Synthesis, Structure, Growth Mechanism, and Physical Properties of Transition Metal Sulfide Nanowire Filled Carbon Nanotubes and Carbon Nanoparticles

Filled carbon nanotubes (CNTs) exhibit unique physical properties due to the synergistic effects between the host CNTs and guest fillers making them attractive for several applications such as energy storage, microwave absorption, sensing applications, and drug delivery, etc. To date, a heterogeneity of inorganic and organic materials has been successfully filled inside the CNT cores and enormous effort has been spent on studying their fundamental electrical, magnetic, electromagnetic, optical, and electrochemical properties. However, the filling of CNTs with transition metal sulfide nanowires has been barely achieved and thus their fundamental properties are still unclear. In this study, nickel sulfide nanowires filled CNTs (Ni3S2@CNTs) were synthesized on different substrates using an in situ chemical vapor deposition method and the samples were characterized by standard techniques such as SEM, TEM, EDX, XRD, FT-IR, TGA, UV-Vis, Raman spectroscopy, etc. The electron microscopy measurements reveal that CNTs are filled with continuous, single-crystalline Ni3S2 nanowires several micrometers long whereas an exceptionally low ratio between the intensities of the D band and G band (ID/IG= 0.26) in the Raman spectrum suggests an ultra-high quality of CNTs. The intrinsic electrical properties of individual Ni3S2@CNTs were studied using two probe and four-point probe methods and a mean resistivity of 6.1×10-5 Ωm was measured. In another study, fluorescent carbon nanoparticles (CNPs) were synthesized using a novel electrochemical method by the oxidation of carbon cloth. CNPs produced by the pulse applied potential exhibited a high fluorescence along with high stability in both optical emission and absorption properties. An electrochemical method was developed to conjugate CNPs with Ni3S2@CNTs and the electrochemical properties of the composite were studied during the electrocatalysis of water. It was found that CNPs can significantly decrease the oxygen evolution reaction (OER) overpotential from 1.15 V to 0.57 V with a corresponding current density of 5 mAcm-2 after conjugating with Ni3S2@CNTs. Also, the electrochemical properties of Ni3S2@CNTs were studied using them as anode material for lithium-ion batteries and the preliminary results show that Ni3S2@CNTs synthesized on nickel foam can deliver a capacity of about 1000 mAhg-1 after 100 cycles at a current density of 100 mAg-1