Post-Synthetic Modifications of Ti(IV)-Based Metal-Organic Frameworks for Enhanced Photocatalysis and Conductivity

Abstract

Metal-Organic Frameworks (MOFs) are coordination networks with organic ligands containing potential voids, ideal for guest-host interactions. These unique characteristics make them interesting materials for several different applications, including catalysis. Unfortunately, most MOFs feature metal oxide nodes that are insulting by nature, which limits their potential in electro- and photochemical catalysts. To combat these issues, post-synthetic modifications (PSM) can be used to tune MOF properties. This research reports on different PSMs incorporated into the Ti(IV)-based MOFs MIL-125(Ti) and MIL-125(Ti)-NH2. PSMs that introduce intentional defect states and dopant metal ions, such as Ce(IV), were explored to determine their influence on the photo-degradation of Rhodamine B in aqueous solution. Post-Synthetic Metal Exchange (PSME) was used to incorporate Ce(IV) at the Ti(IV) sites in MIL-125(Ti) and MIL-125(Ti)-NH2, and intentional defect states were introduced using formic acid during MOF synthesis. In addition, conductive organic polymers were utilized to make novel polymer-MOF hybrid composites that showed enhanced charge transport properties compared to pristine MOF. Ultimately, these results show how PSMs can be used to impart conductivity and enhance photocatalysis in the MOFs MIL-125(Ti) and MIL-125(Ti)-NH2.