Post on 25-Oct-2015
description
Graphene Nanosheets for Capacitive
Deionization
By
Yusufu Abeid Chande Jande
March 27, 2013
Hanyang University, Advanced Polymer Based Nanomaterials
Contents
Overview on desalination
Preparation of graphene nanosheets
Advanced Polymer Based Nanomaterials, March 27, 2013
What is Desalination?
Source of water can be sea/ocean, underground, lakes, or
rivers.
Water from these sources contain undesirable amount of
minerals which are unfavorable for human consumption
or industrial use.
Desalination: The process of removing salts from
brackish water to an acceptable standard either for
domestic or industrial use.
Excessive/unrequired salt ions are removed from the
saline water using different methods.
Common methods used for desalination process: thermal
processes, membrane processes, membrane distillation,
and ion exchange processes i.e., capacitive deionization
(CDI).
Advanced Polymer Based Nanomaterials, March 27, 2013
Capacitive Deionization
Capacitive deionization (CDI) is a promising technology for
desalination of brackish water with different applications such as in
the pharmaceutical industry, semiconductor manufacturing, and
domestic use.
The CDI cell utilizes an electric potential across two electrodes in
which one of the electrodes becomes positively charged and the other
becomes negatively charged.
Cations and anions are attracted towards the anode and cathode,
respectively.
The adsorption and desorption mechanism within the CDI cell
determines the amount of salt in the effluent stream.
Advanced Polymer Based Nanomaterials, March 27, 2013
Electrode Materials for CDI
Graphene nanosheets
Carbon nanotubes–polyacrylic acid composite
Carbide derived carbon
Activated carbon electrode
Activated carbon cloth
Single-walled carbon nanotubes and polyaniline composites
Graphene nano-flakes Carbon aerogels
Advanced Polymer Based Nanomaterials, March 27, 2013
What is Graphene?
Carbon can form three-dimensional lattices by bonding with four other carbon atoms to form diamond
When carbon bonds to three other carbon atoms forms two-dimensional sheets
These sheets are called graphene
Advanced Polymer Based Nanomaterials, March 27, 2013
http://www.understandingnano.com/what-is-graphene.html, March 26,2013
Why Graphene Nanosheets for CDI?
High surface area ~ 464 m2/g High NaCl removal efficiency ~ 83.4 %
High specific capacitance ~ 149.8 F/g
High electrosorptive capacity ~ 8.46 mg/g
High regeneration capacity
Advanced Polymer Based Nanomaterials, March 27, 2013
Graphene sheets
Graphene Nanosheets Preparation
Three steps are used in preparing graphene nanosheets from graphite
oxide (GO)
Partial reduction of GO Sulphonation of partially reduced GO
Reduction by hydrazine
Advanced Polymer Based Nanomaterials, March 27, 2013
Synthesis of GO
GO is synthesized from natural graphite flakes by a modified
Hummers method
Graphite flakes (i.e., 2.5 g) are added into a mixture of concentrated
nitric acid and sulfuric acid (volume ratios = 2:1) at 353 K and stirrer
for 4.5 h
Cool the mixture to room temperature, dilute with deionized (DI)
water (i.e., 0.5 L) and leave it for one night
Put the mixture into the reaction vessel with 120 mL of concentrated
H2SO4; and immerse it into an ice bath Add KMnO4 slowly and then stirrer for 2 h
Dilute with DI water and then add H2O2 (20 mL, 30 wt.%) to the
mixture. The color of the mixture changes to bright yellow and air
bubbles appears
Filter the mixture and wash with HCl aqueous solution (1:10 in
volume) to remove residual metal ions
Wash with DI water until its pH reaches 7 Use ultrasonicator for exfoliation of GO overnight
Advanced Polymer Based Nanomaterials, March 27, 2013
First-stage reduction of GO by Fe
Add Fe powder (1 g) and HCl (10 mL, 35 wt.%) into the GO suspension at ambient temperature.
Stirrer the mixture for 30 min and maintain for a period of time
Add more HCl to the above solution to remove the residual Fe
completely
Collect the resulting product by filtration, wash with water and ethanol
several times and dry at 373 K for 12 h
Advanced Polymer Based Nanomaterials, March 27, 2013
Sulphonation of partially-reduced GO
Prepare the aryl diazonium salt from the reaction of sulphanilic acid
(46 mg) and sodium nitrite (18 mg) in an ice-bathed aqueous mixture
of water (10 mL) and HCl solution (0.5 mL, 35 wt.%).
Add the achieved solution into the dispersion of the partially reduced
GO under constant stirring for over 2 h
Remove the bubbles from the reaction mixture; aggregation can be
observed on the addition of the diazonium salt solution
Centrifuge and rinse with water for several times, then the product is
re-dispersed in the water
Note: Sulpnonation process is for preventing agglomeration of graphene
nanosheets.
Advanced Polymer Based Nanomaterials, March 27, 2013
Second-stage reduction by hydrazine
Add hydrazine into the dispersion and keep the reaction mixture at
373 K for 24 h under constant stirring
Rinse it with water thoroughly and then collect the as-prepared
product using vacuum filtration
Use atomic force microscope to determine the thickness of the as-
prepared graphene nanosheets. Typical value can be 1.2 nm
Advanced Polymer Based Nanomaterials, March 27, 2013
THANK YOU
Advanced Polymer Based Nanomaterials, March 27, 2013
B. Jia, L. Zou, Graphene nanosheets reduced by a multi-step process as high-performance electrode
material for capacitive deionisation, Carbon, 50 (2012) 2315-2321