Multi-functional magnesium hydroxide coating for iron nanoparticles towards prolonged reactivity in Cr(VI) removal from aqueous solutions

In this study, the reactive performance of magnesium hydroxide-coated iron nanoparticles (Fe @Mg(OH)2) was investigated for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. Short-and long-term progressive-release of Fe @Mg(OH)2 reactivity was evaluated through several batch tests. The Multi-functional effect of the environmentally-friendly Mg(OH)2 coating shell was represented by the progressive shell-dissolution in water and preventing the rapid corrosion of Fe-core, which resulted in a controlled release of Fe reactivity towards Cr(VI). Fe @Mg(OH)2 showed good performance in preserving Fe long-term reactivity within a wide range of pH (3.0-9.0) and temperature (15-55 oC). The long-term investigation of Fe @Mg(OH)2 performance towards Cr(VI) removal confirmed the progressive and maintained reactivity, represented by the continuous release of Fe electrons, to achieve 100% removal efficiency of 40 mg/L initial Cr(VI) concentration over 50 days reaction time, to be reported for the first time in the literature. Fe @Mg(OH)2 showed high regeneration abilities up to 5 cycles with 1.36 times average enhancement in Cr(VI) removal efficiency compared to that of Fe. Moreover, Fe @Mg(OH)2 achieved an increase in the shelf-live longevity performance up to 30 days without any storing solution with 90% final Cr(VI) removal efficiency after 180 min reaction time