Fluorescence Quenching and Highly Selective Adsorption of Ag<sup>+</sup> Using N-Doped Graphene Quantum Dots/Poly(vinyl alcohol) Composite Membrane
Ting Wang, Fan Yang, Liang Zhang, Zuobin Tang, Wenwen Liu, Lvling Zhong, Zhixian He, Shouning Chai
Abstract
Fabrication of composite adsorbents with exceptional fluorescence performance has attracted increasing attention. In this study, a nitrogen-doped graphene quantum dots (NGQDs)/poly(vinyl alcohol) (PVA) composite membrane (NGQDs-PVA) with high adsorption selectivity and fluorescence quenching for Ag+ was prepared via simple cross-linking. The SEM characterization showed that the NGQDs were uniformly distributed in PVA, indicating that the material exhibited fluorescence characteristics of quantum dots. C–O, −COOH, −NH2, and −OH functional groups in NGQDs-PVA complexed with a great amount of Ag+, and −NH– reduced a small amount of Ag+ to Ag0. The pseudo-first-order kinetic and Langmuir models were used to describe the adsorption process of heavy metals using the composite. The maximum adsorption capacity was 317.35 mg/g (Langmuir model fitting, pH = 4, T = 40 °C). When the fluorescence of NGQDs-PVA was quenched as the number of Ag+ adsorbed increased, the change in fluorescence intensity was used to qualitatively quantify the adsorption process.