Among the several features of nanostructures, one of the most interesting is the large surface-to-volume ratio, key element for enhancing the material-environment interactions. Still, a good control of nanostructures fabrication is typically obtained with expensive techniques, while low-cost synthesis is often requested for disposable and massive production. ZnO NS are extremely active in gas-, bio-sensing, and in photocatalysis and can be synthesized with a good control via low-cost methods (such as, chemical bath deposition, CBD, involving abundant and non-toxic materials)[1]. Here we report on a novel ZnO nanostructures, named nanowalls (NWs), composed of intertwined nanoplatelets grown vertically on Al covered substrates. NWs have a very large surface-to-volume ratio and can be grown by CBD at 70-90 C, with hexamethylenetetramine (HMTA) and/or ammonium hydroxide, as pH modifier agents. We investigated the effects of the pH and of a prior Al oxidation on the thickness and quality of ZnO NW film. The growth kinetics was investigated and modeled assuming the formation of an Al hydroxide complex. We demonstrated that a good quality ZnO NWs film can be obtained at low temperatures by using anodized Al. The photocatalytic activity of this low-cost ZnO NWs film was tested in a methyl-orange solution, by UV irradiation, evidencing a remarkable degradation reaction constant of about 2× 10-4 min-1.[1] V. Strano et al., J. Phys. Chem. C, Vol. 118, pp. 28189, 2014.