Search

Zeolites are the catalytic workhorses of the refinery and chemicals production industry. Their inherent micropores lead to remarkable shape-selectivity, but also present diffusion limitations on reactions. One scalable approach to further their functionality is to introduce mesopores into the individual zeolite crystal by base leaching. Using cryogenic transmission electron microscopy (cryo-TEM), we are able to capture the pore formation process in ZSM-5 zeolites in the solution state, first forming mesopores, to eventually yielding hollow crystals. Electron tomography indicates that the larger pores in the initial leaching stages tend to exist at the boundary between the aluminum-rich shell and the aluminum-poor core, while multiple small pores are also present within the aluminum-poor core. This indicates that pore formation is based on crystalline and chemical inhomogeneities at the single crystal level. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) is a widespread magnetic iron oxide encountered in many biological and geological systems, and also in many technological applications. The magnetic properties of magnetite crystals depend strongly on the size and shape of its crystals. Hence, engineering magnetite nanoparticles with specific shapes and sizes allows tuning their properties to specific applications in a wide variety of fields, including catalysis, magnetic storage, targeted drug delivery, cancer diagnostics and magnetic resonance imaging (MRI). However, synthesis of magnetite with a specific size, shape and a narrow crystal size distribution is notoriously difficult without using high temperatures and non-aqueous media. Nevertheless, living organisms such as chitons and magnetotactic bacteria are able to form magnetite crystals with well controlled sizes and shapes under ambient conditions and in aqueous media. In these biomineralization processes the organisms use a twofold strategy to control magnetite formation: the mineral is formed from a poorly crystalline precursor phase, and nucleation and growth are controlled through the interaction of the mineral with biomolecular templates and additives. Taking inspiration from this biological strategy is a promising route to achieve control over the kinetics of magnetite crystallization under ambient conditions and in aqueous media. In this review we first summarize the main characteristics of magnetite and what is known about the mechanisms of magnetite biomineralization. We then describe the most common routes to synthesize magnetite and subsequently will introduce recent efforts in bioinspired magnetite synthesis. We describe how the use of poorly ordered, more soluble precursors such as ferrihydrite (FeH) or white rust (Fe(OH)2) can be employed to control the solution supersaturation, setting the conditions for continued growth. Further, we show how the use of various organic additives such as proteins, peptides and polymers allows for either the promotion or inhibition of magnetite nucleation and growth processes. At last we discuss how the formation of magnetite-based organic–inorganic hybrids leads to new functional nanomaterials. [ABSTRACT FROM AUTHOR]

We show that by reacting ferrihydrite (FeH) with Fe(II) ions and subsequently increasing the pH, magnetite is formed through a multi-step nucleation process mediated by monodisperse FeH–Fe(II) primary particles. The interaction of these primary particles with a transient green rust phase leads to the formation of smaller secondary particles which form the feedstock for magnetite formation. Surprisingly, the presence of a polypeptide additive prevents the formation of green rust as an Fe(II)-rich intermediate phase, and leads to the formation of amorphous aggregates of FeH–Fe(II) particles which subsequently transform into the final magnetite nanocrystals. The observation of multiple transitions and the involvement of disordered precursor phases in this bioinspired crystallization route is important for our understanding of the nucleation of magnetite in geological and biological environments, and may lead to new approaches in the sustainable synthesis of this technologically important mineral. [ABSTRACT FROM AUTHOR]

Building blocks for organic solar cells are made from P3HT in a P3HT : PCBM solution in toluene and used to tune the morphology of the photoactive layer. The approach presented here decouples the structure and morphology formation, providing precise control over both the structures in solution and the morphology of the photoactive layer. For the characterization of the nanostructures in the organic casting solutions, cryo-TEM was successfully employed, and reveals the P3HT crystals and even the 1.7 nm lamellar stacking, which in combination with cryogenic low dose electron diffraction clearly proves the high crystallinity of P3HT aggregates realized. The photoactive layers made from pre-crystallized solutions show a morphology that is closely related to the structures in solution. A clear trend of decreasing open circuit voltage and increasing short circuit current with increasing order in the casting solutions and the devices was observed, which correlates with the evolution of the morphology from very intermixed with small fibrillar structures to phase-separated with large polymer crystals, as evaluated from representative devices, characterized in 3D with electron tomography. [ABSTRACT FROM AUTHOR]

The often astonishing material properties of crystalline biominerals are generally related to the hierarchical assembly of specifically interacting organic and inorganic components. To synthesize new materials with similar advanced properties applying nature’s biomimeralization strategies we need to unravel the mechanisms of biologically and biomimetically controlled mineral formation. Since the literature is extensive this tutorial reviewis focussed on CaCO3, the most abundant biomineral. We will first review the different approaches to biomimetic mineralization and describe the most recent advancements in the field. Subsequently the importance of in situand time-resolved experiments, with their possibilities and limitations, is discussed with selected references. [ABSTRACT FROM AUTHOR]

Biomimetic strategies to control mineral nucleation include the development of self-assembled monolayers with appropriate structural properties. We present a bis-urea based surfactant with variable structural adaptability, which induces habit modification in calcite crystals under optimal conditions. In situ surface-sensitive synchrotron X-ray scattering measurements are reported, which yield surprising conclusions for the film structure. In particular, it is found that nucleation of modified calcite is correlated with the release of two-dimensional ordering in the surfactant layer. The model system is discussed in the context of the history of Langmuir films as models for biomineralization. [ABSTRACT FROM AUTHOR]

CryoTEM demonstrates that a CNA35-bearing liposomal MRI contrast agent selectively binds to poorly assembled collagen type I as opposed to well-assembled collagen fibrils, whereas monomeric CNA35 binds to all forms of collagen. It is shown that upon conjugation to liposomes and micelles CNA35 loses its ability to dissociate ordered collagen fibrils and thereby to create its own binding sites. [ABSTRACT FROM AUTHOR]

The size and shape of a surfactant aggregate could be altered by using supersaturation like in crystal growth, rather than applying common laws that drive surfactant aggregate formation.

Chitosan (CS) can mediate the formation of spherical, tabulate, and unique starfruit-like silica in the presence of phosphate ions (Pi). CryoTEM and cryoET were used to examine the CS aggregates in the hydrated state. 3D starfruit-like CS/Pi aggregates were reconstructed, which unambiguously confirmed the templating effect of CS/Pi in biomimetic silicification.

Janus gold nanoparticles are synthesised via a simple preparation method and behave as amphiphiles self-assembling in water into disk-shaped micelles.

Hydrogen bonding between urea groups of amphiphilic tri-block copolymers considerably affects their self-assembly in water, which results in a strong modification of morphology and viscosity of aqueous solutions; the hydrogen bonding motif in these amphiphilic copolymers allows molecular recognition of small molecules with complementary hydrogen bonding units.

Monovalent ligand and divalent ligand have been synthesized, and their thermodynamic parameters of complexation to avidin and streptavidin have been analyzed in terms of multivalent binding.