Perovskite Particles from Phytoplankton
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Perovskite Particles from Phytoplankton Michael R. Weatherspoon, Shawn M. Allan, Christopher S. Gaddis, Ye Cai, Michael S. Haluska, Robert L. Snyder, and Kenneth H. Sandhage School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA ABSTRACT Controlled-shape BaTiO3-based microparticles were synthesized with the use of diatom microshells (frustules) as templates. The SiO2-based frustules of Aulacoseira diatoms were first converted into MgO-based replicas via a gas/solid displacement reaction at 900oC. A BaTiO3 coating was then applied to the MgO-bearing frustules by a sol-gel process. After firing at 700oC for 1.5 h, a conformal nanocrystalline coating of BaTiO3 was generated on the surfaces of the MgO-bearing frustules. The underlying MgO scaffolds were then selectively dissolved away to yield freestanding 3-D BaTiO3-based replicas of the original Aulacoseira diatom frustules. This work demonstrates that microparticles with well-controlled 3-D morphologies and nonnatural multicomponent ceramic compositions can be produced by merging the self-assembly ability of biomineralizing micro-organisms with synthetic chemical tailoring. INTRODUCTION Numerous examples exist in nature of micro-organisms that self assemble rigid, mineralized (bioclastic) structures. For example, diatoms (Bacillariophyceae) are a type of unicellular microalgal phytoplankton that can be found in a wide variety of marine and freshwater environments [1,2]. Diatoms incorporate silica as a structural component of the cell wall to form a rigid three-dimensional (3-D) cytoskeleton called a frustule [2,3]. A single diatom frustule consists of two halves (indeed, the word diatom stems from the Greek word “diatomos” which means “cut in half”) called the epitheca and hypotheca [2,3]. Upon asexual reproduction, the epitheca and hypotheca of the parent diatom separate to become incorporated into two daughter diatoms, with each daughter cell forming another half frustule. The 3-D shapes and fine features of the parent diatom frustule are thereby well preserved in the frustules of the daughter diatoms. Sustained reproduction of a given parent diatom can generate enormous numbers of daughter diatoms with frustules of identical shape. For example, 40 continuous reproduction cycles from a single parent diatom would yield more than 1 trillion (240) descendant diatoms, each with the same frustule morphology [4,5]. No man-made process is currently capable of generating such precisely-replicated 3-D microscale structures on such a massive scale under ambient conditions. With such precise replication capabilities, it has been suggested that diatom colonies could act as “nano-factories” for the production of low-cost 3-D microstructures for certain device applications [6]. A spectacular variety of 3-D frustule morphologies can be found among the estimated 100,000 different diatom species currently in existence [2]. That is, nature provides, through diatoms, thousands of 3-D microstructures that may be selected for specif
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