Enhanced Photocatalytic Activity of Surface-Modified TiO₂ with Bimetallic AuPd Nanoalloys for Hydrogen Generation

Herein, commercial titania (TiO2-P25) is modified with mono- and bi-metallic (Au, Pd, and AuPd) nanoparticles synthesized by chemical reduction method using NaBH4 as a strong reducing agent at room temperature. Bimetallic AuPd nanoalloys homogeneous in size and well dispersed on the TiO2 surface are obtained. The charge-carrier dynamics, which is a key factor in photocatalysis, is studied by time-resolved microwave conductivity. The results reveal that surface modification plays a crucial role in charge-carrier separation, increasing the activity under UV-vis light irradiation. The bimetallic AuPd nanoalloys formation is confirmed by high-angle annular dark field scanning transmission electron microscopy and corroborated by semiempirical molecular dynamics simulations (Gupta-LAMMPS). The surface-modified TiO2 with bimetallic AuPd nanoalloys exhibits higher photocatalytic activity compared to TiO2 modified with their monometallic counterparts. The experimental results are also supported by density functional theory and density functional tight binding calculations, which show that alloying AuPd with low Pd content presents significant synergetic effects for hydrogen generation under UV-vis light from aqueous triethanolamine solutions. Additionally, the AuPd/TiO2 photocatalysts are stable with cycling.