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timescale. It exhibited activity in the degradation of phenol in aqueous solutions com-
parable to that of the commercial TiO 2 . The possible mechanistic proposal suggested
that the photodegradation of phenol could occur through a network of reactions,
including an initial formation of a radical cation by electron transfer from phenol
to MOF-5 hole or the generation of oxygen-active species by the reaction of the
photo-ejected electrons with oxygen [49].
Porphyrins also have been used for photodegradation of organic contaminants. Guo
et al. found morphology-dependent photocatalytic activity in porphyrin-based nano-
fibers and nanospheres in terms of photodegradation of the rhodamine B (RhB) pol-
lutant under visible light irradiation [50]. The photodegradation of the RhB pollutant
over these nanostructures was monitored by measuring the real-time UV-Vis absorp-
tion spectra of RhB at 554 nm. For a blank experiment, where no ZnTPyP nanostruc-
tures were involved, the absorption of RhB displayed a negligible decrease, suggesting
that the self-sensitized photodegradation of RhB could hardly occur under the study’s
experimental conditions. When the ZnTPyP nanospheres that were produced by an
aging time of 15 min were involved in the system, only slight degradation of RhB
occurred. These observations indicated that ZnTPyP nanospheres could not distinctly
promote the photodegradation of RhB, and that they could not work as an efficient
photocatalyst.

10.4 Conclusion

The use of semiconducting nanoparticles in conjunction with conjugated polymers has
presented a variety of tuned band gap materials with desirable optoelectronic proper-
ties. However, these materials require modifications in their structure, charge transfer
efficiency, energy level alignment, and band gap in order to improve their photocatalytic
efficiency. The low band gap of polymers, as compared with metal-oxide semiconduc-
tors, are beneficial for harnessing the visible range of the electromagnetic spectrum in
charge-separation processes. However, better control of post-charge- separation pro-
cesses is required, including efficient and quick charge transfer in order to suppress
recombination. Nanostructures and their different morphologies and hybrid materials
(e.g., metal-organic-framework–supported nanomaterials or porphyrin-based materi-
als) have already shown some initial success under visible light illumination. Going
forward, computational evaluation of known MOFs as well as hypothetical MOFs
may help advance research in this area. High throughput screening can be performed
on MOFs prior to testing analyte adsorption and even prior to MOF synthesis to ex-
pedite the discovery and development of highly effective adsorbents. However, im-
plementing these materials commercially for societal benefit is still a distant reality
because of their current economic unsuitability and industrial requirements. In or-
der to yield optimized band structures for water reduction, the selection of materials
needs to include appropriate band structure, efficiency of the photocatalyst, sacrificial
agents, solvent systems, interface of heterocatalysts, absorption efficiency of absorber,
and charge transfer efficiency.