An Iron-Containing Metal-Organic Framework as a Highly Efficient Catalyst for Ozone Decomposition

SARS-CoV-2 airborne transmission: a review of risk factors and possible preventative measures using air purifiers

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the resulting worldwide death toll have prompted worries regarding its transmission mechanisms. Direct, indirect, and droplet modes are the basic mechanisms of transmission. SARS-CoV-2 spreads by respiratory droplets (size range >10 μm size ranges), aerosols (5 μm), airborne, and particulate matter. The rapid transmission of SARS-CoV-2 is due to the involvement of tiny indoor air particulate matter (PM_2.5), which functions as a vector. SARS-CoV-2 is more contagious in the indoor environment where particulate matter floats for a longer period and greater distances. Extended residence time in the environment raises the risk of SARS-CoV-2 entering the lower respiratory tract, which may cause serious infection and possibly death. To decrease viral transmission in the indoor environment, it is essential to catch and kill the SARS-CoV-2 virus and maintain virus-free air, which will significantly reduce viral exposure concerns. Therefore, effective air filters with anti-viral, anti-bacterial, and anti-air-pollutant characteristics are gaining popularity recently. It is essential to develop cost-effective materials based on nanoparticles and metal-organic frameworks in order to lower the risk of airborne transmission in developing countries. A diverse range of materials play an important role in the manufacturing of effective air filters. We have summarized in this review article the basic concepts of the transmission routes of SARS-CoV-2 virus and precautionary measures using air purifiers with efficient materials-based air filters for the indoor environment. The performance of air-filter materials, challenges and alternative approaches, and future perspectives are also presented. We believe that air purifiers fabricated with highly efficient materials can control various air pollutants and prevent upcoming pandemics.

Exploring an electric-aid ozone decomposition mode to enhance water resistance over manganese oxide monolith catalyst under high humidity

In this work, a facile, green, and effective reaction mode of electric-aid ozone decomposition (EAOD) was developed over a manganese-based monolith catalyst for eliminating ozone under high humidity. The catalyst was prepared by directly growing α-MnO₂ nanorods on Al honeycomb substrate (MnO₂/Al) via a simple hydrothermal process, and the EAOD mode was performed just by connecting the MnO₂/Al monolith catalyst with a DC power supply during ozone decomposition reaction. In the EAOD mode reaction, the MnO₂/Al catalyst exhibited a stable ozone conversion efficiency of over 82 % and excellent stability over 720 min under a relative humidity of 90%, well beyond the performance of catalyst in the conventional ozone decomposition reaction without the help of electric aid. Here, the water evaporation by the external electric field generated from the EAOD mode hinders the competitive adsorption of water vapor on the active sites of MnO₂/Al catalyst, consequently enhances its water resistance. Moreover, increasing input electric current of the DC power supply could further improve the catalytic activity and stability of the monolith catalyst for ozone decomposition in EAOD mode reaction.

Environmentally Benign Biosynthesis of Hierarchical MOF/Bacterial Cellulose Composite Sponge for Nerve Agent Protection

The fabrication of MOF polymer composite materials enables the practical applications of MOF-based technology, in particular for protective suits and masks. However, traditional production methods typically require organic solvent for processing which leads to environmental pollution, low-loading efficiency, poor accessibility, and loss of functionality due to poor solvent resistance properties. For the first time, we have developed a microbial synthesis strategy to prepare a MOF/bacterial cellulose nanofiber composite sponge. The prepared sponge exhibited a hierarchically porous structure, high MOF loading (up to ≈90 %), good solvent resistance, and high catalytic activity for the liquid- and solid-state hydrolysis of nerve agent simulants. Moreover, the MOF/ bacterial cellulose composite sponge reported here showed a nearly 8-fold enhancement in the protection against an ultra-toxic nerve agent (GD) in permeability studies as compared to a commercialized adsorptive carbon cloth. The results shown here present an essential step toward the practical application of MOF-based protective gear against nerve agents.

