Isothermal Titration Calorimetry to Explore the Parameter Space of Organophosphorus Agrochemical Adsorption in MOFs

The expansion of manufacturing and
commercial agriculture alongside
rapid globalization have resulted in the widespread contamination
of freshwater supplies with chemical toxins including persistent organic
pollutants. Effective mitigation of such pollution is paramount to
the safeguarding of human health, animal and aquatic life, and the
environment. Currently, adsorption is the most economically viable
water purification strategy. Owing to their crystallinity and modular
nature, metal–organic frameworks (MOFs) are an excellent platform
material for systematically investigating the physical and chemical
properties which govern adsorption processes. X-ray diffraction techniques
provide atomically precise descriptions of toxin-MOF interactions,
while liquid-phase adsorption isotherms readily allow for the determination
of uptake capacity and kinetics; however, determination of the thermodynamics
of toxin-MOF interactions in aqueous media remains tedious. Herein,
we add isothermal titration calorimetry (ITC) to our arsenal of techniques
for characterizing adsorption mechanisms in MOFs. With this method,
we are able to directly quantify the full thermodynamic profile of
a chemical process (Ka, ΔG, ΔH, TΔS), providing critical details
to support the rational design of next-generation sorbents. We demonstrate
the suitability of ITC through our exploration of the parameter space
of organophosphorus agrochemical adsorption in zirconium-based MOFs.