The photocatalytic activity of ZnO nanowires grown via an aqueous solution approach at 95 degrees C onto sapphire substrates, which were first pre-coated with ZnO seed layers deposited by pulsed laser deposition at various temperatures (400-700 degrees C), was investigated against the degradation of octadecanoic (stearic) acid under UV-A light illumination. The crystallinity of the ZnO seed layers, as well as their growth orientation along the c-axis, increases with deposition temperature. All chemically grown ZnO samples show narrower (0 0 2) reflections with significantly higher intensity than the seed layers deposited by pulsed laser deposition. The grain size, as well as the seed layer roughness, gradually increases with substrate deposition temperature. The nanowires' diameter also rises with seed layer's deposition temperature, ranging from similar to 40 +/- 15 nm for 400 degrees C to similar to 155 +/- 65 nm for 700 degrees C. The chemically grown ZnO nanowires exhibit relatively high transmittance values, especially those grown on sapphire substrates, which were pre-coated with seed layers deposited by pulsed laser deposition at 400 and 500 degrees C. All ZnO samples, including seed layers and nanowires' arrays, show very good photocatalytic activity regarding the degradation of octadecanoic (stearic) acid under UV-A light exposure. In specific, the photocatalytic activity of ZnO nanowires' arrays grown on top of a seed layer deposited by pulsed laser deposition at 600 degrees C is quite remarkable, showing the highest stearic acid disappearance rate, i.e., 4.22 x 10(-8) mol/min (formal quantum efficiency = 4.48 x 10(-3)) at 30 min of UV-A light illumination. (C) 2013 Elsevier B.V. All rights reserved.