Green Preparation of Fluorescent Carbon Dots from Durian Shell Waste for Highly Sensitive Detection of Fe3+ Ions

Carbon dots (CDs) are a novel class of nanomaterials that provide unique optical and electronic properties including tunable photoluminescence, low photobleaching, easy functionalization, aqueous solubility and low toxicity. Production of CDs from cellulose biomass precursors has gained attention over the years due to positive economic and environmental impact. However, the photoluminescence yield of cellulose-based CDs is low in the absence of modification additives. In this study, CDs were produced from Durian shell waste (DSW) in a one-pot process without any modification agents with a mass yield of 13.9% and quantum yield of 6.2%. This was two times higher compared to that of CDs derived from pure cellulose. 90% of the DSW comprised cellulose, hemicellulose and lignin while the remainder consisted of extractives such as carboxylic acids, phenolic compounds, amino acids, aldehydes and esters. These extractives enhanced the oxygenated functional groups in DSW improving the photoluminescence of CDs. The maximum emission was at 436 nm at an excitation wavelength of 360nm and was stable over a wide range of pH and chloride concentration and was resistant to photobleaching. The particles were well dispersed and quasi-spherical with an average particle diameter of 3.2 nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy confirmed the presence of oxygen and nitrogen functional groups on the surface.

The CDs showed high selectivity towards Fe³⁺ and a linear relationship was developed over a concentration range of 0-20 µM with a detection limit of 128 nM (S/N=3). Three actual water samples (lake water, sea water, tap water) were used to validate the model and the relative recoveries of 98.9 -108.6% and an RSD of <4.11%.