The Interlink between the Periodic Table and Water ... · The Interlink between the Periodic Table...

The Interlink between the Periodic Table and

Water Treatment: A Nano PerspectiveEdward Nxumalo, PhD

nxumaen@unisa.ac.za

+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

E: nanows@unisa.ac.za

T: +27 11 670 9480

https://www.un.org/millenniumgoals/

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

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https://www.mesaaz.gov/residents/water-

resources/services/water-treatment-process

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❖ Emerging/new contaminants such as micropollutants!

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❖ 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

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❖ Membranes and membrane processes

❖ Nano-adsorption processes

❖ Photocatalysis

❖ Disinfection and microbial control

❖ Multifunctional nanodevices

❖ Sensing, determination and monitoring

❖ Energy capture and storage

❖ Etc

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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

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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

!

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The 8th International Conference on Nanoscience and Nanotechnology in Africa

NanoAfrica20

April 2020, Johannesburg, South Africawww.sani.org.za