Efficient removal of Congo red dye from aqueous solution using a biosorbent derived from <i>Phoenix dactylifera</i> seeds: exploring kinetic and thermodynamic parameters

Abstract

In this research work, Phoenix dactylifera seeds (PDS) was used as an adsorbent for the removal of Congo red dye from aqueous system. Congo red (CR), a typical anionic diazo dye is very difficult to remove from aqueous solutions because of it thermal physicochemical and optical stability which is due to it aromatic structure. Therefore, the removal of CR from aqueous solutions using low cost and sustainable biosorbent is highly necessary. The adsorbent was characterized using Fourier transform infrared spectroscopy (FTIR). The effect of various adsorption parameters such as initial dye concentration, adsorbent dosage, contact time, pH and temperature were optimized for maximum sorption of dye. It was found that percentage removal of the CR dye decreases as pH increases from acidic to basic region. Freundlich and Langmuir isotherms were applied for the interpretation of experimental data. The Langmuir isotherm model was found to give best fit for the adsorption with maximum adsorption capacity of 51.245 mg g⁻¹. The thermodynamic parameters such as Gibb’s free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) were found to be −4.38 kJ/mol, 54.9 kJ/mol and 0.1836 kJ/mol/K respectively. The kinetic studies showed that the adsorption was best described by pseudo-second order kinetic model. The results of thermodynamic studies inferred that adsorption of CR onto Phoenix dactylifera seeds was highly feasible, spontaneous and endothermic.