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With the rapid growth of population and industrialization, the energy crisis and environmental pollution as two main difficulties urgently need to be solved nowadays. The development and utilization of nuclear energy is of great significance for solving energy support, national security and environmental protection. As the raw material of nuclear energy, a lot of uranium in seawater provide a guarantee for the sustainable and green development of nuclear power plants. Recently, various new carbon-based materials (e.g., carbon nanofibers, multiwalled carbon nanotube, graphene) have been attracted widely intense interest in extraction of uranium from seawater due to large specific surface area, excellent acid-base resistance, high adsorption performance, environmental friendly and low cost. Thus, the systematic reviews concerning the extraction of uranium from seawater on various carbon-based materials were highly desirable. In this review, the extraction methods of uranium from seawater, including electrochemical, photocatalytic and adsorption methods are briefly introduced. Then the application and mechanism of four generation carbon-based materials on the extraction of uranium from seawater are systematically reviewed in details. Finally, the current challenges and future trends of uranium extraction from seawaters are proposed. This review provides the guideline for designing carbon-based materials with high adsorption capacity and exceptional selectivity for U(VI) extraction from seawater., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Precise prediction of uranium adsorption at water-mineral interface is of great significance for the safe disposal of radionuclides in geologic environments. Surface complexation modeling (SCM) as a very useful tool has been extensively investigated for simulating adsorption behavior of metals/metalloids at water-mineral interface. Numerous studies concerning the fitting of uranium adsorption on various adsorbents using SCM are well documented, but the systematic and comprehensive review of uranium adsorption using various SCM is not available. In this review, we briefly summarized the rationale of SCM, including constant-capacitance-model (CCM), diffuse-layer-model (DLM), triple-layer-model (TLM); The recent progress in the application of SCM on the fitting of uranium adsorption towards metal (hydr)oxides, clay minerals and soil/sediments was reviewed in details. This review hopefully provides the beneficial guidelines for predicting the transport and fate of uranium in geologic environments beyond laboratory timescales., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The bioaccumulation of hexavalent uranium (U(VI)) on Candida utilis (C. utilis) and its biological effects were investigated via batch and biologic techniques. The bioaccumulation mechanism of U(VI) and C. utilis were characterized by SEM, TEM, FT-IR and XPS. The batch results showed that C. utilis had a high adsorption capacity (41.15 mg/g wet cells at pH 5.0) and high equilibrium rate (~100% within 3.5 h). The analysis of intracellular hydrogen peroxides and malondialdehyde suggested that the growth of C. utilis was inhibited under different concentrations of U(VI) due to the abundant production of reactive oxide species. The activity of intracellular antioxidants (e.g., super oxide dismutase and glutathione) was significantly enhanced under U(VI) stress, indicating the anti-toxic effect of C. utilis cells under low U(VI) stress. These results indicated that C. utilis is an ideal biosorbent for removing radionuclides in environmental remediation., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Owing to high surface energy, strong chemical reactivity and large surface area, nanoscale zero-valent iron (nZVI) as a novel emerging material has been extensively utilized in environmental cleanup. Although a lot of reviews regarding the removal of organic contaminants and heavy metals on nZVI are summarized in recent years, the advanced progress concerning the removal of radionuclides on nZVI is still scarce. In this review, we summarized the removal of technetium (Tc), uranium (U), selenium (Se) and other radionuclides on nZVI and nZVI-based composites, then their interaction mechanisms were reviewed in details. This review is crucial for the environmental chemist and material engineer to exploit the actual application of nZVI-based composites as the emerging materials of permeable reactive barrier on the removal of radionuclides from aqueous solutions., (Copyright © 2020 Elsevier Inc. All rights reserved.)

