Photo-induced Electron Transfer in Organic Solar Cells and photocatalyst treatment of pollutant

1 The charge transfer process between MO molecules and bulk TiO2 film and nano-sized TiO2 were studied using TCSPC and nanosecond and femtosecond transient absorption spectroscopies. The recombination of electrons and holes in the bulk TiO2 film occurs 1000 times faster than that in nano-sized TiO2 particles. This can be attributed to the bulk TiO2 film becoming a developed crystal that has fewer trapping sites to hinder the electrons and holes recombining. Unlike the broad TA spectra of nano-sized TiO2 in the visible range, the bulk TiO2 film exhibits two sharp and slightly red-shifted peaks at 520 nm and 675 nm. This appears due to that the nano-sized TiO2 has its trapped electrons and holes spread broadly in a certain depth whereas in the bulk TiO2 film most of the holes are shallowly trapped and a small part of them are deeper trapped ones. Both Nano-sized TiO2 and bulk TiO2 film can directly decompose MO dye without aid of radicals. In the nano-sized TiO2 system, the trapped holes are consumed by MO in several hundreds of nanoseconds. In the bulk TiO2 film, electrons are observed to inject into MO in several hundreds of picoseconds. Through cyclic voltammetry measurements, MO can be reduced at -0.28 V and oxidized at 1.4 V (vs SCE ), providing thermodynamic evidence for MO to be degraded by electrons and holes in TiO2. In waste water treatment by nano-sized TiO2, the competition between the holes of TiO2 and the OH∙ radicals towards decomposing MO depends on the concentration of MO. When MO is above 1.6×10-4 M, the degradation is mainly due to direct hole oxidation process, while below 1.6×10-4 M, hydroxyl oxidation competes strongly and might exceed the direct hole oxidation. 2 Photoinduced electron transfer in a self-assembled multi-wall carbon nanotube (CNT)- Pyrene-containing polymer (Polymer) hybrid with Polymer acting as an electron donor and CNT as an electron acceptor has been successfully demonstrated. Toward this, first, CNTs were noncovalently functionalized using pyrene to form Polymer-CNT hybrids by π-π stacking through van der Waals interactions. . The nanohybrids were isolated and characterized by SEM, UV-visible absorption, and Fluorescence spectra methods. Accordingly, steady-state and time-resolved fluorescence studies revealed efficient quenching of the polymer by the MWCNTs.