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• ZIF-8 was fabricated by stirring at room temperature. • Enhancing the adsorption performance of ZIF-8 through thermal modification. • Surface complexation and electrostatic interaction were main removal mechanisms. • U(VI) formed coordination complexes with the N atoms of ZIF-8-400. Zeolite imidazolium framework materials (ZIFs) had been extensively applied for U(VI) removal because of their superior structure, high porosity and large specific surface area. Nevertheless, ZIF-8 tended to accumulate in aqueous solution and it was hard to detach from water, resulting in a decrease in the removal performance. Therefore, it was necessary to conduct thermal modification treatment to solve the above problems. The U(VI) removal capability of ZIF-8 was investigated in this study by subjecting it to various thermal modification temperatures (0 °C, 200 °C, 400 °C, 600 °C). The effect of thermal modification on the removal of U(VI) from ZIF-8 was investigated by a combination of macroscopic and microscopic experiments. Macroscopic experiments revealed ZIF-8, ZIF-8-200, and ZIF-8-400 showed excellent removal efficiency, reaching reaction equilibrium rapidly (about 60 min). The adsorption kinetic and isotherm datum were more consistent with proposed second-order kinetic model and Langmuir model, confirming that removal process of U(VI) was mainly a single-molecule chemisorption reaction. The maximum removal amounts of ZIF-8, ZIF-8-200 and ZIF-8-400 were 470.5, 474.6 and 606.0 mg/g, respectively. Microscopic spectroscopic analysis revealed that there was a synergistic effect between the combination bonds in ZIF-8 during the adsorption reaction. Surface complexation and electrostatic interaction were the main mechanisms used by ZIF-8-400 to remove U(VI). This research offered theoretical guidance on the design of high-performance materials and the migration and transformation laws of radionuclides, which had significant theoretical significance for the future treatment of radioactive nuclides or other pollutants. [Display omitted] [ABSTRACT FROM AUTHOR]

ZIF-8, a sort of zeolitic imidazolate frameworks (ZIFs), had showed superior adsorptive property of typical radionuclide U(VI), but it reminded uncertain how the performance of ZIF-8 would be affected by adding humic acid (HA). HA could significantly change the surface charge of ZIFs and the transport of U(VI) in natural settings, which affected the eradication of U(VI) in aquatic ecology. Thus the impact of HA for the U(VI) removal by ZIF-8 as well as its mechanism had been analyzed by batch experiments and spectral analyses. It was demonstrated that the addition of HA increased the maximum removal capacity towards U(VI) from 781.2 mg g−1 to 1398.5 mg g−1. Moreover, removal property in acidic solution was improved, and the influence of background ions on ZIF-8 was reduced. The detailed mechanism was further explored by microscopic spectral analysis. The zeta potential showed that HA enhanced the electronegativity of ZIF-8 thus enhancing the electrostatic interaction with positive ions. Moreover, FT-IR and XPS further indicated that HA enhanced the removal capacity by affecting the surface complexation phenomena and strong chemical interactions between U(VI) and ZIF-8. Also, investigations indicated that the incorporation of HA improved the removal efficiency for U(VI), which had far-reaching significance for the application of ZIF-8 in practical environment. [Display omitted] • The effect of humic acid on the physicochemical properties of ZIF-8 was studied. • A fresh thinking for future research in practical application are prompted. • The influence of HA on the adsorption of uranium by ZIF-8 was studied. • The mechanisms are surface complexation and electrostatic interactions. • HA as a natural substance is more environmentally friendly in wastewater treatment. [ABSTRACT FROM AUTHOR]

