Zeolite Coatings Research Articles

Efficient Removal of Volatile Organic Compounds by FAU-Type Zeolite Coatings.

Silicone and pure organic binders were used to develop FAU-type zeolite coatings applied on pre-treated aluminum substrates by using a spraying method and then cured under specific conditions. The influence of the amount of binder on adhesion properties of zeolite coatings was first investigated to determine the optimum ratio between zeolite and binder. Zeolite coatings were then elaborated with a high zeolite content (between 70 and 80 wt.%) to ensure high adsorption capacities. The amount of binders involved in different zeolite coatings was sufficient to achieve interesting adhesion and cohesion properties. The accessibility of zeolite microporosity was studied by nitrogen adsorption-desorption measurements, which revealed a very small or no loss of the micropore volume for the optimized coatings. Volatile Organic Compounds (VOCs) adsorption measurements were carried out using n-hexane as probe molecule. FAU-type zeolite in powder form adsorbs 180 mg/ganhydrous zeolite, whereas the amounts of n-hexane adsorbed by zeolite coatings ranged from 131 to 175 mg/ganhydrous zeolite.

Influence of boehmite intermediate layer as covalent linker on synthesis of LTA zeolite coatings

The incorporation of nanostructured materials, such as LTA-type zeolite on the silicon wafers, opens a very interesting door to the use of these materials within silicon based microfabrication technologies. This work studies the deposition and intergrowth of defect-free LTA-type zeolite layer onto 3-inch Silicon wafers with a layer of SiO2 subjected to pretreatment. The main disadvantage associated with zeolite layer synthesis are crack the formation of cracks and difficulty of obtaining a uniform layer. By modifying the supports with boehmite, a substantial improvement was observed in terms of layer continuity and crystal intergrowth in comparrison to coatings prepared on cationic polymer, poly (diallyldimethylammonium chloride). An LTA- type zeolite layer was synthesized in a range of 350 to 1300 nm via hydrothermal ex-situ method at 363 K for 12 h. Tetramethylammonium hydroxide (TMAOH) was used as a template, and aluminum isopropoxide and colloidal silica were used as Al and Si sources, respectively.

Fabrication and characterization of zeolite coatings on aluminum and magnesium alloys

This work presents a methodology to fabricate zeolite coating on aluminum and magnesium alloys. A procedure for coating AA 6082 aluminum and AZ31B magnesium alloys substrates with a homogeneous, adherent and anticorrosive layer of a zeolite filler embedded in a silane matrix is developed. The adhesion of the coating has been probed by scratch and shear tests. Furthermore, the coating strength at high strain rate has been tested by tensile impact testing method. Also, the corrosion resistance of the coated samples has been verified highlighting an improvement with respect to the uncoated materials. The overall results show a very good surface coverage grade and a good level of coating adhesion and strength.

Fabrication of zeolite coatings onto stainless-steel capillary tubes for supercritical hydrocarbon cracking

In tubular reactors, the pressure drop can be decreased, and the heat transfer can be enhanced by coating the catalyst on its inner-wall when compared with the performance of fixed-bed types. This study focused on preparing catalyst coatings in capillary tubes for hydrocarbon cracking. The effect of pretreatment processes on the physicochemical properties of the catalyst was studied, and the influence was negligible. In addition, the preparation process was optimized by adjusting the coating method, binder types and contents. The coating prepared using 10 wt% organic binder with an interval coating method showed optimal adhesion. The mass loss was 3.92% after thermal shock and ultrasonic oscillation treatment. During n-dodecane cracking, the gas production rate (GPR) without coating was 8.27%, while that were 31.62% and 65.42% with ZSM-5 and MFI coatings, respectively. Above all, the coatings inhibited coke formation so that the reaction could be continuously performed at 600 °C.