A robust prediction of U(VI) on Fe 3 O 4 /activated carbon (Fe 3 O 4 /AC, fabricated by co-precipitation method under N 2 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 Fe 3 O 4 /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 Fe 3 O 4 /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 Fe 2+ of Fe 3 O 4 /AC by XPS analysis. Surface complexation modeling showed that a single set of monodentate and mononuclear species (SOUO 2 + ) 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) 2 UO 2 (CO 3 ) 6- ). These findings revealed that magnetic AC as a candidate for immobilization and/or preconcentration of radioactive wastewater in environment management., Competing Interests: Declaration of competing interest Hereby, the authors state no conflicting financial interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The decontamination of U(VI) on graphene oxide/nano-alumina (GO/Al 2 O 3 ) composites were investigated by batch, XRD, FT-IR and XPS techniques. The characterization results showed that GO/Al 2 O 3 composites presented a variety of oxygen-containing functional groups, which provided the more surface reactive sites. The batch experiments indicated that sorption equilibrium of U(VI) on GO/Al 2 O 3 composites was achieved within 30 min, and the maximum sorption capacity derived from Langmuir model was 142.8 mg/g at pH 6.5. In addition, the slight decrease of sorption capacity was observed even after fifth recycling times. These results indicated that GO/Al 2 O 3 composites displayed the fast sorption rate, high sorption capacity and good regeneration performance. No effect of ionic strength revealed the inner-sphere surface complexation of U(VI) on GO/Al 2 O 3 composites. FT-IR and XPS analysis demonstrated that the high adsorption of U(VI) on GO/Al 2 O 3 was attributed to the various oxygen-bearing functional groups. In addition, the nano Al 2 O 3 was transferred to amorphous AlO(OH) mineral phase by XRD pattern, which provided the additional reactive sorption sites. These observations indicated that GO-based composites can be regarded as a promising adsorbent for immobilization and pre-concentration of U(VI) from aqueous solutions in the environmental remediation., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Effect of Staphylococcus epidermidis (S. epidermidis) on U(VI) sequestration by Al-goethite were conducted under different geologic conditions. The batch experiments showed that S. epidermidis significantly enhanced the adsorption rates of U(VI) at pH < 9.0 due to the additional metal binding sites. The maximum adsorption capacities of U(VI) on Al-goethite and Al-goethite +S. epidermidis at pH 4.0 and 310 K were calculated from Langmuir equation to be 13.16 and 47.86 mg/g, respectively. The decreased adsorption of U(VI) on Al-goethite+ S. epidermidis at high carbonate and pH conditions were primarily driven by the electrostatic repulsion between negatively charged U(VI)-carbonate complexes and the negatively charged adsorbents. According to XPS analysis, the adsorbed U(VI) can be reduced to U(IV) by S. epidermidis, whereas inhibited reduction of U(VI) on Al-goethite + S. epidermidis at high pH could be attributed to the complexation of structural Fe(III) with the oxygen-containing functional groups of S. epidermidis. FT-IR analysis further demonstrated that the bonding of structural Fe(III) with functional groups (e.g., carboxyl and phosphate groups) of S. epidermidis. These results herein are important to understand the fate and transport of U(VI) on the mineral-bacteria ternary systems in the near-surface environment., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The combined pollution of radionuclides and heavy metals has been given rise to widespread concern during uranium mining. The influence of As(V) on U(VI) immobilization by Mucor circinelloides (M. circinelloides) was investigated using batch experiments. The activity of antioxidative enzymes and concentrations of thiol compounds and organic acid in M. circinelloides increased to respond to different U(VI) and As(V) stress. The morphological structure of M. circinelloides changed obviously under U(VI) and As(V) stress by SEM and TEM analysis. The results of XANES and EXAFS analysis showed that U(VI) was mainly reduced to nano-uraninite (nano-UO 2 , 30.1%) in U 400 , while only 9.7% of nano-UO 2 was observed in the presence of As(V) in U 400 -As 400 due to the formation of uranyl arsenate precipitate (Trögerite, 48.6%). These observations will provide the fundamental data for fungal remediation of uranium and heavy metals in uranium-contaminated soils., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The adsorption and desorption of U(VI) on graphene oxides (GOs), carboxylated GOs (HOOC-GOs), and reduced GOs (rGOs) were investigated by batch experiments, EXAFS technique, and computational theoretical calculations. Isothermal adsorptions showed that the adsorption capacities of U(VI) were GOs > HOOC-GOs > rGOs, whereas the desorbed amounts of U(VI) were rGOs > GOs > HOOC-GOs by desorption kinetics. According to EXAFS analysis, inner-sphere surface complexation dominated the adsorption of U(VI) on GOs and HOOC-GOs at pH 4.0, whereas outer-sphere surface complexation of U(VI) on rGO was observed at pH 4.0, which was consistent with surface complexation modeling. Based on the theoretical calculations, the binding energy of [G(···)UO2](2+) (8.1 kcal/mol) was significantly lower than those of [HOOC-GOs(···)UO2](2+) (12.1 kcal/mol) and [GOs-O(···)UO2](2+) (10.2 kcal/mol), suggesting the physisorption of UO2(2+) on rGOs. Such high binding energy of [GOs-COO(···)UO2](+) (50.5 kcal/mol) revealed that the desorption of U(VI) from the -COOH groups was much more difficult. This paper highlights the effect of the hydroxyl, epoxy, and carboxyl groups on the adsorption and desorption of U(VI), which plays an important role in designing GOs for the preconcentration and removal of radionuclides in environmental pollution cleanup applications.

The reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) composites were synthesized by chemical deposition method and were characterized by SEM, high resolution TEM, Raman and potentiometric acid-base titrations. The characteristic results showed that the nZVI nanoparticles can be uniformly dispersed on the surface of rGO. The removal of U(VI) on nZVI/rGO composites as a function of contact time, pH and U(VI) initial concentration was investigated by batch technique. The removal kinetics of U(VI) on nZVI and nZVI/rGO were well simulated by a pseudo-first-order kinetic model and pseudo-second-order kinetic model, respectively. The presence of rGO on nZVI nanoparticles increased the reaction rate and removal capacity of U(VI) significantly, which was attributed to the chemisorbed OH(-) groups of rGO and the massive enrichment of Fe(2+) on rGO surface by XPS analysis. The XRD analysis revealed that the presence of rGO retarded the transformation of iron corrosion products from magnetite/maghemite to lepidocrocite. According to the fitting of EXAFS spectra, the UC (at ∼2.9Å) and UFe (at ∼3.2Å) shells were observed, indicating the formation of inner-sphere surface complexes on nZVI/rGO composites. Therefore, the nZVI/rGO composites can be suitable as efficient materials for the in-situ remediation of uranium-contaminated groundwater in the environmental pollution management., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Sorption-desorption experiments show that the majority (ca. 80-90%) of U(VI) presorbed to mesoporous and nanoporous alumina could not be released by extended (2 week) extraction with 50 mM NaHCO(3) in contrast with non-nanoporous α alumina. The extent of reduction of U(VI) presorbed to aluminum oxides was semiquantitatively estimated by comparing the percentages of uranium desorbed by anoxic sodium bicarbonate between AH(2)DS-reacted and unreacted control samples. X-ray absorption spectroscopy confirmed that U(VI) presorbed to non-nanoporous alumina was rapidly and completely reduced to nanoparticulate uraninite by AH(2)DS, whereas reduction of U(VI) presorbed to nanoporous alumina was slow and incomplete (<5% reduction after 1 week). The observed nanopore size-dependent redox behavior of U has important implications in developing efficient remediation techniques for the subsurface uranium contamination because the efficiency of in situ bioremediation depends on how effectively and rapidly U(VI) bound to sediment or soil can be converted to an immobile phase.

