Synthesis of porous MgO-biochar nanocomposites for removal of phosphate and nitrate from aqueous solutions

A new synthesis was developed to create highly porous nanocomposite material consisting of MgO nano-flakes within a biochar matrix that has high sorption ability for ionic contaminations. The synthesis method was used in laboratory to produce MgO-biochar nanocomposites from a variety of carbon-rich biomass. Physical and chemical properties of the synthesized nanocomposites were studied systematically with X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray analysis. In addition, batch sorption experiment was conducted to determine the sorption ability of the MgO-biochar nanocomposites to aqueous phosphate and nitrate. The results showed that the MgO nano-flakes have uniform morphologies and disperse uniformly on the surface of the biochar matrix. HR-TEM indicated that the biochar matrix is mesoporous with average pore size of 50nm and the MgO nano-flakes have spacing between 2 and 4nm, which can serve as adsorption sites for anions. As a result, all the tested MgO-biochar nanocomposites showed excellent removal efficiencies to phosphate and nitrate in water. Nanocomposites made from sugar beet tailings and peanut shells had the best performances with Langmuir adsorption capacities as high as 835mgg ^-1 for phosphate and 95mgg ^-1 for nitrate, respectively, much higher than the reported values of other adsorbents.