Titanium dioxide nanoribbons/multi-walled carbon nanotube nanocomposite blended polyethersulfone membrane for brackish water desalination

Abstract A series of titanium dioxide nanoribbons (TNRs)/multi-walled carbon nanotubes (MWCNTs)/polyethersulfone (PES) blend membranes with different proportions of TNRs/MWCNTs were synthesized via phase inversion method. The nanocomposite (TNRs/MWCNTs) prepared by hydrothermal method followed by chemical vapor deposition (CVD). Energy dispersive X-ray (EDX) analyses and X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) used for characterizing the nanocomposite. The characterization revealed that the nanocomposite consists of a single phase of TiO 2 -B and multi-walled carbon nanotubes. The mass ratio of TNRs/MWCNTs is 1:1. The morphology of TiO 2 -B is a nanoribbons structure with porous pits on its surface. Multi-walled carbon nanotubes (MWCNTs) grow on these nanoribbons and form a network structure-like. The influence of nanocomposite incorporation on the morphology, porosity, contact angle, mechanical properties, and performance of the prepared membranes was investigated as a function of pure water flux and salt rejection %. The hydrophilicity is increased by increasing the nanocomposite content whereas the contact angle and porosity decreased. The SEM images showed that the spongy-like structure of bare-PES is changed by incorporation of TNRs/MWCNTs to a macro-void structure. The nanocomposite reinforces and enhances the mechanical properties of the synthesized membranes. The tensile strength increased from 45.7 to 96.6 kg/cm 2 by blending 0.5 wt% TNRs/MWCNTs. Also, the incorporation of TNRs/MWCNTs increases the ac electrical properties of the membrane regarding the conductivity (σ), dielectric constant (έ) and dielectric loss (e″). The membrane performance was tested using synthetic solution with a salinity of 2000, 5000, 7000, and 20,000 mg/l NaCl. The test is carried out at low-pressure reverse osmosis system (LPRO). The highest average salt rejection of membranes was 99.54%, 99.84%, 98.53%, and 94.06%, respectively with the addition of 0.5% of TNRs/MWCNTs, while the average salt rejection was 61.63%, 50.9%, 41.7%, and 75% using bare-PES. The anti-fouling nature and dye removal for all membranes were tested. The flux recovery ratio (FRR) with (PES/0.5 wt% of TNRs/MWCNTs) membrane reach 89% while the bare-PES showed 58%. In addition, the modified membranes showed high removal of 50 mg/l Congo red dye. (PES/0.5 wt% of TNRs/MWCNTs) rejected 98.1% of the dye while the bare-PES rejected 68.14%. The 0.5 wt% of TNRs/MWCNTs embedded to PES considered the best composite content.