Utilization of leaves powder of Grewia asiatica (falsa) as an efficient bioadsorbent for the removal of Congo red from an aqueous solution

This research reports batch adsorption of Congo red (CR) dye from an aqueous solution onto leaves powder of Grewia asiatica (GA) at 25 °C. The influence of operational parameters on the percentage removal of CR was evaluated in detail. The percentage removal of CR was increased from 48 to 99%, 35 to 99%, and 51 to 77% at optimum contact time, amount of leaves powder of GA, ionic strength respectively whereas decreased from 99 to 45%, 99 to 66% and 96.1 to 92.2% with initial concentration of CR solution, temperature and pH, respectively. Adsorption kinetic results represented that CR adsorption onto leaves powder of GA fitted to pseudo-second-order kinetic model because the value of correlation coefficient was close to unity (R2>0.999). Nonlinear isotherms such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) were applied for CR adsorption onto leaves powder of GA. Results showed that CR adsorption followed nonlinear Langmuir isotherm due to lower value of chi-square test (χ2= 7.84063×10-10). Adsorption thermodynamic study was conducted by measuring the change in Gibb’s free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°). Results showed that CR adsorption onto leaves powder of GA was exothermic (ΔH= -106 KJ/mol) and spontaneous process. The regeneration of adsorbent was also illustrated.