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As one of the typical actinide elements, the chemical and radioactive toxicities of uranium have attracted more attention. In this work, the toxicity mechanism of uranium-238 in HK-2 cells was studied in detail using in vitro approach. The results confirmed that exposure to uranium solution significantly reduced the viability of HK-2 cells. Flow cytometry and double fluorescence AO/PI staining suggested that apoptosis was the main cause of the death of HK-2 cells. Moreover, reactive oxygen species and mitochondrial membrane potential tests further demonstrated that HK-2 cells underwent apoptosis under the combined action of oxidative stress and mitochondrial damage. The tails in the comet assay and the abnormal nuclear morphology in DAPI staining confirmed the genotoxicity of uranium to HK-2 cells. In conclusion, uranium mainly causes apoptosis and genotoxicity after exposure, and the main mechanisms of apoptosis are mainly related to oxidative stress, mitochondrial damage, and DNA damage. [ABSTRACT FROM AUTHOR]

The adsorption of Th(IV) and the structural transformation of phlogopite were explored using batch, extraction, and spectroscopic approaches in this study. The batch experiments showed that ion exchange, surface complexation, and precipitation were predominant for Th(IV) adsorption on phlogopite under the observed pH ranges. XRD patterns showed that phlogopite was indeed transforming into the vermiculite- and/or montmorillonite-like minerals during Th(IV) adsorption, which indicated that the adsorption of Th(IV) could enhance the weathering process of phlogopite. Such weathering process could be attributed to the intercalation of hydrated Th(IV) ions instead of K + ions locating at the interlayer sites, and then induced the expansion of the interlayer with a d-spacing of ~ 14 Å. Higher temperature and initial Th(IV) concentration were benefit for the structural transformation, but the presence of alkaline cations inhibited the expansion process following the order of Rb + > K + > Na + ≈ Li + , which is strictly consistent with their hydrated radii and energy. Fulvic acid (FA) affected the distribution of Th(IV) on phlogopite to a large extent, which induced different adsorption mechanisms for Th(IV) and the alteration process of phlogopite structure. The results clearly showed a positively relationship between the immobilization ability for Th(IV) and alteration degree of phlogopite structure, which is very important to understand the mutual interaction of radionuclides and micaceous minerals in the environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fast reduction of U6+ to U4+ occurs on semiconductors during XPS measurement. • Slower breakage of uranyl occurs on non-semiconductors under X-ray irradiation. • XPS measurement could change the elements state even if far from the center of beam. • Measures are proposed to reduce the beam induced effects in XPS measurement. X-ray photoelectron spectroscopy (XPS) is an efficient technique for recognizing the state of elements. However, the effects of X-ray irradiation on change in the chemical state are sometimes ignored, which may impair the understanding of the environmental behavior of these elements. This study determined the change in the U 4f spectra induced by X-ray irradiation during XPS detection. For U(VI) on non-semiconductors, X-ray irradiation led to a negative shift of U 4f 7/2 to ∼ 380.8 eV due to the break of the uranyl molecules, but not resulting in U(IV) species. However, owing to the photocatalytic reduction of U(VI), the irradiation of U(VI) loaded semiconductors rapidly induced the negative shift of U 4f 7/2 peak to ∼ 379.8 eV, which is the characteristic of U(IV). Moreover, apparent photo-reduction occurred even if the samples were far from the center of the X-ray beam (>3971 μm). Based on these findings, methods for reducing potential error due to X-ray irradiation are suggested, including using the minimum scan time, measuring uranium-containing samples first or independent of other samples, and using X-ray of lower intensity. The results indicated that X-ray induced alteration to the chemical states must be considered when using X-ray techniques. [ABSTRACT FROM AUTHOR]

The behaviors of U(VI) in environmental media around radioactive waste disposal site are important for safety assessment of geological repositories. However, the estimation of environmental behaviors of U(VI) in natural media was insufficient. This work aimed to determine the adsorption of U(VI) on natural soil surrounding a candidate very low-level radioactive waste (VLLW) disposal site in southwest China. Results showed that the adsorption process of U(VI) on soils could be well supported by pseudo-second-order kinetic and Freundlich model. The adsorption of U(VI) was pH-dependent but temperature-independent. High ionic strength (NaCl) strongly affected the adsorption process at low pH (2.0–5.5). CO 3 2− remarkably inhibited the U(VI) adsorption, while the adsorption of U(VI) was promoted by PO 4 3− and SO 4 2−. Naturally occurred soil organic matters (SOMs) showed high affinity for U(VI), while the presence of additional humic acid (HA) strongly inhibited U(VI) adsorption. The occurrence of ferrous iron could result in the reduction of U(VI) at low pH values (pH < 4), leading to the promotion of immobilization of U(VI). These findings would provide some guidance for the safety assessments of the VLLW disposal as well as the remediation of contaminated soil. [Display omitted] • Interactions of U(VI) with natural soil were studied. • Soil organic matters strongly complexed with U(VI). • The reduction of U(VI) by Fe(II) was found in natural soil. • The strong complexation and reduction made the adsorption irreversible. [ABSTRACT FROM AUTHOR]

The biological and environmental toxicity of graphene and graphene derivatives have attracted great research interest due to their increasing applications. However, the cytotoxic mechanism is poorly understood. Here, we investigated the cytotoxic effect of graphene oxide nanoribbons (GORs) on Escherichia coli (E. coli) in an in vitro method. The fabricated GORs formed long ribbons, 200 nm wide. Based on the results of the MTT assay and plate-culture experiments, GORs significantly inhibited the growth and reproduction of E. coli in a concentration-dependent manner. We found that GORs stimulated E. coli to secrete reactive oxygen species, which then oxidized and damaged the bacterial cell membrane. Moreover, interaction between GORs and E. coli cytomembrane resulted in polysaccharide adsorption by GORs and the release of lactic dehydrogenase. Furthermore, GORs effectively depleted the metal ions as nutrients in the culture medium by adsorption. Notably, mechanical cutting by GORs was not obvious, which is quite different from the case of graphene oxide sheets to E. coli. [ABSTRACT FROM AUTHOR]

In this study, the cytotoxicity of graphene oxide (GO) nanosheets with different morphologies regulated with Pb2+ was estimated using A549 cells and an in vitro method. The results showed that after GO interacted with Pb2+, GO could transform to graphite-like, tube-like, and ball-like structures. The cell viability significantly decreased when A549 cells only exposed to GO (called GO group); whilst more cells survived after exposure to GO regulated by Pb2+ (called GO + Pb group). The levels of reactive oxygen species obviously increased in all the groups of Pb, GO, and GO + Pb relative to the control group, which suggested all the exposure of Pb2+, GO, and the mixture of GO and Pb2+ could significantly generate the oxidative stress-lipid peroxidization. GO showed the highest nutrient depletion-induced indirect cytotoxicity. In the GO + Pb group, the cell numbers got approximate 10% increase with respect to the GO group. Moreover, GO had high phospholipid extraction, whilst no phospholipid extraction was observed in the GO + Pb group. After aggregation and/or re-assembly, the membrane puncturing, phospholipid extraction, oxidative stress, nutrient depletion, and sheet adhesion of GO were inhibited to various extent, contributing to the reduced cytotoxicity of GO as well as Pb2+. • GO morphology was regulated with Pb2+. • GO could form graphite-like, tube-like, and ball-like structures. • GO has high cytotoxicity. • The cytotoxicity significantly reduced after GO regulated with Pb2+. [ABSTRACT FROM AUTHOR]

The sorption of Ni(II) on a calcareous aridisol (CA) soil, one of the major soil types in northwestern China, was investigated using batch and extended X-ray absorption fine structure (EXAFS) approaches in a 0.01 mol/L NaClO4 solution at different pH values (6.0-10.0), temperatures (25-60 °C) and contact times (2-15 days). Under alkaline conditions, EXAFS analysis showed that the interatomic distances between Ni and O atoms (RNi-O) were approximately 2.04 Å with a typical coordination number (CN) of ~6.0 O atoms in the contact time range from 2 to 15 days. The RNi-Ni (~3.07 Å) suggested that the structure of the Ni(II) adsorbed on the CA soil was basically the same as that of Ni(OH)2(s), while the Ni-Al shell (RNi-Al ~3.16 Å) gradually formed and grew with the increasing contact time. Under weakly acidic conditions, the sorption mechanism of Ni(II) on the CA soil possibly included at least two processes: (i) a fast accumulation dominated by ion exchange and surface complexation and (ii) the formation of a Ni-Al LDH phase over the long term. A high temperature is beneficial to the fixation of Ni(II) on the CA soil and the formation of a Ni-Al LDH. [ABSTRACT FROM AUTHOR]

Abstract In this study, the incorporation of U(VI) into CaCO 3 under different aging times and U(VI) concentrations was studied by combining batch experiments, X-ray diffraction (XRD), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), and extended X-ray absorption fine structure (EXAFS) approaches. Batch sorption experiments showed that the sorption of U(VI) on calcite was strong pH-dependence, and high pH was beneficial for U(VI) sorption possibly due to the electrostatic attraction between positively charged calcite and negatively charged uranyl tri-carbonate species. XRD patterns showed that the [104] facet of calcite shifted toward low angle at pH ∼10.0, which indicated that the uranyl tri-carbonate species of U(VI) possibly diffused into calcite lattice by replacing Ca atoms, and then induced the expansion of calcite crystal cell. The incorporation of U(VI) into CaCO 3 showed that the uptake of U(VI) gradually decreased within the first 200 h, and then significantly increased with the increasing aging time. U(VI) incorporation into CaCO 3 might experience vaterite, transition from vaterite to calcite, and calcite stages, which were confirmed by XRD, ATR-FTIR, and X-ray absorption near-edge structure (XANES) spectroscopy. As the U(VI) concentration increased, the transition time from vaterite to calcite correspondingly increased, indicating that U(VI) incorporation into CaCO 3 can stabilize vaterite phase. EXAFS analyses suggested that the local structure of uranyl moiety was changing during the incorporation process, and the species of U(VI) incorporation into vaterite was similar to uranyl carbonates, however indeed different from the species of uranyl tri-carbonate presented in calcite. Graphical abstract Image 1 Highlights • U(VI) sorption on calcite was studied using batch and spectroscopies. • The incorporation of U(VI) into CaCO 3 were explored under different aging times and U(VI) concentrations. • XANES, EXAFS and ATR-FTIR were used to explore the incorporation mechanism of U(VI) into CaCO 3. • The incorporation of U(VI) into CaCO 3 experienced three stages. • The species of U(VI) in vaterite is UO 2 CO 3 differing from the uranyl tri-carbonate in calcite. [ABSTRACT FROM AUTHOR]

In this study, the sorption of U(VI) on the farming soil (FS) and natural soil (NS) collected from northwest China was studied using batch and spectroscopic approaches. The sorption of U(VI) on NS, FS, decarbonated NS (DNS) and decarbonated FS (DFS) quickly increased with the pH increased. After removing carbonates, U(VI) sorption on DFS and DNS became slightly lower. The exchangeable fraction was the highest in NS, FS, DNS, and DFS. However, it was noted that the carbonate fraction took up 13–17% in FS and NS, suggesting that carbonate has an essential impact on the species distribution. [ABSTRACT FROM AUTHOR]

• The preparation and characterization of biochar were introduced. • The photocatalytic activity of biochar was summarized. • The photocatalytic process and mechanism of biochar were discussed in detail. • The effects of environmental factors on the photocatalytic reaction were summarized. Biochar has attracted significant attention due to its excellent environmental benefits and extensive applications. Recently, a consensus has been accepted that biochar can act as a photocatalyst and trigger effective photocatalytic reactions in the environment, which is important to energy conversion and the cycle of elements. However, its photocatalytic processes and the corresponding environmental impacts need to receive more and due attention. In this review, we provide a comprehensive summary of the underlying correlations among the pyrolytic evolution of biomass, the structure characteristic of biochar, and the resultant photocatalytic performance. Moreover, the photocatalytic processes and the influence of environmental factors were elaborately investigated on biochar. Finally, future tendencies and challenges in the photocatalysis of biochar have been prospected in the environmental field. This review has offered innovative insights into the photocatalytic essential of biochar and highly enhanced the understanding of its environmental impact. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Sorption of U(VI) onto TiO 2 as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO 2 was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO 2 below pH 4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO 2 was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO 2 was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO 2 particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Clarifying the reaction process and specific mechanism between variable-valence elements and oxidized carbon nanoparticles is essential to evaluate the environmental impact of carbon nanomaterials. In this study, the photocatalytic reduction of Cr(VI) on oxidized carbon nanotubes (OCNTs), oxidized graphene ribbons (OGRs), and graphene oxide sheets (GOs) was explored by batch experiments and spectroscopic analyses. The reaction efficiencies strongly depended on the number of oxygenated groups in the oxidized carbon nanoparticles. The abundant oxygenated groups enabled the GOs to exhibit the highest photocatalytic activity, followed by the OGRs and OCNTs. As a result, the photoreduction efficiency of Cr(VI) reached 96% for GOs, whereas those of OGRs and OCNTs were only 40% and 13%, respectively. In addition, different types of oxygenated groups exhibited various activities based on molecular model tests, following the sequence carboxylic > hydroxyl > carbonyl > ether > aldehyde > edge. Based on the underlying relationship between the oxygenated groups, topological structures, and mechanical strain in the carbon nanoparticles, we speculate that mechanical strain plays a critical role in the formation of oxygenated groups, thereby regulating their photocatalytic activities. The findings in this work provide novel insights into the roles of oxygenated groups and the mechanical strain of carbon nanoparticles in their environmental behavior. [Display omitted] • Carbon nanoparticles with abundant oxygenated groups showed the superior photoreduction efficiency of Cr(VI). • The characteristic oxygenated groups represented distinct photoactivities. • The underlying relationship between oxygenated groups and mechanical strains regulated photocatalytic behavior of carbon nanoparticles. [ABSTRACT FROM AUTHOR]

The interaction behaviors of heavy metals and micaceous minerals are extremely important to understand the environmental behaviors of heavy metals. In this work, the interaction behaviors of Cr(VI) and biotite in the presence and absence of HA were studied combining batch and spectroscopic approaches. Batch experiments showed that biotite had the ability to remove Cr(VI) from the water and the removal markedly increased with decreasing pH. However, sorption of total Cr onto biotite increased with increasing pH (2.0–4.0), whilst quickly decreased above pH ∼ 4.0. It was worth noting that redox process of Cr(VI) to Cr(III), caused by structural Fe(II) on biotite, was another important factor for the high removal of Cr(VI) in a pH range of 2.0–4.0. Ionic strength also influenced Cr(VI) removal that Cr(VI) removal became higher with increasing ion strength. The presence of HA did not show obvious macroscopic effect on Cr(VI) removal, however, HA could cover biotite surface, and promote the sorption of total Cr onto biotite and attenuate the reduction effect caused by Fe(II) on biotite. Spectroscopic approaches, like FT-IR, XRD and XPS further confirmed the existence of Cr(III) on biotite interacting with Cr(VI) and the reduction of Cr(VI) to Cr(III) was drove by the Fe(II) dissolving from biotite to Fe(III). Further, sorption effect and reduction effect competitively contributed to the Cr(VI) removal by biotite, and reduction effect played a more important role at lower pH. [Display omitted] • Biotite removed Cr(VI) from 0% to 100% with pH decreasing from 7.0 to 2.0. • Sorption of total Cr on biotite acted more around pH 4.0. • Cr(VI) reduction caused by structure Fe(II) in biotite increased with the pH decreasing from 4.0 to 2.0. • The presence of HA accelerated Cr(VI) adsorption and attenuated reduction effect. [ABSTRACT FROM AUTHOR]

The regulation effect of Aspergillus niger to the sorption behavior of U(VI) on kaolinite and illite was studied through investigating the enrichment of U(VI) on kaolinite- Aspergillus niger and illite- Aspergillus niger composites. Kaolinite- or illite- A. niger composites were prepared through co-culturation method. Results showed that U(VI) sorption on kaolinite and illite in different pH ranges could be attributed to ion exchange, outer-sphere complexes (OSCs), and inner-sphere complexes (ISCs), while only the ISCs on the bio-composites. Moreover, micro-spectroscopy tests revealed that U(VI) coordinate with phosphate, amide, and carboxyl groups on illite- and kaolinite- A. niger composites. X-ray photoelectron spectroscopy (XPS) further found that U(VI) was partly reduced to non-crystalline U(IV) by A. niger in the bio-composites, occurring as phosphate coordination polymers or biomass-associated monomers. The findings herein provide further insight into the immobilization and migration of uranium in environments. [Display omitted] • Co-culture of A. niger did not change the structures of kaolinite and illite. • U(VI) sorption on kaolinite and illite depended on pH and/or ionic strength. • A. niger changed the sorption mechanism of U(VI) on kaolinite and illite. • U(VI) complexed with various functional groups on the bio-composites. • U(VI) was partly reduced by A. niger to noncrystalline U(IV). [ABSTRACT FROM AUTHOR]

