Updates on Application of Silver Nanoparticles - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 116

It should be noted that the surface amount of metal complexes were much higher than
a monolayer. Thus, the experimental kinetic data describe the collective activity of
associated molecular ensembles of metal porphyrins. It is important that the coordina-
tion and the decomposition rate of hydrogen peroxide are effectively under aggrega-
tion of Chl and porphyrins, in particular, for their dimerization [8].
In the Table k ef is the effective rate constant, N is the number of moles of (photo)
catalyst, V is the volume of the reaction solution, k ob is the observed rate constant that
could be expressed as k ef ( N / V ) n because the rate of H 2 O 2 decompos w = k ef ( N Cat / V ) n
[ɇ 2 Ɉ 2 ] m , where N / V , n and m =1 do not change [4]. The catalyst turnover number (TN)
correspond to the number of mol H 2 O 2 per mol catalyst per hour. Parameter Ș shows
the percentage difference of k ef for dark and light reactions. The coordination sphere of
the metal ion also includes one (for Fe III ) or two (for Sn IV ) chloride anion. Ytterbium
ion additionally contains one molecule of acetylacetone as extraligand on the third
valence. Amount of metal complex deposited per 1 gm of silica.
Recently, in the experiments on the effect of Becquerel on photoelectrodes the
modi¿ ction with various metal complexes of porphyrins,their activity in the genera-
tion photopotential were determined [9]. In this study, a comparative analysis shows
that there is a linear correlation between the photoelectrochemical and photocatalytic
properties of d 0 and d 10 metal complexes of TPP (Figure 2). No similar correlations
were observed for the TPP complexes with the transition metals. Thus, the analogy in
photovoltaic and photocatalytic properties of metal porphyrins are exists only in the
case of metal complexes which are capable to generate long-lived triplet excited states
with high quantum yield. Consequently, these properties are interrelated and could be
used to estimate and predict each other. For example, difference between rates of dark
and light induced decomposition of H 2 O 2 could be a test parameter in the development
of molecular solar energy converters.
To prove a possibility of light energy storage in the form of chemical potential an
electron transfer from ɇ 2 Ɉ 2 to acceptor molecules with Chl participation was studied.
Sodium salt of NADP and MR dye (p-dimetilaminoazobenzol-2-carboxylic acid) were
used as electron acceptors. It should be noted that NADP is photosynthetic electron
acceptor and MR is widely applied synthetic acceptor [8]. Kinetics of NADP reduction
was studied by spectral method in visible range. At the irradiation during ca. 80 min
the supported Chl (v im = 0.015 ȝmol/g) was proved to be active in NADP reduction
(Figure 3(a)). However in the absence of ɇ 2 Ɉ 2 in the system no activity of Chl was
observed in accumulation of reduced form of NADP. The reduction reaction of MR
was investigated by observing the decrease of the intensity of absorption band of the
initial oxidized form. The obtained data con¿ rm the photocatalytic activity of sup-
ported Chl (v im = 0.063 ȝmol/g) in reduction of methyl red (Figure 3(b)). In the pres-
ences of hydrogen peroxide activity of Chl accelerates at conditions of photocatalysis.
It was shown that after the photoexcitation the primary stage is electron transfer to the
¿ rst molecule of hydrogen peroxide and the formation of the radical cation of Chl [3].
Further, the radical cation of Chl oxidizes the second molecule of hydrogen peroxide.
Thus, in threefold system H 2 O 2 - Chl acceptor under the visibility of light irradiation
the reduction of electron acceptors (NADP and MR) takes place what proves the abil-
ity of ɇ 2 Ɉ 2 to function as an electron donor in these conditions.