Hierarchical molybdenum disulfide microspheres: a sustainable and highly efficient adsorbent for removal of methylene blue and congo red from wastewater

Abstract This study reports the facile and cost-effective hydrothermal synthesis of hierarchical molybdenum disulfide (MoS 2 ) microspheres having superior adsorption capacity for organic dye pollutants. The structural and morphological characteristics of as-synthesized MoS 2 microspheres were analyzed by using XRD, SEM, TEM and Raman spectroscopy techniques. Morphological studies revealed that the individual microspheres were composed of many interconnected MoS 2 nanosheets, providing them a huge surface. On account of this unique feature, the MoS 2 microspheres developed in the present study exhibited enhanced adsorption capacity for cationic dye methylene blue (MB) and anionic dye congo red (CR). The effects of pH, adsorbent dosage, initial dye concentration, and contact time on the adsorption of MB and CR were investigated in detail in the present study. A maximum adsorption capacity of 681.10 and 978.43 mg g −1 were attained for MB and CR respectively which were exceptionally high in comparison with most of the previously reported MoS 2 -based adsorbents. The adsorption of MB and CR on MoS 2 microspheres followed the pseudo-second-order kinetics model and the Freundlich isotherm model. The mechanism of adsorption was explored using intraparticle diffusion (IPD) and Richenberg models. The results showed that the adsorption of MB and CR onto MoS 2 microspheres is a multi-step process and IPD has a major contribution in the case of CR adsorption. The MoS 2 microspheres retained more than 90% removal efficiency even after five recycle runs. As the developed adsorbent consists of pristine MoS 2 , there are vast scopes for its functionalization/modification to improve its adsorption ability thereby making it an excellent platform for novel research in the field of environmental remediation.