Fabrication of Ag+, Cu2+, and Zn2+ Ternary Ion-Exchanged Zeolite as an Antimicrobial Agent in Powder Coating

Antimicrobial zeolites and metal-organic frameworks

The current surge in antibiotic resistance and the emergence of pandemics have created an urgent need for novel antimicrobial strategies. The controlled release of antimicrobial active principles remains the most viable strategy to date, and transition metal ions currently represent the main alternative to antibiotics. In this review, we explore the potential of two types of materials, zeolites and metal-organic frameworks (MOFs), for the controlled release of antimicrobial active principles, notably transition metal ions. These materials have unique crystalline microporous structures that act as reservoirs, enabling sustained bactericidal effects in various applications such as coatings, packaging, and medical devices. However, there are currently no convenient and standardised methods for evaluating their metal ion release and antimicrobial efficacy. This work discusses analytical techniques and the proposed mechanisms of action while highlighting recent advances in film, membrane, and coating technologies. By addressing the current limitations, microporous materials can revolutionise antimicrobial approaches, offering enhanced effectiveness and long-term sustainability.

A comprehensive review on zeolite-based mixed matrix membranes for CO2/CH4 separation

Biogas consisting of carbon dioxide/methane (CO₂/CH₄) gas mixtures has emerged as an alternative renewable fuel to natural gas. The presence of CO₂ can decrease the calorific value and generate greenhouse gas. Hence, separating CO₂ from CH₄ is a vital step in enhancing the use of biogas. Zeolite and zeolite-based mixed matrix membrane (MMM) is considered an auspicious candidate for CO₂/CH₄ separation due to thermal and chemical stability. This review initially addresses the development of zeolite and zeolite-based MMM for the CO₂/CH₄ separation. The highest performance in terms of CO₂ permeance and CO₂/CH₄ selectivity was achieved using zeolite and zeolite-based MMM, which exhibited CO₂ permeance in the range of 2.0 × 10^{- 7}-7.0 × 10^{- 6} mol m^{- 2} s^{- 1} Pa^{- 1} with CO₂/CH₄ selectivity ranging from 3 to 300. Current trends directed toward improving CO₂/CH₄ selectivity via modification methods including post-treatment, ion-exchanged, amino silane-grafted, and ionic liquid encapsulated of zeolite-based MMM. Those modification methods improved the defect-free and interfacial adhesions between zeolite particulates and polymer matrices and subsequently enhanced the CO₂/CH₄ selectivity. The modifications via ionic liquid and silane methods more influenced the CO₂/CH₄ selectivity with 90 and 660, respectively. This review also focuses on the possible applications of zeolite-based MMM, which include the purification and treatment of water as well as biomedical applications. Lastly, future advances and opportunities for gas separation applications are also briefly discussed. This review aims to share knowledge regarding zeolite-based MMM and inspire new industrial applications.

Anti-viral organic coatings for high touch surfaces based on smart-release, Cu2+ containing pigments

Viruses such as SARS-CoV-2 can remain viable on solid surfaces for up to one week, hence fomites are a potential route of exposure to infectious virus. Copper has well documented antiviral properties that could limit this problem, however practical deployment of copper surfaces has been limited due to the associated costs and the incompatibility of copper metal in specific environments and conditions. We therefore developed an organic coating containing an intelligent-release Cu²⁺ pigment based on a cation exchange resin. Organic coatings containing a 50 % weight or higher loading of smart-release pigment were capable of completely inactivating (>6 log reduction in titre) SARS-CoV-2 within 4 h of incubation. Importantly these organic coatings demonstrated a significantly enhanced ability to inactivate SARS-CoV-2 compared to metallic copper and un-pigmented material. Furthermore, the presence of contaminating proteins inhibited the antiviral activity of metallic copper, but the intelligent-release Cu²⁺ pigment was unaffected. The approach of using a very basic paint system, based on a polymer binder embedded with "smart release" pigment containing an anti-viral agent which is liberated by ion-exchange, holds significant promise as a cost effective and rapidly deployed coating to confer virus inactivating capability to high touch surfaces.

Rational Design and Characterisation of Novel Mono- and Bimetallic Antibacterial Linde Type A Zeolite Materials

The development of antimicrobial devices and surfaces requires the setup of suitable materials, able to store and release active principles. In this context, zeolites, which are microporous aluminosilicate minerals, hold great promise, since they are able to serve as a reservoir for metal-ions with antimicrobial properties. Here, we report on the preparation of Linde Type A zeolites, partially exchanged with combinations of metal-ions (Ag⁺, Cu²⁺, Zn²⁺) at different loadings (0.1–11.9 wt.%). We combine X-ray fluorescence, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction to monitor the metal-ion contents, distribution, and conservation of the zeolite structure after exchange. Then, we evaluate their antimicrobial activity, using agar dilution and optical-density monitoring of Escherichia coli cultures. The results indicate that silver-loaded materials are at least 70-fold more active than the copper-, zinc-, and non-exchanged ones. Moreover, zeolites loaded with lower Ag⁺ concentrations remain active down to 0.1 wt.%, and their activities are directly proportional to the total Ag content. Sequential exchanges with two metal ions (Ag⁺ and either Cu²⁺, Zn²⁺) display synergetic or antagonist effects, depending on the quantity of the second metal. Altogether, this work shows that, by combining analytical and quantitative methods, it is possible to fine-tune the composition of bi-metal-exchanged zeolites, in order to maximise their antimicrobial potential, opening new ways for the development of next-generation composite zeolite-containing antimicrobial materials, with potential applications for the design of dental or bone implants, as well as biomedical devices and pharmaceutical products.

