Characteristics and batch experiments of acid- and alkali-modified corncob biomass for nitrate removal from aqueous solution.

In this study, modified biochar was adopted as an adsorbent for the nitrate removal in aqueous solutions. Raw material was impregnated in sulfuric acid (H2SO4, 1 mol/L) and sodium hydroxide (NaOH, 2 mol/L) separately and then prepared at 600 °C. After treated with acid, the BET specific surface area was much higher than that of unmodified and alkali-modified biochars. The low adsorption capacity and specific surface area of alkali-modified biochar may be due to the precipitate on the surface according to the results of XRD. In addition, the C-OH and C-H functional groups played a major part during adsorption progress. The batch experiments demonstrated that the acid-modified biochar exhibited a more excellent absorbability (12.75 mg/g) under the circumstance of neutral solution and room temperature. The maximum adsorption capacity of MSA-CC was 34.20 mg/g, which was about 2.4 times higher than that of the unmodified. Low pH value can provide positive charge conditions to enhance the adsorption capacity. Overall, the biochar with excellent pore structure and chargeable functional group can be a potential application for nitrate removal which was low cost and effective. After treated with acid, biochar could adsorb negative charge species like nitrate due to electrostatic interaction. Graphical abstract.