Enhanced Cr(VI) adsorption using ZnO decorated graphene composite: Batch and continuous studies

Background: Hexavalent chromium [Cr(VI)] is a highly toxic heavy metal because of its high movement in cell membranes as HCrO4- and CrO(4)(2-)ions. Metal oxide decorated on graphene-based polymers are highly efficient adsorbents to treat [Cr(VI)], but such studies are scarce. Methods: In this study, a novel adsorbent zinc oxide (ZnO) particles decorated on reduced graphene oxide (RGO) coupled with polyethylene glycol (PEG) was synthesized by improved Hummers method, followed by coupling and calcination. Significant findings: The results indicated that maximum removal occurs at pH 3.0, contact time 75 min, adsorbent dosage 0.8 g/L, and temperature 30 degrees C. Langmuir isotherm and Pseudo-second-order were the best-fitted model indicating a homogeneous and chemical adsorption with maximum uptake of 232.58 mg/g. From the dynamic study, it was witnessed that lower flow rate, concentration, and higher bed height were suitable for maximum adsorption. After five cycles of adsorption-desorption study, the desorption ratio was still 85.6%. The surface deposition of ZnO on RGO-PEG polymer improves the Cr(VI) mobility in the composite, thereby increasing the adsorption capacity as well as adsorption kinetics. The findings of the present study and the reusable nature of ZnO/RGO-PEG signifies this novel composite is an innovative and excellent adsorbent for wastewater treatment.