Manganese Oxychloride-Modified Hydrophobic Silica Targets Removal of Nitrates from Water

Abstract

Poised to gain insight into nitrate adsorption and removal processes from water through employment of modified surfaces, a well-defined inorganic manganese species was used in connection with hydrophobic mesoporous silica. To this end, the surface of hydrophobic mesoporous silica was modified by coating silica with a manganese oxychloride (Mn8O10Cl3) nanoparticle layer. A sol–gel method was utilized for the synthesis of hydrophobic silica, using tetraethyl orthosilicate–methyl triethoxysilane (TEOS–MTES) as precursors. Subsequent coating with Mn8O10Cl3 took place by mixing MnCl2 and NaOH with hydrophobic silica. Physicochemical characterization of the Mn8O10Cl3-coated silica was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 sorption. The achieved surface modification reduced remarkably the specific surface area by 80.7 % and influenced the ability of nitrates to adsorb on Mn-modified silica. Nitrate adsorption kinetics on Mn8O10Cl3-coated silica was studied by a batch reactor. Process parameters including pH, temperature, and initial nitrate concentration were examined thoroughly. The experimental adsorption data were fitted satisfactorily through Langmuir isotherm equations and were found to be well-represented by a pseudo-second-order kinetic model. The collective data emphasize the significance of well-defined inorganic manganese phases, coating hydrophobic silica, in optimally influencing water decontamination from pollutant nitrates.