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