Fluorescent Carbon Quantum Dots (FCQDs), a new generation of carbon nanomaterials, have attracted a lot of attention throughout the years. This paper applied a straightforward and environmentally beneficial way to create water-soluble FCQDs hydrothermally from coconut shells. The as-prepared FCQDs have desirable functional groups and exhibit strong blue-emitting fluorescence with a relative quantum yield of 0.6 and 0.7%. The optical bandgap of FCQDs is calculated using UV–Vis spectra to be between 3.9 and 4.4 eV. Optical studies show that FCQDs have good fluorescence properties when excited at 360 nm. Whereas the fluorescence decay lifetime using TCSPC are 1.6–0.99 ns. The synthesized FCQDs were found by HRTEM to have a spherical shape and a particle-size distribution of 2.8–5.4 nm. As-prepared FCQDs has a very low hemotoxicity of 0.5 to 1.3%, which indicates that they have acceptable biocompatibility and are not hazardous. According to the DPPH antioxidant data, FCQDs had a stronger antioxidant activity compared to earlier reports. These important characteristics enable its applications in biomedical, food packaging, fluorescence imaging, photocatalysis, and sensing. The enhanced antioxidant characteristics of the produced FCQDs make them appropriate for use in biomedical, bioimaging, chemical, and industrial applications. The as-synthesized FCQDs were used for the detection of ferric ions with good selectivity.

Enhancing the capacitive deionization performance requires the inner structure expansion of porous activated carbon to facilitate the charge storage and electrolyte penetration. This work aimed to modify the porosity of coconut-shell activated carbon (AC) through CO2 activation at high temperature. The electrochemical performance of CO2- activated AC electrodes was evaluated by cyclic voltammetry, charge/discharge test and electrochemical impedance spectroscopy, which exhibited that AC-800 had the superior performance with the highest capacitance of 112 F/g at the rate of 0.1 A/g and could operate for up to 4000 cycles. Furthermore, in the capacitive deionization, AC-800 showed salt removal of 9.15 mg/g with a high absorption rate of 2.8 mg/g min and Ni(II) removal of 5.32 mg/g with a rate close to 1 mg/g.min. The results promote the potential application of CO2- activated AC for desalination as well as Ni-removal through capacitance deionization (CDI) technology.

In this work, a simple nonenzymatic glucose sensor has been proposed based on coconut shell charcoal (CSC) modified nickel foil as working electrode in a three-electrode electrochemical cell. Charcoal was prepared by the pyrolysis of coconut shells. The most important advantages of coconut shells are cost-effectiveness and their abundance in nature. The morphology and phase of the CSC powder were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical performance of the CSC powder coated Nickel foil electrode was investigated by cyclic voltammetry and chronoamperometry. The sensor shows a higher sensitivity of 2.992 mA cm−2 mM−1 in the linear range of 0.5–5.5 mM and slightly lower sensitivity of 1.1526 mA cm−2 mM−1 in the range of 7–18.5 mM glucose concentration with a detection limit of 0.2 mM. The anti-interference property of CSC powder also was investigated and found that the response of interfering species was less significant compared to glucose response. The proposed sensor offers good sensitivity, wide linear range, and a very low response to interfering biomolecules.

Activated carbon was synthesized from coconut shells. The Brunauer, Emmett and Teller surface area of the synthesized activated carbon was found to be 1640 m2/g with a pore volume of 1.032 cm3/g. The average pore diameter of the activated carbon was found to be 2.52 nm. By applying the size-strain plot method to the X-ray diffraction data, the crystallite size and the crystal strain was determined to be 42.46 nm and 0.000489897, respectively, which indicate a perfect crystallite structure. The field emission scanning electron microscopy image showed the presence of well-developed pores on the surface of the activated carbon. The presence of important functional groups was shown by the Fourier transform infrared spectroscopy spectrum. The adsorption of methyl orange onto the activated carbon reached 100% after 12 min. Kinetic analysis indicated that the adsorption of methyl orange solution by the activated carbon followed a pseudo-second-order kinetic mechanism (R2 > 0.995). Therefore, the results show that the produced activated carbon can be used as a proper adsorbent for dye containing effluents.