Investigation of interaction between U(VI) and carbonaceous nanofibers by batch experiments and modeling study

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.

The preparation of dodecyl trimethyl ammonium bromide modified titanium dioxide for the removal of uranium

Radioactive contamination, especially the uranium pollution, is threatening the ecological environment. How to efficiently and quickly remove uranium from the environment is a problem to be solved. Herein, the dodecyl trimethyl ammonium bromide embellished titanium dioxide (DTAB/TiO₂) was prepared as an adsorbent to adsorb uranium (U) from water. The introduction of dodecyl trimethyl ammonium bromide can improve the adsorption capacity of titanium dioxide for U(VI). Besides, the excellent chemical stability of DTAB/TiO₂ would not result in secondary pollution, which was the novelty of this work. The DTAB/TiO₂ composite was composed of nanoparticles and presented a spherical morphology with a rough surface. The radius of DTAB/TiO₂ was 0.45 μm, and the specific surface area reached 144.0 m²/g. The removal of U(VI) on DTAB/TiO₂ was a monolayer adsorption process, and the removal process was dependent on the solution pH. The capture of U(VI) improved with the temperature increase, indicating an endothermic process. The adsorption process can reach equilibrium within 240 min. Based on the Langmuir model, the adsorption capacity of DTAB/TiO₂ for U(VI) reached 108.4 mg/g. The surface oxygen-containing functional groups, especially hydroxyl groups, played a crucial role in removing U(VI). This work can provide useful information for the cleanup of uranium and expand the application of surfactants.

Efficient extraction of U(VI) from uranium enrichment process wastewater by amine-aminophosphonate-modified polyacrylonitrile fibers

The enrichment and recovery of U(VI) from low-level radioactive wastewater in the process of uranium enrichment is important for the sustainable development of nuclear energy and environmental protection. Herein, a novel amine-aminophosphonate bifunctionalized polyacrylonitrile fiber (AAP-PAN), was prepared for the extraction of U(VI) from simulated and real uranium-containing process wastewater. The AAP-PAN fiber demonstrated a maximum adsorption capacity of 313.6 mg g^-1 at pH = 6.0 and 318 K in the batch experiments. During the dynamic column experiment, over 99.99% removal of U(VI) could be achieved by the fiber using multi-ion simulated solution and real wastewater with an excellent saturation adsorption capacity of 132.0 mg g^-1 and 72.5 mg g^-1, respectively. It also exhibited an outstanding reusability for at least 5 cycles of adsorption process. The mechanism for U(VI) removal was studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis in the assist of simulation calculation. It suggested that the amine and aminophosphonate groups can easily bind uranyl ions due to U(VI) is more likely to combine with oxygen atoms of CO and PO, respectively.

Targeted synthesis of carbon-supported titanate nanofibers as host structure for nuclear waste immobilization

Inorganic ion-exchange materials show potential application for toxic radioactive ions due to their remarkable high efficiency and selectivity features. Here, two type of carbon-supported titanate (C@TNFs and C@TNFs(H)) nanofibers have been synthesized by a cost-effective in suit growth method. The resulting C@TNFs and C@TNFs(H) microspheres present uniform flower-like morphology and large surface area. The interlayer Na+ in the titanate shell provides docking sites for ion-exchange of radioactive ions (U(VI), Ba(II), and Sr(II)). Interestingly, the exceeding theoretical cation-exchange capacities (CECs) are achieved on C@TNFs for U(VI) ∼4.76 meq g−1 and Ba(II) ∼2.65 meq g−1 and C@TNFs(H) for Ba(II) ∼2.53 meq g−1 and Sr(II) ∼2.24 meq g−1, respectively. The impressive adsorption performance is mainly attributed to the synergistic effects of ion-exchange and surface complexation. More significantly, C@TNFs and C@TNFs(H) maintain high distribution coefficients (K d U) of >104 mL g−1 over a wider pH range (pH = 3.5–9.0) and high adsorption rate with short equilibrium time within 50 min. Competitive ion-exchange investigation shows a selectivity order of U(VI) > Ba(II) > Sr(II) at individual 10 ppm concentration, pH = 6.0 and T = 298 K. The related spectroscopic studies reveal the intercalative mechanism of radionuclides in the deformed titanate structure, as a result of target ions firmly trapped in the interlayer of C@TNFs and C@TNFs(H). These advantageous features allow the C@TNFs and C@TNFs(H) to be promising candidates for the remediation of toxic radioactive ions polluted water.

