Electrocatalytic Removal of Low-Concentration Uranium Using TiO2 Nanotube Arrays/Ti Mesh Electrodes

Geospatial analysis of toxic metal contamination in groundwater and associated health risks in the lower Himalayan industrial region

Once known for its clean and natural environment, the lower Himalayan region is now no exception to human-induced disturbances. Rapid industrial growth in Baddi-Barotiwala (BB) industrial region has led to degradation of groundwater resources in the area. Groundwater samples were collected from 37 locations to study the groundwater chemistry, geospatial variation of 15 toxic metals in groundwater, source apportionment, metals of concern and associated health risks in the region. The results showed rock dominated hydrogeology with decreasing order of anion and cation abundance as HCO3- > Cl- > SO42- > NO3- > Br- > F- and Ca+ > Na+ > Mg2+ > K+ > Li+ respectively. Concentrations of Iron (BDL-3.6 mg/l), Nickel (BDL-0.023 mg/l), Barium (0.22-0.89 mg/l), Lead (0.0001-0.085 mg/l) and Zinc (0.006-21.4 mg/l) were found above the permissible limits at few locations. Principal component analysis (PCA) and coefficient of variance (CV) showed both geogenic and anthropogenic origin of metals in groundwater of the BB industrial region. A consistent concentration of Uranium was detected at all the sampling locations with an average value of 0.0039 mg/l and poor spatial variation indicating its natural presence. Overall, non-carcinogenic (N-CR) risk in the study area via oral pathway was high for adults and children (Hazard Index > 1) with geogenic Uranium as the major contributor (Hazard Quotient > 1) followed by Zinc, Lead and Cobalt. Carcinogenic (CR) risk in the region was high for adults having mean value above the threshold (1E-04) with Nickel and Chromium as the metals of major concern. Spatial variation of health risks was overlayed on village boundaries of the region to identify the potential industrial sources of the metals of major concern. The results highlight the need for immediate remediation of groundwater resources in order to achieve a harmonious coexistence between industrialization and human well-being.

Four-in-one multifunctional self-driven photoelectrocatalytic system for water purification: Organics degradation, U(VI) reduction, electricity generation and disinfection against bacteria

This study addresses the energy-intensive nature of conventional wastewater treatment processes and proposes a solution through the development of a green, low-energy, and multifunctional wastewater treatment technology. The research focuses on a multifunctional self-driven photoelectrocatalytic (PEC) system, exploring its four-in-one applications in eliminating organic pollutants, reducing U(VI), generating electrical energy, and disinfecting pathogenic microorganisms. A TiO2-decorated carbon felt (CF@TiO2) cathode is synthesized to enhance interfacial charge transfer, with TiO2 coating improving surface binding sites (edge TiO and adsorbed -OH) for UO22+ adsorption and reduction. The self-driven PEC system, illuminated solely with simulated sunlight, exhibits remarkable efficiency in removing nearly 100 % of uranium within 0.5 h and simultaneously degrading 99.9 % of sulfamethoxazole (SMX) within 1.5 h, all while generating a maximum power output density (Pmax) of approximately 1065 μW·cm-2. The system demonstrates significant anti-interference properties across a wide pH range and coexisting ions. Moreover, 49.4 % of the fixed uranium on the cathode is reduced into U(IV) species, limiting its migration. The self-driven PEC system also excels in detoxifying various toxic organic compounds, including tetracycline, chlortetracycline, and oxytetracycline, and exhibits exceptional sterilization ability by disinfecting nearly 100 % of Escherichia coli within 0.5 h. This work presents an energy-saving, sustainable, and easily recyclable wastewater purification system with four-in-one capabilities, relying solely on sunlight for operation.

