Masami Fukushima

Effects of pH and organic co-solvents on the oxidation of naphthalene with peroxosulfate catalyzed by iron(III) tetrakis(p-sulfonatophenyl)porphyrin

The oxidation of naphthalene was investigated in a biomimetic catalytic system using KHSO5 and iron(III) tetrakis(p-sulfonatophenyl)porphyrin (FeTPPS) in order to elucidate the influence of solution forms, such as buffer pH and co-solvent types, on the reaction. 1,4-naphthoquinone was the main byproduct and the efficiency of oxidation, particularly 1,4-naphthoquinone formation, was influenced by pH and the type of co-solvent used. The most efficient conversion of 1,4-naphthoquinone was observed at an acidic pH (= 3). At higher pH, the formation of μ-oxo species (OFe2(TPPS)2) leads to a decrease of the percentage of naphthalene oxidized. In addition, the organic co-solvents (methanol, ethanol, 2-propanol and acetonitrile) influenced the amounts of naphthalene conversion. The amounts of 1,4-naphthoquinone formed were related to the electron donating character of the organic co-solvents.

Facilitation of pentachlorophenol degradation by the addition of ascorbic acid to aqueous mixtures of tetrakis(sulfonatophenyl)porphyrin and iron(II)

Abstract Pentachlorophenol (PCP) was degraded in an aqueous mixture of tetrakis(sulfonatophenyl)porphyrin (TPPS) and Fe(II) at pH 6. The degradation was enhanced by the addition of ascorbic acid (ASC), and PCP was largely degraded to tetrachlorohydroquinone (TeCHQ) and tetrachlorocatechol (TeCC). Chloride ions were released during the reaction in molar amounts that were approximately 2–3 times larger than those of PCP degraded. This suggests that further oxidative products are also produced. The percentage of PCP degraded decreased with increasing concentrations of 2-propanol, a hydroxyl radical (OH ) scavenger. This supports the hypothesis that HO is involved in PCP degradation. When an aqueous solution, which contained only TPPS, was shaken under aerobic conditions, H2O2 was generated at mM level after a 24xa0h reaction period. Thus, TPPS appears to be involved in the reduction of dissolved oxygen to O2 −, leading to the generation of H2O2. However, in the presence of both TPPS and ASC, >100xa0μM-levels of H2O2 were generated. This shows that the addition of ASC to TPPS enhances the generation of H2O2. These results lead to the conclusion that the degradation of PCP in the present systems can be attributed to a Fenton-like process.

Photocatalytic reaction by iron(III)‐humate complex and its effect on the removal of organic pollutant

The light irradiation (> 370 run) of the aqueous solution, which contained humic acid (HA), resulted in the generation of hydrogen peroxide (H2O2). However, the generation of H2O2 was decreased by the presence of Fe(III). This is due to the consumption of H2O2 by the light‐induced Fenton reaction. In this reaction, HO is formed by the degradation of H2O2 by Fe(II). The decrease of [H2O2] by the presence of Fe(IIl) (?[H2O2) increased with increasing pH and the HA concentration. This suggests that the complexation of Fe(III) with HA contributes to the acceleration of the reaction. Moreover, it was demonstrated that the removal of organic pollutant, such as aniline, was accelerated by the light‐induced Fenton reaction with the Fe(III)‐HA complex.

Effect of phenolic acids in humic acid on the degradation of pentachlorophenol by the photo‐Fenton reaction

Abstract At pH = 5.0, the degradation of pentachlorophenol (PCP) by the photo‐Fenton reaction was facilitated in the presence of humic acid (HA). To identify the functional groups in HA that contributed to this facilitation, the degradation kinetics of PCP were investigated for six types of phenolic acids. The pseudo‐first‐order rate constants of PCP degradation (K 3) increased with those for the photoreduction of Fe(III) (k 1 ).This indicates that the photoreduction of Fe(III) is an important step in the degradation of PCP by the photo‐Fenton reaction. Moreover, the K 3values for gallic, protocatechuic and caffeic acids were larger than those for syringic, vanillic and ferulic acids. This shows that the phenolic acids in HA, which contain neighboring hydroxyl groups, are major contributors to the facilitation of PCP degradation.

Aniline removal by Photocatalytic reaction of iron(iii) mediated with dissolved organic matter

When light (> 370 nm) was allowed to interact with an aqueous solution containing dissolved organic matter (DOM) and Fe(III), removal of aniline (AN) was observed. This was due to the photocatalytic reaction of Fe(III) mediated by DOM. Syringic acid (SYA) and humic acid (HA) were used as DOM in the present study. The 15N‐NMR spectrum of the product mixture from the light irradiation of the SYA/Fe(III) system demonstrated that AN was covalently bound to SYA. The kinetics of AN removal were, therefore, interpreted by assuming covalent binding between DOM and AN. The amounts of covalent binding sites and the apparent second‐order rate constants could be evaluated, and the amounts of covalent binding sites decreased with the increases of the concentration of DOM. This is attributed that the polymerization of DOM by the photo‐oxidation competed with the covalent binding between AN and DOM.