Phosphorylated biomass-derived porous carbon material for efficient removal of U(VI) in wastewater

A simple strategy to prepare cost-effective adsorbent materials for the removal of U(VI) in radioactive wastewater is of great significance to environmental protection. Here, activated orange peel was used as a precursor for the synthesis of biomass charcoal, and then a phosphorylated honeycomb-like porous carbon (HLPC-PO₄) material was prepared through simple phosphorylation modification. FT-IR and XPS showed that P-O-C, P-C, and P˭O bonds appeared in HLPC-PO₄, indicating that the phosphorylation process is mainly the reaction of C-O bonds on the surface of the material with -PO₄. The results of the batch experiments showed that the uptake equilibrium of HLPC-PO₄ to U(VI) occurred within 20 min, and the kinetic simulation showed that the process was monolayer chemical adsorption. Interestingly, the maximum U(VI) uptake capacity of HLPC-PO₄ at T = 298.15 K and pH = 6.0 was 552.6 mg/g, which was more than 3 times that of HLPC. In addition, HLPC-PO₄ showed an adsorption selectivity of 70.1% for U(VI). After 5 cycles, HLPC-PO₄ maintained its original adsorption capacity of 90.5%. The adsorption mechanism can be explained as the complexation of U(VI) with P-O and P˭O on the surface of the adsorbent, confirming the strong bonding ability of -PO₄ to U(VI).

Memory effect induced the enhancement of uranium (VI) immobilization on low-cost MgAl-double oxide: Mechanism insight and resources recovery

It remains challenging to develop high-performance technologies for uranium (U(VI)) removal/recovery from wastewater/seawater. In this study, MgAl-double oxide (MgAl-LDO-500) was fabricated by calcining MgAl-layered double hydroxide (MgAl-LDH) at 500 ℃ in air. It showed excellent performance in U(VI) removal with an equilibrium time of 15 min and the maximal adsorption capacity of 1098.90 mg g^-1. MgAl-LDO-500 also showed good adaptability in a wide range of pH (from 3 to 10), coexisting ions and different water matrices for U(VI) immobilization. It was found that the anion form of U(VI) intercalated into the layer of MgAl-LDO-500 and caused recombination of layered structures. A series of characterizations (XRD, SEM, FTIR, XPS) proved that memory effect and surface complexation were the key mechanism for the enhancement of U(VI) immobilization on MgAl-LDO-500. Due to the remarkable memory effect, the performance of MgAl-LDO-500 for U(VI) immobilization was superior to MgAl-LDH and other high-cost materials. Besides, the fixed-bed column experiments illustrated that the removal rate achieved 99 % before 1500 BV at initial U(VI) concentration of 20 μg L^-1, and the breakthrough volumes (BVs) were 4500 BVs. These results confirm that MgAl-LDO-500 is a promising material for extracting U(VI) from seawater and wastewater.

A robust prediction of U(VI) sorption on Fe3O4/activated carbon composites with surface complexation model

A robust prediction of U(VI) on Fe₃O₄/activated carbon (Fe₃O₄/AC, fabricated by co-precipitation method under N₂ conditions) under different pH was developed via diffuse layer model, in accordance with FI-IR, XRD and XPS analysis. No influence of ionic strength onto U(VI) adsorption by Fe₃O₄/AC under ambient conditions suggested the inner-sphere surface adsorption, which was attributed to abundant surficial functional groups according to FT-IR and XPS analysis. The batch experiments indicated Fe₃O₄/AC with fast adsorption rate (equilibrium within 60 min), high adsorption capacity (56 mg/g at pH 4.0) towards U(VI). The adsorbed U(VI) was partly reduced by Fe²⁺ of Fe₃O₄/AC by XPS analysis. Surface complexation modeling showed that a single set of monodentate and mononuclear species (SOUO₂⁺) cannot predict U(VI) adsorption at high pH, whereas the robust prediction of U(VI) adsorption over wide pH range was observed by adding the other binuclear and tridentate species ((SO)₂UO₂(CO₃)^6-). These findings revealed that magnetic AC as a candidate for immobilization and/or preconcentration of radioactive wastewater in environment management.

