemblies (MSN@PGMAs), constructed with the aid of atom transfer radical polymerization, host‐guest interactions, or layer‐by‐layer self‐assembly techniques, and their potential bio‐related applications and anti‐bacterial applications as new nanocarriers are reviewed. Finally, the prospects and challenges of such nanoplatforms are also discussed.     

湿空气下制备稳定的CsPbI2Br钙钛矿太阳电池

无机钙钛矿太阳能电池由于具有良好的热稳定性,高吸光系数等优点发展迅速。但无机钙钛矿材料对水分极其敏感,一般在惰性环境下中进行制备,操作复杂。本文通过简单的一步旋涂工艺,在无手套箱空气湿度条件下制备CsPbI₂Br无机钙钛矿薄膜,通过介孔TiO₂厚度的优化,对钙钛矿薄膜的结晶、成膜及稳定性进行了分析,发现在较厚基底介孔层上制备的钙钛矿晶粒大、无孔隙;随着基底厚度的减小,其上所形成的CsPbI₂Br薄膜禁带宽度(E_g)增大;电化学阻抗测试表明在较厚基底介孔层上制备的CsPbI₂Br钙钛矿具有更好的载流子提取与传输能力。对不同厚度介孔层上沉积的钙钛矿薄膜稳定性进行测试,发现CsPbI₂Br钙钛矿的稳定性随着介孔层厚度的增加而提高,在空气中做放置144 h后无明显变化。在空气湿度条件下组装成器件,获得到了8.16%的最佳光电转换效率,并且对器件无任何修饰及封装的情况下,在相对湿地低于35%的空气中放置72 h后保持最初效率的73%。     

Beyond Molecules: Mesoporous Supramolecular Frameworks Self‐Assembled from Coordination Cages and Inorganic Anions

Biological function arises by the assembly of individual biomolecular modules into large aggregations or highly complex architectures. A similar strategy is adopted in supramolecular chemistry to assemble complex and highly ordered structures with advanced functions from simple components. Here we report a series of diamond‐like supramolecular frameworks featuring mesoporous cavities, which are assembled from metal‐imidazolate coordination cages and various anions. Small components (metal ions, amines, aldehydes, and anions) are assembled into the hierarchical complex structures through multiple interactions including covalent bonds, dative bonds, and weak C? H???X (X=O, F, and π) hydrogen bonds. The mesoporous cavities are large enough to trap organic dye molecules, coordination cages, and vitamin B₁₂. The study is expected to inspire new types of crystalline supramolecular framework materials based on coordination motifs and inorganic ions.     

Synthesis and Characterization of Gold Nanoparticle‐Functionalized Ordered Mesoporous Materials

We report the synthesis and characterization of three different ordered mesoporous materials, labeled MCM‐48, SBA‐155, and SBA‐16 type materials, which were functionalized with gold nanoparticles using three different strategies. The functionalization strategies can be categorized as (i) in situ growth of gold nanoparticles, (ii) template loading, and (iii) diffusion loading of prefabricated gold nanoparticles. Two different particle sizes were employed in the latter two strategies, 5 nm and 10 nm. For all mesoporous structures, functionalization strategies, and particle sizes attempted, the materials retained their long‐range order upon incorporation of nanoparticles. From the adsorption isotherms, incorporation of gold nanoparticles altered the pore structure of the mesoporous support of some of the SBA‐15 and SBA‐16 type materials, with the effect on incorporation on the pore structure being particle size dependent in most cases. The majority of gold nanoparticles were found to reside on the external surface of the materials regardless of substrate and functionalization strategy; however, for the in situ synthesis and the template loading strategies, a significant fraction of the particles was determined to reside within the pore system of the material. In situ growth resulted in the highest content of gold nanoparticles in the solid phase. The relative effectiveness in retaining gold nanoparticles in the solid phase for each functionalization strategy was determined to be, in descending order, in situ synthesis, template loading, and diffusion loading.     

Solvent‐Free Self‐Assembly for Scalable Preparation of Highly Crystalline Mesoporous Metal Oxides

Mesoporous metal oxides (MMOs) have been demonstrated great potential in various applications. Up to now, the direct synthesis of MMOs is still limited to the solvent induced inorganic‐organic self‐assembly process. Here, we develop a facile, general, and high throughput solvent‐free self‐assembly strategy to synthesize a series of MMOs including single‐component MMOs and multi‐component MMOs (e.g., doped MMOs, composite MMOs, and polymetallic oxide) with high crystallinity and remarkable porous properties by grinding and heating raw materials. Compared with the traditional solution self‐assembly process, the avoidance of solvents in this method not only greatly increases the yield of target products and synthesis efficiency, but also reduces the environmental pollution and the consumption of cost and energy. We believe the presented approach will pave a new avenue for scalable production of advanced mesoporous materials for various applications.     

Sensitive Voltammetric Determination of Methyl Parathion Using a Carbon Paste Electrode Modified with Mesoporous Zirconia

A mesoporous zirconia modified carbon paste electrode was developed for electrochemical investigations of methyl parathion (MP, Phen‐NO₂). The significant increase of the peak currents and the improvement of the redox peak potential indicate that mesoporous zirconia facilitates the electronic transfer of MP. The oxidation peak current was proportional to the MP concentration in the range from 1.0×10⁻⁸ to 1.0×10⁻⁵ mol L⁻¹ with a detection limit of 4.6×10⁻⁹ mol L⁻¹ (S/N=3) after accumulation under open‐circuit for 210 s. The proposed method was successfully applied to the determination of MP in apple samples.