Graphene/TiO2 nanocrystals hybrid is successfully prepared by directly
growing TiO2 nanocrystals on graphene oxide (GO) sheets. The direct growth of
nanocrystals on GO sheets was achieved by a two-step method, in which TiO2 was
coated on GO sheets by hydrolysis first and crystallized into anatase
nanocrystals by hydrothermal treatment in second step. Slow hydrolysis reaction
through the use of EtOH/H2O mixed solvents and addition of H2SO4 allows the
selectively growing TiO2 on GO and suppressing free growth in solution. The
method offers easy access to the GO/TiO2 nanocrystals hybrid with well
controlled coating and strong interactions between TiO2 and the underlying GO
sheets. The strong coupling could lead to advanced hybrid materials for various
applications including photocatalysis. The prepared graphene/TiO2 nanocrystals
hybrid has demonstrated superior photocatalytic activity in degradation of
rhodamine B over other TiO2 materials, showing an impressive 3-fold
photocatalytic enhancement over P25. It is expected that the hybrid material
could also be promising for various other applications including lithium ion
battery where strong electrical coupling to TiO2 nanoparticles is essential.Comment: Nano Research, in pres

Casalongue, Hernan Sanchez

Chen, Zhuo

Dai, Hongjie

Liang, Yongye

Wang, Hailiang

English

arXiv

Yongye Liang

Hailiang Wang

Hernan Sanchez Casalongue

Zhuo Chen

Hongjie Dai

Crossref

Nano Research

TiO2 nanocrystals grown on graphene as advanced photocatalytic hybrid materials

Springer - Publisher Connector

Nano Res. 2010, 3(10): 701–705 
 
701
 
 
 
TiO2 Nanocrystals Grown on Graphene as Advanced 
Photocatalytic Hybrid Materials 
 
 
Yongye Liang§, Hailiang Wang§, Hernan Sanchez Casalongue, Zhuo Chen, and Hongjie Dai () 
 
Department of Chemistry and Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA 
 
Received: 18 July 2010 / Revised: 11 August 2010 / Accepted: 12 August 2010 
© The Author(s) 2010. This article is published with open access at Springerlink.com 
 
 
ABSTRACT 
A graphene/TiO2 nanocrystals hybrid has been successfully prepared by directly growing TiO2 nanocrystals on 
graphene oxide (GO) sheets. The direct growth of the nanocrystals on GO sheets was achieved by a two-step 
method, in which TiO2 was first coated on GO sheets by hydrolysis and crystallized into anatase nanocrystals 
by hydrothermal treatment in the second step. Slow hydrolysis induced by the use of EtOH/H2O mixed solvent 
and addition of H2SO4 facilitates the selective growth of TiO2 on GO and suppresses growth of free TiO2 in 
solution. The method offers easy access to the GO/TiO2 nanocrystals hybrid with a uniform coating and  
strong interactions between TiO2 and the underlying GO sheets. The strong coupling gives advanced hybrid 
materials with various applications including photocatalysis. The prepared graphene/TiO2 nanocrystals hybrid 
has superior photocatalytic activity to other TiO2 materials in the degradation of rhodamine B, showing an 
impressive three-fold photocatalytic enhancement over P25. It is expected that the hybrid material could also 
be promising for various other applications including lithium ion batteries, where strong electrical coupling to 
TiO2 nanoparticles is essential. 
 
KEYWORDS 
Graphene, titanium oxide, photocatalyst, hydrolysis 
 
 
Its interesting electrical and mechanical properties, 
and high surface area make graphene a novel substrate 
for forming hybrid structures with a variety of nano- 
materials [1–3]. Graphene hybrids with metal oxides, 
metals and polymers have been developed recently 
for various applications [4–6]. Nanocrystal growth on 
graphene sheets is an important approach to produce 
nanohybrids, since controlled nucleation and growth 
affords optimal chemical interactions and bonding 
between nanocrystals and graphene sheets, leading to 
very strong electrical and mechanical coupling within 
the hybrid. Several methods have been proposed to 
form nanocrystals on graphene sheets, such as electro- 
chemical deposition [7], sol–gel process [8] and gas 
phase deposition [9, 10]. Recently, we developed a 
controlled, two-step solution phase synthesis of nano- 
crystals of Ni, Fe, and Co hydroxides or oxides on 
graphene sheets, which is highly selective in that 
there is no growth of free nanocrystals in solution [1]. 
We demonstrated the excellent performance of nickel 
hydroxide nanoplates grown on graphene for electro- 
chemical pseudocapacitive energy storage, utilizing  
Nano Res. 2010, 3(10): 701–705 ISSN 1998-0124
DOI 10.1007/s12274-010-0033-5 CN 11-5974/O4
Research Article  
§ These authors contributed equally. 
Address correspondence to hdai@stanford.edu 
 Nano Res. 2010, 3(10): 701–705 
 
