Synthesis and characterization of onion-like carbons for adsorption of tartrazine dye in water

Abstract

Industrial effluent often can contain a significant amount of synthetic dyes. The discharge of wastewater containing dyes into water streams without proper treatment consequently enters the soil and disturbs the aquatic and terrestrial life. Several wastewater treatment technologies have been proposed that can efficiently reduce the amount of synthetic dyes from the environment, in particular azo dyes. Among all the existing technologies for wastewater treatment, physical adsorption is a popular technology because it is inexpensive, simple, and efficient. The aim of this study is to synthesize, modify, and characterize onion-like carbons (OLCs) derived from four different waste oils for the adsorption of tartrazine dye in water. The OLCs derived from different carbon precursors (waste household oil, restaurant waste oil, engine waste oil, and paraffin oil bath waste) were synthesized using a flame pyrolysis method. The synthesized materials were doped with nitrogen using a chemical vapor deposition technique using 10% ammonia gas as a source of nitrogen. The N-doped OLCs were attached with hydroxyl groups through oxidation reactions to improve their solubility and adsorption efficacy. According to the high-resolution transmission electron microscopy and scanning electron microscopy images, the OLCs from all four-carbon precursor were quasi-spherical, agglomerated, and presented a chain-like structures of multi-layers. The distance between the graphitic layers was found to be 0.32 nm. The average particle size of OLCs was calculated to be 40.2 ± 2.5 nm. Adsorption studies revealed that the initial dye concentration, contact time, and pH of the dye solutions influenced the adsorption capacity of the tetrazine. Nitrogen doping of OLCs increased its capacity to adsorb the tartrazine dye. The nitrogen doped OLCs from household waste oil (H-N-OLCs) and engine waste oil (E-N- OLCs) were used in equilibrium adsorption studies in this work. For a concentration of 20 mg/L of tartrazine dye, an adsorption capacity of 28.9 mg/g was achieved using the N- doped OLCs from household waste oil. The adsorption process follows the pseudo second- order kinetic model. The adsorption isotherm is best fitted to the Freundlich mathematical model. The results obtained show that, the source of oil did not have major effect on the physicochemical properties of OLCs and that incorporation of nitrogen onto carbon matrix enhanced the adsorption of the anionic tartrazine dye in aqueous solution.