Carbon nanotubes (CNTs) in all of their forms are considered “gamechanger” materials that will revolutionize the modern world through many diverse applications. Over 20 years of research has gone into CNT materials, yet we still see their limited use in feasible real-world applications. Part of the reason is because it still remains a challenge for materials scientists to engineer these extraordinary nano-scale building blocks into covalently interconnected three-dimensional (3-D) structures, and to realize macro-scaled sizes via a bulk synthesis process. Another challenge is being able to create CNT-semiconductor hybrid materials by covalently joining other useful semiconductor compounds with CNTs in order to harness their value for electronics applications. The experimental research compiled in the first part of this thesis pioneers an innovative approach to synthesize 3-D macro-structured forms of CNTs by utilizing a heteroatom doping strategy via chemical vapor deposition (CVD). The importance of substitutional doping effects of boron on CNT structural morphology is characterized experimentally and theoretically for the first time so as to create a robust, solid, 3-D networked, CNT “sponge” form. The CNT “sponge” was characterized to exhibit an exotic combination of multifunctional properties including high porosity, high surface area, low density, superhydorphicity, oleophilicity, ferromagnetism, and good elastic mechanical performance. It was also demonstrated that 3-D porous CNT “sponges” could be used for environmental needs as reusable oil spill sorbent materials in seawater. In an effort to combine group III–V semiconductors with CNTs, the second part of this thesis involve a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wall carbon nanotubes. With an aqueous solution of a gallium salt (GaI3), it was possible to form covalent bonds between the Ga3C ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride–carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy.