Layered-double hydroxides and derived oxide as CRM-free highly active catalysts for the reduction of 4-nitrophenol

The present study investigates the possibility to abate 4-nitrophenol (4NP), a well-known persistent contaminant in wastewaters, using Layered-Double Hydroxides (LDH) based catalysts, non-noble metals-based and Critical Raw Materials-free materials used for 4NP reduction with NaBH4. It is reported the study of the effects of several parameters on the overall reaction kinetic by in situ monitoring of the 4NP reduction through UV-Vis Spectroscopy, as: (i) LDH’s trivalent and divalent cation nature, (ii) LDH thermal treatment, (iii) substrate/catalyst ratio, and (iv) stirring rate. The reasons that led to increased activity were identified and correlated with catalyst’s structure characterization. The results pointed out that LDH enhance synergic effect of nickel and copper by increasing reducibility which is further raised when defective mixed oxide by calcination is obtained. This resulted in enhanced 4NP reduction which could be further increased by calcination providing a highly reducible mixed oxide. [Display omitted] •Synthesis and characterization of Ni-based Layered-Double Hydroxides (LDH) and derived oxide.•4-nitrophenol reduction by sodium borohydride in the presence of LDHs or mixed oxide.•Kinetic study of 4-nitrophenol reduction to 4-aminophenol.•Thermal treatment and nickel/copper synergy as key factors for enhanced catalytic behaviour of LDHs.•Demonstrated higher activity than several noble-metal based catalysts.