Synthesis and application of carbon dots towards Fluorescence detection of polycyclic aromatic Hydrocarbons

Abstract

Polycyclic aromatic hydrocarbons are organic pollutants that pose substantial health risks. Consequently, there has been a need for development of cost-effective and highly sensitive analytical techniques for monitoring these compounds. The study reports a rapid, facile, non-toxic and cheap strategy for synthesizing fluorescent CDs from monkey orange (Strychnoscocculoides) fruit for detecting and quantifying fluoranthene and anthracene in water samples. Synthesis of CDs involved hydrous pyrolysis (hydrothermal) of powdered monkey orange shells in a furnace at 200 ℃ for 3 h. Next followed purification steps that involved ultra-sonication, centrifugation, filtration and dialysis of the resultant solution. The synthesized CDs possessed high photoluminescence properties. They showed blue fluorescence when irradiated with Ultra-violet radiation at 365 nm. Characterization of the prepared CDs included extensive review of their optical properties, morphology and structure. Scanning electron microscopy and atomic force microscopy results showed uniform dispersion of the carbon dots with amorphous morphology and little signs of aggregation. The average particle size of the prepared CDs was calculated to be 3.6 nm. Fourier transform infra-red spectroscopy showed existence of hydroxyl, carbonyl, alkene, alkane, ester and ether functional groups. X-ray diffraction revealed the structure of CDs as amorphous with poor crystallinity. Raman spectroscopy results also showed the presence of turbostratic carbon. The synthesized CDs exhibited good solubility in water and excellent stability in aqueous, acidic and alkaline environments. Detection of anthracene and fluoranthene occurred through fluorescence enhancement whereby there is energy transfer between sensor and the specie. The figures of merit being the limit of detection and quantification for the target analytes were ranging from 1.4 μM to 2.0 μM and 4.3 μM to 6.1μM respectively. Moreover, the method yielded percentage recoveries ranging from 95% to102%.