Nitrogen- and oxygen-doped carbon particles produced from almond shells by hydrothermal method for efficient Pb(II) and Cd(II) adsorption

Abstract

In this study, a two-step method was applied to obtain an effective adsorbent for cadmium (Cd) (II) and lead (Pb)(II) adsorption. The first stage includes the production of activated carbon (AC) from almond shells, which is agricultural waste, by microwave heating and potassium hydroxide (KOH) chemical agent. The second stage includes nitrogen and oxygen doping by hydrothermal heating treatment of the obtained ACs with nitric acid. The obtained materials were characterized by thermogravimetric/differential thermal analyser (TG-DTA); Fourier transform infrared spectroscopy (FTIR); scanning electron microscope (SEM); energy-dispersive spectroscopy (EDS); C, H, N, S elemental analysis; and nitrogen adsorption analyses. The adsorption performance, mechanism, kinetics, and thermodynamics of nitrogen- and oxygen-doped activated carbons were evaluated. The obtained isotherm and kinetic results showed that the adsorption of Cd (II) and Pb (II) on nitrogen- and oxygen-doped ACs followed Langmuir isotherm and pseudo-second-order kinetics. The adsorption capacity values (Qm) obtained for Cd (II) and Pb (II) adsorption were 106.38 mg/g and 76.33 mg/g, respectively.