Squaraine-sensitized composite of a reduced graphene oxide/TiO sub(2) photocatalyst: pi - pi stacking as a new method of dye anchoring

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2014-12, Vol.3 (1), p.232-239
• Main Authors: Joseph, KLVincent, Lim, Jonghun, Anthonysamy, A, Kim, Hyoung-il, Choi, Wonyong, Kim, Jin Kon
• Format: Article
• Language: English
• Subjects: Graphene; Molecular orbitals; Nanostructure; Oxides; Shells; Stacking; Titanium dioxide; Wavelengths
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c4ta04313h

We synthesized a near infra-red (NIR)-absorbing squaraine dye (VJ-S) showing strong absorption and emission maxima at 684 and 704 nm, respectively, with a high molar extinction coefficient ( epsilon ) of 1.277 10 super(5) M super(-1) cm super(-1) and a band gap of 1.77 eV. Its oxidation and reduction potentials were found to be 0.889 and -0.795 V, respectively, with HOMO and LUMO levels of -5.21 and -3.53 eV, respectively. We also prepared the self-assembled core/shell nanocomposite r-NGOT, where TiO sub(2) is the core and reduced nano-sized graphene oxide (r-NGO) is the shell. When VJ-S was anchored on r-NGOT, it showed pi - pi stacking with r-NGO, which is confirmed by Fourier-transformed infrared spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and electron energy loss spectroscopy. The optical absorption spectrum of the VJ-S/r-NGOT nanocomposite measured with diffuse reflectance UV/visible absorption spectroscopy covers the whole range of visible light wavelengths up to 800 nm. The photocatalytic activity of VJ-S/r-NGOT at visible light wavelengths ( lambda > 420 nm) is much higher than that of r-NGOT alone.