Oxidative Power of Nitrogen-Doped TiO_2 Photocatalysts under Visible Illumination

Nitrogen doping was recently shown to extend the absorptivity of TiO_2 photocatalysts into the visible. We find that N-doped TiO_2 materials fail, however, to catalyze the oxidation of HCOO^- into CO_2^(•-), or of NH_3OH^+ into NO_3^-, under visible illumination. By N-doping anatase at ambient or high temperature according to the literature we obtained yellow powders A and H, respectively, that absorb up to ∼520 nm. Aqueous H suspensions (pH ∼ 6, 1 atm O_2) photocatalyze the oxidation of HCOO^- into CO_2^(•-) radicals at λ ∼ 330 nm, but the quantum yield of CO_2^(•-) formation at λ > 400 nm remains below ∼2 × 10^(-5) and is probably zero. A is similarly inert toward HCOO^- in the visible region and, moreover, unstable in the UV range. Thus, the holes generated on N-doped TiO_2 by visible photons are unable to oxidize HCOO^- either by direct means or via intermediate species produced in the oxidation of water or the catalyst. Reports of the bleaching of methylene blue (MB) on N-doped TiO_2, which may proceed by direct oxidative or reductive photocatalytic pathways and also by indirect photocatalysis (i.e., induced by light absorbed by MB rather than by the catalyst) even under aerobic conditions are, therefore, rather uninformative about the title issue

Modulating the interaction between gold and TiO2nanowires for enhanced solar driven photoelectrocatalytic hydrogen generation

The interaction strength of Au nanoparticles with pristine and nitrogen doped TiO2 nanowire surfaces was analysed using density functional theory and their significance in enhancing the solar driven photoelectrocatalytic properties was elucidated. In this article, we prepared 4-dimethylaminopyridine capped Au nanoparticle decorated TiO2 nanowire systems. The density functional theory calculations show {101} facets of TiO2 as the preferred phase for dimethylaminopyridine–Au nanoparticles anchoring with a binding energy of 8.282 kcal mol1 . Besides, the interaction strength of Au nanoparticles was enhanced nearly four-fold (35.559 kcal mol1 ) at {101} facets via nitrogen doping, which indeed amplified the Au nanoparticle density on nitrided TiO2. The Au coated nitrogen doped TiO2 (N–TiO2–Au) hybrid electrodes show higher absorbance owing to the light scattering effect of Au nanoparticles. In addition, N–TiO2–Au hybrid electrodes block the charge leakage from the electrode to the electrolyte and thus reduce the charge recombination at the electrode/electrolyte interface. Despite the beneficial band narrowing effect of nitrogen in TiO2 on the electrochemical and visible light activity in N–TiO2–Au hybrid electrodes, it results in low photocurrent generation at higher Au NP loading (3.4 107 M) due to light blocking the N–TiO2 surface. Strikingly, even with a ten-fold lower Au NP loading (0.34 107 M), the synergistic effects of nitrogen doping and Au NPs on the N–TiO2–Au hybrid system yield high photocurrent compared to TiO2 and TiO2–Au electrodes. As a result, the N–TiO2–Au electrode produces nearly 270 mmol h1 cm2 hydrogen, which is nearly two-fold higher than the pristine TiO2 counterpart. The implications of these findings for the design of efficient hybrid photoelectrocatalytic electrodes are discussed. IntroducGlobal Research Laboratory (GRL) Program through the National Research Foundation of Korea (NRF) - Ministry of Science. K20704000003TA050000310 Japan Society for the Promotion of Science (JSPS) University Jaume I. P1.1B2014-51 Government of the Russian Federation. 074-U0