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 (K_a, 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.