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A new, single-step protocol for wrapping individual nanosized β-casein micelles with silica is presented. This biomolecule-friendly synthesis proceeds at low protein concentration at almost neutral pH, and makes use of sodium silicate instead of the common silicon alkoxides. This way, formation of potentially protein-denaturizing alcohols can be avoided. The pH of the citrate-buffered synthesis medium is close to the isoelectric point of β-casein, which favours micelle formation. A limited amount of sodium silicate is added to the protein micelle suspension, to form a thin silica coating around the β-casein micelles. The size distribution of the resulting proteinsilica structures was characterized using DLS and SAXS, as well as 1H NMR DOSY with a dedicated pulsed-field gradient cryo-probehead to cope with the low protein concentration. The degree of silica-condensation was investigated by 29Si MAS NMR, and the nanostructure was revealed by advanced electron microscopy techniques such as ESEM and HAADF-STEM. As indicated by the combined characterization results, a silica shell of 2 nm is formed around individual β-casein micelles giving rise to separate protein coresilica shell nanoparticles of 17 nm diameter. This alcohol-free method at mild temperature and pH is potentially suited for packing protein molecules into bio-compatible silica nanocapsules for a variety of applications in biosensing, therapeutic protein delivery and biocatalysis.

Hexagonally ordered mesoporous silica coined COK-12 was synthesized in a continuous process by combining streams of sodium silicate and citric acid/sodium citrate buffered solution of (ethylene oxide)(20)-(propylene oxide)(70)-(ethylene oxide)(20) triblock copolymer (Pluronic P123) from separate reservoirs. COK-12 precipitated spontaneously upon combining both streams at nearly neutral pH and ambient temperature. Stable intermediates of the COK-12 formation process could be prepared by limiting sodium silicate addition. Investigation of these intermediates using small-angle X-ray scattering revealed COK-12 formed via an assembly process departing from spherical uncharged core-shell P123-silica micelles. The sterical stabilization of these micelles decreased upon accumulation of silicate oligomers in their shell. Aggregation of the spherical micelles led to cylindrical micelles, which aligned and adopted the final hexagonal organization. This unprecedentedly fast formation of P6m ordered mesoporous silica was caused by two factors in the synthesis medium: the neutral pH favoring uncharged silicate oligomers and the high salt concentration promoting hydrophobic interactions with surfactant micelles leading to silica accumulation in the PEO shell. The easy continuous synthesis process is convenient for large-scale production. The platelet particle morphology with short and identical internal channels will be advantageous for many applications such as pore replication, nanotube or fiber growth, catalytic functionalization, drug delivery, film and sensor development, and in nano dyes as well as for investigation of pore diffusion phenomena.

Zeogrids and Zeotiles are hierarchical materials built from assembled MFI zeolite precursor units. Permanent secondary porosity in these materials is obtained through self assembly of nanoparticles encountered in MFI zeolite synthesis in the presence of supramolecular templates. Hereon, the aggregated species are termed nanoslabs. Zeogrids are layered materials with lateral spacings between nanoslabs creating galleries qualifying as supermicropores. Zeotiles present a diversity of tridimensional nanoslab assemblies with mesopores. Zeotile-1, -4 and -6 are hexagonal mesostructures. Zeotile-1 has triangular and hexagonal channels; Zeotile-4 has hexagonal channels interconnected via slits. Zeotile-2 has a cubic structure with gyroid type mesoporosity. The behavior of Zeogrids and Zeotiles in adsorption, membrane and chromatographic separation and catalysis has been characterized and compared with zeolites and mesoporous materials derived from unstructured silica sources. Shape selectivity was detected via adsorption of n- and iso-alkanes. The mesoporosity of Zeotiles can be exploited in chromatographic separation of biomolecules. Zeotiles present attractive separation properties relevant to CO2 sequestration. Because of its facile synthesis procedure without hydrothermal steps Zeogrid is convenient for membrane synthesis. The performance of Zeogrid membrane in gas separation, nanofiltration and pervaporation is reported. In the Beckmann rearrangement of cyclohexanone oxime Zeogrids and Zeotiles display a catalytic activity characteristic of silicalite-1 zeolites. Introduction of acidity and redox catalytic activity can be achieved via incorporation of Al and Ti atoms in the nanoslabs during synthesis. Zeogrids are active in hydrocracking, catalytic cracking, alkylation and epoxidation reactions. Zeogrids and Zeotiles often behave differently from ordered mesoporous materials as well as from zeolites and present a valuable extension of the family of hierarchical silicate based materials.