Effect of Oxidation Treatments of Steel Substrates on the Formation of MFI Zeolite Coatings

The surface of 316L stainless steel flat substrates has been modified by annealing in an air stream, anodizing in an acid solution, and sequential anodizing first in an acid solution and then in an alkali solution. A zeolite of the MFI structure with a Si/Al ratio = 20, 80, or ∞ has been crystallized onto the initial and modified substrates under hydrothermal conditions. The morphology and chemical and phase compositions of the initial and modified substrates and the synthesized zeolite layer have been studied using XRD, SEM, EDS, and XPS methods. On the substrates anodized in the acid solution, a uniform continuous coating with zeolite crystals with a Si/Al ratios of 80 and ∞ is observed as early as after 3 h of crystallization, and further crystallization only leads to an increase in the thickness of the zeolite layer, whereas a continuous layer of the zeolite phase in the case of Si/Al = 20 is observed as late as after 20 h of crystallization. On the unmodified substrates annealed in an air stream and anodized in an alkali solution, a continuous zeolite coating is not formed after 20 h of crystallization.

Corrosion-Resistant Hydrophobic MFI-Type Zeolite-Coated Mesh for Continuous Oil–Water Separation

Efficient separation of oil–water mixtures has become a critical challenge due to frequent oil-spill accidents and enormous release of oil-containing wastewater by households or catering services. Superhydrophobic coatings on metal meshes have been evidenced as the effective and energy-saving materials for oil–water separation. However, it is difficult to fabricate the separating coatings with long-term superhydrophobicity and the outstanding anticorrosion properties for practical application. In this study, we fabricated the hydrophobic Mobil five (MFI)-type zeolite coatings on the pristine stainless steel meshes via an in situ crystallization method and subsequently modified them with an environmentally safe hexadecyltrimethoxysilane compound. The as-prepared coating meshes showed good self-cleaning, antifouling, and anticorrosion properties. Furthermore, the coated meshes were capable of continuously and efficiently separating different kinds of oil–water mixtures under gravity-driven pressure and had more than 99.0% high separation efficiency. More important, the prepared hydrophobic MFI-coated meshes had equivalent separation performance compared to that of superhydrophobic coating meshes. Meanwhile, the hydrophobic MFI-coated meshes demonstrated excellent reusability performance and long-term stability. These as-prepared meshes thus have great potential for applications in separating oily wastewater from oil fields as well as recycling of waste oil from catering services.

Antibacterial effects of silver incorporated zeolite coatings on 3D printed porous stainless steels.

Functionalization of porous metals with antibacterial coatings is hotly pursued in recent decade. Here we fabricated a highly porous stainless steel component by selective laser melting and then coated with silver incorporated zeolite by in situ hydrothermal crystallization method. The morphology of their surface was investigated by scanning electron microscopy. The inhibition of Escherichia coli and Staphylococcus aureus were identified by bacterial viability studies after 24h of incubation. More importantly, the obtained coatings show better osteointegration by spreading bone marrow stromal cells (BMSCs) after cultured with different scaffold extract solutions for 1, 3, and 5days. These results suggest that silver incorporated zeolite coatings on 3D printed porous stainless steels exhibit better antibacterial activity and biocompatibility, showing potential application in the field of medical implant materials.

SAPO-34 based zeolite coatings for adsorption heat pumps

In this work, at first, an overview on SAPO-34 zeolite coating for adsorption heat pumps is presented, highlighting current quality standard and open technological issues (i.e. the need for good mechanical and hydrothermal stability, high aging stability, etc.). Afterwards, we present an improved formulation of adsorbent composite coatings on aluminum support, having improved thermal and mechanical properties, especially when subjected to an impulsive stress. Specifically, the coated samples were prepared by dip-coating method starting from a water suspension of SAPO-34 zeolite and a hybrid polymer binder. Adhesive and mechanical properties were evaluated by pull-off test confirming the good interaction between metal substrate, filler and matrix. Adsorption equilibrium of water vapor on the adsorbent coating was measured in the range T = 30–150 °C and partial pressure of moisture equal to 11 mbar. It was found that binder does not affect the water adsorption capacity and adsorption rate of the original SAPO-34 zeolite.

Wetting Properties and Thin-Film Quality in the Wet Deposition of Zeolites.