The hierarchical core-shell and yolk-shell magnetic titanate nanosheets (Fe 3 O 4 @TNS) were successfully synthesized by employing magnetic nanoparticles (NPs) as interior core and intercrossed titanate nanostructures (NSs) as exterior shell. The as-prepared magnetic Fe 3 O 4 @TNS nanosheets had high specific areas (114.9 m 2  g −1 for core-shell Fe 3 O 4 @TNS and 130.1 m 2  g −1 for yolk-shell Fe 3 O 4 @TNS). Taking advantage of the unique multilayer structure, the nanosheets were suitable for eliminating U(VI) from polluted water environment. The sorption was strongly affected by pH values and weakly influenced by ionic strength, suggesting that the sorption of U(VI) on Fe 3 O 4 @TNS was mainly dominated by ion exchange and outer-sphere surface complexion. The maximum sorption capacities ( Q max ) calculated from the Langmuir model were 68.59, 121.36 and 264.55 mg g −1 for core-shell Fe 3 O 4 @TNS and 82.85, 173.01 and 283.29 mg g −1 for yolk-shell Fe 3 O 4 @TNS, at 298 K, 313 K and 328 K, respectively. Thermodynamic parameters (Δ H 0 , Δ S 0 and Δ G 0 ) demonstrated that the sorption process was endothermic and spontaneous. Based on X-ray photoelectron spectroscopy (XPS) analyses, the sorption mechanism was confirmed to be cation-exchange between interlayered Na + and UO 2 2+ . The yolk-shell Fe 3 O 4 @TNS had more extraordinary sorption efficiency than core-shell Fe 3 O 4 @TNS since the yolk-shell structure provided internal void space inside the titanate shell to accommodate more exchangeable active sites. The flexible recollection and high efficient sorption capacity made core-shell and yolk-shell Fe 3 O 4 @TNS nanosheets promising materials to eliminate U(VI) or other actinides in wastewater cleanup applications. [ABSTRACT FROM AUTHOR]

Uranium(VI) has become one of the most potential contaminants due to its productive and irreversibility impact on the surrounding environment. Titanate nanowires (TNWs) have attracted significant attention because of its high ion exchange ability and facile synthesis. Herein the TNWs were synthesized, and the morphology and structure of TNWs were investigated by Fourier transformed infrared spectroscopy, scanning electron microscope, transmission electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy in detail. The application of TNWs in U(VI) removal was studied under various environmental conditions using batch technique, and the results indicated that the sorption of U(VI) on TNWs was strongly affected by pH and weakly affected by ionic strength. The presence of PO 4 3- and CO 3 2- could overwhelmingly influence U(VI) interaction with TNWs, which was mainly attributed to the formation of anionic and electro-neutral complexes. From the Langmuir model simulation, the maximum sorption capacities were calculated to be 358, 384, and 410 mg g −1 at the temperatures of 298 K, 313 K and 328 K, respectively. The thermodynamic results revealed that the interaction process was spontaneous and endothermic. The extraordinary ion exchange capacity and facile synthesis under mild conditions made TNWs promising materials for the potential application in the efficient elimination of U(VI) or other lanthanides and actinides from aqueous solutions in the environmental radioactive pollution cleanup. [ABSTRACT FROM AUTHOR]

The potential threat of radionuclide uranium from nuclear industry had attracted worldwide attention because both environment and human beings were menaced. Nowadays, modified nanoscale zero valent iron (NZVI) had been reported to be efficient in U(VI) elimination due to its high reactivity, reducibility, and availability. In this study, serial biochar-based sulfide NZVIs (BC-SNZVIs) with different C/Fe and S/Fe were synthesized and applied to the elimination of U(VI) in order to investigate the effect of iron, sulfur, and biochar precursor. The morphological investigations indicated the precursor played an essential role towards BC-SNZVIs on their dispersibility and structure. The XRD analyzes were conducted to study their crystalline structure and the BC 1.0 -S 0.14 NZVI showed outstanding stability after 10-day exposure under atmosphere. The excellent magnetism was confirmed via VSM study, and BC 1.0 -S 0.14 NZVI could be easily and rapidly separated from aqueous solution. The batch kinetic and isothermal studies illustrated the superior performances towards U(VI), and the results revealed the fast kinetics and high capacities of BC-SNZVIs. Finally, the removal mechanism was explored by using XPS technology and pH-effect experiment. U(VI) was adsorbed by BC matrix and SNZVI, while portion of U(VI) was reduced into U(IV) by Fe0 inner core. The elimination process of U(VI) towards BC-SNZVI was confirmed to be a synergistic effect of adsorption and reduction. This study verified the optimal ratio of C/Fe and S/Fe, and explained the removal mechanism in detail, which was beneficial to further investigations of NZVI-based and biochar-based materials. [Display omitted] • The impact of C/Fe and S/Fe ratios on biochar-based SNZVIs were investigated. • BC 1.0 -S 0.14 NZVI showed excellent attraction and outstanding performance to U(VI). • The removal mechanism was a synergistic effect of reduction and adsorption. [ABSTRACT FROM AUTHOR]

