Transition metal hydroxyl phosphate compounds have attracted recent attention for catalytic and magnetic applications. Here, we present a detailed analysis on the properties of (Cu1-xCox)2(OH)PO4 (0 ≤ x ≤ 1) compounds based on the mineral libethenite. Powders were synthesized using hydrothermal methods, and the photocatalytic activity was evaluated with an Fe3+/Fe2+ redox couple. Introduction of small fractions of Co to Cu2(OH)PO4 increased the photocurrent generation, but greater Co substitution caused it to decrease, with Co2(OH)PO4 showing the lowest photocurrent. The electronic band structure and density of states (DOS) were investigated using standard density functional theory (DFT) and hybrid functional methods. Hybrid DFT provided a better description of the electronic properties, especially the localized Cu and Co d electrons, in good agreement with the experimentally observed band gaps. The addition of Co to Cu2(OH)PO4 led to formation of bands within the band gap arising from Co 3d orbitals, which lowered the band gap <3 eV and changed the band-gap transition from a ligand-to-metal charge transfer (LMCT) to a metal-to-metal charge transfer (MMCT). However, higher concentrations of Co were detrimental to photocurrent generation as a result of the formation of a 3.7 eV MMCT and other electronic factors that could hinder charge separation.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- General Energy
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films