Green Synthesis and Characterization of Cobalt Oxide Nanoparticles Using Psidium guajava Leaves Extracts and Their Photocatalytic and Biological Activities

Abstract

The advanced technology for synthesizing nanoparticles utilizes natural resources in an environmentally friendly manner. Additionally, green synthesis is preferred to chemical and physical synthesis because it takes less time and effort. The green synthesis of cobalt oxide nanoparticles has recently risen due to its physico-chemical properties. In this study, many functional groups present in Psidium guajava leaf extracts are used to stabilize the synthesis of cobalt oxide nanoparticles. The biosynthesized cobalt oxide nanoparticles were investigated using UV-visible spectroscopic analysis. Additionally, Fourier-transform infrared spectroscopy revealed the presence of carboxylic acids, hydroxyl groups, aromatic amines, alcohols and phenolic groups. The X-ray diffraction analysis showed various peaks ranging from 32.35 to 67.35°, and the highest intensity showed at 36.69°. The particle size ranged from 26 to 40 nm and confirmed the average particle size is 30.9 nm. The green synthesized P. guajava cobalt oxide nanoparticles contain cobalt as the major abundant element, with 42.26 wt% and 18.75 at% confirmed by the EDAX techniques. SEM images of green synthesized P. guajava cobalt oxide nanoparticles showed agglomerated and non-uniform spherical particles. The anti-bacterial activity of green synthesized P. guajava cobalt oxide nanoparticles was evaluated against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli with a 7 to 18 mm inhibitory zone. The photocatalytic activity was evaluated using green synthesized P. guajava cobalt oxide nanoparticles and observed 79% of dye degradation. The MTT assay of P. guajava cobalt oxide nanoparticles showed an excellent cytotoxic effect against MCF 7 and HCT 116 cells compared to normal cells. The percentage of cell viability of P. guajava cobalt oxide nanoparticles was observed as 90, 83, 77, 68, 61, 58 and 52% for MCF-7 cells and 82, 70, 63, 51, 43, 40, and 37% for HCT 116 cells at the concentration of 1.53, 3.06, 6.12, 12.24, 24.48, 50, and 100 μg/mL compared to control cells. These results confirmed that green synthesized P. guajava cobalt oxide nanoparticles have a potential photocatalytic and anti-bacterial activity and also reduced cell viability against MCF-7 breast cancer and HCT 116 colorectal cancer cells.

Keywords: Co3O4NPs; EDAX; HCT 116 cells; MCF-7; Psidium guajava; XRD; cytotoxicity; photocatalytic activity.

Figure 1

(a) UV–Visible spectrum of Psidium guajava leaf extract and (b) Green synthesized P. guajava Co₃O₄ NPs.

Figure 1

(a) UV–Visible spectrum of Psidium guajava leaf extract and (b) Green synthesized P. guajava Co₃O₄ NPs.

Figure 2

XRD analysis of Psidium guajava Co₃O₄ NPs (JCPDS Card No. 073-1701).

Figure 3

(a) FTIR spectrum of Psidium guajava leaf extract and (b) Green synthesized P. guajava Co₃O₄ NPs.

Figure 3

(a) FTIR spectrum of Psidium guajava leaf extract and (b) Green synthesized P. guajava Co₃O₄ NPs.

Figure 4

SEM image of Psidium guajava Co₃O₄ NPs.

Figure 5

EDAX analysis of Psidium guajava Co₃O₄ nanoparticles.

Figure 6

(a) UV-visible analysis (b) Dye degradation using Psidium guajava Co₃O₄ NPs as a catalyst under solar light irradiation.

Figure 7

Antioxidant activity of Psidium guajava Co₃O₄ NPs using DPPH assay. Results are represented as mean ± SD, triplicate measures.

Figure 8

Antioxidant activity of Psidium guajava Co₃O₄ NPs using ABTS. Results are represented as mean ± SD, triplicate measures.

Figure 9

Anti-bacterial activity of green synthesized Psidium guajava Co₃O₄ NPs against (a) gram-negative bacteria (E. coli) (b) gram-positive (S. aureus).

Figure 10

Cytotoxicity assay of green synthesized Psidium guajava Co₃O₄ NPs against Vero cells, MCF-7 cells, and HCT 116 cells. P. guajava Co₃O₄ NPs reduced the cell viability in a dose-dependent manner. Vero cells, MCF-7 and HCT 116 cells were treated with P. guajava Co₃O₄ NPs at different concentration (1.53, 3.06, 6.12, 12.24, 24.48, 50 and 100 μg/mL) for 24 h. Results are represented as mean ± SD, triplicate measures. * p < 0.05, ** p < 0.01.