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Electrochemical uranium extraction from nuclear wastewater represents an emerging strategy for recycling uranium resources. However, in nuclear fuel production which generates the majority of uranium-containing nuclear wastewater, fluoride ion (F−) co-exists with uranyl (UO22+), resulting in the complex species of UO2Fx and thus decreasing extraction efficiency. Herein, we construct Tiδ+-PO43− ion pair extraction sites in Ti(OH)PO4 for efficient electrochemical uranium extraction in wastewater from nuclear fuel production. These sites selectively bind with UO2Fx through the combined Ti-F and multiple O-U-O bonds. In the uranium extraction, the uranium species undergo a crystalline transition from U3O7 to K3UO2F5. In real nuclear wastewater, the uranium is electrochemically extracted with a high efficiency of 99.6% and finally purified as uranium oxide powder, corresponding to an extraction capacity of 6829 mg g−1 without saturation. This work paves an efficient way for electrochemical uranium recycling in real wastewater of nuclear production. Electrochemical uranium extraction from real nuclear wastewater is appealing but challenging. Herein, Lin et al develop a strategy of ion pair site for enhanced binding of dominant uranium fluoride species in real wastewater, achieving efficient recycling of uranium as powder product. [ABSTRACT FROM AUTHOR]

With the extensive development of nuclear energy, soil uranium contamination has become an increasingly prominent problem. The development of evaluation systems for various uranium contamination levels and soil microhabitats is critical. In this study, the effects of uranium contamination on the carbon source metabolic capacity and microbial community structure of soil microbial communities were investigated using Biolog microplate technology and high-throughput sequencing, and the responses of soil biochemical properties to uranium were also analyzed. Then, ten key biological indicators as reliable input variables, including arylsulfatase, biomass nitrogen, metabolic entropy, microbial entropy, Simpson, Shannon, McIntosh, Nocardioides, Lysobacter, and Mycoleptodisus, were screened by random forest (RF), Boruta, and grey relational analysis (GRA). The optimal uranium-contaminated soil microbiological evaluation model was obtained by comparing the performance of three evaluation methods: partial least squares regression (PLS), support vector regression (SVR), and improved particle algorithm (IPSO-SVR). Consequently, partial least squares regression (PLS) has a higher R2 (0.932) and a lower RMSE value (0.214) compared to the other. This research provides a new evaluation method to describe the relationship between soil ecological effects and biological indicators under nuclear contamination. [ABSTRACT FROM AUTHOR]

In this study, the FH-MoS2-O heterojunction was prepared by a synergistic strategy of oxygen injection and Schottky junction construction, thereby enhancing electron transfer in the material and generating more photoelectrons. This facilitates the continuous reduction of uranium and the photocatalytic degradation of organic matter in wastewater. In simulated radioactive waste liquid with a concentration of 8 mg/L, the FH-MoS2-O heterojunction achieves an impressive U(VI) removal rate of 91.9%. When the initial concentration of U(VI) is 100 mg/L, the removal capacity reaches 251.76 mg/g. Furthermore, the presence of excess interfering ions and the recycling of the FH-MoS2-O heterojunction have negligible effects on the U(VI) removal rate. Mechanistic studies reveal that oxygen injection not only reduces the band gap but also enhances U(VI) adsorption on the FH-MoS2-O heterojunction. Additionally, it lowers the reduction potential of U(VI) and increases the photocurrent, significantly improving U(VI) reduction efficiency. [ABSTRACT FROM AUTHOR]

