Fluorescence of Paraquat by Immobilization on Clay: Theory and Experiments

Abstract

Paraquat (PQ) is a widely used herbicide known forits environmental persistence and low susceptibility to photo-chemical degradation. Despite being nonfluorescent by nature,recent studies have discovered that PQ exhibits fluorescence whenadsorbed on bentonite-type clays. This phenomenon is highlyattractive due to its potential application in environmentalmonitoring and remediation efforts. In this study, we investigatethe fluorescence behavior of PQ on montmorillonite clay (MMT)using a combination of first-principles calculations and experiments.Our results demonstrate that the insertion of PQ into the MMTstructure is energetically favorable, causing minimal alteration inthe clay’s interlayer distance. Additionally, our analysis reveals that PQ adopts a planar geometry within the MMT layers, withrestricted inter-ring rotation. By examining the electronic structure of PQ in both the basal and excited states, we gain insight intothe fluorescence mechanism of the system, which agrees well with experimental results.