Enhanced Pervaporation of the Poly(dimethylsiloxane) (PDMS) Mixed Matrix Membrane Based on the Self-Assembly of Multidimensional Carbon Nanomaterials

Introducing nanomaterials in the poly(dimethylsiloxane) (PDMS)-based membranes and constructing preferential ethanol-permeable nanochannels are important to improve the pervaporation (PV) flux and selectivity in the separation of the ethanol/water binary system. In this work, poly(vinylpyrrolidone) (PVP)-modified carbon nanotubes (P-CNTs) and reduced graphene oxide (rGO) nanosheets were incorporated in the PDMS membrane's matrix simultaneously. Various analysis methods, such as scanning electron microscopy (SEM), high-resolution field emission transmission electron microscope (HR-FETEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and thermogravimetric analyzer (TGA), were introduced to explore the physical structure of the P-CNTs@rGO nanoparticles and their valuable chemical properties in the PDMS matrix. The surface (and cross-section) morphology, surface chemical bond, surface roughness, contact angle, swelling degree, and apparent activation energy of the PDMS-based membranes before and after the P-CNTs@rGO loading were thoroughly characterized and analyzed. Primarily based on the particles' charge repulsion and steric hindrance effect originating from the PVP molecular chains, the agglomeration of the CNT nanotubes and rGO nanosheets was inhibited, which was consistent with other reports. The CNTs and rGO were homogeneously dispersed and self-assembled into multidimensional nanoparticles, which formed preferential channels for ethanol permeation in the PDMS membrane matrix. As a result, the total flux of the prepared P-CNTs@rGO/PDMS mixed matrix membrane (MMM) reached 3.40 kg·m–2·h–1, the ethanol/water separation factor remained 12.40, and the pervaporation separation index (PSI) remained 38.76 at 50 °C. Meanwhile, the PV performances and the apparent activation energies of ethanol and water permeation for the pure PDMS membrane and the P-CNTs/PDMS, rGO/PDMS, and P-CNTs@rGO/PDMS MMMs were also investigated. The P-CNTs@rGO/PDMS MMM showed high competitiveness with other PDMS-based membranes in the PV process. Moreover, the three-dimensional (3D) network formed by the P-CNTs@rGO nanofillers and the polymer chains stabilized the membrane structure and maintained a high-performance operation at 50 °C for a total duration of 140 h.