Oxalic acid destruction at high concentrations by combined heterogeneous photocatalysis and photo-Fenton processes

• DOI: 10.1016/j.cattod.2005.03.002
• Publication Date: 2005-04-02T12:15:01Z
• Authors: Natalia Quici; María E. Morgada; Gabriela Piperata; Paola Babay; Raquel T. Gettar; Marta I. Litter
• Keywords: Oxalic Acid; Reaction rate; Degradation; Peroxide; Molar ratio

Abstract Heterogeneous photocatalysis (HP) using UV/TiO 2 , photo-Fenton (PF) reaction using UV/Fe/H 2 O 2 and the combination UV/TiO 2 /Fe/H 2 O 2 (HP–PF) were tested as processes to degrade oxalic acid (Ox) at relatively high concentrations (0.032 M). PF reactions were generally more efficient than HP including the reaction in the absence of H 2 O 2 . Oppositely to previous results (e.g., with EDTA), HP–PF combinations did not result, in the case of oxalate, better techniques for degradation than systems in the absence of TiO 2 . The kinetic behavior was not unique and two parameters were taken to evaluate the efficiency of each system: initial rates ( R 0 ) and time to 95% of total mineralization (TOC 95 ). Addition of hydrogen peroxide improves the initial HP reaction rate and reduces TOC 95 . Addition of Fe 3+ also affects the reaction parameters but the effect of H 2 O 2 seems to be higher, at least under the present conditions. When both H 2 O 2 and iron were added simultaneously, the efficiency was higher. The optimal H 2 O 2 :Ox:Fe molar ratio was established and the results indicated that, at a fixed iron concentration, H 2 O 2 increased R 0 until a limit beyond which it did not cause any effect. No intermediates were formed in the reaction, oxalate being degraded directly to CO 2 . Analogies and differences with the EDTA system are presented.