Loading walnut shell powder into polymeric matrix of chitosan for enhanced cationic methyl violet 2B dye removal: Process optimization and adsorption mechanism.

Herein, chitosan (CHS) biopolymer was modified with walnut shell (WS) powder by loading different ratios (25 % and 50 %) of WS into the polymeric matrix of CHS to yield a promising bio-adsorbent for cationic methyl violet 2B (MV 2B) dye removal. The best loading ratio of the WS into the polymeric matrix of CHS was found to be 50 % CHS and 50 % WS (CHS/WS-(50:50)). A statistical optimization using Box-Behnken design (BBD) was applied to optimize the influence of three processing variables namely CHS/WS-(50:50) dose (0.02-0.1 g/100 mL), solution pH (4-10), and contact time (10-60 min) on the removal of MV 2B dye. The findings from the equilibrium and kinetic studies suggest that the MV 2B dye is adsorbed onto CHS/WS-(50:50) through a multilayer process according to the Freundlich isotherm model and the pseudo second order (PSO) kinetic model. Thus, CHS/WS-(50:50) shows a maximum adsorption capacity (qmax) of 103.3 mg/g for MV 2B dye removal. The adsorption mechanism of MV 2B involves interactions such as electrostatic forces, n-π stacking, and H-bonding. Reusability study indicates that the CHS/WS-(50:50) could effectively adsorb MV 2B for five cycles. This work introduces CHS/WS-(50:50) as a preferable bio adsorbent for removing harmful cationic dyes from contaminated water.