Integrated Solvent‐Catalyst‐Dopant Strategy via Acidic <scp>DES</scp> for Synthesizing Lignin‐Derived Carbon Dots With High‐Quantum Yield to Achieve Efficient Photocatalytic Degradation of Tetracycline

Compared to the conventional hot water method which are limited by the low lignin solubility and weak acidity, the deep eutectic solvents (DESs) offer a superior integrated platform of solvent, catalyst, and dopant for producing high‐performance carbon quantum dots (CQDs). The acidic DES systems can overcome incomplete dehydration and sp 3 ‐C defects by leveraging strong hydrogen‐bonding networks and efficient acid catalysis to drive deep carbonization and aromatization. Notably, the DES of choline chloride (ChCl)/p‐toluenesulfonic acid (pTSA) (1:1) not only ensures the dispersion of lignin precursor via strong electronegativity and ππ stacking but also directs carbonization through specific SO···HO interactions and facilitates in‐situ sulfur doping. This results in the sample of CQDs‐pTSA samples with a highly conjugated carbon core (82.8% sp 2 ‐C) and an exceptional quantum yield of 56.9% (4.8 times higher than hydrothermal counterparts). When integrated with TiO 2 , the CQDs‐pTSA significantly enhances the photocatalytic performance, achieving a 97.3% tetracycline degradation efficiency with high cyclic stability. This improvement is attributed to the rich surface functionalities (CO, pyrrolic‐N, and thioether‐S), which form TiOC and TiOS bridges. These interfacial bonds, combined with a broadened visible light absorption range (redshifted to 578 nm), effectively suppress carrier recombination and accelerate interfacial charge transfer.