Efficient preparation of nitrogen-doped lignin-based carbon nanotubes and the selectivity of nitrogen speciation for photothermal therapy.

In this study, the lignin was pre-modified using small-molecule nitrogen-containing compounds, and then the nitrogen-doped lignin-based carbon nanotubes (L-NCNTs) were fabricated by pyrolysis using the modified lignin as raw materials. The obtained L-NCNTs were multi-walled carbon nanotubes with diameters between 10 and 80 nm. The modification of lignin had an important effect on the nitrogen morphology of L-NCNTs, and promoted the high selectivity of pyridine-N in the L-NCNTs. Defects and pyridinic-N structure were conducive to boosting photothermal properties of the L-NCNTs. The photothermal conversion efficiency of the L-NCNTs after 808 nm laser irradiation for 5 min reached 58.8 %. The L-NCNTs can be used as photothermal agents in drug delivery system to achieve mild photothermal therapy, and it is basically non-toxic to normal cells, indicating good biocompatibility. This work provides new ideas for development of lignin-based high value-added products from biomass.