Ultrafast and highly capture of U(VI) by hierarchical mesoporous carbon

In this study, the hierarchical mesoporous carbon (HMC) was synthesized by the hydrothermal method. The batch adsorption experiments showed that HMC exhibited the ultrafast equilibrium fate (80 % U(VI) capture efficiency within 5 min), high UO2 2+ capture capacity (210 mg/g, pH = 4.5) and well recyclability. The investigations of XPS techniques indicated the oxygen-containing functional groups were responsible for high efficient UO2 2+ adsorption. The pH-dependent adsorption was simulated by three surface complexation modellings, revealing that UO2 2+ adsorption on HMC was excellently fitted by triple layer model using two inner-sphere complexes (i. e. SOUO2 + and SOUO2(CO3)3 5− species) compared to constant capacitance model and diffuse layer model. These findings are crucial for expanding actual applications of HMC towards the removal of radionuclides under environmental cleanup.

Functionalization of carbon nanomaterials by means of phytic acid for uranium enrichment

A promising strategy for radionuclides immobilization on the functionalized carbon-based materials is a pursuing issue. Here, we developed phosphorylated hydrothermal carbon spheres (HCSs@PO₄) through chemical-grafted method using phytic acid as a phosphorus source. When served as U(VI) scavenger from simulated environmental wastewater, the resulting HCSs@PO₄ showed excellent adsorption capacity toward U(VI) (552.49 mg·g^-1 at pH 5.0 and T = 298 K), outperforming that of HCSs (32.06 mg·g^-1) and state-of the-art materials. A weak ionic strength-dependence of U(VI) enrichment with HCSs@PO₄ was investigated by a series of pH experiments, indicating an inner-sphere surface complexation. Through thermodynamic study, high temperature promoted the adsorptive ability of HCSs@PO₄ toward U(VI), revealing the endothermic and spontaneous nature. Additional selective adsorption applications were conducted to evaluate the ability of HCSs@PO₄ to capture uranium fission byproducts and other radioactive ions. Analyses of characteristic means (FT-IR and XPS) revealed enhanced uptake performance of HCSs@PO₄ originated from grafting abundant phosphate groups, which exhibited the stronger surface complexation toward U(VI) than sluggish hydroxyl and carboxyl groups. The findings herein highlighted a facile and powerful technique for the manufacture of phosphorylated carbon-based materials of radioactive wastewater remediation.

Cr(VI) Adsorption on Engineered Iron Oxide Nanoparticles: Exploring Complexation Processes and Water Chemistry

Surface-functionalized magnetic nanoparticles are promising adsorbents due to their large surface areas and ease of separation after contaminant removal. In this work, the affinity of Cr(VI) adsorption to 8 nm surface-functionalized superparamagnetic magnetite nanoparticles was determined for surface coatings with amine (trimethyloctadecylammonium bromide, CTAB) and carboxyl (stearic acid, SA) functional groups. Cr(VI) adsorbed more strongly to the CTAB-coated nanoparticles than to the SA-coated materials due to electrostatic interactions between positively charged CTAB and anionic Cr(VI) species. The adsorption of Cr(VI) by CTAB- and SA-coated nanoparticles increased with decreasing pH (4.5-10), which could be simulated by a surface complexation model. Cr(VI) removal performance by the nanocomposite was evaluated for two realistic drinking water compositions. The co-occurrence of divalent cations (Ca²⁺ and Mg²⁺) and Cr(VI) resulted in decreased Cr(VI) adsorption as particles were destabilized, leading to the aggregation and lower effective surface area, confirming the importance of the overall water composition on the performance of novel engineered nanomaterials for water treatment applications.

