Abstract
The current research mainly focuses on transforming low-quality waste into value-added nanomaterials and investigating various ways of utilising them. The hydrothermal preparation of highly fluorescent N-doped carbon dots (N–CDs) was obtained from the carboxymethylcellulose (CMC) of oil palm empty fruit bunches and linear-structured polyethyleneimines (LPEI). Transmission electron microscopy (TEM) analysis showed that the obtained N–CDs had an average size of 3.4 nm. The N–CDs were monodispersed in aqueous solution and were strongly fluorescent under the irradiation of ultra-violet light. A detailed description of the morphology and shape was established using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was shown that LPEI were successfully tuned the fluorescence (PL) properties of CDs in both the intrinsic and surface electronic structures, and enhanced the quantum yield (QY) up to 44%. The obtained N–CDs exhibited remarkable PL stability, long lifetime and pH-dependence behaviour, with the excitation/emission maxima of 350/465.5 nm. Impressively, PL enhancement and blue-shifted emission could be seen with the dilution of the original N–CDs solution. The obtained N–CDs were further applied as fluorescent probe for the identification of Cu2+ in aqueous media. The mechanism could be attributed to the particularly high thermodynamic affinity of Cu2+ for the N-chelate groups over the surface of N–CDs and the fast metal-to-ligand binding kinetics. The linear relationship between the relative quenching rate and the concentration of Cu2+ were applied between 1–30 µM, with a detection limit of 0.93 µM. The fluorescent probe was successfully applied for the detection of Cu2+ in real water. Moreover, a solid-state film of N–CDs was prepared in the presence of poly (vinyl alcohol) (PVA) polymer and found to be stable even after 72-h of continuous irradiation to UV-lamp. In contrast to the aqueous N–CDs, the composite film showed only an excitation independent property, with enhanced PL QY of around 47%. Due to the strong and stable emission nature of N–CDs in both aqueous and solid conditions, the obtained N–CDs are ideal for reducing the overall preparation costs and applying them for various biological and environmental applications in the future.
Highlights
Carbon dots (CDs), a new member of the fluorescent carbon nanostructures family, with sizes of less than 10 nm, have drawn considerable attention among researchers since their first fundamental report [1]
Dual precursors, including the usage of cellulose/urea [18], glucose/polyethyleneimine (PEI) [19] and microcrystalline cellulose/ethylenediamine (EDA) [20] were used for the production of N-doped carbon dots (N–CDs), in which one serving as the carbon source, the other as nitrogen source or passivation agent
We demonstrated the use of low-cost wastes of carboxymethylcellulose (CMC) as the carbon material for the production of fluorescent CDs since various physical characteristics of CMC resulted in different degrees of polymerization
Summary
Carbon dots (CDs), a new member of the fluorescent carbon nanostructures family, with sizes of less than 10 nm, have drawn considerable attention among researchers since their first fundamental report [1]. An N-doping source, known as an electron donator, has been shown to be the most convenient element on the stimulating of electronic states of the carbonaceous material by introducing new energy states corresponding to the N-dopants [5] In spite of their promising optical properties and low-toxic behaviour, several drawbacks limit their analytical applications, such as long duration synthesis processes from 7–72 h [16,19,20,21,22,23,24,25,26,27,28,29,30], low quantum yield of using sole precursors [10,14,19,23,24,27,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47], or efficient quantum yield along with long duration synthesis process even after doping CDs with various heteroatoms [16,20,21,22,25,26]. The ease of the processing and no need for high temperature and long duration synthesis processes is of great interest
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