Preparation of Ag-MnFe2O4-bentonite Magnetic Composite for Pb(II)/Cd(II) Adsorption Removal and Bacterial Inactivation in Wastewater

Abstract

An Ag-MnFe2O4-bentonite composite was synthesized by a chemical co-precipitation method and used for adsorption removal of Pb(II), Cd(II) and disinfection. The result of X-ray diffraction indicate that the diffraction peaks of MnFe2O4 and Ag can be perfectly indexed to the cubic spinel MnFe2O4(JCPDS No.88-1965) and metallic Ag(JCPDS No.41-1402), respectively. The results of scanning electron microscopy and energy dispersive X-ray spectroscopy manifest the deposition of MnFe2O4 and Ag on the bentonite surface and the presence of Mn, Fe and Ag. The result of X-ray photoelectron spectroscopy displayed that the composition of Ag-MnFe2O4-bentonite was Mn(II), Fe(III) and metallic Ag. The analysis of Brunauer-Emmett-Teller showed that the specific surface area of Ag-MnFe2O4-bentonite was the largest compared with that of bentonite, MnFe2O4 and MnFe2O4-bentonite. Thermo-dynamic studies revealed that the adsorption of Pb(II) and Cd(II) ions was spontaneous and endothermic. Langmuir model showed an adsorption capacity of 129.87 mg/g for Pb(II) and 48.31 mg/g for Cd(II) ions. The adsorption ki-netics of Pb(II) and Cd(II) ions onto Ag-MnFe2O4-bentonite can be best described by a pseudo-second-order model. The adsorption rate constant of the pseudo-second-order model was 0.0019 g·mg‒1·min‒1 for Pb(II) and 0.0065 g·mg‒1·min‒1 for Cd(II) ions. In addition to the adsorption experiment, the antibacterial properties of Ag-MnFe2O4-bentonite were studied through plate count method. Gram-negative(G‒) bacteria Escherichia coli and Gram-positive(G+) bacteria Lactobacillus plantarum were used to test the antibacterial properties. The results showed that the composite demonstrated excellent antibacterial activity. Thus, Ag-MnFe2O4-bentonite can be em-ployed as an adsorbent as well as an antimicrobial agent.