Are membranes implemented with nanoparticles able to provide a breakthrough in water ...

75 Pages·2014·3.44 MB·English

Faculty of Bioscience Engineering

Academic year 2013 – 2014

Are membranes implemented with nanoparticles able to
provide a breakthrough in water purification?

Ruben Nackaerts

Promotor: Prof. dr. ir. Arne Verliefde

Tutor: Msc. Mahlangu Themba Oranso

Master dissertation presented to obtain the degree of
Master in Bioscience Engineering: Environmental Technology

The author and the promoters give permission to use this thesis for consultation and to copy parts of
it for personal use. Every other use is subject to the copyright laws, more specifically the source must
be extensively specified when using results from this thesis.

De auteur en promotoren geven de toelating deze scriptie voor consultatie beschikbaar te stellen en
delen ervan te kopiëren voor persoonlijk gebruik. Elk ander gebruik valt onder de beperkingen van het
auteursrecht, in het bijzonder met betrekking tot de verplichting uitdrukkelijk de bron te vermelden bij
het aanhalen van de resultaten uit deze scriptie.

Ghent, 6th of June 2014

The author, The promoter,

Ruben Nackaerts Prof. dr. ir. Arne Verliefde

Acknowledgements

"It always seems impossible until it is done." - Nelson Mandela

The past year was surreal for me. If I look back, I'd never thought that I would be writing know the
last words of my thesis. In August I left for Jo'burg/Jozi, South-Africa (after being there you'll never
use Johannesburg ever again) to start my thesis research. It was the best experience of my life. There
were some ups and downs. Being alone in a big city in a strange country is never easy and also
research was not always going like planned. Instruments dropped down like flies as if they didn't
want me to get results!

But I survived. I have met the most kind people who helped me out during my stay. Prof. Sabelo
Mhlanga and dr. Edward Nxumalo, thank you for all the effort you guys have put in me during my
stay: guiding me around, consulting on achieved results, providing me with comfortable
accommodation and giving me all the opportunities to let me grow as a young scientist. The whole
department of Applied Chemistry at the University of Johannesburg was a very welcoming
environment. Someone was always there in case I needed help in the lab.

A special group of people for me will be the best South-African Ultimate Frisbee team ever: Ultitude.
Their acceptance of me in their team made my stay in South-Africa really feel like home. Especially
due to "my personal drivers" Ché and Durban Dave, never shy of helping me out to get to practice.

Leaving South-Africa and returning to Belgium didn't seem easy. But my loving parents and my family
made me feel like I had never left home. Also my friends let me blend in perfectly again in the life I
was used to.

During the weeks after, more stress came as results needed to be delivered and the thesis had to be
written. Thank you, Arne and Oranso for being patient with me and letting me do my thesis at my
own pace. Due to the guidance by both of you, I have delivered something of which I am now proud.
Of course I need to thank everyone at PaInT with helping me out with setting up my experiments,
provision of chemicals and nice conversations in between.

So yeah, looking back over the past months: it seemed indeed always impossible until it is done,
which has just happened now.

Finally I want to thank VLIR-UOS and the Belgian Development Cooperation for providing me with a
scholarship for my stay in South-Africa. It is good to see that support goes to projects for young
students who want to cross borders and blend in with different cultures, while being unified by
scientific research.

III
Abstract

The quality and quantity of available fresh water is declining all across the world. Membranes
provide an ideal separation technology for easily scalable (small and large installations possible)
water treatment installations. They have low energy requirements and are able to produce water of
high purity. Membranes that are used for water purification purposes are made of hydrophobic
polymers such as polyethersulfone. These polymers make the membranes quite water repellent and
prone to fouling. Fouled membranes have been reported to have poor performance in terms of
water flux and rejection of solutes. Due to fouling the applied pressure is normally raised to maintain
water flux. This means more energy usage which makes the technology cost-ineffective. This
therefore results in the need to modify the polymeric membranes for enhanced performance. To
counteract the effect of fouling on membrane application, polyethersulfone (PES) membranes were
successfully implemented with graphene oxide – zinc oxide (GO ZnO) nanoparticles to produce
nanocomposite membranes with increased performance and anti-fouling properties. The successful
synthesis of the nanoparticles was confirmed through FTIR, Raman, EDS and TEM analysis.
Membrane production was eventually achieved by adding different loadings of the nanoparticles to
the casting solution. The membranes were then synthesised following phase inversion techniques.
Another series of membranes were produced as well through adding also a pore forming agent,
polyvinylpyrrolidone (PVP), to the casting solution. All membranes were produced with 22 wt% PES
and varied loading of PVP (0 wt% or 4 wt%) and nanoparticles (0 wt%; 0,2 wt%; 0,05 wt%; 0,0125
wt%). After synthesis the membranes were characterised for various properties such as pure water
fluxes, trans-membrane resistance, salt rejection and anti-fouling properties. They were then applied
for treatment of feed water spiked with trace organic contaminants. The best performing membrane
was the PES PVP 0,02% GO ZnO membrane, although it had not the lowest contact angle with its
68±5°. It showed higher permeability (76 ± 15 L.m-2.h-1.bar-1) compared to the bare PES membrane
(43,6 ± 0,9 L.m-2.h-1.bar-1), but its permeability was 40% less of that of the bare PES PVP membrane
(122 ± 40 L.m-2.h-1.bar-1). The reduced water permeability was probably due to partial blocking of the
pores by the nanoparticles. The PES PVP 0,02% GO ZnO membrane was resistant to fouling by
organics and colloids compared to the rest of the synthesised membranes. It had a relative flux 20%
higher than that of the PES PVP membrane after fouling. The membrane also rejected a handful of
the 23 different trace organic compounds, that were dosed in a cocktail in the feed, with an total
average rejection of 27,4% for all the compounds. The solutes were believed to be removed through
a combination of steric hindrance by same charge species, hydrophilic/hydrophobic interactions and
size exclusion mechanisms based on spatial arrangement instead of molecular weight. The PES PVP
0,02% GO ZnO membrane showed that adding PVP together with the nanoparticles was beneficial
because it was performing better than the membrane with the same loading nanoparticles but
without PVP.

