Multiple defects induced catalytic and optical properties in Se doped ZnO nanorods for environmental and healthcare applications

Abstract

Environment and healthcare are very closely related to each other, and human health is greatly influenced by the surrounding environment. The environment is essential for the survival of the earth planet and its living organisms that are uniquely positioned to be at the forefront of progress. Human beings are exposed to various environmental risk factors and toxic chemicals derived from chlorofluorocarbons, heavy metals, volatile organic compounds, hydrocarbons, and pesticides that are major causes of various diseases. Therefore, in the present thesis work, the preparation and application Se doped ZnO nanorods in biodiesel production, detection of mercury and optical properties for environmental and healthcare applications are reported. Se doped ZnO generates multiple zinc (VZn), oxygen (VO) vacancies and oxygen interstitials (Oi) defects, in the crystal lattice that are characterized by XRD, XPS, EPR and PL studies. Oxygen interstitials (Oi) play essential role in enhancing basic site reactivity in transesterifcation reaction and was found to be usage of 1:20 oil to methanol volume ratio, 5 wt.% catalyst load, 65 oC as reaction temperature to give a maximum yield of 94.7% FAME in 3 h. Photoluminescent Se doped ZnO that was coated with 3-mercaptopropionic acid (3MPA), a chelating ligand to detect mercury ions demonstrate strong affnity for –SH functionality. In the presence of Hg2+ ions, 3MPA–Se doped ZnO nanoprobe show effcient turn-on (restoration) photoluminescence over dual emission-quenching phenomenon owing to increased zeta potential (− 17.06 mV) and anti-aggregation effect induced by rapidly separated 3MPA surface ligands bound to selenium doped ZnO within 30 s. This “turn-on” was employed for selective detection of Hg2+ ions with the lowest limit of concentration to 1 pM. Later, multiple defects induced multicolor emissions by single and two-photon single wavelength excitations show broad emission with and a large Stokes shift of about 250 nm due to overlapping of defects in electronic transitions. The EPR signals also reveal detail information about these defects and show correlation with optical electronic transition states of blue, green and red emissions in Se doped ZnO NRs. Two-photon confocal studies of Se doped ZnO NRs shows multicolor emission at 720, 800 and 860 nm excitations which are consistent with one photon fluorescence at 360, 400 and 430 nm excitations.