Structure engineering of covalent organic frameworks as metal-free sorbents for urea recovery

Abstract

The ubiquitous presence of urea, a nitrogenous compound with diverse biological and industrial applications, poses significant environmental challenges alongside its utility. Efforts to mitigate urea's impact on ecosystems while harnessing its usefulness have motivated research into developing efficient sorbents for urea recovery from wastewater. In this study, we explore the potential of covalent organic frameworks (COFs) as promising urea adsorbents. Molecular dynamics (MD) simulations revealed strong multidentate binding between the COF and urea through hydrogen bonding, with a binding energy of −89.90 kJ mol⁻¹. Moreover, through experimental investigation, we systematically examine the influence of COF surface area, functional groups, and pore size on urea adsorption efficiency. Leveraging the robust stability of the β-ketoenamine linkage, we demonstrate the recycling capability of COFs over four cycles without any loss in performance. Moreover, multivariate COFs exhibited an enhanced urea adsorption capacity of 16.58 mg g⁻¹. These findings not only advance urea-containing wastewater treatment but also hold promise for applications in diverse fields requiring urea removal.