Materials, Methods & Technologies, Volume 19, 2025

Rezumat: In this study, a method for the removal and degradation of colored eluents after desorption from chemically functionalized cellulosic materials was developed. Waste hemp fibers were transformed into an efficient cellulosic adsorbent through a two-step process involving delignification and subsequent quaternization with betaine hydrochloride-urea (QDHF-BHU). The fibers were first subjected to delignification, followed by quaternization using the synthesized Deep Eutectic Solvents (DES), betaine hydrochloride-urea. The adsorbent was evaluated for the removal of anionic dyes, including Metanil Yellow (MY) and Congo Red (CR), in a batch adsorption system. Structural and chemical characterization of the modified fibers was performed using Scanning Electron Microscopy (SEM), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), porosity measurements, and point of zero charge (pHpzc) analysis. Pore size was determined through image analysis and the dry-wet weight method. The adsorption process was found to be endothermic and spontaneous, achieving high adsorption capacities (qm) at 25°C, with the optimal pH for adsorption being 7. Kinetic studies indicated that the adsorption followed both pseudo-first-order (PFO) and pseudo-second-order (PSO) models. After adsorption, the desorbed dyes were subjected to photocatalytic degradation using zinc oxide as a catalyst, with high and rapid decolorization efficiency, particularly for Metanil Yellow. The photocatalytic process ensured that the treated water posed minimal environmental risk. This work demonstrates the application of green chemistry principles in the functionalization of waste lignocellulosic materials and the subsequent degradation of colored eluents, offering an eco-friendly and efficient method for water purification and wastewater treatment.