Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4-Nitrophenol Reduction.

A series of Co-doped ternary CuCoAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids ( = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The CuCoAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an -plane vertically interlaced growth pattern. The CuCoAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially CuCoAl-LDH/rGO with the highest value of 49.2 × 10 s and TOF of 232.8 h, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH, ΔS, and ΔG were estimated. The best activity of CuCoAl-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine CuO NPs (∼4.3 nm) along with a small amount of Cu species, the electron transfer effect induced by atomically dispersed Co species leading to the formation of electron-rich Cu species along with the Co/Co redox couple, the strong CuO-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π-π stacking via an rGO layer. Meanwhile, the CuCoAl-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The CuCoAl-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater.