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Query: UMLS:C1835664 (TOC)
 2,763 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

There is an increasing demand for measurement of organic carbon in solutions both in industry and in environmental research for the purpose of continuous water-quality monitoring. Practically all the methods used are based on a catalytic system in which metal oxides play a major role. The development of a new TOC/DOC measurement system, in our work, uses a mixed anatase-rutile form of TiO(2 )as catalyst of the mineralisation process, and direct measurement of the CO(2) produced, by a gaseous diffusion electrode. The entire research is based on heterogeneous catalysis using an immobilised catalyst, which can offer considerable advantages over other methods of catalysis. Four different catalytic systems were analysed. Three involved thermal immobilisation of TiO(2) on glass supports (glass spheres and glassy particulates) or on an Al metal grid. One further system consisted of direct oxidation of a Ti grid at high temperatures. The system was illuminated using a 350 nm UV source (350 mW cm(-2)) contained in a home-made measurement cell. Five molecules-malic acid, pentachlorophenol, sodium dodecylsulfate, hydroquinone, and citric acid-which were deemed to be representative and had been investigated in several previous studies, were used as photodegradation targets. However, it was not possible to obtain a direct expression of "catalytic efficiency" simply by reading the data obtained, nor any indirect molecular "recalcitrancy" scale. Chemometric analysis, by principal components analysis, allows the five used catalytic systems to be easily compared each other and a single PC component is able to perform classification.
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PMID:Chemometric investigation of the efficiency of different TiO(2)-based catalysts as principal components of TOC photochemical sensors under development. 1274 55

This study compared formation and degradation behaviors of organic acids in landfill leachate under microwave oxidation process (MOP) and under conventional heating oxidation (CHO) and explored derivative mechanisms of organic acids in MOP. The results showed that formation and degradation behaviors of oxalic acid were very similar under CHO and MOP, in which its concentrations decreased in the temperature-raising period, then increased due to decomposition of TOC from 10 to 70 min, decreased due to persulfate oxidation from 70 to 130 min, and stayed the same afterwards. The pH values of the leachate solution dropped 0.51 and 0.65 pH units after MOP and CHO treatment, respectively. Oxalic acid was the dominant organic acid formed in MOP. The derivative mechanisms of organic acids were developed using the experimental results. Lactic acid was generated from decomposition of malic acid, and oxalic acid was formed from oxidation of its precursors. Acetic acid was formed and soon decomposed. Lactic acid had its maximum concentration with a persulfate dose of 0.5M, while lower or higher persulfate doses yielded few or no lactic acid in MOP.
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PMID:Derivative mechanisms of organic acids in microwave oxidation of landfill leachate. 2364 53