Broadband optical properties of Ti3C2 MXene revisited.

The exceptional optical, electrical, and mechanical capabilities of layered transition metal carbides, nitrides, and carbonitrides, called MXenes, revolutionized materials science. Among them, Ti3C2 received the most attention owing to the developed synthesis and processing methods, high conductivity, and pronounced plasmonic response. The latter, however, remains controversial with the open question of whether the peak around 800 nm has plasmonic or interband transition origin. To address this issue, we combine spectroscopic ellipsometry and transmittance results with first-principle computations. Their combination reveals that although Ti3C2 is a metal, its optical response becomes plasmonic (Re ε < 0) above 1415 nm, in contrast to the previous understanding. In addition to fundamental significance, this dual dielectric/plasmonic optical response opens a path for theranostic applications, as we demonstrated on the example of Ti3C2 nanospheres. Thus, our study revisits broadband (300-3300 nm) optical constants of Ti3C2 and broadens its application scope in photonics.

Cu2O Photocathodes Modified by Graphene Oxide and ZnO Nanoparticles with Improved Photocatalytic Properties.

The modification of photocathodes based on copper(I) oxide (COPC) by coating with ZnO nanoparticles or graphene oxide (GO) with different compositions and morphologies is considered. To cover the catalyst surface with graphene oxide, a technique was proposed via freezing of a sprayed aqueous suspension of graphene oxide followed by sublimation drying under vacuum conditions. This method improves the uniformity of the GO layer in comparison with the traditional drop-casting method and, as a result, improves the photocatalytic properties of the COPC. The influence of the composition and morphology of graphene oxide on the photocatalytic activity and stability of COPC has been established. ZnO nanoparticles and GO particles in contact with copper(I) oxide increase the photocurrent density by the more efficient separation of light-generated charge carriers, providing higher photocathode stability required in photocatalytic water splitting.