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Although titanium dioxide (TiO2) has a wide range of potential applications, the photocatalytic performance of TiO2 is limited by both its limited photoresponse range and fast recombination of the photogenerated charge carriers. In this work, the preparation of nitrogen (N)-doped TiO2 accompanied by the introduction of oxygen vacancy (Vo) has been achieved via a facile annealing treatment with urea as the N source. During the annealing treatment, the presence of urea not only realizes the N-doping of TiO2 but also creates Vo in N-doped TiO2 (N-TiO2), which is also suitable for commercial TiO2 (P25). Unexpectedly, the annealing treatment-induced decrease in the specific surface area of N-TiO2 is inhibited by the N-doping and, thus, more active sites are maintained. Therefore, both the N-doping and formation of Vo as well as the increased active sites contribute to the excellent photocatalytic performance of N-TiO2 under visible light irradiation. Our work offers a facile strategy for the preparation of N-TiO2 with Vo via the annealing treatment with urea. [ABSTRACT FROM AUTHOR]

Understanding the binding configuration of uranium on biotite is crucial for elucidating the environmental behavior of U(VI) and addressing emergency scenarios in disposal repositories. This investigation demonstrated that U(VI) adsorption on biotite was significantly affected by pH, while a lesser impact from ionic strength. Moreover, the presence of phosphate and humic acid (HA) exerted a substantial enhancing influence on U(VI) adsorption (adsorption rate increased by over 20%). X-ray photoelectron spectroscopy (XPS) analysis revealed that elevated Fe(II) contents within biotite structures facilitated the reduction of partial U(VI) to form U(V/IV)/U(IV), i.e., mineralization products, under both aerobic and anaerobic conditions. [ABSTRACT FROM AUTHOR]

Natural subsurface environment is a complex heterogeneous system. The key factors affecting the formation of heterogeneous flow and the co-transport behavior of bentonite colloids with Eu(III) under different hydrochemical conditions were investigated in saturated heterogeneous quartz sand column. Quartz sand has a certain filtering effect on Eu(III), the larger sand acts as the preferential flow channel of the heterogeneous media. Media structural configurations and ion strength displayed synergistic effect on the transport and release behaviors of Eu(III) in homogeneous/heterogeneous porous media. Heterogeneous flow in porous media will aggravate the transport risk of bentonite colloid-radionuclide conjugates in the repository environment. [ABSTRACT FROM AUTHOR]

In this work, the effects of the solvents, pH, and concentration on the photolysis of CH3I under UV irradiation were investigated. The photolysis of CH3I mainly occurs in the gas phase and is faster in its aqueous solution compared to in its n-hexane and methanol–water solutions. UV irradiation-induced photolysis of CH3I produces I2 and I3− whereas the formation of the latter is affected by the former. In addition, both the pH and concentration of CH3I aqueous solutions affect the formation and transformation of I3− and I2. The results are helpful and referable to understanding the photolysis behavior of CH3I under UV irradiation. [ABSTRACT FROM AUTHOR]

The application of nanoscale zero-valent iron (NZVI) for U(VI) removal often presents limitations due to its easy aggregation. The anchor of monodisperse NZVI on stable substrate has been verified an effective strategy to maximize the advantages of NZVI and promote the immobilization of U(VI). Herein, NZVI/TiO2 nanofibers were one-step prepared by electrospinning technology and followed by in-situ H2-reduction process, which granted the great dispersion uniformity and negligible aggregation of NZVI. The NZVI/TiO2 nanofiber consisting of Fe and FeTiO3 showed a large saturation magnetization, which enabled the feasible solid–liquid separation by external magnetic field. The NZVI/TiO2 nanofiber exhibited good uranium immobilization ability with an adsorption capacity was 122.3 mg g−1 at pH 7.0. XPS revealed that the U(VI) elimination was conducted by both adsorption and reduction of U(VI) to NZVI/TiO2. The proposed NZVI/TiO2 nanofibers provide a great platform by reduction to efficiently remediate U-uranium wastewater. [ABSTRACT FROM AUTHOR]

In this work, solar light induced photoreduction of water-soluble U(VI) was realized with metahnol under anaerobic conditions at the optimal pH around 5.00. TEM, XPS, and XRD analyses prove that U(VI) is removed from the aqueous solution by forming insoluble brown uranium precipitates containing uranium dioxide (UO2). The photoreduction approach shows obvious selectivity for the removal of U(VI) and the efficiency (95.47%) is comparable to that of the photocatalytic reduction method (99.35%) while only uranium sediments are formed with the photoreduction approach. Photoreduction offers an efficient approach for the rapid removal of U(VI) from the aqueous solution. [ABSTRACT FROM AUTHOR]

