Effect of post-treatment drying processes on the optical and photothermal properties of carbon nanodots derived via microwave-assisted method

Abstract

Carbon nanodots (CNDs) are considered as potential materials for photothermal applications and can be used as solar absorbers to enhance the absorption and conversion efficiency of solar energy to heat. To meet the criteria as solar absorbers, CNDs were synthesized via microwave heating and dried by two different drying processes, namely freeze drying and oven drying, obtaining CNDs powder with the labeled of CND-FD and CND-OD, respectively. The effect of these two drying methods on the optical and photothermal properties of CNDs was investigated. It was observed that soft and light powders were obtained from freeze drying, while oven drying resulted in shiny and agglomerate particles. Oven drying did not alter the absorption profile of CNDs, but freeze-drying resulted in broader and slightly red-shift absorption compared with that of CNDs colloid before drying. Photoluminescence intensity of CND-FD was only half of that of CND-OD. FTIR analysis revealed that CND-FD contained fewer hydroxyl and hydrophilic amine groups, leading to less hygroscopic nature of CND-FD than CND-OD. Because of its better absorption capability, the presence of CND-FD in water significantly increased the water evaporation rate and evaporation efficiency up to 2.2 kg/m2.h and 84%, respectively, three times higher than that of water without CNDs. With a similar photothermal testing condition, CND-OD resulted in a evaporation rate of only 0.9 kg/m2.h and evaporation efficiency of 36%. It can be noticed that freeze drying is more suitable to dry CNDs powder over oven drying to obtain excellent optical and photothermal properties of CNDs.

Development of biomass waste-based carbon quantum dots and their potential application as non-toxic bioimaging agents

“…In contrast, the absorption spectrum of the CQDs becomes broad as the direct sublimation of the ice during freeze-drying process retains the particle dispersion, and the smaller spacing between the particles may lead to the emergence of new energy levels as a result of surface group interaction. 61 The difference in the absorption intensity might be due to the concentration of the CQDs during the sample preparation for the UV-Vis spectrophotometry test.…”

Green synthesis of fluorescent carbon nanodots from sage leaves for selective anticancer activity on 2D liver cancer cells and 3D multicellular tumor spheroids

“…14 This can be achieved by different methods such as electrochemical exfoliation, 15 laser ablation, 16 and arc discharge. 17 In “bottom-up”, methods such as microwave-assisted polymerization, pyrolysis, 18–23 hydrothermal/solvothermal, 24 and carbonization are used to convert small organic molecules contained in the precursor to carbon nanodots. 25–27…”

“…14 This can be achieved by different methods such as electrochemical exfoliation, 15 laser ablation, 16 and arc discharge. 17 In "bottom-up", methods such as microwaveassisted polymerization, pyrolysis, [18][19][20][21][22][23] hydrothermal/solvothermal, 24 and carbonization are used to convert small organic molecules contained in the precursor to carbon nanodots. [25][26][27] CNDs have been synthesized from various resources, such as man-made [28][29][30][31] and natural resources, [32][33][34][35][36] and they have also been synthesized from various herbs and plants and have been used in different biomedical applications.…”