Effect of ZIF-71 Particle Size on Free-Standing ZIF-71/PDMS Composite Membrane Performances for Ethanol and 1-Butanol Removal from Water through Pervaporation

Separation of n-Butanol from Aqueous Solutions via Pervaporation Using PDMS/ZIF-8 Mixed-Matrix Membranes of Different Particle Sizes

The use of mixed matrix membranes (MMMs) to facilitate the production of biofuels has attracted significant research interest in the field of renewable energy. In this study, the pervaporation separation of butanol from aqueous solutions was studied using a series of MMMs, including zeolitic imidazolate frameworks (ZIF-8)-polydimethylsiloxane (PDMS) and zinc oxide-PDMS mixed matrix membranes. Although several studies have reported that mixed matrix membranes incorporating ZIF-8 nanoparticles showed improved pervaporation performances attributed to their intrinsic microporosity and high specific surface area, an in-depth study on the role of ZIF-8 nanoparticle size in MMMs has not yet been reported. In this study, different average sizes of ZIF-8 nanoparticles (30, 65, and 80 nm) were synthesized, and the effects of particle size and particle loading content on the performance of butanol separation using MMMs were investigated. Furthermore, zinc oxide nanoparticles, as non-porous fillers with the same metalcore as ZIF-8 but with a very different geometric shape, were used to illustrate the importance of the particle geometry on the membrane performance. Results showed that small-sized ZIF-8 nanoparticles have better permeability and selectivity than medium and large-size ZIF-8 MMMs. While the permeation flux increased continuously with an increase in the loading of nanoparticles, the selectivity reached a maximum for MMM with 8 wt% smaller-size ZIF-8 nanoparticle loading. The flux and butanol selectivity increased by 350% and 6%, respectively, in comparison to those of neat PDMS membranes prepared in this study.

Enhanced Desulfurization Performance of ZIF-8/PEG MMMs: Effect of ZIF-8 Particle Size

Constructing efficient and continuous transport pathways in membranes is a promising and challenging way to achieve the desired performance in the pervaporation process. The incorporation of various metal-organic frameworks (MOFs) into polymer membranes provided selective and fast transport channels and enhanced the separation performance of polymeric membranes. Particle size and surface properties are strongly related to the random distribution and possible agglomeration of MOFs particles, which may lead to poor connectivity between adjacent MOFs-based nanoparticles and result in low-efficiency molecular transport in the membrane. In this work, ZIF-8 particles with different particle sizes were physically filled into PEG to fabricate mixed matrix membranes (MMMs) for desulfurization via pervaporation. The micro-structures and physi-/chemical properties of different ZIF-8 particles, along with their corresponding MMMs, were systematically characterized by SEM, FT-IR, XRD, BET, etc. It was found that ZIF-8 with different particle sizes showed similar crystalline structures and surface areas, while larger ZIF-8 particles possessed more micro-pores and fewer meso-/macro-pores than did the smaller particles. ZIF-8 showed preferential adsorption for thiophene rather than n-heptane molecules, and the diffusion coefficient of thiophene was larger than that of thiophene in ZIF-8, based on molecular simulation. PEG MMMs with larger ZIF-8 particles showed a higher sulfur enrichment factor, but a lower permeation flux than that found with smaller particles. This might be ascribed to the fact that larger ZIF-8 particles provided more and longer selective transport channels in one single particle. Moreover, the number of ZIF-8-L particles in MMMs was smaller than the number of smaller ones with the same particle loading, which might weaken the connectivity between adjacent ZIF-8-L nanoparticles and result in low-efficiency molecular transport in the membrane. Moreover, the surface area available for mass transport was smaller for MMMs with ZIF-8-L particles due to the smaller specific surface area of the ZIF-8-L particles, which might also result in lower permeability in ZIF-8-L/PEG MMMs. The ZIF-8-L/PEG MMMs exhibited enhanced pervaporation performance, with a sulfur enrichment factor of 22.5 and a permeation flux of 183.2 g/(m^-2·h^-1), increasing by 57% and 389% compared with the results for pure PEG membrane, respectively. The effects of ZIF-8 loading, feed temperature, and concentration on desulfurization performance were also studied. This work might provide some new insights into the effect of particle size on desulfurization performance and the transport mechanism in MMMs.

