Highly-efficient and easy separation of γ-Fe2O3 selectively adsorbs U(Ⅵ) in waters

Constructing Ce-OH groups on CeO2 for enhancing removal and recovery of uranium from wastewater and seawater

Efficient recovery of uranium from wastewater and seawater provides an important guarantee for the sustainable growth of nuclear energy. Herein, we skillfully use the alkali etching method to construct CeO2 hollow spheres rich in Ce-OH groups for the removal and recovery of uranium from water matrixes. It is found that the CeO2 exhibits fast adsorption kinetics (equilibrium time within 10 min) and moderate adsorption capacity (143.1 mg/g), and the removal efficiency of low concentration uranium (0.1 g/L and 1 g/L) reaches 100% within 1 min of adsorption. Moreover, the adsorption of uranium by CeO2 is almost unaffected by common anions and cations in the environment, even if the concentration of anions is 1000 times that of uranium. More importantly, the CeO2 can enrich uranium concentration in seawater by 167.9 times and the recovery rate reaches 83.9%. Mechanistic studies reveal that the adsorption of uranium by CeO2 is mainly attributed to the rich Ce-OH groups on the surface of CeO2, resulting in the rapid adsorption of U(VI) and mainly forms a single-bridge model. The findings of this study provide a green and efficient path for the removal and recovery of uranium from wastewater and seawater.

A Phosphorylated Dendrimer-Supported Biomass-Derived Magnetic Nanoparticle Adsorbent for Efficient Uranium Removal

A novel biomass-based magnetic nanoparticle (Fe3O4-P-CMC/PAMAM) was synthesized by crosslinking carboxymethyl chitosan (CMC) and poly(amidoamine) (PAMAM), followed by phosphorylation with the incorporation of magnetic ferric oxide nanoparticles. The characterization results verified the successful functionalization and structural integrity of the adsorbents with a surface area of ca. 43 m2/g. Batch adsorption experiments revealed that the adsorbent exhibited a maximum adsorption capacity of 1513.47 mg·g-1 for U(VI) at pH 5.5 and 298.15 K, with Fe3O4-P-CMC/G1.5-2 showing the highest affinity among the series. The adsorption kinetics adhered to a pseudo-second-order model (R2 = 0.99, qe,exp = 463.81 mg·g-1, k2 = 2.15×10-2 g·mg-1·min-1), indicating a chemically driven process. Thermodynamic analysis suggested that the adsorption was endothermic and spontaneous (ΔH° = 14.71 kJ·mol-1, ΔG° = -50.63 kJ·mol-1, 298. 15 K), with increasing adsorption capacity at higher temperatures. The adsorbent demonstrated significant selectivity for U(VI) in the presence of competing cations, with Fe3O4-P-CMC/G1.5-2 showing a high selectivity coefficient. The performed desorption and reusability tests indicated that the adsorbent could be effectively regenerated using 1M HCl, maintaining its adsorption capacity after five cycles. XPS analysis highlighted the role of phosphonate and amino groups in the complexation with uranyl ions, and validated the existence of bimodal U4f peaks at 380.1 eV and 390.1 eV belonging to U 4f7/2 and U 4f5/2. The results of this study underscore the promise of the developed adsorbent as an effective and selective material for the treatment of uranium-contaminated wastewater.

Uranium recovery from weakly acidic wastewater using recyclable γ-Fe2O3@meso-SiO2

U(VI)-containing acidic wastewater produced from uranium mining sites is an environmental hazard. Highly efficient capture of U(VI) from such wastewater is of great significance. In this study, a mesoporous core-shell material (i.e. γ-Fe2O3@meso-SiO2) with magnetically and vertically oriented channels was rationally designed through a surfactant-templating method. Batch experiment results showed that the material had an efficiency level of >99.7% in removing U(VI) and a saturated adsorption capacity of approximately 41.40 mg/g, with its adsorption reaching equilibrium in 15 min. The U(VI) adsorption efficiency of the material remained above 90% in a solution with competing ions and in acidic radioactive wastewater, indicating its ability to selectively adsorb U(VI). The material exhibited high adsorption efficiency and desorption efficiency in five cycles of desorption and regeneration experiments. According to the results, the mechanism through which γ-Fe2O3@meso-SiO2 adsorbs U(VI) was dominated by chemical complexation and electrostatic attraction between these two substances. Therefore, γ-Fe2O3@meso-SiO2 is not only beneficial to control the environmental migration of uranium, but also has good selective adsorption and repeated regeneration performance when used to recover U(VI) from weakly acidic wastewater in uranium mining.

Synthesis and fabrication of segregative and durable MnO2@chitosan composite aerogel beads for uranium(VI) removal from wastewater

To address the imperative need for efficient removal of uranium-containing wastewater and mitigate radioactive contamination risks associated with nuclear energy, the development of materials with high removal efficiency and facile separation is crucial. This study designed and synthesised MnO2@chitosan (CTS) composite aerogel beads by in-situ growing δ-MnO2 on porous CTS aerogel beads. This approach not only mitigates the agglomeration of MnO2 nanospheres but also significantly enhances the porous structure and surface area of MnO2@CTS. These cost-effective and eco-friendly millimeter-scale spherical aerogels exhibited convenient separation properties after adsorption. These characteristics help mitigate the risk of equipment seam blockage and secondary pollution that are often associated with powdered adsorbents. Additionally, MnO2@CTS exhibited remarkable mechanical strength (stress approximately 0.55 MPa at 60 % strain), enabling rapid separation and easy regeneration while maintaining high adsorption performance even after five cycles. Significantly, MnO2@CTS exhibited a maximum adsorption capacity of 410.7 mg/g at pH 6 and 298 K, surpassing reported values for most CTS/MnO2-based adsorbents. The chemisorption process of U(VI) on MnO2@CTS followed the pseudo-second-order kinetic and Dubinin-Radushkevish models. X-ray photoelectron spectroscopy analysis further confirmed the reduction of U(VI) to U(V/IV). These findings highlight the substantial potential of MnO2@CTS aerogel beads for U(VI) removal from aqueous solutions, positioning them as a promising solution for addressing U(VI) contamination in wastewater.

