Adhesion of methylene blue and malachite green to the surface of copolymer synthesized by grafting itaconic acid onto cellulose backbone – experimental and computational studies

Abstract

This report describes the graft copolymerization of itaconic acid onto cellulose isolated from plantain trunk, using ammonium persulfate as initiator. Optimum grafting condition was established at 0.025 mol/L initiator concentration, 60 °C, 60 min grafting time and 3 g monomer mass. Characterization of the bio-materials indicated the success of the cellulose isolation and the grafting processes. At optimum grafting condition, about 34.0% grafting yield was obtained. With 25 mg of the co-polymer (PTC-g-IA), MB and MG uptake were 72.5 and 56.9 mg/g, respectively. These values represent about 2-fold sorption enhancement when compared with ungranted cellulose (PTC). The sorption process was influenced by solution pH, contact time, dye concentration and temperature. Modeling of the adsorption process indicated that the Pseudo-second-order kinetic model with R2 of unity and the Langmuir isothermal model (R2: 0.9622 (MB) and 0.9880 (MG)) best described the sorption process. Thermodynamic study described a feasible, spontaneous and exothermic process. Free energy value of 7.07 kJ/mol, and ΔH° values of < 20 kJ / mol , suggested a physisorption process. This was corroborated by the computational study which indicated non-covalent interactions between atoms in the dyes and the adsorbents. These interactions were stronger with the co-polymer. The interaction energies calculated for the dye-adsorbent interaction (-38.215, −52.868, −47.299 and −57.848 kJ/mol for PTC-MB, PTC-MG, PTC-g-IA-MB and PTC-g-IA-MG, respectively) show stronger interactions between PTC-g-IA and the dye molecules compared to pure cellulose in line with experimental observations. In overall, this study portrays the cellulose-based co-polymer as having the potential of easily removing MB and MG from wastewater.