Carbon quantum dots derived from cassava stems via acid/alkali-assisted hydrothermal carbonization: formation, mechanism and application in drug release

Green and sustainable carbon quantum dots from lignocellulosic biomass (LB-CQDs) have been widely used in various fields. However, the recalcitrant nature of lignocellulose leads to the low yield of LB-CQDs. In this work, we proposed an effective strategy for obtaining high yield LB-CQDs from cassava stems through acid/alkali-assist hydrothermal carbonization. The results indicated that LB-CQDs processed by HNO3 +urea (N-U-CQDs) exhibited the best fluorescence characteristics due to their smaller size and higher N content. Compared with unmodified LB-CQDs, the yield and fluorescence efficiency of N-U-CQDs increased by 36% and 80%, respectively. Meanwhile, a speculation was made on the formation route and luminescence mechanism of LB-CQDs from acid/alkali-assist hydrothermal carbonization. In addition, biomass mineral materials CaCO3 was induced by LB-CQDs to prepare carrier materials CQDs/CaCO3 for the loading and sustained-release of anticancer drug (doxorubicin, DOX). The results suggested the retained specific recognition of DOX@CQDs/CaCO3 for diseased cells. Compared to the environment simulating normal tissue with pH= 7.4, DOX@CQDs/CaCO3 exhibited faster release efficiency (52.6%, 4 h) and higher release amount (93.1%, 48 h) of loaded DOX in the environment simulating cancer cells with pH= 5.0. Therefore, it offered a novel strategy for the efficient conversion of lignocellulose into CQDs and the application of LB-CQDs in drug release.