Síntese Verde de Nanopartículas de Prata Utilizando Cascas de Laranja (Citrus sinensis)

• Autor(a) principal: Teixeira, Lídia Marisa Macedo
• 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/10400.22/23857
• topic: Silver nanoparticles; Agro-industrial waste; Biosynthesis; Green solvents; Nanopartículas de prata; Resíduos agroindustriais; Síntese verde; Solventes verdes

Recently, silver nanoparticles (Ag-NPs) derived from biological sources act as an alternative route to reduce heavy chemicals and high costs of energy of physical and chemical approaches. In pursuit of a greener route, this thesis aimed to synthesize Ag-NPs from a green solventmediated orange peel (OP) extract. A screening of four types of natural deep eutectic solvents (NADES) and water OP extracts was reported by evaluating antioxidant activity and Total Phenolic Content (TPC). Water-assisted OP extract was ultimately chosen for Ag-NPs by presenting high TPC (90.7 mg GAE/g OP) and Trolox Equivalent Antioxidant Capacity (TEAC) (3.2 mg TE/g OP); besides, production of NADES was time-consuming and exhibited high viscosity and acidic properties. Ag-NPs were synthesized at 25 ºC in alkaline medium and monitored for 24 hours. Different ratios of Ag+ :TPC content were tested (varying from 0.75-12). Accordingly, Ag+ concentration was kept constant and OP extract volume decreased with an increase in ratio. A gradually colorless to brownish tone appeared after 15 minutes, indicating formation of AgNPs. UV-VIS Spectroscopy (UV-VIS) revealed surface plasmon resonance (SPR) peaks in the region 407-412 nm, related to Ag-NPs absorption band. In addition, a peak at 280 nm associated with UV absorption of polyphenols was reported in all samples, suggesting OP extracts were not capable of completely reducing Ag+ to Ag0 . Dynamic Light Scattering (DLS) data confirmed AgNPs with an average hydrodynamic diameter of 99-112 nm and a polydisperse index of 0.210- 0.263, revealing monodisperse nature of Ag-NPs. Moreover, Ag-NPs confirmed high stability due to a zeta potential value of -21.0 mV. Studied ratios did not show significant differences in particle size characterization but a trend in antioxidant activities was established. TPC and TEAC of Ag-NPs was lower in comparison to H2O-assisted OP extract due to interaction of the reducing agents in the bioreduction; it is also noted that bigger ratios present higher TPC and TEAC content, and vice-versa. Overall results suggested the great potential of OP as a biological source of phenolics for green Ag-NPs synthesis.