Biochar always suffers from low porosity and/or poor surface functionality, which limit its performances. Among various surface engineering strategies, air oxidation favors both pore development and surface oxygenation for biochar. However, there is still a lack of systematic knowledge and critical perspective on air oxidation in surface engineering of biochar-based materials for various applications. Herein, this review analyzed the mechanisms of air oxidation, summarized the routes of air oxidation in surface engineering of biochar-based materials, investigated the impacts of controlling factors (including operation parameters and intrinsic biochar structure) on pore development and surface oxygenation during air oxidation, and discussed the performances of the resultant materials in pollution control, biomass catalytic conversion and energy storage. This review suggested that air oxidation could be conducted in oxidative torrefaction/pyrolysis, and applied as post-modification or pretreatment processes. Interestingly, air oxidation is efficient in enriching the heteroatoms in the heteroatom-doped biochar, and promoting the doping of metal species on biochar by enriching the anchor sites. This review also highlighted the future challenges concerning air oxidation in the surface engineering of biochar-based materials. Finally, this review was intended to attract broad attention and inspire new discoveries for promoting the application of air oxidation in surface engineering of biochar-based materials for various advanced applications. Highlights: • Air oxidation favors pore development and/or surface oxygenation for biochar. • Air oxidation can be conducted in oxidative torrefaction/pyrolysis, and applied as post-modification or pretreatment processes. • Mechanisms and controlling factors for air oxidation were analyzed, and future challenges were highlighted. [ABSTRACT FROM AUTHOR]

Microbial fermentation pretreatment is an effective strategy to solve the problem of low uranium adsorption capacity of traditional biochar materials by introducing some porous structures and special functional groups in the fermentation process. Here, five different microorganisms (Bacillus licheniformis, Aspergillus oryzae, Lactobacillus acidophilus, Bacillus subtilis, and Saccharomyces cerevisiae) were selected to pretreated cotton stalk biochar to find the most suitable microorganism to increase surface area and effective functional groups. Cotton stalk biochar fermented by Aspergillus oryzae has a highest specific surface area and more functional groups than other groups. U(VI) adsorption efficacy of five fermentation biochars and blank control was tested for different contact times and initial concentrations of U(VI). Cotton stalk biochar fermented by Aspergillus oryzae had the best uranium adsorption performance with an adsorption capacity of 100.31 mg/g. Mechanism analysis showed that the adsorption of U(VI) on cotton stalk biochar fermented by Aspergillus oryzae was mainly attributed to the ion exchange with Ca2+ and the complexation with phosphate groups. Based on the above analysis, cotton stalk biochar fermented by Aspergillus oryzae possessed the potential to be applied for removing U(VI) from wastewater. [ABSTRACT FROM AUTHOR]

Uranium extraction from seawater is urgent but challenging part of nuclear energy development and environmental protection. Herein, we develop amidoxime-functionalized konjac glucomannan (AO-KGM) sponges as the efficient adsorbents, through chemical cross-linking of amidoxime groups in the natural biomass. In this paper, for the C 1 s signal of complex polysaccharide-modified materials, we adopt a new XPS calculation method to obtain the carbon peak position after grafting, proving the occurrence of the grafting reaction of the material. Correspondingly, AO-KGM sponges show a relatively stable uranium extraction capability in a complex environment containing uranium. Mechanism studies indicate that the adsorption of uranium by AO-KGM sponges is mainly a chemical process, which can be proved by X-ray adsorption spectroscopy analysis and adsorption kinetic fitting. Besides, electrostatic potential calculations also prove that amidoximes functional groups on the AO-KGM sponges can increase selectivity to uranium in the multi-metal ions system. Benefiting from the low cost of KGM sponges, AO-KGM sponges display broad application prospects in economical extraction of uranium from seawater. This work provides a meaningful paradigm for the rational design of advanced biomass-based adsorbents with surface functional modification for uranium extraction from seawater. [ABSTRACT FROM AUTHOR]

Photoreduction of hexavalent uranium (U(VI)) by semiconductor provides a novel and effective avenue for uranium extraction. Unfortunately, the traditional metal oxide and sulfide semiconductors suffer from the lack of confinement sites to U(VI), which resulted in the long period (∼ 1 h) to achieve a high U(VI) extraction efficiency of > 90%. Herein, we successfully constructed WS2 nanosheets and created in-situ oxidized domains on the surfaces (O-WS2) to promote the uranium extraction and the corresponding removal kinetics. In this system, the O7.7-WS2 nanosheets exhibited a considerable U(VI) extraction efficiency of > 90% within 20 min in 8 mg·L−1 U(VI)-containing solution, which represented the highly efficient U(VI) removal performance. In 200 mg·L−1 U(VI)-containing solution, the O7.7-WS2 nanosheets exhibited an extraction capacity of 652.4 mg·g−1. The mechanism study revealed that the oxidized surface tended to trap hydrogen atom and in-situ form hydroxyl groups in defect sites. Evidenced by a series of experiment, such as kinetic isotope effect, 1H nuclear magnetic resonance (NMR) spectra, and X-ray absorption near-edge structure (XANES) spectra, the in-situ formed hydroxyl groups participated in the uranium reduction, which dramatically enhanced uranium extraction kinetics and efficiency. [ABSTRACT FROM AUTHOR]

