Nanoporous activated carbons derived from water ferns as an adsorbent for removal of paraquat from contaminated water

Abstract

Nanoporous activated carbons (NACs) were prepared from water ferns (Azollar Pinnata) via hydrothermal carbonization (HTC) followed by a chemical activation process using potassium hydroxide (KOH) at 700 °C. The ratio of hydrochar to KOH was varied at 1:1, 1:2, and 1:3. The morphology of the NACs exhibited a uniform sponge-like porous structure with enhanced specific surface area and porosity. With an increase in KOH content, the specific surface area increased from 26 to 2848 m2 g–1 while the pore volume increased from 0.037 to 1.552 cm3 g–1. The significant increase in the specific surface area and pore volume of NACs was attributed to the development of micro- and mesoporosity. Commercial paraquat (Gramoxone) at the concentration of 1.5–45 mg L–1 was used as the pollutant target to evaluate the adsorption ability of NACs. The removal efficiency of paraquat from water reached 100% up to a paraquat concentration of 7.5 mg L–1. Moreover, the paraquat adsorption of NACs could be explained with the Langmuir model. The maximum adsorption capacity of NACs ranged within 15–20 mg g–1, where their enhanced removal efficiency and maximum adsorption capacity for paraquat removal were attributable to the increase in surface area and development of micro- and mesoporosity. The results of this work indicated the practicality of water-fern-derived NACs as an alternative adsorbent for the removal of paraquat and other organic pollutants in water.