Characterization of Mixed Metal Biogenic Manganese Oxide Materials for Catalysis and Rare Earth Element Sequestration

This study explores the potential of utilizing biogenic manganese oxides (BMOs) produced by Mn-oxidizing Pseudomonas putida MnB1 to facilitate metal cation uptake for rare earth element (REE) sequestration and the synthesis of novel materials. Previous studies have shown that P. putida MnB1 efficiently oxidizes environmental Mn(II) to Mn(IV)-oxides, producing BMOs with unique physicochemical properties. Unlike their abiotic counterparts, BMOs exhibit high surface area, reactivity, and amorphous, poorly crystalline structures, making them promising platforms for adsorbing metal cations. This research study, building on the prior work, demonstrates the incorporation of ten different main group, transition, and rare earth metals into the BMO material, with structural characterization conducted via scanning electron microscopy and powder X-ray diffraction. Compositional characterization was determined by inductively coupled plasma optical emission spectroscopy and energy dispersive X-ray spectroscopy via scanning electron microscopy. Following the initial screening of these ten cations, batch adsorption studies were performed for a representative light REE, heavy REE, and transition metal-spiked sample prepared with real wastewater effluent indicating that the BMO material in this study is promising for sequestering REEs from real water streams. These findings advance the understanding of biologically mediated metal adsorption and open pathways for designing new functional materials with potential applications in rare earth sequestration and catalysis. To highlight this later point, the BMO materials with an incorporated main group (Al3+, Ca2+) or transition metal cation (Fe3+, Cu2+) were tested electrochemically for their ability to act as water oxidation catalysts, and each of these materials’ activity was comparable to BMO except for the material with incorporated iron, which showed significantly enhanced activity.