Photocatalytic reduction of U(VI) represents a novel and effective manner for the removal of U(VI) pollutant from radioactive wastewater. Herein, we successfully incorporated hydrogen into VO2 nanosheets, which strengthened the interaction between VO2 and U(VI), thereby achieving a highly active and stable photocatalyst for U(VI) reduction. With the increase of H content in hydric VO2 (HX-VO2) nanosheets, the bandgap shrank from 2.29 to 1.66 eV, whereas the position of conduction bands remained more negative than the reduction potential of U(VI)/U(IV) (0.41 V vs. NHE). When irradiated by simulated sunlight, the U(VI) removal efficiency over H0.613-VO2 nanosheets reached up to 95.4% within 90 min, which largely outperformed 28.3% of pristine VO2 nanosheets. The mechanistic study demonstrated that the hydroxylated surface gave rise to the balanced O confinement sites in VO2 (011), leading to the stabilized adsorption configuration and increased binding strength of UO22+ on HX−-VO2 nanosheets. [ABSTRACT FROM AUTHOR]

Photocatalytic aerobic oxidation by using oxygen molecules (O2) as green and low-cost oxidants is of great attraction, where the introduction of irradiation has been proved as an efficient strategy to lower reaction temperature as well as promote catalytic performance. Moreover, the oxygen vacancies (OVs) of catalyst are highly active sites to adsorb and activate O2 during photocatalytic aerobic oxidation. However, OVs are easily blocked by oxygen atoms from active oxygen species during the catalytic process, leading to the deactivation of catalysis. Herein, a promising catalyst toward photocatalytic aerobic oxidation was successfully developed by recovering the OVs through doping Au atoms into Ti3C2Tx MXene (Au/Ti3C2Tx). Impressively, Au/Ti3C2Tx exhibited remarkable activity under full-spectrum irradiation towards photooxidation of methyl phenyl sulfide (MPS) and methylene blue (MB), attaining a conversion of >90% at room temperature. Moreover, Au/Ti3C2Tx also manifested remarkable stability by maintaining >95% initial activity after 10 successive reaction rounds. Further mechanistic studies indicated that the OVs of Au/Ti3C2Tx served as the active centers to efficiently adsorb and activate O2. More importantly, the doped Au atoms of Au/Ti3C2Tx were conducive to the recovery of OVs during photocatalytic process from the results of theoretical and experimental aspects. The recovered OVs of Au/Ti3C2Tx continuously and efficiently activated O2, directly contributing to the remarkable catalytic activity and stability. [ABSTRACT FROM AUTHOR]

Highlights: A surface oxygen-injection strategy is proposed to synergistically modulate the electronic structure of the SnS2 nanosheets, thereby regulating the oxophilicity of the catalyst surface. The surface oxygen doping facilitates the CO2 activation and enhances the affinity for HCOO* species. The oxygen-injection SnS2 nanosheets exhibit a remarkable Faradaic efficiency of 91.6% for carbonaceous products with a current density of 24.1 mA cm−2 at -0.9 V vs RHE.Surface chemistry modification represents a promising strategy to tailor the adsorption and activation of reaction intermediates for enhancing activity. Herein, we designed a surface oxygen-injection strategy to tune the electronic structure of SnS2 nanosheets, which showed effectively enhanced electrocatalytic activity and selectivity of CO2 reduction to formate and syngas (CO and H2). The oxygen-injection SnS2 nanosheets exhibit a remarkable Faradaic efficiency of 91.6% for carbonaceous products with a current density of 24.1 mA cm−2 at −0.9 V vs RHE, including 83.2% for formate production and 16.5% for syngas with the CO/H2 ratio of 1:1. By operando X-ray absorption spectroscopy, we unravel the in situ surface oxygen doping into the matrix during reaction, thereby optimizing the Sn local electronic states. Operando synchrotron radiation infrared spectroscopy along with theoretical calculations further reveals that the surface oxygen doping facilitated the CO2 activation and enhanced the affinity for HCOO* species. This result demonstrates the potential strategy of surface oxygen injection for the rational design of advanced catalysts for CO2 electroreduction. [ABSTRACT FROM AUTHOR]