IV
Samenvatting

De kwaliteit en de kwantiteit van het beschikbare zoet water is in de wereld aan het verminderen.
Membranen zijn een ideale scheidingsmethode voor eenvoudig schaalbare (zowel kleine als grote
installaties mogelijk) waterzuiveringinstallaties. Ze hebben een lage energiebehoefte en zijn in staat
water met een hoge zuiverheid te produceren. Membranen die in de waterzuivering gebruikt
worden, zijn gemaakt van hydrofobe polymeren zoals polyethersulfon. Deze polymeren maken het
membraan redelijk water afstotend en gevoelig voor fouling. Het is gekend dat gefoulde membranen
slecht water doorlaten en opgeloste stoffen tegenhouden. Door fouling moet de druk over het
membraan opgevoerd worden om een constante stroming van water te kunnen behouden. Dit heeft
als gevolg dat er meer energie gebruikt moet worden, wat de technologie kosteninefficiënt maakt.
Om de effecten van fouling in membraan toepassingen tegen te gaan werden polyethersulfon (PES)
membranen succesvol geïmplementeerd met grafeen oxide - zink oxide (GO ZnO) nanodeeltjes om
zogenaamde nanocomposite membranen te produceren met versterkte prestatie en anti-fouling
eigenschappen. Het succesvol maken van deze deeltjes werd bevestigd door FTIR, Raman, EDS en
TEM analyse. Membraanproductie werd uiteindelijk bereikt door verschillende hoeveelheden van de
nanodeeltjes toe te voegen aan de gietoplossing. Het membraan werd dan gesynthetiseerd door de
techniek van fase omwisseling toe te passen. Een tweede reeks membranen werd gemaakt door het
toevoegen van een porievormende agent, polyvinylpyrrolidon (PVP), toe te voegen aan de
gietoplossing. Alle membranen werden dus gemaakt met 22 wt% PES, een variërende hoeveelheid
PVP (0 wt% of 4 wt%) en nanodeeltjes (0 wt%; 0,2 wt%; 0,05 wt%; 0,0125 wt%). Na de synthese
werden de membranen gekarakteriseerd op basis van verschillende eigenschappen als de flux van
zuiver water, de membraanweerstand, het tegenhouden van zouten en anti-fouling eigenschappen.
Ze werden tenslotte toegepast op het zuiveren van een voedingsstroom gespiked met organische
spoorcontaminaties. Het best presterende membraan was het PES PVP 0,02% GO ZnO membraan,
ondanks het feit dat dit membraan niet de laagste contact hoek had met zijn 68±5°. Het toonde wel
een hogere permeabiliteit (76 ± 15 L.m-2.h-1.bar-1) in vergelijking met het PES membraan zonder
nanodeeltjes (43,6 ± 0,9 L.m-2.h-1.bar-1), maar zijn permeabiliteit lag wel 40% lager dan dat van het
PES PVP membraan zonder nanodeeltjes (122 ± 40 L.m-2.h-1.bar-1). De verminderde permeabiliteit
voor water was waarschijnlijk het gevolg van het blokkeren van de poriën door de nanodeeltjes. Het
PES PVP 0,02% GO ZnO membraan was ook resistent voor organische en colloïde fouling in
vergelijking met de andere gemaakte membranen. Na fouling lag zijn flux 20% hoger dan het PES PVP
membraan. Het membraan weerhield ook enkele van de 23 verschillende organische
spoorcomponenten, die gedoseerd werden als een cocktail in de voedingsoplossing, met een
gemiddelde weerhouding van 27,4% voor alle componenten. Deze opgeloste organische stoffen
werden waarschijnlijk tegengehouden door een combinatie van sterische hindering door gelijke
ladingen, hydrofiele/hydrofobe interacties en uitsluiting op basis van grootte (niet op basis van het
moleculair gewicht, maar eerder de ruimtelijke structuur). Dit membraan toonde ook aan dat het
toevoegen van PVP als extra additief bevorderend was voor de prestatie van het membraan, omdat
het betere resultaten vertoonde dan het membraan met dezelfde hoeveelheid nanodeeltjes maar
zonder PVP.

