State of the art developments in functional hybrid materials

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Abstract

This issue of Journal of Materials Chemistry highlights recent progress in hybrid materials. Clément Sanchez, Guest Editor, introduces the issue and the academic and industrial importance of the field.

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Looking forward to the 21st century, nanosciences will be one of the fields that will contribute at a high level to scientific and technological developments. Hybrid organic–(bio)–inorganic materials will play a major role in the development of advanced functional nanomaterials. Research in functional hybrid organic–inorganic materials is supported by the growing interest of chemists, physicists, biologists and materials scientists who are looking to fully exploit this opportunity for creating smart materials that benefit from the best of the three realms: inorganic, organic and biological. Bio-inspired strategies are now used to “mimic” the growth processes occurring in biomineralisation and design innovative multiscale structured hybrids (from nano- to millimetric scale), hierarchically organized in terms of structure and functions. Moreover, in addition to the high versatility in chemical and physical properties and shaping, hybrid materials present the paramount advantage to facilitate both integration and miniaturization. The field of functional hybrid materials has been widely recognized as one of the most promising and rapidly emerging research areas in materials chemistry. Major advances in knowledge and understanding will be made via a better integration of the different materials science communities. In this context, European Networks of Excellence such as “FAME”,† which integrates both the hybrid materials and the inorganic solid state chemistry communities, should play a major role.

Hybrid organic–inorganic materials are not simply physical mixtures. They can be broadly defined as molecular or nano-composites with organic (or bio) and inorganic components, intimately mixed where at least one of the component domains has a dimension ranging from a few Å to several nanometers. Consequently the properties of hybrid materials are not only the sum of the individual contributions of both phases, but the role of their inner interfaces could be predominant. The nature of the interface has been used to grossly divide these materials into two distinct classes:¹ In Class I, organic and inorganic components are embedded and only hydrogen, van der Waals or ionic bonds give cohesion to the whole structure. In Class II materials, the two phases are partly linked together through strong chemical covalent or iono-covalent bonds.

Molecular approaches of molecular and solid state chemistry and nanochemistry have reached a very high level of sophistication. Chemists can tailor-make many molecular species and design new functional hybrid materials with enhanced properties. Indeed, numerous hybrid materials are synthesised and processed by using soft chemistry routes based on:

• the polymerisation of functional organosilanes, macromonomers and metallic alkoxides;

• the encapsulation of organic components within sol–gel derived organosilicas or hybrid metallic oxides;

• the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures;

• self-assembly or templated growth, nano-building block approaches, hydrothermally processed hybrid zeolites or microporous metal organic frameworks, integrative synthesis or coupled processes, bio-inspired strategies, etc.

These strategies now offered by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, which is able to direct the assembly of a large variety of structurally well-defined nano-objects into complex hybrid architectures. Organic–inorganic hybrid materials do not only represent a creative alternative for the design of new materials and compounds for academic research, but their improved or unusual features open promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology and medicine. Applications include smart membranes and separation devices, functional smart coatings, a new generation of photovoltaic and fuel cells, photocatalysts, new catalysts, sensors, smart microelectronics, micro-optical and photonic components and systems for nanophotonics, innovative cosmetics, intelligent therapeutic vectors that combine targeting, imaging, therapy and controlled release of active molecules, nanoceramic–polymer composites for the automobile or packaging industries, etc.

Today, this potential is becoming reality. Several examples of “commercial hybrids” have been presented in this issue although this is only a small fraction, representing the tip of the iceberg. Indeed many of these hybrid materials are entering niche markets that should expand in the future because new and stricter requirements are now being set up to achieve greater harmony between the environment and human activities. New materials and systems produced by man must in the future aim at higher levels of sophistication and miniaturisation. They must respect the environment and consume less energy with features such as recyclability and reliability. It is just a question of scientists' imagination and of making industry aware of their opportunities and benefits.

