An Efficient Adsorption of Manganese Oxides/Activated Carbon Composite for Lead(II) Ions from Aqueous Solution

The purpose of this study was to prepare a new type of efficient eco-material for removal of \(\hbox {Pb}^{2+}\) from waste water. A manganese oxide/activated carbon composite (\(\hbox {Bio-MnO}_{x}/\hbox {AC}\)) was prepared by carbonizing the biogenic manganese oxides produced by Mn-oxidizing bacterial Marinobacter sp. MnI7-9 in a tube furnace under \(\hbox {N}_{2}\) (20–100 mL/min) at 573 K for 2 h. \(\hbox {Bio-MnO}_{x}/\hbox {AC}\) was found to contain carboxyl and hydroxyl groups, crystalline \(\hbox {Mn}_{3} \hbox {O}_{4}\), and manganosite. The composite’s adsorption capacity for \(\hbox {Pb}^{2+}\) reached \(1128 \pm 42\) mg/g at 298 K, which is nearly 4–9 times higher than that of commercially available activated carbon and chemical Mn oxides and is also higher than those of other biomaterial-sourced activated carbons reported in previous studies. The adsorption kinetics data at 298 K could be described by pseudo-second-order kinetics with \({R}^{2} = 0.9867\), and the adsorption isotherm data could be described by a Langmuir isotherm with \({R}^{2} = 0.9999{-}0.9998\) at 293, 303, 313 and 323 K. The adsorption capacity was observed to increase with increasing pH. In this system, adsorption is weakly affected by ionic strength. Adsorption occurs through chemical sorption and is endothermic. The carboxyl and hydroxyl groups play an important role in \(\hbox {Pb}^{2+}\) adsorption through surface complexation with \(\hbox {Pb}^{2+}\). These results indicate that it is practicable to remove \(\hbox {Pb}^{2+}\) from wastewater using \(\hbox {Bio-MnO}_{x}\)/C and reveal a new use of biogenic Mn oxides.