New insights into the plasmonic enhancement for photocatalytic H₂ production by Cu–TiO₂ upon visible light illumination

Abstract

Cu nanoparticles were deposited on the surface of commercial TiO nanoparticles (Cu-TiO) using different methods aiming at the production of highly efficient visible light photocatalysts. Photocatalytic H evolution rates obtained from methanol/water mixtures revealed no significant influence of the presence of copper oxides on the photoreaction upon visible light illumination. The photocatalytic H production rates were evaluated upon illumination with different spectral ranges (≥420 nm or ≥500 nm) and the results evidenced that the visible light induced charge carrier formation on the Cu-TiO photocatalysts consists of two distinct pathways: the direct excitation of TiO and the induced excitation by the so-called surface plasmon resonance (SPR) effect of the Cu nanoparticles on the TiO surface. Both pathways are present when the full visible range of the spectrum is used (≥420 nm), while for illumination at longer wavelengths (≥500 nm), the photocatalytic activity is solely promoted by the Cu-SPR effect. Electron paramagnetic resonance (EPR) and laser flash photolysis measurements were performed to clarify the underlying mechanism of Cu-TiO photocatalysts upon visible light illumination.

Optimising hydrogen production via solar acetic acid photoreforming on Cu/TiO2

“…The tendency of Cu to become progressively reduced under solar irradiation had been previously demonstrated for alcohols and polyols. [17][18][19][20] The use of acetic acid, a more challenging substrate in terms of selectivity, is herein shown to serve as a sensitive tool to track the oxidation state of copper in parallel to H 2 evolution efficiency. The colour of the suspensions also indicated the changes in copper oxidation states.…”

“…This reasoning was inspired by several investigations reporting dynamic evolution of the oxidation state of copper during alcohol photoreforming. 14,[17][18][19][20][21] In order to explore the possible relationship of both oxidation state and morphology with performance, we checked the speciation of copper in CuIJ1%)/ TiO 2 by various characterisation techniques. No information could be drawn from X-ray diffraction (XRD, Fig.…”

Simultaneous H2 Production and Bleaching via Solar Photoreforming of Model Dye‐polluted Wastewaters on Metal/Titania

“…Passivation of metallic copper nanoparticles is common under ambient conditions, whereas the surface CuO x species formed are prone to reduction under UV-vis light irradiation and inert atmosphere, the process being reversible. [58,[62][63][64][65] The Cu 2p XPS data for the materials presented herein show differences depending on the deposition method. As seen in Figure 6, the spectra of H,DP Cu/TiO 2 and IM Cu/TiO 2 exhibit four signals, while only two are seen for PD Cu/TiO 2 .…”

“…Regarding reductive deposition methods, the resulting small copper nanoparticles in PD Cu/TiO 2 and H,DP Cu/TiO 2 might have been reduced to the metallic state during photodeposition or hydrogenation, respectively, and then oxidised in contact with ambient air. [58,[62][63][64][65] However, the Cu(II) d-d signal in PD Cu/TiO 2 is weaker, probably indicating less extensive or incomplete oxidation, although the expected absorption below 600 nm characteristic of Cu 2 O was not apparent. [63] This might be due to the dynamic behaviour of copper in Cu/TiO 2 materials, in addition to the low metal content, which complicate unambiguous speciation.…”

“…[82] This is apparently inconsistent with DRUV-vis results, which pointed to oxidation of at least part of copper in the form of CuO in PD Cu/ TiO 2 , and can be ascribed to the markedly dynamic chemistry of copper in this type of materials. [58,[62][63][64][65] It is worth noting that increasing the copper loading by an analogous photodeposition method leads to Cu/TiO 2 materials passivated by fullyoxidised CuO instead of Cu 2 O. [58] Surface platinum oxidation states were also dependent to some extent on the deposition method.…”