Development of Sensing Platform based on Rare Earth Nanocomposite Films

Abstract

In the present era, contamination or pollution in water has become one of the global issues because of its serious health consequences and imbalance caused in the ecosystem. There is a continuous rise in the pollution or contamination caused by heavy metals in the atmosphere or in the aquatic ecosystem from the past few decades. Industrial waste plays a great role in polluting the water and is responsible for introducing different pollutants in the form of heavy metals in living beings. Heavy metals like arsenic, mercury, cadmium, cobalt, and many more are highly toxic for human beings. Determination of these heavy metals in the water, soil is a very challenging task. Though, these days a lot of research is going on for removing these heavy metals from the soil, water and atmosphere by adopting different and new methodologies, but those techniques are either expensive, time-consuming or are very complex to use. Current research evaluates the role of different chelating agents and types of substrates on the film evolution, thickness and its characteristics emission when the hydrothermal route is used as a synthesis technique. Moreover, the effect of temperature on the film thickness and surface roughness is also evaluated. Furthermore, a nearly transparent Upconverting (UC) thin-film has been grown entailing capability to ensue fluorescence resonance energy transfer and use it to detect Arsenic in drinking water. The objective of the current thesis is to enhance our understanding of UC film growth over the different glass substrates using the hydrothermal method. This understanding will enable us to use other bio-organic materials such as plant extract to synthesize UC films. Moreover, prepared UC film on glass substrate is proposed to use as a Arsenic sensor, as arsenic contamination in drinking water is very difficult to quantify analytically due to its low detection limit (5 ppb by World Health Organisation (WHO)). Besides, Atomic absorption, Inductively Coupled Plasma (ICP), Inductively Coupled Plasma-Mass Spectrometer (ICP-MS), arsenators and many more are among the few options available for detection. In the first study, simultaneous crystal growth and deposition of Upconverting Yb3+/Er3+ doped NaYF4 Film (UCF) on conducting and non-conducting substrates by one-step hydrothermal method have been developed. The characteristics such as film topography, morphology, crystallographic phase and upconverting luminescence intensity were found to depend both on the chelating agent and nature of the substrate. The characteristics of the prepared films varied interestingly when either the chelating agent or the substrate was changed. The upconversion emission intensities were found to increase with decreasing film roughness. Further, current investigation demonstrated that the NaYF4 films deposited using ethylenediaminetetraacetic acid (EDTA) or diethylenetriamine pentaacetic acid (DTPA) chelating agents on indium tin oxide (ITO) substrate and ethyleneglycol tetraacetic acid (EGTA) chelating agent on plain glass (PG) substrate were more uniform and resulted in greater upconverted emission intensities. We envision plausible use of current technology in the development of affordable optical platforms for several optoelectronic applications. In the second study, a sensitive α-NaYF4:Yb3+, Er3+ solid-phase upconverting platform (UCP) have been developed and realized using Moringa oleifera leaf extract for selective detection of the trivalent arsenic ion [As(III)] contamination in drinking water. The presence of polyphenols in the leaf extract has showed to induce luminescence resonance transfer (LRET), thereby diminishing the Er3+ emission (red and green band) when activated by 980 nm excitation. However, the addition of As(III) species interrupted the LRET process and restored the emissions proportionately. This feature allowed the platform to selectively detect arsenic pollution in water below the safe limit of 10 ppt. The uniqueness of UCP lies in monitoring the As(III) contamination in samples containing heavy ions (Cd2+ and Hg2+) also, without an apparent effect on the signal reproducibility. The UCP was also found to be insensitive to other interfering ions including Pb2+, H2PO4−, F−, Cl−, Ca2+, Mg2+, Sn2+, Cr6+, Fe2+ and Co2+, if present. Fig.1 shows the overall outline of the thesis. Overall, the studies performed shows that we are able to form an optically active thin film for the purpose of sensing which can be formed by using hydrothermal method.