Desalination behavior analysis of interior-modified carbon nanotubes doped membrane by dielectric spectrum and molecular simulation

Smart dynamic hybrid membranes with self-cleaning capability

The growing freshwater scarcity has caused increased use of membrane desalination of seawater as a relatively sustainable technology that promises to provide long-term solution for the increasingly water-stressed world. However, the currently used membranes for desalination on an industrial scale are inevitably prone to fouling that results in decreased flux and necessity for periodic chemical cleaning, and incur unacceptably high energy cost while also leaving an environmental footprint with unforeseeable long-term consequences. This extant problem requires an immediate shift to smart separation approaches with self-cleaning capability for enhanced efficiency and prolonged operational lifetime. Here, we describe a conceptually innovative approach to the design of smart membranes where a dynamic functionality is added to the surface layer of otherwise static membranes by incorporating stimuli-responsive organic crystals. We demonstrate a gating effect in the resulting smart dynamic membranes, whereby mechanical instability caused by rapid mechanical response of the crystals to heating slightly above room temperature activates the membrane and effectively removes the foulants, thereby increasing the mass transfer and extending its operational lifetime. The approach proposed here sets a platform for the development of a variety of energy-efficient hybrid membranes for water desalination and other separation processes that are devoid of fouling issues and circumvents the necessity of chemical cleaning operations.

Molecular modeling of thin-film nanocomposite membranes for reverse osmosis water desalination

The scarcity of freshwater resources is a major global challenge causedby population and economic growth. Water desalination using a reverse osmosis (RO) membrane is a promising technology to supply potable water from seawater and brackish water. The advancement of RO desalination highly depends on new membrane materials. Currently, the RO technology mainly relies on polyamide thin-film composite (TFC) membranes, which suffer from several drawbacks (e.g., low water permeability, permeability-selectivity tradeoff, and low fouling resistance) that hamper their real-world applications. Nanoscale fillers with specific characteristics can be used to improve the properties of TFC membranes. Embedding nanofillers into TFC membranes using interfacial polymerization allows the creation of thin-film nanocomposite (TFNC) membranes, and has become an emerging strategy in the fabrication of high-performance membranes for advanced RO water desalination. To achieve optimal design, it is indispensable to search for reliable methods that can provide fast and accurate predictions of the structural and transport properties of the TFNC membranes. However, molecular understanding of permeability-selectivity characteristics of nanofillers remains limited, partially due to the challenges in experimentally exploring microscopic behaviors of water and salt ions in confinement. Molecular modeling and simulations can fill this gap by generating molecular-level insights into the effects of nanofillers' characteristics (e.g., shape, size, surface chemistry, and density) on water permeability and ion selectivity. In this review, we summarize molecular simulations of a diverse range of nanofillers including nanotubes (carbon nanotubes, boron nitride nanotubes, and aquaporin-mimicking nanochannels) and nanosheets (graphene, graphene oxide, boron nitride sheets, molybdenum disulfide, metal and covalent organic frameworks) for water desalination applications. These simulations reveal that water permeability and salt rejection, as the major factors determining the desalination performance of TFNC membranes, significantly depend on the size, topology, density, and chemical modifications of the nanofillers. Identifying their influences and the physicochemical processes behind, via molecular modeling, is expected to yield important insights for the fabrication and optimization of the next generation high-performance TFNC membranes for RO water desalination.

Analysis of Mg2+/Li+ separation mechanism by charged nanofiltration membranes: visual simulation

The mechanism of the nanofiltration (NF) membrane separation of Mg²⁺ and Li⁺ needs to be further investigated, but some commonly used model theories are abstract, which makes them difficult to understand. More importantly, the relationship between the membrane charge and separation performance of Mg²⁺ and Li⁺ cannot be quantitatively analyzed. It is worth studying these challenges and providing a performance boost for Mg²⁺/Li⁺ filtration applications of NF membranes. Here, various NF membranes, with the membrane volumetric charge density increasing from -4.69 to 7.02 mol · m^-3, were fabricated via interfacial polymerization. For these membranes, the separation factor S _Mg,Li was decreased from 0.41 to 0.20. Importantly, the visual simulation results were consistent with the experimental results as a whole. The separation factor S _Mg,Li decreased with the increase of volumetric charge density, and the minimum separation factor S _Mg,Li of the NF membranes was 0.20 (experiment) and 0.17 (simulation), respectively. This meant that the performance of the positively charged NF membrane was not fully developed. Furthermore, we analyzed the relationship between the membrane charge and separation performance, and visualized the simulation of the NF membrane filtration and separation.