Metal-Organic Frameworks for Phthalate Capture

Indoor air contamination by phthalate ester (PAE) derivatives has become a significant concern since traces of PAEs can cause endocrine disruption, among other health issues. PAE abatement from the environment is thus mandatory to further ensure a good quality of indoor air. Herein, we explored the physisorption-based capture of volatile PAEs by metal-organic frameworks (MOFs). A high-throughput computational screening approach was first applied on databases compiling more than 20,000 MOF structures in order to identify the best MOFs for adsorbing traces of dimethyl phthalate (DMP), considered as a representative molecule of the family of PAE contaminants. Among the 20 top candidates, MOF-74(Ni), which combines substantial DMP uptake at the 10 ppm concentration level (∼0.20 g g-1) with high adsorption enthalpy at infinite dilution (-ΔHads(DMP),0 = 109.9 kJ mol-1), was revealed as an excellent porous material to capture airborne DMP. This prediction was validated by further experiments: gravimetric sorption isotherms were carried out on MOF-74(Ni), replacing DMP by dimethyl maleate (DMM), a molecule with a higher vapor pressure and indeed easier to manipulate compared to DMP while mimicking the adsorption behavior of DMP by MOFs, as evidenced by Monte Carlo calculations. Notably, saturation of DMM by MOF-74(Ni) (∼0.35 g g-1 at 343 K) occurs at very low equivalent concentration of the sorbate, i.e., 15 ppm, while half of the DMM molecules remain trapped in the MOF pores, even by heating the system up to 473 K under vacuum. This computational-experimental study reveals for the first time the potential of MOFs for the capture of phthalate ester contaminants as vapors of key importance to address indoor air quality issues.

Facile One-Step Metal-Organic Framework Surface Polymerization Method

A simple one-step approach that only uses commercially available small-molecule reagents was developed for the construction of metal-organic framework (MOF)@polymer core-shell composite particles. Here, the MOF particles were incorporated into a typical reversible addition-fragmentation chain-transfer (RAFT) polymerization solution containing a solvent, a chain-transfer agent, an initiator, and a monomer mixture with at least one hydrogen-bond-donating monomer such as 2-hydroxyethyl methacrylate or acrylic acid. The elongation of polymer chains during polymerization gradually increases MOF/polymer interfacial interaction and eventually results in the adsorption of a random copolymer onto the MOF surface through hydrogen-bond cross-linking and MOF/polymer interfacial interaction. The continuous growth of the polymer leads to a uniform polymer coating on the MOF. Benefiting from the tacky polymer surface, these well-defined MOF@polymer composite particles can be further assembled into highly ordered monolayer composite thin films either alone or with an additional polymer matrix through the Langmuir-Blodgett technique.