Van Nhuong Vu, Thi To Loan Nguyen, Thi Thanh Huong Nguyen, Thi Mai Viet Ngo, Truong Xuan Vuong
Although Cu-containing layered double hydroxides (LDHs) have been widely investigated for light-assisted oxidation, the relationship between Cu substitution, crystallographic evolution, optical characteristics, and catalytic reactivity remains incompletely resolved. A pristine MgAl hydrotalcite (MgAlH) and Cu-substituted MgAl hydrotalcites (n-CuMgH; nominal Cu : Mg : Al ratios of 0 : 7 : 3-6 : 1 : 3) were synthesized by coprecipitation at a constant divalent-to-trivalent cation ratio. All compositions retained the layered framework, while increasing nominal Cu substitution modified their crystallographic, textural, and optical characteristics. From MgAlH to 5-CuMgH, the apparent band gap decreased to 1.86 eV, whereas the Urbach energy increased to 3.407 eV, corresponding to a pronounced change in the fitted optical absorption-edge response. Under H2O2-assisted visible-light irradiation, 5-CuMgH exhibited the highest CIP removal among the investigated compositions, reaching 95.5% after 210 min with an apparent pseudo-first-order rate constant (k app) of 0.032 min-1. Under dark H2O2-assisted conditions, CIP removal remained high at 89.9%, indicating that H2O2-assisted Fenton-like oxidation provides the major contribution, while visible irradiation affords additional kinetic enhancement. Scavenger experiments implicated ˙OH as an important apparent contributor, whereas AA and EDTA-2Na produced weaker inhibition; the limited selectivity of the scavengers precludes definitive assignment of individual ROS contributions. 5-CuMgH was the most active composition tested, although the investigated nominal composition range does not establish a unique Cu-content optimum. Overall, the concurrent evolution of crystallographic, optical, textural, and surface-chemical characteristics supports a multifactorial composition-property-reactivity relationship, without assigning causality to any single material descriptor.