Seeding-free synthesis of dense zeolite FAU membranes on 3-aminopropyltriethoxysilane-functionalized alumina supports

Fabrication of polysulfone mixed matrix membrane for wastewater treatment

Recent development in separation technologies has envisioned a green and sustainable future that encouraged energy preservation and waste minimization. The concept of a clean future emphasizes on retrieval and reutilization of valuable products from waste streams to improve the water quality. Membrane-based separations are currently explored as an auspicious substitution over traditional separation processes. The present study is designed to purify water using aluminum and gallium mixed matrix membranes from toxic metals (Lead and Mercury) and dyes (Rhodamine B, and Reactive Blue-4). Facile protocol i.e., immersion precipitation phase inversion method was used for the fabrication of mixed matrix membrane. The aluminium and gallium hybrids act as a filler and create heterogeneity and hydrophilicity within the membrane, affirming better water permeability and mechanical strength. The performance of fabricated mixed matrix membranes is evaluated using a lab-based dead-end membrane filtration unit. The result showed 30-71% rejection of Mercury, 24-65% rejection of Lead, 12-66% rejection of Reactive Blue-4, and 15-80% rejection of Rhodamine B.

Organic molecular sieve membranes for chemical separations

Molecular separations that enable selective transport of target molecules from gas and liquid molecular mixtures, such as CO2 capture, olefin/paraffin separations, and organic solvent nanofiltration, represent the most energy sensitive and significant demands. Membranes are favored for molecular separations owing to the advantages of energy efficiency, simplicity, scalability, and small environmental footprint. A number of emerging microporous organic materials have displayed great potential as building blocks of molecular separation membranes, which not only integrate the rigid, engineered pore structures and desirable stability of inorganic molecular sieve membranes, but also exhibit a high degree of freedom to create chemically rich combinations/sequences. To gain a deep insight into the intrinsic connections and characteristics of these microporous organic material-based membranes, in this review, for the first time, we propose the concept of organic molecular sieve membranes (OMSMs) with a focus on the precise construction of membrane structures and efficient intensification of membrane processes. The platform chemistries, designing principles, and assembly methods for the precise construction of OMSMs are elaborated. Conventional mass transport mechanisms are analyzed based on the interactions between OMSMs and penetrate(s). Particularly, the 'STEM' guidelines of OMSMs are highlighted to guide the precise construction of OMSM structures and efficient intensification of OMSM processes. Emerging mass transport mechanisms are elucidated inspired by the phenomena and principles of the mass transport processes in the biological realm. The representative applications of OMSMs in gas and liquid molecular mixture separations are highlighted. The major challenges and brief perspectives for the fundamental science and practical applications of OMSMs are tentatively identified.

The opportunity of membrane technology for hydrogen purification in the power to hydrogen (P2H) roadmap: a review

The global energy market is in a transition towards low carbon fuel systems to ensure the sustainable development of our society and economy. This can be achieved by converting the surplus renewable energy into hydrogen gas. The injection of hydrogen (⩽10% v/v) in the existing natural gas pipelines is demonstrated to have negligible effects on the pipelines and is a promising solution for hydrogen transportation and storage if the end-user purification technologies for hydrogen recovery from hydrogen enriched natural gas (HENG) are in place. In this review, promising membrane technologies for hydrogen separation is revisited and presented. Dense metallic membranes are highlighted with the ability of producing 99.9999999% (v/v) purity hydrogen product. However, high operating temperature (⩾300 °C) incurs high energy penalty, thus, limits its application to hydrogen purification in the power to hydrogen roadmap. Polymeric membranes are a promising candidate for hydrogen separation with its commercial readiness. However, further investigation in the enhancement of H₂/CH₄ selectivity is crucial to improve the separation performance. The potential impacts of impurities in HENG on membrane performance are also discussed. The research and development outlook are presented, highlighting the essence of upscaling the membrane separation processes and the integration of membrane technology with pressure swing adsorption technology.

