Covalently Functionalized MXenes for Highly Sensitive Humidity Sensors

Abstract

Transition metal carbides and nitrides (MXenes) are an emerging class of 2D materials, which are attracting ever-growing attention due to their remarkable physicochemical properties. The presence of various surface functional groups on MXenes' surface, e.g., -F, -O, -OH, -Cl, opens the possibility to tune their properties through chemical functionalization approaches. However, only a few methods have been explored for the covalent functionalization of MXenes and include diazonium salt grafting and silylation reactions. Here, an unprecedented two-step functionalization of Ti 3 C 2 T x MXenes is reported, where (3-aminopropyl)triethoxysilane is covalently tethered to Ti 3 C 2 T x and serves as an anchoring unit for subsequent attachment of various organic bromides via the formation of C-N bonds. Thin films of Ti 3 C 2 T x functionalized with linear chains possessing increased hydrophilicity are employed for the fabrication of chemiresistive humidity sensors. The devices exhibit a broad operation range (0-100% relative humidity), high sensitivity (0.777 or 3.035), a fast response/recovery time (0.24/0.40 s 𝚫H −1 , respectively), and high selectivity to water in the presence of saturated vapors of organic compounds. Importantly, our Ti 3 C 2 T x -based sensors display the largest operating range and a sensitivity beyond the state of the art of MXenes-based humidity sensors. Such outstanding performance makes the sensors suitable for real-time monitoring applications.

“Sweat‐Driven” MXene Composites with Energy‐Storage and Thermal‐Management Multifunctions: A Platform for Versatile Electronic Skins

“…When the MXene SC absorbs sweat, the penetration of water molecules between the MXene nanosheets reduces the conductive pathway of MXene and weakens its conductivity. [ 22 ] Importantly, the paper layer undergoes volume expansion, which leads to relative sliding of the MXene nanosheets deposited on the paper to form cracks under stress. The islands and gaps induced by stress further reduce the conductive pathways of MXene, [ 33 ] thus further weakening its electrical conductivity, as shown in Figure S2a (Supporting Information).…”

“…However, when MXene comes into contact with water, water molecules can penetrate between the MXene nanosheets, which causes an expansion in the distance between them, leading to electron decoupling between the MXene sheets and thus reducing their electrical conductivity. [21,22] In addition, the charge depletion in the presence of adsorbed water molecules also contributes to the decrease in conductivity. [22] Moreover, this effect is aggravated when MXene is deposited on hydrophilic paper substrates, as volume expansion of paper upon water absorption can cause MXene sheets deposited on the paper surface to slide.…”

“…[21,22] In addition, the charge depletion in the presence of adsorbed water molecules also contributes to the decrease in conductivity. [22] Moreover, this effect is aggravated when MXene is deposited on hydrophilic paper substrates, as volume expansion of paper upon water absorption can cause MXene sheets deposited on the paper surface to slide. [23] These characteristics are unfavorable for the application of MXene in energy-storage e-skins that utilize sweat as the electrolyte.…”

Porous crystalline materials for memories and neuromorphic computing systems

“…In comparison to other materials, porous crystalline materials possess unparalleled porosity and exceptional customizability, which equip them with a diverse range of outstanding properties (such as mechanical strength, ionic/electronic conductivity, optoelectronics, adsorption capacity, and stability) through guest loading, structural/compositional design, and post-synthetic modification. [4][5][6]60,62,[91][92][93][94][95] The interest of researchers worldwide in developing next-generation memory/ neuromorphic devices has been significantly piqued by these remarkable properties exhibited by porous crystalline materials.…”

Non-covalent Functionalized Schottky Interface at Ti3C2Tx/n-Si Van der Waals Heterojunction

“…transition metal-based carbides, nitrides and carbonitrides 2D layered ceramics also known as MXene´s has drawn significant attention from the materials research community [8] . Thanks to their impressive physicochemical and charge transport properties this fascinating class of materials has found application in many different fields from energy conversion [9,10] /storage [11] to efficient electromagnetic shielding, photodetectors [12][13][14][15][16][17] , sensors [18,19] and biomedical devices [20] . To this date tens of different MXene compositions has been successfully synthesized and studied whereas possibility of synthesis of more than hundred different compositions has been predicted by the computational studies.…”