Wastewater remediation with ZnO photocatalysts: Green synthesis and solar concentration as an economically and environmentally viable route to application

• Published in: Journal of environmental management Vol. 286; p. 112226
• Main Authors: El Golli, Asma, Fendrich, Murilo, Bazzanella, Nicola, Dridi, Chérif, Miotello, Antonio, Orlandi, Michele
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15-05-2021
• Subjects: Catalysis; Concentrated-light photocatalysis; Economic analysis; Methylene Blue; Pulsed-laser deposition; Sunlight; Waste Water; Wastewater remediation; Zinc Oxide; Zinc oxide nanostructures; Economic analysis; Concentrated-light photocatalysis; Wastewater remediation; Zinc oxide nanostructures; Pulsed-laser deposition
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2021.112226

Green-synthesized materials and solar concentration technology for advanced oxidation processes (AOPs) offer important opportunities in water remediation by giving value to clean, renewable and potentially low-cost resources. Here, Zinc Oxide (ZnO) nanostructures (NSs) were prepared via a green synthesis method based on garlic bulbs (Allium Sativum) extract (ZnO-Green), resulting in crystalline (wurtzite) nanorods (NRs). ZnO nanoparticles (NPs) were also chemically prepared through a standard co-precipitation (ZnO-Chem) for comparative solar photocatalytic (PC) studies. The green-synthesized ZnO NRs exhibited a favorable photocatalytic activity (PCA) in colloidal suspension for the methylene blue (MB) dye degradation upon exposure to concentrated sunlight. Comparison with the chemically synthesized ZnO results in almost equal degradations of 94% in optimal loading condition. To explore the possibility to use immobilized photocatalyst in heterogeneous condition, green-synthesized ZnO NRs coatings were fabricated and compared with a 135 nm thick ZnO thin film produced by pulsed laser deposition (PLD) (ZnO-PLD). PCA on MB degradation (120 min experiments) resulted in degradations of 69% and 73%, respectively, proving the feasibility of the immobilized photocatalyst approach. Finally, an economic analysis of the process shows that the combination of green-synthesis and concentrated sunlight significantly reduces costs, paving the way for large-scale photocatalytic wastewater remediation.
[Display omitted]
•ZnO nanorods were prepared by a green-synthesis using plant extract of garlic bulbs.•ZnO suspension or immobilized coating was used for concentrated-sunlight photocatalysis.•The performance is in both cases equal or better than benchmark ZnO.•Economic analysis shows that green-synthesis and concentrated –sunlight reduces cost by > 35%.