Modified Δ-Mno 2  Based on Transition Metal Doping: Enhanced Adsorption and Stabilization of Dissolved Organic Matter

Abstract

Sodium manganese oxide (δ-MnO2) can oxidize and polymerize dissolved organic matter (DOM) through the Mars-van-Krevelen (Mvk) mechanism. Enhancing this mechanism could achieve rapid stabilization of DOM in water bodies, which is valuable for ecological carbon sink engineering. This study synthesized δ-MnO2 doped with Ni and Zn metals via hydrothermal method. The DOM adsorption and oxidation polymerization performance of original and modified δ-MnO2 were compared and analyzed. Scanning electron microscopy (SEM) and surface area/porosity analyses showed increased adsorption sites on the modified material surfaces. Ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and three-dimensional excitation-emission matrix (3D-EEM) data proved 35% higher DOM adsorption capacity and 45% more humic-like substances formation for modified δ-MnO2, with dry-wet cycling further improving the DOM adsorption and stabilization. EDS spectral analysis revealed decreased O content from 64% to 44%, indicating oxygen vacancy (OV) formation and involvement of lattice oxygen in reactions to accelerate DOM polymerization via the Mvk mechanism. This study presents a transition metal doping method to enhance δ-MnO2 performance for adsorbing and stabilizing DOM, providing an approach for water pollution control and carbon sequestration applications.

Keywords: Keywords: sodium manganese oxide, stabilization, Mvk mechanism, metal doping