STANDARDIZATION PROTOCOL OF PROCESS EFFICIENCIES AND ACTIVATION PARAMETERS IN HETEROGENEOUS PHOTOCATALYSIS - RELATIVE PHOTONIC EFFICIENCIESZETA(R)

The quantum yield Phi is crucial in homogeneous photochemistry; in het erogeneous photocatalysis this term remains elusive since the number o f absorbed photons remains experimentally difficult to assess, A compr ehensive method to standardize and compare process efficiencies in het erogeneous photocatalysis was proposed earlier by describing the relat ive photonic efficiency zeta(r) (J. Photochem. Photobiol., A: Chem., 7 3 (1993) 11) The method of determining zeta(r) is herein tested for th e photocatalyzed degradation of phenol as the standard process and Deg ussa P25 TiO2 as the standard photocatalyst. The effects of light inte nsity, reactor geometry, pH, temperature, concentration of reactant an d concentration of TiO2 on zeta(r) were examined for the photodegradat ion of three substituted phenols: 2-methylphenol, 2,4-dimethylphenol a nd 4-chlorophenol. Relative photonic efficiencies of other phenolic su bstrates are reported for a given set of conditions. Efficiencies on v arying the nature and the source of TiO2 for the photodegradation of p henol were also explored. These zeta(r) are useful to assess process q uantum yields once the actual quantum yield for a standard process (Ph i(stand), for a given photocatalyst and a standard organic substrate) has been rigorously determined; thus Phi = zeta(r) Phi(stand).