Green synthesis of multifunctional carbon coated copper oxide nanosheets and their photocatalytic and antibacterial activities

Abstract

The studies of metal oxides in environmental remediation of chemical and biological pollutants are gaining colossal importance. Herein, we report the facile synthesis of multifunctional copper oxide nanosheets (CuO NS) using an aqueous extract of Rhazya stricta. The phytochemical investigation of R. stricta indicated the presence of saponins, tannins, and reducing sugars, responsible for the reduction and stabilization of CuO NS. A UV-Visible spectrophotometer initially confirmed the fabrication of CuO NS with specific Surface Plasmon Resonance at 294 nm. Field Emission Scanning Electron Microscopy (FE-SEM), Fourier-transform infrared spectroscopy FTIR, and XRD were further used to characterize the CuO NS. The obtained CuO NS were poly-dispersed with an average size of 20 nm. Interestingly these particles were aligned together in 3D cubical sheets layered above each other via self-assembly. The as-synthesized CuO NS showed enhanced antibacterial potential (17.63 mm, overall mean inhibition zone) in comparison to the known antibiotics (11.51 mm, overall mean inhibition zone) against both Solanaceous crop's wilt-causing bacteria (Ralstonia solanacearum and Clavibacter michiganensis). Furthermore, the appreciable photocatalytic potential of CuO NS has also been observed, causing 83% degradation of methylene blue (MB) upon solar irradiation. The synthesis methodology is devoid of any toxic waste or by-products. It could be used to produce eco-friendly CuO nanomaterial for industrial uses.

Figure 1

Photo of Rhazya stricta grown in natural habitat.

Figure 2

(A) Photograph of sample changing color (a) aqueous CuSO₄ solution, (b) aqueous extract of Rhazya stricta, (c) aqueous solution of CuO NS. (B) UV visible absorption spectrum of CuO nanosheets. (C) Tauc’s plot showing the energy bandgap of CuO NS. Both absorption spectrum (B) and Tauc's plot (C) were produced by OriginPro 2018 (64bit).

Figure 3

XRD spectrum of CuO NS synthesized via green synthesis using Rhazya stricta aqueous extract showing major diffraction peaks. XRD spectrum was produced by OriginPro 2018 (64bit).

Figure 4

FTIR spectrum showing various absorption bands. The inset magnified part of the spectrum showing clearly the sharp peak at 630 cm⁻¹ corresponding to the formation of pure CuO nanosheets. OriginPro 2018 (64bit) was used to plot data.

Figure 5

FESEM image as-formed Copper Oxide nanosheets.

Figure 6

Zone of inhibition of (a) Ralstonia solanacearum and (b) Clavibacter michiganensis.

Figure 7

(a) Photocatalytic degradation of MB using CuO NS, (b) degradation efficiency (%) of MB. Both graphs were produced using OriginPro 2018 (64bit).

Figure 8

Mechanism of photocatalytic degradation of methylene blue using CuO NS. Image generated using ChemDraw professional v.17.