Controlled SBU Approaches to Isoreticular Metal-Organic Framework Ruthenium-Analogues of HKUST-1

Scrutinizing ligand exchange reactions in the formation of the precious group metal-organic framework RuII,II-HKUST-1: the impact of diruthenium tetracarboxylate precursor and modulator choice

The precious group metal (PGM) analogues of the iconic metal-organic framework [Cu3(BTC)2] (HKUST-1; BTC = 1,3,5 benzenetricarboxylate) still represent a synthetic challenge, especially if targeting the univalent and ideally defect-free RuII,II variant. Herein we present a systematic study employing the controlled secondary building unit approach (CSA) by using a variety of diruthenium tetracarboxylate complexes [Ru2(RCO2)4] as precursors in the synthesis of univalent Ru-HKUST-1 samples. Carboxylate ligand exchange test reactions suggest the importance of a pKa match between precursor ligand and BTC linker. For example, l-mandelate substituted precursors resulted in the most "perfect" samples of the investigated series with a fourfold increase in crystalline domain sizes compared to the established acetate route (according to PXRD and HR-TEM), high compositional purity (FT-IR, Raman, TGA and elemental analysis) and feature a so far unprecedentedly high BET surface area of 1789 m2 g-1 with the expected pore size distribution and total pore volume all similar to the ideal HKUST-1 parent structure.

Conversion of bimetallic MOF to Ru-doped Cu electrocatalysts for efficient hydrogen evolution in alkaline media

The rational design and construction of inexpensive and highly active electrocatalysts for hydrogen evolution reaction (HER) is of great importance for water splitting. Herein, we develop a facile approach for preparation of porous carbon-confined Ru-doped Cu nanoparticles (denoted as Ru-Cu@C) by direct pyrolysis of the Ru-exchanged Cu-BTC metal-organic framework. When served as the electrocatalyst for HER, strikingly, the obtained Ru-Cu@C catalyst exhibits an ultralow overpotential (only 20 mV at 10 mA cm^-2) with a small Tafel slope of 37 mV dec^-1 in alkaline electrolyte. The excellent performance is comparable or even superior to that of commercial Pt/C catalyst. Density functional theory (DFT) calculations confirm that introducing Ru atoms into Cu nanocrystals can significantly alter the desorption of H₂ to achieve a close-to-zero hydrogen adsorption energy and thereby boost the HER process. This strategy gives a fresh impetus to explore low-cost and high-performance catalysts for HER in alkaline media.

Enhanced stability and activity of Cu–BTC by trace Ru3+ substitution in water photolysis for hydrogen evolution

Constructing stable, efficient and cost-effective cocatalysts is of great significance for photocatalytic H2 evolution in a dye-sensitization system.

Thermal Defect Engineering of Precious Group Metal-Organic Frameworks: A Case Study on Ru/Rh-HKUST-1 Analogues

A methodology is introduced for controlled postsynthetic thermal defect engineering (TDE) of precious group metal-organic frameworks (PGM-MOFs). The case study is based on the Ru/Rh analogues of the archetypical structure [Cu₃(BTC)₂] (HKUST-1; BTC = 1,3,5-benzenetricarboxylate). Quantitative monitoring of the TDE process and extensive characterization of the samples employing a complementary set of analytical and spectroscopic techniques reveal that the compositionally very complex TDE-MOF materials result from the elimination and/or fragmentation of ancillary ligands and/or linkers. TDE involves the preferential secession of acetate ligands, intrinsically introduced via coordination modulation during synthesis, and the gradual decarboxylation of ligator sites of the framework linker BTC. Both processes lead to modified Ru/Rh paddlewheel nodes. These nodes exhibit a lowered average oxidation state and more accessible open metal centers, as deduced from surface-ligand IR spectroscopy using CO as a probe and supported by density functional theory (DFT)-based computations. The monometallic and the mixed-metal PGM-MOFs systematically differ in their TDE properties and, in particular in the hydride generation ability (HGA). This latter property is an important indicator for the catalytic activity of PGM-MOFs, as demonstrated by the ethylene dimerization reaction to 1-butene.

Thermal defect engineering of precious group metal–organic frameworks: impact on the catalytic cyclopropanation reaction

This work highlights the catalytic cyclopropanation and its characteristics as a novel analytical tool to investigate complex MOF structures.

Elucidating the Structure of the Metal-Organic Framework Ru-HKUST-1

Ru-HKUST-1 (Ru 3 ( btc ) 2 X 1.5 ; btc 3 - = 1 , 3 , 5 -benzenetricarboxylate ; X - = chloride , acetate , trimesate , hydroxide ) has received considerable attention as a result of its structure type, tunability, and the redox-active nature of its constituent metal paddlewheel building units. As compared to some of the other members of the HKUST-1 family, its surface area is typically reported as ~25% lower than expected. In contrast to this, a related ruthenium-based porous coordination cage, Ru 24 ( t Bu-bdc ) 24 Cl 12 , displays the expected surface area when compared to Cr 2 + and Mo 2 + analogs. Here, we examine the factors that result in this decreased surface area for the MOF. We show that with appropriate solvent exchange and activation conditions, Ru-HKUST-1 can display a B.E.T. surface areas as high as 1439 m2/g. We utilize a combination of spectroscopic and diffraction techniques to accurately determine the structure of the MOF, which is most accurately described here as Ru 3 ( btc ) 2 ( OAc ) 1.07 Cl 0.43 , as prepared under our conditions. Further, by simply treating the sample as air-sensitive upon isolation, adsorption selectivities toward unsaturated molecu les greatly improve.

