Cobalt-carbon/silica nanocomposites prepared by pyrolysis of a cobalt 2,2'-bipyridine terephthalate complex for remediation of cationic dyes

Abstract

Recently, carbon nanostructures have attracted interest because of their unique properties and interesting applications. Here, CoC@SiO₂-850 (3) and CoC@SiO₂-600 (4) cobalt-carbon/silica nanocomposites were prepared by solid-state pyrolysis of anthracene with Co(tph)(2,2'-bipy)·4H₂O (1) complex in the presence of silica at 850 and 600 °C, respectively, where 2,2'-bipy is 2,2'-bipyridine and tph is the terephthalate dianion. Moreover, Co(μ-tph)(2,2'-bipy) (2) was isolated and its X-ray structure indicated that cobalt(ii) has a distorted trigonal prismatic coordination geometry. 2 is a metal-organic framework consisting of one-dimensional zigzag chains within a porous grid network. 3 and 4 consist of cobalt(0)/cobalt oxide nanoparticles with a graphitic shell and carbon nanotubes embedded in the silica matrix. They were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS revealed that the nanocomposites are functionalized with oxygen-containing groups, such as carboxylic acid groups. In addition, the presence of metallic cobalt nanoparticles embedded in graphitized carbon was verified by XRD and TEM. The efficiency of 3 for adsorption of crystal violet (CV) dye was investigated by batch and column experiments. At 25 °C, the Langmuir adsorption capacity of 3 for CV was 214.2 mg g^-1 and the fixed-bed column capacity was 36.3 mg g^-1. The adsorption data were well fitted by the Freundlich isotherm and pseudo-second-order kinetic model. The adsorption process was spontaneous and endothermic.

Fig. 1. (a) Zigzag chain structure of the trigonal prismatic complex Co(μ-tph)(2,2′-bipy) (2), (b) π–π interaction and (c) 3D network with pores of complex 2.

Fig. 2. SEM images of CoC@SiO₂-600 (4) (a and b), TEM image of CoC@SiO₂-600 (4) (c), SEM images of CoC@SiO₂-850 (3) (d and e) and TEM image of CoC@SiO₂-850 (3) (f).

Fig. 3. Raman spectra of CoC@SiO₂-850 (3) and CoC@SiO₂-600 (4).

Fig. 4. XPS survey of CoC@SiO₂-850 (3), C 1s, O 1s and Co 2p_3/2 spectra.

Fig. 5. XPS survey of CoC@SiO₂-850 (4), C 1s, O 1s and Co 2p_3/2 spectra.

Fig. 6. XRD patterns of CoC@SiO₂-850 (3) and CoC@SiO₂-600 (4).

Fig. 7. Nitrogen adsorption/desorption isotherm of 3 (a), nitrogen adsorption/desorption and carbon dioxide adsorption/desorption isotherms of 5 (b).

Fig. 8. Freundlich and Langmuir non-linear fits of adsorption of CV to CoC@SiO₂-850 (3) at different temperatures.

Fig. 9. Yan et al. non-linear fit of adsorption of CV using column packed with 3.