Photocatalytic O₂ Evolution of Rhodium and Antimony-Codoped Rutile-Type TiO₂ under Visible Light Irradiation

Abstract

The effects upon the photophysical and photocatalytic properties of the codoping of rhodium and antimony in rutile-type TiO2 were investigated. TiO2 codoped with rhodium and antimony (TiO2:Rh/Sb) had an absorption band in the visible light region. Its energy gap was 2.1 eV. The TiO2:Rh/Sb powder showed photocatalytic activity for the oxidation of water to form O2 in the presence of Ag+ ions as an electron acceptor under visible light irradiation (λ > 440 nm), whereas TiO2 doped with only rhodium showed no activity. The photocatalytic activity strongly depended on the amount and ratio of the Sb/Rh dopant. Electron spin resonance, diffuse reflection spectroscopy, and X-ray absorption near-edge structure analyses revealed that the doped rhodium exists in a trivalent oxidation state in the active photocatalyst. The photocatalytic activity was decreased remarkably even by a small amount of Rh4+ ions. Antimony played an important role in suppressing the formation of Rh4+ ions by charge compensation. Thus, it has been clarified that Rh3+ is the species responsible for the photocatalytic activity under visible light irradiation in the TiO2:Rh/Sb photocatalyst.

Photocatalytic H2 evolution by layered perovskite Ca3Ti2O7 codoped with Rh and Ln (Ln = La, Pr, Nd, Eu, Gd, Yb, and Y) under visible light irradiation

“…On the other hand, Niishiro et al reported that rutile-type TiO2 codoped with Rh and Sb showed high photocatalytic O2 evolution from an aqueous silver nitrate solution under visible light irradiation. 22) According to their report, the activity depended upon suppressing the formation of Rh 4+ and promoting the formation of Rh 3+ by codoping high-valence ions, such as Sb 5+ . In addition, codoping with Rh and Sb suppressed the formation of oxygen defects, which act as recombination centers.…”

Combinatorial doping of TiO2 with platinum (Pt), chromium (Cr), vanadium (V), and nickel (Ni) to achieve enhanced photocatalytic activity with visible light irradiation

“…4(a) , which results in the formation of finer and smoother crystalline particles. 28 However, in our case, the doping of 0.3 at.% Pt 2+ (0.94 Å ) does not significantly change either the size of particle or the morphology [ Fig. 4(b)].…”

“…[24][25][26][27][28] Ahmad et al reported that Sc and Nb codoped TiO 2 nanoparticles are relatively more photoactive for 2-chlorophenol degradation under visible light than the particles doped with Sc or Nb alone. 25 Kato ) and TiO 2 codoped with Rh 3+ and Sb 5+ were also shown to improve photocatalytic activity for O 2 evolution under visible light irradiation.…”

“…25 Kato ) and TiO 2 codoped with Rh 3+ and Sb 5+ were also shown to improve photocatalytic activity for O 2 evolution under visible light irradiation. 27,28 However, there have been relatively few studies reported for double metal ion codoping of TiO 2 , while TiO 2 codoped with two nonmetallic elements (e.g., N and F codoping, 29,30 N and S codoping 31,32 ) or with metal ions and nonmetallic elements [33][34][35][36][37][38][39] (e.g., Cr and N codoping 35 Pt and N codoping, 36 V and N codoping, 37 …”

A DFT +Ustudy of (Rh, Nb)-codoped rutile TiO2

“…Kitano et al [13] showed that Rh modified TiO 2 samples exhibit higher level of activity than Cu 2+ modified and the nitrogen-doped samples. On the other hand, Niishiro et al [14] reported that TiO 2 doped with only Rh shows only negligible photocatalytic activity as it creates Rh 4+ ions. They suggested that in such cases, charge compensated codoping with pentavalent ions such as Sb 5+ , Nb 5+ , Ta 5+ becomes necessary for suppressing the formation of Rh 4+ ions and improving photocatalytic activity.…”