organic matter by environmental polyoxometallates as
photocatalysts may constitute alternative possibilities( 264 ).
VI. Concluding RemarksThe mutual stimulation of scientists coming from different
disciplines, viz. photochemistry, electrochemistry, coordination
chemistry, analytical chemistry, biology, medicine, material
chemistry, surface science, electronics, and catalysis, resulted
in the extremely rapid development of photocatalysis( 265 ). This
review shows the fast progress made in our understanding of the
processes occurring in nature that are catalyzed by metal
complexes and driven by solar energy, and demonstrates their
general trends and fine details.
In the environment there are two general opposing trends, viz.
to build organic substances from carbon dioxide and water in photo-
synthesis, and to decompose them by O 2 oxidation, photocatalyzed
by transition metal compounds. The photocatalytic cycles may
be treated as“anti-photosynthesis”as they consume atmospheric
oxygen and organic compounds and thus disperse energy
accumulated by photosynthesis. These processes are of vital impor-
tance, because theoretically, most atmospheric oxygen could be con-
sumed, which would be a threat to life on Earth. Fortunately,
photosynthesis is dominating in nature and photocatalysis by
transition metals plays a minor, although a very useful, role in
cleaning the environment from the excess of useless and harmful
organic matter. The natural processes may as well be used in envi-
ronmental protection procedures of the pollution abatement and in
solar purification of water in arid countries.
The relevance of photocatalysis in solving the environmental
problems manifests itself in effective degradation of many
pollutants, which are not sensitive to biodegradation, like the
majority of synthetic polymers, among others poly(N-
vinylpyrrolidone) (PVP)( 266 ).
Moreover, the environmental systems demonstrate unique
diversity and versatility of the processes depending on the actual
conditions, viz. the reaction directions and rates are sensitive to
many diverse parameters, sometimes even difficult to be per-
ceived. The example may be the dependence of the photocatalytic
activity of Sr AlNb O double perovskite on the cation order-
ing in the oxides( 267 ), or the effect of the in-plane twist of the
quinoline-based co-ligand on the thermal stability and yield of
NO photorelease from the [Ru(NO)]^6 nitrosyl complexes ( 96 ).
METAL COMPLEXES AS SOLAR PHOTOCATALYSTS 333