Modified track-etched membranes using photocatalytic semiconductors for advanced oxidation water treatment processes

[摘要] ENGLISH ABSTRACT: The purpose of this study was to develop modi ed tract-etched membranes usingnanocomposite TiO2 for advanced water treatment processes. Photocatalytic oxidationand reduction reactions take place on TiO2 surfaces under UV light irradiation,therefore sunlight and even normal indoor lighting could be utilised to achieve this effect.In membraneltration, caking is a major problem, by enhancing the anti-foulingproperties of photocatalysts to mineralise organic compounds the membrane life ande ciency can be improved upon.In this study therst approach in nanocomposite membrane development was to directlymodify the surface of polyethylenetherephthalate (PET) track-etched membranes(TMs) with titanium dioxide (TiO2) using inverted cylindrical magnetron sputtering(ICMS) for TiO2 thinlm deposition. The second approach wasrst to thermallyevaporate silver (Ag) over the entire TM surface, followed by sputtering TiO2 overthe silver-coated TM. As a result a noble metal-titania nanocomposite thinlm layeris produced on top of the TM surface with both self-cleaning and superhydrophilicproperties. Reactive inverted cylindrical magnetron sputtering is a physical vapourdeposition method, where material is separated from a target using high energy ionsand then re-assimilated on a substrate to grow thinlms. Argon gas is introducedsimultaneously into the deposition chamber along with O2 (the reactive gas) to formTiO2. The photocatalytic activity and otherlm properties, such as crystallinity canbe inuenced by changing the sputtering power, chamber pressure, target-to-substratedistance, substrate temperature, sputtering gas composition and ow rate. These characteristicsmake sputtering the perfect tool for the preparation of di erent kinds of TiO2 lms and nanostructures for photocatalysis.In this work, the utilisation of ICMS to prepare photocatalytic TiO2 thinlmsdeposited on track-etched membranes was studied in detail with emphasis on bandgapreduction and TM surface regeneration. Nanostructured TiO2 photocatalysts were prepared through template directed deposition on track-etched membrane substratesby exploiting the good qualities of ICMS. The TiO2-TM as well as Ag-TiO2-TM thin lms were thoroughly characterised. ICMS prepared TiO2lms were shown to exhibitgood photocatalytic activities. However, the nanocomposite Ag-TiO2 thinlms wereidenti ed to be a much better choice than TiO2 thinlms on their own. Finally aclear enhancement in the photocatalytic activity was achieved by forming the Ag-TiO2nanocomposite TMs. This was evident from the band-gap improvement from 3.05 eVof the TiO2 thinlms to the 2.76 eV of the Ag-TiO2 thinlms as well as the superiorsurface regenerative properties of the Ag-TiO2-TMs.

[发布机构] Stellenbosch University