Preparation of carbon nanotube/tannic acid/polyvinylpyrrolidone membranes with superwettability for highly efficient separation of crude oil-in-water emulsions

Oil spills and oily industrial wastewater contain insoluble toxic organic molecules, which are harmful to the environment and human health. The preparation of separation membranes with favorable superwettability is crucial for oil-contaminated water treatment. In this study, we prepared a membrane from carbon nanotubes (CNTs), tannic acid (TA), and polyvinylpyrrolidone (PVP) via a green method, without using organic solvents. This membrane exhibited superhydrophilicity and underwater superoleophobicity, along with excellent self-cleaning and anti-fouling properties towards highly viscous crude oil. Furthermore, the CNT/TA/PVP membrane exhibited excellent oil/water separation performance, with very high permeation flux values of up to 7570 and 2634 L m−2 h−1 bar−1for surfactant-free and -stabilized oil-in-water emulsions, respectively. Remarkably, we separated a stabilized crude oil-in-water emulsion using the CNT/TA/PVP membrane. Moreover, these CNT/TA/PVP membranes were resilient under oil accumulation at intermittent pressure during oil/water separation, maintaining a high flux. The high performance of this CNT/TA/PVP membrane, and its green, low-energy, cost-effective preparation, indicate considerable potential for practical applications.