| Summary: | 碩士 === 國立暨南國際大學 === 土木工程學系 === 97 === Generally speaking in environmental technology, carbon nanotubes (CNTs) and titanium dioxide (TiO2) can effectively remove organic from water. The CNTs oxidized by heating at 400℃ and oxidized with sulfuric acid were used to adsorb humic acid from water in this study. It was experimentally demonstrated that the purity of the oxidized CNTs and the quantity of functional groups would be increased and the amorphous carbons would be decreased on the surfaces of the oxidized CNTs. Therefore, the adsorption capacity of the oxidized CNTs on organic compounds would be significantly increased. Experimental results showed that the adsorption capacity of CNTs oxidized by heating at 400℃ was superior than that of CNTs oxidized with sulfuric acid, although the positive charges on the surfaces of the CNTs after being oxidized with sulfuric acid were substantially increased.
The adsorption of humic acid by the oxidized CNTs required 24 hours to reach equilibrium state, and the data of kinetic adsorption experiments could be modeled well by pseudo-second order model in this study. An appropriate ratio between CNTs mass and the solution volume could make CNTs to be well separated and dispersed in the solution. This would be beneficial to the adsorption of humic acid by oxidized CNTs. It also could be observed that the adsorption capacity to humic acid by oxidized CNTs increased with the increase of the ionic strength and the decrease of the pH value in soultion. It implies that decreasing the solubility of adsorbate in solution could promote the adsorption capacity of oxidized CNTs. The maximum adsorption capacity of oxidized CNTs to humic acid is 90.1mgg-1 in the room temperature in this study, according to Langmuir isotherm model. The n value 2.23 of Freundlich isotherm model is greater than 1.0. It indicates that the oxidized CNTs are feasible for the adsorption of humic acid.
Results in the experiments of the photodegradation of humic acid by 0.6gl-1 of TiO2 showed that it only took 6 hours to photodegrade humic acid from 60mgl-1 to 0.62mgl-1, and the photodegradation efficiency was 98.9%. The reaction time was shortened by 18 hours in comparison with the adsorption of CNTs which removal efficiency was only 58.6% at the same experimental conditions. Experimental results also showed that the photodegradation reaction rate could be further raised while increasing the mass of TiO2. By observing the concentration variations of humic acid and dissolved organic carbon (DOC) in the experiment, both followed the same decreasing trend. This indicated that humic acids were directly conversed to carbon dioxide by photodegradation reaction. Intermediate organic compound was not found in the final composition.
Although the past studies indicated that CNTs mixed with TiO2 could promote the photodegradation efficiency, the experimental results showed that it was difficult to promote the photodegradation efficiency by mixing CNTs and TiO2 together. Maintaining adequate contact between CNTs and TiO2 as well as adequate dissolved oxygen in the solution may be the two key points in the combination experiment. Further studies are needed.
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