Noble Metals Can Have Different Effects on Photocatalysis Over Metal–Organic Frameworks (MOFs): A Case Study on M/NH2‐MIL‐125(Ti) (M=Pt and Au)

Abstract

M‐doped NH 2‐MIL‐125(Ti) (M=Pt and Au) were prepared by using the wetness impregnation method followed by a treatment with H 2 flow. The resultant samples were characterized by powder X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), X‐ray absorption fine structure (XAFS) analyses, N 2‐sorption BET surface area, and UV/Vis diffuse reflectance spectroscopy (DRS). The photocatalytic reaction carried out in saturated CO 2 with triethanolamine (TEOA) as sacrificial agent under visible‐light irradiations showed that the noble metal‐doping on NH 2‐MIL‐125(Ti) promoted the photocatalytic hydrogen evolution. Unlike that over pure NH 2‐MIL‐125(Ti), in which only formate was produced, both hydrogen and formate were formed over Pt‐ and Au‐loaded NH 2‐MIL‐125(Ti). However, Pt and Au have different effects on the photocatalytic performance for formate production. Compared with pure NH 2‐MIL‐125(Ti), Pt/NH 2‐MIL‐125(Ti) showed an enhanced activity for photocatalytic formate formation, whereas Au has a negative effect on this reaction. To elucidate the origin of the different photocatalytic performance, electron spin resonance (ESR) analyses and density functional theory (DFT) calculations were carried out over M/NH 2‐MIL‐125(Ti).The photocatalytic mechanisms over M/NH 2‐MIL‐125(Ti) (M=Pt and Au) were proposed. For the first time, the hydrogen spillover from the noble metal Pt to the framework of NH 2‐MIL‐125(Ti) and its promoting effect on the photocatalytic CO 2 reduction is revealed. The elucidation of the mechanism on the photocatalysis over M/NH 2‐MIL‐125(Ti) can provide some guidance in the development of new photocatalysts based on MOF materials. This study also demonstrates the potential of using noble metal‐doped MOFs in photocatalytic reactions involving hydrogen as a reactant, like hydrogenation reactions.