Abstract
Fluorescence quenching is a valuable tool to gain insight about dynamic changes of fluorophores in complex systems. Graphene (G), a single-layered 2D nanomaterial with unique properties, was dispersed in surfactant aqueous solutions of different nature: non-ionic polyoxyethylene-23-lauryl ether (Brij L23), anionic sodium dodecylsulphate (SDS), and cationic hexadecyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB). The influence of the surfactant type, chain length and concentration, G total concentration and G/surfactant weight ratio on the fluorescence intensity of vitamin B2 (riboflavin) was investigated. The quality of the different G dispersions was assessed by scanning and transmission electron microscopies (SEM and TEM). A quenching phenomenon of the fluorescence of riboflavin was found for G dispersions in all the surfactants, which generally becomes stronger with increasing G/surfactant weight ratio. For dispersions in the ionic surfactants, the quenching is more pronounced as the surfactant concentration raises, whilst the non-ionic one remains merely unchanged for the different G/Brij L23 weight ratios. More importantly, results indicate that DTAB solutions are the optimum media for dispersing G sheets, leading to an up to 16-fold drop in the fluorescence intensity. Understanding the mechanism in fluorescence quenching of G dispersions in surfactants could be useful for several optical applications.
Highlights
In recent years, carbon nanomaterials have been investigated due to their outstanding properties
Regarding to the surfactant solutions, the non–ionic surfactant hardly affects the fluorescence of the vitamin, whilst a drop in intensity is found for the ionic surfactants, ascribed to stronger vitamin-surfactant interactions
A remarkable quenching phenomenon has been observed for G dispersions in all the surfactants, both nonionic and ionic, given that all of them act as dispersing agents, promoting the exfoliation of G flakes in the solutions
Summary
Carbon nanomaterials have been investigated due to their outstanding properties. Since its discovery in 2004 [3,6] it has been used in many applications in analytical chemistry [7,8], for the design of electrochemical and optical sensors [9,10,11]. These exceptional properties make G an ideal filler for reinforcing polymeric matrices, and the resulting nanocomposites have similar or even better performance than those incorporating carbon nanotubes (CNTs) [12]. Given that G is a hydrophobic material, for certain applications it needs to be dispersed in liquids such as organic solvents [13] or water, frequently via ultrasonication with the aid of dispersing agents [14]
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