Heterogeneous photocatalytic degradation of gallic acid under different experimental conditions.
UV/TiO(2)-heterogeneous photocatalysis was tested as a process to degrade gallic acid (Gal) in oxygenated solutions at pH 3. In the absence of oxidants other than oxygen, decay followed a zero order rate at different concentrations and was slow at concentrations higher than 0.5 mM. Addition of Fe(3+), H(2)O(2) and the combination Fe(3+)/H(2)O(2) improved Gal degradation. In the absence of H(2)O(2), an optimal Fe : Gal molar ratio of 0.33 : 1 was found for the photocatalytic decay, beyond which addition of Fe(3+) was detrimental and even worse in comparison with the system in the absence of Fe(3+). TiO(2) addition was beneficial compared with the same system in the absence of the photocatalyst if Fe(3+) was added at low concentration (0.33 : 1 Fe : Gal molar ratio), while at high concentration (1 : 1 Fe : Gal molar ratio) TiO(2) did not exert any significant effect. H(2)O(2) addition (1 : 0.33 Gal : H(2)O(2) molar ratio, absence of Fe(iii)) also enhanced the heterogeneous photocatalytic reaction. Simultaneous addition of Fe(3+) and H(2)O(2) was more effective than the addition of the separate oxidants. This system was compared with Fenton and photo-Fenton systems. At low H(2)O(2) concentration (0.33 : 1 : 0.2 Fe : Gal : H(2)O(2) molar ratio), the presence of TiO(2) also enhanced the reaction. The influence of the thermal charge transfer reaction between Gal and Fe(iii), which leads to an important Gal depletion in the dark with formation of quinones, was analysed. The mechanisms taking place in these complex systems are proposed, paying particular attention to the important charge transfer reaction of the Fe(iii)-Gal complex operative in dark conditions.
Quici
Natalia
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Gerencia Química, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica (CNEA), Av. Gral. Paz 1499, CP 1650, San Martín, Prov. de Buenos Aires, Argentina.
Litter
Marta I
MI
D002384:Catalysis; D005707:Gallic Acid / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D014025:Titanium / Q000737:chemistry*
C009495:titanium dioxide; D005707:Gallic Acid; D006861:Hydrogen Peroxide; D014025:Titanium; D007501:Iron; D010100:Oxygen