Photocatalytic Hydrogen Evolution over Exfoliated Rh-Doped Titanate Nanosheets.

Wasusate Soontornchaiyakul,Ryo Sasai,Natsumi Yano,Takuya Fujimura,Yusuke Kataoka

doi:10.1021/acsomega.0c00204

Abstract

Various amounts of Rh-doped titanate nanosheets (Ti3NS:Rh(x), where x is doped amount) were prepared to develop a new nanostructured photocatalyst based on metal oxide compounds that can split water to produce H2 under sunlight. Ti3NS:Rh(x) was obtained by acid exchange, intercalation, and exfoliation of Rh-doped layered sodium titanate compound (Na2Ti3–xRhxO7). A new energy gap was found in the diffuse reflection spectrum of the Ti3NS:Rh(x) colloidal suspension solution; this new energy gap corresponds to electrons in the 4d level of Rh3+ or Rh4+, which are doped in the Ti4+ site. A photocatalyst activity of Ti3NS:Rh(x) for H2 evolution in water with triethylamine (TEA) as an electron donor was investigated. The appropriate amount of Rh doping can improve the photocatalytic activity of Ti3NS for H2 evolution from water using triethylamine (TEA) as a sacrifice agent. The reason was related to the rich state of Rh3+ or Rh4+ doped in the Ti4+ site of Ti3NS. Doping Rh 1 mol % of Ti, Ti3NS:Rh(0.03) shows the H2 evolution rates up to 1040 nmol/h, which is about 25 times larger than that of nondoped Ti3NS under UV irradiation (>220 nm) and 302 nmol/h under near-UV irradiation (>340 nm). These results show that the development of new nanostructured photocatalyst based on Rh-doped titanate compounds that can produce H2 under near-UV irradiation present in sunlight was a success.

Highlights

Hydrogen has become an important source for a promising alternative energy instead of fossil fuel in many factories.[1−3] Hydrogen can be produced by numerous chemical and electrochemical processes
10 nm.[15−19] Due to the conduction band formed by Ti 3p and the valence band formed by O 2p, titanate nanosheet (TiNS) is suitable for sacrificial H2 and O2 evolution or overall water-splitting photocatalyst.[20,21]
We found that Rh doping did not affect the conduction level of Ti3NS; the photocatalytic activity for the degradation of organic compounds under UV-light irradiation was improved

Summary

■ INTRODUCTION

Hydrogen has become an important source for a promising alternative energy instead of fossil fuel in many factories.[1−3] Hydrogen can be produced by numerous chemical and electrochemical processes. The comparison between H2 evolution rate with each irradiation light and the DR spectrum of Ti3NS:Rh(0.03) shows a relation between the absorption band and the H2 evolution reaction (Figure 3C). The photocatalytic activity of Ti3NS:Rh(x) under near-UV (λ > 340 nm) light irradiation was observed only in the Rh-doped Ti3NS This means that the excited electrons did not come from O 2p but from a donor level of Rh3+ 4d to the conduction band (Ti4+ 3d) of Ti3NS. From these results, the effect of Rh doping is quite similar to Rh cocatalyst loading, which results in the improvement of the photocatalytic activity of Ti3NS for H2 evolution from water. The observation of this reaction in real time is too arduous due to the unstable Rh4+

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES