Synthesis of mixed phase crystalline CoNi2S4 nanomaterial and selective mechanism for adsorption of Congo red from aqueous solution

Abstract

Calcination is an important factor to obtain crystalline nanomaterial with well-developed morphologies. A new adsorbent, crystalline CoNi2S4 was synthesized by sulfuration reactions with thioacetamide and metal precursors in the presence of sodium dodecyl sulfate (SDS) followed by calcination at different temperatures. Powder X-ray diffraction (PXRD) patterns suggested that the nanomaterial consists of a mixture of cubic and hexagonal phase, and crystallinity and crystallite size increases upon increasing the calcination temperature. SEM (scanning electron microscopy) micrographs concluded the formation of different shapes and sizes of nanomaterials at different temperatures. TEM (Transmission electron microscopy) analyses confirmed cactus tree-like morphology with hexagonal and cubic lattice fringes. The adsorption performance study showed that the nanomaterial exhibited a selective adsorption mechanism towards the adsorption of congo red (CR) among other dyes. The nanomaterial displayed a very high adsorption capacity of CR i.e. 2884 mg g–1. Moreover, the adsorption of CR is best fitted with pseudo-first-order kinetics and the modified Zhu and Gu isotherm model. The adsorption mechanism was investigated in detail through FTIR (Fourier-transform infrared), zeta potential and UV–Vis studies and thereby deliberate the possible interactions present between CR and CoNi2S4 nanomaterial. These results displayed high adsorption ability towards the dyes containing both amine (–NH2/NH) and azo (–NN–) groups. Adsorption occurred mainly through hydrogen bonding and metal coordination between the molecules of dye and the adsorbent followed by π-π interactions between dyes. Overall results suggested that the nanomaterial could be the prominent adsorbent for the removal of CR pollutants from water.