Fenton chemistry encompasses reactions of hydrogen peroxide in the presence of iron to generate highly reactive species such as the hydroxyl radical and possibly others. In this review, the complex mechanisms of Fenton and Fenton-like reactions and the important factors influencing these reactions, from both a fundamental and practical perspective, in applications to water and soil treatment, are discussed. The review covers modified versions including the photoassisted Fenton reaction, use of chelated iron, electro-Fenton reactions, and Fenton reactions using heterogeneous catalysts. Sections are devoted to nonclassical pathways, by-products, kinetics and process modeling, experimental design methodology, soil and aquifer treatment, use of Fenton in combination with other advanced oxidation processes or biodegradation, economic comparison with other advanced oxidation processes, and case studies.

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Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry

Decontamination and disinfection of water by solar photocatalysis: Recent overview and trends

A surface science perspective on TiO2 photocatalysis

Application of peroxymonosulfate and its activation methods for degradation of environmental organic pollutants: Review

Transparent conductors as solar energy materials: A panoramic review

The photocatalytic peroxidation of E. coli cell, lipo-polysaccharide (LPS), phosphatidyl-ethanolcholine (PE), and peptidoglycan (PGN) of the E. coli membrane wall has been investigated on TiO2 porous films by ATR-FTIR spectroscopy. The fast reactions of the photogenerated charge carriers in TiO2 with E. coli, LPS, and PE were monitored by laser kinetic spectroscopy. ATR-FTIR spectroscopy allowed the identification of E. coli, LPS, PE, and PGN as photocatalytic peroxidation products. The PGN was observed to be the most resistant membrane wall component. Shorter peroxidation times were observed for LPS and PE. Laser photolysis shows that E. coli, LPS, and PE compete in the scavenging of a surface trapped holes (h+) with the recombination reaction of h+ with the generated electrons (e-) within times >50 ns. This scavenging leads to the formation of organic radicals initiating the radical chain peroxidation of E. coli, LPS, PE, and PE.

Evidence for the Mechanism of Photocatalytic Degradation of the Bacterial Wall Membrane at the TiO2 Interface by ATR-FTIR and Laser Kinetic Spectroscopy

Doped TiO2 samples using different preparative procedures were synthesized using either urea or thiourea leading to N- or S-doped TiO2. Photocatalytic peroxidation and oxidation (mineralization) of phosphatidylethanolamine (PE) lipid with doped TiO2 were carried out under light irradiation lambda > 410 nm. The formation of conjugated double bonds in PE molecules was followed to detect the formation of peroxy radicals (peroxidation index) under light excitation (lambda > 410 nm) when doped TiO2 was used. The kinetics of CO2 production was monitored during the mineralization of PE. Colored TiO2 powders were studied in detail by different and complementary physicochemical techniques. The band gap energies of colored TiO2 were determined by diffuse reflectance spectroscopy (DRS). The visible absorption shoulder of TiO2 was observed to follow Urbach's law. The variation of the transient decay after 354 nm laser pulse excitation does not correlate with the different N- and S-TiO2 doping levels introduced by the addition of urea or thiourea. This suggests that the states (recombination centers or traps) introduced by the doping are not effective in varying the decay kinetics within the nanosecond and microsecond time scale. Elemental analysis shows comparable amounts of S- and N-doping of TiO2 when thiourea is used as dopant. X-ray diffraction reveals no rutile in S-TiO2 samples heated to 600 degrees C, suggesting that the addition of sulfur precludes rutilization during sample crystallization. X-ray photoelectron spectroscopy (XPS) of the S-TiO2 samples confirms the preferential localization of S on the 20 topmost layers of S-TiO2 upon calcination at 500 degrees C for 2 h.

Preparation, testing and characterization of doped TiO2 active in the peroxidation of biomolecules under visible light.

The photocatalytic peroxidation of the bovine brain l-α-phosphatidyl-ethanolamine (PE) vesicle was measured and used as a model for phospholipid peroxidation. Synthetic phosphatidyl-ethanolamine, E. coli phosphatidyl-ethanolamine, lipid polysaccharide (LPS), and cardiopilin were used to compare the TiO2 photocatalysis leading to cell wall membrane degradation. During the photocatalytic degradation, the appearance and growth kinetics were followed for (a) conjugated double bond formation, (b) malondialdehyde (MDA), (c) peroxides, and finally (d) the observed CO2 evolution. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was measured of PE bilayers cast on TiO2 films and to a lesser extent for other phospholipids during TiO2 photocatalysis. The decay kinetics induced by photocatalysis of the isolated cis CC−H (3008 cm-1), −CH2, and −CH3 groups and of the acyl-ester bond of the fatty acid in the glycerol backbone were followed in detail. The photocatalysis was also observed to ...

