Sensing with MXenes: Progress and Prospects

Abstract

conventional technology is gradually reaching its limits in terms of further enhancement of sensor performance. Hence, tremendous efforts have been taken to explore the applicability of MXenes in various sensor technologies, including chemical, biological, mechanical, and optical sensors. The large specific surface area, high electrical conductivity, [1,2] and water dispersibility of MXenes, among their various excellent properties, constitute essential characteristics of a sensor material. Particularly, the 2D structure of MXene, which is conducive to functionalization using various terminal groups, provides a large number of active surface sites. These sites can serve as a highly responsive sensory platform for various external stimuli. Furthermore, the high electrical conductivity of MXenes is desirable for achieving low noise in sensory responses. Therefore, these characteristics demonstrate MXenes as a highly promising alternative sensor material for achieving high sensitivity, exceptionally low limit of detection (LOD), and minimum detectable amount of analytes in various sensor applications. Finally, the water dispersibility of MXenes facilitates environment-friendly fabrication and modification treatments; thus, they are further advantageous in processing.Because the fundamental properties of MXenes satisfy the requirements for an alternative sensor material, MXenebased sensor technology has been rapidly evolving over the last few years. The field of MXene-based sensors is facing conventional challenging problems as hurdles to commercialization: achieving reliably high performance, high stability, multifunctionality, and realizing homogeneous and reproducible scale-up processing (Figure 1a) of MXene-based sensors. Several recent studies on MXene-based sensors were aimed at establishing various structural and electrical approaches to utilize the excellent properties of MXene, thus boosting the sensor performance. For example, the macrostructuring of MXenes can significantly increase the sensitivity and lower the LOD of the resultant fabricated sensor. [3,4] Furthermore, the functionalization of MXene surfaces can impart useful properties of the secondary component to the MXene-based sensor to obtain higher performance than that of pristine MXenebased sensors. [5] These approaches have been highly effective and reliable, and thus significantly accelerated the progress of MXene-based sensor research. Figure 1b shows the network of co-occurring keywords in 2375 MXene-based research papers published since the discovery of MXenes in 2011. In an attempt to introduce new low-cost, high-performance, and Various fields of study consider MXene a revolutionary 2D material. Particularly in the field of sensors, the metal-like high electrical conductivity and large surface area of MXenes are desirable characteristics as an alternative sensor material that can transcend the boundaries of existing sensor technology. This critical review provides a comprehensive overview of recent advances in MXene-based sensor technology...

Emerging MXene–Polymer Hybrid Nanocomposites for High-Performance Ammonia Sensing and Monitoring

“…Among all, M 3 × 2 T x and M 2 X 2 T x have been evaluated for NH 3 sensing performance. As revealed by Lee et al [ 41 ], titanium carbide (Ti 3 C 2 T x ) was the first MXene (M 3 X 2 T x ) reported for NH 3 sensing, followed by specific reports [ 42 ]. Further, it has been revealed that M 2 X 2 T x -MXenes (such as niobium carbide: Nb 2 CT x ) possess higher specific surface areas owing to their fewer atomic layers compared to M 3 X 2 T x -MXenes [ 43 ] and are a potential candidate for NH 3 sensing.…”

“…Recently, many techniques to synthesize MXene have been developed, which can be briefed into three main strategies: selective etching techniques (Wet etching from precursors, molten-salt etching), bottom-up techniques (chemical vapor deposition: CVD, salt templated growth) and chemical transformations (ammoniation, deoxygenation and carburization). Numerous advancements in these techniques are already extensively reviewed [ 23 , 42 ].…”

“…It is followed by washing through centrifugation, decantation, or dispersing into freshwater, in which the pH of a remnant is adjusted to neutral. Lastly, single-layer MXene or few layers are obtained through manual shaking, ultrasonication, or by adding intercalants under delamination process [ 23 , 42 ]. The chemical mechanism associated with the synthesis of MXene using preferential HF etching process can be elaborately demonstrated as follows [ 23 , 39 , 54 , 55 ]:…”

“…Chemiresistors are processed in the final stage by fabricating a sensing film over a suitable substrate utilizing various techniques ( Figure 7 ) such as drop-casting, electrospinning, dip coating, and inkjet printing [ 17 , 25 , 36 , 45 , 68 ]. Various flexible and nonflexible substrates used in the processing of chemiresistors include a glass substrate, fluorine-doped tin oxide (FTO) substrate, indium-tin-oxide (ITO) substrate, polyindole (PI), and polyethylene terephthalate (PET) [ 10 , 11 , 27 , 42 ]. Furthermore, suitable conducting electrode configurations such as parallel and interdigitated configured electrodes are deposited on the sensing layer/substrate utilizing suitable techniques such as thermal evaporation, inkjet printing, mask coating, and dip coating [ 11 ].…”

“…For instance, controlling conductivity and morphology of sensing material is a crucial parameter in state-of-the-art sensors. It has been revealed that materials with superior conductivity are utilized to detect reducing analytes such as NH 3 [ 11 , 42 , 69 ] and that lower conductivities are suitable for monitoring oxidizing analytes such as sulfur dioxide [ 70 , 71 , 72 ]. Hence, the desired properties of sensing materials are optimized during the synthesis process by varying operational parameters.…”