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 m 2  g −1 ), followed by reeds-biochars (96.1 m 2  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 –SO 3 H 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.