Titania particles modified with an extremely small amount (<0.01 mol%) of a rhodium species exhibited photocatalytic activity for the oxidative decomposition of acetaldehyde in air under visible-light irradiation. The reaction proceeded via a two-photon band-gap excitation mechanism with a built-in Rh(III)–Rh(IV) redox couple.

Visible light-induced redox reactions of low-concentration rhodium-introduced titania proceeded through two photoexcitation of rhodium(iii) to the conduction band of titania and an electron in the valence band to thus-generated rhodium(iv).

In the pre-Hispanic Central Andes, the mummified bodies of ancestors stood as the basis for the social and cosmic order. This work discusses chemical compositions of the bodies determined by using molecular and elemental analytical methods.

The core-shell NaYb_0.99F₄:Tm_0.01@NaYF₄ upconverting particles (UCPs) with a high UV emission to apply in NIR-driven photocatalysis were synthesized. The influence of the Yb³⁺ doping concentration in NaY_xF₄:Yb_0.99−xTm_0.01 core particles, and the role of the NaYF₄ shell on the upconversion emission intensity of the UCPs were studied. The absorption of NIR light by the obtained UCPs was maximized by increasing the Yb³⁺ concentration in the core, reaching the maximum for Y³⁺-free particles (NaYb_0.99F₄:Tm_0.01). Additionally, covering the NaYb_0.99F₄:Tm_0.01 core with a protective layer of NaYF₄ minimized the surface luminescence quenching, which significantly improved the efficiency of upconversion emission. The high intensity of the UV light emitted by the NaYb_0.99F₄:Tm_0.01@NaYF₄ under NIR irradiation resulted in a high photocatalytic activity of TiO₂ (P25) mixed with the synthesized material.

Preparation of highly active core–shell/hybrid materials based on up-converting particles combined with semiconductors for photocatalytic application usually requires sophisticated and multi-step synthesis procedures. We propose a new design of a highly efficient NIR-driven photocatalytic system composed of spatially separated thin films of upconverting NaYF₄:Yb,Tm particles (UCPs), and TiO₂. Several samples of UCPs were prepared in the form of thin films and suspensions, directly coated with a titania layer or mixed with P25. Photocatalytic and photoelectrochemical studies have shown that thin film samples achieved significantly higher photocatalytic activity than their suspended counterparts. Moreover, the sample consisting of spatially separated layers of UCPs and P25 presented a significant photocatalytic activity and generated the highest photocurrent intensity. Separating the photocatalyst and upconverter layers allows for an interchangeable photocatalytic system active in a wide range of light.