Electrospun rhodamine@MOF/polymer luminescent fibers with a quantum yield of over 90

Tailored luminescent guest@metal-organic framework (Guest@MOF) materials with outstanding photophysical properties are enabling materials for emergent technologies in smart sensors and optoelectronics. However, the practical utility of Guest@MOF currently is impaired by its poor stability and difficult-to-handle powder form. Here, we combine a luminescent-sensing Guest@MOF system with a non-luminescent polymer matrix and, for the first time, demonstrated the easy-to-apply electrospinning of luminescent fibers comprising nanocrystals of RhB@ZIF-71 (rhodamine B@zeolitic imidazolate framework-71) homogeneously dispersed in a polyvinylidene difluoride (PVDF) matrix. The luminescence of RhB@ZIF-71/PVDF fiber is tunable and exhibits a quantum yield exceeding 90%. Compared with RhB fluorophore in PVDF fiber, the ZIF-71 (host) protects the nanoconfined RhB guest molecules (especially the J-aggregates of RhB), giving the composite fiber its unique thermofluorochromic response and enhanced thermal stability to 200°C. Our results reveal the exciting opportunities for implementing electrospun luminescent fibers functionalized with bespoke Guest@MOF nanocrystals for multifunctional device applications.

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Thermofluorochromic fibers incorporating Guest@MOF engineered by electrospinning

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J-aggregates of rhodamine B (RhB) interact through adjacent ZIF-71 nanocrystals

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RhB@ZIF-71/PVDF fiber has a quantum yield exceeding 90%

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ZIF-71 host enhances the thermal stability of nanoconfined RhB guest

A Review on Mixed Matrix Membranes for Solvent Dehydration and Recovery Process

Solvent separation and dehydration are important operations for industries and laboratories. Processes such as distillation and extraction are not always effective and are energy-consuming. An alternate approach is offered by pervaporation, based on the solution-diffusion transport mechanism. Polymer-based membranes such as those made of Polydimethylsiloxane (PDMS) have offered good pervaporation performance. Attempts have been made to improve their performance by incorporating inorganic fillers into the PDMS matrix, in which metal-organic frameworks (MOFs) have proven to be the most efficient. Among the MOFs, Zeolitic imidazolate framework (ZIF) based membranes have shown an excellent performance, with high values for flux and separation factors. Various studies have been conducted, employing ZIF-PDMS membranes for pervaporation separation of mixtures such as aqueous-alcoholic solutions. This paper presents an extensive review of the pervaporation performance of ZIF-based mixed matrix membranes (MMMs), novel synthesis methods, filler modifications, factors affecting membrane performance as well as studies based on polymers other than PDMS for the membrane matrix. Some suggestions for future studies have also been provided, such as the use of biopolymers and self-healing membranes.

Epoxy Functional Composites Based on Lanthanide Metal-Organic Frameworks for Luminescent Polymer Materials

The integration of metal-organic frameworks (MOF) into organic polymers represents a direct and effective strategy for developing innovative composite materials that combine the exceptional properties of MOFs with the robustness of organic polymers. However, the preparation of MOF@polymer hybrid composites requires an efficient dispersion and interaction of MOF particles with polymer matrices, which remains a significant challenge. In this work, a new simple and direct approach was applied for the development of Ln-MOF@polymer materials. A series of Ln-MOF@TGIC composites {Ln-MOF = [Ln(μ₃-BTC)(H₂O)₆]_n (Ln-BTC), where Ln = Eu, Tb, Eu_0.05Tb_0.95; H₃BTC = 1,3,5-benzenetricarboxylic acid; TGIC = triglycidyl isocyanurate} were successfully obtained by applying a grinding method via the chemical bonding between uncoordinated carboxylate groups in Ln-BTC and epoxy groups in TGIC. The Ln-BTC@TGIC materials possess significant fluorescence characteristics with superior emission lifetimes and quantum yields if compared to parent Ln-MOFs. Interestingly, under the UV irradiation, a considerable color change from yellow in Eu_0.05Tb_0.95-BTC to red in Eu_0.05Tb_0.95-BTC@TGIC was observed. The energy-transfer mechanism was also rationalized by the density functional theory (DFT) calculations. The developed Ln-BTC@TGIC composites were further applied as functional fluorescent coatings for the fabrication, via a simple spraying method, of the flexible polyimide (PI) films, Ln-BTC@TGIC@PI. Thus, the present work unveils a new methodology and expands its applicability for the design and assembly of stable, multicomponent, and soft polymer materials with remarkable fluorescence properties.

Membranes for bioethanol production by pervaporation

BACKGROUND

Bioethanol as a renewable energy resource plays an important role in alleviating energy crisis and environmental protection. Pervaporation has achieved increasing attention because of its potential to be a useful way to separate ethanol from the biomass fermentation process.

