Magnetic multi-walled carbon nanotubes modified with polyaluminium chloride for removal of humic acid from aqueous solution

Abstract

Magnetic multi-walled carbon nanotubes (MWCNTs) prepared by chemical co-precipitation method were loaded with polyaluminium chloride (PAC) using microwave irradiation to synthesize magnetic PAC multi-walled carbon nanotubes (M-PAC-MWCNTs) for removal of humic acid (HA) from aqueous solution. M-PAC-MWCNTs were characterized by field emission scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, specific surface area (SSA) and vibrating-sample magnetometer (VSM), respectively. The results showed that PAC and magnetic matters Fe3O4 and γ-Fe2O3 were coated on MWCNTs. The effect of M-PAC-MWCNTs dosage, pH value, HA initial concentration and contact time on removing HA from aqueous solution was also investigated. The HA removal rate was high to 98.57% at M-PAC-MWCNTs dosage of 0.5 g·L−1 and pH 7 for reaction time of 30 min at HA concentration 20 mg·L−1. In addition, kinetic, equilibrium and thermodynamic of the adsorption of HA on M-PAC-MWCNTs were studied. The adsorption process was well fitted by the pseudo-second-order kinetic model and Temkin isotherm model, declaring that chemical adsorption was primary and physical adsorption was complementary. Thermodynamics analysis revealed ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0, suggesting that the HA adsorption on M-PAC-MWCNTs was a spontaneous, endothermic in nature and entropy increase process. After MWCNTs were magnetized and modified by PAC, the adsorption performance of MWCNTs was greatly enhanced, mainly attributed to the interaction between PAC and humic acid through hydrogen-bond and electrostatic attraction.