Mesoporous MnO2/SBA-15 was prepared by a facile route using KMnO4 and MnCl2 as Mn source and used for removal of Cs+. The effects of MnO2 content, initial Cs+ concentration, contact time and pH on the Cs+ adsorption behavior were investigated. It was found that Cs+ adsorption capacity of SBA-15 can be significantly improved by MnO2 loading. The adsorption capacity increased with increasing MnO2 content. Furthermore, the adsorption data can be well fitted by the Langmuir model, and the calculated maximum adsorption capacity of 80%MnO2/SBA-15 is 104.8 mg/g. The Cs+ adsorption process can be better described by the pseudo-second-order model. [ABSTRACT FROM AUTHOR]

Mesoporous ZrO2/SBA-15 materials were prepared for the first time by a one-step method using ZrO2 as zirconium source and their uranium (U(VI)) adsorption behavior were studied. The influence of ZrO2 content on the structure, morphology and hydrothermal stability of the obtained ZrO2/SBA-15 was investigated. It was found that the structural order of ZrO2/SBA-15 decreased with increasing ZrO2 content. The hydrothermal stability of SBA-15 was improved by loading of ZrO2. Furthermore, the effects of pH, initial U(VI) concentration, contact time, temperature and ZrO2 content on the U(VI) adsorption capacity were studied. The results demonstrated that the U(VI) adsorption capacity decreased with increasing ZrO2 content and temperature. The adsorption process was found to be well fitted to the Langmuir and pseudo-second-order model. The calculated maximum adsorption capacities were 326 and 294 mg·g−1 for 0.4ZrO2/SBA-15 and 0.8ZrO2/SBA-15 samples at 283 K, respectively. Furthermore, the analysis of thermodynamic parameters (ΔG, ΔH, and ΔS) revealed that the process of U(VI) adsorption onto ZrO2/SBA-15 was feasible, spontaneous and exothermic. [ABSTRACT FROM AUTHOR]

Uranium is important in the nuclear fuel cycle as both as an energy source and as radioactive waste. Herein, activated carbon (AC) prepared from waste cigarette filters by convenient carbonization and functionalization was chosen as the raw materials for radionuclides adsorption. Batch adsorption experiments showed that AC presented comparable UO22+ adsorption capacity (106 mg g−1) and very outstanding selectivity. The adsorption process accorded with Langmuir model and the pseudo-second-order kinetics model well. This work combines the waste cigarette filters with the radioactive nuclear treatment materials, which may provide a new strategy for the future treatment of waste cigarette butts. [ABSTRACT FROM AUTHOR]

Cotton carbon aerogel was prepared and used as a new water-insoluble adsorbent to remove strontium from aqueous solution. A comprehensive study on adsorption of strontium by cotton carbon aerogel was conducted regarding the effects of initial pH, temperature, initial strontium concentration, and contact time. The adsorbent was characterized by SEM. The results of regression analysis indicated that the adsorption process largely depends on the pH and temperature. The optimum pH range for adsorption process is 5-7. The maximum removal efficiency of strontium from aqueous solution was 60.16%. Moreover, cotton carbon aerogel adsorbent has good reusability before the fifth reuse. [ABSTRACT FROM AUTHOR]

The urease of carbonate-mineralization bacteria (bacillus) secretion is conducive to the formation of carbonate. At the presence of urea and Sr, carbonate-mineralization bacteria could lead to the rapid formation of strontium carbonate precipitation. The mineralization process and efficiency were observed by adding nano-montmorillonite (nano-MMT). The effect of bacillus and bacillus/nano-MMT on the mineralization efficiency of Sr was investigated by atomic spectrophotometer. The results showed that both the bacillus and nano-MMT played an important role in the nucleation, growth, and accumulation of strontium carbonate crystals. And this method can efficiently separate simulated radionuclide strontium from high-level radioactive waste. [ABSTRACT FROM AUTHOR]

