Multifunctional natural sepiolite nanofibre composite demulsifiers for efficient purification of oils and dyes in simulated and actual wastewater

Purifying stubborn wastewater containing stable oil droplets, high levels of oils, and other contaminants such as dyes to obtain fresh water is highly desirable but challenging. Here, a magnetically recyclable multifunctional β -cyclodextrin ( β -CD)-modified sepiolite@Fe 3 O 4 (SP@Fe 3 O 4 /APTES-CD) composite demulsifier with excellent demulsification capability and dye removal efficiency was developed, and the high-efficiency purification of the complex and stable emulsified wastewater with or without dyes was achieved after treatment with the demulsifier. The composition, structure and physicochemical properties of the multifunctional demulsifiers were discussed in detail, and the effects of the components in the emulsion (e.g., salts, oils, and surfactants) on the demulsification efficiency of the demulsifier were evaluated. It was revealed that the usage condition of the SP@Fe 3 O 4 /APTES-CD demulsifier is not limited by the types of water and oils. The demulsifier can purify not only the oil/deionized water emulsions, but also the oil/natural water (seawater, Yellow River water and Yangtze River water) emulsion with a very high oil-water separation efficiency of 99.6%. The oil-water separation efficiency of n-hexane/water, kerosene/water, gasoline/water, carbon tetrachloride/water, and soybean oil/water emulsions by the demulsifier are 98.5%, 99.8%, 99.1%, 98.7% and 99.2%, respectively. The anionic dye Congo red (CR) and cationic dye Methylene blue (MB) in the surfactants-stabilized O/W emulsion can be simultaneously removed after demulsification process with a removal efficiency larger than 99%. The demulsification process of surfactant-stabilized emulsion with the demulsifier can be accelerated by applying an external magnetic field to realize magnetically controlled demulsification. In addition, the SP@Fe 3 O 4 /APTES-CD demulsifier is very effective in separating and purifying the practical emulsified wastewater produced from steel mills within 20 s to obtain clean water. The demulsifier can still keep better demulsification efficiency after being recycled and reused for more than ten cycles.