Techno-economic analysis and optimization of ethylenediamine-doped carbon dots production from kraft lignin via...

This study presents the optimization and techno-economic evaluation of nitrogen-doped carbon quantum dots (KL-CDs) synthesized from kraft lignin and ethylenediamine (EDA) via a hydrothermal process. A response surface methodology (RSM) with 30 experimental runs identified optimal synthesis conditions, yielding a statistically significant linear model (p < 0.05). Doping with ethylenediamine enhanced the quantum yield from 2.7 % to 11.3 % and increased the mass yield fivefold. FTIR and XPS analyses confirmed nitrogen incorporation into the lignin structure, revealing pyrrolic and pyridinic nitrogen species. The KL-CDs exhibited nanoscale dimensions, negative zeta potential (< -20 mV), and excitation-dependent multicolor fluorescence with improved lifetimes. Thermogravimetric and molecular weight analyses revealed distinct thermal behavior and molecular structures for doped and undoped samples. An industrial-scale process simulation demonstrated technical and economic feasibility, with a minimum selling price of US$0.49-0.70/L for a 20 % ROI. These findings validate kraft lignin as a viable precursor for producing high-performance carbon dots, advancing the circular bioeconomy.