Hydroxyl-modified chitosan nanofiber beads for sustainable boron removal and environmental applications

The removal of boron from wastewater is essential for protecting environmental health and supporting sustainable urbanization by preventing toxic accumulation in ecosystems. Existing adsorption technologies face challenges such as limited capacity, slow kinetics, high regeneration costs, and reduced efficiency due to adsorbent saturation. This study develops an eco-friendly adsorbent (CGCNF beads) by modifying chitosan nanofibers with d-(+)-glucono-1,5-lactone (GL) to enhance boron removal. The adsorbents were characterized by ¹H NMR, Cosy NMR, SEM, BET, TGA, FTIR, and colloidal titration. Notably, the hydroxyl functional groups grafted onto chitosan nanofibers (49.5%) were found to be three times higher than those on chitosan flakes (16.4%). The CGCNF beads followed the Langmuir model and pseudo-second-order model with a maximum boron adsorption capacity of 6.05 mg g^-1, surpassing commercial Amberlite IRA-743 resin (5.73 mg g^-1). The adsorption process of CGCNF beads was much faster, reaching equilibrium in 120 minutes, compared to 720 minutes for adsorbent-based chitosan flakes. The adsorption capacity is significantly enhanced by either elevating the pH levels or introducing salts such as NaCl, KCl, CaCl₂, or MgCl₂. The beads showed robust regeneration, maintaining 65.1% of their adsorption capacity after 20 cycles. The developed CGCNF beads also demonstrate simultaneous high-efficiency removal of B(iii) and As(iii) ions from local wet flue gas desulfurization (FGD) wastewater at rates of 94.5% and 100%, respectively, providing a sustainable solution for wastewater contamination.