hydrogen evolution

water splitting

photocatalytic reduction

uv vis

titanium dioxide

methylene blue

Applied catalysis. B, Environmental

• We unravelled the impact of ligand composition on photocatalytic hydrogen evolution over Ti-based MOFs. • MIL-125-Ti outperforms NH2-containing counterparts by up to 38 times in methanol • Photoluminescence spectroscopy shows effective hole scavenging by methanol in MIL-125-Ti. • Triethanolamine leads to corrosion of the MOFs within the first few hours through partial ligand exchange. • We propose three mechanisms for photocatalytic hydrogen evolution for both single-ligand and mixed-ligand MOFs. We synthesized a series of isostructural MIL-125-Ti with various terephthalic: amino-terephthalic acid ratios and evaluated their photostability and performance for photocatalytic hydrogen evolution in aqueous solutions with different hole scavengers. We demonstrate that the commonly used triethanolamine corroded the MOFs under photocatalytic conditions, in contrast to methanol. The combination of MIL-125-Ti and methanol outperformed the photocatalytic activity of NH 2 -MIL-125-Ti by 45 times under broad UV irradiation. Photoluminescence spectroscopy under simulated photocatalytic conditions and in solid-state as well as time-resolved emission studies reveal that the holes residing in the metal-oxo cluster can be effectively scavenged by methanol, leading to high HER activity, while the holes residing in the NH 2 -groups in the ligand favour charge recombination and are thus detrimental to the photocatalytic performance. The mixed-ligand MOFs follow a dual-excitation pathway, introducing new states and transitions. These results are expected to advance our understanding of MOF-based photocatalysis.

Ti-based MOFs: New insights on the impact of ligand composition and hole scavengers on stability, charge separation and photocatalytic hydrogen evolution