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The Interlink between the Periodic Table and
Water Treatment: A Nano PerspectiveEdward Nxumalo, PhD
+27 11 670 9498
Chemical elements for South Africa’s future and the SDGs 16 May 2019, Midrand, South Africa
College of Science, Engineering & Technology
Enrolment in 2018 is ca 360 000 students!
60 postgraduate students, 10 post-doctoral fellows and 12 staff
members
W: www.unisa.ac.za/nanows
T: +27 11 670 9480
4
Vision Our vision is to become the premiere organization to provide
nanotechnology-based water treatment solutions and services for
South Africa through ground breaking water research and training
programmes.
Research, Training, Excellence, Innovation, Sustainability, Impact
Nanotechnology and Water Sustainability
Research Unit
Our Research Focus
(1) Membrane Science and Technology
Membranes (UF, NF, RO, FO) and mixed matrix
membranes i.e. embedded with nanocatalysts and
strong nanomaterials for drinking, sea water and
wastewater purification.
Fabrication and modification of ceramic, ceramic-
polymeric and hollow fibre membranes.
Fabrication, advanced characterization and transport
properties of carbon nanomembranes.
Our Research Focus(2) Composites, bio-nanocomposites and nanomaterials
for water purification and detection
Nanostructured polymeric adsorbents, nanofibres and
nanocomposite materials.
Synthesis, doping and applications of carbon based
nanomaterials (e.g. carbon nanotubes, graphene oxide,
carbon spheres, etc.).
Green synthesis and application of nanostructured
materials.
• Synthesis of photocatalytic nanostructured materials: water
treatment.
Our Research Focus
(3) Analytical/environmental research
Environmental analysis of persistent organic pollutants (PoPs)
and emerging pollutants in the water treatment train.
Assessment and understanding the nature of emerging
inorganic contaminants in water.
Toxicology and nanotoxicology: analysis and remediation of
biotoxins.
Emerging aquatic pathogens and water microbiology.
Development of analytical methods and protocols for the
analysis and quantification of analytes.
Our Research Focus(4) Urban water cycle and rural community
development
• Drinking and wastewater treatment using conventional and
new/integrated technologies based on nanotechnology.
• New water: water recycling, water reclamation and
wastewater treatment.
• Natural organic matter in water systems: characterization,
treatability and removal.
• Water-energy-food nexus.
• Energy efficient water purification technologies.
Polysaccharides
Our Research Focus(5) Bioremediation and analysis
Aquatic toxicology (harmful algae biotoxins-analysis,
monitoring, remediation).
Constructed wetlands.
Fabrication and application of passive sampling devices
for environmental monitoring.
Method development for the analysis of organic and
inorganic molecules in various matrices.
Nanomaterials for detection of pollutants in water.
Polysaccharides
Sustainable Development Goals (UNGC)
GOAL 6: CLEAN WATER AND SANITATION
▪ Improve water quality by reducing pollution, eliminating dumping and minimizing
release of hazardous chemicals and materials, halving the proportion of untreated
wastewater and substantially increasing recycling and safe reuse globally.
▪ Substantially increase water-use efficiency across all sectors and ensure
sustainable withdrawals and supply of freshwater to address water scarcity and
substantially reduce the number of people suffering from water scarcity.
▪ Expand international cooperation and capacity-building support to developing
countries in water- and sanitation-related activities and programmes, including
water harvesting, desalination, water efficiency, wastewater treatment, recycling
and reuse technologies.
▪ Support and strengthen the participation of local communities in improving water
and sanitation management.
SUSTAINABILITY AND DEVELOPMENT
South Africa is the 30th
driest country in the world Worst draught in 23 years
37% of drinkable
water is lost
Increase in stable
food prices
Agriculture, mining and
chemicals industries
present emerging types of
pollutants
Water Challenges
The Link between the Periodic Table and
Water Treatment
Water Treatment Train: Simplified
13
https://www.mesaaz.gov/residents/water-
resources/services/water-treatment-process
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❖ Emerging/new contaminants such as micropollutants!
15
❖ Advancement in technology and enabling technologies!
“New” Technologies in Water Treatment
Drivers!!!!!!
