Silver-exchanged Zeolite Research Articles

Antimicrobial and Oxidative Activities of Different Levels of Silver-Exchanged Zeolites X and ZSM-5 and Their Ecotoxicity

Objectives: The antimicrobial, oxidative activities, and ecotoxicity of synthesized silver-loaded zeolites (X and ZSM-5(MFI), Si-to-Al ratios 12 and 25) were studied, linking antimicrobial properties to material structure and released active silver species. Methods: The materials were characterized by SEM, EDX, TEM, and XRPD. All materials, with a silver content of 1–3%wt for the Ss and about 35%wt for the X-zeolites, were tested against Escherichia coli and Staphylococcus aureus. Redox activity was studied in physiological (pH 7.4/37 °C) and optimal (pH 8.5/37 °C) conditions in chemiluminescent model systems. In the ecotoxicity tests, we used Daphnia magna. Results: A proportional correlation was observed between the bactericidal effect of and the silver content in the zeolites. AgX with a Si/Al ratio of ~1.23 and 35% silver showed a higher antimicrobial efficiency, particularly against Gram-negative E. coli versus Gram-positive S. aureus. The concentration thresholds were as follows: AgXas had a bactericidal effect at 0.003 g/L−1, with an MIC at 0.0015 m/L−1 for E. coli; SA25-Ag, AgXcl, AgXrc had a bactericidal effect at 2.5 g/L−1. The bacteria were more resilient than Daphnia magna, which showed a 90–100% lethality at Ag–zeolite concentrations of 0.00625 to 0.0125 g/L−1. AgXas and AgXrc demonstrated strong reactive oxygen species generation at both the physiological and optimal pH, explaining their bactericidal effects. In general, the tested materials showed an inhibition of the generated reactive oxygen species depending on the model system and conditions. Conclusions: The silver species leached from the new materials explain their higher oxidation and bactericidal activity. While suitable for stringently controlled biological applications, their release into the environment, in concentrations higher than 0.01g/L−1, should be avoided.

Radiation resistance and durability against thermal regeneration cycles of Ag-ETS-10 and Ag-ZSM-5 for collecting radioxenon

Efficient porous adsorbents are crucial for: the mitigation of radioxenon emissions from nuclear installations, the production of Xe and the detection of clandestine nuclear weapon tests. Silver-exchanged zeolites or alike, specifically Ag-ZSM-5 and Ag-ETS-10, are promising candidates for these applications. However, knowledge on their radiation resistance is lacking and further research is necessary on their durability against thermal regeneration cycles. The radiation resistance was investigated for the first time by in situ irradiation with 133Xe up to about 100 MGy on Ag-ETS-10 and Ag-ZSM-5. In parallel, the durability of non-irradiated samples against at least 43 thermal regeneration cycles was investigated on both adsorbents. Fresh, irradiated and thermally regenerated samples were analyzed using different characterization techniques. The characterizations, and more specifically Xe adsorption at 296 K, did not show particular alterations due to the irradiation and thermal regeneration cycles. This is a major step forward for more efficient radioxenon trapping as it proves that both adsorbents can be used up to these irradiation levels and withstand 43 thermal regeneration cycles without any significant loss of Xe adsorption performance. Noteworthily, peak shifting and broadening were observed in the 29Si NMR signals of irradiated Ag-ETS-10 due to the paramagnetic 133Cs decay product.

Exploring the potential use of silver-exchanged zeolites for adsorption of radon traces in low background experiments

Abstract Radon is an important source of radioactive background in experiments searching for rare decays and in the field of low-energy particle physics. Here, we report the first temperature-dependent study of radon adsorption on silver-exchanged zeolites from several commercial producers. Among the three tested zeolites, Ag-ETS-10 showed the best result. Hence, it was chosen for the further study of internal radioactivity and radon emanation, which are important characteristics of materials used in low-activity experiments. The important role of silver in radon adsorption is demonstrated by comparison of the silver-exchanged zeolites with their unexchanged counterparts. Furthermore, the temperature-dependent measurements showed that the enhancement of the radon adsorption upon the introduction of silver in zeolite occurs due to the increase of the heat of adsorption. This opens a new perspective for the search for highly efficient radon adsorbents.

