Carbohydrate-based activated carbon with high surface acidity and basicity for nickel removal from synthetic wastewater

Abstract

The feasibility of preparing activated carbon (AC-CHs) from carbohydrates (glucose, sucrose and starch) with phosphoric acid activation was evaluated by comparing its physicochemical properties and Ni(II) adsorption performance with a reference activated carbon (AC-PA) derived from Phragmites australis. The textural and chemical properties of the prepared activated carbon were characterized by N₂ adsorption/desorption isotherms, SEM, Boehm's titration and XPS. Although AC-CHs had much lower surface area (less than 700 m² g⁻¹) than AC-PA (1057 m² g⁻¹), they exhibited 45–70% larger Ni(II) adsorption capacity which could be mainly attributed to their 50–75% higher contents of total acidic and basic groups. The comparison of XPS analyses for starch-based activated carbon before and after Ni(II) adsorption indicated that Ni(II) cation combined with the oxygen-containing groups and basic groups (delocalized π-electrons) through the mechanisms of proton exchange, electrostatic attraction, and surface complexation. Kinetic results suggested that chemical reaction was the main rate-controlling step, and a very quick Ni(II) adsorption performance of AC-CHs was presented with ∼95% of maximum adsorption within 30 min. Both adsorption capacity and rate of the activated carbon depended on the surface chemistry as revealed by batch adsorption experiments and XPS analyses. This study demonstrated that AC-CHs could be promising materials for Ni(II) pollution minimization.