Carbon dots recovery from waste streams of hydrothermal process

Waste streams from hydrothermal process typically contain high levels of aldehydes, volatile fatty acids, phenols, 5-hydroxymethyl furfural, and some dissolved organic compounds that could contaminate water bodies and soils. To address the problems of high organic content and high disposal costs in waste streams generated in hydrothermal process. This work proposes a process for the recovery and extraction of carbon dots (CDs) from hydrothermal waste streams and a new idea for the preparation of CDs by hydrothermal carbonization (HTC) of high-ash biomass with polyvinyl chloride (PVC). The HTC of corncob (CC), corn stalk (CS), and the co-HTC of PVC with CC, CS waste streams were used as raw materials for the extraction and recovery of CDs. The results showed that the CDs obtained from the HTC of CC, CS (CC-CDs, CS-CDs) were more homogeneous in particle size and distribution and had more hydrophilic functional groups on the surface. Whereas the CDs obtained from the co-HTC of PVC with CC, CS (PCC-CDs, PCS-CDs) were of different particle sizes and had an aggregated distribution. In addition, the incorporation of PVC improved the excitation wavelength dependence of CDs. The relative percentage of Si2p in the PCS-CDs is much higher than that in the other CDs, with higher fluorescence quantum yields. Based on these results, the feasibility of the process for extracting CDs from hydrothermal waste streams was evaluated, providing theoretical guidance for extracting valuable products from hydrothermal waste streams and compensating the cost of wastewater treatment.