The purpose of this themed issue is to highlight recent progress in this multifaceted field. A large number of reviews, written by many of the research leaders of the field, summarise current state-of-the-art advances and identify key challenges in the future developments of advanced hybrid materials with original architectures.

This vast research field is illustrated by several key feature articles including chemistry, processing, physical properties and applications of hybrid materials. These reviews describe diverse subjects including:

• synthetic routes for advanced functional hybrid materials, such as dendrimer-based organic–inorganic materials, chemical modification of titanium alkoxides, interactive materials built via molecular chemistry, promising challenges in the chemistry of periodic mesoporous organosilicas, new Janus-head type micro- and nanoparticles, hybrid monoliths with well-defined macropores and mesopores, nano-building blocks based on octasilsesquioxanes, hybrid star gels, new trends in layered double hydroxide hybrid assemblies, hybrid materials built with organophosphorus coupling molecules, mesostructured hybrid thin films, functional biopolymer nanocomposites based on layered solids, enzymes supported on ordered mesoporous solids;

• exciting new directions concerning the domains of molecular or nanocomposite hybrid materials for electrochemical devices, for GDLC electrooptical devices, for non-linear optics and for optoelectronic devices;

• the most recent progress in lanthanide-doped oxide nanophosphors, in mechanical properties and in applications of hybrid organic–inorganic materials.

This issue also contains many original contributions, highlighting exciting new achievements in hybrid materials science, including innovative materials shaped as double-walled transition-metal oxide nanotubes, macrocellular foams, new periodic porous organosilicas with hierarchical structures, new structured bridged silsesquioxanes, caramel–clay nanocomposites, multifunctional mesoporous hybrids with mixed oxide framework, new metal open frameworks (MOFs), hybrids derived from inorganic nanoclusters and polymers, functional protein–organoclay nanocomposites, hybrid materials applied to biotechnologies, organosilicas for enzyme immobilization, nanostructured bio-hybrids, spectroscopic and optical properties of hybrids, hybrid electrochemical sensors for anion detection, rheological properties of hybrid nanocomposites.

This issue will form a valuable reference for future work in this area and will stimulate the exchange of ideas among different research communities. These very fruitful multifaceted research activities make this field vast and, to be honest, I am sure that some excellent contributions are missing. Therefore I encourage colleagues interested by this expanding field of research to also consult other such journal issues and books devoted to hybrid bio-inorganic and organic–inorganic materials.^2–6

I would like to acknowledge the authors of this themed issue, I am grateful for their efforts in comprehensively presenting their current knowledge of state-of-the-art developments and perspectives of functional hybrids and for submitting their most exciting original work. Furthermore the judgment provided by our reviewers has been extremely valuable in ensuring the high scientific impact required for publication in Journal of Materials Chemistry. Finally, I wish to thank Ruth Needham and Graham McCann for their confidence and kind assistance, and all the staff members of the RSC, for their dedication and devotion to this themed issue.

Plate1

Clément Sanchez, Université Pierre et Marie Curie, Paris.

References

1. C. Sanchez and F. Ribot, New J. Chem., 1994, 18, 1007.
2. Special issue on Hybrid Organic–Inorganic Materials, ed. C. Sanchez and F. Ribot, New J. Chem., 1994, 18.
3. Functional Hybrid Materials, ed. P. Gómez Romero and C. Sanchez, Wiley, New York, 2004; see also Matériaux Hybrides, ed. C. Sanchez, Observatoire Français des Technique Avancées, Masson, Paris, France, 1996.
4. Special issue on Organic–Inorganic Materials, guest editor D. A. Loy, MRS Bull., May 2001, 26(5).
5. Special issue on Nanostructured and Functional Hybrid Organic–Inorganic Materials, ed. H. Eckert and M. Ward, Chem. Mater., 2001, 13.
6. Themed issue on New Developments in Bio-related Materials, ed. J. Aizenberg, J. Livage and S. Mann, J. Mater. Chem., 2004, 14(14).

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Footnote

† FAME: Functional Advanced Materials and their Engineering.

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