Environmentally benign and economical bio-fabrication of ZnO and Cr-doped ZnO nanoparticles using leaf extract of Citrus reticulata for biological activities

Abstract Environmentally safe and economical bio-fabrication of nanoparticles using plant extracts plays a vital role in nanotechnology. The present study focuses on green fabrication of ZnO and Cr-doped ZnO nanoparticles (NPs) using leaf extract of C. reticulata as both stabilizing and reducing agents. Characterization through X-ray diffraction (XRD) revealed crystalline nature of wurtzite ZnO having hexagonal structure with lattice parameters a = 3.25 A, b = 3.25 A and c =5.21 A. Using XRD data, the average crystallite size of ZnO and Cr-doped ZnO NPs was found to be 19.6 and 24.3 nm, respectively. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) confirmed synthesis of ZnO NPs and doping of Cr, while a spheroid like morphology was observed for the NPs. Fourier transform infrared (FT-IR) spectroscopy confirmed presence of various functional groups along with the metallic bonds of zinc and chromiumC. Thermo-gravimetric analysis (TGA) revealed that Cr-doped ZnO-NPs were more thermally stable than pure ZnO. Biological activities of NPs indicated that both ZnO and Cr-doped ZnO-NPs had strong free radical scavenging potential. Moreover, a remarkable antibacterial activity was exhibited by Cr-doped ZnO against E. coli, S. aureus, K. pneumonia and P. aeruginosa with zone of inhibition of 22.4 ± 1.98, 15.5 ± 0.78, 10.2 ± 0.55 and 7.5 ± 1.55 mm, respectively. Significant hemolytic activity was also evident using Cr-doped ZnO-NPs. The higher pharmacological activity of Cr-doped ZnO-NPs than un-doped ZnO is attributed to the excessive production of reactive oxygen species and high penetration power of doped NPs.