Photoreactive Carbon Dioxide Capture by a Zirconium-Nanographene Metal-Organic Framework

The mechanism of photochemical CO₂ reduction to formate by PCN-136, a Zr-based metal-organic framework (MOF) that incorporates light-harvesting nanographene ligands, has been investigated using steady-state and time-resolved spectroscopy and density functional theory (DFT) calculations. The catalysis was found to proceed via a "photoreactive capture" mechanism, where Zr-based nodes serve to capture CO₂ in the form of Zr-bicarbonates, while the nanographene ligands have a dual role of absorbing light and storing one-electron equivalents for catalysis. We also find that the process occurs via a "two-for-one" route, where a single photon initiates a cascade of electron/hydrogen atom transfers from the sacrificial donor to the CO₂-bound MOF. The mechanistic findings obtained here illustrate several advantages of MOF-based architectures in molecular photocatalyst engineering and provide insights on ways to achieve high formate selectivity.

Facile and reversible digestion and regeneration of zirconium-based metal-organic frameworks

The digestion/regeneration of metal-organic frameworks (MOFs) has important applications for catalysis, drug delivery, environmental decontamination, and energy storage, among other applications. However, research in this direction is limited and very challenging. Here, we develop a facile method to digest and regenerate a series of zirconium-based metal-organic frameworks (Zr-MOFs) by bicarbonate or carbonate salts. As an example, UiO-66 demonstrates well the mechanism of reversible digestion/regeneration processes. By analyzing the digested zirconium species via X-ray diffraction, Fourier transform infrared spectroscopy and Raman scattering spectroscopy, a digestion mechanism based on the formation of dissoluble complexes [Zr₂(OH)₂(CO₃)₄]^2- is proposed. Impressively, ultrafine Pd nanoparticles can be extracted from Pd@PCN-224 via this strategy. This work, thus, may provide new insight for the development of renewable MOFs and their practical applications.

Isolated zirconium centres captured from aqueous solution: the structure of zirconium mandelate revealed from NMR crystallography

Zirconium tetramandelate forms from aqueous solution and unusually contains isolated cations; its structure is determined ab initio from a polycrystalline sample using a combined synchrotron X-ray powder diffraction and solid-state NMR approach.

Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ZrO2

Choosing the correct alkali metal as a promoter not only reduces coke formation in dry reforming of methane but also removes coke via gasification.

Trapping It Softly: Ultrasoft Zirconium Metallogels for Macromolecule Entrapment and Reconfiguration

Trapping nanosized drugs in ultrasoft, shear-thinning hydrogels with large pores is of particular interest, yet a persistent challenge in nanomedicine due to the lack of hydrodynamic confinement. Engineering molecular interactions between a macromolecule and a supramolecular gel may address this shortcoming, providing a key route to develop advanced drug carriers without compromising matrix elasticity. Here, we show that ultrasoft zirconium-based metallogels are able to trap and reconfigure model nanodrugs (e.g., dextran) through complexation and hydrogen bonding. The diffusion coefficients of dextran molecules (M_w ∼ 10-2000 kDa, a ∼ 2-20 nm) in zirconium carbonate (ZC) metallogels (G' < 30 Pa) were measured by pulsed field gradient nuclear magnetic resonance (PFGNMR), which revealed the coexistence of hindered and enhanced collective diffusion regimes for the first time. This work may pave the way toward designing next generation ultrasoft drug carriers and functional templates to control biomacromolecular processes, such as protein folding.

Hydrothermal Synthesis of Yttria-Stabilized Zirconia Nanocrystals with Controlled Yttria Content

In this study, we demonstrate for the first time the hydrothermal synthesis of yttria-stabilized zirconia (YSZ) nanocrystals with controlled yttria content (x = 3-12 mol %; xYSZ) with negligible aggregation from aqueous solution. The nanocrystals were grown via the hydrothermal treatment of basic Zr(IV) and Y(III) carbonate complex aqueous solutions in the presence of a cationic ligand, N(CH3)4(+). The nanocrystals were characterized in detail by dynamic light scattering, ζ-potential measurement, X-ray diffraction, specific surface area measurement based on the Brunauer-Emmett-Teller theory, transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. Shorter reaction times and higher Y2O3 content produce aqueous solutions with higher transparencies containing nanocrystals with sizes of 10 nm or less. Nanocrystals with the target composition were obtained by hydrothermal reaction for longer than 3 h, regardless of the Y2O3 content. The main phase is tetragonal for (3-6)YSZ and cubic with disordered oxygen vacancies for (8-12)YSZ. The characteristics of the nanocrystalline material synthesized are consistent with those of bulk YSZ crystals, indicating the growth of high-quality nanocrystals.