MXenes are prone to oxidize and degrade quickly in a matter of days. Here, the use of antioxidants, such as sodium L-ascorbate, is demonstrated as an effective approach to arrest the oxidation of colloidal and dehydrated Ti 3 C 2 T x MXene nanosheets. The success of the method is evident as the Ti 3 C 2 T x nanosheets maintain their composition, morphology, electrical conductivity, and colloidal stability. This method addresses the most pressing challenge in the field of MXene engineering.

groups (OH, O, F), n usually ranges from 1 to 3, and x reflects the number of terminal groups. [1-5] MXenes have drawn much attention for their potential use in energy storage, [1,6] sensing technology, [7,8] functional coatings, [9-11] plasmonics, [12] and catalytic applications [13-15] due to their high electrical conductivity, hydrophilicity, and surface charge. Most of those properties can be traced back to their metallic-like 2D structure and functional groups attached during the etching and delamination processes. [4,5,16-18] However, recent studies suggest that MXenes are prone to react with dissolved oxygen and water molecules, which results in the formation of transition metal oxides and carbon residues. [3,19,20] Initially, Zhang et al. claimed that MXene oxidizes due to the contact with dissolved oxygen in water. [20] However, Huang et al. and our group also demonstrated that water molecules, rather than oxygen molecules, play a critical role in MXene degradation. [21,22] MXenes were reported to oxidize and degrade more rapidly in water rather than in organic solvents, air, or polymer matrixes. [3,23] Zhang et al., Chae et al., and Habib et al. (our group) also found that temperature and humidity have an influence on MXene oxidation. [3,19,20] They proposed that low temperatures and low humidity can mitigate the oxidation of MXene nanosheets due to the slower reaction kinetics and reduced exposure to water molecules, respectively. In addition, MXene nanosheets that are single-to few-layered or have smaller lateral size oxidize faster than multilayered MXene clay particles or larger-size nanosheets. MXenes oxidize rapidly when exposed to oxidizers such as hydrogen peroxide or treated by flash-annealing at high temperatures. [24,25] In addition, elemental composition may influence the oxidation kinetics. [26] VahidMohammadi et al. and Huang et al. reported that M 2 XT x MXenes, such as V 2 CT x and Ti 2 CT x , oxidize and degrade much faster than the more common M 3 X 2 T x , such as Ti 3 C 2 T x. [21,27] Other aspects may also contribute to the oxidation of MXenes, such as the amount and types of terminal groups, etching conditions, ultraviolet exposure, and the number of defects on the MXene nanosheets.

Various methods have been developed to perform atomistic-scale simulations for the cross-linking of polymers. Most of these methods involve connecting the reactive sites of the monomers, but these typically do not capture the entire reaction process from the reactants to final products through transition states. Experimental time scales for cross-linking reactions in polymers range from minutes to hours, which are time scales that are inaccessible to atomistic-scale simulations. Because simulating reactions on realistic time scales is computationally expensive, in this investigation, an accelerated simulation method was developed within the ReaxFF reactive force field framework. In this method, the reactants are tracked until they reach a nonreactive configuration that provides a good starting point for a reactive event. Subsequently, the reactants are provided with a sufficient amount of energy-equivalent or slightly larger than their lowest-energy reaction barrier-to overcome the barrier for the cross-linking process and form desired products. This allows simulation of cross-linking at realistic, low temperatures, which helps to mimic chemical reactions and avoids unwanted high-temperature side reactions and still allows us to reject high-barrier events. It should be noted that not all accelerated events are successful as high local strain can lead to reaction rejections. The validity of the ReaxFF force field was tested for three different types of transition state, possibly for polymerization of epoxides, and good agreement with quantum mechanical methods was observed. The accelerated method was further implemented to study the cross-linking of diglycidyl ether of bisphenol F (bis F) and diethyltoluenediamine (DETDA), and a reasonably high percentage (82%) of cross-linking was obtained. The simulated cross-linked polymer was then tested for density, glass transition temperature, and modulus and found to be in good agreement with experiments. Results indicate that this newly developed accelerated simulation method in ReaxFF can be a useful tool to perform atomistic-scale simulations on polymerization processes that have a relatively high reaction barrier at a realistic, low temperature.

Irradiation of polymer films by a CO 2 infrared laser under ambient conditions converts the polymer into porous graphene or laser-induced graphene (LIG). Here, we simulate the formation of LIG from five different commercially available polymers using reactive molecular dynamics. We determined that the molecular structure of the parent polymer has a significant effect on the final graphitic structure. CO is liberated during the initial part of the LIG formation process when the polymer is converted into an amorphous structure, while H 2 is evolved steadily as the amorphous structure is converted to an ordered graphitic structure. The LIG structure has out-of-plane undulations and bends due to a significant number of 5-and 7-member carbon rings present throughout the structure. We find that the simulated molecular structure compares well with recent experimental observations from the literature. We also demonstrate that the yield of LIG is higher in inert conditions, compared to environments with oxygen. Polybenzimidazole-derived LIG has the highest surface area and yield among the five polymers examined. These findings provide knowledge of LIG formation mechanisms that can be leveraged for bulk LIG applications such as sensors, electrocatalysts, microfluidics, and targeted heating for welding polymers.

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Carbon nanomaterials have been shown to rapidly evolve heat in response to electromagnetic fields. Initial studies focused on the use of microwaves, but more recently, it was discovered that carbon...

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