Real-time colorimetric detection of dissolved carbon dioxide using pH-sensitive indicator based on anthocyanin and PVA coated green iron oxide nanoparticles at room temperature

In this study, a pH-sensitive indicator solution for the colorimetric naked-eye detection of dissolved carbon dioxide at room temperature was developed with the aim of environmental monitoring. The indicator solution was produced by the polyvinyl alcohol-coated green synthesized iron oxide nanoparticles and the natural anthocyanin extracted from red cabbage. The pH change upon carbon dioxide dissociation occurred in the indicator solution. The reaction was investigated using the stopped-flow method by monitoring the pH measurements at different dissolved CO2 concentrations. The indicator solution changed color from blue to pink within a few seconds with pH change on the acidic side and returned to its initial state spontaneously without any treatment at the end of the CO2 gas. The indicator solution showed sensitivity to dissolved CO2 concentrations in the range of 600 - 3200 ppm in a fast reaction time and complete reversibility

Colorimetric detection of mercury ion using chlorophyll functionalized green silver nanoparticles in aqueous medium

© 2020 Elsevier B.V.This study presents an investigation of colorimetric sensing of mercury ions in aqueous medium using chlorophyll (Chl) functionalized green synthesized silver nanoparticles (AgNPs). Chl-AgNPs showed a high visually detectable color change for the selective detection of mercury ions, while the unmodified green synthesized silver nanoparticles did not show any remarkable color change. The surface plasmon resonance absorption band of Chl-AgNPs was obtained at 440 nm area and decreased with a blue shift by the addition of mercury ion. Furthermore, an increase was detected at the absorption band of 290 nm attributed to the blank silver ions. The possible mechanism relies on the redox reaction between the silver nanoparticles and mercury ions. The detection limit of the Chl-AgNPs was obtained as 2.7 µM and 60 µM by the UV-vis spectrophotometer and the naked eye, respectively. The response of Chl-AgNPs towards the mercury ion was excellent over other metal ions. The functionalization of green silver nanoparticles using chlorophyll pigment provided colorimetric detection advantage by the naked eye. The proposed method was successfully applied to river water samples spiked with known concentrations of mercury ions at the recovery values between 94 to 97%