Fluorescent Carbon Dots Embedded Silica Nanocomposites as Tracers for Hydrogeological Investigations; A Sustainable Approach

Abstract

The injected tracer technique using nanoparticles has evoked a lot of research interest in hydrogeological research as it encompasses a broad spectrum of applications in water resources management. The present work deals with developing carbon dots embedded silica-based nanocomposites using a microwave-assisted co-polycondensation method. The synthesized carbon dot-embedded silica nanocomposites have been characterized for their structural and functional characteristics using UV-visible spectroscopy, photoluminescence spectroscopy (PL), Lifetime analysis, Raman spectroscopy, Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared spectroscopy (FTIR) and X-ray Diffractometry (XRD). The results obtained showed that carbon dots having a size of less than 5 nm had been successfully embedded into the silica structure and the nanocomposite as such is showing interesting optical properties. Laboratory scale column experimental studies were further conducted to ascertain the applications of the synthesized carbon dot-embedded silica nanocomposite for hydrological studies. Experiments were performed by varying the filling materials (sand/soil) in the column during which different concentration of the nano tracer was injected under the continuous flow of water at a constant flow rate of 5 ml/min followed by monitoring the detection of carbon dots for a definite time. The developed nanocomposite was found to exhibit satisfactory results in terms of the detection and recovery of carbon dots when injected as a tracer in an experimental hydrological study. About 99% of the nano tracer could be regained when ~0.5 g of the CD-SiO2 nano tracer is injected into the column and the detection was much faster with a peak detection time of 6 minutes. The better traceability and retention of the original optical properties of the developed tracer under different experimental conditions could be attributed to the optimal size of the nanocomposite system. Thus, the current challenges faced in groundwater flow analysis such as huge time consumption/expenses can be resolved to a significant extent considering the better traceability of the developed nano tracer.