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The synthesis of nanostructures with tunable antibacterial properties using green solvents at room temperature is of environmental interest, and antibacterial nanomaterials are used in the fabrication of biofouling-resistant membranes for water purification and wastewater treatment. In this study, we investigate the effect of organic ligands on the antibacterial and structural properties of silver-based metal−azolate frameworks (Ag-MAFs). Three new Ag-MAFs were synthesized with silver, as the metal center, and imidazole-based linkers having different chemistries via a facile and environmentally friendly method conducted at room temperature. The coordination of silver ions with the linkers resulted in the formation of Ag-imidazole, Ag-2 methylimidazole, and Ag-benzimidazole complexes with octahedral, hexagonal nanosheet, and nanoribbon morphologies, respectively. The Ag-MAFs exhibited excellent antibacterial activity (up to 95% die-off of bacteria at a short exposure time of 3 h) in colloidal forms against both Gram-negative Escherichia coli (E. coli) and Gram-positive Bacillus subtilis (B. subtilis) because of synergetic effects of silver and the imidazole-based linkers. Ag-2 methylimidazole showed the highest antibacterial activity, owing to its high silver concentration and special nanocrystal structure that provides better contact with bacteria. This work indicates that the antibacterial activity of Ag-MAF nanostructures can be tailored by changing the organic linker, allowing for creating nanostructures with desired biocidal properties.

Incorporating metal–organic frameworks (MOFs) into the thin layer of thin-film composite (TFC) membranes is an effective way of improving the CO2/CH4 separation performance. In this study, porous polyethersulfone (PES) membranes were surface-coated with a novel CO2-permeable layer consisting of CO2-philic Pebax and nickel-based MOF particles. The MOF particles were synthesized using nickel­(II) acetate tetrahydrate as a metal source and 2-amino-1,4-dicarboxybenzene (NH2-BDC) as an organic linker. The properties and performance of the MOFs and synthesized membranes were assessed using analytical techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), and dynamic light scattering (DLS). DLS analysis showed that the MOF particle size range was in a range of 350–650 nm. Moreover, cross-sectional FE-SEM images depicted that a uniform and dense Pebax layer was shaped on top of the PES substrate. Well dispersion of the particles was demonstrated by surface FE-SEM imaging. DSC analysis showed that embedding Ni-NH2-BDC MOF particles into the Pebax-1657 film increased the crystallinity degree and the glass-transition temperature (T g) of resulted membranes. To evaluate the membrane’s separation performance, permeation experiments were performed with CO2, CH4, and CO2/CH4 mixtures at ambient temperature. Embedding 5 wt % Ni-based MOF particles improved the CO2 permeability and CO2/CH4 selectivity from 19.05 Barrer and 32.2 to 31.55 Barrer and 94, respectively, compared to MOF-free membranes. Loading MOF particles into the Pebax matrix also improved the real gas separation factor. The obtained results demonstrate the great potential of the fabricated TFC membranes for gas separation.

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Membrane technology as an emerging separation process has become competitive with other separation techniques in recent decades. Among pressure-driven and isothermal membrane processes, membrane distillation (MD) as a thermally driven process has come out to put an end to hardships of such processes like distillation. MD process can be used in a wide variety of applications such as desalination and wastewater treatment. Generally, MD is a process which water is a main component of the feed solution and only water vapor can pass through a hydrophobic membrane pores. With four main configurations different from each other by their condensation procedure, the performance of MD process is limited due to the lack of appropriate module, membrane, and energy consumption rate. In recent years, many experiments have been carried out to find well-suited membrane type and module. Also, applying solar or waste heat as heat source and the capability of coupling with other processes like forward osmosis and osmotic distillation distinguish MD process from other membrane processes. This chapter addresses membrane characteristics, MD applications, transport mechanisms, and process challenges.

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