Fabrication of TiO 2 -Reduced Graphene Oxide Nanorod Composition Spreads Using Combinatorial Hydrothermal Synthesis and Their Photocatalytic and Photoelectrochemical Applications.

This study is the first to employ combinatorial hydrothermal synthesis and facile spin-coating technology to fabricate TiO2 -reduced graphene oxide (rGO) nanorod composition spreads. The features of this study are (1) the development of a self-designed spin-coating wedge, (2) the systemic investigation of the structure-property relationship of the system, (3) the high-throughput screening of the optimal ratio from a wide range of compositions for photocatalytic and photoelectrochemical (PEC) applications, and (4) the effective coupling between the density gradient TiO2 nanorod array and the thickness gradient rGO. The formation of rGO in the fabricated TiO2 -rGO sample was monitored through Fourier transform infrared spectrometry. Transmission electron microscopy images also suggested that the TiO2 nanorod surfaces were covered with a thin layer of amorphous rGO. The rutile TiO2 plane evolution along the composition variation was verified through X-ray diffraction. 7% TiO2 -93% rGO on the nanorod composition spread exhibited the most promising photocatalytic ability; the corresponding photodegradation kinetics, denoted by the photodegradation rate constant (k), was determined to be approximately 12.7 × 10-3 min-1 . The excellent performance was attributed to the effective coupling between the TiO2 and rGO, which improved the charge carrier transport, thus inhibiting electron-hole pair recombination. A cycling test implied that 7% TiO2 -93% rGO is a reliable photocatalyst. A photoluminescence spectroscopy study also supported the superior photocatalytic ability of the sample, which was attributed to its markedly poorer recombination behavior. In addition, without further treatment, the sample exhibited excellent PEC stability; the photocurrent density was more than three times higher than that exhibited by the density gradient TiO2 nanorods.