Eriochrome Black T sensing using silver nanoparticle-reduced graphene oxide composite via luminescent “turn-off” mechanism and its biosorption on guava (Psidium guajava) leaf powder

We report label-free sensitive and selective detection of Eriochrome Black T (EBT) in water using luminescent “turn-off” mechanism of silver nanoparticle-reduced graphene oxide composite. Silver nanoparticle-reduced graphene oxide composite was synthesized by simple and cost-effective reflux method utilizing aqueous extracts of Psidium guajava as a reducing agent and silver nitrate and graphene oxide as precursors. Silver nitrate facilitates the formation of defects in graphene in the form of graphene quantum dots. The average size of graphene quantum dots and the silver nanoparticles in the composite is 8.9±0.2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$8.9\pm 0.2$$\end{document} nm and 27.5±0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$27.5\pm 0.5$$\end{document} nm, respectively. By activating the plasmonic field at 350 nm excitation, these particles in the composite help in efficient detection of the dye via strong interaction with the graphene surface. The linear calibration plot for the intensity ratio was obtained with the optimized concentration of EBT between 0.1 and 7.5 μM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {M}$$\end{document}. This composite material selectively detects EBT where a detection limit as low as 6.9 μM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {M}$$\end{document} is achieved. In addition, the kinetics of adsorption of EBT on Psidium guajava powder are also examined. The interaction between the dye and the adsorbent follows pseudo-second-order kinetics with equilibrium adsorption capacity of 25.88 mg/g and 14.56 mg/g for 2 g/L and 5 g/L of adsorbent dose, respectively.