Cu_3–<i>x</i>Ni_<i>x</i>Al-Layered Double Hydroxide-Reduced Graphene Oxide Nanosheet Array for the Reduction of 4-Nitrophenol

Abstract

A series of bi-transition-metal hybrids Cu3–xNixAl-LDH/rGO (x = 2.5, 2.0, 1.5) were synthesized via a facile preadjusted pH citric-acid-assisted coprecipitation method. Systematic characterizations suggest that the hybrids show honeycomb-like nanosheets array morphology with ultrathin CuNiAl-LDH nanosheets (∼72.3 × 4.2 nm) staggered vertically grown on both sides of rGO substrate. The Cu3–xNixAl-LDH/rGO hybrids present a remarkably superior reduction performance for 4-nitrophenol (4-NP) than pure LDH samples. Particularly, Cu1Ni2Al-LDH/rGO shows the best activity with kapp = 3.4 × 10–2 s–1, ∼1.7-fold of Cu1Ni2Al-LDH. It is worth noting that the activity of this bitransition metals hybrid Cu1Ni2Al-LDH/rGO is 37% higher than our previously reported monotransition metal hybrid Cu1Mg2Al-LDH/rGO (kapp = 2.5× 10–2 s–1). These findings can be ascribed to (1) highly dispersed ultrasmall Cu2O nanoparticles (∼3.8 nm) instantaneously formed via in situ reduction of atomic-level dispersed Cu2+ ions in LDH layer lattices of the Cu3–xNixAl-LDH hybrids beneficial from clear isolation and stabilization effect of Ni–OH; (2) strong promotion of the doping of atomic-level dispersed Ni2+ ions in LDH and possible Cu2O–Ni–OH(CuNiAl-LDH)–rGO three-phase synergistic effect; and (3) enhanced adsorption capacity for reactants upon π–π stacking and the unique honeycomb-like nanosheet array morphology. The series of hybrids exhibit not only excellent reduction properties for varied aromatic nitro compounds but also good decolorization ability for anionic azo dyes. Further fixed bed experiments reveal that Cu1Ni2Al-LDH/rGO can efficiently decolorize the mixed solution of 4-NP and methyl orange at high flow rate (8 mL/min) with TOF of 1.68 × 10–3 s–1, suggesting great application potential of the as-obtained nanosheet array bi-transition-metal hybrids for water remediation.