Zeolites are microporous crystalline materials widely used in catalysis and adsorption applications. The fabrication of zeolite thin films and membranes has also opened up the possibility of using zeolites in electronic devices and membrane separations. The existing approach to growing zeolite films involves exposing the substrate to a high-pH environment; however, this process is applicable to only specific types of substrates. Our group has developed the direct wet deposition of zeolites via ultrasonic nozzle spray deposition to address this issue; however, the relationship between wetting properties and thin-film quality has yet to be investigated. In this study, we prepared zeolite CHA (Si:Al:P = 3:10:20) suspensions using different solvents and surfactants in various concentrations. We then examined the relationships among the composition of the cast solution, their wetting behavior on the glass substrate, and the uniformity of the resulting thin films. We found that using ethanol as a solvent with zeolite crystals in low concentrations with added surfactant yielded zeolite films of high quality. We were also able to produce low-haze zeolite coatings on glass. The zeolite coatings with high hydrophilicity and adsorption capacity presented excellent antifogging capability.

A Brief Overview on the Anticorrosion Performances of Sol-Gel Zeolite Coatings

Research activity concerning nanoporous zeolites has grown considerably in recent decades. The structural porosity of zeolites provides versatile functional properties such as molecular selectivity, ion and molecule storage capacity, high surface area, and pore volume which combined with excellent thermal and chemical stability can extend its application fields in several industrial sectors. In such a context, anti-corrosion zeolite coatings are an emerging technology able to offer a reliable high performing and environmental friendly alternative to conventional chromate-based protective coatings. In this article, a focused overview on anti-corrosion performances of sol-gel composite zeolite coatings is provided. The topic of this review is addressed to assess the barrier and self-healing properties of composite zeolite coating. Based on results available in the literature, a property–structure relationship of this class of composites is proposed summarizing, furthermore, the competing anti-corrosion active and passive protective mechanisms involved during coating degradation. Eventually, a brief summary and a future trend evaluation is also reported.

High-Power Adsorption Heat Pumps Using Magnetically Aligned Zeolite Structures.

Adsorption heat pumps offer a clean, zero-emission technology for universally applicable cooling or heating utilizing water as a refrigerant and waste or renewable heat as driving energy instead of electricity. Despite their attractive environmentally friendly prospects, the broader application of such classes of heat pumps has not yet been possible, mainly because of the low power density of adsorption heat exchangers and the corresponding large size and high cost of the adsorption heat pumps. We report an inexpensive route for the fabrication of zeolite coatings with high adsorption power density based on the bottom-up assembly of colloids directed by magnetic and capillary forces. Such an assembly process relies on the chaining of oil droplets under an external magnetic field during deposition of the coating, followed by the formation of a percolating network of bridged adsorbent particles upon drying. This results in vertically open channels and thermal bridges that facilitate directed mass and heat transport across the structured zeolite coating during sorption cycles. By reaching up to 3.3-fold higher performance than their unstructured counterparts using readily available zeolite as an adsorbent material, the architectured coatings produced through this facile, upscalable approach hold great potential for next-generation adsorption heat pumps.

Dielectric properties and temperature dependency of automotive catalyst coatings and substrate materials: Experimental results, influences and approximation approach

For the radio frequency-based catalyst state monitoring of SCR catalysts, the dielectric properties of the used SCR catalyst materials are essential to design the measurement system and to adjust it to the given conditions. This work focuses on the experimental determination of the effective complex dielectric properties of zeolite coatings on cordierite substrates and the approximation of the latter to describe and transfer these systems in an easier manner. Therefore, different influences were investigated to approximate the real and the imaginary part of the complex permittivity of zeolite coatings on cordierite substrates.

Long-Term Stability against H2S Poisoning on Pd Composite Membranes by Thin Zeolite Coatings

Parts per million levels of H2S can lead to fast deactivation of Pd-based membranes due to preferential adsorption on the membrane surface or the formation of metal sulfides. This study provides an...

