Adsorption capacity of oxidized nitrogen-doped bamboo-like carbon nanotubes

Abstract

Nitrogen-doped bamboo-like carbon nanotubes (N-BCNTs) were synthetized by catalytic chemical vapor deposition (CCVD) and characterized by electron microscopy. The produced nanotubes were oxidized in different degree by using of various oxidizing agents (H₂O₂, HClO₄ and HNO₃) in order to change their adsorption potential by creating dissociable functional groups (e.g. -OH) on their surface. The appearance of oxygen containing groups was confirmed by spectroscopic analysis and the zeta potential (ζ of the samples was measured. The HNO₃ treatment has led to the emergence of the most polar groups on the nanotube surface (ζ = −27.1 mV), while the other two oxidizing agents were less effective (H₂O₂ and HClO₄, ζ = −18.3 and −19.8 mV, respectively). The adsorption potential of the oxidized N-BCNT samples were tested with copper(II)-ion. Despite the difference in their surface properties, the oxidized nanotubes adsorbed copper to the same extent. The contribution of the oxidized surface for the adsorption capacity is smaller than the effects of nitrogen doping. Thus, more things involved in the adsorption mechanism not only electrostatic attraction, but sorption-precipitation, and complex formation between copper and heteroatoms of the nanotubes. Thus, it is not enough to discuss the effect of dissociable functional groups, but the contribution of e.g. heteroatoms must also be taken into account to fully understand metal ion adsorption on oxidized carbon materials.

Graphical Abstract

Keywords:

• N-BCNT
• transition metal ions
• adsorption potential
• dissociable functional groups
• heteroatoms

Disclosure statement

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Additional information

Funding

This research was supported by the European Union and the Hungarian State, co-financed by the European Regional Development Fund in the framework of the GINOP-2.3.4-15-2016-00004 project, aimed to promote the cooperation between the higher education and the industry.