Adsorption of Metal Ions on Nitrogen Surface Functional Groups in Activated Carbons

Abstract

A commercially available coconut-shell-derived active carbon was oxidized with nitric acid, and both the original and oxidized active carbons were treated with ammonia at 1073 K to incorporate nitrogen functional groups into the carbon. An active carbon with very high nitrogen content (∼9.4 wt % daf) was also prepared from a nitrogen-rich precursor, polyacrylonitrile (PAN). These nitrogen-rich carbons had points of zero charge (pHpzc) similar to H-type active carbons. X-ray absorption near-edge structure (XANES) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and temperature-programmed desorption (TPD) were used to characterize the nitrogen functional groups in the carbons. The nitrogen functional groups present on the carbon surface were pyridinic, pyrrolic (or indolic), and pyridonic structures. The adsorption of transition metal cations Cd2+, Ni2+, and Cu2+ from aqueous solution on the suite of active carbons showed that adsorption was markedly higher for carbons with nitrogen functional groups present on the surface than for carbons with similar pHpzc values. In contrast, the adsorption characteristics of Ca2+ from aqueous solution were similar for all the carbons studied. Flow microcalorimetry (FMC) studies showed that the enthalpies of adsorption of Cd2+(aq) on the active carbons with high nitrogen contents were much higher than for nitric acid oxidized carbons studied previously, which also had enhanced adsorption characteristics for metal ion species. The enthalpies of adsorption of Cu2+ were similar to those obtained for Cd2+ for specific active carbons. The nitrogen functional groups in the carbons act as surface coordination sites for the adsorption of transition metal ions from aqueous solution. The adsorption characteristics of these carbons are compared with those of oxidized carbons.

Renewable Nitrogen‐Doped Hydrothermal Carbons Derived from Microalgae

“…N-containing heterocyclic aromatic structures, such as the pyrroles identified by NRM, absorb within this wavenumber range. 3 The incorporation of N into pyrroles and other N-containing heterocyclic aromatic structures (pyridine, quaternary-N) has been confirmed by XPS analysis, as described in the paper. On the other hand, the spectrum of HC-A-0.67G-220 shows more defined features in the 690-820 cm -1 region arising from C-H out of plane bending vibrations of aromatic structures, 4 which confirms that increasing HTC temperature leads to a higher extent of aromatization.…”

Facile Synthesis of Nitrogen - Containing Carbon by Carbonization of Furfural in Deep Eutectic Mixtures

“…However, the main synthesis route for N-doped carbon with high structural nitrogen content is an in situ process that derives the N-doped carbonaceous material directly from nitrogen-rich precursors. In situ doping of carbon using nitrogen-containing precursors permits homogeneous incorporation of nitrogen into the carbon material and several nitrogen-doped carbon materials have been prepared using this method [7][8][9] .…”

Activated carbons for applications in catalysis: the point of view of a physical-chemist

“…The principle of this technique is that different surface functionalities can be probed as a function of their neutralization behavior (Boehm et al 1964;Noh and Schwarz 1989). The amount of acid functionalities is measured assuming that NaOH neutralizes carboxyl, phenol and lactone groups; Na 2 CO 3 carboxyl and lactone groups and NaHCO 3 only carboxyl groups (Boehm 1994;Jia et al 2002;Tamon and Okazaki 1996). Surface basic sites can be quantified by using HCl as titrant agent (Jia et al 2002;Papirer et al 1987).…”