The adsorption characteristics of Eu(III) on colloidal bentonite particles were investigated by batch experiments as functions of colloid concentration, pH, foreign ions, and temperature. Bentonite colloids displayed remarkable adsorption ability to Eu(III), the Eu(III) adsorption was significantly affected by solution chemistry. The Eu(III) adsorption increased with colloids concentration and pH increasing. Divalent cations (Ca2+, Mg2+ and Sr2+) and anions (Cl− and SO42−) inhibited Eu(III) adsorption, whereas PO43− greatly enhanced Eu(III) adsorption. High temperature was beneficial for Eu(III) adsorption, the adsorption process was a spontaneous endothermic process. The results suggested that colloids could acted as an efficient carrier for Eu(III) transport. [ABSTRACT FROM AUTHOR]

Detailed information on the An(III)/Ln(III) complexation properties in solution is essential for separation chemistry and the prediction of their potential for radionuclide migration from nuclear waste repositories into natural aquifers. In the present study, to better reveal and confirm the structural information of [Eu(Ox)x (H2O)h−2x]3−2x (h = 8, 9; x = 0–3) aqueous species, especially the variable coordination number (CN), and explore the validity of the spectral linear correlation between the luminescence lifetime and the residual hydration number in the first coordination sphere of Eu(III) compounds in solution, a comparison between the spectral results and the theoretical calculations in a wide parametric space in terms of the pH value and oxalate concentration was carried out by combining time-resolved luminescence spectroscopy (TRLS) with speciation modelling and density functional theory (DFT) calculations. We have found direct and clear evidence for the 9-fold to 8-fold coordination number reduction of Eu(III) atoms upon coordination with more than one oxalate in an aqueous medium, and as well systematically validated the applicability of the spectral linear correlation in an aqueous system (otherwise solid state) involving multiple species with the support of relatively reliable and clear speciation modelling. [ABSTRACT FROM AUTHOR]

U(VI) was found to form intrinsic colloids in the natural groundwater. Fluorescence spectra, TEM, SEM techniques and thermodynamic calculation were used to identify the species of U(VI) and characterize the intrinsic uranium colloidal particles in the groundwater. The effect of pH on the formation of U(VI) colloidal particles was studied. It was found that under near-neutral and strong alkaline conditions, several elements, mainly Ca, Na and Si were responsible for the formation of intrinsic U(VI) colloid, and under weak alkaline conditions, U(VI) colloidal particles were not formed due to the formation of calcium uranyl carbonate complex. [ABSTRACT FROM AUTHOR]

With the development of nuclear energy, large amounts of radionuclides are inevitably released into the natural environment. It is necessary to eliminate radionuclides from wastewater for the protection of environment. Nanomaterials have been considered as the potential candidates for the effective and selective removal of radionuclides from aqueous solutions under complicated conditions because of their high specific surface area, large amounts of binding sites, abundant functional groups, pore-size controllable and easily surface modification. This review mainly summarized the recent studies for the synthesis, fabrication and surface modification of novel nanomaterials and their applications in the efficient elimination and solidification of radionuclides, and discussed the interaction mechanisms from batch experiments, spectroscopy analysis and theoretical calculations. The sorption capacities with other materials, advantages and disadvantages of different nanomaterials are compared, and at last the perspective of the novel nanomaterials is summarized. [ABSTRACT FROM AUTHOR]

The sorption of hexavalent uranium on muscovite as a function of pH, background electrolyte, temperature and humic acid (HA) was investigated in detail using batch experiments. The results showed that the uranium sorpiton on muscovite was kinetic fast, the kinetic process was fitted well by pseudo-second-order kinetic model. The sorption of uranium depended strongly on pH while weakly on background electrolyte concentration, indicating that surface complexation dominated the sorption process. The escalation of temperature and humic acid concentration were favorable to uranium sorption on muscovite. The sorption isotherms at pH 6.0 could be described better by Langmuir model than Freundlich or Dubinin-Radushkevich (D-R) model, thermodynamic data indicated that the uranium sorption process on muscovite was spontaneous and endothermic process. The findings in present work can provide important experimental reference for understanding the environmental behavior of uranium in mica-rich terrains. [ABSTRACT FROM AUTHOR]

Activated bentonite was obtained from acid activation and purification of raw bentonite, sorption of Th(IV) onto activated bentonite was studied by batch experiments. Characterization of activated bentonite and sorption behavior of Th(IV) demonstrated that Th(IV) could quickly absorbed on activated bentonite, and kinetic process fitted well with the pseudo-second-order model. Sorption percentage of Th(IV) on activated bentonite strongly depended on pH, background anion, ionic strength and temperature, which indicated surface complexation was the main sorption mechanism, physisorption and ion-exchange as secondary factors also participated in sorption processes. The results showed activated bentonite was an efficient material for Th(IV) sorption. [ABSTRACT FROM AUTHOR]