Ion exchange of zeolite coatings for adsorption heat pump applications

Coatings of NaA and NaX zeolites with various thicknesses were grown by direct crystallization on stainless steel plates. As a next step, ion exchange was applied to obtain the Li forms of the coatings. The materials obtained were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), inductively coupled plasma (ICP), thermal gravimetry (TG), and N2 adsorption. The stabilities of the coatings in the ion exchange process were also determined. Li+ ions were observed to be readily exchanged with Na+ ions in zeolite coatings of various thicknesses but the percentage of exchange did not attain 100%. Favorable ion exchange conditions for obtaining both zeolite LiNaA and LiNaX coatings were determined. After Li exchange, the surface area of zeolite X increased by about 56% while the water capacities of zeolites X and A were enhanced by about 15 and 14%, respectively, for the conditions investigated. The ion exchange process resulted in some detachment from the coatings, which increased with enhanced coating thickness. Significant improvement was obtained in coating stability by using plates with roughened surfaces. Zeolite coatings in Li form may improve the performances of adsorption heat pumps, provided that relatively thick coatings remain stable to a desired extent during ion exchange.

Improving biocompatibility of titanium alloy scaffolds by calcium incorporated silicalite-1 coatings

Zeolite coatings with excellent biocompatibility have been developed on Ti6Al4V alloys to improve their bioactive and corrosion resistance. In this work, pure silica zeolite silicalite-1 without harmful ions (Al and V) was prepared on titanium alloy scaffolds by secondary growth method. The obtained coatings were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), water contact angle measurement, and corrosion resistance measurements. Silicalite-1 coatings significantly enhanced the attachment and proliferation of rabbit bone marrow mesenchymal stem cells. Additionally, the alizarin red staining showed that calcium incorporated silicalite-1 coatings promote the formation of mineralized nodules. More importantly, silicalite-1 coatings can be also modified on the third-generation titanium alloys, exhibiting excellent application prospect in biomedical field.

Iodine detection in Ag-mordenite based sensors: Charge conduction pathway determinations

Abstract Detection of radiological iodine gas after nuclear accidents or in nuclear fuel reprocessing is necessary for the safety of human life and the environment. The development of sensors for the detection of iodine benefits from the incorporation of nanoporous materials with high selectivity for I2 from common competing gases in air. Silver mordenite zeolite (Ag-MOR) is widely-used material for capture of gaseous iodine (I2). Herein, thin film zeolite coatings were applied to Pt interdigitated electrodes (IEDs) to fabricate iodine gas sensors with direct electrical readout responses. Correlations between occluded ion, exposure to iodine gas, resultant AgI nanoparticle polymorphs and location in zeolite with resultant impedance spectroscopy (IS) properties are described. Furthermore, IS is leveraged to elucidate the changes in charge conduction pathways as determined by the cation-zeolite film incorporated in the sensor. Silver mordenite reveals a significant change in impedance upon exposure to gaseous I2 at 70 °C, and the magnitude and direction of the response is dependent on whether the Ag+-mordenite is reduced (Ag0) before I2 exposure. An equivalent circuit model is developed to describe the movement of charge along the surface and through the pores of the mordenite grains. Relative changes in the impedance of these conduction pathways are related to the chemical changes from Ag+ or Ag0 to resultant AgI polymorph phase. Together, these results inform design of a compact Ag-mordenite sensor for direct electrical detection of gaseous I2.

Anticorrosion Behavior of Zeolite Coatings Obtained by In Situ Crystallization: A Critical Review.

Zeolites are crystalline nanoporous aluminosilicates. Thanks to their intrinsically nanoporous structure they are widely used as molecular sieves, for exchanging ions, or, also thanks to the high surface area of these structures, for catalytic applications. Furthermore, thanks to their thermal and chemical stability, in recent years zeolite coatings have been evaluated for application as anti-corrosion coatings. The non-toxicity of this class of coatings makes it possible that they will be an environmentally friendly alternative to conventional chromate-based coatings. This article provides a brief review of the anti-corrosion performance of zeolite coatings, applied by direct synthesis technique to several metals and alloys, as discussed in the literature. After a short description of the microstructure and properties of zeolites, the discussion addresses the research activities related to this topic, as reported in the literature. Comparative analysis of literature results supported the dry-gel conversion method as a promising approach that combines a simplified synthesis procedure with anti-corrosion coating performance. Based on these considerations, an evaluation of future trends is discussed along with the final remarks.

