Lignin-modified metal-organic framework as an effective adsorbent for the removal of methyl orange

Herein, lignin-modified metal-organic frameworks (NH₂-UIO@L) are prepared using a one-step synthesis as sorbents for the removal of organic dyes from water. The introduction of lignin improved the adsorption sites. NH₂-UIO@L₂ adsorption of MO conforms to Langmuir model, and the adsorption capacity of NH₂-UIO@L₂ on MO was 214.13 mg·L^-1 with an adsorption efficiency up to 99.28 %, which was significantly higher than values for other adsorbents. Due to hydrogen bonds, π-π interactions and electrostatic interactions, MO was effectively removed by NH₂-UIO@L₂ and its adsorption efficiency is maintained at 90.55 % after six cycles. The adsorption kinetics showed that the NH₂-UIO@L₂ adsorption of MO was chemical adsorption and controlled by intraparticle diffusion and external mass transfer. Further, the adsorption performance of NH₂-UIO@L₂ on MO and MB in mixed MO/MB solution was investigated. The adsorption capacity of NH₂-UIO@L₂ in mixed MO/MB solution was 207.04 mg·L^-1 for MO and 243.31 mg·L^-1 for MB; the adsorption of NH₂-UIO@L₂ on MO followed the Dubinin-Radushkevich and pseudo-second-order models, and the adsorption on MB followed the Temkin and pseudo-second-order models. Hydrogen bonds, π-π interactions, and pore filling are all implicated in the removal of MO and MB. In particular, the electrostatic attraction between MB and MO improves the adsorption efficiency of NH₂-UIO@L₂ on MB. NH₂-UIO@L₂ has good reusability, maintaining an adsorption efficiency of 97.66 % for MO and up to 99.15 % for MB after six cycles. Its simple preparation and superior adsorption suggest that NH₂-UIO@L₂ has considerable potential to remove organic dyes from wastewater.