On the mechanism of photocatalytic reactions on Cu_xO@TiO₂ core–shell photocatalysts

Abstract

Titania (titanium(IV) oxide) is highly active, stable, cheap and abundant photocatalyst, and thus commonly applied in various environmental applications. However, two main shortcomings of titania, i.e., charge carriers’ recombination and...

Application of Spinel and Hexagonal Ferrites in Heterogeneous Photocatalysis

“…In addition, the most active titania, i.e., that used in a particulate form, cannot be easily recycled, as already discussed in the introduction. Accordingly, various methods of titania modification, doping, coupling, and immobilizing have been proposed to improve its photocatalytic performance [14,[90][91][92][93][94]. Ferrites have also been proposed as titania modifiers for three main purposes, i.e., (i) improved activity by hindering the charge carriers' recombination, (ii) extension of activity towards vis range of solar spectrum, and (iii) easy and cheap recycling, as presented in this Section.…”

Morphology-Governed Performance of Multi-Dimensional Photocatalysts for Hydrogen Generation

“…It should be mentioned, that H 2 evolution (or even overall water splitting) was firstly, carried out only under UV irradiation, as pristine titania is inactive under vis irradiation. Then, modified titania (via doping or surface modifications), e.g., with nonmetals [53,54], metals [55,56], and by coupling with other materials [57], has been applied. Interestingly, it has also been found that noble metals could be used for titania activation towards vis response because of plasmonic properties ("plasmonic photocatalysts") [58][59][60][61].…”

“…Unfortunately, similar to other plasmonic photocatalysts, though vis activity has been observed for oxidative decomposition of phenol, negligible evolution of hydrogen has been noticed under vis irradiation. An interesting approach has been designed by Wang et al for coreshell Cu x O@TiO 2 formation by microemulsion method [57]. It is well known that coupled oxides, such as titania and copper/silver oxides-despite their enhanced activity under UV irradiation due to the inhibition of charge recombination (either via heterojunction type II or Z-scheme mechanism [84])-are often not stable under irradiation in contrast to titania, as these oxides with a narrower bandgap suffer from photocorrosion [85][86][87].…”

“…It is well known that coupled oxides, such as titania and copper/silver oxides-despite their enhanced activity under UV irradiation due to the inhibition of charge recombination (either via heterojunction type II or Z-scheme mechanism [84])-are often not stable under irradiation in contrast to titania, as these oxides with a narrower bandgap suffer from photocorrosion [85][86][87]. However, obtained core-shell Cu x O@TiO 2 photocatalysts have exhibited high photocatalytic activity under long (6 h) and repeated (3 cycles) UV irradiation [57]. Additionally, based on XPS analysis showing the reduction of copper species, it has been concluded that enhanced activity is caused by Z-scheme mechanisms both for hydrogen generation (methanol as a hole scavenger) and oxidative degradation of acetic acid.…”

“…Unfortunately, most experiments are performed in the presence of scavengers, mainly alcohols, and also other compounds, such as EDTA and Na 2 S/Na 2 SO 3 . Therefore, in some papers the "alcohol dehydrogenation" term is clearly stated rather than "water reduction/splitting" [42,43,50,57]. Obviously, water reduction in the absence of any hole scavenger is most recommended, but it is hardly succeeded, due to positive change in Gibbs free energy (as already pointed in the Introduction), i.e., "photosynthetic process".…”