One-Step Thermal Treatment Route to Obtain ZnO Nanospheres from ZnAlEu LDH Nanotubes

This study presents a novel synthesis route for producing ZnO nanospheres via the controlled calcination of nanotubular layered double hydroxide (LDH) precursors. The thermal treatment promotes the transformation of the nanotubular LDH precursor into ZnO nanospheres through a restructuring process associated with LDH decomposition and oxide formation. Comprehensive characterization using XRD, SEM, HRTEM, and XRF mapping confirmed the formation of highly crystalline wurtzite ZnO-spheres. Although no distinct Eu₂O₃ reflections were initially observed by XRD, XRF mapping and XANES analyses revealed a heterogeneous distribution of europium within the calcined material. Eu-rich domains coexist with regions dominated by crystalline ZnO nanospheres, suggesting partial segregation of europium during the thermal transformation process. XANES analysis verified europium predominantly in the +3 oxidation state. The photocatalytic efficiency of the resulting material was evaluated through the degradation of Rhodamine 6G (R6G) under UV irradiation. The ZnO-spheres achieving ∼90% R6G degradation after 300 min, following pseudo-first-order kinetics (k _app= 0.601 h^-1). This significant activity is attributed to the synergistic effect of the spherical morphology, which provides a surface area and improved light-harvesting efficiency, and the synergistic role of the heterostructure formed between the ZnO-spheres and the Eu³⁺ rich domains, which facilitates spatial charge carrier separation at the interface, reducing electron-hole recombination. This work underscores the potential of LDHs as sacrificial templates for creating morphologically controlled mixed oxide photocatalysts and demonstrates the ZnO-spheres as a highly promising candidate for environmental remediation applications.