Marc-Olivier Coppens

Hierarchically Structured Nanomaterials for Electrochemical Energy Conversion

Hierarchical nanomaterials are highly suitable as electrocatalysts and electrocatalyst supports in electrochemical energy conversion devices. The intrinsic kinetics of an electrocatalyst are associated with the nanostructure of the active phase and the support, while the overall properties are also affected by the mesostructure. Therefore, both structures need to be controlled. A comparative state-of-the-art review of catalysts and supports is provided along with detailed synthesis methods. To further improve the design of these hierarchical nanomaterials, in-depth research on the effect of materials architecture on reaction and transport kinetics is necessary. Inspiration can be derived from nature, which is full of very effective hierarchical structures. Developing fundamental understanding of how desired properties of biological systems are related to their hierarchical architecture can guide the development of novel catalytic nanomaterials and nature-inspired electrochemical devices.

Packaging biological cargoes in mesoporous materials: opportunities for drug delivery

Introduction: Confinement of biomolecules in structured nanoporous materials offers several desirable features ranging from chemical and thermal stability, to resistance to degradation from the external environment. A new generation of mesoporous materials presents exciting new possibilities for the formulation and controlled release of biological agents. Such materials address niche applications in enteral and parenteral delivery of biologics, such as peptides, polypeptides, enzymes and proteins for use as therapeutics, imaging agents, biosensors, and adjuvants. Areas covered: Mesoporous silica Santa Barbara Amorphous-15 (SBA-15), with its unique, tunable pore diameter, and easily functionalized surface, provides a representative example of this new generation of materials. Here, we review recent advances in the design and synthesis of nanostructured mesoporous materials, focusing on SBA-15, and highlight opportunities for the delivery of biological agents to various organ and tissue compartments. Expert opinion: The SBA-15 platform provides a delivery carrier that is inherently separated from the active biologic due to distinct intra and extra-particle environments. This permits the SBA-15 platform to not require direct modification of the active biological therapeutic. Additionally, this makes the platform universal and allows for its application independent of the desired methods of discovery and development. The SBA-15 platform also directly addresses issues of targeted delivery and controlled release, although future challenges in the implementation of this platform reside in particle design, biocompatibility, and the tunability of the internal and external material properties. Examples illustrating the flexibility in the application of the SBA-15 platform are also discussed.

Nature-inspired optimization of hierarchical porous media for catalytic and separation processes

Hierarchical materials combining pore sizes of different length scales are highly important for catalysis and separation processes, where optimization of adsorption and transport properties is required. Nature can be an excellent guide to rational design, as it is full of hierarchical structures that are intrinsically scaling, efficient and robust. However, much of the “inspiration” from nature is, at present, empirical; considering the huge design space, we advocate a methodical, fundamental approach based on mechanistic features.

Anodic alumina-templated synthesis of mesostructured silica membranes – current status and challenges

Numerous fabrication methods have been employed in the preparation of anodic alumina-confined, ordered mesoporous silica membranes. The sol–gel and aspiration techniques appear to be the most promising, but realizing a completely filled, crack free, hybrid membrane is still a challenge on macroscopic scales. Presented in this paper are current synthetic challenges involved in the formation of such a hierarchically structured membrane. Overcoming these challenges is essential to use these hybrid materials for membrane separations.

A lung-inspired approach to scalable and robust fuel cell design

A lung-inspired approach is employed to overcome reactant homogeneity issues in polymer electrolyte fuel cells. The fractal geometry of the lung is used as the model to design flow-fields of different branching generations, resulting in uniform reactant distribution across the electrodes and minimum entropy production of the whole system. 3D printed, lung-inspired flow field based PEFCs with N = 4 generations outperform the conventional serpentine flow field designs at 50% and 75% RH, exhibiting a ∼20% and ∼30% increase in performance (at current densities higher than 0.8 A cm−2) and maximum power density, respectively. In terms of pressure drop, fractal flow-fields with N = 3 and 4 generations demonstrate ∼75% and ∼50% lower values than conventional serpentine flow-field design for all RH tested, reducing the power requirements for pressurization and recirculation of the reactants. The positive effect of uniform reactant distribution is pronounced under extended current-hold measurements, where lung-inspired flow field based PEFCs with N = 4 generations exhibit the lowest voltage decay (∼5 mV h−1). The enhanced fuel cell performance and low pressure drop values of fractal flow field design are preserved at large scale (25 cm2), in which the excessive pressure drop of a large-scale serpentine flow field renders its use prohibitive.

