Selective capture of iodide from solutions by microrosette-like δ-Bi₂O₃

Effect of different synthesis methodologies on the adsorption of iodine

Radioactive nuclides such as cesium, ruthenium, and iodine are difficult to remove in radioactive wastewater, which could be removed by coprecipitation of special chemical precipitants. In this study, dynamic Cu/Ag-mordenite (Cu/Ag-MOR) material was synthesized to be treated as the precipitant to selectively adsorb the iodine ion (I^-) through controlled chemisorption combined with physical adsorption. XRD, XPS, and FTIR characterization demonstrated the successful modification of the MOR carrier surface by Cu/Ag particles and the high selectivity of the active component Cu (I) on the dynamic Cu/Ag-MOR material. SEM, TEM, and BET methods were used to characterize the Cu/Ag-MOR material, demonstrating these results: the MOR carried a stable porous structure, which allowed the silver to be well dispersed on its surface. The silver improved the copper distribution by being well-coated by the copper species. Furthermore, the analysis of the factors influencing the chemical plating of copper showed that the pH, the concentration of EDTA-2Na and the temperature all influenced the deposition rate of Cu₂O. The activation energy for Cu₂O deposition in dynamic Cu/Ag-MOR was 20.31 kJ/mol. The highest removal of I^- in the presence of dynamic Cu/Ag-MOR could reach 99.1% in the adsorption tests. The adsorption kinetics was under a proposed second-order model, with chemisorption being the controlling step of the reaction. The adsorption/desorption experiments demonstrated the reusability of the nano-sorbent. It was also demonstrated that dynamic Cu/Ag-MOR materials showed good applicability in complex situations where multiple pollutants co-exist.

Study of the oxidation process of bismuth nanoparticles using NaClO

Bismuth nanoparticles (NPs) colloids synthesized in deionized water by laser ablation of solids in liquids technique (LASL) were oxidized using NaClO solutions at different concentrations. Oxidized nanomaterials were characterized using several techniques. The crystalline phases of the bismuth compound were determined using Raman microspectroscopy, and the crystallographic structure was identified by x-ray diffraction (XRD). The size and morphology of the obtained nanomaterials were studied by transmission electron microscopy (TEM). The chemical states were determined using x-ray photoelectron spectroscopy (XPS), and the optical properties of the colloids were characterized by UV-vis spectroscopy. The absorption spectra were analyzed using the Tauc method to determine the band gaps of the obtained nanomaterials. Our results showed morphological changes, starting from small nanoparticles to nanosheets and a mixture of nanosheets with hollow nanoparticles. Two kinds of nanomaterials were found depending on the NaClO solution concentration: Bi₂O₂CO₃single phase and a mixture ofδ-Bi₂O₃and Bi₂O₂CO₃. Some samples were tested as photocatalysts and showed good performance in the degradation of methylene blue in solution. To the best of our knowledge, this is the first study on the oxidation process of bismuth colloidal nanoparticles at room temperature.

Recent advances in the removal of radioactive iodine by bismuth-based materials

Nowadays, the demand for nuclear power is continue increasing due to its safety, cleanliness, and high economic benefits. Radioactive iodine from nuclear accidents and nuclear waste treatment processes poses a threat to humans and the environment. Therefore, the capture and storage of radioactive iodine are vital. Bismuth-based (Bi-based) materials have drawn much attention as low-toxicity and economical materials for removing and immobilizing iodine. Recent advances in adsorption and immobilization of vapor iodine by the Bi-based materials are discussed in this review, in addition with the removal of iodine from solution. It points out the neglected areas in this research topic and provides suggestions for further development and application of Bi-based materials in the removal of radioactive iodine.

Highly Sensitive Adsorption and Detection of Iodide in Aqueous Solution by a Post-Synthesized Zirconium-Organic Framework

Effective methods of detection and removal of iodide ions (I^-) from radioactive wastewater are urgently needed and developing them remains a great challenge. In this work, an Ag⁺ decorated stable nano-MOF UiO-66-(COOH)₂ was developed for the I^- to simultaneously capture and sense in aqueous solution. Due to the uncoordinated carboxylate groups on the UiO-66-(COOH)₂ framework, Ag⁺ was successfully incorporated into the MOF and enhanced the intrinsic fluorescence of MOF. After adding iodide ions, Ag⁺ would be produced, following the formation of AgI. As a result, Ag⁺@UiO-66-(COOH)₂ can be utilized for the removal of I^- in aqueous solution, even in the presence of other common ionic ions (NO₂^-, NO₃^-, F^-, SO₄^2-). The removal capacity as high as 235.5 mg/g was calculated by Langmuir model; moreover, the fluorescence of Ag⁺@UiO-66-(COOH)₂ gradually decreases with the deposition of AgI, which can be quantitatively depicted by a linear equation. The limit of detection toward I^- is calculated to be 0.58 ppm.

Water-stable porous Al24 Archimedean solids for removal of trace iodine

In this paper, we report a unique type of core-shell crystalline material that combines an inorganic zeolitic cage structure with a macrocyclic host arrangement and that can remove trace levels of iodine from water effectively. These unique assemblies are made up of an inorganic Archimedean truncatedhexahedron (tcu) polyhedron in the kernel which possesses six calixarene-like shell cavities. The cages have good adaptability to guests and can be assembled into a series of supramolecular structures in the crystalline state with different lattice pore shapes. Due to the unique core-shell porous structures, the compounds are not only stable in organic solvents but also in water. The characteristics of the cages enable rapid iodine capture from low concentration aqueous I₂/KI solutions (down to 4 ppm concentration). We have studied the detailed process and mechanism of iodine capture and aggregation at the molecular level. The facile synthesis, considerable adsorption capacity, recyclability, and β- and γ-radiation resistance of the cages should make these materials suitable for the extraction of iodine from aqueous effluent streams (most obviously, radioactive iodide produced by atomic power generation).

The removal of radioactive elements is important to human health and sustainable development. Here, the authors reveal the synthesis of water-stable Archimedean solids based on the earth-abundant element for the fast removal of trace iodine.

Selective removal of radioactive iodine from water using reusable Fe@Pt adsorbents

Environmental damage from serious nuclear accidents should be urgently restored, which needs the removal of radioactive species. Radioactive iodine isotopes are particularly problematic for human health because they are released in large amounts and retain radioactivity for a substantial time. Herein, we prepare platinum-coated iron nanoparticles (Fe@Pt) as a highly selective and reusable adsorbent for iodine species, i.e., iodide (I^-), iodine (I₂), and methyl iodide (CH₃I). Fe@Pt selectively separates iodine species from seawater and groundwater with a removal efficiency ≥ 99.8%. The maximum adsorption capacity for the iodine atom of all three iodine species was determined to be 25 mg/g. The magnetic properties of Fe@Pt allow for the facile recovery and reuse of Fe@Pt, which remains stable with high efficiency (97.5%) over 100 uses without structural and functional degradation in liquid media. Practical application to the removal of radioactive ¹²⁹I and feasibility for scale-up using a 20 L system demonstrate that Fe@Pt can function as a reusable adsorbent for the selective removal of iodine species. This systematic procedure is a standard protocol for designing highly active adsorbents for the clean separation and removal of various chemical species dissolved in wastewater.

Bi-based photocatalysts for bacterial inactivation in water: Inactivation mechanisms, challenges, and strategies to improve the photocatalytic activity

Bi-based photocatalysts have been considered suitable materials for water disinfection under natural solar light due to their outstanding optical and electronic properties. However, until now, there are not extensive reviews about the development of Bi-based materials and their application in bacterial inactivation in aqueous solutions. For this reason, this work has focused on summarizing the state of the art related to the inactivation of Gram- and Gram + pathogenic bacteria under visible light irradiation using different Bi-based micro and nano structures. In this sense, the photocatalytic bacterial inactivation mechanisms are analyzed, considering several modifications. The factors that can affect the photocatalytic performance of these materials in real conditions and at a large scale (e.g., water characteristics, pH, light intensity, photocatalyst dosage, and bacteria level) have been studied. Furthermore, current alternatives for improving the photocatalytic antibacterial activity and reuse of Bi-based materials (e.g., surface engineering, crystal facet engineering, doping, noble metal coupling, heterojunctions, Z-scheme junctions, coupling with graphene derivatives, magnetic composites, immobilization) have been explored. According to several reports, inactivation rate values higher than 90% can be achieved by using the modified Bi-based micro/nano structures, which become them excellent candidates for photocatalytic water disinfection. However, these innovative photocatalytic materials bring a variety of future difficulties and opportunities in water disinfection.

Polymorphism and Visible-Light-Driven Photocatalysis of Doped Bi2O3:M (M = S, Se, and Re)

δ-Bi₂O₃:M (M = S, Se, and Re) with an oxygen-defective fluorite-type structure is obtained by a coprecipitation method starting from the bismuth oxido cluster [Bi₃₈O₄₅(OMc)₂₄(dmso)₉]·2dmso·7H₂O (A) in the presence of additives such as Na₂SO₄, Na₂SeO₄, NH₄ReO₄, Na₂SeO₃·5H₂O, and Na₂SO₃. The coprecipitation of the starting materials with aqueous NaOH results in the formation of alkaline reaction mixtures, and the cubic bismuth(III)-based oxides Bi₁₄O₂₀(SO₄) (1c), Bi₁₄O₂₀(SeO₄) (2c), Bi₁₄O₂₀(ReO_4.5) (3c), Bi_12.25O_16.625(SeO₃)_1.75 (4c), and Bi_10.51O_14.765(SO₃)_0.49(SO₄)_0.51 (5c) are obtained after microwave-assisted heating; formation of compound 5c is the result of partial oxidation of sulfur. The compounds 1c, 2c, 4c, and 5c absorb UV light only, whereas compound 3c absorbs in the visible-light region of the solar spectrum. Thermal treatment of the as-prepared metastable bismuth(III) oxide chalcogenates 1c and 2c at T = 600 °C provides a monotropic phase transition into their tetragonal polymorphs Bi₁₄O₂₀(SO₄) (1t) and Bi₁₄O₂₀(SeO₄) (2t), while compound 3c is transformed into the tetragonal modification of Bi₁₄O₂₀(ReO_4.5) (3t) after calcination at T = 700 °C. Compounds of the systems Bi₂O₃-SO_x (x = 2 and 3) and Bi₂O₃-Re₂O₇ are thermally stable up to T = 800 °C, whereas compounds of the system Bi₂O₃-SeO₃ completely lose SeO₃. Thermal treatment of 4c and 5c in air results in the oxidation of the tetravalent to hexavalent sulfur and selenium, respectively, upon heating to T = 400-500 °C. The as-prepared cubic bismuth(III)-based oxides 1c-5c were studied with regard to the photocatalytic decomposition of rhodamine B under visible-light irradiation with compound 3c showing the highest turnover and efficiency.

Transformation of phase and heterojunction type by using HAc-adsorbed Bi(NO3)3 as a Bi source

Generally, preparing high-efficiency heterojunction photocatalysts via a facile room-temperature route is attractive from the perspective of energy and labor saving. Herein, by using dried and glacial acetic acid (HAc)-adsorbed bismuth nitrate, instead of Bi(NO₃)₃·5H₂O, as a Bi source, a β-Bi₂O₃/Bi₅O₇I heterojunction with well dispersed flowery hierarchical architecture was synthesized, which endows it with high surface area, open channels and good light harvest. More importantly, the change of the precursor achieved a successful transformation for both of phase and heterojunction type, i.e. from type-Ⅰ BiOI/[Bi₆O₅(OH)₃](NO₃)₅·3H₂O (labeled as BiOI/BBN) to Z-scheme β-Bi₂O₃/Bi₅O₇I heterojunction. Since both β-Bi₂O₃ and Bi₅O₇I are visible light responsive, β-Bi₂O₃/Bi₅O₇I exhibited improved visible-light photocatalytic activity for the degradation of tetracycline (TC) and malachite green (MG) with apparent reactant rate (k_app) values about 10 and 11 times higher than those of BiOI/BBN. Besides, the presence of more oxygen vacancies also contributed to the enhancement in photocatalytic performance.