Brian Owens, 'Pharmaceuticals in the environment: a growing problem', Pharmaceutical Journal, 2015, 294, 7850
Potential Nanotechnology Applications in
Water Treatment: Examples
17
❖ Membranes and membrane processes
❖ Nano-adsorption processes
❖ Photocatalysis
❖ Disinfection and microbial control
❖ Multifunctional nanodevices
❖ Sensing, determination and monitoring
❖ Energy capture and storage
❖ Etc
18
Carbon: Unusual Element
Carbon is unusual element with electronic
configuration (1s22s22p2)
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Carbon AllotropesCarbon: sp3 hybridization
Graphite crystalline
structureDiamond crystalline
structure
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Nanoscale Carbon
Nano-carbon: sp2 hybridization
Carbon Nanotube (CNT)Carbon-60 (C60)Graphene
Carbon materials are based on a graphene sheet:NJ Coville, SD Mhlanga, EN Nxumalo, A Shaikjee, Shaped carbon nanomaterials: A review, SA J.
Sci. 107 (2011) 1
21
Carbon Nanotechnology
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CVD Production: Carbon Nanostructures
JohannesburgUniversity of the Witwatersrand
Prof Neil Coville’s GroupDr Ahmed Shaikjee pictures
200 nm
Diverse
morphologies of
nanostructured
carbon
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Structural Diversity
1. NJ Coville, SD Mhlanga, EN Nxumalo, A Shaikjee, Shaped carbon nanomaterials: A review, SA J. Sci. 107 (2011) 1
2. Sabelo Mhlanga slides, 2018
File name 24
NANOSORBENT PROPERTIES TARGET
CONTAMINANTS
Carbon-based
nanosorbents
•High specific surface area
•Highly accessable adsorption sites
• Diverse contaminant-CNT
interactions
• Modifiable-surface chemistry
• Easy reuse
• Various organic chemicals
• Metal ions - e.g., Cu2+, Pb2+,
Cd2+, and Zn2+
•
Metal-based nanosorbents
e.g., iron oxide, titanium dioxide
and alumina
•High specific surface area
•Short intra-particle diffusion distance
•More adsorption sites
•Compressible without significant
surface area reduction
•Easy reuse
•Some are super-paramagnetic
Heavy metals e.g., As, Pb, Hg,
Cu, Cd, Cr, Ni
Polymeric nanosorbents
eg. Dendrimers
•Tailored shell surface chemistry for
selective Adsorption
•Reactive core for degradation
•Short internal diffusion distance
Various metal ions
Dr Nonhlanhla Kalebaila
CNT Membranes
(i) Combat agglomeration
(ii) Improve dispersion
(iii) Vertical alignment
K Yokwana et al (2015)
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(i) Fabrication of aligned CNT/polymer composites.
(ii) Vertically aligned CNT membrane development.
(iii) CNTs as fillers in a polymer matrix = mixed-matrix
membranes.
(iv) CNT/polymer as support.
Four Types Possible
+
Nanoadditives PES+SPSf
+
DMAc Casting solution
Casting
solutionCast film on glass plate Coagulation bath
1 2 3
1 Degassing at 250C to remove air bubbles.
2 Gap height of casting knife adjusted to 300µm, evaporation time (0s)
3 Coagulation bath consists of water at 25 0C.
Fabrication of nanostructured membranes via
“Phase Inversion Method”
Casting Solution Stability
Casting solutions containing O-MWCNTs
remain thoroughly mixed with polymer after
a period time: hydrogen bond interaction
between O-MWCNTs and SPSf allows for
good and stable dispersion of O-MWCNTs.
NN Gumbi, M Hu, BB Mamba, J Li, EN Nxumalo, Journal of membrane science 566, 288-300, 2018
Diverse Types of Membranes
M3- 0.2wt.%M2- 0.05wt.%
M1- 0.01wt.%M0- 0 wt.%
Ms Nozipho Gumbi slides
Carbon-based Membranes: Properties
❖ Reduction of casting knife gap height assisted in the formation of fully sponge-like
morphology.
❖ Addition of O-MWCNTs transforms membrane morphology from sponge-like with to finger-like
structure.
❖ Tensile strength reduces as O-MWCNT content is increased.