The graphene oxides (GOs) have been studied extensively in multidisciplinary areas owing to their excellent physicochemical properties. The high theoretical surface areas and large amounts of oxygen-containing functional groups at the basal planes and the edge sites ensure their high sorption capacity for heavy metal ions and radionuclides from large volumes of aqueous solutions. Herein, the GOs were applied as adsorbents to remove U(VI) from aqueous solutions at different experimental conditions, and the results showed that the sorption of U(VI) on GOs was strongly dependent on pH and was not affected by ionic strength obviously. The sorption capacity of U(VI) on GOs is calculated to be 1330 mg/g at pH 4.5 and T = 20 °C, which is much higher than any other today’s materials. The interaction mechanism of U(VI) on GOs was simulated by the computational DFT calculations, and the results evidenced that the variation in pH values led to significant changes in the circumstance of functional groups on GOs. As the pH value increased, the weak physical sorption/outer-sphere surface complexation between the GOs and U(VI) at low pH turned into strong chemical sorption/inner-sphere surface complexation with the negative charged –O − or –COO − groups induced by the deprotonation of the functional groups at high pH. [ABSTRACT FROM AUTHOR]

The effect of soluble silicate on the sorption of U(VI) to γ -Al 2 O 3 was investigated by batch experiments and extended X-ray absorption fine structure (EXAFS) method. The presence of silicate enhanced the sorption of U(VI) on γ -Al 2 O 3 surface and the sorption was attributed to inner-sphere surface complexation. The structure of the adsorbed U(VI) and silicate on γ -Al 2 O 3 was investigated in the analysis of EXAFS spectra. The fitting of the experimental EXAFS data was obtained by including two uranium coordination shells with 2 axial (O ax ) and 5 equatorial (O eq ) oxygen atoms at 1 . 79 ± 0 . 02 and 2 . 43 ± 0 . 02 Å, respectively, and the third coordination shells with Al atom at ∼3.35 Å. Silicate contributed to the formation of ternary inner-sphere surface complexes, acting as “bridge” between U(VI) and γ -Al 2 O 3 and enhanced the sorption of U(VI). The observations suggested that the interactions between U(VI) and silicate were important in controlling U(VI) retention. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Dictyophora indusiate -derived biochar supported sulfide NZVI was successfully synthesized. • Sulfidation and supporting technologies could expand a new track for NZVI-based materials. • U(VI) uptake was due to the synergistic effect between adsorptive and reductive reactions. • DI-SNZVI could be a promising scavenger for U(VI) uptake form wastewater. Abstract Nanoscale zero-valent iron (NZVI) has been considered as a potential scavenger for U(VI) elimination from aqueous environment. To decrease the aggregation and to improve antioxidation, sulfidation technology and biochar were applied to modify NZVI. In this work, Dictyophora indusiate -derived biochar supported sulfide NZVI (DI-SNZVI) was synthesized and applied for U(VI) elimination. The excellent behaviors of kinetics (3 h for equilibrium), thermodynamic research and maximum removal amounts (427.9 mg·g−1 at pH = 5.0 and 298 K) revealed the outstanding performances of DI-SNZVI in U(VI) removal. The cycle experiments and different water system investigations further illustrated its potential ability for real applications. Moreover, the abundant functional groups and FeS x shell of DI-SNZVI were proved to be responsible for the enhanced removal of U(VI). In the end, the macroscopic and XPS study revealed that U(VI) elimination mechanisms were synergistic attributed to the adsorptive and reductive processes. This paper highlighted the biochar-based sulfide NZVI for efficient U(VI) elimination in environmental pollution management. [ABSTRACT FROM AUTHOR]

Hydrangea-like carbon sphere@layered double hydroxide (CS@LDH) nanocomposite was fabricated by one-step hydrothermal synthesis strategy using carbon sphere and Ni-Al LDH as monomer molecules. The CS@LDH nanocomposites were then applied as adsorbents to eliminate U(VI) from aqueous solutions and showed excellent elimination performance to U(VI) from aqueous solutions because of its strong synergistic effects between metal-oxygen functional groups (Ni-O and Al-O) and free-metal functional groups (C O, C O C, and O C O). The removal of U(VI) on CS@LDH was mainly dominated by inner-sphere surface complexation, which was confirmed with batch sorption experiments, FTIR and XPS analysis. Furthermore, the maximum sorption capacity of U(VI) on CS@LDH (0.6 mmol/g) was 2.0 times higher than that of U(VI) on Ni-Al LDH (0.3 mmol/g) and approximately 1.5 times higher than that of U(VI) on CS (0.4 mmol/g) at pH = 5.0 and T  = 298 K. The thermodynamic parameters suggested that the sorption of U(VI) was a typical spontaneous and endothermic process. The sorption isotherms were well simulated by Langmuir model, suggesting that the sorption was monolayer coverage. The CS@LDH can be used as superior adsorbent for efficient elimination of radionuclides in environmental pollution remediation. This study also demonstrated a new strategy to improve the physicochemical properties of other low efficiency adsorbents through polymerization reaction. [ABSTRACT FROM AUTHOR]

Uranium has attracted sustained attention due to its high mobility and biotoxicity. Among various techniques, sorption is considered as the most effective technique to treat the U(VI)-containing wastewater. In serving for low-cost adsorbents, layered double hydroxides (LDHs) have been proved to be promising candidates. However, the interaction mechanism of U(VI) with LDHs is still unclear, although plenty of LDHs have been used in this field. Herein, we developed two novel methods to fabricate ternary LDHs (MgFeAl LDHs and NiFeAl LDHs) and applied the ternary LDHs as adsorbents to investigate their sorption performance towards U(VI). The results showed that the sorption was endothermic and followed the pseudo-second-order kinetics through the formation of inner-sphere surface complexes, and the sorption isotherms were simulated by the Langmuir model well. Furthermore, systematic spectroscopy characterization indicated that the sorption occurred on the surface sites of Mg-OH and Ni 2+ –OH, while the CO 3 2− in the gallery space also played an important role. This work highlighted the synthesis of high-efficient materials and their application in wastewater treatment. [ABSTRACT FROM AUTHOR]

Graphical abstract A novel arginine modified hydroxyapatite carbon microsphere (C@HAp/Arg) composite were synthesized by a facile and green method and exhibited superior adsorption efficiency for removal of U(VI). Abstract Uranium was not only the main source of nuclear energy but also one of the long-lived radionuclide. Herein, a novel arginine modified hydroxyapatite carbon microsphere composites (defined as C@HAp/Arg) obtained promptly via a one-step mild hydrothermal method, was applied to remove U(VI) from aqueous solutions. Based on the characterization of transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the synthesized C@HAp/Arg presented globular morphology and abundant functional groups (e.g., COO−), which were beneficial to its combination with U(VI). The interaction mechanism and removal capability of U(VI) on C@HAp/Arg were studied by batch adsorption technique and spectroscopy analysis. The results implied that U(VI) can form strong surface complexes on C@HAp/Arg. The kinetics adsorption of U(VI) followed pseudo-second-order kinetic model with high removal efficiency (∼95% within 5 h at pH 5.0). The adsorption isotherms were well fitted by Langmuir model, implying that U(VI) uptake on C@HAp/Arg was monolayer coverage. It was found that the maximum adsorption capacities of CSs, C@HAp and C@HAp/Arg toward U(VI) were calculated to be 23.16, 72.09 and 569.66 mg/g, respectively, at 298.15 K and pH 5.0, and thermodynamic parameters revealed that the adsorption processes of U(VI) were spontaneous and endothermic. In addition, effect of co-existed ions and CO 3 2− concentrations demonstrated that U(VI) adsorption on C@HAp/Arg was weakly interfered by foreign ions and carbonate concentrations. More importantly, the adsorption performance of U(VI) on C@HAp/Arg was still over ∼87% after five cycles. Therefore, it was noted that the versatile C@HAp/Arg could be potentially used as a powerful building block for the enrichment and disposal of U(VI) from aqueous solutions, which could efficiently reduce the potential toxicity of U(VI) in the U(VI)-contaminated water. [ABSTRACT FROM AUTHOR]

