Simultaneous shaping and confinement of metal-organic polyhedra in alginate-SiO2 spheres

Engineering sodium alginate-SiO2 composite beads for efficient removal of methylene blue from water

The lack of sufficient active binding sites in commonly reported sodium alginate (SA)-based porous beads hampers their performances in adsorption of water contaminants. To address this problem, porous SA-SiO₂ beads functionalized with poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) are reported in this work. Due to the porous properties and the existence of abundant sulfonate groups, the obtained composite material SA-SiO₂-PAMPS shows excellent adsorption capacity toward cationic dye methylene blue (MB). The adsorption kinetic and adsorption isotherm studies reveal that the adsorption process fits closely to pseudo-second-order kinetic model and Langmuir isotherm model, respectively, suggesting the existence of chemical adsorption and monolayer adsorption behavior. The maximum adsorption capacity obtained from Langmuir model is found to be 427.36, 495.05, and 564.97 mg/g under 25, 35, and 45 °C, respectively. The calculated thermodynamic parameters indicate that MB adsorption on SA-SiO₂-PAMPS is spontaneous and endothermic.

A [(M2)6L8] metal-organic polyhedron with high CO2 uptake and efficient chemical conversion of CO2 under ambient conditions

A new metal-organic polyhedron with a high surface area of 407 m² g^-1, possessing high CO₂ uptake, is reported, which is synthesized using 4-connected Cu₂(CO₂)₄ paddle-wheel moieties and 3-connected semi-rigid tripodal carboxylates. This material possesses a high density of Cu(II) Lewis acidic sites and demonstrates excellent performance as a heterogeneous catalyst for the chemical fixation of CO₂ into cyclic carbonates under ambient conditions.

Rhodium-Based Metal-Organic Polyhedra Assemblies for Selective CO2 Photoreduction

Heterogenization of molecular catalysts via their immobilization within extended structures often results in a lowering of their catalytic properties due to a change in their coordination sphere. Metal-organic polyhedra (MOP) are an emerging class of well-defined hybrid compounds with a high number of accessible metal sites organized around an inner cavity, making them appealing candidates for catalytic applications. Here, we demonstrate a design strategy that enhances the catalytic properties of dirhodium paddlewheels heterogenized within MOP (Rh-MOP) and their three-dimensional assembled supramolecular structures, which proved to be very efficient catalysts for the selective photochemical reduction of carbon dioxide to formic acid. Surprisingly, the catalytic activity per Rh atom is higher in the supramolecular structures than in its molecular sub-unit Rh-MOP or in the Rh-metal-organic framework (Rh-MOF) and yields turnover frequencies of up to 60 h^-1 and production rates of approx. 76 mmole formic acid per gram of the catalyst per hour, unprecedented in heterogeneous photocatalysis. The enhanced catalytic activity is investigated by X-ray photoelectron spectroscopy and electrochemical characterization, showing that self-assembly into supramolecular polymers increases the electron density on the active site, making the overall reaction thermodynamically more favorable. The catalyst can be recycled without loss of activity and with no change of its molecular structure as shown by pair distribution function analysis. These results demonstrate the high potential of MOP as catalysts for the photoreduction of CO₂ and open a new perspective for the electronic design of discrete molecular architectures with accessible metal sites for the production of solar fuels.

Heterogeneous postassembly modification of zirconium metal-organic cages in supramolecular frameworks

We report a heterogeneous postassembly modification (PAM) to synthesize a zirconium metal-organic cage decorated with acrylate functional groups, ZrT-1-AA, which cannot be synthesized by direct coordination-driven self-assembly owing to the reactivity and instability of the ligand. The PAM process is carried out in a single-crystal-to-single-crystal transformation under mild reaction conditions with high efficiency, which is confirmed by ESI-TOF-MS and 1H NMR. In addition, ZrT-1-AA is crosslinked into shaped materials to demonstrate its potential applications. The proposed PAM strategy sheds light on the development of Zr-MOCs decorated with reactive functional groups, whose introduction is challenging or impossible via direct self-assembly.