Enhanced near-infrared photocatalysis of NaYF₄:Yb, Tm/CdS/TiO₂composites

Abstract

The previous works by our group (Chem. Commun., 2010, 46, 2304-2306; ACS Catal., 2013, 3, 405-412; Phys. Chem. Chem. Phys., 2013, 15, 14681-14688) have reported the near-infrared-driven photocatalysis of broadband semiconductor TiO2 or ZnO that was combined with upconverting luminescence particles to form a core-shell structure. However, the photocatalytic efficiency is low for this new type of photocatalysts. In this work, NaYF4:Yb,Tm/CdS/TiO2 composites for NIR photocatalysis were prepared by linking CdS and TiO2 nanocrystals on the NaYF4:Yb,Tm microcrystal surfaces. CdS and TiO2 were well interacted to form a heterojunction structure. The energy transfer between NaYF4:Yb,Tm and the semiconductors CdS and TiO2 was investigated by steady-state and dynamic fluorescence spectroscopy. The photocatalytic activities of the as-prepared composites were evaluated by the degradation of methylene blue in aqueous solution upon NIR irradiation. Significantly, it was found that the united adhesions of CdS and TiO2 on the NaYF4:Yb,Tm particle surfaces showed much higher catalytic activities than the individual adhesion of CdS or TiO2 on the NaYF4:Yb,Tm surfaces. This was attributed mainly to the effective separation of the photogenerated electron-hole pairs due to the charge transfer across the CdS-TiO2 interface driven by the band potential difference between them. The presented composite structure of upconverting luminescence materials coupled with narrow/wide semiconductor heterojunctions provides a new model for improved NIR photocatalysis.

Recent advances in energy transfer in bulk and nanoscale luminescent materials: from spectroscopy to applications

“…The increment in photocurrent was ascribed to the UC emission from the UC layer as well as the defect absorption by localized states in amorphous silicon. [245][246][247][248][249] There are generally two different strategies to incorporate the UC ion pairs into the different types of photocatalysts. 238,239 Similar to the Si-based solar cells, the incorporation of UC phosphor into TiO 2 -based dye sensitized solar cells (DSSCs) as well as polymer based cells also demonstrated enhanced NIR response.…”

“…Under simulated solar light irradiation, the system yields a maximum QE of 9.12%, which manifest a 32.7% enhancement as compared to the bare TiO 2 (P25) anode (Fig. [247][248][249] The combination of a UC phosphor with semiconductors like TiO 2 and CdSe can also be used for water splitting under NIR light irradiation in a photoelectrochemical cell. The problem with this system is that the typical red UC emission by the transitions of Er 3+ ( 4 F 9/2 -2 I 15/2 ) at 650 nm cannot be absorbed by the dye in the cell.…”

Optical band structure and photogenerated carriers transfer dynamics in FTO/TiO 2 heterojunction photocatalysts

“…3, and corresponding band gap energy (in the inset of Fig. 3) are calculated by following formula [21]:…”

Preparation and catalytic activity research of the Sr2MgSi2O7:Eu2+, Dy3+/TiO2 composite catalyst

“…co-doped Sr 2 SiO 4 :Eu yellow phosphor was composited with TiO 2 [16], it was revealed that the thin and uniformly TiO 2 coating led to an increase in the photoluminescence efficiency. Up-conversion phosphor NaYF 4 :Yb [5,17,18] was also used to support TiO 2 to prepare a near-IR light-driven photocatalyst. All this research has implied an increase of the catalytic activity without light irradiation.…”