Synthesis and characterization of polytetrafluoroethylene/oleic acid-functionalized carbon nanotubes composite membrane for desalination by vacuum membrane distillation

Abstract

In this study, oleic acid was used to functionalize carbon nanotubes (CNTs), successfully. Then, a novel composite membrane was fabricated by coating of polyvinylidene fluoride (PVDF) solution containing oleic acid-functionalized CNTs on polytetrafluoroethylene (PTFE) support membrane for use in vacuum membrane distillation (VMD) process. The coating process was performed using vacuum filtration method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM) analysis and water contact angle (WCA) measurement were used to characterize the functionalized CNTs and the fabricated membranes. Effects of the functionalized CNTs loading on membrane performance were investigated. It was found that compared to the PTFE/carboxylated CNTs composite membrane, the PTFE/oleic acid-functionalized CNTs composite membrane with WCA of about 133.2° shows better performance (higher permeation flux and salt rejection), in lower CNTs loading. Taguchi method was applied to design a minimum number of experiments to investigate the effects of some operating parameters including feed temperature, feed concentration and feed flow rate on the membrane performance. The optimum conditions were obtained as: temperature of 70 °C, concentration of 10,000 ppm and flow rate of 150 LPH. This work demonstrated that the fabricated PTFE/oleic acid-functionalized CNTs composite membrane is a suitable candidate to achieve high water flux (89 LMH) and salt rejection (99.45% which is 30% higher than unmodified PTFE membrane) in the VMD process.