Variation in chemical, colloidal and electrochemical properties of carbon nanotubes with the degree of carboxylation

Abstract

Multiwalled carbon nanotubes (CNTs) were carboxylated via microwave irradiation where the treatment time was varied to alter the degree of functionalization, and as many as one in 15 carbons in the CNT could be oxidized. Chemical, physical, electrochemical, and colloidal behavior of the carboxylated CNTs was studied. All properties changed with the degree of functionalization to a point beyond which they appeared to remain constant. The surface area increased from 173.9 to 270.9 m2/g while the critical coagulation concentration (CCC) values increased from 142.14 to 168.69 mM in the presence of NaCl, and the corresponding increase was from 0.97 to 5.32 mM in the presence of MgCl2. As seen from cyclic voltammetry curves, the functionalized CNTs showed mainly non-Faradic interactions with Na2SO4, but showed Faradic behaviors in alkaline KOH.

Incorporation of functionalized carbon nanotubes into hydrophobic drug crystals for enhancing aqueous dissolution

“…Carboxylated multiwall carbon nanotubes (f-CNTs) were synthesized following a previously published methodology 49, 59–60 . In short, pre-weighed amounts of purified CNTs were treated in a microwave reactor (Model: CEM Mars) with a mixture of concentrated H 2 SO 4 and HNO 3 at 140°C for 20 min.…”

“…While there is much ongoing effort for using CNTs in drug delivery and biomedical applications, it is worth noting that there have been concerns about the toxicity of CNTs and numerous in vitro and in vivo studies have been carried out with conflicting reports 40–48 . However, functionalization with carboxyl group has shown to be an effective way to mitigate MWCNTs toxicity 49–50 .…”

Controlling the Dissolution Rate of Hydrophobic Drugs by Incorporating Carbon Nanotubes with Different Levels of Carboxylation

“…CNTs were reacted with a mixture of concentrated sulfuric acid and nitric acid at 140 • C for 5, 10, and 40 minutes, respectively, in a microwave reactor (model: CEM Mars). This led to the formation of various amounts of carboxylic groups on the CNTs surface that had different hydrophilicity [28]. The carboxylated CNTs were filtered through a 10µm polytetrafluoroethylene (PTFE) membrane filter, washed to a neutral pH, and dried under vacuum at 65 • C.…”

“…A number of in vitro and in vivo studies have been performed that show conflicting reports from both the type of CNTs and bioactivity of interest [19][20][21][22][23][24][25][26][27]. However, studies have shown that carboxylation is an effective way to reduce toxicity [28,29].…”

Synthesis of Carbon Nanotube Incorporated Metal Oxides for the Fabrication of Printable, Flexible Nickel‐Zinc Batteries

“…[51] We have reported that the treatment of CNTs before using them as electrode ingredients could alter the physical and electrochemical properties. [20,52,53] Based on these data, the CNTs were functionalized for 10 min (FCNT-10) and 40 min (FCNT-40), respectively. The resulted carboxylated CNTs containing different levels of carboxylation (Table 3) were tested as an alternate to raw CNTs to form an equivalent ZnO-CNT 28.3 composite with two different levels of carboxylation.…”