Controlling ZnO morphology in alkaline sol–gel systems without the use of surfactants or templates remains a significant challenge. In this work, we demonstrate that CO 2 -accessible open evaporation conditions promote the formation of surfactant-free ZnO nanospheres via a carbonate-confined growth mechanism. An alkaline ZnCl 2 system was processed under two distinct conditions: open atmosphere evaporation, and CO 2 limited sealed aging. The open evaporation route yielded uniform ZnO nanospheres of approximately 50 nm which preserved their morphology after calcination at 800 °C, indicating that morphology is established during the wet evaporation stage rather than by thermal treatment. In contrast, the sealed CO 2 limited system produced cabbage-like hierarchical microstructures composed of nanosheets with lateral dimensions of approximately 1–1.5 µm. FTIR analysis before calcination presented stronger bands related to carbonate under open atmosphere conditions, consistent with surface carbonate formation contributing to isotropic growth confinement. XRD demonstrated the formation of hexagonal wurtzite ZnO, with crystallite sizes consistent with SEM observations. The spherical ZnO showed improved solar photodegradation efficiency toward methylene blue and ketorolac compared to cabbage-like morphology, relating atmosphere/evaporation-controlled morphology to photocatalytic performance. These findings provide insight into the role of environmental accessibility and evaporation pathway in directing structural evolution in surfactant-free alkaline ZnO synthesis.
Guzmán-Álvarez et al. (Sat,) studied this question.