Standardization protocol of process efficiencies and activation parameters in heterogeneous photocatalysis: relative photonic efficiencies ζr

Abstract

The quantum yield Φ is crucial in homogeneous photochemistry; in heterogeneous photocatalysis this term remains elusive since the number of absorbed photons remains experimentally difficult to asses. A comprehensive method to standardize and compare process efficiencies in heterogeneous photocatalysis was proposed earlier by describing the relative photonic efficiency ζ r ( J. Photochem. Photobiol., A: Chem., 73 (1993) 11). The method of determining ζ r is herein tested for the photocatalyzed degradation of phenol as the standard process and Degussa P25 TiO 2 as the standard photocatalyst. The effects of light intensity, reactor geometry, pH, temperature, concentration of reactant and concentration of TiO 2 on ζ r were examined for the photodegradation of three substituted phenols: 2-methylphenol, 2,4-dimethylphenol and 4-chlorophenol. Relative photonic efficiencies of other phenolic substrates are reported for a given set of conditions. Efficiencies on varying the nature and the source of TiO 2 for the photodegradation of phenol were also explored. These ζ r are useful to assess process quantum yields once the actual quantum yield for a standard process ( Φ stand, for a given photocatalyst and a standard organic substrate) has been rigorously determined; thus Φ = ζ r Φ stand.