Evaluating the antifouling effects of silver nanoparticles regenerated by TiO2 on forward osmosis membrane

In this research, silver (Ag) nanoparticles were deposited by a photoinduced growth approach on the surface of forward osmosis (FO) membranes, followed by the charge-driven self-assembly of titanium dioxide (TiO2) nanoparticles on the layers of silver nanoparticles. The Ag/TiO2-coated membranes were used in pressure retarded osmosis (PRO) mode in the FO process. The surface of the modified membranes was then characterised by measuring the water contact angles and zeta potentials. The morphology and surface roughness of the modified membranes were investigated by scanning electron microscope/ energy dispersive X-ray (SEM/EDX) imaging, X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM) analysis. Accelerated biolouling tests were also conducted. The bacterial populations on fouled membranes were estimated by the adenosine triphosphate (ATP) bioluminescence assay test 111. A cleaning protocol, using deionisecl water only, was employed to clean the fouled membrane. The recoveries of the water flux were compared to evaluate the antifouling effects of the Ag/TiO2 coating. It was found that the bacterial growth on the Ag/TiO2-coatecl membrane was almost 11 times less (2.0 mu g/L), compared to the virgin membrane (23.5 mu g/L). This was primarily due to the antibacterial effects of the silver nanopoarticles. The TiO2 played an effective role in regenerating the silver nanoparticles by decomposing the organic matter that covered the silver nanoparlicles. During the cleaning process, with a flow velocity of 30.0 cm/s, it was observed that a 67-72% recovery of initial water flux was achieved by the Ag/TiO2-coated membranes, whereas only 33% recovery of initial water flux was achieved by the original membrane. This confirms that the fouling layer on the modified surface was much easier to remove than the fouling layer on the original membrane surface. The success of Ag/TiO2 deposition of silver and TiO2 on the membrane surface was evident in SEMIEDX, XPS and AFM images. These results, combined with the ATP and water-flux recovery results, indicate that the Ag/TiO2 coating on the membrane surface effectively inhibited bacteria growth, and altered the interfacial interactions between the membrane and the fouling biofilm, making them easier to be removed and cleaned without using the chemical cleaning agents. (C) 2013 Elsevier B.V. All rights reserved.