Carbon nanotubes pretreatment

Li L, Wu G, Xu B-Q. Electro-catalj tic oxidation of CO on Pt eatalyst supported on carbon nanotubes pretreated with oxidative acids. Carbon 2006 44 2973-2983. 

Lueking, A. Yang, R.T. Hydrogen storage in carbon nanotubes residual metal content and pretreatment temperature. AIChE 2004, 49 (6), 1556-1568. 

Multi-walled carbon nanotubes (PyrografiF-III) were supplied by Applied Science Ltd (USA) and had a specific surfece area of 20 rn. g". The average tube inner diameter was in the range 60 to 100 nm with length up to several hundred micrometers. The carbon nanotubes (CNTs) were used as received without any pretreatment. 

Polymer Grafting of Carbon Nanotubes by Con-trolled/Living Radical Polymerization Polymer grafting techniques that use direct covalent functionalization methods, such as radical reactions, have been developed in order to avoid the problems associated with the functionalization of CNTs using acids. These grafting techniques eliminate the need for nanotube pretreatment before the functionalization and allow attachment of polymer molecules to pristine tubes without altering their original structure. 

Carbon nanotubes can be readily dispersed in a solvent using ultrasound. However, because of a strong van der Waals forces, they can quickly aggregate and precipitate. This problem can be alleviated by various pretreatments. For example, Table 5 shows the effect of HNO3 on properties of nanotubes. An increase in the content of carboxylic, lactone and hydroxyl groups was noted. At the same time, the total amount of base was decreased to zero. However, the CNT prepared by the template technique could be dispersed in water without requiring any pretreatment. °... 

Lertrojanachusit N, Pornsunthomtawee O, Kitiyanan B, Chavadej J, Chavadej S (2013) Separation and purification of carbon nanotubes using froth flotation with three sequential pretreatment steps of catalyst oxidation, catalyst removal, and silica dissolution. Asia-Pac J Chem Eng 8... 

Sul G, Zhong WH, Yang XP, Yu YH, Zhao SH (2008) Preparation and properties of natural rubber composites reinforced with pretreated carbon nanotubes. Polym Adv Technol 19 1543-1549... 

L. Li, G. Wu, B.Q. Xu, Electro-catalytic oxidation of CO on Pt catalyst supported on ctirbon nanotubes pretreated with oxidative acids. Carbon 44, 2973—2983 (2006)... 

Other tubular structures hke carbon nanohorns (SWNH, Section 3.3.4) are able to store large amounts of hydrogen as well. Only the availability of sufficient amounts rendered the use of these materials practicable, and much effort is taken to obtain operational hydrogen storage devices on nanotube basis as soon as possible. Once more, however, it is true that the material is still too expensive for industrial-scale use, and only a mass production of nanotubes would enable such widespread application. Moreover, the reproducibility of results turned out to be problematic. The ability to store hydrogen largely depends on the quality of the nanotubes employed. Their pretreatment and possible defects consequently affect this capacity. Hence it is crucial to establish protocols for a reproducible quality of samples. 

Potentiodynamic and potentiostatic methods can also be used to activate nanotubes. Similar to chemical oxidation, electrochemical pretreatment can effectively remove impurities and cause the creation of carbon-oxygen functional groups at the exposed edge plane and defect sites. The same authors reported on an electrochemical pretreatment that involved potentiostating the electrode at +1.7 V vs. Ag/AgCl in pH 7 phosphate buffer for 3 min followed by 3 min at —1.5 V (84). Both the chemical and electrochemical oxidations improved the electrode response (smaller voltammetric A p and larger values) for Fe(CN)g " , serotonin, and caffeic acid. 

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