Researchers in need of an ordered nanoporous material tend to rely on the original synthesis protocols which often demand hydrothermal synthesis and involve harsh chemical conditions, expensive sacrificial templates and long synthesis times. Considerable efforts have been invested in developing new pathways to simplify synthesis procedures. While in the area of zeolites even with optimum templates intrinsic energy barriers of the crystallization process obstruct the development of easy room temperature synthesis, the synthesis of ordered mesoporous materials and metal organic frameworks (MOFs) are examples of materials for which synthesis can be rationalized and simplified. One key element for the development of room temperature synthesis is the selection of highly efficient templates.

In concentrated clear sol prepared from tetraethylorthosilicate, tetrapropylammonium hydroxide, and water suitable for crystallization of Silicalite-1 zeolite, the main part of the silica is present in nanoparticles. The nature of these nanoparticles and their evolution during the induction period and the stage of early crystal growth was investigated via dissolution experiments in the presence of excess TPAOH. The dissolution process was monitored in situ using static and dynamic light scattering (SLS/DLS) and synchrotron small-angle X-ray scattering (SAXS). The complete dissolution of an individual nanoparticle was observed to occur in one step. Dissolution transformed a nanoparticle into a cluster of silicate oligomers. Larger grown nanoparticles dissolved slower. Exponential dissolution rate constants scaled inversely proportional with the volume of the nanoparticle’s silica core. This experimentally observed dissolution behavior was modeled by assuming that a nanoparticle dissolved to oligomers via a...

Cracking experiments using 2,2,4-trimethylpentane as a model component have been performed on five FAU and three MFI zeolites. In addition to these eight commercially available catalysts, two newly developed zeotype materials with bimodal pore structure, BIPOMs, have been investigated. Both BIPOMs possess an MFI ultramicropore (

Discrete electron tomography is a new approach for three-dimensional reconstruction of nanoscale objects. The technique exploits prior knowledge of the object to be reconstructed, which results in an improvement of the quality of the reconstructions. Through the combination of conventional transmission electron microscopy and discrete electron tomography with a model-based approach, quantitative structure determination becomes possible. In the present work, this approach is used to unravel the building scheme of Zeotile-4, a silica material with two levels of structural order. The layer sequence of slab-shaped building units could be identified. Successive layers were found to be related by a rotation of 120°, resulting in a hexagonal space group. The Zeotile-4 material is a demonstration of the concept of successive structuring of silica at two levels. At the first level, the colloid chemical properties of Silicalite-1 precursors are exploited to create building units with a slablike geometry. At the second level, the slablike units are tiled using a triblock copolymer to serve as a mesoscale structuring agent.

Concentrated clear solutions, as used for the preparation of Silicalite-1 zeolite, were synthesized from tetrapropylammonium hydroxide, tetraethylorthosilicate, and water. The solutions were analyzed using three techniques: quantitative 29Si NMR, synchrotron small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). 29Si NMR showed the coexistence of silicate oligomers and particles. For the first time, both fractions were analyzed simultaneously, providing a global, quantitative description of the clear solution microstructure. The SAXS patterns, typical of interacting particles, could be used together with the 29Si NMR deduced particle volume fraction to estimate a particle size. A careful analysis of DLS data of the dynamics of the suspensions revealed the occurrence of two diffusive processes. The faster process is a collective particle diffusion. The slower process corresponds to the particle self-diffusion and is present because of the presence of polydispersity in size, shape, and/or...

Ordered mesoporous materials with specific microporosity in the mesopore walls can be assembled by a secondary templating synthesis departing from a clear subcolloidal suspension dedicated to the tetrapropylammonium (TPA) mediated synthesis of colloidal Silicalite-1. A typical member of this material family is Zeotile-2. Zeotile-2 is mesostructurally similar to the cubic MCM-48 material with exceptional long-range order of the mesostructure. Zeotile-2 samples in which the TPA was either left or evacuated were prepared by leaching in boiling ethanolic acetic acid and calcination. The evacuation of the TPA gave rise to a substantial micropore volume revealed with nitrogen adsorption isotherms. The mesoporosity was independent of the presence of the TPA. Molecular separations of isooctane/octane mixtures illustrated the occurrence of molecular shape selectivity similar to MFI-type zeolites.

Unraveling the crystallization mechanism of zeolites remains an increasingly important challenge in chemistry. During the last decade, in situ spectroscopic methods have provided an unprecedented level of detail of the underlying molecular mechanisms and their kinetics. Magnetic resonance, vibrational and X-ray absorption techniques have emerged as principal tools for the in situ observation of crystallization. In this tutorial review, we discuss how these in situ methods have contributed to our understanding of the complex and diverse molecular processes that govern zeolite crystallization.

Micron-sized hollow spheres with zeolitic shell were used as inorganic fillers in PDMS-based mixed matrix membranes, overall enhancing solvent permeabilities as compared to traditional zeolite fillers, while selectivities were maintained.

