Adsorption of methyl orange: A review on adsorbent performance

Adsorption as a technique is preferred to these other methods in the mitigation of methyl orange (MO) because of its simplicity in design and operation, indifferent sensitivity towards toxicants and low operational cost. This study is aimed at evaluating the performance of various adsorbent groups in the mitigation of MO from aqueous solutions. It will help reduce the arbitrary choice of adsorbent types for MO adsorption leading to a reduction in the amount of published literature with little/incremental contributions to the field. The study was based on an analysis of over 240 published works of literature on the subject within the last 5 years. The adsorbents were classified into the following seven groups based on their chemical composition; biosorbents, activated carbon, biochar, clays and minerals, polymers and resins, nanoparticles, and composites. In terms of frequency of utilisation of adsorbent group, composites were the most frequently used (>40%). It was observed that nanoparticles and polymers were the most frequently used constituents in the manufacture of composite adsorbents for MO. The choice of nanoparticles in composite adsorbents could be due to their flexibility in going into the matrices of other material types due to their small sizes. Polymers also act as good matrices for immobilising other composite constituents. Nanoparticles was the best adsorbent group for MO uptake. Clays and minerals had the greatest proportion of adsorbents with MO uptake capacity greater than the 1000 ​mg/g threshold. • The performance of various adsorbent groups for MO adsorption was reviewed. • Composites were the most frequently used (>40%) adsorbent group for MO adsorption. • Nanoparticles and polymers were the most frequently used constituents in the composite. • Nanoparticles were the best adsorbents for MO uptake. • Clays and minerals had the greatest proportion of adsorbents with >1000 ​mg/g capacity.