Bio-inspired Synthesis of Oxide Nanostructures

Abstract

Nature is capable of building magnificently intricate and detailed structures out of otherwise boring materials such as calcium carbonate and silica. Anyone who has taken their children to see dinosaurs at a Natural History museum or visited natural wonders such as the Petrified Forest in Arizona are familiar with the natural process called fossilization by which the tissues of dead organisms are eventually replicated by objects of stone. Most living organisms (including humans) are critically dependent on more deliberate and controlled biomineralization phenomena that lead to the production of all hard tissues, including our teeth and bones, seashells and diatom skeletons, egg shells, and the magnetic nanoparticles that provide homing devices from bacteria to birds. All these processes are nothing more than specific examples of highly controlled nucleation and growth phenomena such as those described in generic terms in Chapter 7. At a molecular level, these processes are controlled by the same reaction mechanisms involving oxide surfaces, which were outlined in Chapter 6. However, biomineralization is orders of magnitude more sophisticated than standard nucleation and growth processes. The unique features of biomineralization involve the interplay between organic biomolecules and the nucleation and growth of inorganic phases such as oxides. This interplay is of critical importance in both biology and emerging nanotechnologies, providing specific examples that illustrate many of the concepts of oxide chemistry introduced in Chapters 5 through 7. In this chapter, we highlight the key concepts of biomineralization and provide examples of how researchers can now produce complex nanostructured oxides via biomimetic nucleation and growth strategies that replicate some of the key features used to make hard tissues in living systems. These strategies include the use of (1) molecular complexation and compartmentalization to control supersaturation levels, (2) specific ligands and surface structures to mediate nucleation phenomena, (3) hierarchical self-assembled organic architectures as templates for oxide formation, (4) functionalization to stimulate desired heterogeneous nucleation and growth processes on those templates, and (5) organic surfactants to manipulate both crystal-phase preferences and growth habits.