Zeolitic imidazolate frameworks (ZIFs), a subclass of metal–organic frameworks (MOFs) built with tetrahedral metal ions and imidazolates, offer permanent porosity and high thermal and chemical ...stabilities. While ZIFs possess some attractive physical and chemical properties, it remains important to enhance their functionality for practical application. Here, an overview of the extensive strategies which have been developed to improve the functionality of ZIFs is provided, including linker modifications, functional hybridization of ZIFs via the encapsulation of guest species (such as metal and metal oxide nanoparticles and biomolecules) into ZIFs, and hybridization with polymeric matrices to form mixed matrix membranes for industrial gas and liquid separations. Furthermore, the developed strategies for achieving size and shape control of ZIF nanocrystals are considered, which are important for optimizing the textural characteristics as well as the functional performance of ZIFs and their derived materials/hybrids. Moreover, the recent trends of using ZIFs as templates for the derivation of nanoporous hybrid materials, including carbon/metal, carbon/oxide, carbon/sulfide, and carbon/phosphide hybrids, are discussed. Finally, some perspectives on the potential future research directions and applications for ZIFs and ZIF‐derived materials are offered.
Zeolitic imidazolate frameworks (ZIFs), offer permanent porosity and high thermal and chemical stabilities. The developed strategies for enhancing the functionality of ZIFs, including linker functionalization and hybridization with guest species and polymers, are discussed. Finally, the utilization of ZIFs as templates for fabricating nanoporous hybrid materials and the future trends and prospects in the functionalization of ZIFs are examined.
Functionalization of polyvinylidene fluoride (PVDF) was carried out by two different methodology namely, aza‐Michael addition and free radical reaction from the dehydrofluorinated PVDF. ...Functionalization agents like 2MI, CR, and indole were grafted onto KOH treated PVDF via aza‐Michael addition reaction whereas MAH and MI were grafted onto the same via free radical reaction. The functionalized PVDF was characterized by FTIR, DSC, TGA, WCA measurement, SEM, and EDX. Further, the MAH grafted PVDF was doped with V2O5 nanoparticles to form a catalytic membrane. Transesterification reaction (TER) was done using the PVDF‐g‐MAH/V2O5 membrane but ended with negative results due to the low residential time. Hence, it was done in a conventional technique in the presence of pieces of membrane material as a template. The product with the red shift in the absorbance spectrum confirmed the TER.
Efficient use of solar energy for desalination is one strategy to solve the world's water scarcity issues. In this work, a dual functional, omniphobic−photothermal nanocomposite membrane was ...developed to achieve wetting resistance and low energy consumption in desalination by direct solar membrane distillation (DSMD). The membrane was prepared by forming a hierarchical structure of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS17) modified carbon black (CB) nanoparticles (NPs) on a polyvinylidene fluoride (PVDF) membrane surface. The fluorinated CB NPs absorbed sun light to provide localized heating for DSMD, which increased membrane flux by 25% upon simulated solar irradiation at one sun unit. The utilization efficiency of solar energy in the DSMD process, 75.4%, is more than one order of magnitude higher than the energy efficiency of the conventional direct contact membrane distillation process. Furthermore, the re-entrant structure formed by the CB NPs together with the hydrophobic FAS17 coating led to low surface energy and hence omniphobicity, increasing the contact angle of the 80 vol% ethanol-in-water from 0 to 94.2°. As a result, the dual functional membrane exhibited much higher resistance to wetting by surfactants. Whereas the pristine PVDF membrane was wetted by 0.2 mM SDS, SDS had no effect on the dual function membrane over the whole SDS concentration range tested (0.1–0.4 mM). The photothermal activity, improved thermal efficiency, and strong wetting resistance make the dual functional omniphobic−photothermal membrane an excellent membrane material for the DSMD process.
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•First membrane distillation membrane with omniphobic and photothermal properties.•The membrane achieves wetting-resistance and photothermal heating simultaneously.•Photothermal carbon black provides re-entrant structure for omniphobicity.
Despite much progress in the development of mixed matrix membranes (MMMs) for many advanced applications, the synthesis of MMMs without particle agglomeration or phase separation at high nanofiller ...loadings is still challenging. In this work, we synthesized nanoporous zeolitic imidazole framework (ZIF‐8) nanoparticles with a particle size of 60 nm and a pore size of 0.34 nm in water and directly added them into an aqueous solution of the organic polymer poly(vinyl alcohol) (PVA) without an intermediate drying process. This approach led to a high‐quality PVA/ZIF‐8 MMM with enhanced performance in ethanol dehydration by pervaporation. The permeability of this MMM is three times higher than that of pristine PVA, and the separation factor is nearly nine times larger than that of pristine PVA. The significantly improved separation performance was attributed to the increase in the fractional free volume in the membranes.
