Polymeric photocatalytic systems

A membrane-induced structure-reactivity trend that may be exploited to achieve selective processes has been recently observed in polymeric catalytic membranes prepared embedding polyoxotungstates, W(VI)-oxygen anionic clusters having interesting properties as photocatalysts, in polymeric membranes [17]. These catalytic membranes have been successfully apphed in the photooxidation of organic substrates in water providing stable and recyclable photocatalytic systems. 

It has been reported that tris(2,2 -bipyridine)ruthenium(II) chloride catalyzed the photooxidative polymerization of diaryl disulfides by O2, by which poly(thioarylene)s were efficiently prepared. The polymerization proceeded through the electrophilic reaction of the sulfonium cation which was produced selectively by the photoredox system. The ruthenium(II) complex provided the first photocatalytic system for the polymerization of diphenyl disulfide. The linear structures of the obtained polymers were confirmed (32). 

A membrane-induced structure—reactivity trend, which may be exploited to achieve selective processes, was observed in polymeric catalytic membranes prepared by embedding decatungstate within porous membranes made of PVDF or dense polydimethyl-siloxane (PDMS) membranes. These photocatalytic systems are characterized by different and tunable properties depending on the nature of the polymeric microenvironment (Bonchio et al., 2003). The polymeric catalytic membranes prepared were used for the batch-selective photooxidation of water-soluble alcohols. Membrane-induced discrimination of the substrate results from the oxidations of a series of alcohols with different polarity, through comparison with the homogeneous reactions (Fig. 27.7). 

Willner and coworkers [168] demonstrated the applicability of this method for a range of applications including the magneto-switching of DNA hybridization and polymerization for programmed DNA chips, of photocatalytically activated reactions using CdS nanoparticles for optobioelectronic systems [169], and of quinone oxidation and reduction for write-read-erase information storage systems [170]. 

Dispersed semiconductor PhCs can be easily heterogenized on a polymeric or ceramic support to create photocatalytic installations of practical interest for hydrogen generation in sunlight illumination. Tests on pilot devices of 0.25 m area, based on this type of system, which are capable of producing a few liters of hydrogen on a clear sunny day, have been reported [6], Undoubtedly, the expected serious demand for such systems could create an impetus to develop the respective technologies to the level of their commercial application. 

The first example is the work of Lu et al. [124] who fabricated polypyrrole (PPy)ATi02 coaxial nanocables, where the conductivity of PPy was integrated with the photocatalytic activity of Ti02 for applications in electrochromic devices, nonlinear optical systems, and photoelectrochemical devices. The synthetic approach consisted in (1) preparation of Ti02 fibers by sol-gel electrospinning and calcination of the polymer (PVP in the specific case), (2) physical adsorption of Fe " oxidant on the surface of Ti02 nanofibers, and (3) polymerization of pyrrole (from vapor) on the surface of Ti02 nanofibers. 

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