Electrodeposited Pd/TiO2 Nanotube Arrays with Size-Controlled Pd for High-Performance UV and Visible-Light Photocatalytic Water Remediation

Environmental contamination by persistent industrial dyes such as Amido Black demands highly efficient photocatalysts for advanced water treatment. Structural, chemical, and optical strategies based on TiO2 nanotube engineering are widely explored for this purpose. In this work, highly ordered TiO2 nanotube arrays were fabricated by electrochemical anodization and subsequently decorated with Pd nanoparticles via potentiostatic electrodeposition (10–300 s), enabling precise control of Pd nanoparticle size and loading. The resulting materials were systematically characterized by SEM, TEM, XRD, XPS, UV–vis DRS, and PL spectroscopy, and their properties were correlated with the photocatalytic degradation of Amido Black under both UV and visible light irradiation. The study reveals a clear size-dependent duality in the role of Pd. For intermediate Pd nanoparticles (≈9 nm, 20 s), Pd behaves predominantly as an electron sink, forming an efficient Schottky junction with anatase TiO2 that markedly suppresses charge carrier recombination. This configuration yields ≈ 97% Amido Black removal after 120 min of UV irradiation, with an apparent rate constant about three times higher than that of bare TiO2 nanotubes. In contrast, for ultra-small Pd nanoparticles (≈6 nm, 10 s), interfacial defect states sensitize TiO2 to visible light, enabling ≈ 65% degradation after 270 min and a rate constant roughly four times higher than that of undecorated nanotubes under visible illumination. At long deposition times (≥150 s), Pd agglomeration leads to enhanced photoluminescence and markedly reduced photocatalytic activity, indicating increased recombination and less effective utilization of photogenerated charges. This provides a practical design rule to rationally tailor Pd–TiO2 nanotube photocatalysts for targeted UV or visible light applications in dye removal and broader environmental remediation scenarios