Oxidized g-C₃N₄/polyaniline nanofiber composite for the selective removal of hexavalent chromium

Nanomaterials with selective adsorption properties are in demand for environmental applications. Herein, acid etching and oxidative decomposition of melon units of graphitic carbon nitride (g-C₃N₄) was performed to obtain the oxidized graphitic carbon nitride (Ox-g-C₃N₄) nanosheets. Ox- g-C₃N₄ nanosheets were further decorated on the polyaniline nanofiber (Ox-g-C₃N₄/Pani-NF). Ox-g-C₃N₄/Pani-NF was well characterized and further applied for a selective removal of hexavalent chromium (Cr(VI)) form aqueous solution. The zeta potential analysis indicate that the surface of Ox-g-C₃N₄/Pani-NF was positively charged which could be beneficial to bind anionic Cr(VI) ions electrostatically. In addition, nitrogen and oxygen containing functional groups exist on the Ox-g-C₃N₄/Pani-NF were mainly responsible for adsorption of Cr(VI) ions from aqueous solution. Moreover, the adsorption of Cr(VI) ions was also dependent on solution pH, reaction temperature and initial concentration of Cr(VI) ions. The maximum monolayer adsorption capacity of Ox-g-C₃N₄/Pani-NF for Cr(VI), calculated from Langmuir isotherm was 178.57 mg/g at pH = 2 and 30 °C. The activation energy (Ea = -20.66 kJ/mol) and the enthalpy change (ΔH° = -22.055 kJ/mol) validate the role of physical forces in adsorption of Cr(VI). These results demonstrate that Ox-g-C₃N₄/Pani-NF can be used as a potential adsorbent for environmental remediation applications.