Positively charged nanofiltration membrane has gained significant interest in magnesium and lithium separation due to its separation mechanism, especially in salt lake-based lithium industry. To obtain a high-density positive charged surface and high Li + /Mg 2+ selectivity, a novel thin-film nanocomposite (TFN) nanofiltration (NF) membrane for recovery of Li + from Mg/Li mixtures with Mg 2+ /Li + ratios of 20 was successfully prepared by using polymeric amine polyethyleneimine (PEI) and monomeric amine silane coupling agent (3-diamino-methyl-cyclohexyl triethoxysilane, DTES). Then the effect of DTES on the surface properties and performance of the prepared DTES/PEI/TMC TFN membranes were investigated. Chemical composition analysis revealed that DTES not only hydrolyzed to Si–OH and then self-polymerized to Si–O–Si, but also reacted with the self-carrying acyl chloride of 1,3,5-benzene trichloromethane (TMC). Moreover, SiO 2 nanoparticles were in-situ generated from DTES inside the PA layer with high compatibility. Due to the compatible properties with the positively charged PEI polymer, the reacted DTES was distributed uniformly in the formed TFN selective layer with no noticeable aggregation. The doping of SiO 2 into the polyamide network gave rise to the enlargement of the membrane pore size, enhanced the surface hydrophilicity, and reinforced the surface positive charges. The water flux of the DTES/PEI/TMC membrane improved from 36.9 L m −2 h −1 to 49.58 L m −2 h −1 compared to the PEI/TMC membrane. Additionally, the Mg 2+ and Li + rejection of the optimized membranes was 91.46% and −10.5%, respectively, with permeability and selectivity (S Li, Mg = 12.95) superior to that of the commercial NF membranes. Considering the commercial availability of DTES, this study not only offers a high-performance nanofiltration membrane for recovering lithium from brines but also provides a feasible strategy for industrial separation of other monovalent and divalent ions.
A one-step co-deposition (electro induced) process was used to develop graphene oxide/dodecyltriethoxysilane (GO/DTES) coatings with enhanced protection performance, as well as controlled thickness. The scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM) and X-ray photoelectron spectroscope (XPS) suggested the successful electrochemical synthesis and the inclusion of GO. XPS results and the observation of the strong absorption peak corresponding to COO groups in the diffuse reflectance infrared Fourier transform spectroscope (DRIFT) indicated the covalent bonding and assembly mechanism of OH and COOH groups between the GO and silanol. This revealed the intrinsic reasons for preparing the more compact GO/DTES coatings. Results from the electrochemical impedance spectroscopy (EIS) showed that when the deposition potential and duration were optimized to about −0.8 V and 300 s, respectively, the GO/DTES samples with the maximum average thickness over 400 nm possessed the enhanced corrosion resistance. Analyses on corrosion SEM morphology and energy dispersive X-ray spectroscope (EDX), the long term 3.5% NaCl solution immersion for 480 h, the water contact angle upping to 110°, micro tribology and the adhesion experimental results further proved that there is an improved protection performance of those GO/DTES samples. The enhanced properties of these GO/DTES coatings can be ascribed to the GO doping and the controlled high thickness, inspiring a practical approach towards the fabrication of GO-based protection materials.
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