702
the high electrical conductivity of graphene [4]. 
Here we present a two-step, direct synthesis of 
TiO2 nanocrystals on graphene oxide (GO) and the 
photocatalytic properties of the resulting hybrid 
material. Due to its low cost, high stability and efficient 
photoactivity, TiO2 has been widely used for photo- 
electrochemical and photocatalytic applications [11]. 
Several graphene/TiO2 composites have been reported 
recently for use in lithium ion batteries [12], photo- 
catalysis [13], and dye sensitized solar cells [14], using 
either surfactant-assisted growth or simple physical 
mixing of pre-synthesized TiO2 particles and graphene. 
Here we achieve surfactant-free growth of TiO2 nano- 
crystals on graphene with optimal TiO2–graphene 
coupling. By limiting the rate of hydrolysis, we obtain 
a high degree of control which confines TiO2 nano- 
crystal growth selectively on the graphene oxide sheets, 
without any growth of free TiO2 in solution. The 
resulting hybrid material showed superior photo- 
catalytic degradation of rhodamine B and methylene  
blue relative to a variety of other TiO2 materials. 
GO prepared by a modified Hummers’ method 
[15–18] was used as a substrate for TiO2 growth giving 
TiO2/GO hybrids (containing ~10% GO by mass). 
Details are given in the Electronic Supplementary 
Material (ESM). The functional groups on GO provide 
reactive and anchoring sites for nucleation and growth 
of nanomaterials (Fig. 1) [1]. In the first reaction step, 
fine particles of almost amorphous TiO2 (see the XRD 
pattern in Fig. S-1 in the ESM) were coated on GO 
sheets by hydrolysis of Ti(BuO)4 at 80 °C by addition 
of H2SO4 in a EtOH/H2O (15/1 by volume) mixed 
solvent, designed to slow down the hydrolysis reaction. 
This led to selective growth of TiO2 on GO (Fig. 1(b)) 
without any obvious growth of free TiO2 particles in 
solution. Rapid hydrolysis occurred when water alone 
was used as the solvent, or without the addition of 
H2SO4; in these cases growth of TiO2 particles in 
solution, not associated with GO, was observed (see 
Fig. S-2 in the ESM). In the second step, we carried out 
a hydrothermal treatment of the amorphous TiO2/GO 
at 200 °C in a mixed water/DMF solvent (Fig. 1(c)), 
which led to crystallization of the coating material on  
GO giving anatase nanocrystals (Figs. 2(b)–2(d)). 
We used water/DMF (50/1 by volume) mixed solvent 
in the second step since DMF was found to facilitate 
dispersion of the graphene sheets and reduce aggre- 
gation, as shown by the higher surface area (190 m2/g) 
for the resulting hybrid compared with that of the 
material (134 m2/g) obtained in pure water. Electron 
microscopy images (Figs. 1(c), 2(a) and 2(b)) revealed 
dense TiO2 nanocrystals densely bound to GO sheets, 
which were not detached even under sonication. High 
resolution TEM (Fig. 2(c)) showed that TiO2 grown 
on GO adopts a highly crystalline anatase phase,  
consistent with the XRD pattern (Fig. 2(d)). 
The density of TiO2 nanocrystals coated on graphene 
was controlled by the feed ratio of Ti(BuO)4/GO, 
 
Figure 1 Synthesis of TiO2 nanocrystals on GO sheets. Top panel: Reaction scheme: (a) AFM image of a starting GO sheet; (b) SEM
image of particles grown on a GO sheet after the first hydrolysis reaction step; (c) SEM image of TiO2 nanocrystals on GO after
hydrothermal treatment in the second step. The scale bars are 100 nm 
Nano Res. 2010, 3(10): 701–705 
 
