Fabrication of a Au-loaded CaFe2O4/CoAl LDH p–n junction based architecture with stoichiometric H2 & O2 generation and Cr(vi) reduction under visible light

Abstract

The search for visible-light-active, highly efficient and durable bi-functional photocatalysts is now essential for the development of various renewable energy sources and conversion technologies. Herein, we report a novel magnetically separable Au-loaded CaFe₂O₄/CoAl LDH heterostructure with strong coulombic interfacial interactions fabricated through a simple two-step process. XRD, XPS and TEM analysis of the synthesized samples were carried out for the structural and morphological characterization. The TEM study confirmed the existence of a firm attachment between the Au nanoparticles with the CaFe₂O₄/CoAl LDH heterostructures, which provides a unique support due to an exterior confinement effect. Formation of the heterojunction with a different electronic behaviour was also confirmed from an inverted V-shaped M–S plot, suggesting the presence of a large intimate contact interface between CoAl LDH and CaFe₂O₄ to favour the efficient separation and transfer of photoinduced charge pairs. The CoAl LDH–CaFe₂O₄@Au ternary heterostructure showed a high hydrogen generation rate of 379.1 μmol h⁻¹, oxygen evolution rate of 205.5 μmol h⁻¹ and Cr(VI) reduction rate of 99% under visible light irradiation. The CoAl LDH–CaFe₂O₄@Au heterostructure demonstrated its long-term stability and durability during photocatalytic investigations. The efficient photocatalytic activity of the catalysts was due to the synergistic effect of hot electron transfer by Au nanoparticles and easy mass transport through the interface owing to formation of a p–n junction by increasing the contact area. The mechanism of the photocatalytic activity was also supported by PL, EIS and photocurrent measurements. This work provides a novel strategy to design junction-based nanostructures as a promising photocatalyst for solar energy conversion.