High-performance removal of radionuclides by porous organic frameworks from the aquatic environment: A review

Dealing with unwanted nuclear waste is still a serious issue from the point of view of humans and the environment because of its harmful and dangerous effects. Recently, porous organic frameworks (POFs) have gained an increasing concern as effective materials in the removal of various types of hazardous metal ions, especially radioactive metal ions. POFs are a unique class that included covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) with strong covalent bonds, large surface area, high adsorption capacity, tunable porosity, and a porous structure with more efficient than conventional adsorbents. This review highlights the recent developments of POFs for the rapid elimination of radionuclide. The unique characteristics, adsorption properties, and interaction mechanisms between radioactive metal ions and the POF-based materials are summarized. Also, prospects for enhancing the performance of POFs to capture radioactive metal ions are discussed.

Capture of aqueous radioiodine species by metallated adsorbents from wastestreams of the nuclear power industry: a review

Abstract

Iodine-129 poses a significant challenge in the drive towards lowering radionuclide emissions from used nuclear fuel recycling operations. Various techniques are employed for capture of gaseous iodine species, but it is also present, mainly as iodide anions, in problematic residual aqueous wastestreams, which have stimulated research interest in technologies for adsorption and retention of the radioiodine. This removal effort requires specialised adsorbents, which use soft metals to create selectivity in the challenging chemical conditions. A review of the literature, at laboratory scale, reveals a number of organic, inorganic and hybrid adsorbent matrices have been investigated for this purpose. They are functionalised principally by Ag metal, but also Bi, Cu and Pb, using numerous synthetic strategies. The iodide capacity of the adsorbents varies from 13 to 430 mg g−1, with ion-exchange resins and titanates displaying the highest maximum uptakes. Kinetics of adsorption are often slow, requiring several days to reach equilibrium, although some ligated metal ion and metal nanoparticle systems can equilibrate in < 1 h. Ag-loaded materials generally exhibit superior selectivity for iodide verses other common anions, but more consideration is required of how these materials would function successfully in industrial operation; specifically their performance in dynamic column experiments and stability of the bound radioiodine in the conversion to final wasteform and subsequent geological storage.

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Comprehensive comparison of bismuth and silver functionalized nickel foam composites in capturing radioactive gaseous iodine

Developing an efficient and cheap iodine sorbent is of great practical significance in the modern nuclear industry. In this work, novel bismuth and silver functionalized Ni foam composites as iodine sorption materials (Bi-Ni foam and Ag-Ni foam) were successfully prepared via a simple solvothermal method. Through a series of iodine sorption experiments and characterization methods, iodine capture properties and corresponding sorption mechanism were comprehensively compared and thoroughly revealed. The results show that the core-sheath structure formed by the solvothermal reaction can supply more active sites (Bi⁰ or Ag⁰ particles) for the contact of radioactive iodine gas, thereby improving the sorption capacity of sorbents. Compared with Ag-Ni foam (456 mg/g), Bi-Ni foam exhibits a higher iodine capture capacity (658 mg/g), whereas silver-based material has a faster sorption kinetics. Such excellent sorption performances were attributed to the chemical reaction between Bi⁰/Ag⁰ particles and iodine gas, generating stable BiI₃/AgI. In addition, this type of sorbents inherits the external structure of the Ni foam skeleton, decreasing the physically sorbed iodine, and can be prepared in different shapes and sizes, which is of great practical significance.

