Facile synthesis of Cu₂O/hydrochar composites achieving high-efficiency antibiotic capture in bioretention column

Hydrochar (HC) derived from biomass via hydrothermal carbonization exhibits remarkable effectiveness in the removal of aqueous pollutants. This study reveals that HC also possesses reductive ability, which can reduce CuO to Cu₂O during the hydrothermal process without additional reducing agent. The obtained Cu₂O/HC composite exhibited enhanced capacity to adsorb the antibiotic levofloxacin (LVX). Under the optimal composite ratio (HC@Cu₂O-0.2), the Langmuir adsorption capacity of LVX achieved 226.74 mg/g, representing a 99.97-fold enhancement compared to pure CuO and a 4.19-fold increase relative to pristine HC, respectively. Thermodynamic experimental results revealed that adsorption was a spontaneous endothermic process. The impacts of various environmental conditions on the adsorption of HC@Cu₂O-0.2 were systematically investigated and the results showed that the HC@Cu₂O-0.2 could maintain high removal efficiency under weak acidic and weak alkaline conditions. Bioretention column experiments demonstrate that even trace amounts of HC@Cu₂O-0.2 significantly enhance LVX removal efficiency. The lower adsorption energy of LVX on HC@Cu₂O-0.2 compared to Cu₂O and HC through DFT calculation suggests enhanced adsorption stability. In addition, HC@Cu₂O-0.2 exhibited considerable recyclability and demonstrated promising application potential in practical pollution control scenarios. These findings are of great significance for expanding the synthesis method and application of green and efficient HC composites.