ZnFe2O4 loaded on municipal waste-char: outstanding adsorption and photocatalytic removal of contaminants

Low-cost carbonaceous materials have been synthesized and explored for the removal of harmful colored pollutants from an aqueous medium. However, most of them are not economically viable under continuous-flow conditions and because of their slow kinetics. In this study, we report an economically viable, magnetically reparable adsorbent material synthesized by incorporating spinel zinc ferrite within a waste-char matrix obtained from municipal solid waste (MSW). X-ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and elemental mapping analyses confirm the successful incorporation of cube-shaped ZnFe2O4 into the multichannel system of the waste-char matrix. The as-prepared waste-char-ZnFe2O4 possesses a large surface area with multiple functional groups that aid in fast catalysis and in the removal of contaminants. Waste-char-ZnFe2O4 follows pseudo-first-order kinetics with photocatalytic degradation efficiencies of ∼72% and 92% and first-order rate constant (K1) values equal to 0.023 and 0.0039 min−1 for tetracycline and rhodamine B, respectively. The adsorption of model contaminants onto waste-char-ZnFe2O4 is best described by the Langmuir isotherm model with an R2 value of 0.99 and a pseudo-second-order kinetic model with an adsorption capacity of 25 mg g−1. The as-synthesized composite gives excellent results for real water samples with negligible interference due to other salt ions present in water. Moreover, the superparamagnetic nature of ZnFe2O4 facilitates the separation and reusability of the nanocomposite material. The material offers the advantage of converting MSW into a functional and more robust magnetic nanotrap for contaminants.