Synthesis of Silver-Impregnated Magnetite Mesoporous Silica Composites for Removing Iodide in Aqueous Solution

Mag@silica-Ag composite has a high sorption ability for I- in aqueous solution due to its high surface area and strong affinity for the studied anion. The material adsorbed I- rapidly during the initial contact time (in 45 min, η = 80%) and reached adsorption equilibrium after 2 h. Moreover, mag@silica-Ag proved to selectively remove I- from a mixture of Cl-, NO3- and I-. The adsorption behavior fitted the Langmuir isotherm perfectly and the pseudo-second-order kinetic model. Based on the Langmuir isotherm, the maximum adsorption capacity of mag@silica-Ag was 0.82 mmol/g, which is significantly higher than previously developed adsorbents. This study introduces a practical application of a high-capacity adsorbent in removing radioactive I- from wastewaters.

Effective removal of iodate by coprecipitation with barite: Behavior and mechanism

Radioactive iodine (¹²⁹I) is of great concern owing to its high mobility in the environment and long-term radiotoxicity. However, there is a lack of effective techniques for removing iodate (IO₃^-) from aqueous solution. This study aims to develop a new technique for removing radioactive iodate from contaminated solution by using barite (BaSO₄). We examined the coprecipitation mechanism of iodate by barite at the molecular level to determine the optimum conditions for iodate removal. Results showed that iodate was effectively removed from the aqueous solution by coprecipitation even in the presence of competitive anions. Based on comparison of our method with previous techniques, the iodate removal efficiency by barite was determined to be about two orders of magnitude greater than that by hydrotalcite-like layered double hydroxide at 10 mmol L^-1 Cl^-. Extended X-ray absorption fine structure analysis indicated that the incorporated iodate was strongly bound to the crystal lattice of barite by substituting the sulfate site in the structure when the iodine concentration was low. The charge compensation problem from the IO₃^- substitution in the SO₄^2- site was achieved by the substitution of Na⁺-IO₃^- pairs at the nearest Ba²⁺ site. Given the high removal efficiency and strong binding of iodate to barite, coprecipitation with barite is a promising tool for removing radioactive iodate from various aqueous solutions contaminated with iodate.

Removal of heavy metals and radionuclides from water using nanomaterials: current scenario and future prospects

There is an increase in concern about the hazardous effects of radioactivity due to the presence of undesirable radioactive substances in our vicinity. Nuclear accidents such as Chernobyl (1986) and Fukushima (2011) have further raised concerns towards such incidents which have led to contamination of water bodies. Conventional methods of water purification are less efficient in decontamination of radioisotopes. They are usually neither cost-effective nor environmentally friendly. However, nanotechnology can play a vital role in providing practical solutions to this problem. Nano-engineered materials like metal oxides, metallic organic frameworks, and nanoparticle-impregnated membranes have proven to be highly efficient in treating contaminated water. Their unique characteristics such as high adsorption capacity, large specific surface area, high tensile strength, and excellent biocompatibility properties make them useful in the field of water purification. This review explores the present status and future prospects of nanomaterials as the next-generation water purification systems that can play an important role in the removal of heavy metals and radioactive contaminants from aqueous solutions.

Highly selective anchoring silver nanoclusters on MOF/SOF heterostructured framework for efficient adsorption of radioactive iodine from aqueous solution

A series of Ag-modified MOF/SOF heterostructured framework adsorbents (Ag-MSHC) with strong binding of iodine were prepared by anchoring silver nanoclusters on MOF/SOF heterostructured framework (MSHC). Morphological transformation process of six novel Ag-MSHC adsorbents can be realized by tailoring the molar ratio of Fe³⁺, TMA (1,3,5-Tricarboxybenzen) and MA (melamine), finally resulting in a combination of MOFs (metal-organic frameworks) and SOFs (supramolecular organic framework). Among six adsorbents, Ag-MSHC-6 exhibited an extremely strong affinity towards I^-, whereas the maximum adsorption capacity of I^- reaches 771.6 mg/g. An increased tendency of I^- sorption occurred from Ag-MSHC-1 to Ag-MSCH-6 when the molar ratio of Fe³⁺ gradually decreased because the content of Fe³⁺ in topological structure of Ag-MSHC can hinder the incorporation of silver nanoclusters into Ag-MSHC and further influences the irreversible interactions between Ag₂O and I^-. Besides, FT-IR, XPS, TGA and SEM were used to discuss the microstructures and chemical composition of MSHC and Ag-MSHC, and we also performed batch adsorption experiments to demonstrate the iodine sorption performance and mechanism by Ag-MSHC. Taking advantage of this combination of MOFs and SOFs, high degree of doping of silver nanoclusters as well as its strong binding ability of iodine, Ag-MSHC can be considered as a superior adsorbent for radioactive iodine extraction.

