Bifunctional porous polyethyleneimine-grafted lignin microspheres for efficient adsorption of 2,4-dichlorophenoxyacetic acid over a wide pH range and controlled release

Herbicides pollution is currently a big threat to the environment due to their widespread use in the agricultural field. Herein, we proposed the creation of bifunctional porous polyethyleneimine-grafted lignin microspheres (PLMs) by grafting polyethyleneimine onto lignin via an inverse suspension polymerization method by using polyethylene glycol as a porogen. The porous structure and abundant functional groups of PLMs allowed it to efficiently capture the representative herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), steadily over a wide pH range of 4-10. The maximum adsorption capacity was 909.09 mg/g at 45 C that was much higher than the reported activated carbon (515.46 mg/g) and metal-organic framework (MIL-53, 556 mg/g). The adsorption process followed the Langmuir isotherm model and pseudo-second-order kinetic model, respectively. More importantly, the 2,4-D-loaded PLMs showed a distinct sustained release behavior as the environmental pH values varied. Under acidic (pH = 2) or alkaline (pH = 11) conditions, 57% or 88% of 2,4-D was released after 72 h, respectively, while only 10% of 2,4-D was released even after 96 h under pH = 7. FTIR and XPS analysis indicated that the adsorption mechanism was mainly involved with the electrostatic attraction, hydrogen bonding, 7C-7C stacking and van del Waals forces between the PLMs and 2,4-D molecules. This work proposed an environmentally-friendly biomass-based bifunctional microspheres that could be potentially applied in the management of herbicide pollution through adsorption and controlled release formulations.

Automated summary

This study proposed the creation of bifunctional porous polyethyleneimine-grafted lignin microspheres for efficient capture and controlled release of herbicides, providing a new approach for the management of herbicide pollution.