| Summary: | Carbon dots (CDs) are an emerging nanomaterial that has been used in multidisciplinary areas of energy, environmental and medical fields as a result of its low toxicity, stable and tunable photoluminescence, aqueous solubility and high biocompatibility. In recent years developments in CDs using biomass has gained attention due to the lower cost, high availability and environmentally friendly nature of the latter. In this report durian shell waste (DSW), a lignocellulosic biomass is used to synthesize high fluorescent CDs. Generally, pure cellulose based CDs exhibit poor photoluminescence. However, it is hypothesized that the naturally present oxygen and nitrogen groups in DSW can contribute to the fluorescent enhancement and even provide necessary anchoring points for external doping agents. Thus, this study had aimed to develop a facile synthesis method to convert DSW to high fluorescent CDs, conduct an extractive analysis to identify the various functional groups present in DSW and evaluate the contribution from these functional groups to the photoluminescence, introduce existing and novel dopants to evaluate the effectiveness of these dopants to the optical properties of CDs and finally use the synthesized CDs as a sensor to detect aqueous pollutants.
Based on the results, a facile one-pot hydrothermal method was developed to produce CDs from DSW which showed a quantum yield (QY) two times that of pure cellulose. Through the extractive analysis, it was identified amino and carboxylic acids were pivotal to the higher fluorescence. DSW has a higher response to amino groups and this was subsequently used to develop nitrogen doped CDs with a QY of 12.9%. Moreover, doping DSW with nitrogen-metal mix subsequently yielded a QY of 28.9%, which was one of the highest recorded cellulose biomass QYs reported from a one pot hydrothermal technique. The CDs were successfully used as sensors for Fe3+, Mn7+ ions and the antibiotic tetracycline in aqueous systems. Based on the sensitivity and selectivity tests, CDs showed high selectivity for the targeted species and good linear models for Fe3+, Mn7+ and tetracycline were developed with a lowest detection limit of 128 nM, 46.8 nM and 75 nM respectively. The sensing performances of DSW based CDs showed better sensitivity compared with the current fluorescent probes. The mechanisms governing the sensing were further explored. To validate the CDs sensing capabilities, the sensors were applied in real water systems to detect the targeted analyte and the results exhibited good recoveries with acceptable standard deviations.
It could be concluded DSW has the potential to be used as a carbon precursor for CD synthesis. The resulting material can be used as an efficient fluorescent probe to detect aqueous pollutants.
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