Efficient removal of iodide anion from aqueous solution with recyclable core-shell magnetic Fe3O4@Mg/Al layered double hydroxide (LDH)

Magnetic Mg/Al layered double hydroxides (LDH) with three cationic ratios (Mg/Al = 2:1, 3:1, and 4:1) were successfully synthesized and utilized for the first time in an iodide adsorption study. The effects of the Mg/Al ratio of LDH on iodide adsorption were investigated, and physicochemical properties of synthetic LDHs depending on Mg/Al ratio were confirmed by XRD, TEM, ICP-OES, VSM, Zeta-potential, and BET analyses. The ferrimagnetic property was well preserved even after a coating of LDH on magnetite irrespective of the Mg/Al ratio. Among the three Mg/Al ratios, the calcined Fe₃O₄@4:1 Mg/Al LDH exhibited excellent performance for iodide removal with 105.04 mg/g of the maximum iodide adsorption capacity due to its wide interlayer spacing and largest BET surface area. In the presence of competing carbonate anions, the Fe₃O₄@4:1 LDH showed removal rate of >80% at a dosage of over 3 g/L solid to liquid ratio. The recyclability test of Fe₃O₄@4:1 LDH showed that the removal performance for iodide is maintained at >80% even during the first to the fourth cycles. These results demonstrated that the magnetic Mg/Al LDH adsorbent can be effectively utilized for remediation of radioactive iodide anions with high efficiency and economics.

Enhanced removal of I- on hierarchically structured layered double hydroxides by in suit growth of Cu/Cu2O

To further improve the removal ability of layered double hydroxide (LDH) for iodide (I^-) anions from wastewater, we prepared hierarchically porous Cu₅Mg₁₀Al₅-LDH and used as a matrix for in suit growth of Cu/Cu₂O on its surface, forming Cu/Cu₂O-LDH, which was characterized and applied as an adsorbent. Results displayed high I^- saturation uptake capability (137.8 mg/g) of Cu/Cu₂O-LDH compared with Cu₅Mg₁₀Al₅-LDH (26.4 mg/g) even thermal activated LDH (76.1 mg/g). Thermodynamic analysis showed that the reaction between I^- anions and Cu/Cu₂O-LDH is a spontaneous and exothermic. Uptake kinetics analysis exhibited that adsorption equilibrium can be reached after 265 min. Additionally, the adsorbent showed satisfactory selectivity in the presence of competitive anions (e.g., SO₄^2-), and could achieve good adsorption performance in a wide pH range of 3-8. A cooperative adsorption mechanism was proposed on the basis of the following two aspects: (1) ion exchange between iodide and interlayer anions; (2) the adsorption performance of Cu, Cu(II) and Cu₂O for I^-. Meanwhile, the difference between the adsorption mechanism of Cu/Cu₂O-LDH, Cu₅Mg₁₀Al₅-LDH and Cu₅Mg₁₀Al₅-CLDH adsorbents was also elaborated and verified.

Green Construction of an Oil-Water Separator at Room Temperature and Its Promotion to an Adsorption Membrane

Underwater superoleophobic membranes as an effective means of resisting oil stains are often subjected to cumbersome modification procedures, limited stability, and difficult expansion of assembly. To develop simple, green, stable, and scalable underwater superoleophobic films, herein, cellulose-based oil-water separators with high-efficiency oil purification were constructed by using commercial carboxymethocel (CMC) as a solute and a dimethyl sulfoxide-modified ionic liquid as a solvent. Owing to the superior dissolution, regenerability, and gelation of CMC, the metal mesh and gauze can be imparted with an excellent oleophobic ability through simple dipping, spraying, and coating of the CMC solution. As a result, these modified functionalized devices exhibit a purification capacity of more than 99.5% for various oil-water mixtures. Unexpectedly, the CMC gel coating also shields the gloves from organic solvents. Significantly, when the CMC solution is applied to an adsorption membrane, it not only endows the film with excellent oil-water separation characteristics but also enhances the adsorption amount and rate of the adsorbent. Therefore, CMC-based oleophobic materials can be widely developed and applied to a variety of fields that require oleophobic properties.

Nanometer mixed-valence silver oxide enhancing adsorption of ZIF-8 for removal of iodide in solution

Nano mixed-valence silver oxide (Ag₂O-Ag₂O₃) modified the zeolitic imidazolate framework-8 (ZIF-8) composite (Ag₂O-Ag₂O₃@ZIF-8) was firstly prepared via a simple and efficient method, characterized and applied for iodide ion (I^-) uptake from simulated radioactive wastewater. The results showed that Ag₂O-Ag₂O₃ nanoparticles doped and uniformly dispersed on the surface of ZIF-8 matrix. The adsorption capacity of the as-synthesized adsorbents increased with the increasing Ag doped amount, and the maximum adsorption capacity for 20%-Ag₂O-Ag₂O₃@ZIF-8 was 232.12 mg/g. The calculated thermodynamic parameters indicating that the adsorption was a spontaneous and exothermic. It was worth mentioning that each Ag-based adsorbent exhibited high uptake rate of I^-, and all the adsorption tests were equilibrated for a few minutes. This could be ascribed to its large specific surface area and the absolutely dominant position of chemical adsorption for as-prepared samples. Furthermore, the adsorption was barely affected by pH and competitive anions (e.g. Cl^-, SO₄^2-, CO₃^2-), even in simulated salt lake water. Additionally, a mechanism explaining the excellent properties for adsorbents could be epitomized into three aspects, namely, the uptake performance of Ag₂O for I^-, the strong oxidization of Ag₂O₃ for I^-, and the adsorption of AgI for I₂.

Micro-nanostructured δ-Bi2O3 with surface oxygen vacancies as superior adsorbents for SeOx2- ions

Removal of the toxic selenium compounds, selenite (SeO₃^2-) and selenate (SeO₄^2-), from contaminated water is imperative for environmental protection in both developing and industrialized countries. Providing high selectivity adsorbents to the target ions is a big challenge. Here we report that micro sphere-like δ-Bi₂O₃ (MS-δ-Bi₂O₃) with surface oxygen vacancy defects can capture hypertoxic SeO_x^2- anions from aqueous solutions with superior capacity and fast uptake rate. High capture selectivity to SeO₃^2- anions is observed, since the O atoms of SeO₃^2- anions fill the oxygen vacancies on the (111) facet of δ-Bi₂O₃ forming a stable complex structure. This mechanism is distinctly different from other known mechanisms for anion removal, and implies that we may utilize surface defects as highly efficient and selective sites to capture specific toxic species. Thus, we present a new route here to design superior adsorbents for toxic ions.

Enhanced removal of iodide ions by nano Cu2O/Cu modified activated carbon from simulated wastewater with improved countercurrent two-stage adsorption

