Visible Light Water Oxidation Using a Co-Catalyst Loaded Anatase-Structured Ti_1–(5x/4)Nb_xO_2–y–δN_yCompound

Abstract

The photocatalytic activity of anatase-structured Ti(1-(5x/4))Nb(x)O(2-y-δ)N(y) (x = 0.25, y = 0.02; NbN-25) was examined for water oxidation under UV and visible light irradiation. The semiconductor was prepared by sol-gel processing followed by nitridation in flowing ammonia and exhibits an indirect optical gap of 2.2 eV. Ti(1-(5x/4))Nb(x)O(2-y-δ)N(y) was loaded with RuO2 by an impregnation technique, and optimized conditions reveal that 1 wt % RuO2 generates 16 μmol O2 from water with concomitant IO3(-) reduction after 3 h of illumination under simulated solar radiation at a flux of 600 mW/cm(2) illumination, which corresponds to 6-sun AM1.5G illumination (compared to no detectible O2 without the RuO2 cocatalyst). A series of cut-on filters shows that the catalyst-loaded semiconductor evolves O2 for λ ≤ 515 nm, and a gas-phase mass spectrometry isotope labeling experiment shows that irradiating an iodate solution in H2(18)O in the presence of 1 wt % RuO2 loaded on NbN-25 gives rise to catalytic water oxidation: both (36)O2 and (34)O2 are observed. It is unclear whether (16)O arises from IO3(-) or surface reconstruction on the photocatalyst, but ICP-AES analysis of the postirradiated solution shows no dissolved metal ions.

The Formation of Defect‐Pairs for Highly Efficient Visible‐Light Catalysts

“…Their light absorption range covers the entire visible light regime from 400 nm to 800 nm, which is much broader, relative to the results previously reported for (N, Nb) co-doped TiO2 particles. [10][11][12][13][14][15][17][18][19][20] For the N-equal and N-rich co-doped TiO2 with higher N 3doping levels, the respective (Figure 2c). As seen, the N-equal co-doped TiO2 requires less than 20 minutes to accomplish nearly complete decomposition of RhB.…”

“…Ionic co-doping, especially cation and anion co-doping, is another facile route. Co-doping has recently drawn considerable attention [10][11][12][13][14][15][16][17][18][19][20] as this method can potentially tailor the energy band structure, enhance optical absorption, reduce the number of recombination centers by balancing charges and thus provide a cost-effective way to promote photocatalytic activity. The reported results, on the other hand, have been very diverse.…”

“…Taking (N 3-, M 5+ ) co-doped TiO2 as an example, where M 5+ represents a pentavalent cation and N 3is a nitrogen anion, it has been technologically difficult to introduce equivalent concentrations of M 5+ and N 3ions into a host material. High temperature ammonolysis [10][11][12][13][14][15] was attempted to incorporate nitrogen ions into pre-prepared M 5+ monodoped TiO2 but the achieved N 3doping level was less than 2 at.%. [12,21] In addition, the distribution of N 3ions is often inhomogeneous with its concentration gradually lowering from the surface to the interior of co-doped TiO2.…”

“…High temperature ammonolysis [10][11][12][13][14][15] was attempted to incorporate nitrogen ions into pre-prepared M 5+ monodoped TiO2 but the achieved N 3doping level was less than 2 at.%. [12,21] In addition, the distribution of N 3ions is often inhomogeneous with its concentration gradually lowering from the surface to the interior of co-doped TiO2. [8] Wet chemical methods like sol-gel synthesis have also been tried to directly add nitrogen sources to the reaction solution.…”

Editorial for the ACS Select Virtual Issue on Inorganic Chemistry Driving the Energy Sciences

“…24 Deposition of a cocatalyst (RuO 2 ) onto this light-absorbing material yielded a system that was found to be effective at photocatalytic water oxidation.…”