Journal of Physical Chemistry B, Vol.108, No.16, 4940-4945, 2004
Laser ablation synthesis of spindle-like gallium oxide hydroxide nanoparticles with the presence of cationic cetyltrimethylammonium bromide
Laser ablation of gallium metal was performed to prepare spindle-like GaOOH particles in aqueous solution. Formation of well-defined GaOOH was strongly associated with the addition of cationic CTAB surfactant. It was found that spindle-like GaOOH could be grown in below, near, or above critical micelle concentrations (cmc) of CTAB via an aging process. On the other hand, using anionic SDS surfactant or pure H2O solvent could not exclusively give the final spindle-like GaOOH, but the irregular and amorphous materials were produced. TEM, XRD, FT-IR, SEM, XPS, zeta-potential, and H-1 NMR measurements were carried out to characterize the resulting precipitates. High-resolution TEM indicated that GaOOH crystals formed a type of layered structure and grew along the (001) axis. Without the presence of the surfactants, the nascent colloidal solutions, immediately after laser ablation, were prepared for the zeta-potential measurements. The negative sign of zeta-potential for the laser-ablated surfactant-free colloids indicates that the cationic CTAB would preferentially adsorb onto the colloidal negative surface. It is proposed that the adsorption of the CTAB might have facilitated the development of the ellipsoidal nanocrystals through a slow crystallization process. Calcination of these gallium oxide hydroxides at a temperature of 750 degreesC (18 h) transformed into beta-Ga2O3, but following a stepwise pathway, i.e., 250 degreesC (64 h) --> 250 degreesC (64 h) --> 750 degreesC (18 h), converted as alpha-Ga2O3.