Photocatalytic Hydrogen Evolution over Exfoliated Rh-Doped Titanate Nanosheets

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–x Rh x 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.

Insight into the Light-Driven Hydrogen Production over Pure and Rh-Doped Rutile in the Presence of Ascorbic Acid: Impact of Interfacial Chemistry on Photocatalysts

“…Similarly, Huang et al have also found that Rh­(IV) is the more dominating species as per their XPS data . It is known that the intrinsic electrons at Rh­(III) sites can be excited to the conduction band of TiO 2 for HER by visible light, while Rh­(IV) sites tend to trap electrons and incur recombination with holes . Therefore, the latter is regarded as a liability to be avoided.…”

“…18 It is known that the intrinsic electrons at Rh(III) sites can be excited to the conduction band of TiO 2 for HER by visible light, while Rh(IV) sites tend to trap electrons and incur recombination with holes. 19 Therefore, the latter is regarded as a liability to be avoided. Nevertheless, as revealed next, doping even in the form of Rh(IV) may have benefits.…”

“…Even upon successful doping, the photocatalytic performance can still vary drastically, depending on the valence states of Rh, which can be Rh­(III) and/or Rh­(IV). For instance, many authors have reported significant improvements in photocatalytic activity when doping Rh into TiO 2 nanosheets and nanorods. ,, These reports argue that Rh­(III) sites are the major contributors to the high activities due to the introduction of intra-gap donor levels without causing severe recombination, whereas Rh­(IV) sites are the recombination centers . Unfortunately, Rh quite often takes the form of Rh­(IV), which helps maintain charge neutrality in the TiO 2 lattice.…”

Hydrogen evolution via noble metals based photocatalysts: A review

“…Rh-Ti3NS Solid-state reaction method, water solution (pH triethylamine (TEA) as an electron donor, 500 W Xe lamp, λ > 220 nm 1970 μmolg -1 h -1 [145] Pt@Cu1.94S−ZnxCd1−xS 1D, 0≤x≤1…”

Photocatalytic Reduction of Cr(VI) on a 3.0% Au/Sr0.70Ce0.20WO4 Photocatalyst

“…However, the majority of the tungstates only act in the ultraviolet zone . To improve the photocatalytic activities of the famous g-C 3 N 4 and titanate photocatalysts, the common way is to dope elements into their crystal structures. , Herein, we introduced a visible-light-responsive Ce-doped SrWO 4 sample as a photocatalyst for the application of Cr­(VI) reduction. In this paper, a photocatalytic reduction of a Cr 2 O 7 2– (10 ppm) aqueous solution was carried out in the presence of a methanol solution (8 vol %) under simulated sunlight.…”