AgII doped MIL-101 and its adsorption of iodine with high speed in solution

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.

Efficient Iodine Removal by Porous Biochar-Confined Nano-Cu2O/Cu0: Rapid and Selective Adsorption of Iodide and Iodate Ions

Iodine is a nuclide of crucial concern in radioactive waste management. Nanomaterials selectively adsorb iodine from water; however, the efficient application of nanomaterials in engineering still needs to be developed for radioactive wastewater deiodination. Artemia egg shells possess large surface groups and connecting pores, providing a new biomaterial to remove contaminants. Based on the Artemia egg shell-derived biochar (AES biochar) and in situ precipitation and reduction of cuprous, we synthesized a novel nanocomposite, namely porous biochar-confined nano-Cu₂O/Cu⁰ (C-Cu). The characterization of C-Cu confirmed that the nano-Cu₂O/Cu⁰ was dispersed in the pores of AES biochar, serving in the efficient and selective adsorption of iodide and iodate ions from water. The iodide ion removal by C-Cu when equilibrated for 40 min exhibited high removal efficiency over the wide pH range of 4 to 10. Remarkable selectivity towards both iodide and iodate ions of C-Cu was permitted against competing anions (Cl^-/NO₃^-/SO₄^2-) at high concentrations. The applicability of C-Cu was demonstrated by a packed column test with treated effluents of 1279 BV. The rapid and selective removal of iodide and iodate ions from water is attributed to nanoparticles confined on the AES biochar and pore-facilitated mass transfer. Combining the advantages of the porous biochar and nano-Cu₂O/Cu⁰, the use of C-Cu offers a promising method of iodine removal from water in engineering applications.

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.

Silver-Nanoparticle-Assisted Modulation of NH3 Desorption on MIL-101

Ammonia has recently emerged as a promising hydrogen carrier for renewable energy conversion. Establishing a better understanding and control of ammonia adsorption and desorption is necessary to improve future energy generation. Metal-organic frameworks (MOFs) have shown improved ammonia capacity and stability over conventional adsorbents such as silica and zeolite. However, ammonia desorption requires high temperature over 150 °C, which is not desirable for energy-efficient ammonia reuse and recycling. Here, we loaded silver nanoparticles from 6.6 to 51.4 wt% in MIL-101 (Ag@MIL-101) using an impregnation method to develop an efficient MOF-based hybrid adsorbent for ammonia uptake. The incorporation of metal nanoparticles into MIL-101 has not been widely explored for ammonia uptake, even though such hybrid nanostructures have significantly enhanced catalytic activities and gas sensing capacities. Structural features of Ag@MIL-101 with different Ag wt% were examined using transmission electron microscopy, X-ray powder diffraction, and infrared spectroscopy, demonstrating successful formation of silver nanoparticles in MIL-101. Ag@MIL-101 (6.6 wt%) showed hysteresis in the N2 isotherm and an increase in the fraction of larger pores, indicating that mesopores were generated during the impregnation. Temperature-programmed desorption with ammonia was performed to understand the binding affinity of ammonia molecules on Ag@MIL-101. The binding affinity was the lowest with Ag@MIL-101 (6.6 wt%), including the largest relative fraction in the amount of desorbed ammonia molecules. It was presumed that cooperative interaction between the silver nanoparticle and the MIL-101 framework for ammonia molecules could allow such a decrease in the desorption temperature. Our design strategy with metal nanoparticles incorporated into MOFs would contribute to develop hybrid MOFs that reduce energy consumption when reusing ammonia from storage.

Adsorption of iodine in metal-organic framework materials

Nuclear power will continue to provide energy for the foreseeable future, but it can pose significant challenges in terms of the disposal of waste and potential release of untreated radioactive substances. Iodine is a volatile product from uranium fission and is particularly problematic due to its solubility. Different isotopes of iodine present different issues for people and the environment. 129I has an extremely long half-life of 1.57 × 107 years and poses a long-term environmental risk due to bioaccumulation. In contrast, 131I has a shorter half-life of 8.02 days and poses a significant risk to human health. There is, therefore, an urgent need to develop secure, efficient and economic stores to capture and sequester ionic and neutral iodine residues. Metal-organic framework (MOF) materials are a new generation of solid sorbents that have wide potential applicability for gas adsorption and substrate binding, and recently there is emerging research on their use for the selective adsorptive removal of iodine. Herein, we review the state-of-the-art performance of MOFs for iodine adsorption and their host-guest chemistry. Various aspects are discussed, including establishing structure-property relationships between the functionality of the MOF host and iodine binding. The techniques and methodologies used for the characterisation of iodine adsorption and of iodine-loaded MOFs are also discussed together with strategies for designing new MOFs that show improved performance for iodine adsorption.