Silver-Exchanged Zeolite Y Catalyzes a Selective Insertion of Carbenes into C–H and O–H Bonds

Silver-Exchanged Zeolite Y Catalyzes a Selective Insertion of Carbenes into C–H and O–H Bonds

Toward Optimal Xenon Adsorption Capacity at Low Pressure on Silver-Exchanged Zeolites

Toward Optimal Xenon Adsorption Capacity at Low Pressure on Silver-Exchanged Zeolites

Silver-exchanged zeolites for collecting and separating xenon directly from atmospheric air

More efficient adsorbents for Xe collection and separation from air could provide new alternatives for cost-efficient production of stable Xe as well as for trace measurements of atmospheric radioxenon. Silver-exchanged Zeolites (AgZs) have been reported to be more efficient than Activated Carbon (AC) in collecting Xe at low pressures and room temperature but never for Xe collection from air. Metal-Organic Frameworks (MOFs) have been reported for high Xe/Kr selectivities in Xe and Kr enriched gas streams but never for Xe collection from air either. Two AgZs (Ag-ETS-10 and Ag-ZSM-5), two MOFs (HKUST-1 and Ni-DOBDC) and one AC (Nusorb® GXK) are compared to determine their potential for collecting and separating Xe from air. The acquired adsorbent samples were characterized (by SEM, PXRD, TGA, N2 adsorption at 77 K and CO2 adsorption at 273 K) and the results are in agreement with observations made previously in the literature. Both AgZs show an unprecedented Xe adsorption capacity in N2 at 13.5 mPa (approximately the Xe partial pressure in air) and room temperature with 0.15 and 0.13 mmol/kg for Ag-ETS-10 and Ag-ZSM-5, respectively. This high Xe adsorption capacity at low Xe concentration holds in dry air. Both AgZs have a high Xe selectivity over the major gas components in air at room temperature and they also show an unprecedented Xe selectivity over Kr of 1300 and 470 for Ag-ETS-10 and Ag-ZSM-5, respectively. Finally, it is possible to separate Xe from O2, Ar, CO2, Kr and Rn efficiently in both AgZs but it requires temperatures up to 521 K. The results clearly demonstrate that both AgZs investigated in this work are globally outperforming all other adsorbents for collecting and separating Xe from air. The only limitation found for the moment on these AgZs is the strong co-adsorption of moisture that significantly reduces the Xe collection at 50% R.H.

Adsorption of radon on silver exchanged zeolites at ambient temperatures

Since more than 100 years, the adsorption of the radioactive noble gas radon (222Rn) is performed on activated charcoal at cryogenic temperatures. There is little—if any—progress in the field of radon adsorption at ambient conditions to facilitate the development of simple and compact radon adsorption systems. We report here on the truly remarkable property of the synthetic silver-exchanged zeolites Ag-ETS-10 and Ag-ZSM-5 to strongly adsorb radon gas at room temperature. 222Rn breakthrough experiments in nitrogen carrier gas have shown that these materials exhibit radon adsorption coefficients exceeding 3000 m3/kg at 293 K, more than two orders of magnitude larger than any noble gas adsorbent known to date. Water vapor and carrier gas type were found to strongly influence radon adsorption, practically qualifying these silver exchanged materials as a new class of radon adsorbents. Our results demonstrate that Ag-ETS-10 and Ag-ZSM-5 are materials that show high affinity towards radon gas at ambient temperatures making them candidate materials for environmental and industrial 222Rn mitigation applications. Adsorption systems based on silver loaded zeolites have the potential to replace activated charcoal as material of choice in many radon related research areas by avoiding the necessity of cryogenic cooling.

In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture.

Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I2 molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NOX treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Using silver exchange to achieve high uptake and selectivity for propylene/propane separation in zeolite Y

Adsorptive separation of propylene and propane, an important step of polypropylene production, is more energy-efficient than distillation. However, the challenge lies in the design of an adsorbent which exhibits both high selectivity and uptake. Herein, we hypothesise that enhancing the propylene affinity of the adsorption sites while keeping a suitable pore size can address this challenge. To do so, we performed silver exchange of a commercial zeolite Y, thereby making the adsorbent design easily scalable. We characterised the adsorbent using analytical, spectroscopic and imaging tools, tested its equilibrium and dynamic sorption properties using volumetric and gravimetric techniques and compared its performance to those of state-of-the-art adsorbents as well as other silver-functionalised adsorbents. The silver-exchanged zeolite Y (Ag-Y) exhibited one of the best selectivity vs uptake performances reported so far. Ag-Y also displayed fast adsorption kinetics and reversible propylene sorption, making it a promising new benchmark for propylene/propane separation. Synchrotron-based pair distribution function analyses identified the silver cations’ location which confirmed that the silver sites are easily accessible to the adsorbates. This aspect can, in part, explain the propylene/propane separation performance observed. The overall design strategy proposed here to enhance sorption site affinity and maintain pore size could be extended to other adsorbents and support the deployment of adsorption technology for propylene/propane separation.

Novel adsorption approach for the enrichment of R-Phycoerythrin from marine macroalga Gelidium pusillum

R-Phycoerythrin is a fluorescent and commercially valuable pigment protein present in algae. The extraction, purification and concentration of such biomolecules is a challenge for processing industries. In the present work, enrichment of R-Phycoerythrin was attempted by selective adsorption of other contaminant biomolecules from extract of algal biomass. Different adsorbents (zeolite, molecular sieve, ammonium Y zeolite, silver-exchanged zeolite, mesoporous carbon) and nanoparticles (zinc oxide, graphene oxide, gold and silver) were explored for this purpose. Process conditions such as buffer pH (5, 6, 7 and 8), ionic strength (0.1, 0.35, 0.6, 0.85 and 1.1) and adsorbent levels (w/w) were optimized. Optimization resulted in enrichment of pre-treated R-Phycoerythrin by 3.31 fold with 73.36% yield using zeolite and 2.10 fold with 98.91% yield using gold nanoparticles. This work demonstrates the efficacy of adsorbents and nanoparticles as possible alternatives for enrichment and purification of R-Phycoerythrin with appreciable yield.

Rational approach for an optimized formulation of silver-exchanged zeolites for iodine capture from first-principles calculations

Ab initio calculations have been carried out to investigate in detail the effect of potential inhibiting species (CO, H2O, CH3Cl and Cl2) on the adsorption of iodine species (I2 and CH3I) in silver-exchanged zeolites of different Si/Al ratios and structures.

Application of silver-exchanged zeolite for radioxenon mitigation at fission-based medical isotope production facilities

Atmospheric radioxenon releases from fission-based medical isotope production facilities are the main contributors to the radioxenon background being observed in the International Monitoring System (IMS) for the verification of the Comprehensive Nuclear-Test-Ban Treaty. This background is impacting the detection capability of the IMS network for potential nuclear explosions. Reducing the radioxenon emissions from these facilities requires the optimization of the corresponding filtration process. The investigation of more efficient Xe adsorption materials than Activated Carbon (AC), which is currently used for this application, can play an important role for such an optimization. In this work, the Xe adsorption capacity of silver-exchanged zeolites (AgZs) is compared to the one of ACs in relevant conditions for fission-based medical isotope production facilities. The most promising AgZ candidate, a silver-exchanged titanosilicate (Ag-ETS-10), is investigated in more detail for its application to further reduce radioxenon releases. As operational conditions depend on the production and off-gas treatment processes, the effect of Xe concentration, flow rate, temperature and moisture on the Xe adsorption in Ag-ETS-10 is reported. Furthermore, since AgZs are far more expensive than ACs, it is crucial to be able to regenerate the material, whilst maintaining its full Xe adsorption properties for successive reuse. Accordingly, the durability of Ag-ETS-10 is investigated with regard to desorption and adsorption cycles but also with regard to gamma irradiation.

