Purification and Dispersion of Nanoparticles with 0-D, 1-D, and 2-D Geometries
Nanoparticles (NPs) of different geometries, including 0-dimeansional (0-D) ZnO QDs, 1-D carbon nanotubes (CNTs) and 2-D α-zirconium phosphate nanoplatelets (ZrP), have been purified and dispersed in various media. The individually dispersed ZnO QDs and ZrP can be easily purified by removing ions or dispersants. In the case of CNTs, more elaborate efforts are needed. CNT is an important category of 1-D NPs with many desirable properties. These properties, however, are affected strongly by the dispersion state of CNTs, especially for single-walled CNTs (SWCNTs). Covalent and non-covalent techniques have been developed to disperse SWCNTs by interrupting secondary interactions between nanotubes. However, the application of SWCNTs processed by current dispersion technique is restricted by either the low yield or the property degradation. To obtain purified and individually dispersed SWCNTS with preserved electronic state in large scale, SWCNTs have been first exfoliated with electrostatically tethered ZrP nanoplatelet dispersant. To remove the nanoplatelet dispersant, two approaches have then been developed: the ionic approach and the acid-mediated approach. The ionic approach works by disrupting the electrostatic interaction between SWCNTs and ZrP with extra electrolytes and using non-ionic surfactants to stabilize SWCNTs. Two different mechanisms have been identified for monovalent and divalent cations, respectively. The acid-mediated approach is more versatile for choices of SWCNT stabilizer. When the above isolation procedures are optimized, over 90% of purified SWCNTs can be retrieved and stabilized in aqueous solution. The properties of the obtained SWCNTs are investigated extensively, showing that the electronic state and the structural integrity of SWCNTs are maintained. The acquired SWCNTs can be transferred into various kinds of solvents and polymer matrices. Possible applications include optoelectronic devices, reinforcement agent, and conductive fillers. Individually dispersed SWCNTs can be further purified from the surfactants and stabilized in a good solvent without using surfactants, through the minimization of van der Waals (vdW) attraction. The same concept appears to hold true for stabilization of both purified 0-D QDs and 2-D nanoplatelets. With additional manipulation of ionic strength in solvent, the surfactant-free ZnO QDs can be progressively tuned to exhibit phase transitions similar to that of micro-spheres and even form colloidal crystals.
van der Waals force
Zhang, Xi (2012). Purification and Dispersion of Nanoparticles with 0-D, 1-D, and 2-D Geometries. Doctoral dissertation, Texas A&M University. Available electronically from