Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The purpose of this study was to develop modi ed tract-etched membranes using
nanocomposite TiO2 for advanced water treatment processes. Photocatalytic oxidation
and 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 membrane ltration, caking is a major problem, by enhancing the anti-fouling
properties of photocatalysts to mineralise organic compounds the membrane life and
e ciency can be improved upon.
In this study the rst approach in nanocomposite membrane development was to directly
modify the surface of polyethylenetherephthalate (PET) track-etched membranes
(TMs) with titanium dioxide (TiO2) using inverted cylindrical magnetron sputtering
(ICMS) for TiO2 thin lm deposition. The second approach was rst to thermally
evaporate silver (Ag) over the entire TM surface, followed by sputtering TiO2 over
the silver-coated TM. As a result a noble metal-titania nanocomposite thin lm layer
is produced on top of the TM surface with both self-cleaning and superhydrophilic
properties. Reactive inverted cylindrical magnetron sputtering is a physical vapour
deposition method, where material is separated from a target using high energy ions
and then re-assimilated on a substrate to grow thin lms. Argon gas is introduced
simultaneously into the deposition chamber along with O2 (the reactive gas) to form
TiO2. The photocatalytic activity and other lm properties, such as crystallinity can
be in
uenced by changing the sputtering power, chamber pressure, target-to-substrate
distance, substrate temperature, sputtering gas composition and
ow rate. These characteristics
make 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 thin lms
deposited on track-etched membranes was studied in detail with emphasis on bandgap
reduction and TM surface regeneration. Nanostructured TiO2 photocatalysts were prepared through template directed deposition on track-etched membrane substrates
by exploiting the good qualities of ICMS. The TiO2-TM as well as Ag-TiO2-TM thin
lms were thoroughly characterised. ICMS prepared TiO2 lms were shown to exhibit
good photocatalytic activities. However, the nanocomposite Ag-TiO2 thin lms were
identi ed to be a much better choice than TiO2 thin lms on their own. Finally a
clear enhancement in the photocatalytic activity was achieved by forming the Ag-TiO2
nanocomposite TMs. This was evident from the band-gap improvement from 3.05 eV
of the TiO2 thin lms to the 2.76 eV of the Ag-TiO2 thin lms as well as the superior
surface regenerative properties of the Ag-TiO2-TMs. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om verbeterde baan-ge etste membrane (BMe) met behulp
van nano-saamgestelde titaandioksied (TiO2) vir gevorderde water behandeling
prosesse te ontwikkel. Fotokatalitiese oksidasie- en reduksie reaksies vind plaas op
die TiO2 oppervlaktes onder UV-lig bestraling, en dus kan sonlig en selfs gewone binnenshuise
beligting gebruik word om die gewenste uitwerking te verkry. In membraan
ltrasie is die aanpaksel van onsuiwerhede 'n groot probleem, maar die verbetering
van die self-reinigende eienskappe van fotokatalisators deur organiese verbindings te
mineraliseer, kan die membraan se leeftyd en doeltre endheid verbeter word.
In hierdie studie was die eerste benadering om nano-saamgestelde membraan ontwikkeling
direk te verander deur die oppervlak van polyethylenetherephthalate (PET)
BMe met 'n dun lagie TiO2 te bedek, met behulp van reaktiewe omgekeerde silindriese
magnetron verstuiwing (OSMV).Die tweede benadering was eers om silwer (Ag)
termies te verdamp oor die hele BM oppervlak, gevolg deur TiO2 verstuiwing bo-oor
die silwer bedekte BM. As gevolg hiervan is 'n edelmetaal-titanium nano-saamgestelde
dun lm laag gevorm bo-op die oppervlak van die BM, met beide self-reinigende en
verhoogde hidro liese eienskappe. OSMV is 'n siese damp neerslag metode, waar
materiaal van 'n teiken, met behulp van ho e-energie-ione, geskei word, en dan weer opgeneem
word op 'n substraat om dun lms te vorm. Argon gas word gelyktydig in die
neerslag kamer, saam met O2 (die reaktiewe gas), vrygestel om TiO2 te vorm. Die fotokatalitiese
aktiwiteit en ander lm eienskappe, soos kristalliniteit, kan be nvloed word
deur die verandering van byvoorbeeld die verstuiwingskrag, die druk in die reaksiekamer,
teiken-tot-substraat afstand, substraattemperatuur, verstuiwing gassamestelling
en vloeitempo. Hierdie eienskappe maak verstuiwing die ideale hulpmiddel vir die voorbereiding
van die verskillende soorte TiO2 lms en nanostrukture vir fotokatalisasie. In hierdie tesis word OSMV gebruik ter voorbereiding van fotokatalitiese TiO2
dun lms, wat gedeponeer is op BMe. Hierdie lms word dan in diepte bestudeer,
met die klem op bandgaping vermindering en BM oppervlak hergenerasie. Nanogestruktureerde
TiO2 fotokataliste is voorberei deur middel van sjabloongerigte neerslag
op BM substrate deur die ontginning van die goeie eienskappe van OSMV. Die
TiO2-BM dun lms, sowel as Ag-TiO2-BM dun lms, is deeglik gekarakteriseer. OSMV
voorbereide TiO2 dun lms toon goeie fotokatalitiese aktiwiteite. Nano-saamgestelde
Ag-TiO2 dun lms is egter ge denti seer as 'n veel beter keuse as TiO2 dun lms. Ten
slotte is 'n duidelike verbetering in die fotokatalitiese aktiwiteit bereik deur die vorming
van die Ag-TiO2 nano-saamgestelde BMe. Dit was duidelik uit die bandgapingverbetering
van 3,05 eV van TiO2 dun lms in vergelyking met die 2,76 eV van Ag-TiO2
dun lms. 'n Duidelike verbetering is behaal in die fotokatalitiese aktiwiteit deur die
vorming van die Ag-TiO2 nano-saamgestelde TMs.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80276 |
| Date | 03 1900 |
| Creators | Rossouw, Arnoux |
| Contributors | Perold, W. J., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 120 p. : ill. |
| Rights | Stellenbosch University |
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