Sorption properties of novel-fashioned low-cost hydrogen getters in a high-vacuum-multilayer insulation structure

In a high-vacuum-multilayer insulation structure (HVMLIS), H2 is released into the vacuum jacket by manufactured materials, resulting in the deterioration of the insulation vacuum. Palladium oxide (PdO), which is expensive, is typically used as an H2 getter in HVMLIS. However, PdO generates sparks by vigorously reacting with H2, which are a potential threat to HVMLIS. Therefore, in this work, silver-exchanged zeolite is optimised to obtain an inexpensive and safe Ag–Z getter and a silver molecular sieve (SMS) together with a low-temperature active material getter (AMG). Moreover, an experimental platform was designed to test the H2 sorption properties of the three getters and compare them with traditional PdO. The experiment revealed that the cumulative sorption capacities of PdO, Ag–Z, SMS and AMG were 184.8, 63.1, 124.9 and 5.28 mL/g, respectively. However, the costs of SMS, Ag–Z and AMG were only ~7.37%, 5.08% and 6.13% of the cost of PdO, respectively, indicating that SMS is a promising alternative to PdO, which is expensive. Simultaneously, the microstructure of the H2 getters was analysed via X-ray powder diffraction. Further, PdH0.706 and Pd2H1.5 were obtained in addition to Pd, after H2 was absorbed by PdO. Ag+ was reduced to Ag in SMS, and Cu8O was produced by the reaction of CuO in AMG. These findings provide a basis for the subsequent optimisation of the H2 getters.

Feasibility Study of Using Bi-mna Metal–Organic Frameworks as Adsorbents for Radioiodine Capture at High Temperature

In this study, a bismuth-based metal–organic framework (Bi-MOF) was investigated in its applicability as an iodine adsorbent at high temperatures for possible applications under severe accidents in a nuclear power plant. Bi-mna was selected among Bi-MOF candidates based on its thermodynamic characteristics, which expected to allow chemisorption of iodine by bismuth. Its iodine adsorption performance was compared with zeolitic imidazolate framework-8 and Cu-BTC and other MOFs which were chosen due to their diversity in iodine adsorption mechanisms. Bi-mna was synthesized at the laboratory scale, and the aforementioned three MOFs were tested for iodine adsorption at various temperatures from 350 to 600 K. The adsorption mechanism of Bi-mna was investigated by conducting various analyses including thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller. The results showed that Bi-mna has good adsorption performance (700 mg-I/g-adsorbent) while maintaining good thermal stability even at a high temperature (up to 575–600 K). The iodine capture performance of Bi-mna is better, especially at high temperature, in comparison with those of non-MOF adsorbents such as silver-exchanged zeolites and bismuth-embedded SBA-15. Analysis results confirmed that Bi-mna chemically captured iodine by breaking bonds between bismuth and sulfur to form new chemical bonds between iodine and the bismuth in Bi-mna. The results indicate that Bi-mna has the potential to be used in capturing radioiodine at high-temperature environments, such as during nuclear severe accident management. Its use should also be considered as a potential candidate for waste form development.

Microbes of XVI century Arrases of Krakow Royal Castle

Sixteenth-century Arrases from the Krakow Royal Castle constitute a Polish national cultural heritage; hence, they should be under special protection. The storage of historic objects at strict temperature and humidity conditions is fundamental for their protection against microorganisms. However, sometimes active preservation must be applied to disinfect bio-contaminated objects. In this study, 39 strains of microorganisms, both fungi and bacteria, isolated from Arrases deposited in the Wawel warehouse were isolated and then identified using molecular tools. Fungal ability to colonize and degrade silk and wool laboratory samples was studied. Selected microbial strains were compared concerning their ability to affect silk fibroin using size-exclusion chromatography (SEC). The effectiveness of low-temperature helium-generated plasma in disinfecting the model wool and silk samples inoculated with selected strains was tested. The results showed that plasma, despite its high biocidal activity in the case of paper, was not effective on porous textile materials. The alternative protection mechanism, involving active packaging in the form of textiles impregnated with silver-exchanged zeolites, could be used to separate layers of rolled tapestries in the warehouse. Nevertheless, optimal temperature and humidity conditions should be strictly maintained and controlled.

