Oxygen evolution quantum yield

Fig. 14. Measured quantum yield of oxygen evolution in Chlorella plotted against wavelength of excitation light with out and with supplementary light at 650 nm. Figure source Emerson, Chalmers and Cederstrand (1957) Some factors influencing the long-wave limit of photosynthesis. Proc Nat Acad Sci, USA 43 137.

LA. Flameling, J. Kromkamp (1998). Light dependence of quantum yields for PSII charge separation and oxygen evolution in eukaryotic algae. Limnol. Oceanogr., 43, 284-297. 

Table 2.3 lists various types of schemes that have been examined to date63 -65,69-74 for light-induced oxygen evolution from water. Photolysis of transition metal ions, as for the case for H2-production, requires UV-photons. Only for the Ce4+ system, the quantum yields are high (

energy storing. Oxy anions such as V02, MnO[Pg.49]

Hydrogen is evolved in the photolysis of poly-a-methylstyrene with a quantum yield of 1.7 x 10-2, together with some carbon dioxide and carbon monoxide. This indicates that there are some bonded oxygen atoms in the polymer and it has been suggested that degradation could be due to the scission of a few weak bonds situated at random in the polymer chain [10]. No mention is made of the evolution of methane as a consequence of methyl group abstraction. It has been noticed that a yellow colour is produced on long exposure and that this remains even when the polymer has been reprecipitated [10]. 

Attached leaves of pumpkin (Cucurbita pepo L.) were photoinhibited at 750, 1500 or 2500 umol PAR m 2s either at room temperature (RT) or at 1 0, in saturated humidity. After the treatment, different photosynthetic parameters were measured either from leaf discs (fluorescence induction at 77 K, apparent quantum yield of oxygen evolution), or from thylakoids isolated from treated leaves (electron transfer activities, fluorescence induction in the presence of DCMU or FeCN, atrazine binding). 

The apparent quantum yield of oxygen evolution () for leaves was measured using a computer controlled leaf disc oxygen electrode, over a PPFD range 0-150 ymol.m". s" and in saturating COo (5). 

Table 1. Apparent quantum yields of oxygen evolution (

This possibility was evaluated using an oxygen electrode at saturating CO2 (COp partial pressure of 100 mbar). It has been demonstrated that such very high CO2 concentration can overcome the effect of heterogeneity of stomatal aperture (8, lO). Our results indicate that the apparent quantum yield of oxygen evolution was fairly insensitive to salinity (Table l), being about O.O8 (mol O2 evolved/mol incident quanta) in all salinity treatments. This value is very close to that reported previously for cotton (l ). We could not measure the quantum yield on the basis of absorbed photons. 

A major improvement was reached by substituting [Ru(bpy)3] with the tetranuclear dendrimeric derivative [Ru (p-2,3-dpp)Ru(bpy)2 3] " " (4 in Fig. 2). Using this antenna in combination with citrate-stabilized nano-Ir02 (20 nm) and Na2S20g as sacrificial agent upon irradiation (k> 550 nm), a 6-fold increase in oxygen evolution is observed, together with an overall quantum yield 0(02) of 0.015. ... 

Fujishima and Honda [251] have discussed an electrochemical photocell based on an n-type Ti02 electrode in contact with an aqueous electrolyte and with platinum as counter electrode. The photoreaction in their system is the decomposition of water due to an oxygen evolution at the irradiated Ti02 electrode and a hydrogen evolution at the Pt electrode. Unfortunately, Ti02 has a low quantum yield for the photochemical... 

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