703
increasing as the amount of Ti(BuO)4 increased 
(Fig. 3). The average size of the TiO2 nanocrystals 
depended on the EtOH/water ratio in the first step, 
increasing from ~15 nm in EtOH/water (15/1) to ~30 
nm in EtOH/water (3/1) (Fig. S-3 in the ESM). This is 
because the rate of the hydrolysis reaction increased 
with increasing water content. This was accompanied 
by a decrease in surface area for TiO2/GO synthesized 
in EtOH/water mixtures with higher water concen-  
trations (Table S-1 in the ESM). 
TiO2 nanocrystals directly grown on graphene 
appeared to exhibit strong interactions with the 
underlying GO sheets since sonication did not lead to 
their dissociation from the sheets. This strong coupling 
should lead to advanced hybrid materials for various 
applications, including photocatalysis. TiO2 has been 
widely used as a photocatalytic semiconductor for 
decontamination of organic pollutants. A limiting 
factor in the rate of photocatalysis reaction is the 
rapid electron-hole recombination [19]. In order to 
increase the charge separation lifetime, carbon nano- 
tube (CNT)–TiO2 hybrids have been produced; these  
 
Figure 3 SEM images of graphene/TiO2 hybrids formed with 
various GO/TiO2 mass ratios: (a) 1:1, (b) 1:3, (c) 1:9, (d) 1:18. 
The scale bars are 100 nm. The TiO2 coating density is controlled 
by varying the feed ratio of Ti (BuO)4/GO. The coating of TiO2 
nanocrystals on graphene becomes denser as the Ti (BuO)4/GO 
feed ratio is increased 
 
Figure 2 (a) SEM image, (b) low magnification, and (c) high magnification TEM images of TiO2 nanocrystals grown on GO sheets.
The scale bar is 400 nm for the SEM image in (a) and 20 nm for the TEM image in (b). (d) An XRD pattern of the graphene/TiO2
nanocrystals hybrid 
 Nano Res. 2010, 3(10): 701–705 
 
704
enhance the rate of photocatalysis reaction through  
transfer of photoexcited electrons to the CNTs [20]. 
We tested the photocatalytic performance of our 
graphene/TiO2 nanocrystals hybrid in the photo- 
degradation of rhodamine B under UV irradiation 
(Fig. 4(a)) and compared it with free TiO2 nanocrystals 
synthesized by the same method in the absence of 
GO, and P25 (a well-known commercial TiO2 photo- 
catalyst). The amount of TiO2 was kept the same in 
all these samples. The hybrid sample used for the 
photocatalytic measurements was prepared using 
EtOH/water = 15/1 (volume ratio) in the first step and 
water/DMF = 50/1 (volume ratio) in the second step 
with TiO2/GO = 9/1 (mass ratio). The kinetics of the 
degradation reaction were fitted to a pseudo first- 
order reaction at low dye concentrations: ln(c0/c) = kt, 
where k is the apparent rate constant [21]. The average 
value of k for the hybrid (k = 0.200 min–1) was found 
to be ca. four times that of free TiO2 grown in  
 
Figure 4 (a) Schematic illustration of the photodegradation of 
rhodamine B molecules by the graphene/TiO2 nanocrystals hybrid 
under irradiation by a mercury lamp. The inset shows the solution 
of the graphene/TiO2 nanocrystals hybrid. (b) Photocatalytic 
degradation of rhodamine B monitored as normalized concentration 
change versus irradiation time in the presence of free TiO2, P25, 
graphene/TiO2 nanocrystals hybrid and a graphene/TiO2 mixture. 
(c) Average reaction rate constant (min–1) for the photodegradation 
of rhodamine B with free TiO2, P25, graphene/TiO2 nanocrystals 
hybrid, and the graphene/TiO2 mixture. The error bars are based 
on measurements on at least four different samples 
solution (k = 0.050 min–1) and three times that of P25 
(k = 0.068 min–1). We also prepared a simple mixture 
of P25 and GO and hydrothermally treated the 
mixture as reported in the literature [13]; the resulting 
mixture gave a value of k = 0.090 min–1, less than half 
that for our directly grown graphene/TiO2 hybrid 
(Figs. 4(b) and 4(c)). The three-fold enhancement in 
photocatalytic activity of our hybrid over P25 is 
impressive, considering the low cost of GO and the 
highest reported enhancement factor (ca. two) for 
CNT–TiO2 composites over P25 [20]. The superior 
photocatalytic activity of our graphene/TiO2 hybrid 
was also demonstrated in the degradation of methylene 
blue. The average rate constant for the hybrid 
(k = 0.128 min–1) is much larger than those for P25 
(k = 0.055 min–1) and a simple mixture of P25 and GO  
(k = 0.084 min–1) (Fig. S-4 in the ESM).  
The high photocatalytic activity of our hybrid could 
be a result of the strong coupling between TiO2 and 
GO which facilitates interfacial charge transfer (with 
GO as an electron acceptor) and inhibits electron–hole 
recombination [22]. Another possible contributing 
factor is that the hybrid material has a higher BET 
surface area (190 m2/g) than both free TiO2 grown in 
solution (121 m2/g) and P25 (58 m2/g). In addition, the 
conjugated dye molecules could bind to large aromatic 
domains on GO sheets via π–π stacking, which could  
favor increased reactivity [19]. 
In conclusion, we have successfully grown TiO2 
nanocrystals on graphene with a well-controlled 
coating density by a two step method. This method 
produced a graphene/TiO2 hybrid with strong inter- 
actions between the two components. The resulting 
hybrid material shows superior photocatalytic activity 
to other forms of TiO2. We expect that the hybrid 
material could also be useful for various other 
applications including TiO2-based electrodes for dye- 
sensitized solar cells and lithium ion batteries, where 
strong electrical coupling to TiO2 nanoparticles are also 
important. Our method could be further extended  
to grow other functional materials on graphene for  
advanced hybrid materials. 
Acknowledgements 
This work was supported in part by Intel, MARCO- 
MSD, and ONR. 
Nano Res. 2010, 3(10): 701–705 
 
