A study on synthesis and characterisation of rare earth metal ions Ce³ and Nd³ doped ZnO nanoparticles for their biomedical applications

Abstract

The objective of the present thesis is laid on the synthesis and characterization of various concentrations (0.05,0.10, 0.15) of rare earth metal ion (Ce3+ and Nd3+) doped zinc oxide nanoparticles. The mentioned nanoparticles had been synthesized by co-precipitation method. The synthesized nanoparticles were characterized through X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray analysis (EDAX), PhotoLuminescence (PL) spectra, Fourier Transform Infra-Red spectroscopy (FT-IR) and Micro-Raman studies in order to study the structural, morphological, elemental compositional, optical properties , functional group and phases respectively. The present work is also extended to determine the antibacterial and anticancer properties. The X-ray diffraction of ZnO and various concentration of Ce doped ZnO revealed wurtzite hexagonal structure without any secondary phase of Ce3+/ Ce4+ ions with cerium oxide between CeO2 and Ce2O3. The XPS measurement of Ce doped ZnO confirmed that the oxidation state of Zn (2p) signal has been splitted into two symmetric peaks corresponding to Zn (2P3/2) at 1022.57 eV and Zn (2p1/2) at 1045.57 eV. O (1s) asymmetric signal has been splitted into three symmetric peaks I1 (531.36 eV), I2 (532.63 eV) & I3 (533.64 eV) and the binding energy of Ce (3d) values were observed at 882.57 eV, 888.91 eV, 898.92 eV, 902.32 eV, 909.06 eV, 917.76 eV and 922.88 eV for Zn0.90Ce0.10O NPs. The morphological analysis of ZnO and Ce doped ZnO NPs were found to exihibit nanoflower and spherical like structure respectively. The Ce doped ZnO NPs agglomerates with each other due to the increasing nucleation of Ce3+ ions and subsequent growth of ZnO NPs. The elemental analysis showed the increase in percentage of Ce as the concentration of Ce in Ce doped ZnO increases. This confirmed the incorporation of Ce in Ce doped ZnO nanoparticles. The photoluminescence emission spectra of ZnO and Ce doped ZnO NPs exhibited UV and Visible region which depends on nature as well as concentration of Ce3+ ions. The Photoluminescence spectra of the ZnO and Ce doped ZnO NPs were observed with excitation wavelength 325 nm. The blue emission wavelength at 440 nm, 439 nm, 439 nm and 446 nm for ZnO and Ce doped ZnO NPs, is due to the single ionized Zn vacancies. Thus the changes in emission confirmed the substitution of Ce ion into ZnO lattice. The FT-IR spectra showed the Zn-O stretching vibrations at 418 and 416 cm-1 for ZnO and Ce doped ZnO NPs respectively. Raman studies also confimed the wurtzite structure of ZnO and Ce doped ZnO NPs. The phonon mode intensity has decreased with increase in Ce ion concentration. The antibacterial studies were performed against a set of bacterial strains as Gram positive bacteria (S. aureus and S. pneumonia) and Gramnegative (E. coli, P. aeruginosa, P. vulgaris, K. pneumonia, and S. dysenteriae) bacteria. From the antibacterial activity, Zn0.85Ce0.15O NPs possessed more antibacterial effect as compared to the other ZnO, Zn1-xCexO (x=0.05 and 0.10) NPs. The cytotoxic effect of ZnO and Ce doped ZnO were analyzed in cultured (A549) human lung cancer cell line. Among which, Zn0.90Ce0.10O NPs possesed the highest cytotoxicity activity. With respect to cell death, as low a concentration of 68 ± 0.05 μg/ml of Zn0.90Ce0.10O NPs was good enough to cause loss of viability of 50% of the cell as compared to ZnO and Zn1-xCexO (x=0.05 and 0.15) NPs. vii The X-ray diffraction of ZnO and various concentration of Nd doped ZnO revealed wurtzite hexagonal structure without any secondary phase of Nd3+/ Nd4+ ions with neodymium oxide of Nd2O3. The XPS measurement of Nd doped ZnO nanoparticles confirmed that the oxidation state of Zn (2p) signal has been splitted into two symmetric peaks corresponding to Zn (2P3/2) at 1022.38 eV and Zn (2p1/2) at 1045.50 eV. O (1s) asymmetric signal has been splitted into three symmetric peaks 530.99 eV, 532.60 eV & 534.30 eV respectively. Binding energy of Nd (3d) state values were observed at 978.26 eV, 983.28 eV, 997.29 eV, 1002.18 eV and 1023.37 eV for Zn0.90Nd0.10O NPs. The morphological analysis of ZnO NPs exhibited nanoflower like structure and Nd doped ZnO NPs as nanoflake and spherical like structure. These morphological changes are due to the substitution of Nd3+ ions in ZnO lattice sites or on the ZnO surface. The percentage composition of elements such as Zn, O and Nd were identified using EDAX spectra. The percentage of Nd has been increased since the concentration of Nd in Nd doped ZnO increases. This confirmed the substitution of Nd in Nd doped ZnO. The Photoluminescence spectra of the ZnO and Nd doped ZnO NPs were observed with excitation wavelength 325nm. The green emission bands are observed at 519 nm, 520 nm, 520 nm and 522 nm for ZnO and Nd doped ZnO NPs, is due to the oxygen vacancies and intrinsic defects. These emission changes confirmed the substitution of Nd3+ ions into ZnO lattice surface. From the FTIR spectra, the Zn-O stretching bands were observed at 423, 466, 423 and 452 cm-1 for ZnO and Nd doped ZnO NPs respectively. In Raman spectra, ZnO and Nd doped ZnO NPs confirmed the wurtzite viii hexagonal sturcture. A1 (LO) phonon modes intensity decreased with the increase in concentration of Nd3+ ions. This is due to the incorporation of Nd3+ ions in ZnO lattice surface. The antibacterial studies were performed against a set of bacterial strains such as Gram positive bacteria (S. aureus and S. pneumonia) and Gram-negative (E. coli, P. aeruginosa, P. vulgaris, K. pneumonia, and S. dysenteriae) bacteria. From antibacterial activity, the Zn0.85Nd0.15O NPs possessed more antibacterial effect as compared to the other ZnO and Zn0.95Nd0.05O and Zn0.90Nd0.10O NPs. The cytotoxic effect of pure ZnO, Zn0.95Nd0.05O, Zn0.90Nd0.10O and Zn0.85Nd0.15O were examined in cultured (A549) human lung cancer cell line. Among them, the Zn0.95Nd0.05O NPs produced the highest cytotoxicity activity. With respect to cell death, as low a concentration of 118.5 ± 0.05 μg/mL Zn0.95Nd0.05O NPs was good enough to cause loss of viability of 50% of the cell as compared to the pure ZnO, Zn0.90Nd0.10O and Zn0.85Nd0.15O NPs.