Orange fruit peel biowaste mediated green synthesis of CaO NPs and their antibacterial, radical scavenging activity and ecotoxicity.

This study documents the novel means of production of Cs@CaO NPs (calcium oxide nanoparticles) by utilizing the extract of orange fruit (C. sinensis) peel biowaste. The Cs@CaO NPs were then characterized by various bio-physical techniques. The orange peel extract showed absorbance at 360 nm, whereas, Cs@CaO NPs had an absorbance at 372 nm. XRD spectra clearly revealed the crystalline nature of Cs@CaO NPs with diffraction planes noted at (001) (100), (111), (101), (200), (102), (110), (220), (201), (311) and (222) and lattice parameters (a = 4.8152 A°). FTIR spectroscopy was used to characterize the functional groups in the peel extract that act as reducing agent in the biosynthesis of Cs@CaO NPs in the wavelength from 400 cm-1 to 4000 cm-1. SEM micrograph showed the presence of round, granular, and nanosized particles ranging between 20 and 30nm with an average size of 22.4 nm. EDX detected the prominent peaks for Ca (79.71 %) and O (20.29 %) elements only, thus confirming the purity of prepared NPs. The inhibition of Gram-positive bacteria such as M. luteus (MTCC 7950) and S. pyogenes (MTCC 442) at 100 μg/mL were 20.8 mm and 22.3 mm respectively. At the same concentration, Gram-negative bacteria such as A. hydrophila (MTCC 13049) and P. aeruginosa (MTCC 424) showed 12.1 mm and 11.0 mm respectively. The scavenging of DPPH and H2O2 were 90.7 % and 90.3 % respectively at 100 μg/mL. The ecotoxicity studies have shown that a slight rise in the concentration of Cs@CaO NPs and the exposure time was found to be highly toxic to P. shenops. Fish exposed to 75 and 100 mg/mL for 72 h and 96 h have the mortality of 38 % and 55 % respectively. A significant decrease in the haematological profile such as RBC (120.15 ± 1.7), WBC (132.98 ± 2.3) and hematocrit (28.4 ± 1.4 %) were noticed at 100 mg/mL. Also, significant changes in the histological structures of P. sphenops were noticed after treated with Cs@CaO NPs. This study concludes that the Cs@CaO NPs show potential for therapeutic applications pending further evaluation to mitigate the pathogen infection and improving the oxidative stress defences.