Methylene blue dye: Toxicity and potential technologies for elimination from (waste)water

Abstract: 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.

Abstract: ABSTRACT New derivatives of polyindole were synthesized through polymer‐analogous transformation and studied using a range of physicochemical methods. They have been successfully used for the adsorption of anionic and cationic dyes from water. The influence of pH, adsorption time, dye concentration, and reusability was investigated. The optimal pH for the adsorption of methyl orange (MO) is 7, while for methylene blue (MB) it ranges from 7 to 12. Adsorption is well described by the Langmuir model, and the kinetics follow a pseudo‐second‐order model. Notably, the maximum adsorption capacity of the polyindole derivatives for the cationic dye MB from 46.00 to 87.16 mg/g, more than twice that observed for the anionic dye MO (18.39 to 22.50 mg/g). This significant difference in adsorption performance is likely attributed to stronger electrostatic interactions between the negatively charged nitrogen atoms in the polyindole backbone and the cationic MB molecules. Thermodynamic parameters further confirmed the spontaneous and endothermic nature of the adsorption process. Importantly, the m ‐OMePIn polymer maintained high adsorption efficiency even after multiple reuse cycles: after five consecutive adsorption–desorption cycles, dye removal efficiency remained above 57%. These findings highlight a convenient synthetic approach for the development of polyindole‐based adsorbents with high adsorption capacity, offering promising potential for the removal of dye pollutants from aqueous environments.

TL;DR: An extensive list of various adsorbents such as natural materials, waste materials from industry, agricultural by-products, and biomass based activated carbon in the removal of various dyes has been compiled here.

TL;DR: Electro-Fenton (EF) Process 6585 4.2.1.

TL;DR: It is evident from a literature survey of about 185 recently published papers that low-cost adsorbents have demonstrated outstanding removal capabilities for MB, and these include agricultural wastes, industrial solid wastes, biomass, clays minerals and zeolites.

TL;DR: This review presents in brief the history of adsorption and highlights the progress in theoretical description of the phenomenon under consideration, as well as presenting some of the latest important results and giving a source of up-to-date literature on it.