Juniperus hydrochar decorated with chitosan/zinc oxide nanocomposite for efficient removal of malachite green dye from water

Water pollution is a pressing global concern that adversely affects ecosystems and public health. Therefore, there is a growing interest in developing affordable and high-performance adsorbents for the removal of dyes. In this research, a new JPHC@ZnO@CS composite was synthesized via a one-pot hydrothermal method by integrating chitosan (CS) and zinc oxide (ZnO) nanoparticles with Juniperus-derived hydrochar (JPHC), aiming to efficiently remove malachite green (MG) dye from polluted solutions. The obtained composite was analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, energy-dispersive X-ray analysis, thermogravimetric analysis, surface area, and surface charge. The influence of pH, adsorption time, dye concentration, adsorbent dosage, and temperature on MG removal was investigated. Under optimized conditions (pH 7.2, 300 min, 45 °C, and 0.02 g adsorbent), a removal efficiency of 97.04% was achieved. Adsorption kinetics adhered to a pseudo-second order, while equilibrium data were best described by the Dubinin–Radushkevich isotherm. The Langmuir formula predicted a maximum capacity of 1251.5 mg/g. Mechanistic insights suggest that adsorption predominantly occurs through chemical interactions, involving ionic interactions, H-bonding, π–π stacking, and electrostatic interactions. The thermodynamic analysis confirmed the spontaneous and endothermic process. Reusability tests demonstrated removal efficiency greater than 90% after four cycles. Overall, the JPHC@ZnO@CS composite showed strong potential as an effective and low-cost adsorbent for treating dye-contaminated wastewater.