Bio-inspired synthesis of functional micro/nano-structured materials
Date of Issue2016-02-29
School of Materials Science and Engineering
Materials in the nano-scale can exhibit unique chemical, physical, and electronic properties compared to the bulk materials. However, for practical application, the organization of nanoparticles into superstructures with micrometer dimensions that are easy for handling is necessary. Recently, inspired by the complex structures in nature, scientists have put much attention on applying bio-systems such as DNA, polypeptides, bacteria, and viruses towards the synthesis of controlled and defined micro/nano-structures of functional materials. With the advent of recombinant engineering, it is possible to genetically engineer these bio-molecules to interact with specific precursors under benign conditions, and to create inorganic nanostructures with precise control over their compositions, phase, shape and size. Here, we demonstrate the use of bacteria and polypeptides in directing the synthesis of micro/nano structured functional materials. Bacteria have the natural ability to synthesize inorganic materials, and are considerably low cost and reproducible materials for nanomaterial synthesis. In this work, we developed two routes for bacteria-directed synthesis of functional materials. First, we exploited the inherent ability of magnetotactic bacteria to synthesize well-crystalized Fe3O4 nanoparticles. Further treatment with glucose allowed us to maintain the 1D structure of the Fe3O4 chains. The “candy haw-like” chains exhibited discharge capacities of 947, 857, 757, 615, 518, 388, 282 mA h g-1 at 0.2, 0.5, 1, 3, 5, 8 and 10 C for lithium ion batteries. Likewise, we also investigated the feasibility of using genetically engineered bacteria as templates for nanomaterial synthesis. Here, bacteria with the ability to acquire phosphates from their surroundings were subsequently used as templates for the synthesis of lithium metal phosphates nanostructures. The discharge capacities of the as-synthesized LiFePO4/C nanocomposite electrodes were 145.6, 130.6, 117.8, and 92.3 mA h g-1 at discharge rates of 0.1, 0.5, 1 and 5 C respectively for lithium ion batteries. While bacteria templates provide a promising strategy for the synthesis of nanomaterials, there is little control over their macrostructures. In order to fabricate three-dimensional hierarchical nanostructures, alternative templates are required. Recombinant proteins are ideal templates for nanomaterial synthesis due to their tailorable physical and chemical properties. For instance, elastin-like polypeptides (ELPs) are well-studied for their tunable structural properties, and have been used widely in tissue engineering to generate 3D biomaterials. ELPs exhibit thermo-responsive behaviors, and can be readily purified via inverse thermal cycling. In this work, we showed that recombinant ELPs containing C-terminal hexahistidine tag (His tag) can be used to prepare metal oxides quantum dots encapsulated in 3D porous carbon microspheres. The as-synthesized Fe3O4@C electrode delivered specific charge capacities of 510, 425, 330, 246 and 163 mA h g-1 at 0.2, 0.5, 1, 2 and 5 A g-1 respectively for sodium ion batteries. Finally, we demonstrated a facile strategy for the preparation of Li3V2(PO4)3 and Na3V2(PO4)3 nanostructures supported on hierarchically porous 3D carbon aerogels using recombinant ELPs. The as-synthesized 3D Li3V2(PO4)3 and Na3V2(PO4)3 nanostructures show ultrahigh capacities at ultrafast charging/discharging properties and excellent cycle performance as cathodes for Li/Na secondary batteries. In summary, we show that bio-inspired synthesis is indeed a promising strategy for functional materials fabrication.