Surface hydroxylation of SBA-15 via alkaline for efficient amidoxime-functionalization and enhanced uranium adsorption

N, N-bis (2-hydroxyethyl) malonamide based amidoxime functionalized polymer immobilized in biomembranes for highly selective adsorption of uranium(VI)

Amidoxime compounds have been widely used in metal separation and recovery because of their excellent chelating properties to metal ions, especially to uranium (VI). In this study, N, N-bis (2-hydroxyethyl) malonamide was obtained from ethanolamine and dimethyl malonate, and used to prepare a two-dimensional network polymer, then the obtained polymer was immobilized in an environmentally friendly chitosan biomembrane, which enhanced its stability and hydrophobicity, meanwhile the amidoxime functionalization was achieved by oximation reaction of bromoacetonitrile, the application of the material further extends to uranium (VI) separation in solutions. Due to the synergistic action of amide group and amidoxime group, poly (ethanolamine-malonamide) based amidoxime biomembranes (PEA-AOM) showed extraordinary adsorption effect on uranium (VI), among which the saturation adsorption capacity of PEA-AOM-2 was 748.64 mg/g. PEA-AOM-2 also had good reusability (following five cycles of adsorption-desorption, the recovery rate maintained at 88%) and selectivity for uranium (VI), showing satisfactory results in competitive ion coexistence system and simulated seawater experiments. This study demonstrated that PEA-AOM-2 provided a new option for uranium (VI) separation in complex environment and low-concentration uranium background.

Shear-induced fabrication of SiO2 nano-meshes for efficient uranium capture

The extraction of uranium from seawater and the safe treatment of wastewater containing uranium (VI) were important to ensure the sustainable development of nuclear-related energy sources. Two-dimensional silica nanomaterials have been extensively investigated in the field of uranium adsorption due to their high adsorption capacity, short equilibration times, and easily modified surface groups. However, the two-dimensional mesoporous silica nanomaterial preparation has become a challenge due to the lack of natural sheet templating agents. The reason will hinder the development of silica nanomaterials for uranium extraction. Here, the specific surface area silica nanomeshes (HSMSMs) uranium adsorbent was prepared by a high shear method to induce nanobubble formation. HSMSMs showed a high uranium adsorption capacity of 822 mg_-U/g_-abs in seawater with the uranium adsorption concentration was 50 mg/L, which was approximately 2 times higher than the conventional mesoporous silica nanomaterials. Compared to HSMSMs, the amidoxime-modified high specific surface area silica nanomesh (HSMSMs-AO) demonstrated good selectivity for U(VI), and the uranium ions uptake was 877 mg_-U/g_-abs in 50 mg/L uranium-spiked simulated seawater. Due to HSMSMs-AO's stable chemical properties and high mechanical strength, HSMSMs-AO also displayed long service life. Benefiting from the simple preparation method and high adsorption capacity of HSMSMs, HSMSMs could be a promising candidate for large-scale extraction of uranium from seawater.

Layered double hydroxide intercalated with dimethylglyoxime for highly selective and ultrafast uptake of uranium from seawater

In this study, we demonstrate the first example of a MgAl layered double hydroxide intercalated by a ketoxime compound (dimethylglyoxime, DMG), that is, MgAl-DMG-LDH (abbr. DMG-LDH), which exhibits excellent capture of uranium (U(VI)) both at high (ppm) and low (ppb) concentrations. The as-formed DMG-LDH shows an enormous maximum U(VI) sorption capacity (qUm) of 380 mg g^-1 and an exceptionally rapid sorption rate (k₂ = 2.97 g mg^-1 min^-1), reaching a high uptake of 99.14% within 5 min. For natural and contaminated seawater with high concentrations of Na⁺, Ca²⁺, Mg²⁺ and K⁺ concomitant cations, the DMG-LDH still can trap ∼85% U, displaying highly effective sorption toward U. The interaction mechanism between UO₂²⁺ and DMG^2- provides an important reference for the development of highly effective capture of U(VI) by ketoxime materials. The DMG-LDH is currently the best ketoxime material for uranium extraction from nuclear waste and seawater.

Preparation of novel porous Al2O3-SiO2nanocomposites via solution-freeze-drying-calcination method for the efficient removal of uranium in solution

In this work, the efficient extraction of uranium in solution using Al₂O₃-SiO₂-T was reported. Kinetics and isotherm models indicated that the removal process of uranium on Al₂O₃-SiO₂-T accorded with pseudo-second-order kinetic model and Langmuir isotherm model, which showed that the adsorption process was a uniform mono-layer chemical behavior. The maximum adsorption capacity of Al₂O₃-SiO₂-T reached 738.7 mg g^-1, which was higher than AlNaO₆Si₂(349.8 mg g^-1) and Al₂O₃-SiO₂-NT (453.1 mg g^-1), indicating that the addition of template could effectively improve the adsorption performance of Al₂O₃-SiO₂to uranium. Even after five cycles of adsorption-desorption, the removal percentage of uranium on Al₂O₃-SiO₂-T remained 96%. Besides, the extraction efficiency of uranium on Al₂O₃-SiO₂-T was 72.5% in simulated seawater, which suggested that the Al₂O₃-SiO₂-T was expected to be used for uranium extraction from seawater. Further, the interaction mechanism between Al₂O₃-SiO₂-T and uranium species was studied. The results showed that the electrostatic interaction and complexation played key roles in the adsorption process of Al₂O₃-SiO₂-T to uranium.

Preparation of ZnNiAl-LDHs microspheres and their adsorption behavior and mechanism on U(VI)

Ternary zinc-nickel-aluminum hydrotalcites (ZnNiAl-LDHs) were prepared by hydrothermal synthesis. The structure and morphology of the materials were characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), nitrogen adsorption-desorption (BET) and other test techniques. ZnNiAl-LDHs was applied in the treatment of uranium-containing wastewater, the effects of initial pH of the solution, adsorption temperature and contact time on its adsorption performance were systematically investigated, and the adsorption performance of ZnNiAl-LDHs and ZnAl-LDHs on uranyl ions were compared. The result showed that ZnNiAl-LDHs were 3D microspheres self-assembled from flakes, with a specific surface area of 102.02 m²/g, which was much larger than that of flake ZnAl-LDHs (18.49 m²/g), and the saturation adsorption capacity of ZnNiAl-LDHs for uranyl ions (278.26 mg/g) was much higher than that of ZnAl-LDHs for uranyl ions (189.16 mg/g), so the ternary ZnNiAl-LDHs had a more excellent adsorption capacity. In addition, kinetic and thermodynamic studies showed that the adsorption process of ZnNiAl-LDHs on uranyl ions conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. The positive value of ΔH and the negative value of ΔG indicated that the adsorption process was endothermic and spontaneous. The adsorption mechanism was analyzed by X-ray energy spectroscopy (EDS), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The results showed that the adsorption of uranyl ions by ZnNiAl-LDHs mainly consisted of complexation and ion substitution. The research results prove that ZnNiAl-LDHs is an adsorbent with low cost and excellent performance, and it has a good application prospect in the field of uranium-containing wastewater treatment.

Enhanced uranium removal from acidic wastewater by phosphonate-functionalized ordered mesoporous silica: Surface chemistry matters the most

The removal of uranium species from aqueous phases using non-hazardous chemicals is still an open challenge, and remediation by adsorption is a prosperous strategy. Among the most crucial concerns regarding the design of an efficient material as adsorbent are, except the cost and the green character, the feasibility to be stable and effective under acidic pH, and to selectively adsorb the desired metal ion (e.g. uranium). Herein, we present a phosphonate functionalized ordered mesoporous silica (OMS-P), prepared by a one-step co-condensation synthesis. The physicochemical features of the material were determined by HR-TEM, XPS, EDX, N₂ sorption, and solid NMR, while the surface zeta potential was also measured. The removal efficiency was evaluated at two different temperatures (20 and 50 °C) in acidic environment to avoid interferences like solid phase formation or carbonate complexation and the adsorption isotherms, including data fitting with Langmuir and Freundlich models and thermodynamic parameters are presented and discussed. The high and homogeneous dispersion of the phosphonate groups within the entire silica's structure led to the greatest reported up-todays capacity (345 mg/g) at pH = 4, which was achieved in less than 10 min. Additionally, OMS-P showed that the co-presence of other polyvalent cation like Eu(III) did not affect the efficiency of adsorption, which occurs via inner-sphere complex formation. The comparison to the non-functionalized silica (OMS) revealed that the key feature towards an efficient, stable, and selective removal of the U(VI) species is the specific surface chemistry rather than the textural and structural features. Based on all the results and spectroscopic validations of surface adsorbed U(VI), the main interactions responsible for the elevated uranium removal were proposed.

Effective Interactions of Ag Nanoparticles on the Surface of SBA-15 in Performing Deep Desulfurization of Real Diesel Fuel

SBA-15 materials as-synthesized and impregnated with Ag nanoparticles were applied to perform adsorptive desulfurization of real diesel fuel. High-angle annular dark-field scanning transmission electron microscopy and field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (HAADF-STEM-EDX and FESEM-EDX) and X-ray photoelectron spectroscopy (XPS) results confirmed that there is uniform distribution of Ag nanodomains on the surface and in the channels of a 2AgSBA-15 (2% Ag) sample. The interaction between sulfur compounds and adsorbent mainly occurred via π-complexation mechanisms, as observed via XPS and equilibrium data. The kinetic results for 2AgSBA-15 were better fitted to the pseudo-second-order model (R2 > 0.9999), indicating that the determining step of the adsorptive process is chemisorption, whereas the equilibrium results were better fitted to the Langmuir model (R2 > 0.9994), thus indicating that the adsorption occurs on the adsorbent surface monolayer with significant adsorption capacity (qm = 20.30 mgS/g), approximately two times greater than that observed for pure SBA-15. The mean desulfurization reached by the adsorbents was up to 86.8% for six recycling steps.