Greener Synthesis of Nanoparticles Using Fine Tuned Hydrothermal Routes
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Greener Synthesis of Nanoparticles Using Fine Tuned Hydrothermal Routes Hyunjoo Han, Gianna Di Francesco, Amber Sexton, Andrew Tretiak, Mathew M. Maye* Department of Chemistry, Syracuse University, Syracuse New York, 13244. *[email protected] ABSTRACT The wet chemical synthesis of energy and sensor relevant nanomaterials often requires large amounts of high boiling point solvents, grams of reactants, solvent-based purification, and the use of oxygen free atmospheres. These synthetic routes are also prone to poor scalability due to requirements of precise control of high temperatures. Because of this, the potential use of metallic nanoparticles and semiconductive quantum dots (q-dots) in energy transfer and real time biosensor applications is labor intensive and expensive. We have explored a green alternative route that involves the colloidal synthesis of CdSe and CdTe quantum dots under well-controlled hydrothermal conditions (100-200 oC) using simple inorganic precursors. The resulting nanomaterials are of high quality, and are easily processed depending upon application, and their synthesis is scalable. Temperature control, and synthetic scalability is provided by the use of a synthetic microwave reactor, which employs computer-controlled dielectric heating for the rapid and controllable heating. INTRODUCTION The field of soft-nanotechnology has emerged as a premier scientific discipline, catalyzed by work on wet chemical synthesis routes for colloidal nanoparticles, including semiconductive quantum dots (q-dots). Since the founding reports, the knowledge base of q-dot synthesis and their remarkable photophysical characteristics has grown rapidly (1). The approach for q-dot synthesis is a synergy of traditional wet-chemical approaches using inorganic precursors, with that of solid-state processing, which utilizes high temperature annealing, nucleation and growth, and epitaxial deposition. Despite this synthetic progress, there are still a number of areas where research in needed. For instance, while the quantum confinement of excitons is sensitized greatly in organically encapsulated q-dots, thus leading to optimized quantum yields of >50% (1), this same encapsulation limits e- transport, limiting potential in photovoltaic efficiency for instance. In addition, this same encapsulation leads the q-dots to be challenging to functionalize for aqueous processing, such as those steps required for high coverage of biomaterials for selfassembly or sensing utility (1-6). Along these lines, research has begun to revisit the synthesis of q-dots under aqueous conditions (1,5), the original fabrication route. One significant limitation of this approach is the inability to achieve the high temperatures required for crystal growth and processing, owing in large part to the limited reflux temperatures. The ability to synthesize semiconductive q-dots under aqueous conditions may allow for the better integration of the novel properties into a number of devices in a more straightforward manner. Such devices include, biodi
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