Investigation of radionuclide 60Co(II) binding to TiO2 by batch technique, surface complexation model and DFT calculations

Removal of extremely low concentration cobalt by intercalation composite material of carbon nitride/titanium dioxide

Due to the high toxicity and the great harm of radioactive cobalt to the human body and the environment, the removal of heavy metal cobalt ions from radioactive wastewater had attracted more and more scientific researchers. In this paper, the intercalation composite material of carbon nitride itanium dioxide (g-C₃N₄/TiO₂) composite material which combined the advantages of the two materials was prepared and its actual effect of removing Co (Ⅱ) from wastewater was evaluated. Batch experimental method was employed for the investigation of the impact of solution pH during adsorption, adsorption kinetics, adsorption thermodynamics and adsorption isotherms. In this experiment, the saturation adsorption capacity of the composite material to Co (Ⅱ) was 91.55 mg/g, while the bulk g-C₃N₄ was only 13.2 mg/g. The adsorption kinetics showed that the adsorption process followed a pseudo-second-order kinetic model. The adsorption thermodynamic showed that the adsorption of Co (Ⅱ) was a spontaneous endothermic process. The Langmuir isotherm adsorption model was more consistent with the adsorption isotherm than the Freundlich model. The experimental results proved that g-C₃N₄/TiO₂ composite material had a good adsorption and removal effect on extremely low concentration of Co (II) and was a promising adsorbent for removal radioactive Co (II) from nuclear industrial wastewater.

Effect of co-existing Co2+ ions on the aggregation of humic acid in aquatic environment: Aggregation kinetics, dynamic properties and fluorescence spectroscopic study

The fate and transport of humic substances in the aquatic environments depend significantly on their interactions with co-existing ions. Herein, we employed dynamic light scattering (DLS) measurement, molecular dynamic (MD) simulation and fluorescence spectrometry to investigate the aggregation of humic acid (HA) in the presence of Co²⁺ ions. The aggregation kinetics was depicted by hydrodynamic diameter (<D_h>) and the attachment efficiency (α) of HA aggregates. α increases gradually in the reaction-limited (slow) regime due to the decrease of the double layer repulsion, and the energy barrier is eliminated to a certain extent in the diffusion-limited reaction while α close to unity. The complexation between functional groups (i.e. carboxylic and phenolic groups) of HA and Co²⁺ ions contributes significantly to the aggregation process of HA. MD simulation and density functional theory (DFT) calculation demonstrate that the aggregation process of HA can be promoted by Co²⁺ through several inter- or intra-molecular interactions between HA and the Co²⁺ ions. The results provide a pathway for insight into the interactions between HA and metal ions, which is important for deeply understanding the environmental behaviors of HA in natural aqueous systems.