Zeolite-Supported Aggregate as Potential Antimicrobial Agents in Gypsum Composites

Relatively easy treatment of glass aggregates can lead to the formation of a highly porous zeolite aggregate. This study focuses on the possibility of using such an aggregate as an active additive to a gypsum binder. The physical properties of hardened gypsum composites with zeolite fillers doped with various metal ions (Ni²⁺, Cu²⁺, and Zn²⁺) have been compared. In addition to studies of the basic physical properties of the composites, structural and microstructural studies as well as antimicrobial tests were performed. It was found that the parameters of the composites with the addition of various ions do not differ significantly from the reference but modifies the microstructure. Among other things, the ions analyzed reduce the microporosity of gypsum composites. Using all aggregates, a product with adequate strength (above 2 MPa) and thermal conductivity (about 0.35 W/m·K) appropriate for typical lightweight gypsum composites can be obtained. The bacteriostatic effect of formulations with copper and zinc against Escherichia coli and with copper against Staphylococcus aureus was found.

Quaternized Polydopamine Coatings for Anchoring Molecularly Dispersed Broad-Spectrum Antimicrobial Silver Salts

Because of the broad-spectrum antimicrobial efficacy, silver-based coatings have emerged as the popular choice to apply over frequently touched surfaces for mitigating the spread of nosocomial infections. Despite the advancements through various coating strategies, clustering of the active component remains a bottleneck in achieving the molecular-scale dispersion of silver. To circumvent this, the current study takes advantage of the recent findings of quaternary ammonium moieties forming molecular complexes with silver salts that differ from the simple adduct between the individual components. Here we demonstrate the quaternization of oxidatively cross-linked polydopamine coatings over magnetite nanoparticles to anchor ionic silver at a molecular-scale dispersion. The silver-derivatized materials exhibit remarkable broad-spectrum antimicrobial properties against representative microbes like E. coli, S. aureus, and A. niger. Also, the study reveals the materials' antibiofilm efficacy (∼80-90%) against both bacteria. Further recyclability studies have proven the sustained bactericidal properties up to five cycles. The surface derivatization strategy has then been extended to cover glass slips that have also shown the retention of the bactericidal properties even after wiping 20 times with artificial sweat. The biocompatibility of the materials has been ascertained with treated water against the mouse fibroblast and human embryonic kidney cell lines. The current study offers insights in developing coatings with molecular-scale dispersion of ionic silver to achieve broad-spectrum antimicrobial properties in an atom-economical and sustainable manner.

Development of a novel silver ions-nanosilver complementary composite as antimicrobial additive for powder coating

Applying silver into coatings has become a prevalent method in fabricating antimicrobial surfaces. However, the concerns about durability always exist and limit its applications. Here, a highly inhibitory, active, durable, and easy-to-use silver ions-nanosilver antimicrobial additive for powder coatings was fabricated in this study. Silver nanoparticles were chemically bonded to the Ag, Cu, and Zn-ternary ion-exchanged zeolite by α -lipoic acid, which was then encapsulated by hydrophilic polymers. The fabricated silver ions and silver nanoparticles (Ag+-AgNPs) complementary structure provides a synergistic effect. Ag+ is the main antimicrobial agent, while AgNPs act as a supplementary reservoir of Ag+. As well, the formed thin layer of silver nanoparticles and hydrophilic film prolongs the release of active Ag+ from zeolite, and Ag+ facilitates the activation of AgNPs. The results show that this additive indicates excellent antimicrobial activity to E. coli, S. aureus, P. aeruginosa, and C. albicans, and that the coatings with the additive exhibit over 99.99% reduction rate for the tested bacteria and fungi. The coating film is able to maintain over 99% antimicrobial reduction even after 1200 repeated solution wipings, or over 30 wash cycles of artificial sweat solution, indicating high durability. Furthermore, the yellowness of the coating is not evident (Δb < 2) despite the high loading of silver, and the silver nanoparticles have little impact on gloss, haze, and distinctness of the coating film image.

Alternative Control of Phragmidium rubi-idaei Infecting Two Rubus Species

Organic berry plantations have been gaining popularity among farmers during recent years. Even so, farmers experience serious challenges in disease control management, which is a concern in organic farming. Phragmidium rubi-idaei (DC) P. Karst is the pathogen responsible for blackberry and raspberry rust disease, one of the most present and active diseases in plantations. The antifungal certified products found on the organic farming market offer the opportunity for an efficient control strategy over plant pathogens in fruit shrub plantations. In this study, 5 natural based products—namely Altosan, Mimox, Canelys, Zitron, and Zeolite—were tested for their fungistatic effect over P. rubi-idaei. The experiments were carried out under laboratory conditions, performing observations over the impact of organic products, used at different concentration levels, on rust conidia germination. Moreover, field experiments were conducted in order to evaluate the efficiency of different treatments for rust control on raspberry (‘Polka’, ‘Veten’ and ‘Heritage’) and blackberry (‘Thorn Free’, ‘Chester’ and ‘Loch Ness’) varieties. Data analysis based on ANOVA tests showed significant differences between the tested variants and the control sample at p < 0.001. Furthermore, LSD test confirmed differences between all substances tested (p < 0.005). The natural products Canelys (formulated with cinnamon) and Zytron (based on citrus extract) have proven the highest inhibitory capacity for conidia germination during in vitro tests registering values of 80.42% and 78.34%, respectively. The same high inhibitory rates against rust pathogen were kept also in the field tests using the same two natural-based products mentioned earlier. In addition, outcomes from this study demonstrated that Zeolite is not recommended for raspberry or blackberry rust control.