Preparation of Halloysite/Ag2O Nanomaterials and Their Performance for Iodide Adsorption

Halloysite/Ag2O (Hal/Ag2O) nanomaterials were prepared by growing Ag2O nanoparticles on the surface of nanotubular halloysite using silver nitrate solution under alkaline conditions. The nanomaterials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption. Good dispersion of Ag2O nanoparticles with average sizes of 6.07 ± 2.5 nm and 8.04 ± 3.8 nm was achieved in the nanomaterials when using different concentrations of alkali. The nanomaterial with 6.36% Ag2O (Hal/Ag2O-2) exhibited rapid adsorption to iodide (I−); adsorption equilibrium can be reached within 100 min. The adsorption capacity of I− on Hal/Ag2O-2 is 57.5 mg/g, which is more than 143 times higher than that of halloysite. The nanomaterial also showed a better adsorption capacity per unit mass of Ag2O due to the better dispersion and less coaggregation of Ag2O in the nanomaterial than in the pure Ag2O nanoparticles. Importantly, Hal/Ag2O-2 exhibited high selectivity for I−, and its I− removal efficiency was hardly affected by the coexistence of Cl−, Br−, or SO42−, as well as the initial pH of the solution. With an excellent adsorption performance, the prepared Hal/Ag2O nanomaterial could be a new and efficient adsorbent capable of the adsorption of radioactive I− from aqueous solution.

Impact of Structural Functionalization, Pore Size, and Presence of Extra-Framework Ions on the Capture of Gaseous I2 by MOF Materials

A computational approach is used on MOF materials to predict the structures showing the best performances for I2 adsorption as a function of the functionalization, the pore size, the presence of the compensating ions, and the flexibility on which to base future improvements in selected materials in view of their targeted application. Such an approach can be generalized for the adsorption of other gases or vapors. Following the results from the simulations, it was evidenced that the maximum capacity of I2 adsorption by MOF solids with longer organic moieties and larger pores could exceed that of previously tested materials. In particular, the best retention performance was evidenced for MIL-100-BTB. However, if the capacity to retain traces of gaseous I2 on the surface is considered, MIL-101-2CH3, MIL-101-2CF3, and UiO-66-2CH3 appear more promising. Furthermore, the impact of temperature is also investigated.

Cu-Zn bimetal ZIFs derived nanowhisker zero-valent copper decorated ZnO nanocomposites induced oxygen activation for high-efficiency iodide elimination

Studies on the elimination of iodide anions (I^-) by Cu-based adsorbents have been conducted for decades, however its unsatisfactory adsorption performance and its non-reusability are still the main obstacles for large-scale practical applications. Here, an efficient technique was proposed for the elimination of iodide using nanowhisker zero-valent copper (nwZVC) decorated ZnO nanocomposites obtained by two steps pyrolysis of Cu-Zn bimetal ZIFs precursors. The as-synthesized materials were extensively characterized and the results clearly revealed that nanoscale ZVC were well-dispersed in the ZnO matrix, and the morphology and the amount of nanoscale ZVC could be tuned by adjusting the molar ratio of Cu/Zn in ZIF precursors. The following batch adsorption experiments demonstrated that the resultant materials exhibited high adsorption capacity of 270.8 mg g^-1 under condition of adequate oxygen, as well as high selectivity, strong acidity resistance and an excellent reusability. The mechanism investigations revealed that the elimination of I^- by as-fabricated materials involved adsorption process coupled with oxidation, and the existence of nwZVC was responsible for this since nwZVC could activate molecular oxygen to generate H₂O₂ accompanied by the release of Cu⁺, thus leading to I^- adsorbed by the released Cu⁺ and oxidized by the H₂O₂.

Zinc-based triazole metal complexes for efficient iodine adsorption in water

Radioactive iodine is extremely harmful to the environment, and it is of great significance to develop materials that efficiently remove iodine. We prepared two triazole metal complexes with simple method, denoted as Zn(tr)(OAc) and Zn(ttr)(OAc), which were used to adsorb iodine from aqueous solution. The properties and adsorption mechanism of the two materials were studied by different techniques including XRD, SEM, N2 porosimetry at 77 K, FTIR, TGA, elemental analysis (EDS), and X-ray photoelectron spectroscopy (XPS). The results showed that both materials had good water and thermal stability. Pseudo-second-order kinetic model was better at describing the iodine adsorption kinetics onto the adsorbents. It was proved that chemical adsorption dominated, iodine mainly enriched on the materials in the form of I3-1. Zn(ttr)(OAc) had a higher adsorption capacity than Zn(tr)(OAc) due to the electron-donating group -NH2. The maximum adsorption capacity of the two materials for iodine reached 714.501 mg·g-1 and 846.108 mg·g-1 at 25 °C.

