Expanding the processing space of quantum confined, one-dimensional titania-based lepidocrocite nanofilaments

Abstract

In this study, we expand the processing space of new, quantum-confined one-dimensional lepidocrocite (1DL) titania-based nanofilaments (NFs). Our previous work to date entailed reacting Ti-precursors (e.g., TiB₂, TiOSO₄, TiN, TiC, etc.) with the quaternary ammonium compound (quat) tetramethylammonium hydroxide (TMAH) for tens of hours under ambient pressures at temperatures ranging from 50°C to 80°C. Herein, we expand the list of quats that result in 1DL NFs to tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), and choline hydroxide (ChoH). We also show that tetrabutylphosphonium hydroxide (TBPH) can be used to the same end result. These quats and TBPH are less toxic than TMAH, especially Cho⁺, which is fully biocompatible. And, while all the quats and TBPH result in the same 1D product, their de-flocculation in various organic solvents is different. Reacting with less polar quats (e.g., TBA) and washing with less polar solvents (e.g., dichloromethane) favors the formation of porous mesostructured particles. 2D structures are favored if the opposite is chosen. Said otherwise, by the judicious choice of a quat (e.g., TPAH) and solvent (e.g., tert-butanol) combination, we produced stable 1DL colloidal suspensions in dimethyl sulfoxide, methanol, ethanol, acetonitrile, isopropyl alcohol, butanol, and acetone. This enhanced colloidal stability is critical in applications in coatings, inks, and catalytic systems where non-aqueous stable dispersions are paramount. The high band-gap energies, E_g, measured (3.8–3.9 eV) confirm quantum confinement. The E_g are also quite insensitive to d spacings between the 2D sheets. These 1DLs exhibit significant adsorption and dye (rhodamine 6G) degradation capabilities. For example, TEA-1DL colloidal suspensions adsorb 64% of the dye in the dark in about 5 min and decolorize 99% of the remaining dye within 30 min under the irradiance of one sun.