Kinetic Studies on MB Adsorption by Graphene like Material from Coconut Shell Charcoal

Abstract

Coconut shell (CS) activated carbon is widely used for water purification, but its adsorption capacity is inferior compare to graphene oxide (GO). GO has oxygen functional groups so it can effectively bind pollutants like methylene blue (MB). In this study we synthesized graphene-like material from CS charcoal using the modified Hummers method by varying its oxidation times. The XRD decomposition results for H-CS3.2 show a structural composition similar to GO material. The diffraction peak at 10.7° (3.04%) falls within GO's characteristic range of 8°-11°, supported by a Raman ID/IG ratio of 0.95. In contrast, H-CS3.1 material does not exhibit GO's structural composition, with a diffraction peak at 13.9° (1.09%). An increasing of oxidation time, enhanced adsorption capacity in the equilibrium state of H-CS3.2 (22.368 mg/g) surpassing H-CS3.1 (17.079 mg/g). The heightened adsorption was linked to an increased O/C ratio or higher % of atomic oxygen (0.04 for H-CS3.1 and 0.17 for H-CS3.2). The pseudo second-order Ho (PSO) adsorption kinetic model demonstrated the adsorption mechanism, with active sites (oxygen functional groups) such as carbonyl (C = O) and epoxy (C – O) at basal plane carbon. Steric hindrance caused by hydroxyl functional groups (C – OH) led to a reduction in π-π interactions and decreased adsorption ability of the H-CS3.1 material. Desorption of H-CS3.1 material was influenced by MB detachment through interface diffusion.