Smart carbon dots as chemosensor for control of water contamination in organic media

Abstract

A novel nanoprobe was synthesized by functionalizing gluthatione/citric acid–carbon dots (CDs) with a benzo-isoquinolin-based molecule, methyl 3-(4-(2-(5-((methylsulfonyl)oxy)pentyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)piperazin-1-yl)propanoate (water chemosensor, WCS), to detect trace amounts of water in non-aqueous media via on-off fluorescence. The design and synthesis of the free molecule WCS and the functionalized nanoprobe (CD-WCS) are described in detail and as well as their full characterization by different spectroscopic methods. WCS was found to be an excellent indicator of pH in aqueous media and exhibited, in solvents of different polarity, solvatochromic behaviour. On the other hand, the modified fluorescence intensity of CD-WCS was found to be an excellent indicator for water in non-aqueous media (organic solvents and oil-based lubricants). In these media, CD-WCS showed weak fluorescence intensity due to a photoinduced electron transfer (PET) process. Sequential addition of trace amount of water led to revival of CD-WCS fluorescence intensity. The fluorescence on-off mechanisms are proposed for WCS in aqueous media as well as for CD-WCS in non-aqueous media. The analytical performance characteristics of CD-WCS showed a limit of detection for water of 0.00021 % (v/v) in toluene and 0.00014 % v/v in base-oil lubricant. The potential application of CD-WCS as chemosensor of water contamination in oil-based lubricants as well as green anti-wear/anti-friction lubricant additive are outlined.