Three-dimensional graphene oxide/phytic acid composite for uranium(VI) sorption

Efficient uranium(VI) adsorbing bioinspired nano-sized hydroxyapatite composites: synthesis, tuning, and adsorption mechanism

The production of large amounts of uranium-containing wastewater and its potential hazards has stimulated green and efficient material removal of uranium (VI). Inspired by the natural mineralization of bone, a facile and eco-friendly biomimetic synthesis of nano-hydroxyapatite (HAP) was carried out using chitosan (CS) as a template. It was found that the reaction temperature and the amount of precursors influence the particle size, crystallinity and specific surface area of the CS/HAP nanorods, and consequently their U(VI) adsorption efficiency. Moreover, the synthesized CS/HAP-40 with smaller particle size, lower crystallinity, and larger specific surface area show a more efficient U(VI) removal compared with CS/HAP-55 and CS/HAP-55-AT. It has a maximum adsorption capacity of 294.12 mg·g^-1 of the CS/HAP-40. Interestingly, the U(VI) removal mechanism of CS/HAP-40 in acidic (pH = 3) and alkaline (pH = 8) aqueous solutions was found to be different. As one of the main results, the U(VI) adsorption mechanisms at pH 8 could be surface complexation and ion exchange. On the contrary, three different mechanisms could be observed at pH 3: dissolution-precipitation to form chernikovite, surface complexation, and ion exchange.

Graphene-based materials for the adsorptive removal of uranium in aqueous solutions

Ground water contamination by radioactive elements has become a critical issue that can pose significant threats to human health. Adsorption is the most promising approach for the removal of radioactive elements owing to its simplicity, effectiveness, and easy operation. Among the plethora of functional adsorbents, graphene oxide and its derivatives are recognized for their excellent potential as adsorbent with the unique 2D structure, high surface area, and intercalated functional groups. To learn more about their practical applicability, the procedures involved in their preparation and functionalization are described with the microscopic removal mechanism by GO functionalities across varying solution pH. The performance of these adsorbents is assessed further in terms of the basic performance metrics such as partition coefficient. Overall, this article is expected to provide valuable insights into the current status of graphene-based adsorbents developed for uranium removal with a guidance for the future directions in this research field.

Decontamination of radioactive cesium-contaminated soil/concrete with washing and washing supernatant- critical review

We reviewed washing of radioactive Cs-contaminated concrete and soil based on the fate of Cs in concrete and soil, including sorption materials for treatment of supernatant solution. In non-aged cement materials (the calcium silicate hydration (C-S-H) phase), it was possible to decontaminate Cs using ion exchange with monovalent cations, such as NH₄⁺. The clay components in the soil and aggregates were important factors in optimization of the efficiency and mechanism for Cs decontamination with washing solution. The parameters (reagent component, pH, and temperature) of the washing solution should be determined considering soil mineral type (here, weathered biotite (WB) with vermiculite), since monovalent cations such as NH₄⁺ and K⁺ can inhibit Cs decontamination due to collapse of the hydrated and expanded interlayer regions with cation exchange. In this case, hydrothermal treatment or H₂O₂ dosing was necessary to expand the collapsed interlayer region for Cs removal by washing with cation exchange or organic acids. Acid and a chelating agent significantly enhanced Cs-release with dissolution of the adsorbent layer containing iron and aluminum oxides. The important characteristics of important and emerging sorption materials for treatment of the radioactive Cs-contaminated supernatant after washing treatment are discussed. Sorbents for treatment of washing supernatant are divided in to two main categories. Clay minerals, metal hexacyanoferrates, and ammonium molybdophosphates are discussed in the inorganic class of materials. Hypercrosslinked polymers, supramolecular sorbents, carbon nanotubes, and graphene oxide are covered in the carbon-based sorbents for Cs removal from water.

Study of Graphene Oxide Structural Features for Catalytic, Antibacterial, Gas Sensing, and Metals Decontamination Environmental Applications

This study represents a comprehensive review about the structural features of graphene oxide (GO) and its significance in environmental applications. Two dimensional (2D) GO is tremendously focused in advanced carbon-based nanomaterials for environmental applications due to its tunable physicochemical characteristics. Herein, we report foundational structural models of GO and explore the chemical bonding of oxygen moieties, with graphite basal plane using various characterization tools. Moreover, the impact of these oxygen moieties and the morphology of GO for environmental applications such as removal of metal ions and catalytic, antibacterial, and gas sensing abilities have here been critically reviewed for the first time. Environmental applications of GO are highly significant because, in the recent era, the fast progress of industries, even in the countryside, results in air and water pollution. GO has been widely investigated by researchers to eradicate such environmental issues and for potential industrial and clinical applications due to its 2D structural features, large surface area, presence of oxygen moieties, nonconductive nature, intense mechanical strength, excellent water dispersibility, and tunable optoelectronic properties. Thence, particular emphasis is directed toward the modification of GO by varying the number of its oxygen functional groups and by coupling it with other exotic nanomaterials to induce unique properties in GO for potential environmental remediation purposes.