Waste plastic filter modified with polyaniline and polypyrrole nanoparticles for hexavalent chromium removal

Chromium (Cr) is a toxic heavy metal for environmental compartments and human health. In this study, waste polypropylene hollow filters (PPF) with an optimal pore size of 5 μm were amino-functionalized with an optimized amount of polyaniline (PANI) and polypyrrole (PPy) as an adsorbent for removing Cr (VI). The adsorbent was characterized by scanning electron microscope, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and the Brunauer-Emmett-Teller method, showing the successful polymerization of co-polymer on the surface of PPF and increasing the surface area up to 15.08 m² g^-1. A Box-Behnken design was applied by a quadratic model with 99.15% accuracy, revealing a significant impact of the initial concentration of Cr (VI) on the removal efficiency. Dynamic adsorption was conducted in a continuous and semi-continuous system with over 99% removal efficiency for various initial concentrations of Cr(VI). The fitted data showed that the adsorption process followed the pseudo-second-order kinetics and Langmuir isotherm models at the optimum pH of 2 with the predicted maximum adsorption capacity of 510.9 mg g^-1 of PANI+PPy, which was significantly higher than some reported adsorbents. The effect of coexisting cations (Cu²⁺, Ni²⁺, and Zn²⁺) and anions (SO₄^2-, Cl^- and NO₃^-) on the removal efficiency revealed selective adsorption of Cr(VI) by the adsorbent. The produced adsorbent was capable of removing 76.6% of Cr(VI) from real electroplating wastewater. Regeneration of the adsorbent was performed by NaOH 1 mol L^-1 up to three cycles with a 20% reduction in adsorption performance. All data showed that PPF@PANI+PPy was a promising adsorbent for Cr(VI) removal from aqueous solutions and real-world wastewater.