Synthesis and characterization of a new magnetic adsorbent for removal of 4-nitrophenol: application of response surface methodology

Magnetic modified graphene oxide was synthesized as a new modified magnetic nano-composite (MMNC) by a simple sonochemical-hydrothermal method. The sonochemical reaction was employed to exfoliate, functionalize and decorate neomycin on graphene oxide sheets. Nickel ferromagnetic particles were synthesized by hydrothermal co-precipitation method and decorated on neomycin-modified graphene oxide. The morphology and chemical structure of MMNC were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction spectroscopy. The adsorption capability of MMNC for removal of phenolic compounds was assessed through adsorption of 4-nitrophenol (4-NP) from aqueous solution. The three-factor Box-Behnken design coupled with response surface method was applied to evaluate and optimize the important variables which affect the adsorption process. A significant quadratic model (p-value <0.05, R-(adj)(2) = 0.9593) was derived using analysis of variance. The maximum adsorption capacity of 125.4 mg 4-NP/g MMNC at pH 6 was obtained, which was comparable in some cases and higher than most adsorbents reported in the literature. The presence of neomycin on graphene oxide sheets improved the maximum adsorption capacity of the nano-sorbent up to 28% (from 98.7 to 125.4 mg 4-NP/g adsorbent). The adsorption isotherms fitted well with the Langmuir model (Langmuir constant b = 0.064 l/mg, R-2 = 0.9989) and the kinetic study showed that the nitrophenol uptake process followed the pseudo-second-order rate expression (R-2 >= 0.9960, pseudo-second-order constant K-2 >= 1.7 x 10(-3)).