Sodium ions removal by sulfuric acid-modified biochars

Sulfuric acid modifies the biochar derived from corn cobs, stalks, and reeds. Amongst the modified biochar, corn cobs-biochar has the highest BET (101.6 m² g^-1), followed by reeds-biochars (96.1 m² g^-1). The Na⁺ adsorption capacities for pristine biochars are corn cobs-pristine biochar: 24.2 mg g^-1, corn stalks-pristine biochar: 7.6 mg g^-1, and reeds-pristine biochar: 6.3 mg g^-1, relatively low for field applications. The acid-modified corn cobs biochar has a superior Na⁺ adsorption capacity of up to 221.1 mg g^-1, much higher than literature reports and the other two tested biochars. This corn cobs-modified biochar has also a satisfactory Na⁺ adsorption capacity (193.1 mg g^-1) from actual water collected from a sodium-contaminated city, Daqing, China. The FT-IR spectroscopy and XPS spectrum reveal that the embedded surface -SO₃H groups onto the biochar correlate with its superior Na ⁺ adsorption, attributable to the ion exchange mechanisms. The biochar surface accessible to sulfonic group grafting can generate a superior Na⁺ adsorbing surface, which is for the first time reported and has great application potential for the remediation of sodium-contaminated water.