Enhanced Photocatalytic Hydrogen Evolution from Transition-Metal Surface-Modified TiO(2)

[Image: see text] This study describes the UV solution photodeposition of several earth-abundant 3d transition metals (Co, Ni, and Cu) onto the surface of nanoparticulate TiO(2). Irradiated methanolic metal dichloride solutions with suspended Degussa P25-TiO(2) (1–2 wt % metal to TiO(2)) yield visibly colored titanias, whereas the bulk TiO(2) structure is unchanged; X-ray photoelectron spectroscopy confirms that metals are present on the titania surface in either reduced metal (Cu/Cu(+)) or metal cation states (Co(2+) and Ni(2+)), and UV–vis diffuse reflectance spectroscopy shows new visible absorbance features. The analyzed bulk metal contents (∼0.04–0.6 at. %, highest for copper) are lower than the nominal metal solution content. Mixed-metal solution photodeposition reactions roughly parallel observations for single metals, with copper deposition being most favored. These 3d metal surface-modified titanias show significant (∼5–15×) improvement in UV photocatalytic H(2) evolution versus unmodified TiO(2). H(2) evolution rates as high as 85 μmol/h (8500 μmol h(–1) g(–1)) were detected for Cu-coated TiO(2) using continuous monitoring of reactor headspace gases by portable mass spectrometry. Control experiments verify the necessity of the methanol sacrificial oxidant in both metal deposition and H(2) evolution. In situ metal surface deposition is quickly followed by enhanced H(2) evolution relative to TiO(2), but at lower levels than isolated metal surface-modified titanias. The photodeposited 3d metal species on the TiO(2) surface likely act to reduce electron–hole recombination by facilitating the transfer of photoinduced TiO(2) conduction band electrons to protons in solution that are reduced to H(2). This study demonstrates a facile method to modify photoactive TiO(2) nanoparticles with inexpensive 3d transition metals to improve photocatalytic hydrogen evolution, and it shows the utility of quantitative real-time gas evolution monitoring by portable mass spectrometry.