Pulsed laser deposition of CoFe2O4/CoO hierarchical-type nanostructured heterojuction forming a Z-scheme for efficient spatial separation of photoinduced electron-hole pairs and highly active surface area.

The ablation of a target, composed of a homogeneous mixture of Fe & Co metal with H 3 BO 3 powder, produces core-shell type particles on the as-deposited coating surface. Annealing at 600 °C in air transforms the core-shell into urchin-like particles having nanowires of 10–30 nm in diameter and 0.5–1 μm in length, grown radially from the particle surface as a result of the stress created between core and shell. Microstructural and analytical characterization confirms that nanowires are composed of CoFe 2 O 4 and CoO phases forming a heterojunction, which showed outstanding performance as a photocatalyst, requiring half the time for an organic water pollutant degradation reaction in comparison to similarly nanostructured single-metal oxide counterparts (Co 3 O 4 and Fe 2 O 3). Degradation reactions conducted in controlled conditions demonstrate that the urchin-like mixed oxide coatings are highly efficient both in direct photocatalysis and in photo-Fenton reaction. This overall enhancement in activity is due to a synergistic effect created at the heterojunction of CoFe 2 O 4 /CoO that allows the formation of a Z -scheme mechanism to facilitate the spatial separation of photoinduced electron-hole pairs. Moreover, the hierarchical urchin-like nanostructures provide a large number of active sites for photocatalytic reactions, while the lower band gap of CoFe 2 O 4 permits better visible light absorption to effectively degrade organic pollutants even under visible light. Based on all the results, a plausible reaction mechanism is proposed related to Z -scheme heterojunction formed with CoFe 2 O 4 /CoO. Unlabelled Image • A coating of urchin-like nanostructured CoFe 2 O 4 /CoO heterojunction is synthesized by PLD. • Implementation of a Z-scheme design greatly improves charge separation. • Hierarchical nanostructuring provides large number of active sites for photocatalytic reactions. • The coating shows outstanding photocatalytic activity towards a model pollutant. [ABSTRACT FROM AUTHOR]