Adsorption of MB and Pb(II) before and after magnetic modification: Performance and mechanism

Abstract

This study described the simple fabrication process of manganese dioxide decorated composites(Mn@RS) and magnetic-functional modified composites (MC-Mn@RS) that can effectively adsorb MB and Pb(II) in the aqueous medium. The structural and physicochemical characteristics of the as-prepared composites were evaluated by BET, XRD, SEM, FTIR, XPS, point of zero charge (pHPZC), TGA and VSM techniques. The effect of the contact time, pH value, and initial concentration on the adsorption capacity of MB and Pb(II) onto Mn@RS and MC-Mn@RS were investigated by using batch equilibrium experiments. The results exhibited that in single system, the adsorption capacity of Mn@RS against MB and Pb(II) were obtained 128.5 mg g−1 and 196.04 mg g−1, respectively. The adsorption capacity of MC-Mn@RS against MB and Pb(II) were obtained 325.8 mg g−1 and 98.07 mg g−1, respectively. Till now, the mutual effects and competitive adsorption of MB and Pb(II) onto biochars have never been reported. In the binary systems, the Pb (II) adsorption on Mn@RS was severely inhibited, while the uptake of MB was not affected significantly, clearly demonstrating the adsorption affinity was in the order of MB > Pb(II) in the coexisting solution. The electrostatic attraction, complexation, surface precipitation and physical adsorption were the main adsorption mechanism of Pb (II) on Mn@RS and MC-Mn@RS. The adsorption mechanism of MB on Mn@RS mainly contained electrostatic attraction, π-π interaction, n–π interaction and electrostatic attraction, while that on MC-Mn@RS mainly were determined by pore filling and n–π interactions. In addition, the MC-Mn@RS exhibited excellent reusability (retained 90.76% removal efficiency after five cycles) and solid–liquid separation efficiency due to strong magnetism(24.78 emu g−1). The gained results were powerful proof for removing MB and Pb(II) from wastewater, economically and effectively, and for paving the way to the preservation of cleaner fresh water resources and a greener society.