Ultra-high adsorption capacity of MgO/SiO₂ composites with rough surfaces for Congo red removal from water

Due to its high isoelectric point, relative safety and low environmental toxicity, magnesium oxide has attracted much attention for its role in the removal of toxic dyes from wastewater. Herein, MgO-SiO₂ composites with rough surfaces were synthesized by a one-step method. The as-prepared composites were characterized for the adsorption of Congo red from water using adsorption kinetics and isotherms. The adsorption capacity of the 20% MgO-SiO₂ sample could be as high as ∼4000mg/g at 25°C, which is the highest value reported to date. The adsorption process of Congo red on the as-synthesized samples obeyed the Langmuir adsorption model. The MgO-SiO₂ composite sample could be regenerated by calcination, and the regeneration efficiency remained for up to 5 cycles of the regeneration.