Mechanism, behaviour and application of iron nitrate modified carbon nanotube composites for the adsorption of arsenic in aqueous solutions

Abstract

In this study, ferric nitrate modified carbon nanotube composites (FCNT) were prepared by isovolumetric impregnation using carbon nanotubes (CNTs) as the carrier and ferric nitrates the active agent. The batch experiments showed that FCNT could effectively oxidize As(III) to As(V) and react with it to form stable iron arsenate precipitates. When the dosage of FCNT was 0.1 g·L–1, pH value was 5–6, reaction temperature was 35 °C and reaction time was 2 h, the best arsenic removal effect could be achieved, and the removal rate of As(V) could reach 99.1%, which was always higher than 90% under acidic conditions. The adsorption results of FCNT were found to be consistent with Langmuir adsorption by static adsorption isotherm fitting, and the maximum adsorption capacity reached 118.3 mg·g−1. The material phase and property analysis by scanning electron microscopy, Brunauer–Emmett–Teller, Fourier transform infrared spectoscopy, X-ray photoelectron spectroscopy and other characterization methods, as well as adsorption isotherm modeling, were used to explore the adsorption mechanism of FCNT on arsenic. It was found that FCNT has microporous structure and nanostructure, and iron nanoparticles are loosely distributed on CNTs, which makes the material have good oxidation, adsorption and magnetic separation properties. Arsenic migrates on the surface of FCNT composites is mainly removed by forming insoluble compounds and co-precipitation. All the results show that FCNT treats arsenic at low cost with high adsorption efficiency, and the results also provide the experimental data basis and theoretical basis for arsenic contamination in groundwater.