A newly developed adsorbent nano Cu₂O/Cu-modified activated carbon composite (nano Cu₂O/Cu-C) was used to remove radioactive iodide ions (I^-) from simulated wastewater. The emphasis of this research is to improve adsorption performance and obtain higher I^- removal efficiency compared with the single-stage adsorption. To fully develop the amount of adsorption by nano Cu₂O/Cu-C, and to increase the decontamination factor (DF) of I^-, an improved countercurrent two-stage adsorption (ICTA) process was introduced. In the ICTA process, measures dealing with desorption of loaded adsorbent in the stage-two adsorption were taken and more extensive application of countercurrent two-stage adsorption (CTA) process could be made after the improvement to ICTA process in this study. Furthermore, in order to analyze the process and determine the I^- concentration in the effluent, a calculation method was devised based on the Langmuir isotherm equations and adsorption accumulation principle. The mean DFs were 177, 166, and 89.7, respectively, when the initial I^- concentrations were 5.00, 10.0, and 20.0 mg/L; and the adsorbent dosage was 1.25 g/L. These results were approximately 8.76, 8.97, and 6.79 times higher, respectively, than with conventional single-stage adsorption. The experimental values of the I^- concentration were higher than the calculated ones, which could be ascribed to desorption of the residual loaded adsorbent and formation of CuI in the adsorption at stage 1. Formation of CuI in the adsorption at stage 1 was considered to be the predominant reason.

Enhanced Uptake of Iodide from Solutions by Hollow Cu-Based Adsorbents

Cu₂O exhibits excellent adsorption performance for the removal of I⁻ anions from solutions by doping of metallic Ag or Cu. However, the adsorption process only appears on the surface of adsorbents. To further improve the utilization efficiencies of Cu content of adsorbents in the uptake process of I⁻ anions, hollow spheres of metallic Cu, Cu/Cu₂O composite and pure Cu₂O were prepared by a facile solvothermal method. Samples were characterized and employed for the uptake of I⁻ anions under various experimental conditions. The results show that Cu content can be tuned by adjusting reaction time. After the core was hollowed out, the uptake capacity of the samples increased sharply, and was proportional to the Cu content. Moreover, the optimal uptake was reached within only few hours. Furthermore, the uptake mechanism is proposed by characterization and analysis of the composites after uptake. Cu-based adsorbents have higher uptake performance when solutions are exposed to air, which further verified the proposed uptake mechanism. Finally, hollow Cu-based adsorbents exhibit excellent selectivity for I⁻ anions in the presence of large concentrations of competitive anions, such as Cl⁻, SO₄²⁻ and NO₃⁻, and function well in an acidic or neutral environment. Therefore, this study is expected to promote the development of Cu-based adsorbents into a highly efficient adsorbent for the removal of iodide from solutions.

Synergistic and simultaneous biosorption of phenanthrene and iodine from aqueous solutions by soil indigenous bacterial biomass as a low-cost biosorbent

The removal of phenanthrene and iodine from aqueous solutions in single and binary systems by inactivated soil indigenous bacterial biomass (SIBB), as well as affecting factors, were evaluated. Sorption kinetic and isotherm studies were carried out to investigate the synergistic effects of phenanthrene and iodine. Optimal parameters for the biosorption process included a solution pH of 6.0 and biosorbent dosage of 0.75 g L⁻¹. The ionic strength significantly decreased the biosorption of both phenanthrene and iodine in single conditions, while no obvious influences were found in the binary conditions. A pseudo-second-order model was well fitted to the kinetic biosorption data for both phenanthrene and iodine. The results showed that the presence of co-solute accelerated the biosorption processes and the pseudo-second-order biosorption rates (k₂) for phenanthrene and iodine increased from 0.005441 to 0.009825 g mg⁻¹ min⁻¹ and from 0.000114 to 0.000223 g mg⁻¹ min⁻¹, respectively. The SIBB showed strong affinity with both phenanthrene and iodine, with a partition coefficient K_d (Linear model) of 6892.4 L kg⁻¹ for phenanthrene and affinity parameter K_L (Langmuir model) of 232 500 L kg⁻¹ for iodine. The presence of co-solute illustrated a synergistic effect on the biosorption of phenanthrene and iodine due to intermolecular forces between phenanthrene and iodine, enhancing the K_d of 34.7% for phenanthrene and K_L of 107.0% for iodine, respectively. The results suggested that SIBB was an effective material for the simultaneous biosorption of phenanthrene and iodine from aqueous solutions.

Co-solute significantly enhanced the sorption affinity of phenanthrene and iodine by bacterial biomass.