Metal-salen-bridged ionic networks as efficient bifunctional solid catalysts for chemical fixation of CO 2 into cyclic carbonates

Enhancement in the active site exposure in a porphyrin-based PIL/graphene composite catalyst for the highly efficient conversion of CO2

Poly(ionic liquid)s (PILs) have gained widespread attention in recent years due to their excellent properties similar to both ionic liquids and polymers. However, their further applications are limited because abundant and flexible ions easily block nanopores in the PIL catalysts, thus blocking the active sites and ultimately leading to decreased catalytic activity. This work reports the synthesis of a PIL/graphene composite catalyst (iPOP-ZnTPy@GNFs) based on an in situ surface preparation strategy, which effectively controlled the particle size and dispersion state of ionic liquids. The iPOP-ZnTPy@GNFs exhibited a larger surface area and more exposed active sites, which intensified the catalytic activity in the CO₂ cycloaddition reaction with propylene oxide with almost double the reaction rate as compared to that of iPOP-ZnTPy-2 at 100 °C and S/C = 1000. As expected, the iPOP-ZnTPy@GNF catalyst efficiently converted epoxides to cyclic carbonates at room temperature or atmospheric pressure, which can significantly reduce the process cost. In addition, iPOP-ZnTPy@GNFs exhibited excellent broad substrate scope, catalytic diversity, and remarkable reusability. The reaction mechanism of CO₂ cycloaddition was studied via density functional theory calculations and was validated by experimental findings. This work provides a feasible method for improving the utilization of active sites in PILs as a highly robust catalyst for CO₂ cycloaddition and can be further extended to other types of catalytic reactions in practical applications.

Modulating carbon dioxide activation on carbon nanotube immobilized salophen complexes by varying metal centers for efficient electrocatalytic reduction

Electrocatalytic CO₂ reduction (ECR) into valuable chemicals, especially driven by renewable energy, presents a promising pattern to realize carbon neutrality. Site-isolated metal complexes flourish in the area of ECR as single-atom-like catalysts because of their competent and tailorable activity. In this study, salophen-based metal (Fe, Co, Ni and Cu) complexes were anchored onto carbon nanotubes (CNTs) to construct efficient catalysts for electrochemically converting CO₂ to CO. Both experimental and theoretical results verified that CO₂ activation was the rate-determining step for the catalytic performance of these hybrid molecular catalysts. The coordinate activation ability can be manipulated by varying the metal centers. The as-synthesized Fe-salophen hybrid CNT (Fe-salophen/CNT) shows the best activity and selectivity of -13.24 mA·cm^-2 current density with 86.8% Faradaic efficiency for generating CO (FE_CO) at -0.76 V vs. RHE in aqueous solution, whereas Cu-salophen/CNT only achieved a -2.22 mA·cm^-2 current density and 57.9% FE_CO under the same reaction conditions. These distinct catalytic performances resulted from the different coordination activation abilities of CO₂ on various metal centers.

Ionic Covalent-Organic Framework Nanozyme as Effective Cascade Catalyst against Bacterial Wound Infection

The increasing resistance risks of conventional antibiotic abuse and the formed biofilm on the surface of wounds have been demonstrated to be the main problems for bacteria-caused infections and unsuccessful wound healing. Treatment by reactive oxygen species, such as the commercial H₂ O₂ , is a feasible way to solve those problems, but limits in its lower efficiency. Herein, an ionic covalent-organic framework-based nanozyme (GFeF) with self-promoting antibacterial effect and good biocompatibility has been developed as glucose-triggered cascade catalyst against bacterial wound infection. Besides the efficient conversion of glucose to hydrogen peroxide, the produced gluconic acid by loading glucose oxidase can supply a compatible catalytic environment to substantially improve the peroxidase activity for generating more toxic hydroxyl radicals. Meanwhile, the adhesion between the positively charged GFeF and the bacterial membrane can greatly enhance the healing effects. This glucose-triggered cascade strategy can reduce the harmful side effects by indirectly producing H₂ O₂ , potentially used in the wound healing of diabetic patients.

Cobalt-Salen-Based Porous Ionic Polymer: The Role of Valence on Cooperative Conversion of CO2 to Cyclic Carbonate

Cobalt-salen-based porous ionic polymers, which are composed of cobalt and halogen anions decorated on the framework, effectively catalyze the CO₂ cycloaddition reaction of epoxides to cyclic carbonates under ambient conditions. The cooperative effect of bifunctional active sites of cobalt as the Lewis acidic site and the halogen anion as the nucleophile responds to the high catalytic performance. Moreover, density functional theory results indicate that the cobalt valence state and the corresponding coordination group influence the rate-determining step of the CO₂ cycloaddition reaction and the nucleophilicity of halogen anions.

Self-assembly of tetranuclear 3d–4f helicates as highly efficient catalysts for CO2 cycloaddition reactions under mild conditions

A series of 4-nuclear lanthanide clusters supported by organic ligands Zn3LnL4 (Ln = Dy(1), Gd(2), Er(3)) were synthesized. These helicates could be used to convert CO₂ into cyclic carbonates with TOF up to 38 000 h⁻¹, without being influenced by moisture or air.

Metallopolymers for advanced sustainable applications

Since the development of metallopolymers, there has been tremendous interest in the applications of this type of materials. The interest in these materials stems from their potential use in industry as catalysts, biomedical agents in healthcare, energy storage and production as well as climate change mitigation. The past two decades have clearly shown exponential growth in the development of many new classes of metallopolymers that address these issues. Today, metallopolymers are considered to be at the forefront for discovering new and sustainable heterogeneous catalysts, therapeutics for drug-resistant diseases, energy storage and photovoltaics, molecular barometers and thermometers, as well as carbon dioxide sequesters. The focus of this review is to highlight the advances in design of metallopolymers with specific sustainable applications.

Post-modified porphyrin imine gels with improved chemical stability and efficient heterogeneous activity in CO2 transformation

Gel catalysts have been developed based on dynamic covalent chemistry and post-modification methods for improved chemical stability and catalytic activity.

Cationic Zn-Porphyrin Polymer Coated onto CNTs as a Cooperative Catalyst for the Synthesis of Cyclic Carbonates

The development of solid catalysts containing multiple active sites that work cooperatively is very attractive for biomimetic catalysis. Herein, we report the synthesis of bifunctional catalysts by supporting cationic porphyrin-based polymers on carbon nanotubes (CNTs) using the direct reaction of 5,10,15,20-tetrakis(4-pyridyl)porphyrin zinc(II), di(1H-imidazol-1-yl)methane, and 1,4-bis(bromomethyl)benzene in the presence of CNTs. The bifunctional catalysts could efficiently catalyze the cycloaddition reaction of epoxides and CO₂ under solvent-free conditions with porphyrin zinc(II) as the Lewis acid site and a bromine anion as a nucleophilic agent working in a cooperative way. Furthermore, a relative amount of porphyrin zinc(II) and quaternary ammonium bromide could be facilely adjusted for facilitating cooperative behavior. The bifunctional catalyst with a TOF up to 2602 h^-1 is much more active than the corresponding homogeneous counterpart and is one of the most active heterogeneous catalysts ever reported under cocatalyst-free conditions. The high activity is mainly attributed to the enhanced cooperation effect of the bifunctional catalyst. With a wide substrate scope, the bifunctional catalyst could be stably recycled. This work demonstrates a new approach for the generation of a cooperative activation effect for solid catalysts.