The effect of chlorine on the morphology of carbon nanotubes (CNTs) prepared from a Fe-Co/CaCO 3 catalyst was investigated using chlorobenzene (CB), dichlorobenzene (DCB), trichlorobenzene (TCB), dichloroethane (DCE), trichloroethane (TCE) and tetrachloroethane (TTCE) as chlorine sources using a catalytic chemical vapour deposition (CCVD) method. Toluene was used as a chlorine-free carbon source for comparison. Multi-walled carbon nanotubes (MWCNTs) were successfully synthesized. The physicochemical properties of the CNTs were studied using transmission electron microscopy (TEM), Raman spectroscopy, thermal gravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The inner and outer diameters of the MWCNTs increased with an increase in the number of chlorine atoms contained in the reactant. Chlorine incorporation into the MWCNTs was observed by EDS analysis for all reactants. Formation of 'bamboo-like' structures for the MWCNTs generated from TCE and TTCE was also observed, facilitated by the presence of the high percentage of chlorine in these reactants. Numerous MWCNTs revealed the presence of small carbon nanostructures that grew on top of the dominant CNTs, suggesting an unexpected secondary carbon growth mechanism.
The 2-oxomalonylbis(arylimidoyl) chlorides [C 6 H 3 (R 2 -2,6)N CCl] 2 CO (R = Me, 3a; Pr i , 3b; H, 3c) were synthesized from C 6 H 3 (R 2 -2,6)NHCHO and an excess of (COCl 2 ) 3 and their reaction with various nucleophiles was studied. Successive hydrolysis of 3a led to the formation of [C 6 H 3 (Me 2 -2,6)N CCl] 3 COH 4a and [C 6 H 3 (Me 2 -2,6)NHCO] 3 COH 5a, while treatment of 3a with HAuCl 4 (H 2 O) x gave {[C 6 H 3 (Me 2 -2,6)N(H) CCl][C 6 H 3 (Me 2 -2, 6)NHCO] 2 COH}AuCl 4 6a. All compounds were fully characterized by microanalysis, NMR spectroscopy, mass spectrometry, and, in the case of 3a, 4a, 5a, and 6a, by X-ray crystallography.
The synthesis of both covalently bonded chlorine and nitrogen-doped carbon materials (Cl-N-CNMs) has been little studied. In this paper we report on the investigation of the synthesis of Cl-N-CNMs using a feedstock containing a mixture of dichlorobenzene (DCB), acetylene and acetonitrile over a Fe-Co/CaCO3 catalyst using an injection CVD method at 800 °C. By varying the acetonitrile:DCB concentration ratio (66.7:33.3; 33.3:66.7 and 20:80), the morphology and physicochemical properties of the CNMs was varied. The products contained varying amounts of Cl (0.5%–1.2%) and N (0.88%–1.47%) and the total amount of Cl and N increased with the Cl content in the feed, as determined by XPS. A graphitic N environment dominated in feeds containing 33.3 and 66.7 vol.% DCB, whilst pyrrolic N dominated in feeds containing pure acetonitrile and 80 vol.% DCB. The chlorine in the feed promoted the formation of CNMs with various shapes namely horn-shaped, spaghetti-like, and pencil-like shapes, some with open-ends and others with closed-ends as determined by TEM and SEM studies. Although no direct correlation with the amounts of the reactants used and the morphology of the products was established, trends in the product shapes were noted with highly defected products produced from 66.7 vol.% DCB, and feeds containing 33.3 and 80 vol.% had tubes with similar open-ended horn-shaped morphology and less defects.
The use of carbon nanostructures doped with heteroatoms as electrocatalysts for oxygen reduction reaction (ORR) has attracted intense research in recent years because they are highly conductive, have good durability, and are highly electro-active. One of the strategies to modify the characteristics of carbon nanomaterials (CNMs) to render them suitable for certain applications is to dope them with boron (B) and nitrogen (N). The effect of doping CNMs with boron has been a subject of little study, and hence, it is not well understood, as compared to nitrogen doping studies. In this study, nitrogen was unintentionally doped into carbon nanotubes (CNTs) by chlorination and decomposition of triphenylborane in a catalytic vapor deposition (CVD) reactor. N-doping resulted from the use of nitrogen as a carrier gas. Microscopic and spectroscopic techniques revealed that N bonding of carbon nanostructures together with the presence of defects played pivotal roles in determining the extent of ORR performance of produced CNMs. The introduction of N in the carbon matrix during B molecule decomposition resulted in the reduction in the amount of B doped into the matrix, due to competitive incorporation of N which inhibited B introduction. The presence of pyridinic N species was responsible for a 2e− ORR performance.
In this study, various-sized nitrogen-doped carbon nanotubes (NCNTs) were fabricated by varying the concentration of chlorine in the feed. The diameter of the NCNTs was found to influence the sensing ability of the nanomaterials when coated onto the glassy carbon electrode (GCE) and used for the detection of catechol (CC) and resorcinol (RS). Larger diameter NCNTs (denoted NCNTs (2 : 1)) were produced when a low concentration of chlorine was added into the acetonitrile feed, whereas smaller diameter NCNTs (denoted NCNTs (1 : 2)) were produced when a large concentration of chlorine was added. This investigation revealed that the addition of controllable amounts of chlorine during the fabrication of NCNTs led to the creation of nanostructures with different properties. The greatest current response which was evidenced by an enhanced anodic peak of CC and RS was obtained when GCE was coated with NCNTs (2 : 1), and this was attributed to their large diameter and high graphitic nature which facilitated electron transfer as evidenced by scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis. A linear response was obtained when varying the concentration of both CC and RS, with the limits of detection of about 0.059 μM (CC) and 0.034 μM (RS) (3S/M) obtained.
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