New Evidence for TiO2 Photocatalysis during Bilayer Lipid Peroxidation

Photodissociation of FeOH2+ and FeCl2+ complexes has been studied by pulsed laser spectroscopy (λ = 347 nm) techniques. Transient bleaching of FeOH2+ was observed due to the dissociation FeOH+ → Fe2+ + OH• (at λ = 347 nm). The observed bleaching involved the photoreduction of the species FeOH2+ to iron(II) complexes. These latter species showed a much lower absorption. Concomitant formation of the Cl2•- anion radical was observed due to the reactions FeCl2+ → Fe2+ + Cl• (at λ = 347 nm) and Cl• + Cl- → Cl2•-. The experimental findings allowed us to suggest a reaction sequence involving Cl•, Cl2•-, ClOH•- and OH• radicals. The quantum yields found by laser kinetic spectroscopy for FeOH2+ and FeCl2+ photodissociation were 0.21 ± 0.04 and 0.5 ± 0.1, respectively.

Photolysis of FeOH2+ and FeCl2+ in Aqueous Solution. Photodissociation Kinetics and Quantum Yields

This study presents the detailed nature of iron clusters formed on Fe3+-Nafion membranes. The catalytic nature of these clusters during immobilized Fenton processes was observed to be a function of the deposition method of Fe ions on the Nafion. The nonbiodegradable azo-dye Orange II and 2-propanol were utilized as convenient organic model compounds in photoassisted Fenton degradation processes. The highest photocatalytic activity was observed when samples were prepared by ion exchange between iron(III) aqua-complexes and H+ or Na+ as counterions of the Nafion SO3- group. Spectroscopic techniques show that iron(III) in the membrane was present mainly as a mononuclear complex of [Fe(H2O)(6)](3+) and binuclear complexes [Fe(H3O2)Fe](5+) and [Fe-O-Fe](4+). If NaOH or ammonia was added to the former samples prepared by ion exchange, Nafion-Fe membranes with low photocatalytic activity were obtained showing alpha-Fe2O3 and [Fe-O-Fe](4+). Detailed high-resolution transmission electron microscopy was carried out for the Nafion-Fe ion-exchariged and also base-treated membranes showing alpha-Fe2O3 nanocrystallites of 3.5-5 nm. Spectral bands were found for iron oxides in the Fe3+-Nafion by femtosecond laser spectroscopy. The alpha-Fe2O3 nanocrystallites in the Nafion exchanged base-treated membranes presented a relaxation dynamics for the excited states close to that observed with alpha-Fe2O3 nanocrystallite colloids taken as reference compounds. Multiexponential transient absorption decay of alpha-Fe2O3 in SO3--water clusters was observed with time constants close to 320 fs, 1.5 ps, and 31 ps after the excitation pulse. Samples of Fe3+-Nafion membranes with-high activity show different transient dynamics relative to the Fe3+-Nafion with low activity. Correlation of the photocatalytic activity of Fe3+-Nafion with UV-vis, Fourier transform infrared, Mossbauer, and X-ray photoelectron spectroscopic results suggests that the photocatalytic activity correlates with the amount of mononuclear [Fe(H2O)(6)](3+), binuclear complexes [Fe(H3O2)Fe](5+) and oxo-bridged [Fe-O-Fe](4+) found in the membranes.

V. Nadtochenko

Papers

Evidence for the Mechanism of Photocatalytic Degradation of the Bacterial Wall Membrane at the TiO2 Interface by ATR-FTIR and Laser Kinetic Spectroscopy

Preparation, testing and characterization of doped TiO2 active in the peroxidation of biomolecules under visible light.

New Evidence for TiO2 Photocatalysis during Bilayer Lipid Peroxidation

Photolysis of FeOH2+ and FeCl2+ in Aqueous Solution. Photodissociation Kinetics and Quantum Yields

Catalytic Fe3+ Clusters and Complexes in Nafion Active in Photo-Fenton Processes. High-Resolution Electron Microscopy and Femtosecond Studies