Stable and efficient demulsifier of functional fluorinated graphene for oil separation from emulsified oily wastewaters

Abstract A series of functional fluorinated graphene (FG) materials including urea modified FG (UFG), alkali modified FG (AFG) and hydrazine hydrate modified FG (HFG) with different fluorine contents were prepared and introduced as demulsifiers for efficient separation of oil from oil-in-water (O/W) emulsion. Their demulsification performances were evaluated by measuring oil absorbance in separated water phase. Effects of demulsifier dosage, pH of wastewater and the NaCl concentration on demulsification efficiency have been studied detailedly. The demulsification mechanism was also explored. Results showed that demulsification efficiency increased with the decrease of fluorine content of functional FG and the oil concentration in the separated water phase decreased to the lowest value when the 600 mg/L HFG was added into the wastewater. In particular, the HFG has superior demulsification performances ranging from acidic to alkaline conditions. The strong π–π interaction and electrostatic attraction between HFG and oil droplets promote the separation of oil from oily wastewater. Besides, the HFG also presents high demulsification efficiency at different concentrations of NaCl wastewater solution, suggesting the excellent salt resistance. This work indicates that the HFG is a simple and highly efficient demulsifier to separate the oil from the oily wastewater in a wide range of pH levels.