Visible-light-active photocatalytic heterojunctions
based on nanostructured β-Bi2O3/Cu2O semiconductors were
successfully coupled by high-energy ball milling, exhibiting
enhanced charge carrier separation, transfer, and reaction properties.
The optical, structural, and photoelectrochemical properties of
the catalysts and their heterojunctions were analyzed to evaluate
the coupling efficiency. The optimal stoichiometric ratio of (1 −
x)β-Bi2O3/xCu2O (x = 25, 50, and 75 wt %) and the milling time
significantly influenced the optical properties, including photoluminescence
(PL). A notable decrease in PL intensity was
observed for the heterojunction with x = 25%, compared to that
of the single semiconductors. This effect was further enhanced with
increasing milling time, which is attributed to the mechanical
energy input. The formation of nanosized mixed-phase transition heterojunctions was confirmed by scanning electron microscopy
(SEM), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive spectroscopy (EDS). Structural
characterization revealed increased lattice parameters and reduced crystallite size due to mechanical milling. Milling-induced
structural deformations led to decreased PL intensity and band gap energy. Photocatalytic efficiency was the highest for
heterojunctions prepared with shorter milling times; longer milling times introduced structural defects that reduced photocatalytic
performance. Flat band potential (EFB) analysis identified a p−n junction with staggered band edge alignment. The heterojunction,
which was milled for 60 min, exhibited an absorption range extending up to 1.84 eV. Notably, the 75β-Bi2O3/25Cu2O sample milled
for 5 min achieved 98% photocatalytic efficiency under visible light irradiation. Mechanical milling is a simple, inexpensive, one-step
process for fabricating nano-sized heterojunctions with well-mixed interfaces that enhance charge carrier separation. While structural
defects are detrimental in excess, they can enhance photocatalytic activity at optimal concentrations.
