Controlled surface functionalization of carbon nanotubes by nitric acid vapors generated from sub-azeotropic solution

Abstract

Controlled surface modification of nanocarbons is crucial for their use in applications. The paper deals with the functionalization of carbon nanotubes (CNTs) with HNO 3 vapors. Sub-azeotropic HNO 3 + H 2 O + Mg(NO 3 ) 2 solution is used for the generation of nitric acid vapors. Because this approach allows tuning the HNO 3 concentration in the vapor phase, the effect of its variation on the surface chemistry and structural properties of the CNTs is investigated. A combination of analytical techniques is applied to evaluate oxidation extent of the CNT surface, selectivity towards the formation of carboxyl groups compared with other oxygenated functionalities, and CNT integrity. The comparison with liquid-phase functionalization in H 2 SO 4 + HNO 3 mixture (1 : 3-3 : 1 v/v), conventionally utilized for oxidizing CNTs, shows that vapor-phase functionalization affords greater surface oxygen uptakes and higher selectivity towards the formation of carboxyl groups, with smaller tube damage; more importantly, it evidences that, regardless of the method and conditions chosen, the selectivity towards carboxyl groups increases linearly with the surface oxygen concentration. The presented results prove that the product of HNO 3 concentration in the vapor-phase (25-93 wt%) and vapor-phase functionalization duration (0.5-5 h) controls the surface oxygen concentration. A simple rate model is proposed to account for its increase.

Transition Metal Oxides on Reduced Graphene Oxide Nanocomposites: Evaluation of Physicochemical Properties

“…Contributions ascribed to oxygenated carbon species fall in the 286-290 eV BE range. They include C-O species in phenols and ethers (at 286.1−286.3 eV), C=O species in carbonyls/quinones (at~287.5 eV), and O-C=O bonds in carboxylic acid and anhydrides and esters (at 288.7 −289.3 eV) [36]. As evident, solvothermal treatment brings about a drastic decrease of the C-O and C=O species present on the carbon surface.…”

“…The D/G integrated intensity ratio (I D /I G ) is commonly utilized to monitor the sp 2 defect density in the carbon lattice [36]. It enhances from 2.75 in GO to 3.01 in rGO, proving that the density of sp 2 carbon defects (the only ones contributing to the D-band intensity [35]) increases at expenses of non-sp 2 defects.…”

“…It enhances from 2.75 in GO to 3.01 in rGO, proving that the density of sp 2 carbon defects (the only ones contributing to the D-band intensity [35]) increases at expenses of non-sp 2 defects. In addition, the G-band, sensitive to charge transfer, local distortions, and hybridization changes of the C-C bonding [36], downshifts from 1600 cm -1 in GO to 1588 cm -1 in rGO owing to the oxidation degree lowering.…”

“…As evident, solvothermal treatment brings about a drastic decrease of the C-O and C=O species present on the carbon surface. In addition, the appearance in the HRXPS spectrum of rGO of a weak contribution at 290.5 −291.0 eV (shake-up π-π * transition [36]), absent in the HRXPS spectrum of GO, indicates the partial restoration of the π network following the release of oxygenated functionalities upon thermal treatment. Finally, Figure S5 compares the morphology of GO support before and after solvothermal reaction.…”

Are Electrospun Fibrous Membranes Relevant Electrode Materials for Li‐Ion Batteries? The Case of the C/Ge/GeO2 Composite Fibers

“…The latter, originating from the stretching of CC pairs, is the fingerprint of the graphitic crystalline arrangement . Therefore, the G/D intensity ratio ( I G / I D ) is commonly regarded as a graphitization index . The higher the I G / I D value is, the higher the graphitization degree of the carbonaceous material is, with I G / I D > 1 for well‐graphitized carbons …”