Multiwalled carbon nanotubes (MWCNTs) have exhibited high sorption capacity for radionuclides due to the unique hollow structure and large surface area. In this study, surface properties of oxidized MWCNTs were characterized by using XRD, SEM, FTIR and potentiometric acid-base titration. The sorption of U(VI) on oxidized MWCNTs as a function of contact time, U(VI) concentration, pH, ionic strength, humic acid/fulvic acid (HA/FA) and carbonate was investigated by using batch technique. The removal of U(VI) by oxidized MWCNTs was strongly dependent on pH and ionic strength. The presence of HA/FA enhanced U(VI) removal on oxidized MWCNTs at low pH while inhibited U(VI) sorption at high pH. The mechanism of U(VI) sorption on oxidized MWCNTs was assumed to be cation exchange/outer-sphere surface complexation in acidic pH and to form precipitation under circum neutral conditions. The oxidized MWCNTs exhibit higher sorption capacity and stronger chemical affinity than pristine MWCNTs., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

Graphitic carbon nitride (g-C3N4) has been paid increasingly attentions in U(VI) removal due to the visible-light response, whereas the high recombination of photogenerated electron and holes limited the actual environmental application. Herein, Z-scheme MoS2/g-C3N4 heterojunction was fabricated to enhance removal of U(VI) from aqueous solution. The microscopic and spectroscopic characterizations showed that addition of MoS2 on surface of g-C3N4 increased separation efficiency of photogenerated charge, decreased the bandgap and improved the intensity of light adsorption. Approximate 82% of UO22+ was photo-reduced by MoS2/g-C3N4 after 1 h of light irradiation at pH 4.5. The high effective photocatalytic reduction of U(VI) on MoS2/g-C3N4 was attributed to ·O2− radials according to quenching experiments. XPS analysis showed that the adsorbed U(VI) was photo-reduced into U(IV). These findings are crucial for the design of C3N4-based composites with high efficient photocatalytic performance and exclusive selectivity into actual environmental cleanup. [ABSTRACT FROM AUTHOR]

Perovskite‐based composites have been widely investigated in photocatalysis due to their narrow bandgap width and high separation efficiency of photogenerated charges. Herein, the novel perovskite/carbon nitride heterojunction (SrTiO3/g‐C3N4) was synthesized by a simple calcination method and then was applied in the photocatalytic reduction of U(VI) from aqueous solutions. The characterizations indicated that incorporation of SrTiO3 increased the charge separation efficiency and light absorption range, while it decreased electron‐hole recombination. Specifically, the SrTiO3/g‐C3N4 composite exhibited the high U(VI) removal rate (100 % in 15 min), high selectivity (88 % U(VI) from seawater within 15 min), chemical stability, and excellent regeneration performance due to the improved electron utilization efficiency. Electrons play an important role in U(VI) photocatalytic reduction according to quenching experiments, XPS, and electron paramagnetic resonance analysis. These findings are crucial for the application of perovskite‐based composites in the actual environmental cleanup under visible‐light to improve solar energy utilization. [ABSTRACT FROM AUTHOR]

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 UO22+ 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 UO22+ adsorption. The pH-dependent adsorption was simulated by three surface complexation modellings, revealing that UO22+ adsorption on HMC was excellently fitted by triple layer model using two inner-sphere complexes (i. e. SOUO2+ and SOUO2(CO3)35− 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. [ABSTRACT FROM AUTHOR]

