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Preparation, Characterization And Application Of Carbon Nano-Tubes (CNTs) Grown On Thin-sheet Sinter-locked Ni-/SS-316L-microfibers (SMF_M)

Posted on:2011-12-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:F T JiangFull Text:PDF
GTID:1101360302464118Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Carbon nanotubes (CNTs) have great potential for extensive scopes of applications in heterogeneous, electrocatalysis, energy storage, and electrode materials due to their high specific surface areas, desirable length-to-diameter ratio, good electrical conductivity, chemical inertness, and unique chemical and mechanical properties.However, the practical use of CNTs in the future technologies is particularly challenging, as robust macroscopic/monolithic structure of CNTs that can fully utilize the novel properties of the individual CNTs is required in the real world forms rather than the powders. One approach is to agglutinate CNTs by adding the binders and subsequently pressing at high pressure, yet inconsecutive contact between CNTs and the use of binders unfortunately introduce high internal resistance within the monolithic structure, occlusion of the surface area and low accessibility of CNTs surface that are detrimental for many applications (e.g., in electrochemistry). An alternative way is to incorporate CNTs into or directly grow CNTs onto the substrates to form composites with well defined sizes/shapes, controlled growth orientations, and large-area structure.The monolithic mico-nano CNTs/SMFm composites are prepared by catalytic decomposition of carboneous compounds on SMFm (SMFni and SMFSS) with many beneficial properties in terms of large void volume, three-dimensional micro-grade pore structure and large surface area to volume ratio. The composites are characterized by N2 adsorption-desorption, SEM, TEM, Raman and TG. These noval approaches present substantial potential in many applications such as capacitive deionization for water purification, electro-catalytic synthesis of p-MBA from oxidation of p-MT, and catalyst for oxidative dehydrogenation of ethylbenzene to styrene.In the first part, the CNTs/SMFm composites, which are formed from various carbon source on different substrates (SMFni, SMFni modified by Al(NO3)3 or Mg(NO3)2 and SMFSS), have shown merits of large specific surface areas and monolithic structure by anchoring of CNTs to the metal fibers. The CNTs/SMFni composites, which are formed from catalytic cracking of ethylene on SMFni at 750℃ with H2 as dilute gas, have robust monolithic structure with 3~4μm CNTs layer uniformly anchoring to the SMFni surface. The weight is decreased by less than 5 wt% for the composites using ethylene as carbon source within 10-min supersonic treatment in methanol and then almost remains constant with prolonged treatment time (up to 30 min), indicating that CNTs are rooted firmly on the surface of SMFni network. Nevertheless, the weight loss of more than 20 wt% is obverved for the SMFNi-composite using ethanol or n-butanol as carbon source and for SMFSS-composite using ethylene as carbon source. The specific feature of the CNTs within CNTs/SMFNi (ethylene as carbon source) is large hollow core (without internal blockage), entirely opened tip-like tube mouth, thin wall thickness of 8-10 nm, and stacked truncated cone morphology.In the second part, the CNTs/SMFNi composites were employed as double electro-layer capacitor electrodes for deionization. Capacitive electrosorption of 82.5μmol/g and 42.4μmol/g can be obtained for 50 ml 100 ppm NaCl solution and 50 ppm CrCl3 solution at flow rate of 5.0 ml/min at work voltage of 1.2 V. The capacitance of the composites CNTs/SMFNi electrode is approximately 80 F/g in 5.0 M KOH at scan rate of 100 mV/s.In the third part, the electrocatalytic activity of the CNTs/SMFni composites as electrode for oxidation of p-MT to p-MBA is investigated. In comparison with other material electrodes such as Pt, carbon fiber and graphite, our composites electrode for synthesis of p-MBA in methanol using KF as supporting electrolyte delivers high conversion of 96.9% with selectivity of 86.8% using Pt anode with current of 0.13 A at 20℃in air atmosphere. Good current efficiency of 82.8% can be obtained.In the fourth part, oxidative dehydrogenation of ethylbenzene to styrene using the CNTs/SMFNi composites as catalysts is studied. The best conversion and selectivity of 42.1% and 99.7% can be obtained, respectively, using O2/EB=1/1, WHSV=1.25 h-1 at 400℃. TPD results reveal that the type and amount of the surface O-containing groups on the CNTs play key roles in selectively converting the ethylbenzene into styrene.
Keywords/Search Tags:thin-sheet SMFNi, SMFSS, CNTs/SMFNi composites, capacitive desalinization, electrosynthesis, catalytic oxidative dehydrogenation
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