Tailoring the reaction mixture composition for preparing zeolite coatings on aluminum supports in alkaline environments

Various alkaline reaction mixture compositions were tested for determining their suitability to be used in the direct crystallization of zeolites on aluminum supports. No organic materials, such as templates, complexing agents, and corrosion inhibitors were included in the reaction mixtures. It was observed that aluminum supports remained quite stable in alkaline synthesis mixtures when suitable reaction mixture compositions with relatively high silica content were used. These favorable compositions might be recognized from their sodium silicate/(sodium hydroxide + sodium aluminate) mass ratios, as depicted in this study. Coatings were prepared on aluminum by using some of these compositions. It was determined that aluminum hydroxide phases commonly forming on the support could be eliminated to a great extent and consequently, crystalline coatings of zeolites P and Y were obtained on aluminum surfaces. The coatings exhibited trivial mass loss in the mechanical stability tests applied.

Sorption rate enhancement in SAPO-34 zeolite by directed mass transfer channels

The rate of water adsorption in SAPO-34 zeolite coatings for adsorption heat pumps has been shown to be limited by mass transfer. In the present contribution, uniformly spaced longitudinal channels of width 75 µm were introduced into SAPO-34 coatings and their effect on the heat and mass transport limitations during water sorption was explored. Different channel spacings at constant adsorbent mass per unit area were tested by means of temperature-swing adsorption measurements and thermal impedance analysis (TIA). The optimal ratio between the characteristic transport length (CTL) for heat transfer and the CTL for mass transfer was 6, which is in agreement with the TIA predictions and was validated experimentally. Geometries with CTL ratios greater or less than 6 exhibited higher thermal impedance and lower rates of water sorption. At the optimal CTL ratio, the water sorption rate was enhanced 2x at the same adsorbent mass per unit area when compared to unstructured SAPO-34 coatings. Compared to other adsorbent structures reported in literature, the structured coatings exhibit the highest power density and energy density at short cycle times. These findings may be used to improve efficiency and/or power in temperature-swing processes in which mass transfer in adsorbent coatings is rate-limiting. It is recommended to develop methods to structure coatings at the scales relevant for commercial adsorption heat pump modules, and further investigate the rate-limiting transport mechanisms in large adsorption heat exchanger modules.

On developing ferrisilicate catalysts supported on silicon carbide (SiC) foam catalysts for continuous catalytic wet peroxide oxidation (CWPO) reactions

Fe supported catalysts show great promise for enabling practical environmental catalysis, exemplified by the catalytic wet peroxide oxidation (CWPO) process. In order to mitigate the Fe leaching issue, a strategy of assembling zeolitic coatings with intraframework Fe (ferrisilicate) on SiC foams was developed, showing a good stability in CWPO and a low Fe leaching of 2.0 mg l−1. Direct hydrothermal synthesis of ferrisilicate/SiC foam composites was systematically studied, showing that their characteristics depend on the growth time, pH value and iron concentration of the growth solution. Selected ferrisilicate/SiC foam composite was evaluated using the continuous CWPO of phenolic aqueous solution at 60 °C. The open-cell size of SiC foam was varied between 800 and 2,000 μm and showed insignificant effect on the hydrodynamics of the flow process at 1 ml min −1, but the process efficiency in terms of phenol and total-organic-carbon (TOC) conversions was favored by a high surface-to-volume ratio (i.e. small open-cell sizes). Ferrisilicate/SiC foam catalysts (average open-cell size = 800 μm) showed good stability in the model system with the stable conversions of phenol (97%), H2O2 (84%) and TOC (37%) over 24 h time-on-stream.