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2D carbides and nitrides of transition metals, also known as MXenes, are an emerging class of 2D nanomaterials that have shown excellent performances and broad application prospects in the fields of energy storage, catalysis, sensing, electromagnetic shielding, electronics and photonics, and life sciences. This unusual diversity of applications is due to their superior hydrophilicity and conductivity, high carrier concentration, ultra-high volumetric capacitance, rich surface chemistry, and large specific surface area. However, it is difficult to make MXenes with the desired surface functional groups that deliver high reactivity and high stability, because most MXenes are extracted from ceramics (MAX phase) by an etching process, where a large number of metal atoms are inevitably exposed on the surface, with other anions and cations embedded uncontrollably. The exposed metal atoms and implanted ions are thermodynamically unstable and readily react with trace oxygen or oxygen-containing groups to form the corresponding metal oxides or degrade chemically, resulting in a sharp decline in activity and loss of excellent physicochemical properties. The addition of certain synergistic additives during the intercalation and chemical modification of surface functional groups under non-hazardous conditions can result in stable and efficient MXene-based materials with exceptional optical, electrical, and magnetic properties. This review discusses several such methods, mainly additive-mediated intercalation and chemical modification of the surface functional groups of MXene-based materials, followed by their potential applications. Finally, perspectives are given to discuss the future challenges and promising opportunities of this exciting field. [ABSTRACT FROM AUTHOR]

Research on 2D materials has recently become one of the hottest topics that has attracted broad interdisciplinary attention. 2D materials offer fascinating platforms for fundamental science and technological explorations at the nanometer scale and molecular level, and exhibit diverse potential applications for future advanced nano-photonics and electronics. The chemical vapor deposition (CVD) technique has shown great promise for producing high-quality 2D materials with superior electro-optical performance. However, it is difficult to synthesize continuous single-crystal 2D materials with large domain sizes and good uniformity due to the low vapor pressure of their precursors. It has been observed that the addition of selected synergistic additives to the CVD process under mild conditions can result in uniformly large-area and highly crystalline monolayer 2D materials with exceptional optical/electrical properties. Moreover, the 2D material-based devices chemically modified by synergistic additives can achieve superior performances compared to those previously reported. In this review, we compare several typical synergistic additive-mediated CVD growth processes of 2D materials, as well as their superior properties, and provide some perspectives and challenges for the future of this emerging research field. [ABSTRACT FROM AUTHOR]