3D Anodic Alumina Nanoarchitectures: A Decade of Progress from Foundational Science to Functional Metamaterials

Three-dimensional (3D) nanostructures are redefining materials engineering by shifting control from composition to architecture. This review charts the rise of 3D anodic aluminum oxide (3D-AAO), beginning with the 2014 introduction of ordered, interconnected nanoarchitectures that established a new paradigm. We detail fabrication advances that enable precise control of geometry, pore shape, and periodicity, including hybrid pulse anodization that alternates between hard anodization (HA) and mild anodization (MA) conditions. These architected templates used empty or as scaffolds for magnetic, semiconducting, and polymeric phases act as metamaterials with tunable properties. In magnetism, geometry enables easy-axis reversal and uncovers magnetoelastic anisotropy. In semiconductors, 3D nanonetworks raise the dimensionless thermoelectric figure of merit (zT) relative to similarly prepared bulk via geometry-driven phonon scattering. In polymers, 3D-AAO guides flexible photonic devices with full-gamut structural color and biodegradable, biocompatible triboelectric nanogenerators with high power density. Empty 3D-AAO offers passive daytime radiative cooling properties. Delivering 〉10 °C sub-ambient cooling, passively reduces building air-conditioning demand. The field's influence spans energy storage, catalysis, and biosensing. We conclude with pathways to industrial scalability through cost-efficient, room-temperature processing on low-purity aluminum, positioning 3D-AAO to bridge nanoscale physics and macroscale function.