β-Zeolite was synthesized and modified with TiO2. The synthesized materials were characterized and used for removal of U(VI) from aqueous solutions. The influences of pH, contact time and temperature on U(VI) adsorption onto modified β-zeolite by TiO2 were studied by batch technique and XPS was employed to analysed the experimental data. The dynamic process showed that the adsorption of U(VI) onto TiO2/β-zeolite matched the pseudo-second-order kinetics model, and the adsorption of U(VI) were significantly dependent on pH values. Through simulating the adsorption isotherms by Langmuir, Freundlich and Dubini--Radushkevich (D-R) models, it could be seen, respectively that the adsorption patterns of U(VI) onto TiO2/β-zeolite were mainly controlled by surface complexation, and the adsorption processes were endothermic and spontaneous. The modification of β-zeolite by TiO2 it shows a novel material for the removing of U(VI) from water environment for industrialized application. [ABSTRACT FROM AUTHOR]

β-Zeolite-EDA was modified with ethylenediamine (EDA) after synthesized. The synthesized material was characterized and used for removal of Th(IV) from aqueous solutions. The influences of pH, ionic strength, contact time, temperature and humic acid (HA) on Th(IV) sorption onto synthesized β-zeolite-EDA was studied by batch technique. The dynamic process showed that the sorption of Th(IV) onto β-zeolite-EDA matched the pseudosecond- order kinetics model. The sorption of Th(IV) on β-zeolite-EDA was significantly dependent on pH values, the sorption percentage increased markedly at pH 3.5-4.5, and then maintained a steady state as pH values increased. Through simulating the sorption isotherms by Langmuir, Freundlich and Dubini-Radushkevich (D-R) models, it could be seen respectively that the sorption pattern of Th(IV) on β-zeolite-EDA was mainly controlled by surface complexation, and that the sorption processes was endothermic and spontaneous. The presence of HA increased Th(IV) sorption on β-zeolite-EDA. [ABSTRACT FROM AUTHOR]

The interactions between contaminations of U(VI) and silicon oxide nanoparticles (SONPs), both of which have been widely used in modern industry and induced serious environmental challenge due to their high mobility, bioavailability, and toxicity, were studied under different environmental conditions such as pH, temperature, and natural organic matters (NOMs) by using both batch and spectroscopic approaches. The results showed that the accumulation process, i.e., sorption, of U(VI) on SONPs was strongly dependent on pH and ionic strength, demonstrating that possible outer- and/or inner-sphere complexes were controlling the sorption process of U(VI) on SONPs in the observed pH range. Humic acid (HA), one dominated component of NOMs, bounded SONPs can enhance U(VI) sorption below pH~4.5, whereas restrain at high pH range. The reversible sorption of U(VI) on SONPs possibly indicated that the outer-sphere complexes were prevalent at pH 5. However, an irreversible interaction of U(VI) was observed in the presence of HA (). It was mainly due to the ternary SONPs-HA-U(VI) complexes (Type A Complexes). After SONPs adsorbed U(VI), the particle size in suspension was apparently increased from ~240 nm to ~350 nm. These results showed that toxicity of both SONPs and U(VI) will decrease to some extent after the interaction in the environment. These findings are key for providing useful information on the possible mutual interactions among different contaminants in the environment. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP) was a highly efficient decontamination material for its strong adsorption capacity used in the immobilization of heavy metals, while the particle-size effect was insufficiently investigated during the sorption process. In the present study, the mechanisms of nickel (Ni(II)) adsorption on HAPs with two different particle sizes were investigated by combing batch experiments, desorption, and XRD analysis. The results showed that the adsorption capacity of 20 nm HAP (nano-HAP) was much higher than that of 12 μ m HAP (micro-HAP). It was noticed that the results of the present study also clarified the distinct mechanisms in each adsorption process. As for micro-HAP, Ni2+ adsorbed through slow diffusion and replacement with Ca2+ and then incorporated in the lattice at pH between 6.5 and 9.0, which was confirmed by the results of kinetics, thermodynamics, and desorption. And a more compact crystalline structure and irreversible desorption behavior of micro-HAP after Ni(II) adsorption was confirmed by results of XRD and desorption isotherms, respectively. At pH > 9.0 , lattice incorporation and precipitation controlled together. However, for nano-HAP, the sharp increase of Ni(II) adsorption and ionic strength dependent at pH 6.5 to 9.0 revealed that the dominant mechanisms were ionic exchange and inner-sphere complexation. XRD results showed that characteristic peaks of cassidyite appeared in Ni(II)-loading nano-HAP. At pH > 9.0 , a precipitate of Ni(II) was the dominant mechanism. The experimental finds demonstrated that nanoscale HAP was a more fast, efficient, and desorbable adsorbent than micro-HAP for Ni(II) removal. These findings would be favorable for investigating the removal mechanisms of heavy metals on the HAP materials and designing the synthesis methods. [ABSTRACT FROM AUTHOR]

