Abstract
ABSTRACTTo enhance the water flux and salt rejection of reverse osmosis membranes, thin film nanocomposite reverse osmosis membranes were prepared by incorporating functionalised single-walled carbon nanotubes (SWNTs). The functionalised SWNTs were obtained by chemical process such as mixed acid oxidation and substitution reaction. The SWNTs were characterised by HRTEM, FTIR, TGA, Raman spectra, UV-Vis and XPS, etc. The surface morphology and structure of membrane were characterised by SEM and contact angle measurement, respectively. The results showed that carboxyl, acyl, amide and amine were successfully grafted on the tip and inner wall of the single-walled carbon nanotubes. The dispersity of the functionalised SWNTs in water was tested, indicating a good hydrophilic property. The polyamide/modified CNT nanocomposite reverse osmosis membrane was prepared. Compared with the bare polyamide membrane, the SWNT-polyamide thin film nanocomposite membranes showed higher property in hydrophilic surface and its water flux, as along with salt rejection, improved dramatically. The experimental results revealed that the modified SWNTs (especially those containing hydrophilic groups such as carboxyl groups and amino groups) well dispersed in the polyamide thin film layer, and hence improved the water permeation, and the salt rejection.
Highlights
Since CNTs was discovered by Iijima [1] in 1991, it has become a viable candidate for a wide applications and has caused a worldwide interest such as extraordinary optical properties, electronics, thermal and mechanical properties [2,3,4,5,6,7,8,9,10]
Our research group have done a series of simulations on water flux and salt rejection of modified single-walled and multi-walled carbon nanotubes [27,28], The results showed that when certain number and type of functional group (-COOH, -CONH2 and -NH2) were added to the interior and/or on the tip of single-walled (10, 10)(1.356 nm) or (13, 13)(1.763 nm), 100% salt rejection could be obtained and high water flux (13 times of the traditional reverse osmosis membrane) be maintained
This article modified the single-walled carbon nanotubes (SWNTs) with 3.5 nm diameter by using mixed acid (H2SO4, HNO3) oxidation and further modification
Summary
Since CNTs was discovered by Iijima [1] in 1991, it has become a viable candidate for a wide applications and has caused a worldwide interest such as extraordinary optical properties, electronics, thermal and mechanical properties [2,3,4,5,6,7,8,9,10]. In order to improve the hydrophilicity and the dispersity of carbon nanotubes, a great many of researches such as oxidation with HNO3 [11,12,13], or mixed acid H2SO4/HNO3 (1:1; 1:1.6; 3:1; 3:2, v/v) [14,15,16,17] have been reported in recent years. It proved that acid oxidation could remove the amorphous carbon in the carbon nanotubes but improve the dispersity, concentration and the stability of CNTs in polar solvent.
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