705
Electronic Supplementary Material: Supplementary 
material (details of the synthesis of the graphene/ 
TiO2 hybrid and additional experimental data) is 
available in the online version of this article at 
http://dx.doi.org/10.1007/s12274-010-0033-5 and is  
accessible free of charge. 
Open Access: This article is distributed under the terms 
of the Creative Commons Attribution Noncommercial 
License which permits any noncommercial use, 
distribution, and reproduction in any medium,  
provided the original author(s) and source are credited. 
References 
[1] Wang, H. L.; Robinson, J. T.; Diankov, G.; Dai, H. J. 
Nanocrystal growth on graphene with various degrees of 
oxidation. J. Am. Chem. Soc. 2010, 132, 3270–3271. 
[2] Si, Y. C.; Samulski, E. T. Exfoliated graphene separated  
by platinum nanoparticles. Chem. Mater. 2008, 20, 6792– 
6797. 
[3] Lee, D. H.; Kim, J. E.; Han, T. H.; Hwang, J. W.; Jeon, S.; 
Choi, S. Y.; Hong, S. H.; Lee, W. J.; Ruoff, R. S.; Kim, S. O. 
Versatile carbon hybrid films composed of vertical carbon 
nanotubes grown on mechanically compliant graphene films. 
Adv. Mater. 2010, 22, 1247–1252. 
[4] Wang, H. L.; Sanchez Casalongue, H.; Liang, Y. Y.; Dai, H. 
J. Ni(OH)2 nanoplates grown on graphene as advanced 
electrochemical pseudocapacitor materials. J. Am. Chem. 
Soc. 2010,132, 7472–7477. 
[5] Yoo, E. J.; Okata, T.; Akita, T.; Kohyama, M.; Nakamura, J.; 
Honma, I. Enhanced electrocatalytic activity of Pt sub- 
nanoclusters on graphene nanosheet surface. Nano Lett. 
2009, 9, 2255–2259. 
[6] Murugan, A. V.; Muraliganth, T.; Manthiram, A. Rapid, facile 
microwave-solvothermal synthesis of graphene nanosheets 
and their polyaniline nanocomposites for energy storage. 
Chem. Mater. 2009, 21, 5004–5006. 
[7] Williams, G.; Seger, B.; Kamat, P. V. TiO2–graphene 
nanocomposites. UV-assisted photocatalytic reduction of 
graphene oxide. ACS Nano 2008, 2, 1487–1491. 
[8] Wang, D. H.; Kou, R.; Choi, D. W.; Yang, Z. G.; Nie, Z. M.; 
Li, J.; Saraf, L. V.; Hu, D. H.; Zhang, J. G.; Graff, G. L.; 
Liu, J.; Pope, M. A.; Aksay, I. A. Ternary self-assembly of 
ordered metal oxide–graphene nanocomposites for electro- 
chemical energy storage. ACS Nano, 2010, 4, 1587–1595. 
[9] Wang, X. R.; Tabakman, S. M.; Dai, H. J. Atomic layer 
deposition of metal oxides on pristine and functionalized 
graphene. J. Am. Chem. Soc. 2008, 130, 8152–8153. 
[10]  Lu, G. H.; Mao, S.; Park, S.; Ruoff, R. S.; Chen, J. H. Facile, 
noncovalent decoration of graphene oxide sheets with nano- 
crystals. Nano Res. 2009, 2, 192–200. 
[11]  Chen, X. B.; Mao, S. S. Titanium dioxide nanomaterials: 
Synthesis, properties, modifications, and applications. Chem. 
Rev. 2007, 107, 2891–2959. 
[12]  Wang, D. H.; Choi, D. W.; Li, J.; Yang, Z. G.; Nie, Z. M.; 
Kou, R.; Hu, D. H.; Wang, C. M.; Saraf, L. V.; Zhang, J. G.; 
Aksay, I. A.; Liu, J. Self-assembled TiO2–graphene hybrid 
nanostructures for enhanced Li-ion insertion. ACS Nano, 
2009, 3, 907–914. 
[13]  Zhang, H.; Lv, X. J.; Li, Y. M.; Wang, Y.; Li, J. H. 
P25-graphene composite as a high performance photocatalyst. 
ACS Nano 2010, 4, 380–386. 
[14]  Yang, N. L.; Zhai, J.; Wang, D.; Chen, Y. S.; Jiang, L. 
Two-dimensional graphene bridges enhanced photoinduced 
charge transport in dye-sensitized solar cells. ACS Nano, 
2010, 4, 887–894. 
[15]  Hummer, W. S.; Offeman, R. E. Preparation of graphitic 
oxide. J. Am. Chem. Soc. 1958, 80, 1339–1339. 
[16]  Wang, H. L.; Wang, X. R.; Li, X. L.; Dai, H. J. Chemical self- 
assembly of graphene sheets. Nano Res. 2009, 2, 336–342. 
[17]  Sun, X. M.; Liu, Z.; Welsher, K.; Robinson, J. T.; Goodwin, 
A.; Zaric, S.; Dai, H. J. Nano-graphene oxide for cellular 
imaging and drug delivery. Nano Res. 2008, 1, 203–212. 
[18]  Wang, H. L.; Robinson, J. T.; Li, X. L.; Dai, H. J. 
Solvothermal reduction of chemically exfoliated graphene 
sheets. J. Am. Chem. Soc. 2009, 131, 9910–9911. 
[19]  Ravelli, D.; Dondi, D.; Fagnoni, M.; Albini, A. Photocatalysis. 
A multi-faceted concept for green chemistry. Chem. Soc. 
Rev. 2009, 38, 1999–2011. 
[20]  Woan, K.; Pyrgiotakis, G.; Sigmund, W. Photocatalytic 
carbon-nanotube–TiO2 composites. Adv. Mater. 2009, 21, 
2233–2239. 
[21]  Wang, X. H.; Li, J. G.; Kamiyama, H.; Moriyoshi, Y.; 
Ishigaki, T. Wavelength-sensitive photocatalytic degradation 
of methyl orange in aqueous suspension over iron(III)-doped 
TiO2 nanopowders under UV and visible light irradiation. J. 
Phys. Chem. B, 2006, 110, 6804–6809. 
[22]  Wang, W. D.; Serp, P.; Kalck, P.; Faria, J. L. Photocatalytic 
degradation of phenol on MWNT and titania composite 
catalysts prepared by a modified sol–gel method. Appl. 
Catal. B 2005, 56, 305–312. 
 


