Adsorption of anionic dye from aqueous environment using surface-engineered Zn/Cu hydroxy double salt-based material:...

Herein, ethylene glycol (EG)-modified Zn/Cu hydroxy double salts (HDS) were synthesized using a facile synthetic approach. The formation of layered structure and presence of EG in the interlayer region were confirmed using PXRD and FTIR techniques. Furthermore, XPS analysis was used to confirm presence of metal ions in synthesized HDS. The surface area and pore size diameter of the HDS was found to be 32.30 m² g^-1 and 2.22 nm, respectively, using BET. The role of HDS was evaluated for its potential application as a sorbent for Congo red (CR) dye uptake. Batch studies were conducted to examine the impact of key variables, i.e., pH, time, adsorbent dosage and dye concentration on adsorption efficiency of HDS. Linear-nonlinear isotherm and kinetic models were employed for detailed analysis of experimental data. Langmuir, Freundlich and Temkin isotherm models were subsequently utilized to fit equilibrium data, among which Langmuir demonstrated to be most accurate. The maximum monolayer adsorption capacity estimated using Langmuir model was computed to be 181.81 mg g^-1. The kinetic data follows pseudo-second-order model having good R² value (0.999). Additionally, thermodynamic study suggested spontaneous and endothermic nature of adsorption process having reusability up to 5 cycles with removal efficiency more than 85%.