Simultaneous adsorption of organic pollutants on Mo-doped NiFe2O4 nanoparticles: Experimental and computational studies

Polluted water remediation by adsorption entails repeated adsorbent separation costs. While superparamagnetic adsorbents can reduce these costs to negligible levels, their adsorption properties towards most organic pollutants are poor. Appropriate doping of such materials can alter their adsorption properties drastically. Here, we synthesized three Mo-doped NiFe₂O₄ nanoparticles with 1, 2, and 4 atomic percent Mo-doping and examined the co-adsorption of methyl orange (MG) and ciprofloxacin (CIP) from an aqueous solution on each adsorbent sample. Molybdenum (Mo) has higher electronegativity than Ni or Fe. XPS analysis and DFT calculations show doping affects electron distribution in the doped material causing three types of adsorbent sites specific to different adsorbates. Latter is essential for efficient concurrent co-adsorption of multiple organic pollutants from an aqueous solution. The one-percent Mo-doped NiFe₂O₄ (1MNIF) nanoparticles demonstrated optimum CIP and MG co-adsorption removal from their aqueous solution under near-neutral pH conditions. The adsorption capacities of 1MNIF were 22.70 mg·g⁻¹ for CIP and 18.95 mg·g⁻¹ for MG. These values are approximately 5 times higher than those observed for the co-adsorption of CIP and MG using the pure NiFe₂O₄ nanoparticles. The equilibrium isothermal adsorption data best fitted the extended Freundlich isotherm model, keeping with co-adsorption on heterogeneous sites on the adsorbent.