MXenes are a newer class of 2D materials, possess with desirable properties such as large specific surface area, conductivity, and hydrophilicity, making them attractive for various environmental applications, including remediation and as membranes for water treatment. Until recently, the practical implementation of MXenes was hindered by their instability in water, although improved synthesis procedures have largely addressed this issue. Consequently, it is now important to assess the stability of MXenes in engineered environments relevant to drinking water and membrane operation (e.g. backwashing). In this study, Ti3C2Tx MXenes were found to remain stable upon exposure to an aqueous environment saturated with oxygen and to UVC and UVA light at circumneutral pH, but were transformed upon exposure to Fe(III) chloride and free chlorine. The chlorination reaction kinetics are 1st order with respect to Ti3C2Tx and free chlorine concentration, with a rate constant that increased at pH ≤ 7.5, implicating HOCl as the reactive species. We propose that MXene reactions with HOCl occur by an electrophilic attack of Cl+, forming TiO2 and degrading the MXene. AFM data shows that transformations are initiated at the edges of the MXene sheets and localized areas on the MXene, suggesting that the initial sites for Cl+ attack are defect sites and/or uncoordinated Ti atoms. During the initial stages of the oxidative degradation, the sheet-like structure of colloidal MXenes is preserved, although prolonged chlorine exposure leads to three-dimensional crystalline (anatase) TiO2 formation. The degradation of MXenes during chlorinationThis contrasts with the inertness of nanoscale TiC, highlighting the need to devise surface modification processes that will allow MXenes to resist the oxidative conditions associated with membrane regeneration/backwashing.
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Ion‐Selective MXene‐Based Membranes: Current Status and Prospects
Water pollution is a major global challenge, as conventional polymeric membranes are not adequate for water treatment anymore. Among emerging materials for water treatment, composite membranes are promising, as they have simultaneously improved water permeation and ions rejection. Recently, a new family of 2D materials called MXenes has attracted considerable attention due to their appealing properties and wide applications. MXenes can be incorporated into many polymeric materials due to their high compatibility. MXenes/polymer composite membranes have been found to have appealing electrical, thermal, mechanical, and transport properties, because of strong interactions between polymer chains and surface functional groups of MXenes and the selective nanochannels that are created. This article reviews advances made in the area of ion‐selective MXene‐based membranes for water purification. It puts the advances into perspective and provides prospects. MXenes’ properties and synthesis methods are briefly described. Strategies for the preparation of MXene‐based membranes including mixed‐matrix membranes, thin‐film nanocomposite membranes, and laminated membranes are reviewed. Recent advances in ion‐separation and water‐desalination MXene‐based membranes are elucidated. The dependence of ion‐separation performance of the membranes on fabrication techniques, MXene's interlayer spacing, and MXene's various surface terminations are elucidated. Finally, opportunities and challenges in ion‐selective MXene‐based membranes are discussed.
more » « less- Award ID(s):
- 1804285
- NSF-PAR ID:
- 10449377
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Technologies
- Volume:
- 6
- Issue:
- 10
- ISSN:
- 2365-709X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The mutations of bacteria due to the excessive use of antibiotics, and generation of antibiotic‐resistant bacteria have made the development of new antibacterial compounds a necessity. MXenes have emerged as biocompatible transition metal carbide structures with extensive biomedical applications. This is related to the MXenes’ unique combination of properties, including multifarious elemental compositions, 2D‐layered structure, large surface area, abundant surface terminations, and excellent photothermal and photoelectronic properties. The focus of this review is the antibacterial application of MXenes, which has attracted the attention of researchers since 2016. A quick overview of the synthesis strategies of MXenes is provided and then summarizes the effect of various factors (including structural properties, optical properties, surface charges, flake size, and dispersibility) on the biocidal activity of MXenes. The main mechanisms for deactivating bacteria by MXenes are discussed in detail including rupturing of the bacterial membrane by sharp edges of MXenes nanoflakes, generating the reactive oxygen species (ROS), and photothermal deactivating of bacteria. Hybridization of MXenes with other organic and inorganic materials can result in materials with improved biocidal activities for different applications such as wound dressings and water purification. Finally, the challenges and perspectives of MXene nanomaterials as biocidal agents are presented.
