Upcycling Discarded Aluminum Cans into Nanoporous Membranes as an Eco-Friendly and Cost-Effective Strategy for Fabricating Polymer Nanoarrays and Self-Cleaning Surfaces

In recent years, most of the dedication to waste recycling and upcycling has been focused on plastic polymers. There is less development in utilizing discarded iron or aluminum cans for upcycling. In this study, we aim to prepare anodic aluminum oxide membranes from the top of discarded aluminum cans (T-AAO) and from the side of discarded aluminum cans (S-AAO) and demonstrate their application values. The T-AAO and S-AAO membranes are obtained by anodically oxidizing the top and the side of discarded aluminum cans separately, and the pore sizes of both membranes can be enlarged by using 5 wt % phosphoric acid with different pore-widening times. The physical, chemical, and morphological properties of T-AAO and S-AAO membranes are analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), thermogravimetric analysis (TGA), X-ray diffraction (XRD) (wide-angle X-ray scattering (WAXS) and grazing-incidence wide-angle X-ray (GIWAX)), X-ray fluorescence (XRF), electron backscatter diffraction (EBSD), and contact angle measurement, and the properties are also compared with those of AAO membranes made by high-purity (99.997%) aluminum sheets. The thermal annealing method is also applied to aluminum cans for fabricating more stereoscopic AAO membranes attributed to changes of primary lattice planes. One of the application values of T-AAO and S-AAO membranes is demonstrated by infiltration of polymer materials, poly(methyl methacrylate) (PMMA) and polystyrene (PS), into the nanopores of the membranes with the thermal annealing method, followed by releasing the polymer nanoarrays from the T-AAO and S-AAO membranes with NaOH solutions. Moreover, functional self-cleaning surfaces of T-AAO and S-AAO membranes are produced by grafting hydrophobic octadecyltrimethoxysilane (OTMS) and 1 H,1 H,2 H,2 H -perfluorodecyltriethoxysilane (PFDTES) molecules. This work not only provides a feasible approach to recycle and upcycle aluminum waste but also gives a promising strategy for fabricating widely applicable nanomaterials in eco-friendly and low-cost ways.