Metal-organic frameworks for active food packaging. A review

Food wastage is a major concern for sustainable health and agriculture. To reduce food waste, classical preservation techniques such as drying, pasteurization, freeze-drying, fermentation, and microwave are available. Nonetheless, these techniques display shortcomings such as alteration of food and taste. Such shortcomings may be solved by active food packaging, which involves the incorporation of active agents into the packaging material. Recently, metal-organic frameworks, a class of porous hybrid supramolecular materials, have been developed as an active agent to extend food shelf life and maintain safety. Here, we review metal-organic frameworks in active packaging as oxygen scavengers, antimicrobials, moisture absorbers, and ethylene scavengers. We present methods of incorporation of metal-organic frameworks into packaging materials and their applications.

Encapsulate α-MnO2 nanofiber within graphene layer to tune surface electronic structure for efficient ozone decomposition

Major challenges encountered when developing manganese-based materials for ozone decomposition are related to the low stability and water inactivation. To solve these problems, a hierarchical structure consisted of graphene encapsulating α-MnO₂ nanofiber was developed. The optimized catalyst exhibited a stable ozone conversion efficiency of 80% and excellent stability over 100 h under a relative humidity (RH) of 20%. Even though the RH increased to 50%, the ozone conversion also reached 70%, well beyond the performance of α-MnO₂ nanofiber. Here, surface graphite carbon was activated by capturing the electron from inner unsaturated Mn atoms. The excellent stability originated from the moderate local work function, which compromised the reaction barriers in the adsorption of ozone molecule and the desorption of the intermediate oxygen species. The hydrophobic graphene shells hindered the chemisorption of water vapour, consequently enhanced its water resistance. This work offered insights for catalyst design and would promote the practical application of manganese-based catalysts in ozone decomposition.

Ozone is a major air pollutant, but its elimination is challenging. Here the authors encapsulate defective α-MnO₂ nanofiber within ultrathin graphene shells to construct a hierarchical MnO₂@graphene catalyst for ozone decomposition that possesses high activity and stability under humid conditions.

Dual-Selective Catalysis in Dephosphorylation Tuned by Hf6-Containing Metal-Organic Frameworks Mimicking Phosphatase

Selective dephosphorylation is full of great challenges in the field of biomimetic catalysis. To mimic the active sites of protein phosphatase, Hf-OH-Hf motif-containing metal-organic frameworks (MOFs) were obtained and structurally characterized, which are assembled from [Hf48Ni6] cubic nanocages and exhibit good stability in various solvents and acid/base solutions. Catalytic investigations suggest as-synthesized Hf-Ni and Hf-Ni-NH 2 display accurate type-selectivity (selectively catalyzed P-O rather than S-O or C-O bonds) and position-selectivity (selectively catalyzed phosphomonoesters over phosphodiesters) for the hydrolysis of phosphoesters. Reaction kinetic studies further revealed the high activity of the catalytic sites in these catalysts, and the unique catalytic selectivity and high activity are comparable to phosphatase. Additionally, these MOF catalysts possess good recursivity and hypotoxicity. Control experiments (including Hf- and Zr-based isomorphous MOFs) and theoretical calculations indicate that both triplet nickel and Hf6 clusters play significant roles in the unique binding site and favorable binding energy. To our knowledge, this is the first example of selective dephosphorylation through MOF catalysts as mimic enzymes, which paves a potential way for the development of specific therapeutic MOFs.