The regulation effect of Aspergillus niger to the sorption behavior of U(VI) on kaolinite and illite was studied through investigating the enrichment of U(VI) on kaolinite- Aspergillus niger and illite- Aspergillus niger composites. Kaolinite- or illite- A. niger composites were prepared through co-culturation method. Results showed that U(VI) sorption on kaolinite and illite in different pH ranges could be attributed to ion exchange, outer-sphere complexes (OSCs), and inner-sphere complexes (ISCs), while only the ISCs on the bio-composites. Moreover, micro-spectroscopy tests revealed that U(VI) coordinate with phosphate, amide, and carboxyl groups on illite- and kaolinite- A. niger composites. X-ray photoelectron spectroscopy (XPS) further found that U(VI) was partly reduced to non-crystalline U(IV) by A. niger in the bio-composites, occurring as phosphate coordination polymers or biomass-associated monomers. The findings herein provide further insight into the immobilization and migration of uranium in environments. [Display omitted] • Co-culture of A. niger did not change the structures of kaolinite and illite. • U(VI) sorption on kaolinite and illite depended on pH and/or ionic strength. • A. niger changed the sorption mechanism of U(VI) on kaolinite and illite. • U(VI) complexed with various functional groups on the bio-composites. • U(VI) was partly reduced by A. niger to noncrystalline U(IV). [ABSTRACT FROM AUTHOR]

• Pb(II) sorption on micas strongly depended on pH or/and ionic strength. • Pb2+ could enter the interlayer of biotite and phlogopite causing expanded interlayer. • Co-culture of micas and T. viride resulted in the weathering of micas. • Sorption capacity of Pb(II) on micas was greatly improved in the presence of T. viride. • T. viride caused biomineralization of Pb(II) on micas forming lead phosphates. In this study, batch and spectroscopic approaches were used to explore the sorption of Pb(II) on micas (i.e., muscovite, biotite and phlogopite) in the presence of Trichoderma viride (T. viride). Batch sorption showed that ion exchange, outer-sphere complexes (OSCs) and inner-sphere complexes (ISCs) contributed to Pb(II) sorption on biotite and phlogopite in the pH range of 2.0–7.4, whereas the ISCs were predominant for Pb(II) sorption on muscovite. X-ray diffraction and Fourier transform infrared (FT-IR) analyses have confirmed the changes of structure and surface properties of micas after co-culturing with T. viride , which could improve the sorption capacity of micas to Pb(II). Scanning electron microscopy revealed the bio-mineralization of Pb(II) on T. viride and mica– T. viride composites forming lead phosphates. Furthermore, FT-IR analysis showed that the groups of Si−OH, Al−OH from micas, and carboxyl, phosphate and amino groups from T. viride were synergistically contributing to Pb(II) sorption on mica– T. viride composite. X-ray photoelectron spectroscopy further confirmed that both OSCs and ISCs formed for Pb(II) sorption on micas; however, in the case of mica– T. viride composites, the synergistic effects of T. viride and micas were contributing to Pb(II) sorption through forming the ISCs and biomineralization. [ABSTRACT FROM AUTHOR]

• Recent progress of heterogeneous U(VI) photoreduction was reviewed for the first time. • The influence of environmental factors on the photocatalytic reduction of U(VI) was discussed. • Photoconversion mechanisms of U(VI) were discussed in detail. • Future perspectives of the photocatalytic U(VI) reduction were presented. The utilization of light-driven heterogeneous photocatalytic technology is extremely appealing for the uranium(VI) reduction since it is promising in seawater uranium extraction and uranium wastes treatment. U(VI) recovery through heterogeneous photocatalysis is more efficient, economic, non-pollutant, and of high selectivity compared to other methods. However, the systematic summarization on U(VI) photocatalytic reduction from water system is indeed scarce, especially, there are several discrepant hypotheses on the photocatalytic process and mechanisms of the reduction of U(VI). Therefore, this review would provide an overview and recent progress in the photocatalytic U(VI) reduction for the first time. The background of the photocatalytic U(VI) reduction is firstly introduced, followed by the discussion of the photocatalytic reduction mechanisms of U(VI). Thereafter, the photocatalysts widely used in the photocatalytic reduction of U(VI) are summarized. Subsequently, the influence of environmental factors such as organic matters, pH, coexisting ions, and dissolved oxygen on the photocatalytic U(VI) reduction is described. Finally, the challenges and the future perspectives of the photocatalytic reduction of U(VI) are addressed. [ABSTRACT FROM AUTHOR]