Enhancing oxidative capability of Ferrate(VI) for oxidative destruction of phenol in water through intercalation of Ferrate(VI) into layered double hydroxide

In this study, ferrate intercalated Ca/Al-layered double hydroxide (Ferrate-LDH) was synthesized and characterized for water treatment. In the new Ferrate(VI) material, ferrate was stably present in the LDH interlayers, in agreement with results of the Density Functional Theory simulation. The oxidative capability of Ferrate-LDH was examined in terms of the mineralization of phenol in water. The Ferrate-LDH could achieve up to 86.8% utilization efficiency during oxidative destruction of phenol in water (pH = 6.5, TOC = 38.3 mg/L), advantageous over direct ferrate addition that only achieved 12.6% utilization efficiency. A slower evolution of dioxygen (a final product of Ferrate(VI) self-decay) was observed in the Ferrate-LDH water system, suggesting that the LDH structure inhibited Ferrate(VI) self-decay. Therefore, the better phenol removal achieved by Ferrate-LDH was likely ascribed to an increased oxidant exposure caused by the increased lifetime of Fe(VI) in water. Characterization of the LDH products before and after oxidation of phenol revealed that ferric (hydr)oxides capable of surface catalyzing Ferrate(VI) self-decay were formed on the LDH surface, not inside the LDH interlayers, suggesting that ferric(III), the product of Fe(VI) reduction, was repelled from the LDH interlayers. Isolation of Fe(VI) present in the LDH structure from these active iron products may be responsible for the inhibited Ferrate(VI) self-decay when Ferrate-LDH was dosed to water. This study demonstrates that the intercalation of ferrate in LDH represents a promising approach to more efficiently and economically utilizing Ferrate(VI) for the elimination of water pollutants.