Mechanism and in-situ crystal growth kinetics of ultrathin binary transition metal hydroxide/oxide nanowire self-assembly

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Gayani Chathurika Pathiraja (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Hemali Rathnayake

Abstract: The controlled synthesis of anisotropic one-dimensional metal hydroxide/oxide nanostructures with versatile properties, are most fascinating for applications in electronics, optical, and energy storage devices, due to their superior performance based on quantum confinement and nanoscale size effects. However, the in-depth investigation of their corresponding crystal growth mechanism and kinetics have yet to be clearly understood to tailor their properties for a specific application. Towards this goal, the first part of this dissertation focuses on investigating the nanocrystal growth mechanism and kinetics in a sol-gel colloidal system to make ultrathin metal hydroxide/oxide nanowires. The second part of the project explore the self-assembly pathways to make bionanomaterial of metal hydroxide nanowires with phospholipids. Utilizing base-catalyzed hydrolysis followed by the directed self-assembly and crystal growth of nanocrystals, a novel, facile and environmentally benign sol-gel approach was developed to make ultrathin Cu(OH)2 nanowires. During the subsequent post-annealing process, the Cu(OH)2 nanowires transformed into CuO nanowires. We captured step by step crystal growth process at each stage of the sol-gel process using HR-TEM and optical changes at each stage of the sol-gel process was also examined by UV-visible spectroscopy. We identified an Oriented Attachment (OA) mechanism as the dominant crystal growth process of ultrathin Cu(OH)2 nanowire fabrication using this surfactant free, one-pot sol-gel route. Then, we proposed a new kinetic model for OA-directed crystal growth correlating the chemical reaction kinetics of the stages of sol-gel process for the sol-gel synthesis of Cu(OH)2 nanowire formation. The chemical kinetic model follows the sigmoidal second order growth kinetic for the hydrolysis and condensation process and the sigmoidal zeroth order growth kinetic for the polycondensation step respectively. The Cu(OH)2-decorated bioinspired supramolecular nanowires were fabricated via the developed sol-gel method in the presence of a zwitterionic phospholipid as a surfactant in H2O/CHCl3 solvent system. We identified OA-directed controlled crystal growth of synthesized nanowires using HR-TEM and single crystallinity using Fast Fourier Transform analysis. Then powder XRD pattern shows that the prominent crystal growth plane of supramolecular nanowires is [020] due to the preferential adsorption of phospholipids. In conclusion, we fabricated ultrathin Cu(OH)2 nanowires without any surfactants by introducing novel Sigmoidal kinetic models that considers the directed growth of the length. Cu(OH)2-decorated bioinspired supramolecular ultrathin nanowires was also fabricated with the presence of phospholipids using the greener and facile sol-gel route. This research lays the fundamental understanding, which enables the creation of guiding principles that drive the nanocrystal growth of size-and shape-controlled anisotropic metal hydroxides/oxides and bioinspired supramolecular nanowires for potential applications. [This abstract may have been edited to remove characters that will not display in this system. Please see the PDF for the full abstract.]

Additional Information

Language: English
Date: 2021
Kinetics, Oriented attachment mechanism, Sol-gel, Surfactants, Transition metal hydroxide/oxides, Ultrathin nanowires
Self-assembly (Chemistry)

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