A novel low-cost, effective and environmental-friendly laminated carbon nitride decorated with polydopamine (PDA) and grafted with polyethyleneimine (PEI) brush ( l -C 3 N 4 /PDA/PEI 3 ) was successfully synthesized and applied as environmental cleaner for removing U(VI) ions from aqueous solutions under various environmental conditions. The adsorption isotherms fitted well by the Langmuir model, suggesting that the removal of U(VI) on l -C 3 N 4 /PDA/PEI 3 was monolayer coverage. The effects of different PEI contents were also investigated and the results demonstrated that the adsorption capacity of U(VI) on l -C 3 N 4 /PDA/PEI x decreased at higher content of PEI. Typically, various cations (Ca 2+ and Mg 2+ ) and SO 4 2− could inhibit the adsorption through competitive coordination with U(VI), while CO 3 2− promoted U(VI) sorption owing to the formation of indissolvable complexes. The main driving force between U(VI) and l -C 3 N 4 /PDA/PEI 3 was surface complexation with various functional groups (C C, C O, N C C, and C C or C H) and electrostatic attraction. According to the analysis of EXAFS spectra, the occurrence of U-C and U-U shell revealed that inner-sphere complexation and surface co-precipitation dominated the adsorption of U(VI) on l -C 3 N 4 /PDA/PEI 3 at pH 5.0. The composites were also applied to remove 243 Am(III), Cu(II) and Pb(II) ions at different pH values, and similar results were also found for these metal ions. Such a facile synthesis method and efficient removal performance suggested that the l -C 3 N 4 /PDA/PEI 3 materials might be a promising adsorbent for efficient elimination of radionuclides and heavy metal ions in environmental pollution management. [ABSTRACT FROM AUTHOR]

Hierarchical silicon dioxide-@-layered double hydroxide (SiO 2 @LDH) nanocomposites were synthesized by a facile in situ co-precipitation method, and characterized by XRD, FESEM, FT-IR and XPS in detail. The sorption of uranium (U(VI)) and methyl orange (MO) on SiO 2 @LDH were investigated as a function of pH, ionic strength, contact time and temperature. The results indicated that the sorption of U(VI) and MO were strongly dependent on pH, and weakly dependent on ionic strength, demonstrating that the interaction of U(VI) was mainly dominated by inner-sphere surface complexation and the sorption of MO was mainly attributed to electrostatic attraction due to the high removal efficiency (∼98% within 4 h for U(VI) ions, and ∼92% within 10 min for MO). The kinetics sorption of U(VI) and MO both followed the pseudo-second-order model well, suggesting that the sorption processes were chemical sorption. The sorption isotherms of U(VI) and MO on SiO 2 @LDH were well fitted by the Langmuir model, and the maximum sorption capacities of SiO 2 @LDH were calculated to be 303.1 mg·g −1 for U(VI) and 166.1 mg·g −1 for MO. The thermodynamic parameters revealed that the sorption of U(VI) and MO was spontaneous process. Integrating the experimental result analysis, the hierarchical SiO 2 @LDH may be a promising material for the efficient elimination of radionuclides and dyes from aqueous solutions in natural environmental pollution cleanup. [ABSTRACT FROM AUTHOR]

