Chelating Effect of Siderophore Desferrioxamine-B on Uranyl Biomineralization Mediated by Shewanella putrefaciens.

In contaminated water and soil, little is known about the role and mechanism of the biometabolic molecule siderophore desferrioxamine-B (DFO) in the biogeochemical cycle of uranium due to complicated coordination and reaction networks. Here, a joint experimental and quantum chemical investigation is carried out to probe the biomineralization of uranyl (UO22+, referred to as U(VI) hereafter) induced by Shewanella putrefaciens (abbreviated as S. putrefaciens) in the presence of DFO and Fe3+ ion. The results show that the production of mineralized solids {hydrogen-uranium mica [H2(UO2)2(PO4)2·8H2O]} via S. putrefaciens binding with UO22+ is inhibited by DFO, which can both chelate preferentially UO22+ to form a U(VI)-DFO complex in solution and seize it from U(VI)-biominerals upon solvation. However, with Fe3+ ion introduced, the strong specificity of DFO binding with Fe3+ causes re-emergence of biomineralization of UO22+ {bassetite [Fe(UO2)2(PO4)2·8(H2O)]} by S. putrefaciens, owing to competitive complexation between Fe3+ and UO22+ for DFO. As DFO possesses three hydroxamic functional groups, it forms hexadentate coordination with Fe3+ and UO22+ ions via these functional groups. The stability of the Fe3+-DFO complex is much higher than that of U(VI)-DFO, resulting in some DFO-released UO22+ to be remobilized by S. putrefaciens. Our finding not only adds to the understanding of the fate of toxic U(VI)-containing substances in the environment and biogeochemical cycles in the future but also suggests the promising potential of utilizing functionalized DFO ligands for uranium processing.

Efficient purification of low-level uranium-containing wastewater by polyamine/amidoxime synergistically reinforced fiber.

The removal and recovery of uranium [U(VI)] from organic containing wastewater has been a challenging in radioactive wastewater purification. Here, we designed a polyamine/amidoxime polyacrylonitrile fiber (PAN-AO-A) with high removal efficiency, excellent selectivity, excellent organic resistance and low cost by combining the anti-organic properties of amidoxime polyacrylonitrile fiber (PAN-AO-A) with the high adsorption capacity of polyamine polyacrylonitrile fiber, which is used to extract U(VI) from low-level uranium-containing wastewater with high ammonia nitrogen and organic content. PAN-AO-A adsorbent with high grafting rate (86.52%), high adsorption capacity (qe = 618.8 mg g-1), and strong resistance to organics and impurity interference is achieved. The adsorption rate of U(VI) in both real organic and laundry wastewater containing uranium is as high as 99.7%, and the partition coefficients (Kd) are 7.61 × 105 mL g-1 and 9.16 × 106 mL g-1, respectively. The saturated adsorption capacity of PAN-AO-A in the continuous system solution can reach up to 505.5 mg g-1, and the concentration of U(VI) in the effluent is as low as 1 µg L-1. XPS analysis and Density functional theory (DFT) studies the coordination form between U(VI) and PAN-AO-A, where the most stable structure is η2-AO(UO2)(CO3)2. The -NH-/-NH2 and -C(NH2)N-OH groups of PAN-AO-A exhibit a synergistic complex effect in the U(VI) adsorption process. PAN-AO-A is a material with profound influence and limitless potential that can be used for wastewater containing U(VI) and organic matter.

Uranium speciation and distribution on the surface of Shewanella putrefaciens in the presence of inorganic phosphate and zero-valent iron under anaerobic conditions.

Shewanella putrefaciens (S. putrefaciens) is one of the main microorganisms in soil bioreactors, which mainly immobilizes uranium through reduction and mineralization processes. However, the effects of elements such as phosphorus and ZVI, which may be present in the actual environment, on the mineralization and reduction processes are still not clearly understood and the environment is mostly in the absence of oxygen. In this study, we ensure that all experiments are performed in an anaerobic glove box, and we elucidate through a combination of macroscopic experimental findings and microscopic characterization that the presence of inorganic phosphates enhances the mineralization of uranyl ions on the surface of S. putrefaciens, while zero-valent iron (ZVI) facilitates the immobilization of uranium by promoting the reduction of uranium by S. putrefaciens. Interestingly, when inorganic phosphates and ZVI co-exist, both the mineralization and reduction of uranium on the bacterial surface are simultaneously enhanced. However, these two substances exhibit a certain degree of antagonism in terms of uranium immobilization by S. putrefaciens. Furthermore, it is found that the influence of pH on the mineralization and reduction of uranyl ions is far more significant than that of inorganic phosphates and ZVI. This study contributes to a better understanding of the environmental fate of uranium in real-world settings and provides valuable theoretical support for the bioremediation and risk assessment of uranium contamination.

