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Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for the solution of energy- and environmental-related problems. It is seen that the energy conversion and storage capacity of MXenes can be enhanced by changing the material dimensions, chemical composition, structure, and surface chemistry. Hence, it is also essential to understand how one can easily improve the structure–property relationship from an applied point of view. In the current review, we reviewed the fabrication, properties, and potential applications of MXenes. In addition, various properties of MXenes such as structural, optical, electrical, thermal, chemical, and mechanical have been discussed. Furthermore, the potential applications of MXenes in the areas of photocatalysis, electrocatalysis, nitrogen fixation, gas sensing, cancer therapy, and supercapacitors have also been outlooked. Based on the reported works, it could easily be observed that the properties and applications of MXenes can be further enhanced by applying various modification and functionalization approaches. This review also emphasizes the recent developments and future perspectives of MXenes-based composite materials, which will greatly help scientists working in the fields of academia and material science.

The aggregation of perylene diimide (PDI) strongly affects the efficiency of organic optoelectronic devices. Here, a simple N,N′-bis(6-undecyl)perylene-3,4,9,10-bis(dicarboximide) (PDI) was prepared. The steady-state absorption spectrum revealed that PDI showed a monomer state in dimethylformamide (DMF). In contrast, a binary DMF/water (25−50% volume percentage of water) solvent showed an aggregation state due to the hydrophobic effect. Further, we examined the excited state relaxation dynamics of both monomeric and aggregated states of PDI using transient absorption (TA) spectroscopy. We found that the aggregated state of PDI in binary DMF/water solvent with the volume percentage of water at 30% strongly coupled with each other due to the hydrophobic effect, which is favorable to the intermolecular symmetry-breaking charge separation (SB-CS) process. Notably, the TA spectroscopy reveals that the SB-CS state is disfavored for the simple flat structure of monomeric PDI in DMF solvent. Therefore, our work provided the photophysical understanding of PDI aggregation caused by hydrophobicity. Since the hydrophobic effect is significant for the aggregation of PDI, it is possible to change the hydrophobicity by controlling the molecular structure of the PDI derivative, to achieve a more effective charge separation state.

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The use of porous hard carbons (PHCs) as electrode materials in sodium-ion batteries has great potential; however, the exposure of large surface areas to electrolyte flow results in irregular and irreversible solid electrolyte interfaces (SEIs), leading to deteriorated ionic and electronic mobility and inferior initial Coulombic efficiency (ICE). These issues can be addressed through suitable structural modifications of PHC materials. Herein, the integration of high-surface-area PHCs with carbon nanofibers (CNFs) was accomplished by a simple electrospinning technique, which resulted in a uniform and reversible SEI layer. In the meantime, the CNFs’ mesh provided connectivity and conductivity in the as-integrated electrodes, whereas PHCs offered fast diffusion kinetics and high Na+ ion storage capacity. Additionally, PHC integration with CNFs demonstrated an excellent ICE of 77% and a specific capacity of 505 mAh/g at 25 mA/g. Furthermore, the conjugated microstructure also provided flexibility and stability to the electrode (260 mAh/g after 500 cycles). This remarkable synergy may promote the development of free-standing, flexible, and highly porous properties in a single material for advanced energy storage applications.