Lead and cadmium adsorption by electrospun PVA/PAA nanofibers: Batch, spectroscopic, and modeling study

Water-stable PVA/PAA nanofibers were fabricated through electrospinning and evaluated for their performance in lead (Pb(II)) and cadmium (Cd(II)) removal from water in a batch experiment. The adsorption mechanism of Pb(II) was explored using the extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The PVA/PAA nanofibers showed a pH-dependent behavior for heavy metal removal, and its adsorption capacities for Pb(II) and Cd(II) could reach as high as 159 and 102 mg/g, respectively. The calcium ion (Ca(II)) had no effect on Pb(II) removal at pH 5.0 whereas it significantly reduced Cd(II) removal at pH 7.0. The adsorption of Pb(II) and Cd(II) was spontaneous and exothermic in nature with a decrease in randomness. The saturated PVA/PAA nanofibers could be regenerated using acidic solutions for reuse. The Fourier-transform infrared (FTIR) spectroscopic analysis indicated the formation of surface complexes between adsorbed Pb(II) and Cd(II) and carboxyl groups on PVA/PAA nanofibers. Moreover, EXAFS analysis suggested that a Pb(II) cation was chelated with three carboxyl groups on the nanofibers. This molecular-level adsorption structure was successfully implemented into a surface complexation model for the prediction of the macroscopic Pb(II) and Cd(II) adsorption behaviors. The results gained from this study provided complementary information on heavy metal removal by a new generation of adsorbents and improved the fundamental understanding for the removal process.

A simple method for preparing ultra-light graphene aerogel for rapid removal of U(VI) from aqueous solution

In this study, graphene aerogel (GA) was successfully prepared through a simple hydrothermal method. The resulting GA exhibited a porous network structure with a large specific surface area (350.8 m²/g), ultra-light mass and easy separation from water. The pH_IEP value of the GA was estimated to be 3.5. The adsorption process and the factors that affect adsorption capacity were studied. The adsorption could be conducted in a wide pH range from 2.0 to 7.0. The maximum adsorption capacity of GA towards U(VI) at pH 4.0 and T = 298 K was 238.67 mg/g calculated from the Langmuir model. The GA had greatly rapid adsorption property for the removal of U(VI) at pH 4.0. Kinetic data showed good correlation with pseudo-second-order equation. Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry characterizations showed that GA adsorbed U(VI) through chemical interaction by oxygen-containing and nitrogen-containing groups functional groups. The results show that GA has excellent application potential as an adsorbent material for removing U(VI) from aqueous solution.

Self-assembly of graphene oxide/PEDOT:PSS nanocomposite as a novel adsorbent for uranium immobilization from wastewater

In recent years, water pollution caused by radionuclides has become a rising concern, among which uranium is a representative class of actinide element. Since hexavalent uranium, i.e. U(VI), is biologically hazardous with high migration, it's essential to develop efficient adsorbents to minimize the impact on the environment. Towards this end, we have synthesized a novel material (GO/PEDOT:PSS) by direct assembling graphene oxide (GO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through a facile ball milling method, which shows impressing performance for the immobilization of U(VI). On the basis of the batch experiments, GO/PEDOT:PSS exhibits ionic strength-independent sorption edges and temperature-promoted sorption isotherms, revealing an inner-sphere complexation with endothermic nature. The sorption kinetics can be illustrated by the pseudo-second-order model, yielding a rate constant of 1.09. × 10^-2 g mg^-1∙min^-1, while the sorption isotherms are in coincidence with the Langmuir model, according to which the maximum sorption capacity is measured to be 384.51 mg g^-1 at pH 4.5 under 298 K, indicating a monolayer sorption mechanism. In the light of the FT-IR and XPS investigations, the surface carboxyl/sulfonate group is responsible to the chelation of U(VI), indicating that the enhanced sorption capacity may be ascribed to the PSS moiety. These findings can greatly contribute to the design strategy for developing highly efficient adsorbents in the field of radioactive wastewater treatment.

Fully phosphorylated 3D graphene oxide foam for the significantly enhanced U(VI) sequestration

Efficient sequestration of U(VI) from complex aqueous solution is of vital importance for environmental remediation. In this work, the fully phosphorylated graphene oxide foam (phos-GOF) was synthesized via a facile hydrothermal method and the as-prepared 3D phos-GOF was served as an adsorbent to capture U(VI) from aqueous solution. The introduction of abundant phosphorus-containing groups via phytic acid endows phos-GOF good hydrophilia and excellent affinity for U(VI). The adsorption performance of phos-GOF for U(VI) was carefully evaluated under different environments. phos-GOF shows rapid and high efficiency for U(VI) adsorption. The maximum adsorption capacity of phos-GOF for U(VI) is ∼483 mg/g, which is much higher than that of pristine graphene oxide foam (GOF). In addition, the spent 3D phos-GOF can be easily regenerated by a simple and low-cost desorption process using 0.02 mol/L HNO₃. The interaction mechanism between phos-GOF and U(VI) is mainly attributed to the inner-sphere complexation between phosphoric functional groups and U(VI) based on a series of spectroscopic analyses. The 3D phos-GOF exhibits favorable sequestration performance towards U(VI) which can be used as a potential candidate in uranium-bearing wastewater treatment and disposal.