Surface biomineralization of uranium onto Shewanella putrefaciens with or without extracellular polymeric substances.

The influence of extracellular polymeric substances (EPS) on the interaction between uranium [U(VI)] and Shewanella putrefaciens (S. putrefaciens), especially the U(VI) biomineralization process occurring on whole cells and cell components of S. putrefaciens was investigated in this study. The removal efficiency of U(VI) by S. putrefaciens was decreased by 22% after extraction of EPS. Proteins were identified as the main components of EPS by EEM analysis and were determined to play a major role in the biosorption of uranium. SEM-EDS results showed that U(VI) was distributed around the whole cell as 500-nanometer schistose structures, which consisted primarily of U and P. However, similar uranium lamellar crystal were wrapped only on the surface of EPS-free S. putrefaciens cells. FTIR and XPS analysis indicated that phosphorus- and nitrogen-containing groups played important roles in complexing U (VI). XRD and U LIII-edge EXAFS analyses demonstrated that the schistose structure consisted of hydrogen uranyl phosphate [H2(UO2)2(PO4)2•8H2O]. Our study provides new insight into the mechanisms of induced uranium crystallization by EPS and cell wall membranes of living bacterial cells under aerobic conditions.

Mutual effects of Shewanella putrefaciens-montmorillonite and their impact on uranium immobilization.

This study investigated the immobilization behavior of U(VI) by the mixture of Shewanella putrefaciens (S. putrefaciens) and montmorillonite with batch experiment. The relevant mechanisms were discussed based on the experimental results and characterizations. It was found that the immobilization of U(VI) by S. putrefaciens-montmorillonite was inhibited at pH < 7.0 and enhanced at pH > 7.0. The inhibition effect was due to the aggregation and coverage between S. putrefaciens and montmorillonite, whereas the association of microbial dissolvable organic matters (DOM) on montmorillonite could promote immobilization of U(VI). The evidences of X-photoelectron spectroscopy (XPS) and density functional theory (DFT) simulation confirmed that the carboxyl-, hydroxyl-, nitrogen-based DOM do have the ability to interacted with U(VI). This work highlights a comprehensive and overlook perspective to understand the immobilization behavior of U(VI) in environmental organo-minerals.

Nano zero valent iron encapsulated in graphene oxide for reducing uranium.

Nano zero-valent iron (Fe0) has been widely used to remove Uranium (U(VI)). In order to enhance the performance of Fe0 toward U(VI) removal, the Fe0 was assembled into graphene oxide (GO) sheets via 3-aminopropyl triethoxysilane (APTES) as Fe0/APTES-GO composites. The Fe0/APTES-GO composites were triumphantly prepared, characterized and analyzed by means of Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) together with Energy Dispersive Spectrometer (EDS), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). SEM and TEM-EDS results manifested that Fe0 particles were encapsulated into rolled-up GO, which greatly improved the stability of Fe0. Batch experiment showed that only a small amount of Fe2+ was leached in the first two leaching cycles of Fe0/APTES-GO composites. The removal capacity of Fe0/APTES-GO composites was up to 1357.99 mg/g at pH = 4.1 and T = 50 °C, which was mainly attributed to the reducing activity of Fe0 and an abundance of functional groups (i.e., -COOH, C-OH and -OH) on the Fe0/APTES-GO composites. The electrostatic potential (ESP) from the calculation also supported that U(VI) tended to be reduced at the back side of the GO-Fe0 cluster.

Adsorption and desorption of U(VI) on functionalized graphene oxides: a combined experimental and theoretical study.

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.

Simultaneous adsorption and reduction of U(VI) on reduced graphene oxide-supported nanoscale zerovalent iron.

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.