Interaction of uranium(VI) with titanate nanotubes by macroscopic and spectroscopic investigation

Architecture and active motif engineering of N-CoS2@C yolk-shell nanoreactor for boosted tetracycline removal via peroxymonosulfate activation: Performance, mechanism and destruction pathways

Rational construction of yolk-shell architecture with regulated binding configuration is crucially important but challengeable for antibiotic degradation via peroxymonosulfate (PMS) activation. In this study, we report the utilization of yolk-shell hollow architecture consisted of nitrogen-doped cobalt pyrite integrated carbon spheres (N-CoS₂@C) as PMS activator to boost tetracycline hydrochloride (TCH) degradation. The creation of yolk-shell hollow structure and nitrogen-regulated active site engineering of CoS₂ endow the resulted N-CoS₂@C nanoreactor with high activity for PMS activating toward TCH degradation. Intriguingly, the N-CoS₂@C nanoreactor exhibits an optimal degradation performance with a rate constant of 0.194 min^-1 toward TCH via PMS activation. The ¹O₂ and SO₄^•- species are demonstrated as the dominant active substances for TCH degradation through quenching experiments and electron spin resonance characterization. The possible degradation mechanism, intermediates and degradation pathways for TCH removal over the N-CoS₂@C/PMS nanoreactor are unveiled. Graphitic N, sp²-hybrid carbon, oxygenated group (C-OH) and Co species are verified as the possible catalytic sites of N-CoS₂@C for PMS activation toward TCH removal. This study offers a unique strategy to engineer sulfides as highly efficient and promising PMS activators for antibiotic degradation.

Hydrothermally synthesized titanate nanomaterials for the removal of heavy metals and radionuclides from water: A review

Hazardous heavy metals and radionuclides in water and wastewater are of drastic concern owing to their detrimental impacts on the organisms as well as the circumambient ecosystem. To remove them as much as we can, both technique and materials were studied in the past years. The adsorption technique as superior water remediation method with the simplicity of design, environmental friendliness and high efficiency was well established. Consequently, it is practically important to explore advanced and economically feasible absorbents for removing these poisonous pollutants from aqueous solutions. So far, large numbers of experiments proved hydrothermally synthesized titanate nanomaterials (TNMs) could be a prospectively excellent adsorbent extracting heavy metals and radionuclides from water due to the high specific surface area, tunable pore size, abundant surface active sites, favorable hydrophilic properties. The objective of this work is to give an overview of hydrothermal synthesis, adsorption performance of TNMs for heavy metals and radionuclides, as well as the various influencing factors for water purification. It comprehensively reviews the structural changes and regenerability of TNMs after adsorption, and different modification methods adopted for improving removal capacity. Additionally, it uniquely highlights the efficient decontamination of the pollutants through a synergistic effect of adsorption and photocatalysis by TNMs. This review provides detailed information for the development, application, and research challenges faced by hydrothermally synthesized TNMs for the removal of heavy metals and radionuclides from aqueous solutions, which will serve as a reference guide for scientists in related fields.

Adsorption of U(VI) on the natural soil around a very low-level waste repository

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). CO₃^2- remarkably inhibited the U(VI) adsorption, while the adsorption of U(VI) was promoted by PO₄^3- and SO₄^2-. 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.

Efficient extraction of antimony(III) by titanate nanosheets: Study on adsorption behavior and mechanism

Antimony has been listed as a critical pollutant in many countries because of its toxic effects on earth organisms. In this study, titanate nanosheets (TNS) were prepared with a high specific surface area by alkaline hydrothermal method. The adsorption mechanism and adsorption capacity of removing Sb(III) from aqueous solutions with TNS as an adsorbent were investigated for the first time. The FTIR and XPS analysis indicated that the interlayer sodium ions of TNS were responsible for Sb(III) adsorption. The batch experiments were conducted on solution pH, adsorbent dosage, initial concentration and reaction time. The results exhibited that when pH was 2, the removal rate was about 90% with the dosage of TNS was 0.1 g/L. The adsorption reaction was exceedingly rapid in the initial 5 min, and then the reaction was in equilibrium after about 30 min. The experimental data were better fitted with Langmuir isotherm model, and the maximum adsorption amount could attain 232.56 mg/g. The experiments showed that TNS had outstanding anti-interference performance to common cations. Therefore, TNS were considered to be an excellent material for removing Sb(III) from aqueous solutions.

