Design, Fabrication, and Modification of Cost-Effective Nanostructured TiO for Solar Energy Applications - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 43

Recently, graphene quantum dots (GQDs) have become an active area of
research. Compared to graphene with 2D nanosheets and 1D nanoribbon structures,
0D GQDs possess strong quantum confinement and edge effects when their sizes
approach 10 nm or less. At this scale, new physical properties become apparent
[ 385 - 387 ]. Zhuo et al. presented the synthesis of GQDs with excellent PL properties
using a direct and simple ultrasonic reaction process. The composite photocatalysts
(rutile TiO 2 /GQD and anatase TiO 2 /GQD systems) were prepared by mixing GQDs
with TiO 2 nanoparticles (Fig. 18 d) in order to harvest the visible spectrum of
sunlight using the upconversion photoluminescence (PL) properties of GQDs
(Fig. 18 e). It was observed that the photocatalytic activity of the rutile TiO 2 /GQD
composite was superior to that of the anatase TiO 2 /GQD composite under visible
light (k [ 420 nm) irradiation in the degradation of MB (Fig. 18 f) [ 388 ].
3 Conclusion
The challenge of effectively converting solar energy into useful energy will require
more advanced materials. As one of the most promising functional materials for
efficient, high performance, and cost-effective solar energy applications, TiO 2
nanostructures of various morphologies will continue to be an area of active
research. It has been shown that every structure possesses its own advantages, such
as large surface area for nanoparticle systems, effective charge separation, and
transport for vertically ordered nanotubes or nanorods, a high percentage of reactive
(001) facets for nanosheets, and efficient light scattering for 3D hierarchical
structures, to name a few. Correspondingly, the different morphologies are derived
from different characteristic synthesis methods. The sol-gel method, for example, is
a simple and low-cost process to prepare nanoparticles. The hydrothermal method
can be used to fabricate several structures (e.g., nanosheet, nanorod and hierarchical
architecture), whereas the facile electrochemical anodization can lead to oriented
nanotube arrays. Clearly, numerous strategies have been exploited to modify pure
TiO 2 , which suffers from the shortcomings of a narrow light absorption range
(restricted to UV) and rapid charge recombination. With more efforts geared toward
the fabrication of high-quality TiO 2 -based nanomaterials and economically feasible
synthesis procedures, there is little doubt that the future of solar energy technology
and its practical applications will remain bright.
References
1. Liu J, Cao GZ, Yang ZG, Wang DH, Dubois D, Zhou XD, Graff GL, Pederson LR, Zhang
JG (2008) ChemSusChem 1:676-697
2. Hagfeldt A, Boschloo G, Sun LC, Kloo L, Pettersson H (2010) Chem Rev 110:6595-6663
3. Kamat PV (2007) J Phys Chem C 111:2834-2860