Exploiting π–π Interactions to Design an Efficient Sorbent for Atrazine Removal from Water

Abstract

The United States Environmental Protection Agency (EPA) recognizes atrazine, a commonly used herbicide, as an endocrine disrupting compound. Excessive use of this agrochemical results in contamination of surface and ground water supplies via agricultural runoff. Efficient removal of atrazine from contaminated water supplies is paramount. Here, the mechanism governing atrazine adsorption in Zr6-based metal–organic frameworks (MOFs) has been thoroughly investigated by studying the effects of MOF linkers and topology on atrazine uptake capacity and uptake kinetics. We found that the mesopores of NU-1000 facilitated rapid atrazine uptake saturating in <5 min and that the pyrene-based linkers offered sufficient sites for π–π interactions with atrazine as demonstrated by the near 100% uptake. Without the presence of a pyrene-based linker, NU-1008, a MOF similar to NU-1000 with respect to surface area and pore size, removed <20% of the exposed atrazine. These results suggest that the atrazine uptake capacity demonstrated by NU-1000 stems from the presence of a pyrene core in the MOF linker, affirming that π–π stacking is responsible for driving atrazine adsorption. Furthermore, NU-1000 displays an exceptional atrazine removal capacity through three cycles of adsorption–desorption. Powder X-ray diffraction and Brunauer–Emmett–Teller surface area analysis confirmed the retention of MOF crystallinity and porosity throughout the adsorption–desorption cycles.

The Effects of Functional Groups and Missing Linkers on the Adsorption Capacity of Aromatic Hydrocarbons in UiO-66 Thin Films

“…The calculations revealed that the dispersion energy at the UiO-66 pore center was similar for the NH 2 and NO 2 functional groups. In our study, it is most likely that pi-pi interactions between the aromatic molecules and organic linkers dominate the strength of adsorption, as seen in a recent study by Akpinar et al [46]. Overall, we conclude that the missing linkers play a more important role in our films than the nature of the functional group.…”

Pyrene-based metal organic frameworks: from synthesis to applications

“…Atrazine is a widely used herbicide in the agricultural industry, which contaminates the surface and groundwater supplies. Akpinar et al 207 studied the effect of the linkers in Zr-MOFs on atrazine uptake capacity and uptake kinetics. Results showed that although UiO-67, DUT-52, and NU-1000 have similar pore sizes and surface areas, NU-1000 showed an exceptional atrazine uptake because of p-p interactions between the pyrene and the atrazine.…”

Pore Chemistry of Metal–Organic Frameworks

“…Intermolecular interactions include π–π stacking between organic linkers and guest molecules. [ 28 ] Coulombic interactions can be established between charged framework backbone and counterions residing in the pore. [ 29 ] The presence of hydrogen bond donors or acceptors in MOF backbone can recognize the matching partners with relatively high affinity.…”