Simultaneous Hydrogen Production and Acid Black 1 Decolorization in Alkaline and Neutral Media Using Cu, Zn, Fe, and Hydroxyapatite-Doped Titania Photoelectrocatalysts

TiO2-based photocatalysts modified with CuO and co-doped with Fe, Zn, and hydroxyapatite (HA) were evaluated for the simultaneous production of H2 and the decolorization of Acid Black 1 (AB1). Under anodic galvanostatic operation in a neutral medium, ternary materials followed second-order kinetics, with Zn-Cu-TiO2 exhibiting the highest rate constant (k = 0.0064 L/mg*min), while binary systems followed first-order kinetics and HA600-TiO2 showed the best performance. Under these conditions, H2 production was negligible. Under cathodic operation, both galvanostatic and potentiostatic modes led to first-order decolorization kinetics. The best performance was achieved in an alkaline medium under potentiostatic operation at −120 mV vs. Ag/Agcl, using Zn-Cu-TiO2, reaching a rate constant of 0.11 min−1, a maximum dissolved H2 concentration of approximately 1810 ppb, and a cumulative H2 production of 37,093 ppb/gcatalyst within 30 min, while maintaining more than 90% AB1 decolorization. In addition, an initial AB1 concentration of 25 mg·L−1 favored both hydrogen production and dye removal. These results identify Zn-Cu-TiO2 as the most promising photocatalyst for integrating wastewater remediation with sustainable hydrogen generation, particularly under cathodic potentiostatic operation in an alkaline medium.