Photoinduced reactivity of titanium dioxide

The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

An overview of semiconductor photocatalysis

Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination—A review

Advanced oxidation processes (AOPs) constitute a promising technology for the treatment of wastewaters containing non-easily removable organic compounds. Chlorophenols (CPs) are a group of special interest due to their high toxicity and low biodegradability. Data concerning the degradation of CPs by means of AOPs reported during the period 1995–2002 are evaluated in this work. Among the AOPs, the following techniques are studied: processes based on hydrogen peroxide (H2O2+UV, Fenton, photo-Fenton and Fenton-like processes), photolysis, photocatalysis and processes based on ozone (O3, O3+UV and O3+catalyst). Half-life times and kinetic constants for CP degradation are reviewed and the different mechanistic degradation pathways are taken into account.

Degradation of chlorophenols by means of advanced oxidation processes: a general review

The photocatalytic properties of titanium dioxide are well known and have many applications including the removal of organic contaminants and production of self-cleaning glass. There is an increasing interest in the application of the photocatalytic properties of TiO2 for disinfection of surfaces, air and water. Reviews of the applications of photocatalysis in disinfection (Gamage and Zhang 2010; Chong et al., Wat Res 44(10):2997–3027, 2010) and of modelling of TiO2 action have recently been published (Dalrymple et al. , Appl Catal B 98(1–2):27–38, 2010). In this review, we give an overview of the effects of photoactivated TiO2 on microorganisms. The activity has been shown to be capable of killing a wide range of Gram-negative and Gram-positive bacteria, filamentous and unicellular fungi, algae, protozoa, mammalian viruses and bacteriophage. Resting stages, particularly bacterial endospores, fungal spores and protozoan cysts, are generally more resistant than the vegetative forms, possibly due to the increased cell wall thickness. The killing mechanism involves degradation of the cell wall and cytoplasmic membrane due to the production of reactive oxygen species such as hydroxyl radicals and hydrogen peroxide. This initially leads to leakage of cellular contents then cell lysis and may be followed by complete mineralisation of the organism. Killing is most efficient when there is close contact between the organisms and the TiO2 catalyst. The killing activity is enhanced by the presence of other antimicrobial agents such as Cu and Ag.

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Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity

Near-UV photocatalytic disinfection was accomplished in aqueous titanium dioxide suspensions. A level of inactivation of phage MS2 of 90% increased to 99.9% after 2 μM ferrous sulfate was added. Hydroxyl radical oxidation, with Fenton reaction enhancement, is suspected to be primarily responsible for the viral degradation observed.

Inactivation of Phage MS2 by Iron-Aided Titanium Dioxide Photocatalysis.

Twelve samples were obtained from a groundwater basin containing significant levels of color caused by the humic constituents of dissolved organic matter (DOM). The DOM present in raw source samples was characterized according to apparent molecular size (AMS) distribution. The resultant AMS distributions - expressed in terms of dissolved organic carbon, UV absorbance, and trihalomethane formation potential - were found to provide insight into potential treatment process applicability. Ozonation showed the most merit for lower-color, lower-AMS sources, whereas coagulation or membrane treatment was more suitable for higher-color, higher-AMS sources. No clear treatment niche (i.e., AMS range) was identified for activated carbon adsorption. It is well known that naturally occurring color is often caused by humic substances. Aquatic humic substances generally account for approximately 50 percent of the dissolved organic matter

https://www.jstor.org/stable/info/41293759

Molecular Size Distributions of Dissolved Organic Matter

Contaminated water is treated by adsorbing contaminant onto a sorbent to concentrate the contaminant and then oxidizing the contaminant via the Fenton and related reactions. Iron is attached to the sorbent or can be added in solution with an oxidant. Both systems, iron attached to the sorbent or iron in solution, can be used to oxidize contaminants on or near the surface of the sorbent. The process can be used to treat contaminated water in above-ground and below-ground treatment systems.

Contaminant adsorption and oxidation via the fenton reaction

Influence of peat on Fenton oxidation.

The spin trap compound α-(4-pyridyl-1-oxide)N-tert-butylnitrone (4-POBN) served as a probe to estimate the activity of Fenton-derived hydroxyl radicals (•OH) in a batch suspension comprised of silica sand and crushed goethite ore. The rate of probe disappearance was used to analyze system kinetics and oxidation efficiency under heterogeneous, Fenton-driven conditions. The •OH−(4-POBN) adduct produced by the reaction of 4-POBN with •OH was observed via electron paramagnetic resonance to confirm the mechanism of 4-POBN transformation. The disappearance of 4-POBN with •OH in the sand/goethite slurry amended with H2O2 (150 mM) was first-order in 4-POBN. Under the conditions of this experiments, the effective steady-state •OH concentration ([•OH]ss) was estimated at 1.2 × 10-15 and 6.5 × 10-16 M, when 4-POBN was initially present at 700 and 1440 μM, respectively. Observed kinetics were in qualitative agreement with a conceptual model in which H2O2 is consumed in both Fenton and non-Fenton reactions and 4-POBN ...

Raymond A. Sierka

Papers

Inactivation of Phage MS2 by Iron-Aided Titanium Dioxide Photocatalysis.

Molecular Size Distributions of Dissolved Organic Matter

Contaminant adsorption and oxidation via the fenton reaction

Influence of peat on Fenton oxidation.

Measurement of Hydroxyl Radical Activity in a Soil Slurry Using the Spin Trap α-(4-Pyridyl-1-oxide)- N-tert-butylnitrone