Spectroscopic studies of plasma-modified silver-exchanged zeolite and chitosan composites

Composite biomaterials can be formed by combining natural or synthetic, organic or inorganic materials which are exactly or partially compatible when in contact with a living organism. To greatly improve the utilization of these biomaterials, understanding its interaction with its environment or host is essential. In this work, naturally-occurring and locally-abundant materials such as zeolite (Z) and chitosan (Ch), were fabricated as a silver-exchanged zeolite/chitosan (AgZ-Ch) composite using a solvent casting approach. The composites were subsequently exposed to argon (Ar) plasma excited by a 13.56 MHz radio frequency (RF) power source. Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) techniques were utilized to investigate the surface and subsurface properties of the AgZ-Ch composites. Results revealed different interactions within the bulk and on the surface of the composite. The interactions for the composite formation are dominated by the attraction of the AgZ species with the –OH and –NH2 functional groups of Ch. On the other hand, the surface composition of Ch was influenced by the etching effect of Ar with the –COCH3 termination from the Ch. This study showed that the surface layer prefers to be terminated with amine and hydroxyl groups instead of amide functional groups. The present work also demonstrated the use of plasma irradiation to tune AgZ-Ch composite surface and tailor the reactivity of the functional groups on the surface.

Examining Practical Application Feasibility of Bismuth-Embedded SBA-15 for Gaseous Iodine Adsorption

The purpose of this study is to examine the feasibility of using bismuth-embedded SBA-15 (Bi-SBA-15) as gaseous iodine filtration material for applications at higher temperatures, such as environmental release severe accident mitigation, while reducing the cost of production and maintaining its iodine adsorption capacity. It was shown that Bi-SBA-15 can be produced in a much more economically feasible way by (1) increasing the amount of the chemical reagents for SBA-15 synthesis, (2) decreasing the amount of other chemicals required to facilitate the chemical reactions, and (3) reducing the synthesis time, all while maintaining the iodine adsorption capability. Through both closed and open iodine adsorption experiments, it was shown that Bi-SBA-15 has a much higher adsorption capacity than silver-exchanged zeolites at 423°K (150°C) but decreases sharply as the temperature increases, resulting in about half of the iodine adsorption capacity of AgX at 523 K (250°C). Assuming that the commercialized cost of Bi-SBA-15 could be less than half of silver-exchanged zeolites, Bi-SBA-15 may be able to replace silver-exchanged zeolites at higher-temperature applications but only if the temperature of the gaseous iodine is less than 423 K (150°C) or if there is a presystem such as a pool scrubber to reduce the temperature of the gaseous iodine reaching the iodine filtration system. If Bi-SBA-15 can be produced much less expensively at a small fraction of cost compared with silver-exchanged zeolites, it may even be used at a temperature up to 523 K (250°C) with high enough iodine capture efficiency by simply increasing the mass of Bi-SBA-15 to more than double the mass of the required silver-exchanged zeolites.

Silver clusters based sensor for Low content formaldehyde detection in colorimetric and fluorometric dual Mode

Formaldehyde is harmful to human health and can cause carcinogenic, central nervous system injury and skin allergies. Formaldehyde sensor with fast detection and low limit of detection (LOD) is highly desirable. Herein we report a strong green emitting material by heating the silver-exchanged zeolites of faujasite Y type (FAUY) under a mild condition of 60 °C, originating from silver clusters (Ag CLs), which can be used as an effective sensor for detecting formaldehyde via colorimetric and fluorometric dual mode. The LOD meets with World Health Organization (WHO) and Occupational Safety and Health Administration (OSHA) permissible limit, showing a prospect for the formaldehyde sensing.

Silver Zeolite Composite-Based LEDs: Origin of Electroluminescence and Charge Transport.

In this contribution, we report on the first time use of silver-exchanged zeolites embedded in the nonconductive polystyrene (PS) and their use as hybrid emitters in light-emitting diodes (ZEOLEDs). The turn on voltage and EL intensity are strongly dependent on the concentration of metal clusters. It is shown that the key to optimize this technology is improving the zeolite anode contact. Such an optimized device based on cheap abundant materials could provide an alternative for the commercial phosphor converted LEDs. A ZEOLED with a voltage polarity dependent color is demonstrated.