Oxidation resistance of nanoscale zero-valent iron supported on exhausted coffee grounds

In this study, nanoscale zero-valent iron (NZVI) was supported by exhausted coffee grounds. Exhausted coffee grounds are a crucial waste generated in enormous amounts. Since supported nanoscale particles have a lower free energy than bare particles, oxidation resistance of supported NZVI on coffee grounds (NZVI-Coffee ground) is postulated. The main aim of this study was to ascertain the enhanced oxidation resistance of NZVI-Coffee ground. Synthesized materials were dried and stored in the air at temperatures of 4, 20, and 35 °C. Changes in the surface characteristics and cadmium removal efficiency of the supported NZVI were investigated. Fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy showed that supported NZVI underwent less oxidation compared to bare NZVI. Cadmium removal efficiencies of supported NZVI did not deteriorate with age, while those of bare NZVI decreased by 9.5 ± 0.1, 13.0 ± 0.1, and 18.3 ± 0.2% compared to their initial removal efficiencies when stored 8 weeks at 4, 20, and 35 °C, respectively. This is because the surface free energy of the NZVI decreased via strong interaction with the functional groups of the coffee grounds. According to the results, exhausted coffee grounds are an effective supporting material for NZVI to enhance its storage stability. [Display omitted] •NZVI supported by coffee ground is more resistant to oxidation than bare NZVI.•Binding to functional groups of coffee ground lowered the surface energy of NZVI.•Lowered surface energy contributes to the stability of NZVI-Coffee ground.•Gibbs adsorption equation demonstrated the lowered energy of NZVI-Coffee ground.