Efficient adsorption of europium (III) and uranium (VI) by titanate nanorings: Insights into radioactive metal species

Radioactive wastewater containing high concentration of radionuclides poses severe threats to ecosystem and human health, so efficient removal of these toxic heavy metals is urgently needed. Titanate nanomaterials have been demonstrated good adsorbents for heavy metals due to ion exchange property. In this study, titanate nanorings (TNRs) were synthesized using the facile hydrothermal-cooling method. The TNRs were composed of sodium trititanate, with a chemical formula of Na_0.66H_1.34Ti₃O₇•0.27H₂O and a Na content of 2.38 mmol/g. The TNRs demonstrated sufficient adsorption performance to radionuclides europium (Eu) and uranium (U) ions. Specifically, even at a high initial concentration of 50 mg/L, 86.5% and 92.6% of the two metal ions can be rapidly adsorbed by the TNRs within 5 min, and equilibrium was reached within 60 min at pH 5. The maximum adsorption capacity (Q _max) obtained by the Langmuir isotherm model was 115.3 mg/g for Eu(III) and 282.5 mg/g for uranium U(VI) at pH 5, respectively. The adsorption capacities of the two metals under various water chemical conditions were highly related to their species. Ion exchange between metal cations and Na⁺ in the TNR interlayers was the dominant adsorption mechanism, and adsorption of U(VI) was more complicated because of the co-existence of various uranyl (UO₂ ²⁺) and uranyl-hydroxyl species. The spent TNRs were effectively regenerated through an acid-base or ethylenediamine tetraacetic acid (EDTA) treatment and reused. Considering the large adsorption capacity and quick kinetic, TNRs are promising materials to remove radionuclides in environmental purification applications, especially emergent treatment of leaked radionuclides.

Sorption of Eu (III) onto Nano-Sized H-Titanates of Different Structures

Hydrogen titanates (H-titanates) of different nanostructures (nanotubes, nanowires, nanosheets) have been synthesized by hydrothermal methods. The europium (III) sorption from aqueous solutions onto nano-sized H-titanates was studied as a function of contact time, pH values, and initial Eu (III) concentration in batch experiments. Reversibility of adsorption of europium has been investigated as well. Nano-sized H-titanates can be used for tri-valent f-elements removal in polluted water treatment due to fast and efficient sorption of Eu (III).

Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

Sorption of U(VI) onto TiO₂ 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 TiO₂ was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO₂ below pH4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO₂ 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 TiO₂ was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO₂ 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.

Detoxification of U(VI) by Paecilomyces catenlannulatus investigated by batch, XANES and EXAFS techniques

Paecilomyces catenlannulatus (P. catenlannulatus) as a genus of entomogenous fungus presented a variety of surface reactive groups by batch characterizations. The detoxification of U(VI) by P. catenlannulatus was investigated under different water chemistry (pH, incubation time, foreign anions and U(VI) concentration) by batch techniques. Approximately 75% of U(VI) was reduced to U(IV) (i.e., U^(IV)O₂(s)) by P. catenlannulatus at pH 5.5 and 7 days under glovebox conditions, therefore the formation of precipitates decreased the toxicity of U(VI) for P. catenlannulatus. In addition, phosphate facilitate the U(VI) reduction, whereas carbonate and sulfate inhibited the U(VI) reduction. The activities of catalase (CAT), superoxide dismutase (SOD) and glutathione (GSH) level were stimulated exposure to 1-30 mg/L U(VI), indicating that CAT, SOD and GSH were antagonized for the oxidant stress derived from U(VI) at low concentrations. According to XPS and XANES analysis, the occurrence of U(IV) revealed the reduction of adsorbed U(VI) to U(IV) by P. catenlannulatus. The results of EXAFS analysis indicated that the fitting of U-O and U-U shell for U-loaded P. catenlannulatus was similar to that of U^(IV)O₂(s)). The formation of U-bearing precipitates decreased the toxicity of U(VI) for P. catenlannulatus. These findings indicated that P. catenlannulatus is capable to detoxify U(VI) by extracellar/intracellar defense systems. Therefore, P. catenlannulatus can be utilized as a promising bioadsorbents for remediation of uranium-contaminated wastewater in environmental cleanup.

