Biochar modified by ammonium pyrrolidine dithiocarbamate for high selective adsorption of copper in wastewater

Abstract

Biochar application in wastewater purification is extremely appealing. Although heteropolysaccharides like Gum Seyal biochar (BC GS500) display great surface area and porosity, the adsorption capacity for Cu (II) was relatively low due to the week-binding surface functional groups. In this work, an innovative modification with the chelating agent ammonium pyrrolidine dithiocarbamate (APDC) capable of selectively and effectively adsorbing Cu (II) was conducted. Gum Seyal biochar was grafted with pyrrolidine dithiocarbamate (C5H8NS2–), amine (–NH2), and imine (–NH) groups using APDC based on the “hard and soft acids and bases theory” (HSAB). Batch studies, along with characterization (FITR, XPS, and SEM-EDS), molecular electrostatic potential (MEP) mapping, and density functional theory (DFT) calculations, were implemented to investigate the adsorption performance and mechanism responsible for selectively adsorptive Cu (II) removal. It was found that Cu (II) adsorption by modified biochar occurred endothermically and spontaneously. The adsorption data at pH 5 matched the pseudo-second-order kinetic model and the Langmuir isotherm (211.24 mg/g). DFT calculations show that modified biochar selectively binds Cu (II) superior to common ions such as Mg (II) and Ca (II) through a unique chelating mechanism. Their performance in real electroplating wastewater was investigated, and the production cost was estimated. It was concluded that the modified biochar (BC APDC) could have high applicable potential for Cu (II)-laden wastewater purification.