ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY http://dx.doi.org/10.14233/ajchem.2016.19660 INTRODUCTION The photocatalytic degradation of organic pollutants based on wide band gap semiconductors has attracted increasing attention during the past decades due to their capability of simultaneous harvesting solar energy and driving chemical reactions via photo-excited charge carriers and activated electronic states [1]. Among various semiconductor materials studied, TiO2 has been recognized as the most common candidate for widespread environmental applications because of its long-term stability, non-toxicity, controllable structure and morphology and low price [2,3]. However, there are three bottlenecks to hinder its practical applications. One is that the band gap of TiO2 is 3.2 eV, hence it can absorb only the ultraviolet light (radiation with wavelength, λ < 400 nm), which accounts for about 4 % of the sunlight. The second drawback comes from the low separation probability of photo-induced electron-hole pairs in photocatalysts leading to the recombination of electron-hole pairs and therefore reducing the photocatalytic efficiency. The last one is due to the difficulty in collecting it for reusing because TiO2 in the form of nano-particles can be dispersed in aqueous solution and, therefore, swept away after use. Up to now, various processes have been proposed via either doping or compound modification to narrow its band gap and enhance the photocatalytic activity in the range of the visible wavelength radiation [1,2,4,5]. However, further study is needed to produce materials which can offer the better requirements. Synthesis of Graphene Titanium Dioxide Composites as Photocatalytic Materials for Degradation of Moderacid Black THANH XUAN NGUYEN 1 , MO THI NGUYEN 1 , HUNG VAN NGUYEN 2 and HUNG VAN HOANG 1,* 1 Faculty of Chemistry, Hanoi National University of Education, 136 Xuan Thuy Cau Giay, Hanoi, Vietnam 2 Faculty of Physics, Hanoi National University of Education, 136 Xuan Thuy Cau Giay, Hanoi, Vietnam *Corresponding author: Tel: +84 4 38330842; E-mail: hunghv@hnue.edu.vn; hvhungsp@yahoo.com Received: 8 October 2015; Accepted: 15 January 2016; Published online: 29 February 2016; AJC-17795 Graphene titanium dioxide composites with different ratios of graphene to TiO2 have been successfully synthesized by a facile hydrothermal method using graphite and titanium tetrachloride as precursors. The composites were characterized by scanning electron microscope, Raman and ultraviolet-visible spectroscopies, X-ray diffraction and thermogravimetric analysis. A composite with titanium content of 20 % was revealed to be the most thermally stable in comparison to other composites, with the most uniform distribution of TiO2 on graphene sheets. The photodegradation study and thermogravimetric analysis showed that the composite with 20 % of titanium is a very stable material. After 15 times use, the photodegradation efficiency remained almost constant with the value of 99.38 %. Keywords: Graphene, TiO2, Hydrothermal method, Photocatalyst, Moderacid black. Asian Journal of Chemistry; Vol. 28, No. 6 (2016), 1297-1303 Graphene, a flat one-atom-thick monolayer consisting of carbon atoms tightly packed into a two dimensional (2D) honeycomb sp 2 carbon lattice, is another allotrope of carbon beside fullerenes and carbon nanotube. It has been intensively considered due to the unique physical, chemical and mechanical properties. It processes high conductivity at room temperature [6], high specific surface area up to 2630 m 2 g -1 , complex band structure with conduction and valence bands overlapping for a multi-layer graphene, etc. [7]. Among the applications of graphene, integrating graphene with other inorganic materials to fabricate composites or hybrids is the focus. Particularly, the composite of TiO2 and graphene has been considered as a potential photocatalyst in the treatment of polluted air and water [8,9]. It is believed that, a combination of graphene and TiO2 forming composite can reinforce photocatalytic efficiency in which graphene acts as an excellent conductor to spread generated electron-hole pairs on TiO2 due to the interaction of TiO2 and graphene and therefore hinder the recombination of these electron-hole pairs raising the photocatalytic efficiency [10]. Graphene-TiO2 composites have been successfully fabricated by various ways in recent years. Liang et al. [11] reported that graphene-TiO2 nanocrystal hybrid has been prepared by directly growing TiO2 nanocrystals on graphene oxide sheets. The direct growth of the nanocrystals on graphene oxide sheets was achieved by a two-step method, in which TiO2 was first coated on graphene oxide sheets by hydrolysis and crystallized into anatase nanocrystals by hydrothermal