Microporous framework membranes for precise molecule/ion separations

Microporous framework membranes such as metal-organic framework (MOF) membranes and covalent organic framework (COF) membranes are constructed by the controlled growth of small building blocks with large porosity and permanent well-defined micropore structures, which can overcome the ubiquitous tradeoff between membrane permeability and selectivity; they hold great promise for the enormous challenging separations in energy and environment fields. Therefore, microporous framework membranes are endowed with great expectations as next-generation membranes, and have evolved into a booming research field. Numerous novel membrane materials, versatile manipulation strategies of membrane structures, and fascinating applications have erupted in the last five years. First, this review summarizes and categorizes the microporous framework membranes with pore sizes lower than 2 nm based on their chemistry: inorganic microporous framework membranes, organic-inorganic microporous framework membranes, and organic microporous framework membranes, where the chemistry, fabrications, and differences among these membranes have been highlighted. Special attention is paid to the membrane structures and their corresponding modifications, including pore architecture, intercrystalline grain boundary, as well as their diverse control strategies. Then, the separation mechanisms of membranes are covered, such as diffusion-selectivity separation, adsorption-selectivity separation, and synergetic adsorption-diffusion-selectivity separation. Meanwhile, intricate membrane design to realize synergistic separation and some emerging mechanisms are highlighted. Finally, the applications of microporous framework membranes for precise gas separation, liquid molecule separation, and ion sieving are summarized. The remaining challenges and future perspectives in this field are discussed. This timely review may provide genuine guidance on the manipulation of membrane structures and inspire creative designs of novel membranes, promoting the sustainable development and steadily increasing prosperity of this field.

Synthesis of FAU-Type Zeolite Membranes with Antimicrobial Activity

In this study, a layer of a pure and dense phase of FAU-type zeolite was synthesized directly on the surface of α-Al₂O₃ plane macroporous support. Before hydrothermal synthesis, a step of cleaning of the support by an anionic detergent was performed, a roughness surface is created, allowing the anchoring of the zeolite nuclei and then their growth, favoring in this sense the formation of a homogeneous zeolite layer. The obtained membranes were fully characterized using X-ray diffraction analysis (XRD), nitrogen sorption, scanning electron microscopy (SEM), and mercury porosimetry. After 24 h of thermal treatment at 75 °C, a homogeneous zeolite layer composed of bipyramidal crystals of FAU-type zeolite is obtained with a thickness of about 2.5 µm. No obvious defects or cracks can be observed. It was found that the increase in heating temperature could lead to the appearance of an impurity phase, GIS-type zeolite. Then the ideal zeolite membrane was exchanged with Ag⁺ or Zn²⁺ cations to studies their antimicrobial properties. Zeolites membranes exchanged with Ag⁺ showed an agar-diffusive bactericidal activity against gram negative Escherichia coli (E. coli) bacteria. Zn²⁺ exchanged zeolite membrane presented a bacteriostatic activity that is less diffusive in agar. As expected, non-exchanged zeolite membrane (in its Na⁺ form) have no effect on bacterial activity. This process is particularly interesting for the synthesis of a good quality FAU-type zeolite membranes with antimicrobial properties.

Ultrasound-assisted synthesis of gallium hybrids for environmental remediation application

Micron-sized, rhombohedral shaped gallium hybrids with different indole derivatives (indole, 2-methyl-indole, indole-2-carboxylic acid) were successfully synthesized with precipitation method coupled with ultrasound followed by the post-grafting method. The as-synthesized hybrid materials were characterized using FTIR, SEM, XPS, XRD, and BET techniques. FTIR spectra showed characteristic absorption bands of gallium oxide and gallium hybrids at 400-700 cm^-1 and 1400-1600 cm^-1. SEM, XRD, and BET showed that ultrasound-assisted gallium micro-particles are porous, crystalline possessing high surface to volume ratio as compared to that synthesized in the absence of ultrasound. Survey scan of XPS revealed the presence of gallium, oxygen, nitrogen, and carbon. The as-synthesized gallium hybrids were applied as a potential photocatalyst towards Reactive Blue 4 (model pollutant) using batch adsorption experiment under visible light. It showed maximum 30-65% degradation within two hours and followed a pseudo-first-order kinetic model with R² > 0.9.

Dense and thin 13X membranes on porous α-Al2O3 tubes: preparation, structure and deep purification of oxygenated compounds from gaseous olefin flow