Rational design of carbonaceous nanofiber/Ni-Al layered double hydroxide nanocomposites for high-efficiency removal of heavy metals from aqueous solutions

Heavy metal pollution of water sources has raised global environmental sustainability concerns, calling for the development of high-performance materials for effective pollution treatment. Herein, we report a facile approach to synthesize carbonaceous nanofiber/NiAl layered double hydroxide (CNF/LDH) nanocomposites for high-efficiency elimination of heavy metals from aqueous solutions. The CNF/LDH nanocomposites were characterized by three-dimensional architectures formed by the gradual self-assembly of flower-like LDH on CNF. The nanocomposites exhibited excellent hydrophilicity and high structural stability in aqueous solutions, guaranteeing the high availability of active sites in these environments. High-efficiency elimination of heavy metal ions by the CNF/LDH nanocomposites was demonstrated by the high uptake capacities of Cu(II) (219.6 mg/g) and Cr(VI) (341.2 mg/g). The sorption isotherms coincided with the Freundlich model, most likely because of the presence of heterogeneous binding sites. The dominant interaction mechanisms consisted of surface complexation and electrostatic interaction, as verified by a combination of X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy analyses and density functional theory calculations. The results presented herein confirm the importance of CNF/LDH nanocomposites as emerging and promising materials for the efficient removal of heavy metal ions and other environmental pollutants.

Recent advances in layered double hydroxide-based nanomaterials for the removal of radionuclides from aqueous solution

Layered double hydroxides (LDHs), one of the most important two-dimensional layered compounds, have enabled massive developments in effective pollution treatments. Their derivative materials have also attracted multidisciplinary attention owing to the intrinsic advantages of their moderate chemiostability, low cost and nontoxicity. Over the past few decades, significant advances have been made in the synthesis of novel LDH-based composites and the optimization of characterization techniques. In this review, we give an overview of the recent advances in LDH-based nanomaterials, from a brief introduction to their preparation and modification methods to an overview of their application in the removal of radionuclides and an exploration of their underlying adsorption mechanisms. In the end, a summary and outlook are also briefly addressed. This review intends to provide deep insight into the design of high-performance LDH-based materials for the potential elimination of radionuclides from aqueous solutions during environmental pollution cleanup.

Synthesis of rod-like metal-organic framework (MOF-5) nanomaterial for efficient removal of U(VI): batch experiments and spectroscopy study

With the widespread application of radionuclide ²³⁵U(VI), it is inevitable that part of U(VI) is released into the natural environment. The potential toxicity and irreversibility impact on the natural environment has become one of the most forefront pollution problems in nuclear energy utilization. In this work, rod-like metal-organic framework (MOF-5) nanomaterial was synthesized by a solvothermal method and applied to efficiently adsorb U(VI) from aqueous solutions. The batch experimental results showed that the sorption of U(VI) on MOF-5 was strongly dependent on pH and independent of ionic strength, indicating that the dominant interaction mechanism was inner-sphere surface complexation and electrostatic interaction. The maximum sorption capacity of U(VI) on MOF-5 was 237.0 mg/g at pH 5.0 and T = 298 K, and the sorption equilibrium reached within 5 min. The thermodynamic parameters indicated that the removal of U(VI) on MOF-5 was a spontaneous and endothermic process. Additionally, the FT-IR and XPS analyses implied that the high sorption capacity of U(VI) on MOF-5 was mainly attributed to the abundant oxygen-containing functional groups (i.e., CO and CO). Such a facile preparation method and efficient removal performance highlighted the application of MOF-5 as a candidate for rapid and efficient radionuclide contamination's elimination in practical applications.

The novel PEI-modified biochars and their application for the efficient elimination of Cr(VI) from aqueous solutions

In this study, the polyethyleneimine (PEI) was grafted onto the biochars from chestnut shells and nori via the cross-linking reaction. Scanning electron microscopy, transmission electron microscopy and Fourier transferred infrared spectroscopy analysis indicated that the PEI was successfully grafted on the surface of biochars. The PEI modified and pristine biochars were used as adsorbents to remove Cr(VI) from aqueous solutions as a function of pH, ionic strength, contact time and initial concentrations of Cr(VI) through batch technique. The strongly pH-dependent and ionic strength-independent of Cr(VI) sorption indicated that the sorption was mainly dominated by electrostatic interaction and inner-sphere surface complexation. The maximum sorption capacities of PEI modified chestnut shell and nori biochars were 141.42 and 222.84 mg/g, respectively, which were significantly higher than those of pristine biochars. The PEI grafted onto the biochars significantly enhanced Cr(VI) sorption capacity because PEI, which contains volumes of amine/imine groups, provided an excellent platform for Cr(VI) ions removal. In addition, the sorption-desorption experimental results indicated that the PEI modified biochars possessed a stable and recyclable performance. All these results manifested that the PEI modified biochars could be applied as environmentally friendly and efficient adsorbents for the removal of Cr(VI) from wastewater.

Enhanced adsorption of U(VI) and 241Am(III) from wastewater using Ca/Al layered double hydroxide@carbon nanotube composites

Ca/Al layered double hydroxide decorated carbon nanotube (Ca/Al-LDH@CNTs) composites were fabricated by co-precipitation method and hydrothermal aged treatment. The prepared Ca/Al-LDH@CNTs was characterized by SEM, TEM, EDS, XRD, FT-IR, UV-vis and XPS techniques, and applied to remove U(VI) from aqueous solutions under various environmental conditions (i.e., pH, ionic strength, temperature and contact time). The results indicated that the adsorption of U(VI) on Ca/Al-LDH@CNTs was four times higher than that of U(VI) on bare CNTs. The kinetic investigations reflected the chemisorption of U(VI) on Ca/Al-LDH@CNTs through oxygen-containing functional groups. The adsorption isotherms demonstrated that the adsorption of U(VI) was well fitted by Langmuir model and the maximum adsorption capacity of U(VI) on Ca/Al-LDH@CNTs was calculated to be 382.9 mg g^-1 at 289.15 K. The thermodynamic parameters calculated from temperature-dependent isotherms suggested that U(VI) adsorption on Ca/Al-LDH@CNTs were endothermic and spontaneous process. Furthermore, Ca/Al-LDH@CNTs could remove ∼91% of ²⁴¹Am(III) at pH = 8.0, which confirmed Ca/Al-LDH@CNTs as a promising material for multiply low level radionuclides' pollution remediation.

Plasma-Facilitated Synthesis of Amidoxime/Carbon Nanofiber Hybrids for Effective Enrichment of 238U(VI) and 241Am(III)

Plasma- and chemical-grafted amidoxime/carbon nanofiber hybrids (p-AO/CNFs and c-AO/CNFs) were utilized to remove ²³⁸U(VI) and ²⁴¹Am(III) from aqueous solutions, seawater, and groundwater. Characteristic results indicated more nitrogen-containing groups in p-AO/CNFs compared to c-AO/CNFs. The maximum adsorption capacities of p-AO/CNFs at pH 3.5 and T = 293 K (588.24 mg of ²³⁸U(VI)/g and 40.79 mg of ²⁴¹Am(III)/g from aqueous solutions, respectively) were significantly higher than those of c-AO/CNFs (263.18 and 22.77 mg/g for ²³⁸U(VI) and ²⁴¹Am(III), respectively), which indicated that plasma-grafting was a highly effective, low-cost, and environmentally friendly method. Adsorption of ²³⁸U(VI) on AO/CNFs from aqueous solutions was significantly higher than that of ²³⁸U(VI) from seawater and groundwater; moreover, AO/CNFs displayed the highest effective selectivity for ²³⁸U(VI) compared to the other radionuclides. Adsorption of ²³⁸U(VI) onto AO/CNFs created inner-sphere complexes (e.g., U-C shells) as shown by X-ray absorption fine structure analysis, which was supported by surface complexation modeling. Three inner-sphere complexes gave excellent fits to pH-edge and isothermal adsorption of ²³⁸U(VI) on the AO/CNFs. These observations are crucial for the utilization of plasma-grafted, AO-based composites in the preconcentration and immobilization of lanthanides and actinides in environmental remediation.

