Facile and scalable synthesis of magnetite/carbon adsorbents by recycling discarded fruit peels and their potential usage in water treatment

•Magnetic adsorbents were synthesized via a soak-calcination method using fruit peels.•These adsorbents feature the merits of appropriate ferromagnetism (>4emug−1).•These adsorbents exhibit high adsorption capacity for dyes and Cr6+ ions. In this study, apple, banana and orange peels were used as precursor compounds for the mass production of magnetite/carbon adsorbents. A so-called “soak-calcination” procedure was employed by firstly soaking these waste fruit peels in FeCl3 aqueous solutions and secondly calcining these precursors in the nitrogen atmosphere to yield final magnetite/carbon composites. This approach is quite simple and effective to synthesize carbon-based adsorbents on an industrial scale. The as-produced adsorbents feature the merits of appropriate ferromagnetism (>4emug−1), high adsorption capacity (several hundreds of milligrams per gram for adsorption of methyl blue, Congo red, rhodamine B and Cr6+ ions), and good regenerability (>85%).