The decontamination of U(VI) on graphene oxide/nano-alumina (GO/Al 2 O 3) composites were investigated by batch, XRD, FT-IR and XPS techniques. The characterization results showed that GO/Al 2 O 3 composites presented a variety of oxygen-containing functional groups, which provided the more surface reactive sites. The batch experiments indicated that sorption equilibrium of U(VI) on GO/Al 2 O 3 composites was achieved within 30 min, and the maximum sorption capacity derived from Langmuir model was 142.8 mg/g at pH 6.5. In addition, the slight decrease of sorption capacity was observed even after fifth recycling times. These results indicated that GO/Al 2 O 3 composites displayed the fast sorption rate, high sorption capacity and good regeneration performance. No effect of ionic strength revealed the inner-sphere surface complexation of U(VI) on GO/Al 2 O 3 composites. FT-IR and XPS analysis demonstrated that the high adsorption of U(VI) on GO/Al 2 O 3 was attributed to the various oxygen-bearing functional groups. In addition, the nano Al 2 O 3 was transferred to amorphous AlO(OH) mineral phase by XRD pattern, which provided the additional reactive sorption sites. These observations indicated that GO-based composites can be regarded as a promising adsorbent for immobilization and pre-concentration of U(VI) from aqueous solutions in the environmental remediation. Image 1036392 • A variety of oxygenated functional groups was demonstrated by characterization. • U(VI) removal on GO/Al 2 O 3 was inner-sphere surface complexation. • Nano Al 2 O 3 was transferred to amorphous AlO(OH) mineral phase by XRD analysis. • GO/Al 2 O 3 presented fast sorption rate, high sorption capacity and good regeneration. The transformation of nano Al 2 O 3 to amorphous AlO(OH) provided the additional reactive sorption sites for high efficient sorption of U(VI). [ABSTRACT FROM AUTHOR]

Functional β-cyclodextrin-attapulgite nanorods ( β-CD-APT) were synthesized to remove U(VI) under varied environmental conditions. Adsorption results demonstrated that the removal capacity of β-CD-APT nanorods for U(VI) (51 %) was higher than bare APT (38 %). The thermodynamic data indicated that the adsorption of U(VI) onto β-CD-APT nanorods was an endothermic and spontaneous process. The desorption results showed a reversible hysteresis loop for β-CD-APT, suggesting complete U(VI) desorption could happen without intervention. It is demonstrated that the β-CD-APT nanorods can be a promising material for the preconcentration and solidification of U(VI) in environmental cleanup. [ABSTRACT FROM AUTHOR]

Aluminum co-precipitated with goethites (Al-FeOOHs) are ubiquitous within (sub)-surface environments, which are considered one of the most important sinks for radionuclide pollution management. Accordingly, various mole ratios Al-FeOOH were synthesized and characterized by XRD, FT-IR, TEM, specific surface area and potentiometric acid-base titration. According to XRD and TEM images, the morphology of Al-FeOOH was transformed from acicular-like goethite to cotton-like gibbsite with increasing Al content. The adsorption and sequential desorption of U(VI) on Al-FeOOHs were conducted by batch techniques under N2 conditions. The batch adsorption results showed that the adsorption of U(VI) on Al-FeOOHs slightly increased at pH < 4.0, then the significant increase of U(VI) adsorption was observed at pH from 4.0 to 7.0, whereas the suppressed adsorption at pH > 8.0 was due to the electrostatic repulsion between negative charge surface and negative carbonato-complexes. The adsorption of U(VI) on Al-FeOOHs was independent of ionic strength at pH > 5.0, indicating that the inner-sphere surface complexation predominated their adsorption behaviors, whereas U(VI) adsorption on Al-FeOOH could be the outer-sphere surface/cation exchange reaction. The sequential extraction texts showed that the desorption of U(VI) from Al-FeOOHs decreased with increasing Al content. These findings highlighted the effect of Al content on the sequestration and immobilization of U(VI) onto Al-FeOOHs from (sub)-surface environments in pollution management. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the sorption and desorption of U(VI) from contaminated groundwater by nanoporous and non-nanoporous alumina were investigated under ambient conditions. The nanoporous and non-nanoporous alumina were characterized by XRD, specific surface area analysis, TEM and potentiometric acid–base titration. The nanoporous alumina exhibited high sorption capacity, large specific surface area, high surface acidity constants, low difference of surface acidity constants and high pHPNZC (point of net zero charge) due to the nanoporous effect. The worm-like shape nanoporous alumina was transferred into the floc-like shape gibbsite after the sorption in terms of TEM images. Sorption kinetics and sorption isotherms of U(VI) on both nanoporous and non-nanoporous alumina can be interpreted by pseudo-second order kinetic model and the Langmuir model, respectively. The sorption of U(VI) on nanoporous alumina is strongly dependent on pH and independent of ionic strength, whereas U(VI) sorption on non-nanoporous alumina is dependent on pH and ionic strength. The sorption mechanism is assumed to be mainly inner-sphere surface complexation for nanoporous alumina and outer-sphere surface complexation for non-nanoporous alumina. Approximately 100% of U(VI) was desorbed from non-nanoporous alumina while only ∼5% of U(VI) was extracted from nanoporous alumina when the concentration of NaHCO3 was increased to 0.01M in terms of sequential desorption experiments. The nanoporous alumina can be used as an efficient material for in situ immobilization of U(VI) from contaminated groundwater. [Copyright &y& Elsevier]

