Cobalt–Carbon Nanoparticles with Silica Support for Uptake of Cationic and Anionic Dyes from Polluted Water

Abstract

Silica-supported hierarchical graphitic carbon sheltering cobalt nanoparticles Co-HGC@SiO2 (1) were prepared by pyrolysis at 850 °C of [Co(phen)(H2O)4]SO4·2H2O complex with silica in the presence of pyrene as a carbon source under nitrogen atmosphere. Nanocomposites (2) and (3) were obtained by acid treatment of (1) with HCl and HF acid, respectively. The nanocomposites showed rough hierarchical carbon microstructures over silica support decorated with irregular cobalt nanospheres and nanorods 50 to 200 nm in diameter. The nanoparticles consist of graphitic shells and cobalt cores. SEM, EDAX and TEM elemental mapping indicate a noticeable loss of cobalt in the case of (2) and loss of cobalt and silica in the case of (3) with an increase in porosity. Nanocomposite (3) showed the highest BET surface area 217.5 m2g−1. Raman spectrum shows defect D-band and graphitic G-band as expected in carbon nanostructures. PXRD reveals the presence of cobalt(0) nanoparticles. XPS indicates the presence of Co(II) oxides and the successful doping of nitrogen in the nanocomposites. Moreover, TEM elemental mapping provides information about the abundance of Si, Co, C, N and S elements in zones. Nanocomposite (1) showed maximum uptake capacity of 192.3 and 224.5 mg/g for crystal violet CV and methyl orange MO dyes, respectively. Nanocomposite (2) showed a capacity of 94.1 and 225.5 mg/g for CV and MO dyes, respectively. Nanocomposite (4) obtained after treatment of (1) with crystal violet proved successful adsorption of CV. Co-HGC (5) prepared without addition of silica has a capacity for CV equal to 192 mg/g, while it is 769.2 mg/g with MO. Electrostatics and π–π interactions of graphite and cobalt species in the nanocomposites with aromatic rings of cationic and anionic dyes are responsible for the adsorption. Yan et al. was the best model to describe column kinetics. The thomas column adsorption model showed that the maximum uptake capacity of (1) was 44.42 mg/g for CV and 32.62 mg/g for MO. for a column packed with 0.5 gm of (1) and dye concentration of 100 mg/L at a flow rate of 1 mL/min. The column was recycled three times with no noticeable clogging or degradation of nanocomposites. Thus, Co-HGC@SiO2 adsorbents can be used efficiently to treat water contaminated with cationic and anionic dyes.

Photodegradation of Congo Red by Modified P25-Titanium Dioxide with Cobalt-Carbon Supported on SiO2 Matrix, DFT Studies of Chemical Reactivity

“…This was observed in CoC@SiO 2 -bipy (s1) [19] and CoHGC@SiO 2 [20]. CoC@SiO 2 -bipy (s1) showed a moderate BET surface area of 98 m 2 /g [19], while CoC@SiO 2phen should have a higher surface area, since CoHGC@SiO 2 showed 144.8 m 2 /g for BET surface area [20]. It should be noted that the addition of SiO 2 in the preparation of (s1) and (s2) increased its surface area compared to CoC nanomaterials without silica matrix [19,20].…”

“…TEM of CoC@SiO 2 show a graphitized structure around the cobalt nanoparticle embedded in the silica matrix. This was observed in CoC@SiO 2 -bipy (s1) [19] and CoHGC@SiO 2 [20]. CoC@SiO 2 -bipy (s1) showed a moderate BET surface area of 98 m 2 /g [19], while CoC@SiO 2phen should have a higher surface area, since CoHGC@SiO 2 showed 144.8 m 2 /g for BET surface area [20].…”

“…These types of structures can have high specific surface areas [18]. Co 2+ and Co 3+ ions appeared in XPS analysis of CoC@SiO 2 -bipy (s1) prepared from pyrolysis of cobalt bipyridine chloride [19] and XPS of CoHGC@SiO 2 prepared from cobalt phenanthroline sulfate complex [20] indicating that some cobalt atoms were oxidized to Co 3 O 4 . However, PXRD of these nanocomposites showed the presence of metallic cobalt (0).…”

“…CoC@SiO 2 -bipy (s1) showed a moderate BET surface area of 98 m 2 /g [19], while CoC@SiO 2phen should have a higher surface area, since CoHGC@SiO 2 showed 144.8 m 2 /g for BET surface area [20]. It should be noted that the addition of SiO 2 in the preparation of (s1) and (s2) increased its surface area compared to CoC nanomaterials without silica matrix [19,20]. As the SEM indicated, the cobalt nanoparticles pointed out from the surface of the silica and were surrounded by tinny layer of graphitic carbon.…”

“…On the other hand, SEM-EDX revealed the elemental composition of CoC@SiO 2 nanocomposites. CoC@SiO 2 -bipy (s1) [19] showed weight %C = 34.5, %N = 4.1, %O = 21.0, %Si = 30.8, and %Co = 10.5, while CoHGC@SiO 2 nanocomposite prepared from pyrolysis of cobalt phenanthroline sulfate complex had similar weight % distribution, but with higher cobalt and lower silicon content: %C = 36.4, %O = 20.4, %Si = 11.4, and %Co = 25.8 [20].…”