Fabrication of Carboxylate-Functionalized 2D MOF Nanosheet with Caged Cavity for Efficient and Selective Extraction of Uranium from Aqueous Solution

The efficient removal of radioactive uranium from aqueous solution is of great significance for the safe and sustainable development of nuclear power. An ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately fabricated based on a calix[4]arene ligand. Incorporating the permanent cavity structures on MOF nanosheet can fully utilize its structural characteristics of largely exposed surface area and accessible adsorption sites in pollutant removal, achieving ultrafast adsorption kinetics, and the functionalized cavity structure would endow the MOF nanosheets with the ability to achieve preconcentration and extraction of uranium from aqueous solution, affording ultrahigh removal efficiency even in ultra-low concentrations. Thus, more than 97% uranium can be removed from the concentration range of 50-500 µg L-1 within 5 min. Moreover, the 2D nano-material exhibits ultra-high anti-interference ability, which can efficiently remove uranium from groundwater and seawater. The adsorption mechanism was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) analysis, and density functional theory (DFT) calculations, which revealed that the cavity structure plays an important role in uranium capture. This study not only realizes highly efficient uranium removal from aqueous solution but also opens the door to achieving ultrathin MOF nanosheets with cavity structures, which will greatly expand the applications of MOF nanosheets.

Flexible self-supporting Na3MnTi(PO4)3@C fibers for uranium extraction from seawater by electro sorption

As an eco-friendly technique with the superior adsorption performance, electroadsorption has shown great potential for application in uranium (U(VI)) recovery in recent years. However, the electrodes used in the electrosorption generally suffer the adsorbent to be loaded on the conductors, which greatly limited the adsorption performance of the electrodes for uranyl ions. In present study, a flexible self-supporting Na3MnTi(PO4)3@C fibers (NMTP@C fibers) electrode material was rationally designed and prepared by electrostatic spinning method and annealing technique, and its ability to capture U(VI) efficiently was preliminarily demonstrated by batch adsorption and electro sorption. The plentiful phosphate groups provide sufficient active sites for adsorption, while the axially continuous electron conduction and radially short-range ion transport give NMTP@C fibers fast charge/ion transport capability. The NMTP@C fiber can remove 99% of 5 ppm U(VI) in seawater by electro absorption within 1 h. After several cycles of adsorption under seawater conditions, the adsorbent can still maintain a stable adsorption capacity. The adsorption mechanism of NMTP@C nanofibers for U(VI) was investigated by XPS, FT-IR, Raman, SEM-EDS, and XRD, which was electrostatic interactions and surface complexation. These results suggest that NMTP@C fibers are promising high-capacity adsorbents for efficient and selective capture of U(VI) from seawater.

Unveiling the Critical Role of Surface Hydroxyl Groups for Electro-Assisted Uranium Extraction from Wastewater

The electro-driven extraction of uranium from fluorine-containing uranium wastewater is anticipated to address the challenge of separating fluoro-uranium complexes in conventional technologies. Herein, we developed hydroxy-rich cobalt-based oxides (CoOx) for electro-assisted uranium extraction from fluorine-containing wastewater. Relying on theoretical calculations and other spectral measurements, the hydroxy-rich CoOx nanosheets can enhance the affinity for uranium due to the existence of a substantial quantity of hydroxyl groups. Accordingly, the CoOx nanosheets exhibit outstanding U(VI) removal efficiency in the presence of fluorine ions. Through the utilization of X-ray absorption fine structure (XAFS), we confirm that hydroxy-rich CoOx nanosheets capture free uranyl ions to form a sturdy 2Oax-1U-3Oeq configuration, which can be achieved through electro-driven fluorine-uranium separation. Notably, for the first time, the whole reaction process of uranium species on the CoOx surface from the initial uranium single atom growth to uranium oxide nanosheets is monitored by aberration-corrected transmission electron microscopes (AC-TEM). This work provides a paradigm for the advancement of novel functional materials as electrocatalysts for uranium extraction, as well as a new approach for studying the evolution mechanism of uranium species.

Enhancing Uranium Removal with a Titanium-Incorporated Zirconium-Based Metal-Organic Framework

The urgent need to efficiently and rapidly decontaminate uranium contamination in aquatic environments underscores its significance for ecological preservation and environmental restoration. Herein, a series of titanium-doped zirconium-based metal-organic frameworks were meticulously synthesized through a stepwise process. The resultant hybrid bimetallic materials, denoted as NU-Zr-n%Ti, exhibited remarkable efficiency in eliminating uranium (U (VI)) from aqueous solution. Batch experiments were executed to comprehensively assess the adsorption capabilities of NU-Zr-n%Ti. Notably, the hybrid materials exhibited a substantial increase in adsorption capacity for U (VI) compared to the parent NU-1000 framework. Remarkably, the optimized NU-Zr-15%Ti displayed a noteworthy adsorption capacity (∼118 mg g-1) along with exceptionally rapid kinetics at pH 4.0, surpassing that of pristine NU-1000 by a factor of 10. This heightened selectivity for U (VI) persisted even when diverse ions exist. The dominant mechanisms driving this high adsorption capacity were identified as the robust electrostatic attraction between the negatively charged surface of NU-Zr-15%Ti and positively charged U (VI) species as well as surface complexation. Consequently, NU-Zr-15%Ti emerges as a promising contender for addressing uranium-laden wastewater treatment and disposal due to its favorable sequestration performance.

