Nanocomposition
A research team in France, writing in the journal Angewandte Chemie, has introduced a novel, highly versatile approach to the large-scale synthesis of a new family of bioorganic-inorganic nanocomposites. Their approach used X-ray diffraction and spectroscopy to monitor the previously unattainable degree of control over the composition and structure of the materials.
Natural diversity inspires
Nature uses countless self-organization processes to build nucleic acids, proteins, membranes and as the underlying mechanism on which many biochemical functions hinge. Chemists and materials scientists are increasingly interested in exploiting these principles to make novel materials without having to turn to complicated synthetic schemes that are plagued by side reactions. For example, self-organization might be used in the production of highly ordered nanocomposites, materials that are highly porous, or materials with particular properties tuned for a specific application.
Writing in the journal Angewandte Chemie, Bruno Alonso and Emmanuel Belamie from the Charles Gerhardt Institute in Montpellier, France, have introduced a novel, highly versatile approach to the large-scale synthesis of a new family of nanocomposites with their origins in both biology and inorganic materials. They have achieved a previously unattainable degree of control over the final composition of their composites and the structure of the materials they produced.
Nanocomposites is a rather generic term but can be considered to engulf any solid materials comprising different substances, at least one of which exists in the form of particles of dimensions on the nanoscale, which usually can mean having diameters from a few tens of nanometres to several hundred . Nevertheless, the properties of such composites are highly desirable because particles in this size range can behave very differently from their counterparts in the bulk and most certainly their equivalents at the atomic or even the atomic cluster level. Conversely, nanocomposites can act as templates or moulds for preparing another material that has a porous structure on the scale of the nanoparticles. Nanotechnologists are keen to investigate almost any emergent material based on nanoparticles or nanopores for applications in gas storage, carbon sequestration, catalysis, sensors, materials separation and many other areas.
Solving sol-gel solution
Now, Alonso and Belamie have used a sol-gel process for their production of their nanocomposite. Sol-gel synthesis is a popular technique for making porous inorganic network structures but the French team was not interested solely in the inorganic. In the first step of their hybrid approach that mashed together both inorganic and biological, the team needed to generate a sol: a suspension of finely divided nanoscopic particles in a solvent. Their challenge was to obtain co-suspension of the two different components, silicon dioxide precursors (siloxane oligomers) and chitin nanorods from shrimp shells (a renewable resource). Unfortunately, these two substances require entirely different conditions in order to form a stable suspension without their simply precipitating out of the liquid as solids aggregates.
In order to overcome this problem the team generated an alcohol suspension by slowly replacing the water with ethanol. Through slow removal of the solvent, they were able to produce a gel, a solid with loose cross-links between its molecules that gives rise to a flexible three-dimensional polymer structure.
The team explains that the sol can then be poured into a desired mould and dried or it can be spray-dried into spherical particles. This process results in a nanocomposite made of chitin rods that are fully embedded in a silicon dioxide matrix. The mechanism by which this occurs is based on a self-organized aggregation of the chitin molecules and weak attractive forces between chitin and siloxane oligomers, the researchers add.
The stability of the alcohol suspensions opens up a wide range of possibilities for the production of materials whose volume ratios, spatial arrangements, and morphologies can be controlled. For instance, if a magnetic field is applied during preparation of the material, the chitin rods can be made to line up in parallel. If the nanocomposite is instead heated, the chitin rods can be burned off to leave behind cavities in a highly porous material.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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