Synthesis of Polypyrrole-Modified Layered Double Hydroxides for Efficient Removal of Cr(VI)

Designing a stable, selective, and efficient adsorbent for the removal of pollutants like chromium poses serious concern. Herein, an organic-inorganic hybrid material, polypyrrole (PPY)-modified Mg-Al layer double hydroxide, has been reported as an adsorbent for Cr(VI) removal. The inorganic framework Mg-Al layer double hydroxides (LDHs) are synthesized via coprecipitation followed by hydrothermal treatment. The synthesized LDHs are enriched with polypyrrole coating via in situ oxidative polymerization followed by microwave irradiation. The structure of the as-synthesized composite was delineated using various characterization techniques like field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier-transform infrared spectroscopy, Raman, Brunauer-Emmett-Teller, thermogravimetric analysis-differential thermal analysis, and X-ray photoelectron spectroscopy. The PPY-LDHs are applied toward the abatement for Cr(VI) from aqueous solutions at varying temperatures. The maximum Langmuir adsorption capacity of PPY-LDHs is 76.21 mg g^-1. The high distribution coefficient (K_d) value (>10⁴ mL g^-1) reveals the great affinity of the PPY-LDHs for Cr(VI). The PPY-LDHs showed poor regeneration efficiency. The adsorption mechanism is proposed, which asserts that the removal of Cr(VI) onto the adsorbent was a combined effect of reduction of Cr(VI) to Cr(III) and chemical sorption that takes place through ion exchange in the interlayer regions on the surface through electrostatic attractions and hydrogen bonding. Hence, PPY-LDHs is an ideal adsorbent for the treatment of Cr(VI).