Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, are most intensively investigated carbon allotropes because of their outstanding physical and chemical properties. Recently, it has been realized that threedimensional (3D) carbon-based structures with nanoscale interconnection provide the remarkably improved properties required for critically needed applications. The properties of 3D-CNTs and graphene architectures can be tweaked for various applications. Therefore, 3D carbon-based solids with nanoscale intermolecular junctions present an exciting research area and provide opportunities for fabrication of various 3D-macroscopic architectures with unexpected properties. The creation of nanoengineered 3D-macroscopic structures in a scalable synthetic process still remains a challenge. The fundamental problem is the difficulty in introducing atomic-scale junctions between individual nanoscale structures so that they can be organized as covalently interconnected nanostructured networks with controllable physical characteristics, such as density and porosity. Here, 3D structures have been created using chemical vapor deposition method, solutionbased chemistry technique and welding method via hypervelocity impact method to generate atomic-scale junction between carbon nanostructures. The scalable fabrication of 3D macroscopic scaffolds with different hierarchical interconnected structures and soldering-like junctions between CNTs using chemical vapor deposition (CVD) technique is reported. These intermolecular junctions of CNTs result in a high thermal stability, high electrical conductivity, excellent mechanical properties, as well as excellent structural stability in a concentrated acid, base, and organic solvents. The CNT solids with such tremendous properties represent the next generation of carbon-based materials with a broad range of potential applications; we demonstrate here a couple such utility impact damping, removal oil from contaminated water and as a marker for the oil industry. Additionally, in situ nano-indentation inside a scanning electron microscopy (SEM) were used to determine the mechanical response of individual covalent junction, formed in different configurations such as “X”, “Y” and “” shapes between individual CNTs. Fully atomistic reactive molecular dynamics simulations are used to support the experimental results as well as to study the deformation behavior of junctions. Vertically aligned multiwall carbon nanotube forests (NTF) synthesized by water assisted CVD method and both sides functionalized with different functionalities as hydrophobic and hydrophilic. The produced hygroscopic nanotube forest demonstrate for water harvesting from air. The second approach has been used in this work is solution chemistry to generate crosslinking nanotube structures. The scalable synthesis of 3D macroscopic solids made of covalently connected nanotubes via Suzuki cross-coupling reaction, a well-known carbon-carbon covalent bond forming reaction in organic chemistry. The resulting CNTs solids are made of highly porous, interconnected structures made of chemically crosslinked carbon nanotubes after freeze-drying process. CNTs solids demonstrated one such utility in the removal of oil from contaminated water. In another approach hypervelocity impact method was used to investigate mechanical behavior of CNTs. The hypervelocity impact of CNT bundles against metallic targets resulted their unzipping along the tube axis, which leads to the formation of graphene nanoribbons, nanodiamonds and covalently interconnected carbon nanostructures depending on the velocity and impact geometry. This new process can produce chemical-free, high-quality graphene nanoribbons. The experimental results supported by fully atomistic reactive molecular dynamics simulations were used to gain further insights of the pathways and deformation and fracture mechanisms