Impact of H2O2 on the Lactic and Formic Acid Degradation in Presence of TiO2 Rutile and Anatase Phases under UV and Visible Light

Annika Holm,Karima Sahel,Frederic Dappozze,Marwa Hamandi,Chantal Guillard

doi:10.3390/catal10101131

Abstract

The degradation rates of formic acid and lactic acid in the presence and absence of H2O2 were studied, utilizing several TiO2 catalysts: PC105 (100% anatase), MPT 625 (100% rutile), and P25 (80% anatase/20% rutile), and the results were discussed with regards to the current literature. The impact of hydrogen peroxide on the photocatalytic efficiency of eleven TiO2 samples was then determined, using commercial anatase structures (PC105, PC500, UV100), commercial mixed anatase/rutile (P25 and P90), and six rutile (two commercial samples: MPT 625 and C-R160, and four home-made rutile samples were synthesized by TiCl4 hydrolysis). The effect of catalyst surface area and TiO2 phase on the degradation rate of lactic acid (LA) and the decomposition of H2O2 was studied and discussed in regard to the active species generated. The intermediate products formed in the absence and presence of H2O2 were also an important factor in the comparison. Finally, the efficiency of the degradation of LA and formic acid (FA) in the presence of rutile and H2O2 was determined under visible light, and their reactivity was compared. The intermediate products formed in the degradation of LA were identified and quantified and compared to those obtained under UV (Ultra-Violet).

Highlights

Several publications [1,2,3,4,5,6,7,8,9,10,11,12,13,14] have mentioned the impact that H2 O2 addition has on the degradation of different organic compounds in the presence of TiO2
No oxidation of formic acid and lactic acid was observed within a 2 h period of darkness at room temperature, indicating that the possible degradation of hydrogen peroxide in the absence of light can be ruled out for all experiments
The impact of H2 O2 on lactic acid and formic acid was determined in the presence of three commercial TiO2 samples: PC105, C-R100 and P25—a commonly used reference in photocatalysis

Summary

Introduction

Several publications [1,2,3,4,5,6,7,8,9,10,11,12,13,14] have mentioned the impact that H2 O2 addition has on the degradation of different organic compounds in the presence of TiO2. Most studies performed using P25 TiO2 found that H2 O2 has a favorable impact. It was explained by the elevated hydroxyl radical production, either due to hydrogen peroxide’s reaction with conduction band electrons, or to indirect formation via. Some researchers have shown an unfavorable effect of H2 O2 on TiO2 [2,3] which is explained by the competition between H2 O2 and a pollutant for the adsorption sites. H2 O2 is proposed to be in competition with photoproduced holes, since H2 O2 competes with the reaction of water (Equation (3)), which limits the formation of OH radicals (Equations (3) and (4)): H2 O2 + h+ → H+ + HO2 ◦ (3)

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Conclusion