Strong Amphoteric Adsorption of Reactive Red-141 onto Modified Orange Peel Derivatives: Optimization, Characterization, and Mechanism.

Abstract

This study investigates the adsorption performance of Reactive Red-141 (ReR-141) using three modified orange peel derivatives: raw orange peel (ROP), oil-free orange peel (NOOP), and cellulose extract (CE). The adsorbents were prepared through sequential treatments and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy to investigate their surface morphology and functional groups. Batch adsorption experiments were conducted under varying conditions of pH, temperature, time, and adsorbent amount. NOOP displayed the highest adsorption capacity (99.72% removal efficiency), followed by CE (86.99%) and ROP (77.55%), under optimal conditions. The adsorption kinetics followed a PSO model, while the equilibrium data were best described by Langmuir, indicating monolayer adsorption. Thermodynamic factors confirmed that the process was self-generated and primarily determined by physisorption. Desorption studies using 0.2 M NaOH demonstrated that NOOP retained 98.16% efficiency after three cycles, indicating its strong reusability. The adsorption mechanism is determined by different interactions, such as electrostatic forces, H-bonding, and π-π stacking. These findings suggest that orange peel derivatives, particularly NOOP, serve as optimal and environmentally sustainable adsorbents for the yield of ReR-141 from synthetic aqueous media.