Revealing the impact of membrane adsorption on phenol transmembrane mass transfer in aqueous-aqueous membrane extraction

Nanoparticle doping in membranes is an ideal strategy for improving performance of aqueous-aqueous membrane extraction (AAME). However, its derived adsorption has not been investigated regarding performance enhancement/deterioration of phenol transmembrane mass transfer they might bring, especially in porous membranes. Therefore, supercapacitor-activated carbon (YEC-8)-doped (>30 mg/g) and silica-doped membranes (<0.1 mg/g) only with differentiated adsorption capacity were prepared to identify adsorption impact on phenol extraction from saline-wastewater. Surprisingly, membrane adsorption significantly inhibited phenol transmembrane mass transfer regardless of adsorption saturation rather than enhancement as we hypothesized. Compared to PVDF membrane, extraction performance of silica-doped membrane decreased by 24.0% while YEC-8-doped membrane further decreased by 44.1% at 2 g/L phenol. Facing different phenol concentrations, performance of YEC-8-doped membrane also decreased by 40%–50%. These results stated the important role of volatilization-diffusion in phenol transmembrane mass transfer in comparison with solution-diffusion. Membrane characterization and Hagen-Poiseuille model analysis demonstrated that membrane pore complexity would induce partial performance degradation. DFT calculation further confirmed that adsorption of gaseous phenol (−1.7292 eV) within membrane pores was primary limiting step in transmembrane mass transfer. Overall, this study elucidates transmembrane mass transfer pathway, process, and mechanism of phenol in AAME with nanoparticle-doped porous membrane for the first time.