Photocatalytic Hydrogen Evolution over Exfoliated Rh-Doped Titanate Nanosheets

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 (Na₂Ti_3- Rh O₇). 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.