Functional membranes prepared by using nano-materials such as TiO<inf>2</inf> and carbon nanotubes (CNTs)

Abstract

Two different types of water treatment membranes have been prepared using nano-materials; one was a polysulfone (PSf) ultrafiltration (UF) membrane with carbon nanotubes (CNT) and the other was a nanofiltration (NF) membrane with TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nano-particles on its surface. Both membranes were prepared to improve membrane performances in the water treatment process. The PSf UF membrane with CNT was expected to have better permselective properties, and the NF membrane with TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nano-particles was expected to have better antifouling properties. PSf membranes with CNT were prepared by a phase inversion process, and CNTs were treated with strong acid before blending with PSf to make the membrane. The prepared PSf membranes showed more hydrophilic surface than the others without CNTs due to the hydrophilic surface of the acid treated CNT. The CNTs added into the PSf membrane also affected on the membrane pore formation so that the morphology and permeation properties of the membranes varied substantially depending on the amounts of CNTs added. A polyamide (PA) NF composite membrane with TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nano-particles on its surface was prepared by a little complicated process using 3-aminopropyltrimethoxysilane (APTMOS), titanium (IV) isopropoxide (TIP) to improve its antifouling property. In particular, for this membrane, SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layers were formed between the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer and the crosslinked polyamide layer of the membrane to protect the organic parts of the membrane from the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> catalyzed UV degradation. The prepared membrane was then characterized using several analytical methods: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and permeation tests. The prepared membrane was found to be stable; especially the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer of the membrane was stable after several times of permeation test. The membrane showed a typical NF property, despite the presence of the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer. From long time tests with or without UV light, it was found that there was good antifouling effect on the membrane by the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer.