Coconut Coir-Derived CC@NiO–CuO Nanocomposite for Enhanced Removal of Crystal Violet Dye From Wastewater

Abstract

The increasing release of synthetic dyes into aquatic systems poses significant ecological and health risks due to their toxicity and persistence. This study investigates the effectiveness of a novel nanocomposite synthesized from coconut coir and nickel oxide–copper oxide (NiO–CuO) nanoparticles for the removal of crystal violet (CV) dye from water. The composite's physicochemical properties were characterized using powder X-ray diffraction (P-XRD), Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analysis. A series of adsorption experiments was conducted to optimize key process parameters, including adsorbent dosage, contact time, initial dye concentration, pH, sample volume, and temperature. The nanocomposite exhibited excellent adsorption efficiency, achieving approximately 99% removal of CV at pH 6 with a 5 mg adsorbent dose, 30-min contact time, and 15 ppm dye concentration. The adsorption process conformed to the Temkin isotherm model, indicating a decrease in sorption energy with increasing surface coverage due to adsorbent–adsorbate interactions. Kinetic studies revealed that the process followed a pseudo-second-order model, suggesting the predominance of chemical adsorption mechanisms. Thermodynamic analysis showed a negative Gibbs free energy (−ΔG), along with positive enthalpy (ΔH) and entropy (ΔS) values, confirming that the adsorption process was spontaneous, endothermic, and associated with increased randomness at the solid–liquid interface. This study underscores the potential of biomass-derived nanocomposites as sustainable and efficient materials for dye removal from wastewater.