Onion-like Nanocarbons from Diesel Particulate Soot for the Adsorption of Uranium and Thorium Ions from Water

Abstract Herein, we propose a simple approach for using onion-like nanocarbons (ONC) isolated from black diesel soot particulate matter as an adsorbent for uranium (U(VI)) and thorium (Th(IV)) ions from aqueous solutions. Oxidized-ONC (Oxi-ONC), having surface functionalities as carboxylic and hydroxyl groups, was synthesized by the oxidative treatment of ONC using nitric acid. The adsorption capabilities of Oxi-ONC have been optimized under various pH values, adsorbent dosages, contact time, and initial concentrations. Compared to ONC, Oxi-ONC showed better results, removing U(VI) and Th(IV) ions with ∼ 86.25% (∼43.58% for ONC) and ∼ 97.46% (∼74.11% for ONC) removal efficiency at 50 mg/L(U(VI) and 100 mg/L Th(IV), respectively, under optimized conditions. In continuation, we have compared the adsorption capabilities of Oxi-ONC with those of commercially available adsorbents like activated carbon (AC) and found better adsorption capacity, which supports the viability of the reported process for utilizing the pollutant soot as an adsorbent material. Different kinetics studies revealed that the adsorption of U(VI) and Th(IV) on Oxi-ONC follows pseudo-second-order kinetics, with the Langmuir adsorption isotherm providing a suitable fit, demonstrating maximum adsorption capacities (∼151.28 for U(VI) and ∼553.07 mg/g for Th(IV) respectively). Regarding recyclability, Oxi-ONC was tested over 6 adsorption–desorption cycles with minimal reduction in removal efficacy.