Roles of different intermediate active species in the mineralization reactions of phenolic pollutants under a UV-A/C photo-Fenton process

Pyridine, 1-2-dimethoxybenzene, morpholine and lindane are mineralized by the TiO2-UV process. In the studies briefly reviewed here, their intermediate products, in particular the aliphatics, were identified both to determine what are the compounds that may be left in the treated water and to increase our understanding of the photocatalytic pathways. In addition to the oxidation and cleavage of the bonds, H(Cl) atom addition (or transfer) and coupling reactions were found to occur, which illustrates the complexity of photocatalytic degradations. Moreover, a comparison of the primary products of quinoline degraded either by photocatalysis or by the photo-Fenton process (Fe ions-H2O2-UV) showed that OH° radicals are not the only active species involved in photocatalytic degradations. From the effects of adding superoxide dismutase, it was inferred thatin situ formed O2−o anion-radicals intervene chemically, possibly by reacting with quinoline cation-radicals generated via electron transfer from quinoline to TiO2.

Download Full-text

Degradation of Methyl Violet over Fenton-Like Hydroxyapatite Catalysts, Kinetics and Thermodynamics Studies

10.21203/rs.3.rs-569149/v1 ◽

2021 ◽

Author(s):

Yasmina Roumila ◽

Djaafar Meziani ◽

Saadia Debaghi ◽

Kaïssa Abdmeziem

Keyword(s):

Dye Degradation ◽

Methyl Violet ◽

Active Species ◽

Precipitation Method ◽

Maximum Efficiency ◽

Fenton Process ◽

Optimal Conditions ◽

Optimum Conditions ◽

First Order ◽

Initial Ph

Abstract Hydroxyapatite (HA), a calcium hydroxyphosphate was prepared via precipitation method and used as a catalyst in a Fenton like process for methyl violet (MV) dye degradation. This study is aimed to evaluate the effect of hydrogen peroxide concentration, HA dose, initial pH, temperature and MV concentration on the catalyst performance to find out the optimum conditions leading to maximum efficiency of the Fenton process. The results showed that MV dye with a concentration of 20 mg L-1 can be removed within just 10 minutes at the optimal conditions of 36 mmol L–1 H2O2 and 2.5 g L–1 HA at pH of 6.65 and T = 48 °C). The experimental outcome of this study also demonstrates that HA displayed a good recyclability over three cycles; while the use of scavenger highlighted that the hydroxyl radical HO• was the main active species for MV degradation. The catalytic tests result of MV dye degradation were analyzed by the first-order, second-order and Benhnajady-Modirshahla-Ghanbery (BMG) kinetic models, those showing that the Fenton like reaction follows the first-order and BMG models. The activation energy of the reaction and the values of thermodynamic parameters such as standard enthalpy (ΔH*0), entropy (ΔS*0) and Gibbs free energy (ΔG*0) were also evaluated. Those results revealed that the degradation of MV over the as-synthesized material is an endothermic and non-spontaneous process.

Download Full-text