Cluster-Engineered Titanium Metal-Organic Aerogels as Tunable Platforms for Post-synthetic Doping and Enhanced Photocatalytic Hydrogen Production.

Metal-organic gels (MOGs) and their derived aerogels (MOAs) offer an alternative to crystalline MOFs, combining the coordination-driven tunability with the flexibility, hierarchical porosity, and easy processability of sol-gel polymers. Their noncrystalline nature enables the integration of functional units without crystallization constraints, facilitating diverse uses, and drawing recent attention for photocatalytic applications. Herein we report the design of a new approach to prepare a titanium-based MOA synthesized via a two-step strategy involving a preformed titanium oxo-cluster ([Ti8O8(benzoato)16]), and a subsequent ligand exchange with benzene-1,3,5-tricarboxylato ligands. A combined chemical, microstructural, and NEXAFS analysis confirms the retention of Ti8 cluster and the presence of uncoordinated -COOH groups after meso-macroporous gel formation. Those enabled a subsequent homogeneous incorporation of single-atom site co-catalysts via coordination with Ru, Co, Ni, and Cu complexes bearing terpyridine, bipyridine, and phenanthroline N-ligands. Photocatalytic hydrogen evolution under 365 nm LED irradiation exhibited significant activity (110 μmol·g-1·h-1), which further increased upon functionalization. The MOAs functionalized with Ru- and Cu-terpyridine complexes showed the highest performance (167 and 164 μmol·g-1·h-1, respectively), surpassing even Pt-loaded analogues and highlighting the role of terpyridine in facilitating multielectron storage. The system also showed stable long-term performance up to 24 h.