Abstract
MXenes, new two-dimensional transition metal carbides and nitrides, are attracting considerable attention as multifunctional materials in various research fields due to their high surface area, hydrophilicity, good mechanical properties, metallic-like conduction and adsorption characteristics, combined with the ability to tailor the surface properties with functional groups. In this review, the applications of MXenes as electrochemical sensors are summarised and discussed. The review is focused on Ti3C2Tx as these are the only MXenes that have so far been considered as electrochemical sensors, primarily due to the fact that they have metallic-like conduction and can be easily formed as single and multi-layered flakes through chemical etching of the parent MAX phase. The fabrication of the Ti3C2Tx-based sensors is first described and then followed by an account of their applications as electrochemical sensors, for the detection of small molecules, environmental contaminants and biosensors for biomedical sensing applications. Finally, their overall stability when exposed to aqueous media, which will have implications in the future development of MXene-based sensors, is discussed together with their future prospects as electrochemical-based sensors.
Highlights
To cite this article: Tian Yu and Carmel B
In many of the published papers where a comparison is made with graphene or carbon nanotubes, the MXenes exhibit higher sensitivities and lower detection limits, out-performing graphene and carbon nanotube based sensors
They are only emerging as electrochemical sensors and there is a number of challenges that must be overcome before MXenes can be fully exploited as sensors
Summary
To cite this article: Tian Yu and Carmel B. Depending on the experimental conditions employed in etching, such as the etchant, temperature and time, Tx may represent –F, –Cl, –O or –OH terminal groups.[1,15] This etching step is followed by an exfoliation step to give colloidal suspensions of single or a few layers of MXenes.[15,18] It is possible to use liquid exfoliation by selecting molecules that have the capacity to weaken the inter-layer interactions in the MXenes layers.[19] This is normally achieved as the molecules are intercalated and induce swelling of the interlayer space and this method can be employed to convert the multilayers into single nanoflakes, with a high yield of the 2-dimensional flakes Using this top-down synthetic approach a variety of different MXenes have been formed including, Ti3C2Tx, Ti2CTx, Mo2CTx, Ti4N3Tx, Nb2CTx and Zr3C2Tx.[20,21] Double transition metal MXenes such as Mo2TiC2Tx and Mo2Ti2C3Tx have been formed.[22,23] Until recently, Al was the only element that could be etched from the parent MAX phase, but recently it was shown that Si could be selectively removed from Ti3Si2C2 using HF and H2O2.24. This review is focused on the preparation of MXenes, their applications as electrochemical sensors and biosensors and their overall stability when exposed to aqueous media, which will have implications in the future development of MXene-based sensors
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