NaAlO2 and γ-Al2O3 Nanoparticles by Pulsed Laser Ablation in Aqueous Solution

Pulsed laser ablation on an Al target in water spiked with 0.05 and 1 M NaOH was employed to fabricate epitaxial beta-NaAlO2 and gamma-Al2O3 nanoparticles for X-ray diffraction and electron microscopic and spectroscopic characterizations. A higher NaOH concentration in the pulsed laser ablation in liquid (PLAL) process caused a higher content of NaAlO2 center dot 4/5H(2)O and beta-NaAlO2 besides the predominant gamma-Al2O3 nanoparticles. Upon settling on the silica substrate at room temperature, the NaAlO2 center dot 4/5H(2)O tended to develop as micrometer sized plates for the sample fabricated under a relatively low (i.e., 0.05 M) NaOH concentration. However, the crystal structures, d-spacings, mismatch strain, and morphology of the coexisting phases are almost the same for the samples fabricated under different NaOH concentrations. The beta-NaAlO2 phase (denoted as N), presumably derived from NaAlO2 center dot 5/4H(2)O, was found to form intimate intergrowth with the defective gamma-Al2O3 following the crystallographic relationship (0 (1) over bar1)(gamma)//(1 (1) over bar0)(N); [111](gamma)//[001](N) and alternatively ((1) over bar 01)(gamma)//((1) over bar 10)(N); [141](gamma)//[001](N). The epitaxial composite phases have a significant internal compressive stress, (OH-, Na+) cosignature, and a mixed charge state of Al+, Al2+, and Al3+ and hence a smaller band gap (ca. 5.3 eV) for potential applications in the UV region.