Electrochromic titania nanotube arrays for the enhanced photocatalytic degradation of phenol and pharmaceutical compounds

Vertically aligned, electrochromic-coloured, amorphous titania nanotube arrays (TNAs) were fabricated using a facile room-temperature, solution-based electrochemical cathodisation method. Rapid cathodisation within 30s converted pristine TNAs into their dark analogues. Compared to their untreated counterparts, the cathodised dark TNAs exhibited significantly enhanced optical absorbance, covering the full spectrum of visible light. Further annealing of the electrochromic coloured amorphous TNAs in a N₂ atmosphere induced their transformation into dark crystalline TNAs, which directly harnessed simulated sunlight for the photocatalytic degradation of organic contaminants, including phenol, ibuprofen, carbamazepine and caffeine. Compared to the pristine crystalline TNAs (annealed in air), the dark crystalline TNAs showed higher optical absorbance, larger charge carrier density, lower electron transport resistance, and an enhancement of 107-131% in degradation kinetics for the target organic contaminants.