Graphene nickel silica supported nanocomposites as an efficient purifier for water treatment

Abstract

This work reports the preparation of graphene nickel silica GCNi@SiO2 (1) and GCNi@1/2SiO2 (2) adsorbents in high yield. The preparation is a simple pyrolysis of readily prepared Ni(2,2′-bipyridine)Cl2.H2O complex with cheap abundant silica support and an extra carbon source anthracene, at 850 °C. The nanocomposites showed rough porous carbon microstructures over silica particles with some nickel nanoparticles forming rods, cubes, octahedron, pyramids, and cuboids within 5 μm size. The agglomerated nickel nanoparticles bursting out of graphitic sheets caused increase in surface porosity and noticeable electroactivity. The current density for electrode coated with (2) is three time greater than in (1) when testing K4Fe(CN)6. TEM of GCNi (3) indicated the presence of 15 to 45 nm nanoparticles made up of graphitic shell and nickel cores, graphene flakes and bamboo-like multiwall carbon nanotubes MWCNT. Although in (2), graphene and MWCNT were condensed on silica. Raman and EDX indicated higher carbon to silica ratio in (2) compared to (1), as expected. The presence of Ni(0) and Ni2+ in nanocomposites is evidenced by XPS and Xrd. The nanocomposites were applied as adsorbent of aromatic cationic dyes for water treatment. Langmuir adsorption capacity qmax of (1) for methylene blue was 39.5 mg/g. While qmax of (1) and (2) for crystal violet were 23.9 and 26.0 mg/g, respectively. The mechanism of adsorption is the best described as π–π interactions between graphitic carbon and aromatic cationic dyes. The column adsorption capacity of (2) for crystal violet was 9.8 mg/g, and the data was best fitted with Thomas model. The column was recycled three times with no clogging.