V
Table of Contents

ACKNOWLEDGEMENTS................................................................................................................ III
ABSTRACT ................................................................................................................................... IV
SAMENVATTING........................................................................................................................... V
TABLE OF CONTENTS ................................................................................................................... VI
LIST OF FIGURES ........................................................................................................................ VIII
LIST OF TABLES ............................................................................................................................ IX
LIST OF ABBREVIATIONS ............................................................................................................... X
1. INTRODUCTION ..................................................................................................................... 1
2. LITERATURE REVIEW .............................................................................................................. 3
2.1 WATER SUPPLY PROBLEM .............................................................................................................. 3
2.1.1 Water Scarcity ..................................................................................................................... 3
2.1.2 Water Pollution .................................................................................................................... 3
2.2 CONVENTIONAL WATER TREATMENT METHODS ............................................................................... 4
2.3 MEMBRANE PROCESSES FOR REMOVAL OF TRACE ORGANICS ................................................................ 5
2.3.1 Membrane separation ......................................................................................................... 5
2.3.2 Removal of trace organics by high-pressure membranes (NF/RO) ..................................... 7
2.3.3 Membrane manufacturing .................................................................................................. 8
2.4 CHALLENGES AND POTENTIAL SOLUTIONS FOR MEMBRANES IN WATER TREATMENT – REMOVAL OF TRACE
ORGANICS ............................................................................................................................................... 9
2.4.1 Challenges ............................................................................................................................ 9
2.4.2 Membrane Modifications to limit organic fouling ............................................................. 10
2.4.3 Nanocomposite Membranes ............................................................................................. 11
2.4.4 Materials of interest .......................................................................................................... 12
2.4.4.1 Polyethersulfone ....................................................................................................... 12
2.4.4.2 Polyvinylpyrrolidone .................................................................................................. 13
2.4.5 Nanoparticles ..................................................................................................................... 14
2.4.5.1 Graphene Oxide ......................................................................................................... 14
2.4.5.2 Zinc Oxide .................................................................................................................. 16
2.4.5.3 Graphene Oxide/Zinc Oxide nanohybrid ................................................................... 17
2.5 GAPS IN KNOWLEDGE – GOAL OF THE THESIS................................................................................... 18
3. MATERIALS AND METHOD ................................................................................................... 20
3.1 MATERIALS ............................................................................................................................... 20
3.2 SYNTHESIS AND CHARACTERISATION OF GRAPHENE OXIDE - ZINC OXIDE NANOPARTICLES ........................ 20
3.2.1 Synthesis of Graphene Oxide (GO) nanoparticles .............................................................. 20
3.2.2 Synthesis of Graphene Oxide – Zinc Oxide Nanoparticle hybrid ........................................ 21
3.2.3 Characterisation of GO and GO ZnO nanoparticles ........................................................... 21
3.3 MEMBRANE SYNTHESIS AND CHARACTERISATION ............................................................................. 22
3.3.1 Membrane synthesis .......................................................................................................... 22
3.3.2 Membrane characterisation .............................................................................................. 23
VI
3.3.3 Surface and Cross-sectional morphology .......................................................................... 24
3.4 MEMBRANE FILTRATION TESTS ..................................................................................................... 24
3.4.1 Filtration setups ................................................................................................................. 24
3.4.1.1 Dead-end Setup ......................................................................................................... 24
3.4.1.2 Cross-Flow Setup ....................................................................................................... 25
3.4.2 Filtration Protocol .............................................................................................................. 25
3.4.2.1 Dead-end Experiments .............................................................................................. 25
3.4.2.2 Cross-flow Experiments ............................................................................................. 26
3.4.3 Trace contaminants and analysis ...................................................................................... 27
3.4.3.1 Solid Phase Extraction ............................................................................................... 27
3.4.3.2 Sample Analysis ......................................................................................................... 28
3.4.4 Fouling experiments .......................................................................................................... 28
4. RESULTS & DISCUSSION ....................................................................................................... 29
4.1 CHARACTERISATION OF NANOPARTICLES ........................................................................................ 29
4.1.1 FTIR .................................................................................................................................... 29
4.1.2 TEM ................................................................................................................................... 31
4.1.3 EDS ..................................................................................................................................... 32
4.1.4 Raman Spectroscopy ......................................................................................................... 33
4.2 MEMBRANE PRODUCTION AND CHARACTERISATION ......................................................................... 34
4.2.1 Contact Angle and Interfacial Free Energies ..................................................................... 34
4.2.2 Pure Water Flux and Membrane Permeability .................................................................. 37
4.2.3 Salt Rejection ..................................................................................................................... 40
4.2.4 SEM images ....................................................................................................................... 43
4.3 FOULING BEHAVIOUR ................................................................................................................. 45
4.3.1 Organic Fouling ................................................................................................................. 45
4.3.2 Colloidal Fouling ................................................................................................................ 48
4.4 APPLICATION IN REJECTION OF TRACE ORGANIC POLLUTANTS ............................................................. 49
5. CONCLUSIONS AND RECOMMENDATIONS ........................................................................... 53
5.1 CONCLUSIONS ........................................................................................................................... 53
5.2 RECOMMENDATIONS FOR FUTURE RESEARCH ................................................................................. 54
REFERENCES ............................................................................................................................... 55