Polymer–Magnetic Composite Fibers for Remote-Controlled Drug Release

An efficient method is reported, for the fabrication of composite microfibers that can be magnetically actuated and are biocompatible, targeting controlled drug release. Aqueous solutions of polyvinyl alcohol, incorporated with citric acid-coated Fe3O4 magnetic nanoparticles (MNPs), are subject to infusion gyration to generate 100-300 nm diameter composite fibers, with controllable MNP loading. The fibers are stable in polar solvents, such as ethanol, and do not show any leaching of MNPs for over 4 weeks. Using acetaminophen as an example, we demonstrate that this material is effective in immobilization and triggered release of drugs, which is achieved by a moving external magnetic field. The remote actuation ability, coupled with biocompatibility and lightweight property, renders enormous potential for these fibers to be used as a smart drug release agent.

Titano-silicates: highlights on development, evolution and application in oxidative catalysis

Titano-silicates are a class of highly useful zeolite materials, predominantly used as heterogeneous catalysts in selective oxidation. This chapter reviews the history and significant advances in synthesis, characterisation and application of various types of titano-silicates. In particular, selective oxidation catalysis of alkenes to epoxides is discussed in detail as a key application of the material, while highlighting its potential in green chemical processes. Finally, a brief overview of recent advances and future prospects is given.

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

An efficient approach to improve the catalytic activity of titanosilicates is introduced. The Doehlert matrix (DM) statistical model was utilized to probe the synthetic parameters of mesoporous titanosilicate microspheres (MTSM), in order to increase their catalytic activity with a minimal number of experiments. Synthesis optimization was carried out by varying two parameters simultaneously: homogenizing temperature and surfactant weight. Thirteen different MTSM samples were synthesized in two sequential ‘matrices’ according to Doehlert conditions and were used to catalyse the epoxidation of cyclohexene with tert-butyl hydroperoxide. The samples (and the corresponding synthesis conditions) with superior catalytic activity in terms of product yield and selectivity were identified. In addition, this approach revealed the limiting values of each synthesis parameter, beyond which the material becomes catalytically ineffective. This study demonstrates that the DM approach can be broadly used as a powerful and time-efficient tool for investigating the optimal synthesis conditions of heterogeneous catalysts.

Titanium(IV)-induced cristobalite formation in titanosilicates and its potential impact on catalysis

Cristobalite, a crystalline form of silica, is shown to be formed within an amorphous titanosilicate, at previously unknown conditions. Mesoporous titanosilicate microspheres (MTSM) were synthesized as efficient catalysts for the epoxidation of cyclohexene with tert-butyl hydroperoxide. High-resolution transmission electron microscopy revealed the presence of crystals in this predominantly amorphous material, after calcination at 750xa0°C. When calcined at 800xa0°C, the crystals were identified via PXRD as predominantly cristobalite, which possibly marks its first observation in titanosilicates at such a low temperature, without adding any alkali metals during synthesis. Catalytic experiments conducted with MTSM materials calcined at temperatures varying from 650 to 950xa0°C, reveal that the amount of cristobalite formed increases with temperature, and that it has a significant impact on the pore structure, and, remarkably, correlates with the catalytic activity of titanosilicates.

Nature-Inspired Optimization of Transport in Porous Media

Materials combining pore sizes of different length scales are highly important for catalysis and separation processes, where optimization of adsorption and transport properties is required. Nature can be an excellent guide to rational design, as it is full of such “hierarchical” structures that are intrinsically scaling, efficient and robust. In technology, as well as in nature, the performance of the transport systems is significantly affected by their structure over different length scales, which provides abundant room to optimize transport through manipulating the multiscale structure, such as transport channel size and distribution. Following this avenue, the chapter discusses a nature-inspired (chemical) engineering (NICE) approach to optimize mass transport for catalytic systems employing porous media, with particular emphasis on the optimization of porous catalysts and proton exchange membrane (PEM) fuel cells.