A new sustainable filamentous fungi-based process is reported to synthesize mycelium/bayberry tannin (BT) hybrid materials. The hybrid materials are produced with fungi growing in solution, where the cell wall interacted with BT by hydrogen-bond from the phenolic hydroxyl and amino in protein. In the adsorption experiment, This hybrid biologic material show excellent performances for strontium ions adsorption and experimental data obey a pseudo second-order model of the chemical adsorption process. This study reported a new method for the producing of bio-based materials, which had the potential applications in waste water treatment. [ABSTRACT FROM AUTHOR]

The coatings of microorganism-induced calcium carbonate onto the stone surface carried out by using both of the immersion method and coating method were investigated. Various analysis and testing techniques such as scanning electron micrograph (SEM) and X-ray diffraction (XRD) were used to characterize the deposited mineral layer. The adhesive property, acid resistance, frost resistance, light and aging resistance, water adsorption and permeability were investigated in detail. The results showed that both immersion method and coating method could produce calcium carbonate granules with sizes ranging from 1 to 10 μm and form a layer of dense mineralization membrane which is about 50 to 100 μm thick. Immersion method was more efficient than coating method. The large cohesive force between calcium carbonate layer and stone materials could improve the acid rain resistance as well as excellent heat tolerance, frost resistance and light aging resistance. The coating process could not only help the stone materials maintain its original permeability with the aid of calcium carbonate layers but also improve the penetration resistance significantly. Therefore, this type of technology shows a great potential in the protection of stone relics. [ABSTRACT FROM AUTHOR]

As a promising hydrogen carrier, formic acid (HCOOH) is renewable, safe and nontoxic. Although noble-metal-based catalysts have exhibited excellent activity in HCOOH dehydrogenation, developing non-noble-metal heterogeneous catalysts with high efficiency remains a great challenge. Here, we modulate oxygen coverage on the surface of Ti3C2Tx MXenes to boost the catalytic activity toward HCOOH dehydrogenation. Impressively, Ti3C2Tx MXenes after treating with air at 250 °C (Ti3C2Tx-250) significantly increase the amount of surface oxygen atoms without the change of crystalline structure, exhibiting a mass activity of 365 mmol·g−1·h−1 with 100% of selectivity for H2 at 80 °C, which is 2.2 and 2.0 times that of commercial Pd/C and Pt/C, respectively. Further mechanistic studies demonstrate that HCOO* is the intermediate in HCOOH dehydrogenation over Ti3C2Tx MXenes with different coverages of surface oxygen atoms. Increasing the oxygen coverage on the surface of Ti3C2Tx MXenes not only promotes the conversion from HCOO* to CO2* by lowering the energy barrier, but also weakens the adsorption energy of CO2 and H2, thus accelerating the dehydrogenation of HCOOH. Developing non-noble-metal heterogeneous catalysts with high efficiency in HCOOH dehydrogenation is significant for the acquisition of hydrogen, but remains a great challenge. Here, the authors modulate oxygen coverage of Ti3C2Tx MXenes to boost the catalytic activity toward HCOOH dehydrogenation. [ABSTRACT FROM AUTHOR]

Mesoporous gold sponges were prepared using 4-dimethylaminopyridine (DMAP)-stabilized Au seeds. This is a general process, which involves a simple template-free method, room temperature reduction of HAuCl4·4H2O with hydroxylamine. The formation process of mesoporous gold sponges could be accounted for the electrostatic interaction (the small Au nanoparticles (~3 nm) and the positively charged DMAP-stabilized Au seeds) and Ostwald ripening process. The mesoporous gold sponges had appeared to undergo electrostatic adsorption initially, sequentially linear aggregation, welding and Ostwald ripening, then, they randomly cross link into self-supporting, three-dimensional networks with time. The mesoporous gold sponges exhibit higher surface area than the literature. In addition, application of the spongelike networks as an active material for surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol (4-ATP) molecules as a probe. [ABSTRACT FROM AUTHOR]