A graphene/TiO2 nanocrystals hybrid has been successfully prepared by directly growing TiO2 nanocrystals on graphene oxide (GO) sheets. The direct growth of the nanocrystals on GO sheets was achieved by a two-step method, in which TiO2 was first coated on GO sheets by hydrolysis and crystallized into anatase nanocrystals by hydrothermal treatment in the second step. Slow hydrolysis induced by the use of EtOH/H2O mixed solvent and addition of H2SO4 facilitates the selective growth of TiO2 on GO and suppresses growth of free TiO2 in solution. The method offers easy access to the GO/TiO2 nanocrystals hybrid with a uniform coating and strong interactions between TiO2 and the underlying GO sheets. The strong coupling gives advanced hybrid materials with various applications including photocatalysis. The prepared graphene/TiO2 nanocrystals hybrid has superior photocatalytic activity to other TiO2 materials in the degradation of rhodamine B, showing an impressive three-fold photocatalytic enhancement over P25. It is expected that the hybrid material could also be promising for various other applications including lithium ion batteries, where strong electrical coupling to TiO2 nanoparticles is essential. © 2010 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.link_to_subscribed_fulltex

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TiO<inf>2</inf> Nanocrystals grown on graphene as advanced photocatalytic hybrid materials

TiO2 Nanocrystals Grown on Graphene as Advanced Photocatalytic Hybrid
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TiO2 Nanocrystals Grown on Graphene as Advanced Photocatalytic Hybrid Materials

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