Abstract
Deposition of UiO-66 metal–organic framework nanoparticles onto a porous polymer support is a promising approach to designing highly-permeable, size-selective, flexible, and stable membranes for water filtration. In this article, a series of UiO-66 nanoparticles having different particle sizes were synthesized and employed to prepare UiO-66-deposited composite membranes. It was found that the size of the UiO-66 nanoparticles had great influences on the performance of the composite membranes for the filtration of a methylene blue aqueous solution. The deposition of smaller nanoparticles afforded a selective layer having a greater external surface area and narrower interparticle voids. These features made the deposition of smaller nanoparticles more advantageous in terms of the flux and rejection, while the deposition of greater nanoparticles afforded a selective layer more tolerant for fouling. Bimodal composite membranes were prepared by depositing mixed UiO-66 nanoparticles of smaller and bigger sizes. These membranes successfully combined the advantages of nanoparticles of a distinct size.
Highlights
Clean water scarcity is one of the serious global challenges, which is a consequence of exponential population growth, drastic climate change, and rapid industrialization
A series of UiO-66 samples were prepared by varying the addition amount of water during the synthesis at the fixed molar ratio between ZrCl4 and terephthalic acid
UiO1 formed the interparticle voids in the mesopore dimension, the voids for UiO5 were in the range of macropores, and so on. These results suggested that the microscopic corrugation of the surfaces of the deposition layer led to an enlargement of the effective membrane area, as is the case for cross-linked polyamide composite membranes having the crumpled textures [41,42]
Summary
Clean water scarcity is one of the serious global challenges, which is a consequence of exponential population growth, drastic climate change, and rapid industrialization. Membrane-based filtration plays a vital role in accessing superior water quality with an integrated sustainability in terms of no chemical additives, low energy consumption, minimal land usage, and ease of operation [1]. Filtration is generally classified into microfiltration, ultrafiltration, nanofiltration, and reverse/forward osmosis [2] according to the size of the solute to be rejected, in which the use of polymeric membranes is predominant due to certain advantages. The mechanical flexibility of polymeric membranes is suitable for large-scale roll-to-roll processing and integration in advanced filtration modules. Polymeric membranes tend to suffer from insufficient resistance to fouling, mechanical instability in the process stream, and a tradeoff between the permeability and selectivity [5,6,7]. One of the approaches to tackle these problems is hybridization of polymeric membranes with other materials, especially nanomaterials [4,8,9,10]
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