A new method was developed for rapid and direct measurement of polybrominated diphenyl ethers (PBDEs) in aqueous samples using fluorescence spectroscopy. The fluorescence spectra of tri- to deca-BDE (BDE 28, 47, 99, 153, 190, and 209) commonly found in environment were measured at variable emission and excitation wavelengths. The results revealed that the PBDEs have distinct fluorescence spectral profiles and peak positions that can be exploited to identify these species and determine their concentrations in aqueous solutions. The detection limits as determined in deionized water spiked with PBDEs are 1.71–5.82 ng/L for BDE 28, BDE 47, BDE 190, and BDE 209 and 45.55–69.95 ng/L for BDE 99 and BDE 153. The effects of environmental variables including pH, humic substance, and groundwater chemical composition on PBDEs measurements were also investigated. These environmental variables affected fluorescence intensity, but their effect can be corrected through linear additivity and separation of spectral signal contribution. Compared with conventional GC-based analytical methods, the fluorescence spectroscopy method is more efficient as it only uses a small amount of samples (2–4 mL), avoids lengthy complicated concentration and extraction steps, and has a low detection limit of a few ng/L. [ABSTRACT FROM AUTHOR]

For the selective extraction of Am(III) and Eu(III), quadridentate divalent phenolic Schiff bases-bis-salicylaldehyde ethylenediamine (Hsalen) was investigated as a kind of extractant. The influences of alkaline cation, inorganic anion, ionic strength, pH and the concentration of Hsalen on the distribution ratio of Am(III) and Eu(III) were investigated in detail. As a result, Am(III) and Eu(III) made anionic 1:1 complexes with the ligand (Hsalen) and could be extracted into nitrobenzene as ion-pairs with a suitable monovalent counter anion in the aqueous solution, the extracted species were possibly of the type Am(Hsalen) Eu(salen)Cl and Eu(Hsalen)Cl, respectively. The extractability of Eu(III) was significantly stronger than that of Am(III) and the maximum separation factor, SF, was 96 at pH 4.0. The results indicated that Hsalen had good selectivity for Am(III) and Eu(III). [ABSTRACT FROM AUTHOR]

The surface properties of intrinsic and activated attapulgite were studied using potentiometric titration. The sorption mechanisms of Th(IV) on intrinsic and activated attapulgite were investigated by employing surface complexation model and FITEQL 3.2 code. The results indicated that the sorption sites of intrinsic attapulgite involved in the sorption process were main ion exchange site (≡ XNa/K), strong site (≡ SOH) and weak site (≡ SOH), while only strong site (≡ SOH) and weak site (≡ SOH) were predominant for activated attapulgite. At pH < 2.5, the species of Th(IV) was main Th in aqueous solution; then the hydrolysis species of Th(IV) (i.e., Th(OH), Th(OH) and Th(OH)) gradually formed as pH increasing. For the sorption of Th(IV) on intrinsic attapulgite, both ion exchange species (≡ XTh) and inner-sphere surface complexes (≡ SOTh) were dominant, while only inner-sphere surface complexes (i.e.,≡ SOThOH and≡ SOTh) were observed for Th(IV) sorption to activated attapulgite. In the presence of humic acid (HA), the sorption of Th(IV) on activated attapulgite was obviously enhanced; and both≡ SOH-HA-Th and≡ SOTh were the predominant speciation. It was also interesting to find that the addition of HA obviously provoked the desorption behavior of Th(IV). [ABSTRACT FROM AUTHOR]

The low cost β-zeolite and ethylenediamine modified β-zeolite (EDA@β-zeolite) were prepared by self-assembly method and used for Cu(II) removal from contaminated aqueous solution. Removal ability of β-zeolite toward Cu(II) was greatly improved after ethylenediamine (EDA) modification, the removal performance was greatly affected by environmental conditions. XPS results illustrated that the amide group played important role in the removal process by forming complexes with Cu(II). The EDA@β-zeolite showed desirable recycling ability. The finding herein suggested that the proposed composite is a promising and suitable candidate for the removal of Cu(II) from contaminated natural wastewater and aquifer. [ABSTRACT FROM AUTHOR]