VII
List of Figures
Figure 2.1: Molecular structure of PES (Ahmad, et al., 2013) ............................................................... 12
Figure 2.2: Structure of polyvinylpyrrolidone (Haaf, Sanner, & Straub, 1985) ..................................... 13
Figure 2.3: Molecular structure for GO (Hong et al., 2011) .................................................................. 15
Figure 2.4: Example of the production route for GO ZnO nanoparticles (Li et al., 2012) .................... 18
Figure 3.1: Scheme from the reaction of potassium permanganate in sulfuric acid to diamanganese
heptoxide (Dreyer et al., 2010) ............................................................................................................. 20
Figure 3.2: Membrane filtration dead-end setup .................................................................................. 25
Figure 3.3: Membrane filtration cross-flow setup ................................................................................ 25
Figure 4.1: FTIR spectrum of graphite, graphene oxide nanoparticles and the nanohybrid graphene
oxide - zinc oxide ................................................................................................................................... 29
Figure 4.2: Zoomed in FTIR spectrum of graphene oxide and graphene oxide - zinc oxide ................. 30
Figure 4.3: TEM images of graphene oxide - zinc oxide nanohybrid31
Figure 4.4: ED - spectra (spectrum 2 and spectrum 5) for graphene oxide - zinc oxide ....................... 32
Figure 4.5: Raman spectrum for graphene oxide and graphene oxide - zinc oxide .............................. 33
Figure 4.6: Water contact angles with the different membranes ......................................................... 36
Figure 4.7: Pure water flux under different pressures for PES membranes in a dead-end setup ........ 37
Figure 4.8: Pure water flux under different pressures for PES PVP membranes in a dead-end setup . 38
Figure 4.9: Pure water flux under different pressures for PES membranes in a cross-flow setup ....... 39
Figure 4.10: Pure water flux under different pressures for PES membranes in a cross-flow setup ..... 39
Figure 4.11: Salt rejection for PES membranes in a cross-flow setup ................................................... 41
Figure 4.12: Salt rejection for PES PVP membranes in a cross-flow setup............................................ 41
Figure 4.13: SEM images of cross sections of different membranes .................................................... 44
Figure 4.14: Influence of organic fouling (alginate) on water flux for PES membranes........................ 46
Figure 4.15: Influence of organic fouling (alginate) on water flux for PES PVP membranes ................ 46
Figure 4.16: Influence of organic fouling on the rejection of NaCl for PES membranes ....................... 47
Figure 4.17: Influence of organic fouling on the rejection of NaCl for PES PVP membranes ............... 48
Figure 4.18: Influence of colloidal fouling on the relative flux for PES membranes ............................. 48
Figure 4.19: Influence of colloidal fouling on the relative flux for PES PVP membranes ...................... 49
Figure 4.20: Rejection of pharmaceuticals (ranked by decreasing MW) for PES membranes .............. 50
Figure 4.21: Rejection of pharmaceuticals (ranked by decreasing MW) for PES PVP membranes ...... 50
Figure 4.22: Rejection of pharmaceuticals (ranked by charge) for PES membranes ............................ 51
Figure 4.23: Rejection of pharmaceuticals (ranked by charge) for PES PVP membranes ..................... 51
Figure 4.24: Rejection of pharmaceuticals (ranked by log D value) for PES membranes ..................... 52
Figure 4.25: Rejection of pharmaceuticals (ranked by log D value) for PES PVP membranes .............. 52

VIII