Novel chitosan--[DBN][AcOH] beads and their application in removing malachite green from an aqueous solution

The persistent presence of synthetic dyes in industrial effluents poses severe environmental and health hazards, particularly due to their complex aromatic structures and resistance to conventional treatment. Chitosan (Ch) is regarded as a promising, accessible and cost-effective adsorbent derivable from by-product of seafood industry and other sources. In this study, novel chitosan–protic ionic liquid (Ch-[DBN][AcOH]) beads were synthesised using 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBN][AcOH]) to develop a green and biodegradable adsorbent for efficient removal of malachite green (MG) from aqueous solutions. The synthesized materials were thoroughly characterized using Fourier-Transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) surface analysis. The BET results revealed a surface area of 1.0096 m²/g, a total pore volume of 0.001451 cm³ /g, and a mean pore diameter of 10.38 nm, indicating a mesoporous structure consistent with Type IV isotherm and H4-type hysteresis loop. Adsorption studies demonstrated that the MG removal efficiency was influenced by pH, initial dye concentration, contact time, temperature, ionic strength and dosage. The equilibrium adsorption data best fitted the Langmuir isotherm model, suggesting monolayer adsorption with a maximum capacity (80.6401–106.6561 mg/g) influenced by bead composition. Kinetic modelling can be described by pseudo-second order and Elovich models. Thermodynamic parameters further indicated that the adsorption process was spontaneous and exothermic. Overall, Ch-[DBN][AcOH] beads synthesised via environmentally benign routes offer a promising and reusable adsorbent for dye-laden wastewater treatment.