Facile synthesis of 2D nanoflakes and 3D nanosponge-like Ni1−xO via direct calcination of Ni (II) coordination compounds of imidazole and 4-nitrobenzoate: Adsorptive separation kinetics and photocatalytic removal of Amaranth dye contaminated wastewater

Abstract

This study reports a simple method of direct calcination of Ni (II) coordination compounds with N-donor and O-donor ligands such as imidazole and 4-nitrobenzoate to form 2D and 3D Ni1−xO nanostructures. Controlled calcination of imidazole coordinated compound [Ni(Im)6](4-nba)2.2H2O (I) produced 2D nanoflakes in comparison to 4-nitrobenzoate coordinated compound [Ni(H2O)4(4-nba)2].2H2O which formed Ni1−xO nanosponge. Replacement of four coordinated imidazole ligands in compound I with an equivalent number of 4-nitrobenzoate and water molecules as in [Ni(H2O)2(Im)2(4-nba)2] (II) lead to the collapse of flake-like structure upon combustion with the induction of porosity, confirming the dominant effect of 4-nitrobenzoate ligand to form porous structures of Ni1−xO. Material characterization studies revealed that all Ni1−xO nanostructures exhibit cubic phase wherein increase in surface area, pore-volume, and reduction in particle size from 2D nanoflakes to 3D nanosponge is evident. The adsorptive removal of Amaranth dye as a model pollutant using synthesized Ni1−xO nanostructures exhibited high dye removal efficiency of up to 82.81% in the case of 3D nanosponge. The adsorption process is well explained based on the Sips isotherm model and pseudo-first-order reaction kinetics. Photocatalytic Amaranth dye degradation efficiency of 93.80% in 70 min with highest kapp = 4.04×10−2 min−1 is achieved which is attributed to the high surface area and reduction in charge carrier recombination rate as a result of extensive and robust mesoporous structure.