Band Gap Engineering toward Semimetallic Character of Quinone-Rich Polydopamine

Semiconductor|melanin interfaces have received increasingly more attention in the fields of photocatalysis and applied electrochemistry because their facile synthesis, unique electrical properties, strong capability toward photosensitization. In this work, we describe electropolymerization quinone-rich polydopamine (PDA) on surface hydrogenated TiO2 nanotubes with enhanced photoactivity visible spectrum. PDA is deposited uniformly nanotube walls, chemical structures resulting layer strongly depend pH supporting electrolyte. The film thickness varies range 2–8 nm depending number cycles. Optical electrochemical experiments coupled density functional theory simulations revealed evidence a semimetallic character junction broad distribution midgap states induced by PDA. As result modification, 20-fold increase photocurrent response observed. Quantum efficiency measurements show that enhancement occurs mainly at wavelengths between 500 550 nm. Additionally, nonlinear impedance spectroscopy suggest that, TiO2|PDA junction, behaves as set redox mediators distributed rather than semiconducting polymer. This concept might be crucial for understanding electronic properties semiconductor|melanin junctions.