Copper-Modified TiO₂ and ZrTiO₄: Cu Oxidation State Evolution during Photocatalytic Hydrogen Production

Abstract

In the present work, two H evolution photocatalysts were prepared by employing two different oxides, TiO and zirconium titanate (ZrTiO), as the support of various copper phases. For both the supports the same Cu loading (0.5% w/w) was adopted, but two different impregnation procedures have been followed, leading to different forms of Cu in the final composite material that are: (i) Cu(II) species dispersed on the oxide surface and (ii) CuO particles dispersed on the oxide surface. The present paper based on the parallel use of photocatalytic test and spectroscopic analysis performed in catalytic conditions illustrates the evolution of photocatalytic systems occurring during the H evolution reaction tests, pointing out that the as-prepared materials represent a pre-catalyst and they are modified during irradiation leading to the real working systems different from the starting ones. The herein presented spectroscopic analysis aims to contribute to the living debate on the oxidation state of copper in mixed Cu/oxide materials and on its role in hydrogen evolution under photocatalytic conditions.

Assessment of Photocatalytic Hydrogen Production from Biomass or Wastewaters Depending on the Metal Co-Catalyst and Its Deposition Method on TiO2

“…However, copper oxide species on TiO2 produced by passivation under ambient air might be readily and reversibly reduced during irradiations and in the presence of glucose, acting as an electron donor. This behavior is commonly observed for similar Cu/TiO2 systems [33,[40][41][42][43][44]. A deeper study on the oxidation states and surface speciation of these photocatalysts will be described elsewhere, thus complementing the preliminary results presented herein.…”

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

“…Diffuse reflectance UV-vis spectroscopy (DRUV) of CuIJ1%)/TiO 2 revealed a weak broad signal (>550 nm, and extending beyond 800 nm, Fig. S3 †) indicative of CuIJII) species, 19,21 in support of the existence of oxidised layers suggested above. Since no evidence for Cu(0) species were found, it could be inferred that the small Cu particles in CuIJ1%)/TiO 2 might have become totally oxidised to CuO.…”

“…Copper co-catalysts have been in fact used for H 2 evolution in other photoreforming processes employing alcohols or polyols, and the dynamic evolution of its oxidation state under operation found to be a crucial aspect affecting performance. [17][18][19] It is thus interesting to focus on copper as a promising inexpensive metal co-catalyst for the photoreforming of carboxylic acids. In this work, we have delved into the capability and mode of action of such Cu cocatalysts to optimise H 2 production.…”

“…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.…”

“…Upon solar irradiation, photogenerated electrons from the conduction band of TiO 2 are capable of migrating to CuO nanoparticles and reduce them. 14,18,19 For smaller particles, this process can proceed to completion, although the more extensive CuO crusts on larger particles might be more resistant to photoreduction (Fig. 3c).…”