Red, yellow, green, and blue light-emitting highly crystallized graphene quantum dots derived from lignin: controllable syntheses and light-emitting diode applications

Abstract

“Lighting up” lignin: synthesis of multicolour-emitting GQDs with high crystallinity from lignin within 12 h and their successful application to multicolour LEDs.

The effect of lignin molecular weight on the formation and properties of carbon quantum dots

“…18 It can be found that the C–H signals of L-CQDs are weaker compared to the C–H signals in the corresponding lignin samples, which is due to the demethylation of lignin during the hydrothermal process. 17 The intensity of the absorption peaks of L-CQDs-1–5 at 1595 cm −1 shows a trend of increasing and then decreasing, which is consistent with the fluorescence data (Fig. 3), suggesting that the CC group has a direct effect on the fluorescence performance of L-CQDs.…”

“…The hydrothermal method provides high-temperature and high-pressure reaction conditions, similar to the chemical reaction environment of the crusting reaction, which promotes the formation and growth of aromatic compounds. 17 Based on the similar absorption characteristics of the UV spectra of L-CQDs and the similar optimal excitation wavelengths and emission wavelengths, it can be reasonably assumed that the L-CQDs formed from lignin with different molecular weights using the hydrothermal method have similar core–shell structures. 34 The difference in the fluorescence intensity of L-CQDs is due to the different content of conjugated structures in their carbon cores.…”

“…11–13 It is generally believed that the hydrothermal process of using lignin as a carbon source to synthesize lignin-based CQDs (L-CQDs) mainly involves two reactions: depolymerization of lignin macromolecules and repolymerization of small molecules. 14–17 In the hydrothermal reaction, the hydrogen ions dissociated from water first attack the ether bonds of lignin, 18 causing them to break and form a large number of lignin fragments. The hydrophobic aromatic structures and hydrophilic hydroxyl groups in the lignin fragments can condense to form primary clusters.…”

“…Finally, under high temperature and long reaction time conditions, these primary aromatic clusters undergo rapid π–π bond accumulation, a sp 2 hybridization increase, and aromatic polymerization to form L-CQDs. 17 Through the formation mechanism described above, it can be found that the depolymerization of lignin macromolecules is a necessary factor for the formation of L-CQDs, and the degree of depolymerization is mainly closely related to the molecular weight of lignin. For lignin, which is a macromolecular compound with the molecular weight spanning from several hundreds to several hundred thousands, the molecular weight of lignin has an extremely great influence on the properties of the subsequent reaction products.…”

Driving multicolor lignin-based carbon quantum dots into selective metal-ion recognition and photocatalytic antibiotic decomposition

“…Ultimately, the aromatic refusing of heterogeneous lignin oligomers occurred by means of the prompt π–π stacking and increased sp 2 hybridization. 23 The cleaved lignin ethers disassembled the methyl groups to generate aromatic molecules with phenolic hydroxyls. Subsequently, the lignin aliphatic alcohol structure can be attacked via hydroxide ions, thus removing hydrogen atoms to form carbonyl groups.…”