Selective removal of anionic dyes with exceptionally high adsorption capacity and removal of dichromate (Cr2O72-) anion using Ni-Co-S/CTAB nanocomposites and its adsorption mechanism

[Display omitted] •Developed a simple strategy for synthesis of Ni-Co-S/CTAB nanocomposites in water.•Selective adsorption of anionic adsorbates with very high adsorption capacity.•The electrostatic interaction is predominating factor for the adsorption.•The adsorption follow modified Zhu and Gu model.•The adsorbent is recycled for five times with good adsorption capacity. An adsorbent Ni-Co-S/CTAB nanocomposites have been synthesized at low temperature in aqueous medium using nickel acetate, cobalt acetate, thioacetamide and hexadecyltrimethyl ammonium bromide (CTAB) as reagents. The nanocomposites exhibited exceptionally high adsorption capacity towards anionic adsorbates with high selectivity. The maximum adsorption capacity of nanocomposites were 1995.02 mg g−1 for Congo red (CR), 2223.15 mg g−1 for Methyl orange (MO) anionic dyes and 790.69 mg g−1 for Cr2O72- metal anion. They exhibit negligible adsorption ability towards cationic dyes 2.33 mg g−1 for MB and 42.05 mg g−1 for RhB. The nanocomposite is able to adsorb anionic dyes from a binary mixture of cationic and anionic dyes with high separation factor. It also shows good results with synthetic effluents. The removal of adsorbates followed modified Zhu and Gu isotherm model. FTIR and Zeta-potential measurement confirmed that electrostatic interactions are predominating factor for the adsorption of anionic adsorbates followed by hydrophobic interactions between adsorbates. Moreover, ethanol is used to regenerate the adsorbent and reused up to five times with good adsorption capacities. Thus, the nanocomposite can be used as an efficient adsorbent for the removal and seperation of anionic adsorbates from binary mixtures as well as synthetic effluents.