An Eco-friendly Approach to ZnO NP Synthesis Using Citrus reticulata Blanco Peel/Extract: Characterization and Antibacterial and Photocatalytic Activity

Zorka Vasiljevic; Jovana Vunduk; Dragana Bartolic; Goran Miskovic; Milos Ognjanovic; Nenad B Tadic; Maria Vesna Nikolic

doi:10.1021/acsabm.4c00079

An Eco-friendly Approach to ZnO NP Synthesis Using Citrus reticulata Blanco Peel/Extract: Characterization and Antibacterial and Photocatalytic Activity

ACS Appl Bio Mater. 2024 Apr 10. doi: 10.1021/acsabm.4c00079. Online ahead of print.

Authors

Zorka Vasiljevic¹, Jovana Vunduk², Dragana Bartolic¹, Goran Miskovic³, Milos Ognjanovic⁴, Nenad B Tadic⁵, Maria Vesna Nikolic¹

Affiliations

¹ University of Belgrade-Institute for Multidisciplinary Research, 11030 Belgrade, Serbia.
² Institute of General and Physical Chemistry, 11158 Belgrade, Serbia.
³ Silicon Austria Laboratories GMBH, High Tech Campus Villach, A-9524 Villach, Austria.
⁴ Institute of Nuclear Sciences Vinca, University of Belgrade, 11000 Belgrade, Serbia.
⁵ Faculty of Physics, University of Belgrade, 11000 Belgrade, Serbia.

PMID: 38597359
DOI: 10.1021/acsabm.4c00079

Abstract

Emission of greenhouse gases and infectious diseases caused by improper agro-waste disposal has gained significant attention in recent years. To overcome these hurdles, agro-waste can be valorized into valuable bioactive compounds that act as reducing or stabilizing agents in the synthesis of nanomaterials. Herein, we report a simple circular approach using Citrus reticulata Blanco (C. reticulata) waste (peel powder/aqueous extract) as green reducing and capping/stabilizing agents and Zn nitrate/acetate precursors to synthesize ZnO nanoparticles (NPs) with efficient antimicrobial and photocatalytic activities. The obtained NPs crystallized in a hexagonal wurtzite structure and differed clearly in their morphology. UV-vis analysis of the nanoparticles showed a characteristic broad absorption band between 330 and 414 nm belonging to ZnO NPs. Fourier transform infrared (FTIR) spectroscopy of ZnO NPs exhibited a Zn-O band close to 450 cm^-1. The band gap values were in the range of 2.84-3.14 eV depending on the precursor and agent used. The crystallite size obtained from size-strain plots from measured XRD patterns was between 7 and 26 nm, with strain between 16 and 4%. The highly crystalline nature of obtained ZnO NPs was confirmed by clear ring diffraction patterns and d-spacing values of the observed lattice fringes. ZnNPeelMan_400 and ZnNExtrMan showed good stability, as the zeta potential was found to be around -20 mV, and reduced particle aggregation. Photoluminescence analysis revealed different defects belonging to oxygen vacancies (V_O⁺ and V_O⁺²) and zinc interstitial (Zn_i) sites. The presence of oxygen vacancies on the surface of ZnAcExtrMan_400 and ZnAcPeelMan_400 increased antimicrobial activity, specifically against Gram-negative bacteria Escherichia coli (E. coli) and Salmonella enteritidis (S. enteritidis). ZnNExtrMan with a minimal inhibitory concentration of 0.156 mg/mL was more effective against Gram-positive bacteria Staphylococcus aureus (S. aureus), revealing a high influence of particle size and shape on antimicrobial activity. In addition, the photocatalytic activity of the ZnO NPs was examined by assessing the degradation of acid green dye in an aqueous solution under UV light irradiation. ZnAcPeelMan_400 exhibited excellent photocatalytic activity (94%) within 90 min after irradiation compared to other obtained ZnO NPs.

Keywords: Citrus reticulata; ZnO; agro-waste; antibacterial activity; green synthesis; photocatalysis.