The low contact efficiency, large mass transfer resistance and high operational cost of traditional 13X molecular sieve particle adsorbents (MSPs) have greatly limited their application in deep purification of trace oxygenated compounds from gaseous olefins. Herein, we successfully fabricated dense and thin 13X molecular sieve membranes on a porous α-Al₂O₃ tube (MSCMs) by a combination of 3-aminopropyl triethoxy silane (APTES) surface modification and vacuum pre-coating sol technology for purifying the above impurities. By a solid–solution transformation process, 13X molecular sieve membranes on MSCMs that were continuous and integral without any cracks, pinholes or other defects, and mainly composed of 1–1.5 μm regular 13X crystals with a thickness of 5–6 μm have been achieved. The purification performance of the MSPs, non-APTES functionalized MSCMs (nMSCMs) and MSCMs was evaluated by dynamic adsorption of N₂ or C₂H₄ feed flow containing dimethyl ether, methanol and propanal impurities at room temperature. The results demonstrated that both the nMSCMs and MSCMs could deeply purify the trace amounts of the three oxygenated compounds to below 1 × 10⁻⁶ (mol mol⁻¹) from gaseous olefins at an initial concentration of 20 × 10⁻⁶ (mol mol⁻¹), exhibiting much more excellent purification performance than that of MSPs. In particular, the breakthrough times of MSCMs for dimethyl ether, methanol and propanal were 7 h, 32 h and 51 h in a N₂ system, and 12.1 h, 53 h and 90 h in a C₂H₄ system. The cumulative adsorption amounts of MSCMs for dimethyl ether, methanol and propanal were 12.108 mg g⁻¹, 35.812 mg g⁻¹ and 103.129 mg g⁻¹ in a N₂ system, and 25.88 mg g⁻¹, 94.19 mg g⁻¹ and 256.26 mg g⁻¹ in a C₂H₄ system, respectively. The regeneration experiment also indicated that the MSCMs had a more stable structure and a longer lifetime. The excellent purification performance of MSCMs could be attributed to the continuous 13X molecular sieve layers without non-adsorption interfacial voids. Hence, the MSCMs have great potential for future industrial application of trace oxygenated compound removal from gaseous olefins.

Dense and thin 13X molecular sieve membranes on porous α-Al₂O₃ tubes were successfully fabricated by a combination of 3-aminopropyl triethoxy silane surface modification and vacuum pre-coating sol for purifying trace oxygenated compounds from gaseous olefins.

Synthesis of zeolite membranes on calcium silicate support and their bioactive response

The synthesis of calcium silicate supported zeolite membrane was carried out by second growth method. The chemical nature of the functionalizing agent on the formation of homogenous zeolite membrane was evaluated. One monomer and two cationic polymers were used: 3-aminopropyltriethoxysilane (APS), polyethylenimine (PEI) and polydiallyldimethylammonium chloride (PDDA). The support was subjected to chemical functionalization and then it was rubbed with zeolite crystals. The W zeolite was used as zeolite seed in two different Si/Al ratios. The functionalized and rubbed supports were submitted to hydrothermal treatment at 150 °C for 48 h. The bioactivity of the homogeneous zeolite membranes was evaluated by the biomimetic method through the membranes soaking in a simulated body fluid (SBF) at 37 °C for 21 days. Two immersion methods were evaluated. The products were characterized by XRD and SEM techniques. The results indicated that the supported functionalization with PDDA and the Si/Al ratio (higher than 1.8) of zeolite enhanced the interaction between the support and the zeolite precursor enhancing the formation of homogeneous zeolite membrane on the surface. The presence of the functional groups of PDDA on the membrane was detected by FTIR. After immersion in SBF, the zeolite membrane was stable and led to the formation of Ca-P layer on its surface. The re-immersion method led to the formation of richer Ca/P layer (1.36). These findings allowed generating a zeolite membrane with combined properties of calcium silicate and the controllable porosity of zeolitic material making it potentially useful for bone regeneration and drug releasing.

Synthesis of a ZSM-5/NaA hybrid zeolite membrane using kaolin as a modification layer

A kaolin modification layer, which makes the surface of the support smooth and covers the defects on the support, not only attracts Si/Al active materials to the surface of the ceramic tube, but also dissolves under alkaline conditions to assist the growth of zeolite membranes.

Tunable molecular separation by nanoporous membranes

Metal-organic frameworks offer tremendous potential for efficient separation of molecular mixtures. Different pore sizes and suitable functionalizations of the framework allow for an adjustment of the static selectivity. Here we report membranes which offer dynamic control of the selectivity by remote signals, thus enabling a continuous adjustment of the permeate flux. This is realized by assembling linkers containing photoresponsive azobenzene-side-groups into monolithic, crystalline membranes of metal-organic frameworks. The azobenzene moieties can be switched from the trans to the cis configuration and vice versa by irradiation with ultraviolet or visible light, resulting in a substantial modification of the membrane permeability and separation factor. The precise control of the cis:trans azobenzene ratio, for example, by controlled irradiation times or by simultaneous irradiation with ultraviolet and visible light, enables the continuous tuning of the separation. For hydrogen:carbon-dioxide, the separation factor of this smart membrane can be steplessly adjusted between 3 and 8.

