Efficient adsorption of ammonia on activated carbon from hydrochar of pomelo peel at room temperature: Role of chemical components in feedstock

Abstract

Activated carbon derived from the organic solid waste is a promising material for ammonia removal. The components in the feedstock would affect the performance of activated carbon, but the detailed effect mechanism remains unknown. To reveal the correlations between the components of the feedstock and different ammonia adsorption styles of activated carbon, this study used pomelo peel to prepare ZnCl2-loaded activated carbon for ammonia adsorption via hydrothermal carbonization and KOH activation, focusing on the effect of the chemical components (cellulose, xylan, pectin, and lignin) on the physicochemical properties and adsorption performance of activated carbon. For raw activated carbon in moist conditions, ammonia was mainly adsorbed in the form of Lewis/Brønsted acid-base (37.8 mg/g), followed by the ZnCl2 coordination compound and organic amine forms (22.3 mg/g). Lignin-added activated carbon had the highest adsorption capacity, 91.2 mg/g in moist conditions, followed by cellulose-added and xylan-added activated carbon. The presence of lignin was beneficial for the formation of the phenolic group of activated carbon (increased by 111.3%), which promoted ammonia adsorption in the form of Lewis acid-base, especially in dry condition. Cellulose and xylan enhanced the formation of carboxylic (i.e., increased by 53.0% for cellulose) and lactonic groups (i.e., increased by 73.4% for cellulose) of activated carbon, leading to an increase of ammonia adsorption in the form of Brønsted acid-base and organic amines in moist conditions. The results illustrated the detailed effect of the chemical components in the feedstock on the ammonia adsorption styles, which could guide the selection of appropriate materials to prepare activated carbon for highly efficient ammonia adsorption under various situation.