Cellulose nanocrystal-alginate hydrogel beads as novel adsorbents for organic dyes in aqueous solutions

A new generation of recyclable adsorbents comprising of cellulose nanocrystals and alginate (CNC-ALG) with superior adsorption capacity was developed. Sustainable nanomaterials like cellulose nanocrystals derived from pulp fibres and cellulosic biomass are ideal systems to remove contaminants in our water systems. Their use will reduce our dependence on adsorbents, such as activated carbon that contribute to greenhouse gases production. Adsorption characteristics of CNC-ALG hydrogel beads were evaluated using batch adsorption studies of methylene blue (MB) in aqueous solution. The influence of various parameters, such as contact time, adsorbent dosage, initial dye concentration, pH, temperature, ionic strength, crosslinking time and bead size on the MB adsorption were investigated. Thermodynamic analyses confirmed that the adsorption process is spontaneous and exothermic. The kinetics and mechanism of adsorption were best described by a pseudo-second order kinetic model and intra-particle diffusion model. Equilibrium adsorption data fitted well to the Langmuir adsorption isotherm yielding a maximum adsorption capacity of 256.41 mg/g, which is comparable to activated carbon. We demonstrated that after five adsorption-desorption cycles, the removal efficiency of MB remained at similar to 97 %, and the CNC-ALG hydrogel beads are effective adsorbents for the removal of organic dyes from wastewaters.