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

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A series of Co-doped ternary Cu x Co 3– x Al-layered double hydroxide (LDH)/rGO nanosheet array hybrids ( x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The Cu x Co 3– x Al-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab -plane vertically interlaced growth pattern. The Cu x Co 3– x Al-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu 1.5 Co 1.5 Al-LDH/rGO with the highest k app value of 49.2 × 10 –3 s –1 and TOF of 232.8 h –1, 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 Cu 1.5 Co 1.5 Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu 2 O NPs (∼4.3 nm) along with a small amount of Cu 0 species, the electron transfer effect induced by atomically dispersed Co 2+ species leading to the formation of electron-rich Cu species along with the Co 2+ /Co 3+ redox couple, the strong Cu 2 O-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 Cu 1.5 Co 1.5 Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu 1.5 Co 1.5 Al-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.