Fabrication of a porous polyacrylonitrile nanofiber adsorbent for removing radioactive 60Co

Eco-friendly synthesis of rod-like hydroxyapatite on spherical carbon: A dual-function composite for selective cobalt removal and enhanced oxygen evolution reaction

The presence of cobalt ions (Co2 +) and radionuclides (60Co) in industrial and radioactive effluents pose serious threats to environmental ecosystems and human health. This paper presents the synthesis of dual-functional hydroxyapatite (HAp)-incorporated spherical carbon (SC) composite (HAp/SC) towards the selective adsorption of cobalt from wastewater and the utilization of the Co2+-adsorbed HAp/SC composite (Co2+- HAp/SC) as an electrocatalyst for the oxygen evolution reaction (OER). Herein, we prepared a series of HAp/SC composites by varying HAp weight percentages of 10 %, 20 %, 30 %, 40 %, and 50 %. Among the prepared composites, 20 wt% HAp/SC exhibited the highest Co2+ adsorption capacity of 111.03 mg g⁻1 which was higher than those of individual HAp and SC. The excellent Co2+ adsorption performance of 20 wt% HAp/SC composite might be due to the synergistic effects of phosphate groups in HAp, which selectively capture Co2+, along with large number of surface -OH and -COOH functional groups of SC through electrostatic, ion-exchange, and surface complexation mechanisms. Batch adsorption experimental data fit well with the Langmuir model (R2 = 0.97) suggesting monolayer adsorption of Co2+ onto the adsorption sites of HAp/SC. Also, the 20 wt% HAp/SC composite exhibited rapid Co2+ adsorption kinetics and effectively describing the pseudo-first-order model (R2 = 0.97) with a rate constant (k1) of 0.14893 min-1. Additionally, the Co2+-HAp/SC composite demonstrates potential as an electrocatalyst for the oxygen evolution reaction (OER), exhibiting an overpotential of 380 mV and a Tafel slope of 39.3 mV dec-1. This dual functionality suggests the HAp/SC composite for the cobalt removal, with the resulting product serving as an electrocatalyst for OER.

Facile preparation of UiO-66-Lys/PAN nanofiber membrane by electrospinning for the removal of Co(II) from simulated radioactive wastewater

In this study, metal-organic framework (MOF) nanofiber membranes (NFMs) UiO-66-Lys/PAN were prepared by electrospinning using polyacrylonitrile (PAN) as the matrix, UiO-66-NH2 as the filler, and lysine (Lys) as the functional monomer. The membranes were subsequently employed to extract cobalt ions from simulated radioactive wastewater. The findings showed that the best performance of the membrane was obtained with a 3 % MOF content (3%UiO-66-Lys/PAN). Specifically, the pure water flux (PWF) of the 3 % UiO-66-Lys/PAN membrane reached 872 L m-2 h-1 with a cobalt ion retention of 45.4 %. In addition, adsorption experiments indicated that the NFMs had a theoretical maximum adsorption capacity of 41.4 mg/g for cobalt ions. The Langmuir isotherm model and the pseudo-second-order kinetic model were observed in the adsorption process, suggesting that the membrane material showed uniform adsorption of cobalt ions on a monolayer level, with an endothermic absorption process. XPS analysis confirmed that 3%UiO-66-Lys/PAN facilitated the adsorption of cobalt ions through a coordination effect, with the N and O atoms serving as coordinating atoms. Moreover, the material displayed excellent radiation stability even when exposed to doses ranging from 20 to 200 kGy. This study validated the stability of the MOF NFMs under real irradiation with radioactive nuclides (60Co) and demonstrated efficient cobalt ion separation. This study has important practical implications for the treatment and disposal of small volumes of 60Co-containing radioactive wastewater for engineering applications.