Effects of surface modification on photocatalytic activity of CdS nanocrystals studied by photoluminescence spectroscopy

Abstract

The surface features of semiconductors play very important roles in photocatalytic processes but they are far from being well understood. In this work, we used CdS nanocrystals (NCs) as a model semiconductor photocatalyst to investigate the influence of surface features on photocatalytic activity.The effects of surface modification on the recombination behavior were studied by photoluminescence (PL) spectroscopy. The surface of CdS NCs was modified by tuning the surface S/Cd ratio or by co-loading with Pt and/or PdS co-catalysts. It was found that the surface modifications significantly affect the emission bands at B540 nm due to shallow traps and B650 nm assigned to S 2À vacancies, and consequently the photocatalytic activities. Without co-catalysts loading, the excited carriers are readily transferred to the shallow traps, while they are readily transferred to the co-catalysts upon co-catalystsloading. These results demonstrate that the surface features are crucial to photocatalytic activity of the CdS NCs. The surface modification is helpful for the excited carriers to transfer to either the shallow trap states or co-catalysts, resulting in higher quantum efficiency of photocatalytic H 2 production.

Photoexcited Properties of Tin Sulfide Nanosheet-Decorated ZnO Nanorod Heterostructures

“…Furthermore, the ZnO and ZnO–Sn 2 S 3 nanorods exhibited broad emission bands centered at approximately 560 and 530 nm, respectively. These broad visible light emission bands are referred to as deep-level or trap-state emission bands and might be associated with structural defects arising from the oxygen vacancies of the ZnO core and the shallow trap caused by the surface states of the sulfide shell layer [19, 26]. In comparison with the broad emission bands, the intensity of the near-band edge emission from ZnO was markedly quenched when the Sn 2 S 3 crystallites were sputtered onto the surfaces of the ZnO nanorods.…”

State‐of‐the‐Art Progress in Diverse Heterostructured Photocatalysts toward Promoting Photocatalytic Performance

“…As shown in Figure 1 b-e, Bi 2 S 3 /CdS heterostructure also exhibited superior effi ciency for photodegradation of methyl red (MR). [ 41,63 ] Compared to the island type heterostructured photocatalysts, for most the core/shell heterostructured photocatalysts ( Figure 2 a), the photogenerated electron-hole pairs near the interface of junction tend to be easily confi ned to the core semiconductor, which are not available for photocatalytic reactions on the shell semiconductor surface. Moreover, the unique confi guration of the Bi 2 S 3 nanowire/CdS nanoparticle allows both the charge carriers to expose to the liquid phase and effectively involve in the photocatalytic reactions, resulting in the improvement of photocatalytic activity.…”

Ligand removal from CdS quantum dots for enhanced photocatalytic H2 generation in pH neutral water

“…1--3 Many synthetic systems have been developed with the hope of emulating natural photosynthesis to produce renewable fuels such as H 2 . 7--9 Although photocatalytic H 2 generation systems using bulk and nanostructured metal chalcogenides have been studied for many years, 10--15 systems using QDs have been pioneered only relatively recently, employing CdX (X = S, Se, Te) QDs coupled to a wide range of co--catalysts, including noble metals, 16,17 enzymes, 18--21 and molecular complexes or salts of iron, 22--24 cobalt, 25--27 and nickel. 4--7 Semiconductor quantum dots (QDs) are well suited as light absorbers for photocatalysis due to their high light absorption coefficient, high surface area, tuneable optical and electronic properties, and relatively high photostability compared to molecular dyes.…”