Green synthesis of ZnO nanostructures

• Autor(a) principal: Deitado, Beatriz Fidalgo da Costa
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/163875
• topic: zinc oxide; nanostructures; green synthesis; natural extracts; photocatalysis; Barbatimão; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

Zinc oxide (ZnO) is a wide direct band gap semiconductor with high exciton binding energy. Thus, it has superior photocatalytic performance, effectively in the photodegradation of organic pollutants. Nanostructures based on ZnO have many other applications such as antibacterial and antimicrobial. They can be synthesized by various methods, physical or chemical. Traditional approaches are costly and challenging to scale up while generating toxic chemicals. This work uses natural extracts to synthesize more biocompatible ZnO nanostructures that are eco-friendly, safe, simple, cost-effective, and energy-saving. These include various types of acacias (A. mearnsii and A. melanoxylon) and pines (P. nigra, P. sylvestris, P. pinea, and P. pinaster), Schoeno-plectus lacustris, and Stryphnodendron. A thorough examination was conducted on each plant and the respective nanostructures synthesized from them. X-ray diffraction (XRD) analysis confirmed the pres-ence of ZnO in the samples, as well as the crystallinity index. Their structural and elemental character-ization was carried out by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Plant-based ZnO nanostructures were successfully obtained by solvothermal microwave-as-sisted synthesis at 140ºC, 100W, for 20 minutes, using a high pH solvent, with zinc acetate as the pre-cursor. The most favorable plant-based ZnO nanostructures were obtained from A. mearnsii, P. syl-vestris, and Stryphnodendron. Due to its substantial opportunity to complement the literature, this work has been centered on the latter. Afterward, optimal plant-based ZnO nanostructures were applied as photocatalyst agents and bacterial inactivators. The photocatalytic activity was evaluated under solar radiation, rhodamine B was the model-test contaminant indicator, and the best photocatalytic action was achieved with barbatimão-based ZnO, reaching 59% dye degradation, compared with the reference with just 13%. However, these nanostructures showed no significant antibacterial properties against Escherichia coli. It is necessary to conduct further tests in this area to understand their antibacterial potential.