Fabrication of a TiO2−BDD Heterojunction and its Application As a Photocatalyst for the Simultaneous Oxidation of an Azo Dye and Reduction of Cr(VI)

Abstract

A TiO₂-boron doped diamond (TiO₂−BDD) heterojunction was employed as a photocatalyst to simultaneously oxidize an azo dye C.I. reactive yellow 15 (RY15) and reduce hexavalent chromium (Cr(VI)). This heterojunction was fabricated first by depositing a BDD film on a Ti sheet in a hot filament chemical vapor deposition reactor, followed by covering a layer of TiO₂ in a metal−organic chemical vapor deposition system. The morphology of this heterojunction was characterized by using a scanning electron microscope (SEM). X-ray diffraction (XRD), Raman spectroscopy, and current–voltage (I−V) measurement were used to characterize its structures. Additionally, the characterization of surface photovoltage showed that the TiO₂−BDD heterojunction exhibited a higher photovoltage response and a better ability for charge separation than the photocatalyst of TiO₂ directly deposited on a Ti sheet (TiO₂−Ti). The photocatalytic experiments revealed that the kinetic constants for the oxidation of RY15 and the reduction of Cr(VI) were, respectively, increased by 85 and 71% when the photocatalyst of TiO₂−Ti was replaced by the TiO₂−BDD heterojunction. Meanwhile, a significant synergy was confirmed in the simultaneous oxidation of RY15 and reduction of Cr(VI). The enhanced photocatalytic ability of the TiO₂−BDD composite could be attributed to the heterojunction. The possible photocatalytic mechanism was also discussed.