Efficient Copper Adsorption from Wastewater Using Silica Nanoparticles Derived from Incinerated Coconut Shell Ash

The coconut (Cocos nucifera) is renowned for its endocarp, commonly referred to as the coconut shell, which is believed to harbor a high concentration of silicon, potentially serving as a source for the production of silicon nanoparticles (SiO₂NPs). This study demonstrated the synthesis of SiO₂NPs derived from coconut shells and their application in the removal of metal contaminants, notably copper. SiO₂NPs were synthesized with a recovery rate of 25.6%, yielding a white powder through the sol–gel method. Analysis via ultraviolet–visible (UV–Vis) spectroscopy revealed an absorbance peak maximum at 345 nm, indicative of strong surface plasmon resonance, thus confirming SiO₂NPs formation. Morphological characterization conducted through field-emission scanning electron microscopy (FE-SEM) and field-emission transmission electron microscopy (FE-TEM) confirmed the smooth-faced nature of the SiO₂NPs, presenting finely clumped particles with an average size of 62 nm. Furthermore, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) analyses exhibited distinct peaks corresponding to oxygen (O) and silicon (Si), confirming SiO₂NPs formation. X-ray diffraction (XRD) analysis confirmed the amorphous nature of the particles, with a 25% weight loss observed at 500 °C according to thermogravimetric analysis (TGA). Assessment of the adsorption capacity for heavy metals from water solutions by spiking various copper (II) sulfate concentrations indicated the highest adsorption rate at 0.05 M copper, diminishing with increased copper ion concentrations. Evaluations utilizing different SiO₂NPs concentrations demonstrated optimal copper (Cu) removal efficiency at 0.2 g/mL SiO₂NPs.