The molecular steps involved in the self-assembly of Cu(3)(BTC)(2) (BTC=1,3,5-benzenetricarboxylic acid) metal-organic frameworks that enclose Keggin-type H(3)PW(12)O(40) heteropolyacid molecules were unraveled by using solution (17)O, (31)P, and (183)W NMR spectroscopy, small-angle X-ray scattering, near-IR spectroscopy, and dynamic light scattering. In aqueous solution, complexation of Cu(2+) ions with Keggin-type heteropolyacids was observed. Cu(2+) ions are arranged around the Keggin structure so that linking through benzenetricarboxylate groups results in the formation of the Cu(3)(BTC)(2) MOF structure HKUST-1. This is a unique instance in which a templating mechanism that relies on specific molecular-level matching and leads to explicit nanoscale building units can be observed in situ during formation of the synthetic nanoporous material.

Colloidal silicalite-1 zeolite was crystallized from a concentrated clear sol prepared from tetraethylorthosilicate (TEOS) and aqueous tetrapropylammonium hydroxide (TPAOH) solution at 95 degrees C. The silicate speciation was monitored by using dynamic light scattering (DLS), synchrotron small-angle X-ray scattering (SAXS), and quantitative liquid-state (29)Si NMR spectroscopy. The silicon atoms were present in dissolved oligomers, two discrete nanoparticle populations approximately 2 and 6 nm in size, and crystals. On the basis of new insight into the evolution of the different nanoparticle populations and of the silicate connectivity in the nanoparticles, a refined crystallization mechanism was derived. Upon combining the reagents, different types of nanoparticles (ca. 2 nm) are formed. A fraction of these nanoparticles with the least condensed silicate structure does not participate in the crystallization process. After completion of the crystallization, they represent the residual silicon atoms. Nanoparticles with a more condensed silicate network grow until approximately 6 nm and evolve into building blocks for nucleation and growth of the silicalite-1 crystals. The silicate network connectivity of nanoparticles suitable for nucleation and growth increasingly resembles that of the final zeolite. This new insight into the two classes of nanoparticles will be useful to tune the syntheses of silicalite-1 for maximum yield.

Zeolite synthesis is driven by structure-directing agents, such as tetrapropyl ammonium ions (TPA+) for Silicalite-1 and ZSM-5. However, the guiding role of these organic templates in the complex assembly to highly ordered frameworks remains unclear, limiting the prospects for advanced material synthesis. In this work, both static ab initio and dynamic classical modeling techniques are employed to provide insight into the interactions between TPA+ and Silicalite-1 precursors. We find that as soon as the typical straight 10-ring channel of Silicalite-1 or ZSM-5 is formed from smaller oligomers, the TPA+ template is partially squeezed out of the resulting cavity. Partial retention of the template in the cavity is, however, indispensable to prevent collapse of the channel and subsequent hydrolysis.

Magnetohydrodynamic nanoparticle dispersion is an energy efficient method to deaggregate nanoparticles, combining hydrodynamic forces of turbulent flow with Lorentz forces generated by a magnetic field.

n-Alkane hydroisomerisation and hydrocracking experiments reveal that ZSM-5 materials synthesized by self-assembly of nanoslabs show different molecular shape selectivity than ZSM-5 synthesized by hydrothermal methods.

Transparent and smooth silica thin films with a very high porosity were prepared by linking zeolitic nanoslabs into open mesoporous networks. Calcined films characterized by ellipsometric porosimetry presented pore sizes in the range of 6–18 nm and porosities of 70–90% depending on the temperature of assembly of the nanoslabs in the presence of Pluronic P123 triblock copolymer. The films were disordered according to grazing incidence small angle X-ray scattering and transmission electron microscopy. The most spacious film had a very low refractive index of 1.08 (at 632.8 nm) and exhibited reversible shrinkage of up to 30% of its original thickness upon capillary condensation of adsorbate vapor. The mechanical flexibility of the film was confirmed by the low Young modulus of 0.9 GPa determined by nano-indentation. The full accessibility of the porosity and the convenience for chemical functionalization were demonstrated using Atomic Layer Deposition (ALD) of TiO2 monitored with Rutherford Backscattering Spectroscopy. Using ALD the porosity and mechanical flexibility of the film could be fine tuned.

A new synthesis procedure is presented to prepare P6m ordered mesoporous silica at room temperature and quasi-neutral pH in a buffered medium using a cheap silicon source.

Hexagonally ordered mesoporous silica with a very narrow mesopore size distribution and exceptionally high stability paired with unusually thin pore walls was prepared using piperidine and cetyltrimethylammonium bromide.