Congo red dye adsorption onto cationic amino-modified walnut shell: Characterization, RSM optimization, isotherms, kinetics, and mechanism studies

Abstract

Congo red (CR) dye contamination in aquatic ecosystems often threatens human and aquatic health. This work synthesized a chemically modified, cationic amino-modified walnut shell (CMWS) adsorbent to treat CR dye-contaminated water. Central composite design (CCD) using standard response surface methodology design was performed to understand optimal conditions for removing dye with minimal experimentation. Maximum removal efficiency (94.12%) was achieved through CMWS than the raw walnut shell (RWS). Hydrogen bonding, pore filling, and electrostatic attractions effectively removed CR dye using CMWS. To understand cost-effectiveness and practical applicability, an adsorption-desorption analysis of CMWS was performed up to the third cycle with a removal efficiency of 82.18% with biomass loss of 26%. This study recommends CMWS as a potential adsorbent for CR dye removal and is worth investigating in the future.