In situ investigation of water on MXene interfaces

Abstract

A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.

Highly Selective H2S Gas Sensor Based on Ti3C2Tx MXene–Organic Composites

“…We particularly note that H 2 S and H 2 O bind very strongly to mixed surfaces (much stronger than to the pure O-terminated surface) because the S atom of H 2 S and O atom of H 2 O can bind to the OH group and the H atoms to O groups. In fact, this result is fully consistent with reports of interlayer and surface water in MXenes (as observed, e.g., in TGA experiments), arising from its high hydrophilicity . NH 3 appears to have even stronger adsorption energy, although this situation is somewhat different.…”

“…In fact, this result is fully consistent with reports of interlayer and surface water in MXenes (as observed, e.g., in TGA experiments), 54 arising from its high hydrophilicity. 55 NH 3 appears to have even stronger adsorption energy, although this situation is somewhat different. Because when NH 3 is adsorbed on the mixed surface, it captures a proton from one of the surface OHgroups (and 0.288e), resulting essentially in NH 4 + adsorbed on negatively charged MXenes.…”

Toward Smart Sensing by MXene

“…[ 1 ] One example of MXene, Ti 3 C 2 F x , satisfies the stoichiometric ratio of n + 1/ n , in which M, X, and T stand for transition metals, carbon or nitrogen, terminal groups at surfaces, respectively. The MXene has exhibited extraordinary electrical, [ 2–4 ] optical, [ 5 ] mechanical, [ 6–8 ] and electrochemical properties [ 9 ] since its first discovery, [ 10 ] which has become an emerging material for sensing, [ 11,12 ] communication, [ 13,14 ] energy, [ 15,16 ] environmental, [ 17 ] and healthcare applications. [ 18–20 ]…”

Photo-response of water intercalated Ti3C2O2 MXene

“…63 It has been demonstrated that Ti 3 C 2 T x can generate strong surface plasmons at energies as low as 0.30 eV. Despite extensive research into the impact of water intercalation on the structural and electrochemical characteristics of MXenes, 64 to the best of our knowledge, little is known about the optical modulations driven by water intercalation. This paper's major goal is to investigate how Ti 3 C 2 O 2 MXene's electronic and optical characteristics are affected by water intercalation.…”