Metal oxides as dual-functional adsorbents/catalysts for Cu2+/Cr(VI) adsorption and methyl orange oxidation catalysis

The LDO, calcined product of the Mg/Al-CO3 hydrotalcite, was used as a dual-functional adsorbent/catalyst material for the removal of binary heavy metal ions and the catalytic degradation of methyl orange (MO). The adsorption properties for Cu2+ cations and Cr(VI) anions were investigated in depth in single and co-adsorption systems. The results showed that the LDO demonstrated 0.80 and 2.90 mmol/g adsorption capacities in single Cu2+ (1.6 mmol/L) and Cr(VI) (4.0 mmol/L) systems, respectively. In co-adsorption system, Cu2(OH)3Cl precipitation, isomorphic substitution of Mg2+ sites by Cu2+ and intercalation of CrO42– into the interlayers played important roles. On the LDO, Cu2+ and Cr(VI) presented synergetic effect, resulting in an increase in both Cu2+ and Cr(VI) adsorption capacities. In addition, the spent adsorbents were employed as a catalyst for methyl orange (MO) degradation. The Cr-Cu-RLDO, a calcined product of the spent adsorbent in the co-adsorption system, indicated the high activity with 86.5% degradation rate of MO in the presence of H2O2. The existence of Cu and Cr elements in the catalyst was one of the causes of the enhanced degradation of MO.