Quinizarin-based Simple and Convenient Colorimetric Sensor for Carbon Dioxide

Abstract

Abstract Quinizarin-based Simple and Convenient Colorimetric Sensor for Carbon Dioxide MinSeok Seong Department of Materials Science and Engineering The Graduate School Seoul National University

In search of simple and fast method to estimate the concentration of atmospheric carbon dioxide, the quinizarin and TBD system was discovered and its mechanism was studied and the applications were tried. From UV-VIS spectrum, the reason behind the change in color of the solution was found to be the different electronic forms of quinizarin. In other words, the color of the quinizarin solution was orange yellow when quinizarin was neutral while its color changed to purple once mixed with TBD as a result of deprotonation. Also, the molar ratio of quinizarin to TBD was 1 to 1 because there was no increase in the strength of the absorption band when TBD was excessive whilst there was a decrease when TBD was deficit. Also, the shift of the absorption band was observed as a result of TBD binding with carbon dioxide and giving back protons to quinizarin. From 1H-NMR spectrum, the hydroxyl proton of quinizarin was observed initially but it was soon given to TBD. Also, the fact that TBD bound itself with carbon dioxide was verified by the 13C-NMR spectrum as a new peak was observed at 161 ppm. In assistance with FT-IR spectrums, the proposed mechanism was supported once more. Quinizarin loses a proton to TBD and the protonated TBD loses the proton as it binds with carbon dioxide. As a result, the color of the solution changed from purple to yellow. The intensity of the vibrational modes for the corresponding functional groups changed accordingly

N-H bond decreased and O-H bond increased. For the experimental parts, the saturation volume of carbon dioxide was studied

the total volumetric capacity of the detecting system at different concentrations were measured and it was used to estimate the approximate response time and detectable concentration of carbon dioxide for each concentration of the system. The response time of the system at given concentration of carbon dioxide was figured out in the next step. As predicted, the system with lower concentrations of the chemicals had a shorter response time. However, the systems with the other organic bases such as DBU and piperidine were found to be not fast enough to detect the concentration of carbon dioxide fast compared to the system with TBD at the same concentration. Most importantly, the system could be recycled for at least 3 to 5 times and the performance was maintained relatively well. The system could actually be re-used upto 10 times but it became harder and harder to notice the color change when re-used too many times. Known the properties of the system as sensor, new applications were tried.. For solidification, TBD was physically fixed onto silica and it was successfully done. Nextly, the solid TBD was dipped in the quinizarin solution to become blue. Although the system was seemingly ready, it was not be able to interact with the atmospheric carbon dioxide and did not undergo any color change. Obviously, the solid system failed to interact with carbon dioxide because of too high thermodynamic barrier between solid and gas. The other option was an Agarose gel technique. The quinizarin and TBD solution was made and mixed with hot agarose solution and cooled down. However, the gel had too much viscosity so the response time was significantly increased.

Keywords: Carbon dioxide, Chemical dye, Organic base, Protonation, Deprotonation, Adduct, Colorimetric sensor, Student Number: 2015-20829