Abstract
Interactions between metal nanoparticles (NPs) and metal–organic frameworks (MOFs) in their composite forms have proven to exhibit beneficial properties, such as enhanced catalytic performance through synergistic effects. Herein, we show that Lewis basic sites can be created within an anionic defective MOF by engineering the electronic state of the pendant carboxylate groups situated at the defect sites. This is achieved from the concerted interactions between the pendant carboxylate groups, embedded Pd NPs and charge-balancing cations (Mn+ = Ce3+, Co2+, Ni2+, Cu2+, Mg2+, Li+, Na+ or K+). This work is the first example of generating a new collective property, i.e. Lewis basicity, in metal-carboxylate MOFs. Importantly, the choice of Mn+, used during cation exchange, acts as a convenient parameter to tune the Lewis basicity of the MOF-based nanocomposites. It also provides a facile way to incorporate active metal sites and basic sites within carboxylate-based MOFs to engineer multifunctional nanocatalysts.
Highlights
Interactions between metal nanoparticles (NPs) and metal–organic frameworks (MOFs) in their composite forms have proven to exhibit beneficial properties, such as enhanced catalytic performance through synergistic effects
The creation of basicity is attributed to the localised charge imbalance on the pendant carboxylate groups, which is resulted from the concerted interaction between pendant carboxylate groups, Pd NPs and Mn+
Transmission electron microscopic (TEM) image clearly shows that Pd NPs in Pd/HKUST-1-R are evenly distributed on the host support and they have a uniform size distribution of 4.0 nm (Fig. 2a, b)
Summary
Interactions between metal nanoparticles (NPs) and metal–organic frameworks (MOFs) in their composite forms have proven to exhibit beneficial properties, such as enhanced catalytic performance through synergistic effects. We show that Lewis basic sites can be created within an anionic defective MOF by engineering the electronic state of the pendant carboxylate groups situated at the defect sites This is achieved from the concerted interactions between the pendant carboxylate groups, embedded Pd NPs and charge-balancing cations (Mn+ = Ce3+, Co2+, Ni2+, Cu2+, Mg2+, Li+, Na+ or K+). We present a unique approach to immobilise Pd NPs and, more importantly, to generate tunable basic sites within an anionic defective MOF, establishing a new synthetic route to design multifunctional MOF-based nanocomposites. The creation of basicity is attributed to the localised charge imbalance on the pendant carboxylate groups, which is resulted from the concerted interaction between pendant carboxylate groups, Pd NPs and Mn+ This is the first example of activating pendant carboxylate groups in MOFs to form Lewis basic sites. As a proof of concept, in this work we use multistep catalytic reactions to showcase the tunable multifunctionality of Pd/M-HKUST-1-R
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