Comparisons of glyphosate adsorption properties of different functional Cr-based metal-organic frameworks

A Cr-based metal-organic framework, namely, MIL-101(Cr), was modified with amino (NH₂ -) and urea (UR₂ -) groups, and the materials were evaluated as adsorbents for glyphosate, and a comparison with commercial activated carbon was also discussed. The effects of the adsorption factors, such as adsorbent concentration, adsorption time, pH and ionic strength were mainly investigated. The results showed that a pseudo-second-order rate equation described the adsorption kinetics mechanisms well, while the Langmuir model and the Freundlich model fitted different adsorption isotherms, respectively. Among the adsorbents we studied, NH₂ -MIL-101(Cr) showed the maximum adsorbing capacity, which is 64.25 mg/g when pH = 3.0, while UR₂ -MIL-101(Cr) did not reach the best adsorption performance due to the steric hindrance. The work opens up a new way for the modification of metal-organic frameworks for adsorption process.