The tunable pore size and functionalization of metal-organic frameworks offers great potential for efficient and selective separation of molecular mixtures. Here, the authors report a metal-organic membrane containing photoresponsive linkers which offers a dynamic control of selectivity by remote signals

Cross flow ultrafiltration of Cr (VI) using MCM-41, MCM-48 and Faujasite (FAU) zeolite-ceramic composite membranes

This work describes the removal of Cr (VI) from aqueous solution in cross flow mode using MCM-41, MCM-48 and FAU zeolite membranes prepared on circular shaped porous ceramic support. Ceramic support was manufactured using locally available clay materials via a facile uni-axial compaction method followed by sintering process. A hydrothermal technique was employed for the deposition of zeolites on the ceramic support. The porosity of ceramic support (47%) is reduced by the formation of MCM-41 (23%), MCM-48 (22%) and FAU (33%) zeolite layers. The pore size of the MCM-41, MCM-48 and FAU membrane is found to be 0.173, 0.142, and 0.153 μm, respectively, which is lower than that of the support (1.0 μm). Cross flow ultrafiltration experiments of Cr (VI) were conducted at five different applied pressures (69-345 kPa) and three cross flow rates (1.11 × 10(-7) - 2.22 × 10(-7) m(3)/s). The filtration studies inferred that the performance of the fabricated zeolite composite membranes is optimum at the maximum applied pressure (345 kPa) and the highest rejection is obtained with the lowest cross flow rate (1.11 × 10(-7) m(3)/s) for all three zeolite membrane. The permeate flux of MCM-41, MCM-48 and FAU zeolite composite membranes are almost remained constant in the entire duration of the separation process. The highest removal of 82% is shown by FAU membrane, while MCM-41 and MCM-48 display 75% and 77% of Cr (VI) removal, respectively for the initial feed concentration of 1000 ppm with natural pH of the solution at an applied pressure of 345 kPa.

A graphene oxide layer as an acid-resisting barrier deposited on a zeolite LTA membrane for dehydration of acetic acid

A graphene oxide layer (GO) was deposited as acid-resisting barrier to avoid the degradation of zeolite LTA membrane by acetic acid, leading to a high selectivity and stability of the zeolite LTA membrane for the dehydration of acetic acid.

Bendable Zeolite Membranes: Synthesis and Improved Gas Separation Performance

Separation and sequestration of CO2 emitted from fossil energy fueled electric generating units and industrial facilities will help in reducing anthropogenic CO2, thereby mitigating its adverse climate change effects. Membrane-based gas separation has the potential to meet the technical challenges of CO2 separation if high selectivity and permeance with low costs for large-scale manufacture are realized. Inorganic zeolite membranes in principle can have selectivity and permeance considerably higher than polymers. This paper presents a strategy for zeolite growth within the pores of a polymer support, with crystallization time of an hour. With a thin coating of 200-300 nm polydimethylsiloxane (PDMS) on the zeolite-polymer composite, transport data for CO2/N2 separation indicate separation factors of 35-45, with CO2 permeance between 1600 and 2200 GPU (1 GPU = 3.35 × 10(-10) mol/(m(2) s Pa)) using dry synthetic mixtures of CO2 and N2 at 25 °C. The synthesis process results in membranes that are highly reproducible toward transport measurements and exhibit long-term stability (3 days). Most importantly, these membranes because of the zeolite growth within the polymer support, as contrasted to conventional zeolite growth on top of a support, are mechanically flexible.

Microwave synthesis of high-flux NaY zeolite membranes in fluoride media

High-flux NaY zeolite membranes were synthesized using low-cost mullite supports by microwave heating in fluoride media.

Mussel-inspired polydopamine modification of supports for the facile synthesis of zeolite LTA molecular sieve membranes

Inspired by bio-adhesive ability of marine mussel, a versatile and effective synthesis strategy was developed to prepare dense zeolite LTA membranes.

Stepwise synthesis of sandwich-structured composite zeolite membranes with enhanced separation selectivity

Sandwich-structured composite zeolite membranes with enhanced hydrogen selectivity were prepared on porous α-Al(2)O(3) supports by using 3-aminopropyltriethoxysilane as an interlayer.