Adsorption of Cr(VI) in aqueous solution by polypyrrole nanotube and polypyrrole nanoparticle; Kinetics, isotherm equilibrium, and thermodynamics

Abstract

Hexavalent chromium is a toxic pollutant because it may harm human health. So, the effective removal of hexavalent chromium in wastewater is still an important problem. In this study, polypyrrole nanoparticles (PPynp) and polypyrrole nanotubes (PPynt) were prepared by different polymerization conditions of pyrrole monomers to compare the ability to adsorb Cr (VI) in an aqueous solution. The X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results demonstrated that the two prepared polypyrrole were essentially identical, but the Transmission electron microscope (TEM) results demonstrated that the upper one is a nanotube and the other is a particle. Cr (VI) is highly pH-dependent on the adsorption of PPy adsorbent, and the removal efficiency of PPynt was much higher than PPynp. The adsorption kinetics follow a pseudo-second-order kinetic model, reaching equilibrium in 100 – 180 min. Langmuir isotherm model was adopted to match the adsorption isotherm data, and the maximum adsorbing capacity was 119.33–205.34 mg/g. The PPynt material can undergo three continuous adsorption–desorption cycles without the loss of the Cr (VI) removal efficiency. In addition, its large surface area, superior Cr (VI) adsorption properties and regeneration properties make the single component PPynt a good material for the removing of Cr (VI) from wastewater.