Adsorption of Methylene Blue Cationic Phenothiazine Dye with Mono and Few‐Layered Tungsten Disulfide Nanosheets (WS ₂ )

Abstract Effluents from the textile industry contain high concentrations of synthetic dyes, such as methylene blue, which are released into the environment (water bodies) and have the potential to negatively impact aquatic life, humans, and animals due to their neurotoxicity, photosynthesis disruption, and oxygen depletion. Thus, the importance of finding viable solutions for the removal of methylene blue from wastewater is emphasized. It is with this regard that the current study focuses on the effective removal of methylene blue using adsorption and WS 2 nanosheets. The nanosheets were fabricated at different residence times and yielded black and grey WS 2 . The morphological and surface characteristics of the nanosheets were determined by using microscopic and spectroscopic techniques. The Fourier transform infrared spectroscopy revealed typical characteristic functional groups for the WS 2 materials between 650–1250 and 1600–3300 cm −1 , respectively. Meanwhile, scanning electron microscopy revealed flake‐like nanosheet morphologies. The point of zero charge was found to be 1.90 for grey WS 2 and 2.47 for black WS 2 nanosheets. The optimized adsorption conditions were found to be pH 7, initial concentration of 250 mg/L, the adsorbent dosage of 60 mg, and a contact time of 60 min. The maximum removal efficiency was 95.8% grey (WS 2 ) and 98.9% black (WS 2 ), respectively. The theoretical q e values (148, 41, and 164, 02 mg g −1 ) were found to be closer to the experimental values (145,07 and 167, 56 mg g −1 ). The thermodynamics shows that the reaction was endothermic in nature, indicated by positive Δ H 0 , and the positive Δ S 0 indicted the increased randomness at the solid–liquid interface. The reusability tests at optimum conditions show that the black tungsten disulfide is highly stable and is rendered an economically feasible catalyst.