Facile synthesis of 2D nanoflakes and 3D nanosponge-like Ni sub(1-x) O 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 Ni sub(1?x) O nanostructures. Controlled calcination of imidazole coordinated compound [Ni(Im) sub(6) ](4-nba) sub(2) .2H sub(2) O (I) produced 2D nanoflakes in comparison to 4-nitrobenzoate coordinated compound [Ni(H sub(2) O) sub(4) (4-nba) sub(2)].2H sub(2) O which formed Ni sub(1-x) O nanosponge. Replacement of four coordinated imidazole ligands in compound I with an equivalent number of 4-nitrobenzoate and water molecules as in [Ni(H sub(2) O) sub(2) (Im) sub(2) (4-nba) sub(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 Ni sub(1-x) O. Material characterization studies revealed that all Ni sub(1-x) O 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 Ni sub(1-x) O nanostructures exhibited high dye removal efficiency of up to 82.81 percent 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 percent in 70 min with highest k sub(app) = 4.04x10 sub(-2) min sub(-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.