The effects of Bacillus subtilis ( B . subtilis , a typical model bacterium) on the reduction of U(VI) by nanoscale zero-valent iron (nano-Fe 0 ) were investigated using batch techniques. The reaction products were analysed using spectroscopic techniques, and a kinetics model was developed to elucidate the mechanisms of U(VI) reduction by nano-Fe 0 . The presence of B . subtilis enhanced the U(VI) sorption rate at pH 3.5–9.5 but inhibited the reduction rate of U(VI) to U(IV) at pH > 4.5. According to the FTIR and XRD analysis, the reduction of U(VI) to U(IV) was inhibited due to the formation of inner-sphere surface complexes between the oxygen-containing functional groups of B . subtilis or extracellular polymeric substances with the Fe(II)/Fe(III) generated by nano-Fe 0 , which blocked electron transport from the Fe 0 core to U(VI). Based on the EXAFS analysis, a fitting of U–Fe shell at ∼3.44 Å revealed inner-sphere bidentate complexes between uranyl and the oxide film of nano-Fe 0 . For the nano-Fe 0 + B. subtilis system, the U–Fe shell (at ∼3.44 Å) and the U–C/P shell (at ∼2.90 Å) further indicated the formation of inner-sphere surface complexes. The kinetics model supported that U(VI) reduction was triggered by U(VI) sorption on the oxide shell of nano-Fe 0 . The XPS and XANES analyses showed that reductive precipitation was the main mechanism of U(VI) removal by nano-Fe 0 , whereas the sorption process dominated the removal of U(VI) in the presence of B . subtilis, which was further demonstrated by TEM images. [ABSTRACT FROM AUTHOR]

A new adsorbent of fungus/attapulgite (F/ATP) composites was synthesized by one-pot hydrothermal carbonization method under mild conditions and characterized by scanning electron microscope, X-ray diffraction, thermogravimetric analysis and Fourier transform infrared spectroscopy. The characterized results showed that the fungus ( Geotrichum sp. dwc-1) can be as a superior template for the assembly of nanoscale attapulgite by covalent bonding. According to batch experiments, the maximum sorption capacity of F/ATP for U(VI) was 125 mg/g at pH 4.0 and T = 303 K. The thermodynamic parameters calculated from sorption isotherms showed that U(VI) sorption on F/ATP was a spontaneous and endothermic process. The fixed-bed column experiment further demonstrated that F/ATP presented the excellent adsorption performance. It was determined from regeneration experiments that the F/ATP composites exhibited high sorption of U(VI) (∼91%) over six cycles. Therefore, F/ATP can be as a promising candidate for the removal of U(VI) from aqueous solution due to its low-cost, sustainable, and efficient feature. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • HA enhanced dispersion and decreased zeta potential of CaTiO 3 at low pH. • HA enhanced U(VI) sorption at pH < 5.0 due to the abundant oxygenated groups. • U(VI) inhibited sequestration at pH > 6.0 was due to the electrostatic repulsion. • HA enhanced and inhibited U(VI) adsorption and reduction, respectively. Abstract The influence of humic acid (HA) on U(VI) sequestration by calcium titanate (CaTiO 3) was investigated by batch experiment and spectroscopic techniques. Various characterizations, including zeta potentials, average hydrodynamic diameters, specific surface area and pore volume, have been demonstrated that HA significantly changes the surface properties of CaTiO 3. In addition, the obtained results revealed that HA enhanced U(VI) adsorption at pH < 5.0 attributed to the strong electrostatic attraction, the dispersion of particles exposed more adsorption sites and abundant oxygen-groups of surface loaded HA, whereas U(VI) sequestration was inhibited assigned to the stronger electrostatic repulsion between anionic U(VI) species and more negative surface of CaTiO 3 at pH > 6.0. XPS analysis showed that the higher sequestration of U(VI) in the existence of HA, which was ascribed to the enhanced dispersity, decreased zeta potential and more abundant surface functional groups of CaTiO3 at low pH. In addition, HA inhibited the reduction of U(VI)–U(IV) at low pH under ambient conditions. These information are significant for the understanding the surface properties of perovskite-type titanate materials and its sequestration performance of uranium in HA-rich environments. [ABSTRACT FROM AUTHOR]

The β-cyclodextrin/Al(OH) 3 composites (β-CD/Al(OH) 3 ) were synthesized using the plasma-induced grafting technique and were employed to remove UO 2 2 + from aqueous solutions under ambient conditions. Based on the characteristic results of SEM, FT-IR, XRD, and TGA techniques, β-CD was satisfactorily grafted onto the Al(OH) 3 surface. The maximum adsorption capacity of β-CD/Al(OH) 3 composites calculated from Langmuir model at pH 6.0 and 303 K was 63.29 mg/g, which was significantly higher than Al(OH) 3 (23.31 mg/g). The high adsorption capacity of β-CD@Al(OH) 3 composites was due to the inner cores of the hydrophobic cavity of CD incorporated with UO 2 2 + ions. The calculated thermodynamic parameters showed that the adsorption of UO 2 2 + on Al(OH) 3 and β-CD@Al(OH) 3 composites was an endothermic and spontaneous process. The batch desorption indicated that the adsorption of UO 2 2 + on β-CD@Al(OH) 3 composites was an irreversible process. Based on the surface complexation modeling, the adsorption mechanism of UO 2 2 + on Al(OH) 3 and β-CD@Al(OH) 3 composites was outer-sphere surface complexation at pH < 5.0, whereas inner-sphere surface complexation dominated the UO 2 2 + adsorption on Al(OH) 3 and β-CD@Al(OH) 3 composites at pH > 6.0. These observation showed that β-CD/Al(OH) 3 composite can be used as a promising adsorbent for the preconcentration and immobilization of UO 2 2 + ions in environmental pollution cleanup. [ABSTRACT FROM AUTHOR]

Uranium contamination derived from nuclear mining and nuclear waste has caused severe environmental and public health problems. Photocatalysis has been proved to be an available method for U(VI) elimination. However, photoinduced uranyl(VI) photocatalysis process tends to be overlooked. Herein, we reported that three-dimensional g-C 3 N 4 boosted the production of photocatalytic H 2 O 2 during recycling of U(VI). UO 2 2+ was first excited to *UO 2 2+ under visible light irradiation, then *UO 2 2+ was further converted to UO 2 + under organics, whereas UO 2 + transferred into UO 2 2+ and H 2 O 2 was generated under the dissolving O 2 condition (UO 2 2+ → *UO 2 2+ → UO 2 + → UO 2 2+). Meanwhile, massive H 2 O 2 was produced from photogenerated electrons derived from the converting dissolving O 2 on 3D g-C 3 N 4 under visible light irradiation. The high-efficiency U(VI) immobilization was ascribed to the reaction of U(VI) and H 2 O 2 to form uranyl peroxides (nano-metastudtite, UO 2 (O 2)•2H 2 O, ∼20 nm width˟40 nm length). These observations give valuable insights into the photoinduced U(VI) immobilization in actual environment. Capsule ：g-C 3 N 4 boosts the conversion of photogenerated electrons and formation of uranyl peroxides under visible light. [ABSTRACT FROM AUTHOR]