Removal of ofloxacin from water by natural ilmenite-biochar composite: A study on the synergistic adsorption mechanism of multiple effects

The preparation cost is one of the major constraints for adsorbent applied to practical situations. Here, a novel, economical and eco-friendly ilmenite biochar composite (ILM-BC) was successfully prepared by co-cracking of natural ilmenite and corn stover for the removal ofloxacin from water. The adsorption experiments indicated that the removal ofloxacin by ILM-BC was chemisorption and belonged to a spontaneous and entropy-increasing heat absorption process. Among composites, ILM-BC5 had superior adsorption capacity and stability, with a removal rate 1.6 times higher than that of biochar, and it could remove more than 90% ofloxacin in the pH range of 2-10. Multiple characterization results indicated that the adsorption of ILM-BC was the result of the synergistic effect of pore filling, hydrogen bonding, and π-π interactions. The introduction of ilmenite promoted hydrogen bonding formation and π-π interactions by enriching -OH and -COO on the surface of ILM-BC, which could enhance the adsorption capacity of ILM-BC.

Highly selective adsorption and lattice process of cesium by cubic cyanide-based functional materials

Cesium (Cs) is a byproduct of nuclear bombs, nuclear weapons testing, and nuclear fission in nuclear reactors. Cs can enter the human body through food or air and cause lasting damage. Highly efficient and selective removal of ¹³⁷Cs from low-level radioactive effluents (LLREs), which contain many radionuclides and dissolved heavy metal species, is imperative for minimizing LLRE volume, and facilitating their final disposal. Prussian blue analogs (PBAs) have received much attention as materials for the removal of radioactive Cs because of their affinity for adsorbing Cs⁺. In this study, an inexpensive and readily available cyanide-based functional material (PBA_Cu) exhibiting high efficiency and excellent selectivity toward Cs capture was designed through a facile low-temperature co-precipitation process. Nano-PBA_Cu, crystallizing in the cubic space group (Fm-3m (225)), has an average pore size of 6.53 nm; consequently, PBA_Cu can offer abundant atomic occupation sites for capturing and incorporating Cs. Here, the pseudo-second-order kinetic model and Langmuir model fitted well with the adsorption of Cs ⁺ on PBA_Cu, with a maximum capture capacity of 95.75 mg/g within 5 min, confirming that PBA_Cu could rapidly capture Cs ions. PBA_Cu strongly and selectively interacted with Cs even in a simulant containing large Na⁺, NH₄⁺, Ca²⁺, and Mg²⁺ ion concentrations in an aqueous solution. The process of Cs ⁺ adsorption by cyanide-based functional crystals was confirmed to involve the entry of Cs⁺ into cyanide-based functional crystals to replace K⁺ and finally achieve the lattice incorporation of Cs. The current results broaden the lattice theory of radionuclide Cs removal and provide a promising alternative for the immobilization of Cs from radioactive wastewater.

Applications of Nano Hydroxyapatite as Adsorbents: A Review

Nano hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has aroused widespread attention as a green and environmentally friendly adsorbent due to its outstanding ability in removing heavy metal ions, radio nuclides, organic pollutants and fluoride ions for wastewater treatment. The hexagonal crystal structure of HAp supports the adsorption mechanisms including ionic exchange reaction, surface complexation, the co-precipitation of new partially soluble phases and physical adsorption such as electrostatic interaction and hydrogen bonding. However, nano HAp has some drawbacks such as agglomeration and a significant pressure drop during filtration when used in powder form. Therefore, instead of using nano HAp alone, researchers have worked on modificationsand composites of nano HAp to overcome these issues and enhance the adsorption capacity. The modification of cationic doping and organic molecule grafting for nano HAp can promote the immobilization of ions and then increase adsorption capacity. Developing nano HAp composite with biopolymers such as gelatin, chitosan and chitin has proven to obtain a synergetic effect for improving the adsorption capacity of composites, in which nano HAp fixed and dispersed in polymers can playmuch more of a role for adsorption. This review summarizes the adsorption properties and adsorbent applications of nano HAp as well as the methods to enhance the adsorption capacity of nano HAp.

Adsorption of Methylene Blue on Azo Dye Wastewater by Molybdenum Disulfide Nanomaterials

In this study, flower-like MoS2 nanomaterials were synthesized by hydrothermal method with excess thiourea. The adsorption performance of MoS2 adsorbent for methylene blue (MB) in azo dye wastewater was studied. The morphology, crystal phase, and microstructure of nano MoS2 samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The effects of adsorption isotherm, kinetics, different hydrothermal time, and pH on the adsorption experiment were studied. The results showed that the MoS2 adsorbent with a hydrothermal time of 1 h had good adsorption properties for MB. The adsorption data accord with the Langmuir isotherm model, and the maximum adsorption capacity of MoS2 adsorbent is 200 mg/g, and the adsorption kinetics agrees well with the pseudo two-level model. The removal rate of MB is not significantly affected by the pH values. The large pH range can still maintain the removal rate above 93.47%, and the regeneration and recovery properties of MoS2 were also explored. Finally, the adsorption mechanism of MoS2 on MB is discussed.