Mixed precious-group metal–organic frameworks: a case study of the HKUST-1 analogue [RuxRh3−x(BTC)2]

Mixed precious-group metal–organic frameworks [Ru_xRh_3−x(BTC)₂] of the HKUST-1-type were synthesized and characterized (PXRD, BET, IR, Raman, XPS, TGA, SS-UV/VIS, EA, and HR-TEM).

Synthesis of heterometallic metal–organic frameworks and their performance as electrocatalyst for CO2 reduction

The solventless synthesis of heterometallic metal–organic frameworks and their proficient behavior as electrocatalysts in the CO₂ reduction to alcohols is presented.

Using Predefined M3(μ3-O) Clusters as Building Blocks for an Isostructural Series of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have attracted much attention in the past decade owing to their unprecedented internal surface areas, tunable topologies, designable surfaces, and various potential applications. One bottleneck in the field regarding MOF synthesis is controlling the metal-containing secondary building unit (SBU) incorporated into the structure. In this work we report the synthesis and characterization of five trimeric [M₃(μ₃-O)(CH₃CO₂)₆]^x clusters (where M = Fe³⁺, Cr³⁺, Fe³⁺/Cr³⁺, Fe³⁺/Co²⁺, or Fe³⁺/Ni²⁺ and x = +1 or 0). The monocarboxylate capping ligand, acetate in this case, readily undergoes exchange with several difunctional counterparts, including 1,4-benzenedicarboxylic acid (H₂-BDC) and biphenyl-4,4'-dicarboxylic acid (H₂-BPDC), for the formation of an isostructural series of MOFs, several of which are newly reported (for M = Fe³⁺/Cr³⁺, Fe³⁺/Co²⁺, and Fe³⁺/Ni²⁺) and show excellent CO₂ adsorption properties. In this report, a host of techniques including NMR, ICP, and ESI-MS are used to probe the ligand exchange process and composition of the SBUs, and XAS is used to monitor the Fe³⁺ and Cr³⁺ environment throughout the reactions, giving strong evidence that the clusters stay intact throughout the MOF synthesis. This work reveals that predefined SBUs is an effective means to create metal-substituted analogues of known frameworks. Further, CO adsorption and in situ IR are used to probe accessibility of the metals after solvent removal. We show for the first time that the incorporation of the neutral clusters, containing weaker Lewis acids like Ni²⁺ and Co²⁺, can promote the formation of open metal sites in the MOF frameworks, structural features known to enhance the binding energy of small guest molecules like CO₂.

Ultrasonically assisted hydrothermal synthesis of activated carbon-HKUST-1-MOF hybrid for efficient simultaneous ultrasound-assisted removal of ternary organic dyes and antibacterial investigation: Taguchi optimization

Activated carbon (AC) composite with HKUST-1 metal organic framework (AC-HKUST-1 MOF) was prepared by ultrasonically assisted hydrothermal method and characterized by FTIR, SEM and XRD analysis and laterally was applied for the simultaneous ultrasound-assisted removal of crystal violet (CV), disulfine blue (DSB) and quinoline yellow (QY) dyes in their ternary solution. In addition, this material, was screened in vitro for their antibacterial actively against Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO1) bacteria. In dyes removal process, the effects of important variables such as initial concentration of dyes, adsorbent mass, pH and sonication time on adsorption process optimized by Taguchi approach. Optimum values of 4, 0.02 g, 4 min, 10 mg L(-1) were obtained for pH, AC-HKUST-1 MOF mass, sonication time and the concentration of each dye, respectively. At the optimized condition, the removal percentages of CV, DSB and QY were found to be 99.76%, 91.10%, and 90.75%, respectively, with desirability of 0.989. Kinetics of adsorption processes follow pseudo-second-order model. The Langmuir model as best method with high applicability for representation of experimental data, while maximum mono layer adsorption capacity for CV, DSB and QY on AC-HKUST-1 estimated to be 133.33, 129.87 and 65.37 mg g(-1) which significantly were higher than HKUST-1 as sole material with Qm to equate 59.45, 57.14 and 38.80 mg g(-1), respectively.

Zirconium Phosphate Supported MOF Nanoplatelets

We report a rare example of the preparation of HKUST-1 metal-organic framework nanoplatelets through a step-by-step seeding procedure. Sodium ion exchanged zirconium phosphate, NaZrP, nanoplatelets were judiciously selected as support for layer-by-layer (LBL) assembly of Cu(II) and benzene-1,3,5-tricarboxylic acid (H3BTC) linkers. The first layer of Cu(II) is attached to the surface of zirconium phosphate through covalent interaction. The successive LBL growth of HKUST-1 film is then realized by soaking the NaZrP nanoplatelets in ethanolic solutions of cupric acetate and H3BTC, respectively. The amount of assembled HKUST-1 can be readily controlled by varying the number of growth cycles, which was characterized by powder X-ray diffraction and gas adsorption analyses. The successful construction of HKUST-1 on NaZrP was also supported by its catalytic performance for the oxidation of cyclohexene.