Ternary layered double hydroxide and its calcined product for Indigo Carmine removal: experimental investigation, DFT, and modelling

In response to the challenge of dye pollution in wastewater, a remediation approach was established based on the synthesis of ZnCdAl-layered double hydroxides (ZnCdAl-LDH) through a coprecipitation method. The synthesis was performed with a molar ratio Zn:Cd:Al of 2:1:1, followed by calcination of the obtained material at 550 °C (ZnCdAl-O).The resulting products were analyzed by X-ray diffraction (XRD), scanning-electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR) and Brunauer–Emmett–Teller (BET) surface analysis. For the purpose of determining how contact time, initial dye concentration, solution pH and temperature affect adsorption performance, several batch adsorption tests were realized. The materials exhibited excellent adsorption capacities for Indigo Carmine (IC) dye, with maximum values of 340 mg g −1 for ZnCdAl-LDH and 674 mg g −1 for ZnCdAl-O at 55 °C. The equilibrium adsorption times were determined to be 120 min for ZnCdAl-LDH and 240 min for ZnCdAl-O. Kinetic study revealed that the adsorption process was explained by the pseudo-second-order model. The adsorption isotherm data were most effectively provided by the Langmuir and Redlich-Peterson models for both ZnCdAl-LDH and ZnCdAl-O, indicating monolayer adsorption onto homogeneous surface sites. The adsorption process was endothermic and spontaneous, according to the thermodynamic study. Electrostatic interactions are the main interactions responsible for dye fixation on the LDH surface. Theoretical study by DFT confirms the result and that hydrogen bonding cannot take place. The results of this study demonstrate that ZnCdAl-LDH and ZnCdAl-O materials exhibit high efficacy in the deletion of Indigo Carmine dye from contaminated water.