Carbon quantum dots: An environmentally friendly and valued approach to sludge disposal

Abstract

Sewage sludge, produced daily and inherent to urban development, presents problems of disposal that are still challenging today. Its disposal still offers palliative solutions, where the final destination is generally in landfills or, restrictively, to use in agriculture. The synthesis of carbon quantum dots (CQDs) from sewage sludge is a better alternative to use the stock of organic material present in the sludge. The present work aims to produce Carbon quantum dots (CQDs) using principles of green chemistry and to use an alternative raw material intrinsic stock of carbon present in sewage sludge, making its final disposal more sustainable. The material obtained has a core structure mainly composed of sp2 carbon and nitrogen. The surface functional groups containing sulfur, nitrogen, and oxygen of CQDs were investigated using FTIR and TG/DSC coupled FTIR techniques. The CQDs showed a luminescence decay time equivalent to fluorescent compounds and with satisfying quantum yield since no passive/oxidizing agent or material purification process was used. The photoluminescence spectroscopy analysis showed that the CDQs excitation λmax was at 360 nm and caused a λmax emission at 437 nm (CQDsa) and 430 nm (CQDsb). The CQDs obtained showed sizes of 9.69 ± 2.64 nm (CQDsa) and 10.92 ± 2.69 nm (CQDsb). In vitro experiments demonstrated the uptake of CQDs by the endothelial cell line EAhy 926 and their nontoxicity. However, the production of CQDs can be used for the sustainable disposal of sewage sludge.

Thermal Evaluation of Silica-Based Insulated Magnet Wires from the Sol–Gel Process

“…From the FTIR analysis shown in Figure 12 , the absence of a broad band between 3000 and 3500 cm −1 indicates the absence of OH groups and the full polycondensation of Si-OH to the Si-O-Si network. The character of the asymmetric stretching mode vibration of the Si-O-Si group was observed as a doublet at intense peaks in the range of 1091–1073 cm −1 , confirming the formation of network Si-O-Si [ 12 , 13 , 14 ]. From the PAI signature, the amide C=O region is observed around 1710 cm −1 and, at 1774 cm −1 , the absorbance is associated with the imide carbonyl band, and the absorption band for symmetric stretching of C-N was observed at 1385–1363 cm −1 .…”

Microwave-Prepared Quantum Dots and Their Potential Applications as Adsorbents and Chemosensors

“….78 and 26.59%, respectively, was due to depolymerization and the combustion process [3]. The Ea for the first split step (i.e., 19.49 and 19.34 kJ mol −1 ) was higher than the second split step for the second decomposition step (i.e., 18.00 and 18.47 kJ mol −1 ), so it is suggested that the first split step is related to carbon core burn of CQDs (ML≈13.29 and 1.78%) [31]. At the same time, the CS/B QDs decomposition curves revealed three decomposition steps.…”

“…The second main decomposition step was split between 266.27-357.27 and 357.40-978.72, and 277.83-361.05 and 362.71-979.81 • C, with a maximum of 331.02 and 397.27, and 330.05 and 400.36 • C, respectively, and ML% of 13.29 and 25.86, and 10.78 and 26.59%, respectively, was due to depolymerization and the combustion process[3]. The Ea for the first split step (i.e.,19.49 and 19.34 kJ mol −1 ) was higher than the second split step for the second decomposition step (i.e., 18.00 and 18.47 kJ mol −1 ), so it is suggested that the first split step is related to carbon core burn of CQDs (ML≈13.29 and 1.78%)[31]. At the same time, the CS/B QDs decomposition curves revealed three decomposition steps.…”