Electrochemical reduction of wastewater by non-noble metal cathodes: From terminal purification to upcycling recovery

A shift beyond conventional environmental remediation to a sustainable pollutant upgrading conversion is extremely desirable due to the rising demand for resources and widespread chemical contamination. Electrochemical reduction processes (ERPs) have drawn considerable attention in recent years in the fields of oxyanion reduction, metal recovery, detoxification and high-value conversion of halogenated organics and benzenes. ERPs also have the potential to address the inherent limitations of conventional chemical reduction technologies in terms of hydrogen and noble metal requirements. Fundamentally, mechanisms of ERPs can be categorized into three main pathways: direct electron transfer, atomic hydrogen mediation, and electrode redox pairs. Furthermore, this review consolidates state-of-the-art non-noble metal cathodes and their performance comparable to noble metals (e.g., Pd, Pt) in electrochemical reduction of inorganic/organic pollutants. To overview the research trends of ERPs, we innovatively sort out the relationship between the electrochemical reduction rate, the charge of the pollutant, and the number of electron transfers based on the statistical analysis. And we propose potential countermeasures of pulsed electrocatalysis and flow mode enhancement for the bottlenecks in electron injection and mass transfer for electronegative pollutant reduction. We conclude by discussing the gaps in the scientific and engineering level of ERPs, and envisage that ERPs can be a low-carbon pathway for industrial wastewater detoxification and valorization.

Strengthening Fe(II)/Fe(III) Dynamic Cycling by Surface Sulfation to Achieve Efficient Electrochemical Uranium Extraction at Ultralow Cell Voltage

Electrochemically mediated Fe(II)/Fe(III) redox-coupled uranium extraction can efficiently reduce the cell voltage of electrochemical uranium extraction (EUE). How to regulate the surface structure to enhance the uranium acyl ion adsorption capacity and strengthen the Fe(II)/Fe(III) redox cycle process is crucial for EUE. In this work, we developed surface sulfated nanoreduced iron (S-NRI) for EUE and exhibited improved properties for EUE at an ultralow cell voltage (-0.1 V). Compared with a nanoreduced iron (NRI) adsorbent, S-NRI displayed faster electrochemical extraction kinetics properties and higher extraction efficiency and capacity for uranium. In a more complex seawater electrolyte containing uranyl ion concentration ranging from 1 to 20 ppm, the removal efficiency could reach almost ∼100% after EUE for 24 h. At a higher 50 ppm uranium acyl ion concentration in a seawater electrolyte, S-NRI exhibited higher extraction capacity (755.03 mg/g), which is better than 528.53 mg/g of NRI at a cell voltage of -0.1 V. Outstanding EUE property could be attributed to the fact that sulfate species (M-SO42-) on the S-NRI surface not only enhanced selective adsorption of uranyl ions but also strengthened the Fe(II)/Fe(III) redox cycle, which accelerated electron transfer between Fe(II) and U(VI), promoted the regeneration of Fe(II) active sites, and finally enhanced the EUE property.

Electrocatalytic and green system coupling strategy for simultaneous recovery and purification of uranium from uranium-containing wastewater

The recycling of uranium in wastewater is not only beneficial to the protection of ecological safety but also has great significance for the sustainable development of nuclear energy. However, there is no satisfactory method to recover and reuse uranium efficiently up to now. Here, we have developed an efficient and economical strategy that can achieve uranium recovery and direct reuse in wastewater. The feasibility analysis verified that the strategy still had good separation and recovery ability in acidic, alkaline, and high-salinity environments. The purity of uranium recovered from the separated liquid phase after electrochemical purification was up to about 99.95%. Ultrasonication could greatly increase the efficiency of this strategy, and 99.00% of high-purity uranium could be recovered within 2 h. We further improved the overall recovery rate by recovering the residual solid-phase uranium, and the overall recovery of uranium was increased to 99.40%. Moreover, the concentration of impurity ions in the recovered solution met the World Health Organization guidelines. In summary, the development of this strategy is of great importance for the sustainable use of uranium resources and environmental protection.

