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.制造业与商业农业的扩张，叠加快速全球化进程，导致淡水供应被包括持久性有机污染物在内的化学毒素广泛污染。有效缓解此类污染，对于保障人类健康、陆生与水生生物生存以及生态环境至关重要。当前，吸附法是最具经济可行性的水处理策略。金属有机框架（metal–organic frameworks, MOFs）凭借其结晶性与模块化特性，成为系统研究调控吸附过程的物理化学性质的理想平台材料。X射线衍射技术可实现毒素与MOFs相互作用的原子级精准表征，而液相吸附等温线则可便捷测定吸附容量与动力学参数；但在水相介质中测定毒素与MOFs相互作用的热力学特性，仍较为繁琐。在此研究中，我们将等温滴定微量热法（isothermal titration calorimetry, ITC）纳入表征MOFs吸附机制的技术工具箱。借助该方法，我们可直接量化某一化学过程的完整热力学特征（结合常数Ka、吉布斯自由能变ΔG、焓变ΔH与熵变项TΔS），为下一代吸附剂的理性设计提供关键支撑细节。我们通过探究锆基MOFs吸附有机磷农药的参数空间，验证了ITC技术的适用性。