RESULTS

This overview of ethanol separation via pervaporation primarily concentrates on transport mechanisms, fabrication methods, and membrane materials. The research and development of polymeric, inorganic, and mixed matrix membranes are reviewed from the perspective of membrane materials as well as modification methods. The recovery performance of the existing pervaporation membranes for ethanol solutions is compared, and the approaches to further improve the pervaporation performance are also discussed.

CONCLUSIONS

Overall, exploring the possibility and limitation of the separation performance of PV membranes for ethanol extraction is a long-standing topic. Collectively, the quest is to break the trade-off between membrane permeability and selectivity. Based on the facilitated transport mechanism, further exploration of ethanol-selective membranes may focus on constructing a well-designed microstructure, providing active sites for facilitating the fast transport of ethanol molecules, hence achieving both high selectivity and permeability simultaneously. Finally, it is expected that more and more successful research could be realized into commercial products and this separation process will be deployed in industrial practices in the near future.

Polypropylene/Polyvinyl Alcohol/Metal-Organic Framework-Based Melt-Blown Electrospun Composite Membranes for Highly Efficient Filtration of PM2.5

Particulate matter 2.5 (PM2.5) has become a public hazard to people's lives and health. Traditional melt-blown membranes cannot filter dangerous particles due to their limited diameter, and ultra-fine electrospinning fibers are vulnerable to external forces. Therefore, creating highly efficient air filters by using an innovative technique and structure has become necessary. In this study, a combination of polypropylene (PP) melt-blown and polyvinyl alcohol (PVA)/zeolite imidazole frameworks-8 (ZIF-8) electrospinning technique is employed to construct a PP/PVA/ZIF-8 membrane with a hierarchical fibrous structure. The synergistic effect of hierarchical fibrous structure and ZIF-8 effectively captures PM2.5. The PP/PVA composite membrane loaded with 2.5% loading ZIF-8 has an average filtration efficacy reaching as high as 96.5% for PM2.5 and quality factor (Qf) of 0.099 Pa-1. The resultant membrane resists 33.34 N tensile strength and has a low pressure drop, excellent filtration efficiency, and mechanical strength. This work presents a facile preparation method that is suitable for mass production and the application of membranes to be used as air filters for highly efficient filtration of PM2.5.

Dye-Encapsulated Zeolitic Imidazolate Framework (ZIF-71) for Fluorochromic Sensing of Pressure, Temperature, and Volatile Solvents

Luminescent metal-organic frameworks (MOFs) offer a multifunctional platform for creating noninvasive sensors and tunable optoelectronics. However, fluorochromic materials that are photophysically resilient and show high sensitivity toward different physical and chemical stimuli are scarce. We report a facile host-guest nanoconfinement strategy to construct a fluorescent hybrid material with multiple sensing capabilities. We design and fabricate a new Guest@MOF material: comprising a zeolitic MOF (ZIF-71) as a nanoporous host for encapsulating rhodamine B (RhB dye) guest molecules, resulting in an RhB@ZIF-71 system with mechanochromic, thermochromic, and solvatochromic sensing response. The fluorochromic sensing properties stem from the nanoconfinement effect that ZIF-71 imposes on RhB monomers, yielding the H- or J-type aggregates with tunable photophysical and photochemical properties. For mechanochromism, the external pressure causes an emission red shift in a linear fashion, switching RhB guests from H-type to J-type aggregates through a shear deformation. For thermochromism, we demonstrate a linear scaling as a function of temperature due to the spatial restriction imposed on J-type aggregates incarcerated in ZIF-71 pores. Harnessing the solvatochromism of RhB@ZIF-71, we interrogated its photochemical response by employing three diverse groups of volatile organic compounds. The multimodal sensing response paved the way to smart applications like photonic pressure sensors, noninvasive thermometers, and ultrasensitive chemosensors.

Recent trends in integrated bioprocesses: aiding and expanding microbial biofuel/biochemical production

Microbial biosynthesis of fuels and chemicals represents a promising route for their renewable production. Product toxicity, however, represents a common challenge limiting the efficacy of this approach. Integrated bioprocesses incorporating in situ product separation are poised to help address this intrinsic problem, but suffer their own unique shortcomings. To improve and expand the utility of this versatile bioprocessing strategy, recent innovations have focused on developing more effective separation materials and novel process configurations, as well as adapting designs to accommodate semi-continuous modes of operation. As a result, integrated bioprocesses are finding new applications to aid the biosynthesis of an ever-growing list of bioproducts. Emerging applications, meanwhile, are exploring the further expansion of such designs to interface microbial and chemical catalysts, leading to new and versatile routes for the one-pot synthesis of an even greater diversity of renewable products.