Highly porous zeolitic imidazolate frameworks (ZIFs), with disparate metal ions (ZIF-8 and ZIF-67), disparate organic ligands (ZIF-9 and ZIF-67), single or double central metal atoms (ZIF-8, Zn/Co-ZIF and ZIF-67) were prepared and used in the elimination of typical radionuclide U(VI). The detailed interaction mechanisms were studied by batch experiments, spectral analyses and DFT calculation. Langmuir isotherms model revealed a decreasing tendency to remove U(VI): ZIF-8 (540.4 mg/g) > Zn/Co-ZIF (527.5 mg/g) > ZIF-9 (448.6 mg/g) > ZIF-67 (368.2 mg/g). Based on the effects of pH and foreign ions, FTIR and XPS spectra analyses, the possible interaction mechanisms of U(VI) onto ZIFs were surface complexation and electrostatic interaction. Among them, ZIF-8 with Zn metal center and 2-methylimidazolate organic ligand had the best elimination capacity for U(VI) because of its large surface area, active metal ion and abundant nitrogen-containing groups (e.g., C–N, Zn–N and C N). Specially, the adsorption energy of ZIF-8-Zn2-UO 2 2+ structure was −2.299 eV obtained by DFT calculation, illustrating that U(VI) and N atoms were formed the most stable bidentate coordination compounds. This paper highlights the effects of the hydroxylated metals, the functional groups of the imidazole ring on the elimination of U(VI), which can provide constructive suggestions for further adsorbent materials amelioration. Image 1 • ZIF-8, ZIF-9, ZIF-67 and Zn/Co-ZIF were fabricated by stirring at room temperature. • Excellent structural performances endowed four ZIFs outstanding sorption capacity. • The differences in adsorption mechanism of four ZIFs were investigated in detail. • The N atoms of ZIF-8 formed bidentate coordination compounds with U(VI). [ABSTRACT FROM AUTHOR]

• Water stable Fe 3 O 4 @ZIF-8 was fabricated through a facile modification strategy. • Excellent structural performances endowed Fe 3 O 4 @ZIF-8 outstanding absorbability. • Multi-factors influence demonstrated the practical application potential. • The mechanisms were electrostatic attraction and inner-sphere surface complexation. • The excellent uptake capabilities made Fe 3 O 4 @ZIF-8 a promising adsorbent. The water stable core-shell microspheres (Fe 3 O 4 @ZIF-8) with strong magnetism were successfully fabricated through a facile modification strategy. Concrete procedures included firstly pretreatment of Fe 3 O 4 core with anionic polyelectrolyte to acquire negatively charged Fe 3 O 4 particle surface, followed by nucleation through attracting Zn2+ cation, and then growth of a thin layer of ZIF-8 (~25 nm). Various characterization techniques (SEM, TEM, FT-IR, XRD, VSM, BET and XPS) indicated that the Fe 3 O 4 @ZIF-8 microspheres were highly stable and magnetic with a large specific surface area (606.91 m2/g) and fairly sufficient functional groups (NH , OH, COOH, Zn O, N O and C N). Multi-factors affecting the radionuclides removal performance on Fe 3 O 4 @ZIF-8 was adequately explored, comprising contact time, temperature, pH, ionic strength, co-existing ions and extreme conditions. And the results showed that Fe 3 O 4 @ZIF-8 exhibited fast reaction kinetics (~30 min to achieve equilibrium), excellent uptake capabilities (539.7 mg U/g and 255.6 mg Eu/g), remarkable selectivity and favorable physicochemical stability. These researches suggested that Fe 3 O 4 @ZIF-8 could not only simultaneously achieve favorable stability and functionality, but also easily to be separated by external magnetic field after used in radioactive sewage treatment, which was of considerable practical utility in extracting radioactive wastes though in harsh circumstance. [ABSTRACT FROM AUTHOR]