Photogeneration of Hydrogen from Polymeric Viologen Systems

Abstract

Abstract. Polymers containing pendant viologen groups were prepared and studied for their quenching efficiencies of the Rutbpyj}' excited state, their back reactions following the quenching, their viologen radical yields, and finally for their effectiveness in hydrogen production in the presence of colloidal platinum. Results are compared with those from methyl viologen containing systems to evaluate the performance of the polymeric viologen systems.

Charge separation in photoinitiated electron-transfer systems with polyviologen polyelectrolytes as quenchers

“…This is indeed the usual reason given for the reduced rate of reaction observed between a neutral species capable of diffusing freely in solution and a charged species trapped by a polyelectrolyte with a much lower ability to diffuse.3,4 It has also been suggested as the reason for the lowering of the quenching rate constants of Ru(bpy)32+* with other polymeric viologen species. 14 In high molecular weight polyviologens containing many viologen units per polymer, the viologen moieties are concentrated in specific regions in solution, and hence the average distance each Ru(bpy)2(CN)2* molecule must initially diffuse in order to collide with a quenching viologen unit is greater than in systems containing only low molecular weight species. This will lead to a larger fraction of Ru(bpy)2(CN)2* escaping quenching by the polyviologen and hence to a lower overall rate constant for the quenching reaction.…”

“…Previous work with polyviologens of lower charge density than those investigated in this study also gave back-reaction rates with Ru(bpy)33+ much larger than that for methylviologen, and they even exceeded the diffusion-controlled limit. 14 The question must therefore be asked of why significant inhibition of reactions of cationic polyviologens with positively charged bipyridine complexes of ruthenium does not occur. It should be noted here that inhibition factors of more than 2 orders…”

Capture, Store, and Discharge. Shuttling Photogenerated Electrons across TiO2–Silver Interface

“…Semiconductor–metal nanocomposites are effective in facilitating photocatalytic processes. − The coupling of semiconductor and metal nanoparticles provides a unique pathway for the discharge of electrons at the electrolyte interface. − One such application of this process is in the photocatalytic production of hydrogen. , Many recent efforts of photocatalytic splitting of water require inclusion of a metal cocatalyst such as Pt. , The noble metals such as Au and Ag possess electron storage properties which in turn facilitates improved charge separation in semiconductor–metal composite systems. , Recent studies have also focused on surface plasmon excitation of metal nanoparticles and improvement in solar cell and photocatalytic performance of semiconductor–metal nanocomposites. − Although evidence is presented in these studies for observing electron injection from metal nanoparticles into semiconductor and/or plasmon resonance induced field effects, often these reported enhancements are small compared to the bulk semiconductor excitation effects.…”

Effect of ionic polymer environment on the photoinduced electron transfer from zinc porphyrin to viologen

“…because the dimer formation does not occur within the time scale of the flash experiment. 12 The value of Ae(*ZnTMPyP4+) at 470 nm was 4.6 X 104 M"1 cm"1 and predominates over e(MV+ •) and Ae(ZnTMPyP5+). Therefore, from the decay profile at 470 nm such as shown in Figure 5, the decay rate for *ZnTMPyP4+ can be calculated.…”