Green synthesis of titanium dioxide nanoparticles with volatile oil of Eugenia caryophyllata for enhanced antimicrobial activities

Abstract

Different chemo-physical methods are used to synthesise titanium oxide nanoparticles (TiO₂ NPs), which are often expensive, unfriendly to the environment, toxic, not biocompatible, with a small yield. To resolve these problems, the researchers use green procedures to synthesise TiO₂-NPs by plant extracts of Capsicum annum L. and Allium cepa (onion) and characterise using atomic force microscopy, scanning electron microscopy, transmission electronic microscopy, X-ray diffraction, ultraviolet (UV)-visible (Vis) spectra and Fourier transform infrared spectroscopy. The results indicate that most NPs synthesised by the first and second procedures of onion had an average diameter of 95.7 and 89.1 nm, while NPs synthesised by C. annum had an average diameter of 103.60 and 90.07 nm, respectively. In UV-Vis spectra, strong absorption was below 470 nm, and energy gap was 3.3 eV in each of the first procedure of A. cepa and the second procedure of C. annum compared with 270 nm, 6.3 eV for each of the second procedure of A. cepa and the first procedure of C. annum. The antimicrobial activities of NPs were evaluated and an attempt was made to enhance these activities by Eugenia caryophyllata plant's oil in combination therapies. There were synergistic effects between NPs and plant's oil.

Fig. 1

Granularity volume distribution chart of TiO₂ ‐NPs synthesised by the first and second procedures of (a) A. cepa, (b) C. annum

Fig. 2

AFM topographic images of TiO₂ NPs synthesis by (a) First procedure of A. cepa, (b) Second procedure of A. cepa, (c) First procedure of C. annum, (d) Second procedure of C. annum

Fig. 3

SEM images of TiO₂ ‐NPs synthesised by (a) First procedure of A. cepa (<100 nm), (b) Second procedure of A. cepa (<100 nm), (c) First procedure of C. annum (<95 nm), (d) Second procedure of C. annum (<90 nm)

Fig. 4

TEM of TiO₂ produced by using (a) First procedure of A. cepa plant extracts (68.7 nm) at 92,000× magnification, (b) Second procedure of A. cepa plant extracts (20, 40 nm) at 130,000× magnification, (c) First procedure of C. annum plant extracts (15, 46 nm), (d) Second procedure of C. annum plant extracts (38, 108 nm) at 130,000× magnification

Fig. 5

X‐ray pattern of TiO₂ ‐NPs synthesised by (a) First procedure of A. cepa, (b) Second procedure of A. cepa, (c) First procedure of C. annum, (d) Second procedure of C. annum

Fig. 6

UV‐vis study of green synthesis TiO₂ NPs using the first and second procedures of A. cepa and the first and second procedures of C. annum plants extracts. (a) absorptions spectrum, (b) (ahv)² versus photon energy and estimated optical absorption bandgap.

Fig. 7

FT‐IR spectra of TiO₂ produced by using (a) First procedure of A. cepa plant extracts, (b) Second procedure of A. cepa plant extracts, (c) First procedure of C. annum plant extracts, (d) Second procedure of C. annum plant extracts

Fig. 8

Antibacterial activity of (a) Bulk TiO₂ particles alone, (b) TiO₂ NPs alone synthesised by A. cepa, (c) TiO₂ NPs alone synthesised by the second procedure of C. annum. IR%: inhibition rate, Con.: concentration. The numbers above the bars are standard errors

Fig. 9

Antibacterial activity of E. caryophyllata oil alone. IR%: inhibition rate, Con.: concentrations. The numbers above the bars are standards errors

Fig. 10

Antibacterial activity of combination therapy between oil of E. caryophyllata and each NP synthesised by the second procedure of (a) A. cepa, (b) C. annum. IR%: inhibition rate, Con.: concentrations. The numbers above the bars are standards errors