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 β-NaAlO 2 and γ-Al 2 O 3 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 NaAlO 2 ·4/5H 2 O and β-NaAlO 2 besides the predominant γ-Al 2 O 3 nanoparticles. Upon settling on the silica substrate at room temperature, the NaAlO 2 ·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 β-NaAlO 2 phase (denoted as N), presumably derived from NaAlO 2 ·5/4H 2 O, was found to form intimate intergrowth with the defective γ-Al 2 O 3 following the crystallographic relationship (01̅1) γ //(11̅0) N; [1̅11] γ //[001] N and alternatively (1̅01) γ //(1̅10) N; [141] γ //[001] N . The epitaxial composite phases have a significant internal compressive stress, (OH −, Na + ) cosignature, and a mixed charge state of Al +, Al 2+, and Al 3+ and hence a smaller band gap (ca. 5.3 eV) for potential applications in the UV region.