Surface versus Bulk Ni-Cu Doping in TiO₂- Nanoparticles: Visible-Light Absorption Enhancement for Photocatalytic Water Splitting Mulda Muldarisnur (a*), Noni Novianti (a), Darma Septian (a), Diana Vanda Wellia (b), and Yetria Rilda (b)
a) Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Andalas, Padang, Indonesia
*muldarisnur[at]sci.unand.ac.id
b) Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Andalas, Padang, Indonesia
Abstract
TiO₂- has been widely studied as a photocatalyst for hydrogen production through water splitting. Its large band gap, however, limits absorption mainly to the ultraviolet region, which is only a very small fraction of sunlight. This work reports optical simulation of visible-light absorption enhancement in surface- and bulk-doped Ni-Cu TiO₂- nanoparticles. TiO₂- nanoparticles were assumed to be 20-50 nm in diameter, while Ni and Cu dopants having diameters of 1-5 nm were homogeneously distributed either inside the TiO₂- bulk or on the particle surface. The total metal fraction was varied below 5% to represent low dopant loading. The optical absorption, scattering, and extinction cross sections were calculated using Mie theory. The optical properties of surface-doped TiO₂- nanoparticles were investigated using the effective refractive index models. The visible-light absorption of Ni-Cu doped TiO₂- was compared with pure, Ni-doped, and Cu-doped TiO₂- nanoparticles. The Ni-Cu co-doping was found to enhance visible-light absorption more effectively than the pure and single-metal doping. The modified dielectric response and stronger light-matter interaction at the metal-TiO₂- interface result in improvement of absorption. Surface-doped Ni-Cu TiO₂- shows stronger absorption enhancement than bulk-doped TiO₂- because the metal domains interact more directly with incident light. The enhancement of visible light absorption strongly depends on diameter and filling fraction of metal doping. These findings provide a simulation-based guideline for designing Ni-Cu doped TiO₂- nanoparticles with improved visible-light activity for photocatalytic hydrogen production.