M0 (0wt%) M1 (0.005wt%) M2 (0.01wt%) M3 (0.03wt%) M4 (0.05wt%)
Membrane Porosity
(%)
Mean pore
radius
(nm)
Thickness
(µm)
Pure water
flux
(L/m2.h)
Tensile
strength
(MPa)
M0 71.8 66.2±2.0 146±2.8 666.9±4.0 2.29±0.23
M1 86.2 48.9±2.6 142±2.5 524.0±5.1 2.19±0.20
M2 87.8 47.8±4.9 139±3.9 514.5±5.4 1.94±0.06
M3 88.3 35.3±0.2 128±2.1 333.5±3.0 2.39±0.1
M4 90.8 42.0±1.3 130±3.6 498.6±2.9 1.97±0.09
Contact angle and mechanical strength analyses:
Effect of O-MWCNT wt%.
❖ Contact angle decreases with an increase in O-MWCNT content: Hydrophilicity is
enhanced.
❖ Mechanical strength is improved with increments in O-MWCNT content- highest tensile
strength of for blended UF membrane of 4.02 MPa reached.
Membrane Tensile
strength (MPa)
Contact angle (0)
M0 2.78 ± 0.11 67.2 ± 1.13
M1 3.48 ± 0.37 58.7 ± 2.22
M2 3.50 ± 0.15 56.2 ± 0.18
M3 3.48 ± 0.26 52.2 ± 0.12
M4 3.52 ± 0.07 50.6 ± 0.45
M5 4.02 ± 0.08 47.6 ± 0.46
Zhang et al (2017) PES/SPSf 3.0 ± 0.20
Fang et al (2017) PES/SPES
Vilakati et al (2014) PSf blend
supported on non-woven fabric
3.2 ± 0.08
4.05± 0.33
Performance Evaluation: Carbon Membranes
M0 M1 M2 M3 M4 M5
0
10
20
30
40
50
60
70
80
90
100
Poro
sity (
%)
Membrane type
❖ Membrane porosity increases to a certain extent with an increase in O-MWCNT content, and
reduces with further increments.
❖ PWF initially increases with inclusion O-MWCNT (0.01wt%) and then reduces with further
increments (combined effect of enhanced hydrophilicity and agglomeration of OMWCNTs at
higher loadings).
M0 M1 M2 M3 M4 M5
0
100
200
300
400
500
600
700
800
Pure
wa
ter
flu
x (
L/m
2.h
)
Membrane type
Pure water flux
BSA rejection
0
10
20
30
40
50
60
70
80
90
100
BS
A r
eje
ctio
n (
%)
NN Gumbi, M Hu, BB Mamba, J Li, EN Nxumalo, Journal of membrane science 566, 288-300, 2018
K Yokwana, N Gumbi, F Adams, E Nxumalo, S Mhlanga, B Mamba. J. Appl. Poly. Sci. 132 (2015) 41835
N Phao, EN Nxumalo, BB Mamba, SD Mhlanga, J. Phys. Chem. Earth Parts A/B/C, 66 (2013) 148
M Ben-Sasson, X Lu, E Bar-Zeev, et al (2014). Water Research, 62 (2014) 260
- Contamination with metal catalysts, impurities and physical heterogeneities.
- Functionalization add positive (−NH3+), negative (−COO–, sulfonic acids) & oxidation.
- Hydrophobic (aromatic rings) groups on CNT surfaces; prato functionalise, etc.
- This make CNT membranes selective for particular pollutant retention and increase water influx
through the nanotube hole.
Soak in MPD aqueous solutionImmerse in TMC (in n-hexane) organic
solution
Rinse with DI water/cure
TFC membrane
NaBH4
AgNO3 solution
for 10 min
Supported on Carbon
Multifunctional Nanotechnologies
Qu et al., 2012
Crossflow Testing Units
Affordable sustainable potable water production filtration
systems (UF/NF).
Solar Driven Filtration System
Arne.Verliefde, Bhekie Mamba, Edward Nxumalo, Lebea Nthunya, Sabelo Mhlanga et al… solar driven filtration systems
Technology Testing: Module and Filter
• Temperature
• Pressure
• Wall Temperature• Temperature
• Pressure
Technology Station
❖ Emerging contaminants such as micropollutants can be tackled
with these advanced techniques.
❖ In particular, nanotechnology and membrane technology are in
the forefront.
❖ The periodic table continue to be critical player in the design of
“new materials” such as carbon nanomaterials to address current
issues of human kind such as water pollution.
Takehome Message
❖ The use of new technologies in water treatment applications is
escalating.
JohannesburgUniversity of the Witwatersrand
!
20
The 8th International Conference on Nanoscience and Nanotechnology in Africa
NanoAfrica20
April 2020, Johannesburg, South Africawww.sani.org.za
