Hydrothermal synthesis of TiO2 nanotube/Graphene

oxide composite and its application in photocatalytic

purification of water

Zahra Gholamvand*, Anne Morrissey, Kieran Nolan, John Tobin* School of Biotechnology, Dublin City University, Dublin, Ireland

Email: Zahra.gholamvand2@mail.dcu.ie

Using graphene sheets as a support to prepare

graphene/ TiO2 nanotubes composite by

hydrothermal in-situ synthesis of TiO2 nano-

nanotubes on the surface graphene oxide sheets

Characterizing Graphene and Graphene/ TNTs

composite structurally and physically and obtain

a composite with high conductivity, crystallinty

and surface area

Finding the most efficient composite by changing

the weight percentage of graphene and TiO2 , the

reduction condition of Graphene Oxide (GO) to

Graphene, temperature, PH and calcinations

temperature

Investigate the efficiency of the composite to

adsorb and degrade organic species such as

VOC, pigments and pharmaceuticals

Designing and building up an efficient

photocatalytic system to work under UV and

sunlight

Comparing the photocatalytic performance of the

Graphene- TiO2 composite with other composites

such as zeolite- TiO2, activated carbon- TiO2 and

Dolomite–TiO2

Finding the most economic and efficient system

to remove organic compounds such as

pesticides, volatile organic compounds and

pharmaceuticals from water and waste water

The authors wish to acknowledge the financial support of,

the Marie Curie Initial Training Network funded by the EC

FP7 People Programme, ATWARM (Advanced Technologies

for Water Resource Management).

Electron diffraction pattern SAD of TNT/GO

composite in Fig.6 shows the sharp diffraction

pattern which shows GO reduced partially

during hydrothermal treatment

All TNTs are attached to the GO surface and

there is no free particle in the solution which

increases the composite functionality and it

might be because of functional groups available

on GO surface.

TNTs growth takes place on the graphene

surfaces which encourages the formation of

nano tubes uniformly dispersed on the

graphene surface and also mimics the

topography of GO into a fractal like shape

(SEM image shown in Fig.10)

The dimensions of the composite sheets were

about 3-5 micro-meter both in length and width,

which allows for an easy separation of the

composite with conventional filtration (SEM

image Fig.9).

In the natural PH TiO2 forms solid wire and

they grow uniformly on the surface of GO with

the average length of 1-2 micrometer and 10-

20 nano meter in diameter

Photo-degradation of famotidine as a pollutant

model is shown in Fig.3. Before the

photocatalytic experiment, the suspension of 1

liter solution with a famotidine concentration of

100 mg/lit and 0.2 gr/lit catalyst was

magnetically stirred for 2 h in dark to discount

the adsorption on the catalyst. The rapid

degradation of famotidine over GO/TiO2 is

clearly shown in Fig.11. About 90% of the

famotidine was degraded within 180 min which

is a significant photo-degradation in

comparison with P25 powder and neat TNTs

powder that exhibited less than 50 degradation

over the same time.

After photo-degradation the catalyst can be

removed easily by filtration or settling down in

the reactor this is another advantage of using

composite over TiO2nano powderNatural Energy

usage

Advanced

Technologies

New Materials

Photocatalysis

Abstract Objectives Results Results

Conclusions

Acknowledgment

Fig.2. Degradation mechanism and recombination of

trapped electrons

MethodBackground

Nanocrystalline semiconductors, such as titania,

are important in many energy-saving processes

including: water purification, air purification,

disinfection and self-cleaning.

Over the past decades degradation of organic

pollutants using titanium dioxide has attracted

increasing attention for the purification of

water. One of the newest methods is

combining titanium dioxide and an adsorbent

material to create integrated photocatalytic

adsorbents (IPCAs) which overcome some of

the limitations of TiO2 nano-particles such as

low photocatalytic efficiency at low pollutant

concentrations and complicated separation

after purification. Recently, nanostructured

carbon materials, such as carbon nanotubes

and graphene sheets, offer an exciting

research area owing to their structurally

interesting and unusual properties. TiO2

nanotube (TNT) also is considered as a

modified structure in photo-catalysis owing to

its special electronic and mechanical

properties, high photocatalytic activity, large

specific surface area and high pore volume. In

the present work TNTs were prepared via

hydrothermal method from commercial TiO2

and GO in basic environment followed by acid

washing that encourages nanotube formation.

After calcination the prepared powder were

used in photodegradation experiments to

degrade pharmaceuticals.

1gr P25 +70 ml NaOH 10 M stirring + 0.2 gr GO sonication 30 min

Hydrothermal treatment at 130 ⁰C for 24 hours

Washing with 1 liter HCl 0.1 M until PH 7 reached

Washing with water + drying at 80 ⁰C

Calcinations at 400 ⁰C for 2 hours

Mixing 0.2 gr composite with 1 liter of water containing 100 ppm of pharmaceuticals

Adsorption and photodegradation experiment taking samples regularly, analysis with HPLC

The novel composite exhibited excellent

photocatalytic activity for adsorption- degradation

of pharmaceuticals which is attributed to a thin

two-dimensional sheet support, a large surface

area and a good electron acceptor favoring the

transfer of photo-generated electrons from the

conduction band of TiO2 to the graphene sheet. In

summery adsorption, transparency, conductivity

and very large planar structure of graphene are

the key enhancing factors for photo-degradation

of the pollutants with graphene/ TiO2 composites.

This new composite may find promising

applications in the field of environmental

Photocatalysis specially water purification and it

has the potential to become the ideal substrate

for a number of catalytic and sensing processes.

Fig.3. Electron transfer enhancement by Graphene

Expandable flaked graphite was used as

graphene source and P25 Aeroxide powder as a

TiO2 precursor. In the present work, three simple

strategies have been proposed to synthesize

TNTs on the surfaces of GO: direct mixing of GO

with pre-hydrothermally synthesised TNT powder,

hydrothermal treatment of p25 and GO in high PH

NaOH solution followed by acid washing and

hydrothermal treatment of p25 with GO in natural

aqueous solution. The photo-degradation

experiments were carried out using a 1 litre

cylindrical reactor and an immersion well as

shown in Fig.2. The UV irradiation source was a

125 W mercury lamp. Before the illumination, the

suspension was stirred in the dark for 120 min to

establish the adsorption-desorption equilibrium.

HPLC method was used to measure Famotidine

concentration.

Fig.7. SAD pattern of GO/TNT

Fig.10. SEM image of TNTs/GO composite

synthesised at natural PH

Fig.11. Famotidine UV Photo-degradation

Fig.5. Immersion well

photo-reactor

Fig.1. Importance of photocatalytic remediation

Fig.4

Clean

Environment

Fig.6. TEM image of TNTs

Fig.8. TEM image of GO/TNTs synthesised in

NaoH solution

Fig.9. TEM image of GO/TNTs composite by

mixing

Fig.10. SEM image of GO/TNTs composite in

natural PH