Elucidating the role of noble metals in Ag- and Pd-modified TiO2 visible-light photocatalysts: Theoretical validation of experimental evidence

Abstract

A combined experimental–theoretical understanding of the noble metal-modified TiO 2 photocatalysis for environmental remediation remains relatively unexplored. This study investigates the influence of silver (Ag) and palladium (Pd) modifications on the visible-light photocatalytic performance of nanosized TiO 2 for the degradation of the sulfur-containing pollutant 2-mercaptobenzothiazole (2-MBT), and correlates experimental findings with density functional theory (DFT) calculations. Structural and spectroscopic analysis of the synthesized Ag- and Pd- modified TiO 2 (AgT and PdT) nanoparticles (NP) and nanotubes (NT) confirmed phase-pure anatase-TiO 2 NP (T NP) and low crystalline titanate NT (T NT), respectively, with uniformly distributed Ag and Pd. Tauc plots revealed enhanced visible-light absorption, with band gaps decreasing from 3.21 to 2.93 and 2.45 eV, for pristine TiO 2, AgT, and PdT, respectively. AgT additionally exhibited a surface plasmon resonance (SPR) band at 420–426 nm. X-ray photoelectron spectroscopy (XPS) identified Ag predominantly as Ag + (Ag 2 O) and Pd mainly as Pd 0 with minor Pd 2+ , while Ti 3+ species and oxygen vacancies were observed in AgT, indicating defect-assisted charge separation, further supported by pronounced photoluminescence (PL) quenching. Photocatalytic studies demonstrated substantially enhanced 2-MBT degradation with noble metal modification compared with pristine TiO 2 and Degussa P25, with AgT NP achieving 99% degradation following pseudo-first-order kinetics. DFT calculations validate experimental results, revealing stronger 2-MBT adsorption, enhanced Ag-TiO 2 interfacial interactions, and improved electron transfer in AgT. The combined experimental-theoretical study correlating structure–property–activity relationships establishes Ag-modified TiO 2 as a promising visible-light photocatalyst for sulfur pollutant remediation.