Coconut shell carbon via phosphoric acid activation for rhodamine B, malachite green, and methylene blue adsorption - equilibrium and kinetics

This study was aimed at evaluating the removal of different cationic dyes onto phosphoric acid-activated coconut shell carbon. The activated carbon was characterized for surface functional groups, thermal decomposition profiles, surface morphology, and textural properties. The specific area was recorded as 1,221 m2/g with 100% mesoporosity. On molecular basis, the activated carbon adsorbs malachite green, methylene blue, and rhodamine B at maximum capacities of 1.52 mmol/g, 0.80 mmol/g, and 0.58 mmol/g, respectively. It indirectly implies the selectivity of activated carbon toward malachite green, and behaves differently due to steric hindrance of dye molecules. All equilibrium data obeyed Langmuir model, while the kinetic data are closely fitted to pseudo-second order model as concentration increases. To conclude, coconut shell activated carbon is more effective to remove malachite green compared to methylene blue and rhodamine B. This paper is expected to give a further insight into the valorization of coconut shell into activated carbon, and its re-purpose for the remediation of dye-contaminated streams, for which methylene blue, malachite green and rhodamine B were used as model pollutants. This study aims to contribute to the growing body of research on the selective removal of malachite green over the other two dyes onto coconut shell activated carbon, which to the best of our knowledge is still absent in the open literature.