Green synthesis of a nicotinamide-functionalized cobalt ferrite nano-adsorbent for aqueous phase removal of some virulent dyes: evaluation of adsorption isotherms, kinetics, and mechanisms

Abstract

Biogenic processes are increasingly appealing alternatives to standard synthesis approaches. They are environmentally conscious approaches, employing nontoxic and biocompatible substances and yielding materials with exceptional characteristics. Herein, an eco-friendly production of cobalt ferrite (CoFe₂O₄) nanoparticles by employing the fruit extract of orange citrus (Citrus sinensis) via a green synthesis method is reported. The surface modification of super magnetic CoFe₂O₄ nanoparticles with nicotinamide (ex situ approach) produced ecofriendly and novel NAM/CoFe₂O₄ nanoparticles. Following their structural elucidation using XRD, the nanoparticles were further characterized using FTIR spectroscopy; surface analysis was performed using SEM-EDX, TEM, and BET (S_BET: 22 m² g⁻¹ and pore diameter: 2–50 nm), and the point of zero charge (7.0) and magnetic strength (CoFe₂O₄: 158 emu g⁻¹; NAM/CoFe₂O₄: 158 emu g⁻¹) of the NPs were determined using VSM. The produced NAM/CoFe₂O₄ NPs displayed good dye removal efficiencies, with maximum adsorption capacities of 101 and 177 (mg g⁻¹) for Celestine blue (CB) and Bismarck brown (BB), respectively, at 298 K. The operational parameters, including the dose (CB: 0.55 g L⁻¹; BB: 0.7 g L⁻¹), time (CB, BB: 40 min), pH (CB, BB: 8.0) and concentration (CB, BB: 30 mg L⁻¹), were optimized using batch adsorption technique. The equilibrium observations predicted using isotherm models fitted well with the Freundlich and pseudo-second order models for CB and BB. In particular, the adsorption process correlated well with the pseudo-second order kinetic model. The adsorption mechanisms for Celestine Blue and Bismarck brown were principally controlled via intermolecular H-bonding, π–π interactions, and electrostatic interactions. The most economical (560 INR per kg) method for removing CB and BB was found to be NAM/CoFe₂O₄ NPs. The reusability of the spent NPs was consistent for up to five adsorption–desorption cycles.