Cationic waste hemp fibers-based membrane: Case study of anionic pollutants removal through environmentally friendly processes

Abstract

In this study, waste hemp fibers were transformed into cationically modified lignocellulosic adsorbent through a three-step process. First, a delignification/defibrillation pretreatment was performed, followed by quaternization of fibers using the synthesized ionic liquid chlorocholine chloride-urea (CCC-U). Pressure-assisted cross-linking of modified fibres, using a citric acid, produced new membrane (CCC-UHM). The removal of anionic dyes (Acid Yellow 36 (AY36), Congo Red (CR), Acid Green 25 (AG25), and Acid Blue 92 (AB92)), and oxyanions (As(V) and Cr(VI)) was tested in batch and column system. The structural characteristics and chemical properties of the syntesised materials were investigated by SEM, FTIR, Raman, XPS, XRD, specific density, porosity and point of zero charges analysis. The endothermic and spontaneous equilibration of the system resulted in high capacity (qm), i.e., 302.9 mg g−1 (AY36), 456.8 mg g−1 (CR), 812.8 mg g−1 (AG25), 587.6 mg g−1 (AB92), 107.9 mg g−1 (As(V)), and 67.84 mg g−1 (Cr(VI)) at 25 °C, using the Langmuir model. The optimum pH for the adsorption process was 7. The multi-cycle adsorption/desorption process was followed by either decolorization, using laccase from M. thermophile expressed in Aspergillus oryzae (Novozym 51,003® laccase) immobilized on amino-modified fibers as biocatalyst, or photocatalytic degradation, in the presence of zinc oxide. The high decolorization efficiency (96%) observed for AG25 and AB92 underscores the considerable potential of laccase immobilized preparations as sustainable and eco-friendly approach for treating dye-contaminated wastewater. Photodegradation process provided low environmental threat of processed water, and biodegradabilty of exhausted membrane confirmed the circularity of the developed technology with implemented principles of sustainability.