In-situ modification of PVDF membrane during phase-inversion process using carbon nanosphere sol as coagulation bath for enhancing anti-fouling ability

Mixed matrix membranes (MMMs) hold a great potential in preparing low-fouling and robust membranes for water and wastewater treatment due to their hierarchical structures and multiple functionalities. In this work, a facile approach was proposed for in-situ preparation of polyvinylidene fluoride (PVDF) and carbon nanosphere (CNS) MMMs (PVDF/CNS MMMs) during phase-inversion process for enhancing anti-fouling ability. This protocol, dipping casted films into various dosages of CNS sol as coagulation bath, allowed the formation of membranes and immobilization of CNS onto membrane surfaces simultaneously. Results showed that MMMs had enhanced surface physicochemical properties such as decreased contact angle and increased negatively charged potential with the increase of CNS dosages from 0 mg/L to 400 mg/L. X-ray photoelectron spectroscopy (XPS) analysis and electrochemical measurements confirmed the immobilization of CNS on MMMs. However, the further increase of CNS dosage to 800 mg/L resulted in an evident decrease in porosity and permeability for MMMs. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory evaluation and batch filtration experiments demonstrated improved anti-fouling behaviors for MMMs, which was further confirmed by the long-term membrane bioreactor (MBR) tests, with the best anti-fouling performance for MMM at a CNS dosage of 400 mg/L. XPS analysis also showed that the immobilized CNS on membrane surfaces had satisfactory stability (no significant release) during the long-term operation in MBR.