| Summary: | Biotemplating utilizes a bottom-up approach to synthesize functional nanomaterials with tunable physical and chemical properties. Many naturally available biological materials have been investigated for their unique architectures, and have been successfully used as templates for nanomaterial synthesis. For example, DNA, viruses, proteins and botanical matter have been reported as bio-templates for the preparation of hybrid inorganic nanomaterials. In these reports, only nanomaterials with relatively simple stoichiometric chemistries have been successfully prepared. Preparation of nanomaterials with more complex chemical composition using biotemplating has yet to be investigated.
In this thesis, botanical biotemplates are hypothesized to be useful in synthesizing nanomaterials with complex stoichiometric chemistries. Plants are not only generally abundant in nature, but can also offer unique surface chemistries and 3D porous architectures that could influence nanomaterial synthesis. To investigate this, a simple, facile biotemplating method was developed to prepare a variety of functional nanomaterials. Several land and aquatic botanical species which are known to be hydrophilic were examined. Of the species examined, moss was identified to be the most promising; moss is exceptionally hydrophilic and is able to take up a large amount of metallic precursors. The moss plant also provides a 3D interconnecting pore network which could be preserved after annealing.
The 3D interconnected framework conferred by moss was found to be beneficial to electrode materials in metal-ion battery technologies. In particular, the monoclinic lithium vanadium phosphate Li3V2(PO4)3 (LVP) is known to be an outstanding cathode material due to its high energy storage capabilities, cycling rates and good thermal stability. Here, the moss plant was successfully utilized as a template to prepare pure, crystalline and mesoporous LVP nanomaterials. The investigation of the formation mechanism of LVP on moss was carried out, and found that the negatively-charged surface of moss was in fact critical for the molecular recruitment of LVP precursors. Finally, the electrochemical performance of the as-annealed LVP nanomaterials was also examined.
Next, the same synthesis strategy was extended to prepare LiNi0.5M1.5O4 (LNMO). The LNMO is also a promising cathode material, widely pursued for metal-ion battery applications to increase energy density with high operational voltages. A pure phase of non-stoichiometric disordered cubic spinel (Fd3m) of LiNi0.5M1.5O4-δ using moss as a biotemplate was obtained. After examining the electrochemical performance of the as-synthesized LNMO, it was found to exhibit superior charging capabilities, comparable to other LNMO nanomaterials prepared using conventional chemical methods.
In summary, plants are demonstrated to be promising materials of use in biotemplating approaches. In particular, the moss plant provides a suitable surface chemistry that can be used to recruit metallic precursors. Utilizing this capability of the moss plant, successful functional nanomaterials were synthesized with complex compositions (LVP and LNMO). Both nanomaterials were found to exhibit good electrochemical properties, demonstrating the promise of biotemplating as a green and sustainable nanomaterial synthesis strategy.
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