Publication: Development of carbon quantum dots for photocatalysis degradation of methylene blue
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Date
2024-08-01
Authors
Merlyn Anne Xavier
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Abstract
In this research, Carbon quantum dots were synthesized from butterfly pea flower using the hydrothermal method in different reaction temperatures and times. The temperature used are 60°C, 90°C, 120°C, 150°C and reaction times used are 6h, 9h, 12h and 15h. Next, TiO2 nanoparticles and CQDs/TiO2 composite were synthesized using sol-gel method. Various characterizations were utilized to characterize CQDs, including UV-Visible spectroscopy, Atomic Force Microscope (AFM), Field Emission Scanning Electron Microscopy and EDX. The reaction solution of CQDs turned brown from blue colour after hydrothermal reaction at specific reaction time and temperature. Based on the band gap measurement, the band gap energy found to be increasing when the wavelength at absorption peak reduces. The wavelength at absorption peak 400nm has the highest energy is 3.10 eV for CQD whereas for TiO2, the band gap energy of TiO2 is the highest which is 3.46 eV due to its extremely low absorption peak at 357.93nm. Atomic Force Microscope (AFM) was conducted to study the morphology and measure the particle size of CQDs. The highest particle size found in temperature 150°C at 15hr which is 23.55nm whereas the lowest particle size found in temperature 120°C at 6hr is 3.56nm. CQDs/TiO2 shows the highest photocatalytic activity which is 76.59% compared to TiO2, and the two CQDs (150°C-15hr, 150°C-12hr). CQDs (150°C-12hr) recorded the lowest photocatalytic rate due to their lower band gaps than TiO2. In FESEM analysis, CQDs appear as quasi-spherical nanoparticles being well-dispersed with some agglomeration. TiO2 and CQD/TiO2 are characterized using X-ray diffraction analysis to determine the crystallographic structure of pure TiO2. In XRD analysis, the high intensity of XRD peaks of the TiO2 and CQDs/TiO2 composite reflects that the formed nanoparticles are highly crystalline and broad diffraction peaks indicate very small size crystallite. However, there is no peak found for CQDs in CQDs/TiO2 due to amorphous nature of CQDs, and low quantity of CQD. The peak at 25.4816° and 25.5632◦ for TiO2 and CQDs/TiO2 powder respectively confirms the TiO2 anatase structure. There is no spurious diffraction peak found in both TiO2 and CQDs/TiO2 powder. FTIR was conducted to determine the chemical bonds in the TiO2 and CQD/TiO2. The result of EDX of CQD shows that there is 87.59wt% C, 2.22wt% N and 10.19wt% O in the sample, which determines the presence of carbonyl, hydroxyl and carboxyl groups in CQD content.