A Comprehensive Review on Filled Carbon Nanotubes: Synthesis, Properties and Applications

approaches. We critically examined the diverse range of materials encapsulated within CNTs, highlighting how confinement at the nanoscale influences their chemical reactivity, phase stability, and emergent quantum phenomena. Special attention is given to the wide range of applications of filled CNTs in addressing societal challenges. These include biomedicine, catalysis, energy storage, gas separation, filtration membranes, sensing technologies, and nanoelectronics. Beyond revisiting the current state-of-the-art, this review offers a critical discussion of future directions and challenges in this field.