Abstract
Analysis methods that require small volumes of aqueous samples can be of large benefit for applications when expensive chemicals are involved or available volumes are substantially small and concentrations are low. A new method is presented to allow microvolume liquid injections on TOC equipment using a special designed Shimadzu gas injection kit® in combination with a high precision syringe and Chaney adapter. Next to details on the methodology of microvolume TOC injections, the technique is shown to be beneficial to evaluate the efficiency of photocatalytic dye degradation on titania materials in terms of CO2 conversion simultaneously with classic UV-Vis analysis measurements within a lab scale photocatalytic test setup (volume <100 mL). The possibility to allow multiple microvolume samplings in short time intervals during several hours without a substantial decrease in volume/catalyst ratio is of particular value for the evaluation of photocatalysts. By combining both techniques at short time intervals, additional knowledge of the degradation process/mechanism, kinetics and the efficiency can be obtained in a direct way. Moreover, the developed μV-TOC analysis is specifically useful in those applications in which low sample volumes in combination with low concentrations are involved. For example, μV-TOC can similarly be put into service in a wide range of small volume setups, e.g., analytes from high-throughput screening, pharmaceutical applications and other advanced oxidation processes that formally could not be analyzed due to limited sample volumes and often low concentrations.
Highlights
Titanium dioxide based photocatalysis became an established, significant and still expanding area of research, since it has been proven that the photoinduced “advanced oxidation processes” (AOP) are very efficient in the degradation of harmful, organic pollutants towards CO2 [1,2,3,4,5,6].Various methods for assessing and characterizing the photoactivity of these materials have been developed
After 60 min of UV irradiation, 36% of the initial amount of carbon has been oxidized to CO2 whereas 91% of the initial dye molecule has been photodegraded into smaller compounds (UV-Vis analysis, photobleaching), indicating a long lifetime of intermediates
A Shimadzu® designed gas injection kit, in combination with a high precision syringe equipped with a Chaney Adapter, was applied to perform microvolume Total Organic Carbon (TOC) measurements on liquids
Summary
Various methods for assessing and characterizing the photoactivity of these materials have been developed Most of these techniques study the photobleaching process of dye molecules (e.g., methyl orange and Rhodamine 6G) by plotting the decrease in concentration of the dye as a function of time determined via UV-Vis analysis measured at only one wavelength, that of maximum absorption of the original dye [2,3,6]. It is a fast, non-destructive and inexpensive method, it only allows evaluating the decrease in concentration of the initial test molecule in function of time. UV-Vis analysis can only be correlated to the initial degradation steps (photobleaching) and not to the total degradation process into CO2
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