Lignin-Modified Metal-Organic Frameworks for Fluorescence Detection of Cr6+ and Adsorption of Congo Red

Herein, a lignin-modified metal-organic framework (MIL-NL) was successfully assembled by grafting aminated lignin onto MIL-101-Fe-NH2. With the introduction of aminated lignin via the Schiff base reaction, MIL-NL possesses not only the crystal structure of MIL-101-Fe-NH2 but also that of Fe2O3. The benefits of the amine and hydroxyl groups of the aminated lignin on MIL-NL allow it to interact with different objects through hydrogen bonding. MIL-NL emits blue fluorescence at 435 nm under an excitation light of 380 nm. The MIL-NL was built to detect Cr6+ by fluorescence "off" and ascorbic acid (AA) by fluorescence "on". The detection limits of MIL-NL for Cr6+ were 0.14 (1.5-20 mu M) and 0.18 mu M (40-200 mu M), respectively, and AA in the range of 5-60 nM and 0.5-1.8 mu M with LOD values of 0.425 and 15.90 nM, respectively. MIL-NL can detect Cr6+ quickly and sensitively (<1 min). Furthermore, MIL-NL showed a strong adsorption capacity of up to 1495.23 mg/g for Congo red. Multifunctional lignin-modified MOFs offer great potential in the field of environmental detection.