Ali Bakhshi-Zadeh, Janelle Balzer, Negar Fahimi, Nael Yasri, Linda J Eastcott, Krista Stevenson, Edward P. L. Roberts, Anne M. Benneker, Sathish Ponnurangam
on the heterogeneous GAC surface (Sips model), whereas N/S-functionalized GAC follows the Freundlich model, indicating heterogeneous adsorption through the formation of Cr(III) hydroxides near functional groups. Kinetic studies indicated that the adsorption follows a revised pseudo-second order kinetic model on both surfaces, where chemisorption is the rate-controlling step. The rate of adsorption is similar for both types of GAC in the initial regime with fast kinetics. However, after 200 min, N/S functionalized GAC exhibits a higher uptake, likely associated with the additional Cr(VI) adsorption through a reduction process. Regeneration experiments revealed that NaOH and KOH solutions achieved significantly higher desorption efficiencies (>90% for unmodified GAC and >70% for N/S functionalized GAC) compared to acidic regeneration using HCl solution (<40% for GAC and <25% for N/S-GAC).