Theoretical studies of metal-organic frameworks: Calculation methods and applications in catalysis, gas separation, and energy storage

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

Precise Anchoring of Fe Sites by Regulating Crystallinity of Novel Binuclear Ni-MOF for Revealing Mechanism of Electrocatalytic Oxygen Evolution

Bimetallic metal-organic framework (BMOF) exhibits better electrocatalytic performance than mono-MOF, but deciphering the precise anchoring of foreign atoms and revealing the underlying mechanisms at the atomic level remains a major challenge. Herein, a novel binuclear NiFe-MOF with precise anchoring of Fe sites is synthesized. The low-crystallinity (LC)-NiFe0.33 -MOF exhibited abundant unsaturated active sites and demonstrated excellent electrocatalytic oxygen evolution reaction (OER) performance. It achieved an ultralow overpotential of 230 mV at 10 mA cm-2 and a Tafel slope of 41 mV dec-1 . Using a combination of modulating crystallinity, X-ray absorption spectroscopy, and theoretical calculations, the accurate metal sequence of BMOF and the synergistic effect of the active sites are identified, revealing that the adjacent active site plays a significant role in regulating the catalytic performance of the endmost active site. The proposed model of BMOF electrocatalysts facilitates the investigation of efficient OER electrocatalysts and the related catalytic mechanisms.

A Readily Achieved Potentiostatic Method in Density Functional Theory Calculation for Improved Prediction of the Performance for Electrocatalytic Nitrogen Reduction Reaction

Accurate prediction of the catalytic performance of nitrogen reduction reaction catalysts based on density functional theory (DFT) calculation is of great significance for developing catalytic materials for nitrogen fixation. However, the applied electrode potential induced the fixation of Fermi level and solvation effect are commonly ignored in the current computational hydrogen electrode method, which leads to the large deviation between the calculation predicted limit potential and the experimentally measured limit potential. In this work, the simple external iteration method is proposed to simulate the Fermi level of the catalysts that are fixed by the applied electrode potential, along with the hybrid solvent model to describe the strong interaction, such as hydrogen bond, between the solvent molecules and the intermediates. This method allowed the theoretical and experimental limit potentials to be in good agreement, indicating the significant effect of the electrode potential and solvation in the DFT calculation. These results will guide the calculation-based prediction of other reaction systems in the field of electrocatalysis.

Abundant Surface Defects in Cobalt Hydroxides/Oxyhydroxides Induced by Zinc Species Facilitate Water Oxidation

The complex process of the anodic oxygen evolution reaction (OER) severely hinders overall water splitting, which further limits the large-scale production and application of hydrogen energy. In this work, one type of bimetallic coordination polymer of ZnCoBTC using the MOF-on-MOF strategy has been synthesized where both Co(II) and Zn(II) cations exhibit the same coordination environment. By applying an electric potential, the predesigned bimetallic MOF precursor can be conveniently degraded into CoOxHy as an active species for efficient OER. Owing to the dissolution of ZnOxHy species, in situ formed disordered defects on the external surface of the catalyst increase the specific surface area as well as expose abundant active materials. Therefore, the ZnCoOxHy nanosheet shows excellent OER performance and reaches an overpotential of only 334 mV at 10 mA cm-2 with a Tafel slope of 66.4 mV dec-1, indicating fast reaction kinetics. The results demonstrate that metals with the same coordination environment can undergo in situ replacement or secondary growth on the pristine MOF, and they can be electrochemically degraded into highly efficient catalysts for future energy applications.

Industrial Separation Challenges: How Does Supramolecular Chemistry Help?

The chemical industry and the chemical processes underscoring it are under intense scrutiny as the demands for the transition to more sustainable and environmentally friendly practices are increasing. Traditional industrial separation systems, such as thermally driven distillation for hydrocarbon purification, are energy intensive. The development of more energy efficient separation technologies is thus emerging as a critical need, as is the creation of new materials that may permit a transition away from classic distillation-based separations. In this Perspective, we focus on porous organic cages and macrocycles that can adsorb guest molecules selectively through various host-guest interactions and permit molecular sieving behavior at the molecular level. Specifically, we summarize the recent advances where receptor-based adsorbent materials have been shown to be effective for industrially relevant hydrocarbon separations, highlighting the underlying host-guest interactions that impart selectivity and permit the observed separations. This approach to sustainable separations is currently in its infancy. Nevertheless, several receptor-based adsorbent materials with extrinsic/intrinsic voids or special functional groups have been reported in recent years that can selectively capture various targeted guest molecules. We believe that the understanding of the interactions that drive selectivity at a molecular level accruing from these initial systems will permit an ever-more-effective "bottom-up" design of tailored molecular sieves that, in due course, will allow adsorbent material-based approaches to separations to transition from the laboratory into an industrial setting.

Recent progress of theoretical studies on electro- and photo-chemical conversion of CO2 with single-atom catalysts

The CO₂ reduction reaction (CO₂RR) into chemical products is a promising and efficient way to combat the global warming issue and greenhouse effect. The viability of the CO₂RR critically rests with finding highly active and selective catalysts that can accomplish the desired chemical transformation. Single-atom catalysts (SACs) are ideal in fulfilling this goal due to the well-defined active sites and support-tunable electronic structure, and exhibit enhanced activity and high selectivity for the CO₂RR. In this review, we present the recent progress of quantum-theoretical studies on electro- and photo-chemical conversion of CO₂ with SACs and frameworks. Various calculated products of CO₂RR with SACs have been discussed, including CO, acids, alcohols, hydrocarbons and other organics. Meanwhile, the critical challenges and the pathway towards improving the efficiency of the CO₂RR have also been discussed.

Advances in Hybrid Composites for Photocatalytic Applications: A Review

Heterogeneous photocatalysts have garnered extensive attention as a sustainable way for environmental remediation and energy storage process. Water splitting, solar energy conversion, and pollutant degradation are examples of nowadays applications where semiconductor-based photocatalysts represent a potentially disruptive technology. The exploitation of solar radiation for photocatalysis could generate a strong impact by decreasing the energy demand and simultaneously mitigating the impact of anthropogenic pollutants. However, most of the actual photocatalysts work only on energy radiation in the Near-UV region (<400 nm), and the studies and development of new photocatalysts with high efficiency in the visible range of the spectrum are required. In this regard, hybrid organic/inorganic photocatalysts have emerged as highly potential materials to drastically improve visible photocatalytic efficiency. In this review, we will analyze the state-of-art and the developments of hybrid photocatalysts for energy storage and energy conversion process as well as their application in pollutant degradation and water treatments.