Measurement and Surface Complexation Modeling of U(VI) Adsorption to Engineered Iron Oxide Nanoparticles

Surface-functionalized magnetite nanoparticles have high capacity for U(VI) adsorption and can be easily separated from the aqueous phase by applying a magnetic field. A surface-engineered bilayer structure enables the stabilization of nanoparticles in aqueous solution. Functional groups in stearic acid (SA), oleic acid (OA), and octadecylphosphonic acid (ODP) coatings led to different adsorption extents (SA≈ OA > ODP) under the same conditions. The impact of water chemistry (initial loading of U(VI), pH, and the presence of carbonate) has been systematically examined for U(VI) adsorption to OA-coated nanoparticles. A diffuse double layer surface complexation model was developed for surface-functionalized magnetite nanoparticles that could simulate both the measured surface charge and the U(VI) adsorption behavior at the same time. With a small set of adsorption reactions for uranyl hydroxide and uranyl carbonate complexes to surface sites, the model can successfully simulate the entire adsorption data set over all uranium loadings, pH values, and dissolved inorganic carbon concentrations. The results show that the adsorption behavior was related to the changing U(VI) species and properties of surface coatings on nanoparticles. The model could also fit pH-dependent surface potential values that are consistent with measured zeta potentials.

Characteristics of uranium biosorption from aqueous solutions on fungus Pleurotus ostreatus

Uranium(VI) biosorption from aqueous solutions was investigated in batch studies by using fungus Pleurotus ostreatus biomass. The optimal biosorption conditions were examined by investigating the reaction time, biomass dosage, pH, temperature, and uranium initial concentration. The interaction between fungus biomass and uranium was confirmed using Fourier transformed infrared (FT-IR), scanning electronic microscopy energy dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. Results exhibited that the maximum biosorption capacity of uranium on P. ostreatus was 19.95 ± 1.17 mg/g at pH 4.0. Carboxylic, amine, as well as hydroxyl groups were involved in uranium biosorption according to FT-IR analysis. The pseudo-second-order model properly evaluated the U(VI) biosorption on fungus P. ostreatus biomass. The Langmuir equation provided better fitting in comparison with Freundlich isotherm models. The obtained thermodynamic parameters suggested that biosorption is feasible, endothermic, and spontaneous. SEM-EDX and XPS were additionally conducted to comprehend the biosorption process that could be described as a complex process involving several mechanisms of physical adsorption, chemisorptions, and ion exchange. Results obtained from this work indicated that fungus P. ostreatus biomass can be used as potential biosorbent to eliminate uranium or other radionuclides from aqueous solutions.

Macroscopic and Microscopic Investigation of U(VI) and Eu(III) Adsorption on Carbonaceous Nanofibers

The adsorption mechanism of U(VI) and Eu(III) on carbonaceous nanofibers (CNFs) was investigated using batch, IR, XPS, XANES, and EXAFS techniques. The pH-dependent adsorption indicated that the adsorption of U(VI) on the CNFs was significantly higher than the adsorption of Eu(III) at pH < 7.0. The maximum adsorption capacity of the CNFs calculated from the Langmuir model at pH 4.5 and 298 K for U(VI) and Eu(III) were 125 and 91 mg/g, respectively. The CNFs displayed good recyclability and recoverability by regeneration experiments. Based on XPS and XANES analyses, the enrichment of U(VI) and Eu(III) was attributed to the abundant adsorption sites (e.g., -OH and -COOH groups) of the CNFs. IR analysis further demonstrated that -COOH groups were more responsible for U(VI) adsorption. In addition, the remarkable reducing agents of the R-CH2OH groups were responsible for the highly efficient adsorption of U(VI) on the CNFs. The adsorption mechanism of U(VI) on the CNFs at pH 4.5 was shifted from inner- to outer-sphere surface complexation with increasing initial concentration, whereas the surface (co)precipitate (i.e., schoepite) was observed at pH 7.0 by EXAFS spectra. The findings presented herein play an important role in the removal of radionuclides on inexpensive and available carbon-based nanoparticles in environmental cleanup applications.