Studies on the effect of parameters controlling an adsorption process for anionic dye removal by using commercial activated carbon

In the present study, commercial activated carbon (CWZ-14) is tested for the removal of the anionic azodye Direct Red 23 (DR23) from aqueous solutions. The effect of parameters such as initial dye concentration (10‒50 mg/L), pH (3.4‒11.4), and temperature (20‒60 °C) on the adsorption process is studied. The structure and morphology of the commercial activated carbon, as the quality attributes of the adsorbents, are characterized by scanning electron microscope (SEM), N2 adsorption/desorption isotherms (BET), and Fourier transform infrared spectroscope (FTIR). To understand the adsorption behavior of DR23 onto CWZ-14, the experimental kinetic data are analyzed using the pseudo-first-order and pseudo-second-order models. The kinetics of the adsorption of the dye followed the pseudo-second-order kinetics. The isotherms of adsorption data are analyzed via the Langmuir and the Freundlich models. It is observed that the experimental data effectively fits the Langmuir model. The maximum adsorption capacity calculated from the Langmuir isotherm, qm, is 104.2 mg/g. The experimental findings showed that the adsorption is a pH-dependent process, with the maximum adsorption capacity occurring at a pH of 7. Thermodynamic parameters, such as changes in standard free energy (∆G°), enthalpy (∆H°), and entropy (∆S°), are also evaluated. The thermodynamic analysis shows that the adsorption process is endothermic, spontaneous, and a physisorption process.