Ultrathin reduced graphene oxide/MOF nanofiltration membrane with improved purification performance at low pressure

Here we demonstrated an alternative partial reduction graphene oxide/metal-organic frameworks nano-scale laminated membrane for dyes and heavy metal ions removal at low pressure. Compared with pure prGO membranes, the novel UiO-66-(COOH)₂/prGO membranes with loose structure and excellent selective permeability demonstrated significant enhancements of permeation for low-pressure nanofiltration. The UiO-66-(COOH)₂/prGO membranes possess more nanochannels structure, high surface charge and stability, which were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The experiment result indicated that the flux of composite membranes for pure water was 20.0 ± 2.5 Lm^-2h^-1bar^-1, about 2.9 times higher than that (6.5 ± 1.2 Lm^-2h^-1bar^-1) of the pristine prGO membranes at the same prGO loading. The high rejection of UiO-66-(COOH)₂/prGO membranes for organic dyes (98.2 ± 1.7% for negatively charged congo red and 92.55 ± 2.5% for positively charged methylene blue) were exhibited. Moreover, the rejection for heavy metal ions also can be efficiently improved up to 96.5-83.1% for Cu²⁺ and 92.6-80.4% for Cd²⁺, indicating the positive effect of the electrostatic interaction on the nanochannels for ions. Therefore, it is reasonable to believe that novel UiO-66-(COOH)₂/prGO membranes have great potential application in water treatment.