Efficient extraction of uranium from aqueous solution using an amino-functionalized magnetic titanate nanotubes

In this paper, titanate nanotubes/cobalt ferrite/tetraethylenepentamine (TNTs/CoFe₂O₄/TEPA) adsorbents were prepared for the adsorption of uranium (VI) from the solution. Its morphology was observed by transmission electron microscopy (TEM) and exhibited the uniform well tubular structure. TNTs/CoFe₂O₄/TEPA composites were easily separated from solution by an external magnetic field. The removal of uranium (VI) from aqueous solution (ppm level) and simulated seawater (ppb level) were investigated by the TNTs/CoFe₂O₄/TEPA composites. Batch adsorption experiments were conducted to determine the effect of varying pH, contact time, and reaction temperature. The best fit for uranium (VI) adsorption was obtained with the Langmuir model, and the highest adsorption of TNTs/CoFe₂O₄/TEPA composites reached 509.89 mg-U/g-adsorbent at pH 6. From an investigation of the adsorption by XRD, FTIR and XPS, it is suggested that the surface complexation and cation exchange were the main adsorption mechanism. In addition, TNTs/CoFe₂O₄/TEPA composites maintained good adsorption properties after five sorption-desorption cycles. Therefore, we conclude that the adsorbents are promising materials for the removal of uranium (VI) from aqueous solutions.

Rationally designed core-shell and yolk-shell magnetic titanate nanosheets for efficient U(VI) adsorption performance

The hierarchical core-shell and yolk-shell magnetic titanate nanosheets (Fe₃O₄@TNS) were successfully synthesized by employing magnetic nanoparticles (NPs) as interior core and intercrossed titanate nanostructures (NSs) as exterior shell. The as-prepared magnetic Fe₃O₄@TNS nanosheets had high specific areas (114.9 m² g^-1 for core-shell Fe₃O₄@TNS and 130.1 m² g^-1 for yolk-shell Fe₃O₄@TNS). Taking advantage of the unique multilayer structure, the nanosheets were suitable for eliminating U(VI) from polluted water environment. The sorption was strongly affected by pH values and weakly influenced by ionic strength, suggesting that the sorption of U(VI) on Fe₃O₄@TNS was mainly dominated by ion exchange and outer-sphere surface complexion. The maximum sorption capacities (Q_max) calculated from the Langmuir model were 68.59, 121.36 and 264.55 mg g^-1 for core-shell Fe₃O₄@TNS and 82.85, 173.01 and 283.29 mg g^-1 for yolk-shell Fe₃O₄@TNS, at 298 K, 313 K and 328 K, respectively. Thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) demonstrated that the sorption process was endothermic and spontaneous. Based on X-ray photoelectron spectroscopy (XPS) analyses, the sorption mechanism was confirmed to be cation-exchange between interlayered Na⁺ and UO₂²⁺. The yolk-shell Fe₃O₄@TNS had more extraordinary sorption efficiency than core-shell Fe₃O₄@TNS since the yolk-shell structure provided internal void space inside the titanate shell to accommodate more exchangeable active sites. The flexible recollection and high efficient sorption capacity made core-shell and yolk-shell Fe₃O₄@TNS nanosheets promising materials to eliminate U(VI) or other actinides in wastewater cleanup applications.

Macroscopic and spectroscopic studies of the enhanced scavenging of Cr(VI) and Se(VI) from water by titanate nanotube anchored nanoscale zero-valent iron

Herein, a promising titanate nanotubes (TNT) anchored nanoscale zero-valent iron (NZVI) nanocomposite (NZVI/TNT) was synthesized, characterized and used for the enhanced scavenging of Cr(VI) and Se(VI) from water. The structural identification indicated that NZVI was uniformly loaded on TNT, thereby, the oxidation and aggregation of NZVI was significantly minimized. The macroscopic experimental results indicated that NZVI/TNT exhibited higher efficiency as well as rate on Cr(VI) and Se(VI) scavenging resulted from the good synergistic effect between adsorption and reduction. Besides, TNT can weaken the inhibitory effect of co-existing humic acid (HA) and fulvic acid (FA) on the scavenging of Cr(VI) and Se(VI) by NZVI, since TNT showed strong adsorption for HA and FA that inhibit potential reactivity. XPS analysis suggested that surface-bound Fe(II) played a critical role in Cr(VI) and Se(VI) scavenging. XANES analysis demonstrated that TNT acted as a promoter for the almost complete transformation of Cr(VI) into Cr(III), and Se(VI) into Se(0)/Se(-II) in NZVI system. EXAFS analysis indicated that TNT acted as a scavenger for insoluble products, and thus more reactive sites can be used for Cr(VI) and Se(VI) reduction. The excellent performance of NZVI/TNT provide a potential material for purification and detoxification of Cr(VI) and Se(VI) from wastewater.