THE EFFECT OF NITROGEN DOPED CARBON DOTS ON PHOTOTERMAL PROPERTIES FOR SOLAR EVAPORATION APPLICATIONS

• Main Author: Rahmawati, Ita
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/65085
• Institution: Institut Teknologi Bandung

Carbon dots (CDs) are promising candidates for solar evaporation applications due to its high light absorption capacity and efficient light-to-heat conversion. However, CDs possess high absorbance only in the UV region, so it needs to be functionalized to expand the absorbance across the solar spectrum range. Incorporating nitrogen into CDs through doping has been reported to broaden the absorption to visible region. In addition, excessive nitrogen can increase non-radiative relaxation, which is dissipated as heat. Hitherto, research on nitrogen-doped CDs for solar evaporation applications have not been explored. This research aims to develop nitrogen-doped CDs (NCDs) as photothermal material to improve the efficiency of solar evaporation. NCDs derived from citric acid and urea were synthesized using microwave-assisted pyrolysis. CDs showed blue to green emission as their nitrogen content increases. Photoluminescence (PL) spectra exhibit a redshift that could be induced by surface state and showed the minimum intensity was obtained from NCDs with molar ratio of citric acid and urea 1:3. Incorporating nitrogen into CDs with the molar ratio of 1:3 up to 1:6 exhibited new absorbance peaks at 280 nm and 405 nm that might be affected by the surface functional group as well. Furthermore, NCDs with molar ratio of citric acid and urea 1:3 have particle size distribution (4.98 ± 1.23 nm) smaller than that of NCDs with molar ratio of citric acid and urea: 1:1 (24,86 ± 3,77 nm) that can be explained by the more the number of atoms on the surface of CDs, the more stress/strain and concomitantly structural pertubasion. The functional groups of surface NCDs are carboxyl, hydroxyl, amine, and carbonyl. From the FTIR spectra, the addition of nitrogen at a molar ratio of 1:1 to 1:3 indicated the presence of C=N. The nitrogen content increased from 1:4 to 1:6, C=N decreased and a new C-N= peak appeared. According to this finding, C=N may play a role in photothermal NCDs. NCDs with a molar ratio of citric acid and urea 1:3 exhibited the highest changes in temperature (15.7oC), evaporation rate (1.14 kg m-2 h-1) and evaporation efficiency (71.48%). This evaporation measurement correlates to absorbance but inversely to PL intensity. This indicates that PL (radiative relaxation) and thermal (non-radiative relaxation) of NCDs are in competition. NCDs with a molar ratio of 1:3 is the optimal absorber material for solar evaporation applications.