Rana R. Haikal

Marjoram essential oil was successfully loaded onto Zn-ascorbate MOF. The antioxidant activity of the composite originated from the l -ascorbic acid ligand, while the antibacterial activity bacteria demonstrated the synergistic activity of Zn ²⁺ ions and encapsulated oil.

With the fast-growing global water crisis, the development of novel technologies for water remediation and reuse is crucial. Industrial wastewater especially contains various toxic pollutants that pose an additional threat to the environment; thus, efficient removal of such contaminants can ensure safe reprocessing of industrial wastewater, thereby alleviating the demand for fresh water. Herein, we describe a novel and efficient approach for preparing porous polycaprolactone (PCL) membranes with a hierarchical architecture via a simple solvent/non-solvent methodology. A mixed-matrix membrane (MMM) was further constructed utilizing an amine-functionalized metal–organic framework as the sorbent filler nanoparticles and PCL as the polymer support matrix (MOF@PCL) for wastewater treatment applications. The MOF@PCL MMM demonstrated homogeneous morphology as well as exceptional performance towards the removal of both cationic (methylene blue, MB) and anionic (methyl orange, MO) organic dyes, where the maximum adsorption capacities reached 309 mg g⁻¹ and 208 mg g⁻¹, respectively. Kinetic and thermodynamic investigations revealed that the adsorption process was endothermic with a fast intraparticle diffusion rate constant. The MOF@PCL MMM also displayed excellent mechanical stability and recyclability, where the removal efficiency was maintained after 10 cycles.

MWCNTs composite with UiO-66-NH ₂ MOF doped with Ni( ii ) ions produced a highly efficient heterogeneous electrocatalyst for the water oxidation reaction.

Adenosine is a small molecule directly involved in maintaining homeostasis under pathological and stressful conditions. Due to its rapid metabolism, delivery vehicles capable of exhibiting extended release of adenosine are of paramount interest. Herein, we demonstrate a superior long-term (9 days) release profile of adenosine from biocompatible MOFs in a physiologically relevant environment. The key to the biocompatibility of MOFs is their stability under biologically relevant conditions. This study additionally highlights the interplay between the chemical stability of prototypal MOFs, assessed under physiological conditions, and their cytotoxicity profiles. Cytotoxicity of the prototypal Zn-based MOF (ZIF-8) and three Zr-based MOFs (UiO-66, UiO-66-NH₂, and MOF-801) on six cell types was assessed. The cell types selected were valve interstitial cells (VICs), valve endothelial cells (VECs), adipose tissue-derived stem cells (ADSCs), and cell lines U937, THP1, and HeLa. Zr-based MOFs demonstrated a wide tolerance range in the cell culture cytotoxicity assays, demonstrating cell viability up to a very high dose of ∼1000 μg mL⁻¹, as compared to ZIF-8 which showed notable cytotoxicity in as little as ∼100 μg mL⁻¹ dose. This study demonstrates, for the first time, the utilization of biocompatible MOFs for adenosine delivery as well as establishes a direct link between structural instability in the cell culture medium and the observed cytotoxicity of the studied MOFs.

Several approaches have recently been investigated with the aim of enhancing the specific capacitance of polyaniline (PANI). We herein report a novel pathway to boost the specific capacitance of PANI, which is highly tunable and versatile, based on wet chemistry techniques. In this approach, utilization of a specific metal–organic framework (MOF), UiO-66-NH₂, as a nanopore generator (Nanogen) is demonstrated. This systematic study demonstrates a tight interplay between the enhanced electrolyte accessibility to the PANI chains, through the incorporation of MOF nanogens, and the optimal relative amount of the conductive PANI, necessary to attain a charge percolation threshold in the binary system (MOF@PANI). Satisfying the charge percolation while maintaining porosity is necessary to arrive at a maximized specific capacitance of the PANI as the active phase. The enhancement in the specific capacitance of the PANI was fully exploited through a systematic investigation that helped to pinpoint the saddle point at which the two orthogonal properties, namely porosity (electrolyte diffusivity) and charge mobility (PANI inter-chain electronic conductivity) can be fine-tuned via controlling the materials composition. Of the different compositions investigated, the composite containing 23 wt% PANI of the total weight, doped with MOF nanogens, resulted in an enhanced specific capacitance of 872 F g⁻¹ for the PANI, in comparison to only 469 F g⁻¹ for the pristine PANI investigated under identical conditions.