A one-pot synthesis of a monolithic Cu2O/Cu catalyst for efficient ozone decomposition

Nowadays, it is necessary and challenging to prepare monolithic catalysts, which are ready for use, preventing the tedious and complicated integration procedure of the powder materials onto a porous substrate. Herein, Cu2O nanoparticles are successfully synthesized onto a porous Cu foam in one pot via the surface oxidation, coordination and precipitation reactions in a NH4OH and HCl solution, and the optimum synthesis conditions are a NH3 : HCl ratio of 1 : 0.9, oxidation temperature of 80 °C and time of 18 h. The obtained Cu2O/Cu catalyst (mostly <100 nm) shows a highly active O3 decomposition performance with >98% and >80% conversion efficiency in dry and 90% relative humidity air for >10 h at an O3 concentration of 20 ppm and a gas hourly space velocity of 12 500 h-1. The high efficiency can be attributed to the porous Cu foam providing a large contact area, abundant crystal defects in the nanometer-sized Cu2O materials serving as the active sites, and also to the Schottky barrier formed in the Cu2O/Cu interface facilitating the electron transfer for O3 degradation. All these results show the potency of the easily fabricated monolithic Cu2O/Cu catalyst for the highly efficient O3 contaminant removal.

Gram-scale synthesis of ultra-fine Cu2O for highly efficient ozone decomposition

Dozens of grams of ultra-fine Cu₂O with efficient ozone decomposition was prepared by a facile liquid phase reduction method at room temperature.

Cancer-Cell-Activated Photodynamic Therapy Assisted by Cu(II)-Based Metal-Organic Framework

Activation of photosensitizers (PSs) in targeted lesion and minimization of reactive oxygen species (ROS) depletion by endogenous antioxidants constitute promising approaches to perform highly effective image-guided photodynamic therapy (PDT) with minimal non-specific phototoxicity. Traditional strategies to fabricate controllable PS platforms rely on molecular design, which requires specific modification of each PS before PDT. Therefore, construction of a general tumor-responsive PDT platform with minimum ROS loss from endogenous antioxidant, typically glutathione (GSH), is highly desirable. Herein, MOF-199, a Cu(II) carboxylate-based metal-organic framework (MOF), is selected to serve as an inert carrier to load PSs with prohibited photosensitization during delivery. After cellular uptake, Cu (II) in the MOFs effectively scavenges endogenous GSH, concomitantly induces decomposition of MOF-199 to release the encapsulated PSs, and recovers their ROS generation. In vitro and in vivo experiments demonstrate highly effective cancer cell ablation and anticancer PDT with diminished normal cell phototoxicity. This strategy is generally applicable to PSs with both aggregation-induced emission and aggregation-caused quenching to implement activatable and enhanced image-guided PDT.

Metal-organic frameworks with photocatalytic bactericidal activity for integrated air cleaning

Air filtration has become an essential need for passive pollution control. However, most of the commercial air purifiers rely on dense fibrous filters, which have good particulate matter (PM) removal capability but poor biocidal effect. Here we present the photocatalytic bactericidal properties of a series of metal-organic frameworks (MOFs) and their potentials in air pollution control and personal protection. Specifically, a zinc-imidazolate MOF (ZIF-8) exhibits almost complete inactivation of Escherichia coli (E. coli) (>99.9999% inactivation efficiency) in saline within 2 h of simulated solar irradiation. Mechanistic studies indicate that photoelectrons trapped at Zn⁺ centers within ZIF-8 via ligand to metal charge transfer (LMCT) are responsible for oxygen-reduction related reactive oxygen species (ROS) production, which is the dominant disinfection mechanism. Air filters fabricated from ZIF-8 show remarkable performance for integrated pollution control, with >99.99% photocatalytic killing efficiency against airborne bacteria in 30 min and 97% PM removal. This work may shed light on designing new porous solids with photocatalytic antibiotic capability for public health protection.

Personal protective air filtration masks are becoming increasingly desirable, but most commercial air purifiers have poor biocidal capabilities. Here the authors fabricate metal–organic framework-based air filters with both high particulate matter removal efficiencies and photocatalytic bactericidal properties.

Efficient catalytic removal of airborne ozone under ambient conditions over manganese oxides immobilized on carbon nanotubes

MnO_x–CNT nanocomposites are efficient towards ozone decomposition owing to the electron transfer from the CNTs to MnO_x that facilitates the activation of ozone.