“…Self-ordered anodic aluminium oxide (AAO) membranes with hexagonally packed nanochannel arrays have become promising candidates for versatile applications including nanofluidic transport, 1 filtration, 2 separation, 3 ionic current rectification, 4 sensors, 5,6 and biodetection, 7 as well as the construction of various nanostructures (such as nanorods, 8,9 nanowires, 10,11 nanoparticles 12 and nanopillars 13 ), and the design of optical devices, 13 biosensor 14,15 and energy conversion devices 16 through the AAO template-based assembly approach, where the composition and the structural characteristics of the AAO membranes play key roles in their functional applications. Interestingly, the compositions of the AAO membranes are not completely composed of aluminium oxide; partially acid anion-contaminated species have been inevitably incorporated into the membrane during the formation of the nanochannels, 17,18 and the alumina composition in the barrier layer produces a different pattern of surrounding hexagonal walls.…”