Enhanced mechanism of calcium towards uranium incorporation and stability in magnetite during electromineralization

Doping uranium into a room-temperature stable Fe₃O₄ lattice structure effectively reduces its migration. However, the synergistic or competitive effects of coexisting ions in an aqueous solution directly affect the uranium mineralization efficiency and the structural stability of uranium-bearing Fe₃O₄. The effects of calcium, carbonate, and phosphate on uranium electromineralization were investigated via batch experiments and theoretical calculations. Calcium incorporated into the Fe₃O₄ lattice increased the level and stability of doped uranium in Fe₃O₄. Uranium and calcium occupied the octahedral and tetrahedral sites of Fe₃O₄, respectively; the formation energy was only -10.23 eV due to strong hybridization effects between Fe1s, U4f, O2p, and Ca3d orbitals. Compared to the uranium-doped Fe₃O₄, uranium leaching ratios decreased by 19.2 % and 48.9 % under strongly acidic and alkaline conditions after 120 days. However, high concentrations of phosphate inhibited Fe₃O₄ crystallization. These results should provide new avenues for the development of multi-metal co-doping technologies and mineralization optimization to treat uranium-containing complex wastewater.

Intrinsically morphological effect of perovskite BaTiO3 boosting piezocatalytic uranium extraction efficiency and mechanism investigation

Developing a convenient, efficient and eco-friendly approach for the recovery of U(VI) ion is a key measure to solve the environmental problems arising from the utilization of nuclear energy. Herein, the high efficiency of uranium extraction is realized by the piezo property of perovskite BaTiO₃, revealing the intrinsically morphological engineering effect on the piezocatalytic performance. Especially, BaTiO₃ nanowires (BTO NWs) exhibit not only an excellent piezocatalytic activity with U(VI) extraction rate of 96.8% in a UO₂(NO₃)₂ aqueous solution compared to 71.3% of BaTiO₃ nanoparticles (BTO NPs), but also a promising piezocatalyst for U extraction in a real U-mining wastewater with various pH ranges. Piezo response force microscopy and finite elemental simulation show that the piezo response of BTO NWs is much higher than BTO NPs. Additionally, some factors (pH, various ions, different powers) are explored on piezocatalytic efficiency for U(VI) extraction. The results from electron spin resonance and the charge/radical capture experiments confirm that the active species (e^-, •O^2-, •OH) stemmed from the piezo induction of BTO NWs and BTO NPs in the piezocatalytic U(VI) reduction process. The present work reveals the structure-performance correlation during piezocatalysis and highlights the crucial role of piezocatalysis in dealing with environmental problems.

The Role of Substrate Surface Geometry in the Photo-Electrochemical Behaviour of Supported TiO2 Nanotube Arrays: A Study Using Electrochemical Impedance Spectroscopy (EIS)

Highly ordered TiO₂ nanotube (NT) arrays grown on Ti mesh and Ti foil were successfully prepared by a controlled anodic oxidation process and tested for water photo-electrolysis. Electrochemical impedance spectroscopy (EIS), combined with other electrochemical techniques (cyclic voltammetry and chronoamperometry) in tests performed in the dark and under illumination conditions, was used to correlate the photoactivity to the specific charge transfer resistances associated with a 3D (mesh) or 2D (foil) geometry of the support. The peculiar structure of the nanotubes in the mesh (with better light absorption and faster electron transport along the nanotubes) strongly impacts the catalytic performances under illumination. H₂ production and current density in water photo-electrolysis were over three times higher with the TiO₂NTs/Ti mesh, compared to the foil in the same conditions. The results obtained by the EIS technique, used here for the first time to directly compare TiO₂ nanotubes on two different supports (Ti foil and Ti mesh), led to a better understanding of the electronic properties of TiO₂ nanotubes and the effect of a specific support on its photocatalytic properties.