Design of sodium alginate/soybean extract beads loaded with hemp hurd and halloysite as novel and sustainable systems for methylene blue adsorption

This work concerns the fabrication of a green, novel, and sustainable system for the efficient removal of methylene blue from aqueous solutions. The proposed system is obtained by using sodium alginate/soybean extract blend reinforced with hemp hurd from agro-waste resources and halloysite nanotubes (HNTs). The ionotropic gelation methodology, using calcium chloride as a crosslinking agent, was easily applied to obtain composite beads. The adsorption studies were carried out up to 24 h using methylene blue as model system. The effect of HNTs on adsorption capacity was investigated proving that an increase in inorganic filler determined an increase in adsorption capacity from 32 to 49 mg/g by adding 35% wt of HNTs. The experimental data were fitted through four different models, demonstrating that the adsorption phenomenon is described by second-order process. Film diffusion and pore diffusion values were evaluated to better investigate the rate controlling mechanisms. Isotherm studies were then carried out to extrapolate thermodynamic parameters. Finally, a possible mechanism of adsorption was proposed on the basis of chemisorption mechanism. Here, we demonstrate that the proposed novel, inexpensive, and sustainable composite material obtained from agro-waste resources has high efficiency in removing a cationic dye from wastewaters.