Surfactants represent an emerging class of persistent organic pollutants whose incomplete biodegradation often leads to the formation of long-lived and potentially more toxic intermediates. In this preliminary study, a series of ZnO nanostructures was synthesized via a hydrothermal route and systematically correlated with their structural, morphological, and optical properties to elucidate the role of crystallinity, defect chemistry, and polar facet exposure in the photocatalytic degradation of nonionic surfactants. ZnO Hy_2h_150, composed of well-defined nanoplate-like crystallites with preferentially exposed {0001} polar planes, exhibited the highest degradation efficiency toward diethylene glycol diethyl ether (DEGDEE) (similar to 70% under UV irradiation). Photoluminescence analysis revealed reduced defect-related emission, indicating lower electron-hole recombination and rationalizing its superior activity. Although ZnO Hy_2h_150 did not induce measurable TOC removal in DEGDEE degradation, it was selected as the ZnO component for constructing a 50:50 wt% ZnO/Fe-CeO2 heterostructure due to its superior oxidative breakdown capability. The incorporation of Fe-CeO2 preserved the crystallographic orientation of ZnO (texture coefficient approximate to 1.42) but partially reduced the accessibility of exposed polar facets through surface coverage effects. Under UV irradiation, the heterostructure exhibited lower DEGDEE degradation (similar to 30%) compared to ZnO alone, yet enabled measurable mineralization (similar to 9%), corresponding to a significantly higher mineralized-to-degraded carbon ratio than pristine ZnO. When applied to Triton X-100, the heterostructure achieved similar to 90% degradation under UV and complete degradation under simulated solar irradiation, while showing slightly higher TOC removal than ZnO under solar conditions. Scavenger experiments performed under solar irradiation identified photogenerated holes as the dominant reactive species. Mulliken-based band alignment calculations supported the formation of a type-I heterostructure, favoring charge confinement within the Fe-CeO2 phase and promoting interfacial hole-mediated oxidation pathways. Combined with enhanced surfactant adsorption on the heterostructure surface, these effects contribute to improved mineralization efficiency despite similar degradation kinetics. These preliminary findings demonstrate that coupling ZnO with redox-active, visible-light-responsive Fe-CeO2 enables complementary degradation-mineralization pathways, highlighting the importance of facet accessibility, adsorption phenomena, and interfacial charge-transfer dynamics in designing advanced photocatalysts for nonionic surfactant removal.
Influence of exposed {0001} polar facets in ZnO and ZnO/Fe–CeO₂ heterostructures: Preliminary structure–reactivity relationships for the UV- and solar-driven photocatalytic degradation and mineralization of nonionic surfactants
Rescigno R.;Sacco O.;Iannece P.;Venditto V.;Vaiano V.
2026
Abstract
Surfactants represent an emerging class of persistent organic pollutants whose incomplete biodegradation often leads to the formation of long-lived and potentially more toxic intermediates. In this preliminary study, a series of ZnO nanostructures was synthesized via a hydrothermal route and systematically correlated with their structural, morphological, and optical properties to elucidate the role of crystallinity, defect chemistry, and polar facet exposure in the photocatalytic degradation of nonionic surfactants. ZnO Hy_2h_150, composed of well-defined nanoplate-like crystallites with preferentially exposed {0001} polar planes, exhibited the highest degradation efficiency toward diethylene glycol diethyl ether (DEGDEE) (similar to 70% under UV irradiation). Photoluminescence analysis revealed reduced defect-related emission, indicating lower electron-hole recombination and rationalizing its superior activity. Although ZnO Hy_2h_150 did not induce measurable TOC removal in DEGDEE degradation, it was selected as the ZnO component for constructing a 50:50 wt% ZnO/Fe-CeO2 heterostructure due to its superior oxidative breakdown capability. The incorporation of Fe-CeO2 preserved the crystallographic orientation of ZnO (texture coefficient approximate to 1.42) but partially reduced the accessibility of exposed polar facets through surface coverage effects. Under UV irradiation, the heterostructure exhibited lower DEGDEE degradation (similar to 30%) compared to ZnO alone, yet enabled measurable mineralization (similar to 9%), corresponding to a significantly higher mineralized-to-degraded carbon ratio than pristine ZnO. When applied to Triton X-100, the heterostructure achieved similar to 90% degradation under UV and complete degradation under simulated solar irradiation, while showing slightly higher TOC removal than ZnO under solar conditions. Scavenger experiments performed under solar irradiation identified photogenerated holes as the dominant reactive species. Mulliken-based band alignment calculations supported the formation of a type-I heterostructure, favoring charge confinement within the Fe-CeO2 phase and promoting interfacial hole-mediated oxidation pathways. Combined with enhanced surfactant adsorption on the heterostructure surface, these effects contribute to improved mineralization efficiency despite similar degradation kinetics. These preliminary findings demonstrate that coupling ZnO with redox-active, visible-light-responsive Fe-CeO2 enables complementary degradation-mineralization pathways, highlighting the importance of facet accessibility, adsorption phenomena, and interfacial charge-transfer dynamics in designing advanced photocatalysts for nonionic surfactant removal.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