Current interest in investigating non-precious group (NPG) metals for catalyzing the oxygen evolution reaction (OER) has revealed that doping of Ni hydroxides with Fe results in the dramatic enhancement of catalytic activity. Herein, a facile pathway to construct tetrataenite, an NiFe alloy of extraterrestrial origin and to address the limited electrical conductivity of metal oxides/hydroxides by directly constructing them atop graphene sheets is described. In this approach, a one-pot, bottom-up assembly of hybrid ultramicroporous materials (HUMs) was carried out, in the presence of suspended graphene (G), to homogeneously deposit the HUMs on unmodified graphene sheets, affording HUMs@G. Single metal (SIFSIX-3-Ni@G) and mixed metal (SIFSIX-3-NiFe@G) HUMs can be readily synthesized from their respective metal salts to afford a well-designed catalyst for the OER. The pyrolysis of SIFSIX-3-NiFe@G resulted in the deposition of the nanoalloy tetrataenite on G, demonstrating an exceptionally low OER onset potential of 1.44 V vs. RHE and reduced overpotential at 10 mA cm⁻² (η₁₀ = 266 mV). The synergy between the composition of the active catalyst and the electronically conductive support was attained by designing a reaction system encoding the self-assembly of a crystalline pre-catalyst on G sheets.

A comprehensive model to describe the water stability of prototypical metal–organic frameworks (MOFs) is derived by combining different types of theoretical and experimental approaches. The results provide an insight into the early stages of water‐triggered destabilization of MOFs and allow detailed pathways to be proposed for the degradation of different MOFs under aqueous conditions. The essential elements of the approach are computing the pK_a values of coordinated water molecules and geometry relaxations. Variable‐temperature and pH infrared spectroscopy techniques are used to corroborate the main findings. The model developed herein helps to explain stability limits observed for several prototypical MOFs, including MOF‐5, HKUST‐1, UiO‐66, and MIL‐101‐Cr, in aqueous solutions, and thus, provides an insight into the possible degradation pathways in acidic and basic environments. The formation of a metal hydroxide through the autoprotolysis of metal‐coordinated water molecules and the strength of carboxylate–metal interactions are suggested to be two key players that govern stability in basic and acidic media, respectively. The methodology presented herein can effectively guide future efforts, which are especially significant for in silico screening, for developing novel MOFs with enhanced aqueous stability.

The recent progress and challenges in developing highly active microporous materials as heterogeneous electrocatalysts for oxygen reduction reaction (ORR) are discussed. Due to the slow kinetics of ORR, the search for novel highly stable catalysts that can outperform Pt‐based ones is a growing demand. Functional microporous materials and exceptional chemical stability are of great interest due to their unique catalytic properties. The crucial rule of porosity and catalyst design strategies are thoroughly discussed with emphasis on the influence of the degree of microporosity on the material's intrinsic catalytic activity and the current best practice for catalyst testing and activity reporting. This Review focuses on microporous materials, which are classified into crystalline as metal–organic frameworks (MOFs), covalent–organic frameworks (COFs), or amorphous porous–organic polymers (POPs) as to their recent utilization in constructing efficient ORR electrocatalysts. The fundamental challenges in obtaining stable catalysts with appreciable kinetics from non‐noble metal ions, and ways to form them utilizing microporous solids as catalyst matrices, are reviewed. The fundamental criteria for future generation ORR catalysts based on microporous solids, including stability in acidic medium, high electrical conductivity, and accessibility of the active sites within the matrix are highlighted for guidance to future works.

The remarkable water stability of Zr-carboxylate-based metal–organic frameworks (MOFs) stimulated considerable interest toward their utilization in aqueous phase applications. The origin of such stability is probed here through pH titration and pK_a modeling. A unique feature of the Zr₆(μ₃-OH)₄(μ₃-O)₄(RCO₂)₁₂ cluster is the Zr-bridging oxo/hydroxyl groups, demonstrating several pK_a values that appear to provide for the water stability at a wide range of pH. Accordingly, the tunability of the cage/surface charge of the MOF can feasibly be controlled through careful adjustment of solution pH. Such high stability, and facile control over cage/surface charge, can additionally be augmented through introducing chemical functionalities lining the cages of the MOF, specifically amine groups in the UiO-66-NH₂ presented herein. The variable protonation states of the Zr cluster and the pendant amino groups, their H-bond donor/acceptor characteristics, and their electrostatic interactions with guest molecules were effectively utilized in controlled experiments to demonstrate high uptake of model guest molecules (137 mg/g for Cr(VI), 1275 mg/g for methylene blue, and 909 mg/g for methyl orange). Additionally, a practical form of the silica-supported MOF, UiO-66-NH₂@SiO₂, constructed in under 2 h reaction time, is described, generating a true platform microporous sorbent for practical use in demanding applications.