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Hydrochar supported Mg–Fe layered double hydroxide hybrid for efficient and reusable removal of tetracyclines from water

Abstract:

A hybrid photocatalyst, Mg–Fe-LDH@HC (layered double hydroxide supported on corn-stalk hydrochar), was synthesized via coprecipitation and evaluated for the removal and photodegradation of tetracyclines in water. X-ray diffraction (XRD) confirmed the formation of a hydrotalcite-like phase with partial amorphous carbon contribution, while SEM–EDS mapping evidenced a uniform dispersion of Mg–Fe-LDH over the hydrochar surface. The hybrid exhibited an apparent optical bandgap of 1.81 eV, favoring visible-light absorption. Under ultraviolet irradiation and optimized operational conditions (H<inf>2</inf>O<inf>2</inf> = 5.4 μM, pH = 6.0, 25 °C), Mg–Fe-LDH@HC achieved 99.09 % total tetracycline degradation after 120 min. Kinetic fitting followed a pseudo-second-order model (R<sup>2</sup> > 0.94), indicating a chemisorption-dominated mechanism coupled with reactive oxygen species (ROS) generation. Radical scavenging and EDTA inhibition tests demonstrated that photogenerated electrons and •OH radicals were the main oxidative agents, with additional contributions from a heterogeneous Fenton pathway with no evidence of a homogeneous Fenton mechanism. The catalyst retained 91.3 % of its initial efficiency after five reuse cycles, with partial recovery after mild regeneration. Acute toxicity assays using Artemia salina, Daphnia magna, and Raphidocelis subcapitata revealed a 65–80 % reduction in post-treatment toxicity compared to the untreated effluent. These results demonstrate that Mg–Fe-LDH@HC is an efficient, recyclable, and eco-compatible photocatalyst for the degradation of antibiotic contaminants in water systems.