Interparticle Electron Transfer Research Articles

Exploiting the interparticle electron transfer process in the photocatalysed oxidation of phenol, 2-chlorophenol and pentachlorophenol: chemical evidence for electron and hole transfer between coupled semiconductors

The photocatalysed oxidation of phenol, 2-chlorophenol and pentachlorophenol was re-examined under conditions in which TiO 2 anatase was sensitized by CdS in air-equilibrated aqueous media; this was to assess whether or not the interparticle electron transfer pathway, first discovered a decade ago (N. Serpone, E. Borgarello and M. Gratzel, J. Chem. Soc., Chem. Commun., (1984) 342) and subsequently applied to enhance reductive processes on titania, could also be applied to photo-oxidative processes. The results indicate that combinations such as CdS/TiO 2 lead to an enhanced rate of disappearance of the initial substrate by a factor greater than two, consistent with the notion that (irradiated) CdS electrons are vectorially displaced onto the non-illuminated TiO 2 particulates. Cadmium sulphide is a poorer photo-oxidation catalyst than titania. Other semiconductor materials have also been examined under a variety of conditions of pH and irradiation wavelength. The data also show that when both semiconductors in a coupled system are illuminated simultaneously and their valence and conduction bands are suitably disposed, both electron and hole transfer occur (as in the CdS/TiO 2, ZnO/TiO 2, TiO 2/Fe 2O 3 and ZnO/Fe 2O 3 couples), which will influence the efficiency of photo-oxidation. N 2O-saturated aqueous dispersions of TiO 2 have no effect on the photo-oxidation of phenol, although it was expected that nitrous oxide would scavenge the photogenerated electrons in a manner similar to chemisorbed molecular oxygen, and enhance the efficiency. It is suggested that the role of oxygen in photo- oxidations may be more than just a simple electron scavenger.

Femtosecond studies of interparticle electron transfer in a coupled CdS–TiO2 colloidal system

We report the direct femtosecond measurements of the electron transfer process from CdS to TiO2 particles in a coupled colloidal system. The electrons initially created in the conduction band and quickly trapped at the liquid–solid interface in aqueous CdS colloids are found to be transferred to the colloidal TiO2 particles with a time constant of 2 ps, resulting in significantly slower electron–hole recombination. These coupled semiconductor colloids provide a potentially useful system for achieving efficient charge separation, which is important for many chemical reactions involving heterogeneous electron transfer.

ChemInform Abstract: Utilization of the Semiconductor Particle as a Microphotoelectrochemical Cell. Electrochemical Evidence for Interparticle Electron Transfer and Application to Photocatalysis.

AbstractThe effects of chemical etching and addition of a second semiconducting material on the photocatalytic activity of CdS suspensions for the photocleavage of H2S in alkaline solution are studied.

Utilization of the Semiconductor Particle as a Microphotoelectrochemical Cell: Electrochemical Evidence for Interparticle Electron Transfer and Application to Photocatalysis

Illuminated semiconductor particulate systems mimic the properties of photoelectrochemical cells; electron/hole pair separation and the rapid movement of the photogenerated charge carriers to the particle surface form anodic and cathodic sites at which efficient redox chemistry can take place. It is shown that chemical etching of well‐defined spherical (2–20 μm) particles changes the nature of the surface (SEM) and bears on the efficiency of the photocatalytic cleavage of in aqueous alkaline media. Coupling and semiconductor results in interparticle electron transfer (IPET) and significantly improves the rate of production; this electron transfer process was probed photocatalytically and by photoelectrochemical techniques.

Photodecomposition of H 2S in aqueous alkaline media catalyzed by RuO 2-loaded alumina in the presence of cadmium sulfide. Application of the inter-particle electron transfer mechanism

The photodecomposition of hydrogen sulfide by visible light (>400 nm) has been investigated in alkaline aqueous media (0.1 m Na 2S and 1 M NaOH) in the presence of naked CdS dispersions and in mixtures composed of the combination CdS + Al 2O 3/RuO 2. A 5-fold increase in the hydrogen evolution rate is obtained through the coupling of the excited semiconductor and the redox catalyst. The data are interpreted in terms of the inter-particle electron transfer pathway in which the conduction band electrons of the excited CdS (bandgap 2.4 eV; threshold wavelength 520 nm) are transferred to the redox catalyst via the alumina support or directly, in competition with electron/hole pair recombination. The engineering energy efficiency is estimated at 1.2% from the total incident light energy and the heat of combustion of hydrogen.

Visible light induced generation of hydrogen from H2S in mixed semiconductor dispersions; improved efficiency through inter-particle electron transfer

Electron transfer from the conduction band of CdS to that of TiO2 particles occurs in alkaline suspensions containing SH– ions and is exploited to improve the performance of a system that decomposes H2S with visible light.