Organic pollutants photosensitization

DHS have been shown to effect the interaction mechanisms between various organic pollutants and solid phases. The following paragraphs will discuss how DHS can significantly decrease the chance of interactions in the pollutant-solid phase interface. This includes solubilization, hydrolysis, catalysis, and photosensitization effects. 

Degradation of many organic pollutants under the action of sunlight was found to proceed with involvement of humic substances as photocatalysts or photosensitizers (see sections 6.5 and 6.6 in Chapter 6). HSs absorb solar radiation in the range 300-500 nm and excitation by laser pulse of X 355 nm was found to induce two different processes ... 

The most common sacrificial electron acceptor in the environment is molecular oxygen, whereas the main sacrificial donors are organic compounds. In consequence, the self-cleaning processes consist in oxidation of organic pollutants by molecular oxygen in its triplet ground state the reactions are driven by energy from solar radiation. In nature, many different photoinitiators or photosensitizers are reactive, but the most common environmental photosensitizers include hiunic substances (HS), whereas the best photoinitiators are transition metal complexes. 

Cimningham JA-SG, Sedlak P, Caffrey J. Aerobic and anaerobic TiO -photocatalysed purifications of waters containing organic pollutants. Catal Today 1999 53 145-158. Penuela GAB, Damia. Photosensitized degradation of organic pollutants in water processes and analytical applications. Trends Anal Chem 1998 17 605-612. 

Functionalization of nanoparticles with porphyrins and analogous macrocycles opened the way to important applications, such as, to name only a few gelators [8], phototherapy of cancer [9], degradation of organic pollutants by singlet oxygen photosensitization [10], and photoexcited electron transfer [11]. The interest in porphyrin-based nanoreactors lies in the possibility of using a variety of metals that can enter in catalytic processes [12]. 

Kim H, Kim W, Mackeyev Y, Lee G-S, Kim H-J, Tachikawa T, Hong S, Lee S, Kim J, Wilson LJ, Majima T, Alvarez PJJ, Choi W, Lee J. Selective oxidative degradation of organic pollutants by singlet oxygen-mediated photosensitization tin porphyrin versus C q aminofullerene systems. Environ Sci Technol 2012 46 9606-13. 

Cunningham J., Al-Sayyed G., Sedlak R, Caffrey J. Aerobic and anaerobic TiOj-photocatalysed purifications of waters containing organic pollutants. Catal. Today 1999 53 145-158 Damrauer N.H., Cerullo G., Yeh A., Boussie T., Shank C.V., McCusker J.K. Femtosecond dynamics of excited-state evolution in Ru(bpy)j. Science 1997 275 54-57 Das T.K., Khan L, Rousseau D.L., Friedman J.M. Preservation of the native structure in myoglobin at low pH by sol-gel encapsulation. J. Am. Chem. Soc. 1998 120 10268-10269 Desilvestro J., Pons S., Vrachnou E., Gratzel M. Electrochemical and FUR spectroscopic characterization of ferrocyanide-modified Ti02 electrodes designed for efficient photosensitization. J. Electroanal Chem. 1988 246 411-422... 

Oxidation/hydroxylation of aromatic compounds by OH and HOONO is expected to enhance their degradation rate and hence decrease their lifetime on particulate matter, which in the case of pollutants is beneficial from the point of view of human health. Oxidation of PAHs could also lead to the production of photosensitizers such as quinones and aromatic carbonyls [10, 40, 41]. These compounds, if present in the gas phase, are also able to form aggregates and are therefore involved in the formation of secondary organic aerosol [42]. In contrast, nitration induced by OH + N02 or HOONO could lead to highly mutagenic nitro-PAHs [43] or phytotoxic nitrophenols [44, 45], in which case the health and environmental impact of the reaction intermediates is not negligible and is sometimes higher than that of the parent molecules. 

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