Homogeneous mixed‐matrix membranes (MMMs) based on poly(vinyl alcohol) (PVA) and ZIF‐8 were synthesized in water in a drying‐free process and used for ethanol dehydration by pervaporation. The permeability and the separation factor of this MMM are three and nine times higher than those of pristine PVA.
Oil spills not only cause significant economic losses; they also harm the environment. In this study, high‐melt‐strength polypropylene (HMSPP) and linear polypropylene (PP) were compounded at ...different ratios and foamed by supercritical CO2 at various temperatures and pressures to develop open‐cell foams for oil absorption applications. The experimental results show that adding HMSPP increased the foam expansion ratio and the open‐cell content and that the foam processing window widened with increasing HMSPP content. The oil absorption experiment results show that the amount of oil absorption increased with the foam expansion ratio and that low oil viscosity resulted in high oil absorption. In addition, the amount of oil absorption remained unchanged after 10 cycles of oil absorption experiments. The oil absorption kinetics study shows that the oil absorption process complied with the pseudo‐second‐order law.
Membrane distillation (MD) is a relatively less-explored membrane operation with the potential to achieve high recovery factor by using low grade heat. The current study proposes the design of a ...continuous direct contact MD process to achieve high recovery factors by using a commercial hollow fiber membrane. The design consists of multiple MD stages connected in series to achieve a predefined final solution concentration. Depending upon the outlet temperatures of feed and permeate, the design considers the option of heat recovery from permeate. Under a given set of operating conditions, there exists a module length (named as optimum module length) where the net thermal energy consumption and overall permeate productivity are optimum. The optimum module length has been analyzed as function of feed to permeate flow rate (F/P) ratio, feed temperature and concentration. It has been observed that for given feed temperature and concentration, the optimum module length can be tuned by changing F/P ratio. The minimum value of the optimum length is observed at the highest F/P ratio considered. Mathematical analysis was extended to evaluate the appropriate length and the corresponding thickness for each stage. The results reveal a strong nexus among membrane thickness, solution concentration and optimum length.
•A continuous MD process to achieve high recovery factor is proposed.•Optimum module length is analyzed as function of operating conditions and membrane thickness.•Optimum module length can be tuned by changing operating conditions.
Spectacular applications of anaerobic membrane bioreactors (AnMBRs) are emerging due to the membrane enhanced biogas production in the form of renewable bioresources. They produce similar energy ...derived from the world's depleting natural fossil energy sources while minimizing greenhouse gas (GHG) emissions. During the last decade, many types of AnMBRs have been developed and applied so as to make biogas technology practical and economically viable. Referring to both conventional and advanced configurations, this review presents a comprehensive summary of AnMBRs for biogas production in recent years. The potential of biogas production from AnMBRs cannot be fully exploited, since certain constraints still remain and these cause low methane yield. This paper addresses a detailed assessment on the potential challenges that AnMBRs are encountering, with a major focus on many inhibitory substances and operational dilemmas. The aim is to provide a solid platform for advances in novel AnMBRs applications for optimized biogas production.
•The challenges of different types of AnMBRs for biogas production are reviewed.•Advanced AnMBRs are emerging in producing good fuel quality biogas.•Various inhibitory compounds that affect biogas yield from AnMBRs are reviewed.•Operational conditions and suggestions for optimizing biogas yield are discussed.•Future opportunities of biogas production from AnMBRs are presented.
Photocatalytic membrane reactors (PMRs) have been widely used in wastewater treatment over the past few years. In this study, P-doped g-C3N4 (PCN), a metal-free, visible light (Vis)-driven ...photocatalyst, was prepared and coated on an Al2O3 substrate followed by integration with an inorganic Al2O3 hollow fiber membrane module for use as a PMR. The 10 wt % of PCN exhibited the highest degradation activity for methyl blue (MB) removal under Vis irradiation because the C sites and vacancies within the heptazine rings of the CN units were substituted with P to improve charge separation and reduce the number of unpaired electrons. The PMR exhibits higher efficiency and stability in the removal of MB, methyl orange, phenol solution, and a mixture of the three organic compounds than do individual hollow fiber membranes or photocatalysis systems. The TOC (total organic carbon) analysis revealed that more than 92% of the phenol was decomposed and mineralized in the PMR, which also had a MB removal efficiency of greater than 90% when repeatedly used for four times. These results indicate that the PMR developed in this study is highly active and stable, and can serve as a promising system for effective removal of organic pollutants in wastewater.
Photocatalytic membrane reactor integrated with P-doped g-C3N4 with Al2O3 hollow fiber membrane module exhibits excellent photocatalytic activity. Display omitted
•P replaces C in g-C3N4 structure to improve charge separation and photocatalysis.•P-doped g-C3N4 was fabricated and integrated with photocatalytic membrane reactor.•PMR can be used for wastewater treatment under irradiation of simulated sunlight.•PMR degrades MB under irradiation with light of wavelength larger than 400 nm.
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