Low-sintering-temperature borosilicate glass to immobilize silver-coated silica-gel with different iodine loadings

To better deal with the radioactive iodine generated during the development of nuclear energy, B₂O₃, Bi₂O₃, ZnO, and SiO₂ were used to sinter borosilicate glass for the immobilization of iodine. The effect of B₂O₃ on glass formation was discussed by changing the molar ratio of B₂O₃ in the matrix. When B₂O₃ content is 50 mol% and sintering temperature is 600 ℃, the amorphous degree of quaternary glass is the highest. The sintered body with the highest degree of amorphous was selected to study radioactive iodine. Then, the effects of different iodine loading concentrations for sintering borosilicate glass in terms of microstructure and phase change were discussed. With the increase in iodine content on silica-gel, the degree of amorphous of the specimens presented a decreasing trend, and there are obvious SiO₂ peaks. When the content was 20 wt.%-30 wt.%, a large number of new phases were generated. When the iodine content is 20 wt.%, in addition to the enrichment of Si and O elements, the elemental distribution for B, Bi, Zn, I, and Ag was even. TEM results also showed that there was a crystalline phase in the sinter.

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.

Surface Interactions and Mechanisms Study on the Removal of Iodide from Water by Use of Natural Zeolite-Based Silver Nanocomposites

In this work a natural zeolite was modified with silver following two different methods to derive Ag2O and Ag0 nanocomposites. The materials were fully characterized and the results showed that both materials were decorated with nanoparticles of size of 5-25 nm. The natural and modified zeolites were used for the removal of iodide from aqueous solutions of initial concentration of 30-1400 ppm. Natural zeolite showed no affinity for iodide while silver forms were very efficient reaching a capacity of up to 132 mg/g. Post-adsorption characterizations showed that AgI was formed on the surface of the modified zeolites and the amount of iodide removed was higher than expected based on the silver content. A combination of experimental data and characterizations indicate that the excess iodide is most probably related to negatively charged AgI colloids and Ag-I complexes forming in the solution as well as on the surface of the modified zeolites.

Preparation and Applications of Metal-Organic Frameworks (MOFs): A Laboratory Activity and Demonstration for High School and/or Undergraduate Students

The chemistry of metal-organic frameworks (MOFs), a new class of emerging crystalline porous solids with three-dimensional (3D) networks composed of metals and multidentate organic molecules, was introduced by using three differently-shaped crystals. We reported new and mild MOF synthesis methods that are simple and devised to be performed in high school or primarily undergraduate school settings. MOF applications were demonstrated by use of our synthesized MOFs in the capture of iodine as a potentially hazardous molecule from solution and as a drug delivery system. These applications can be visually confirmed in minutes. Students can gain knowledge on advanced topics, such as drug delivery systems, through these easy-to-prepare MOFs. Furthermore, students can gain an understanding of powder X-ray analysis and ultraviolet-visible near-infrared spectroscopy. This laboratory experience is practical, including synthesis and application of MOFs. The entire experiment has also been recorded as an educational video posted on YouTube as a free public medium for students to watch and learn. In this article we first report the steps we took to synthesize and analyze the MOFs, followed by a description of a simple demonstration that we verified to effectively exhibit adsorption by MOFs. We conclude with a description of how the laboratory activity and demonstration was implemented in an undergraduate chemistry laboratory.

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.

Halide removal from water using silver doped magnetic-microparticles

This study proposes the use of new materials based on core-shell structure magnetic microparticles with Ag⁰ (Ag(0)-MPs) on their surface to remove bromides and chlorides from waters intended for human consumption. Hydrogen peroxide was used as oxidizing agent, Ag(0)-MPs is thereby oxidized to Ag (I)-MPs, which, when in contact with Cl^- and Br^- ions, form the corresponding silver halide (AgCl and AgBr) on the surface of Ag-MPs. The concentration of Cl^- and Br^- ions was followed by using ion selective electrodes (ISEs). Silver microparticles were characterized by high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy, while the presence of AgCl and AgBr on Ag-MPs was determined by microanalysis. We analyzed the influence of operational variables, including: hydrogen peroxide concentration in Ag-MP system, medium pH, influence of Cl^- ions on Br^- ion removal, and influence of tannic acid as surrogate of organic matter in the medium. Regarding the influence of pH, Br^-and Cl^- removal was constant within the pH range studied (3.5-7), being more effective for Br^- than for Cl^- ions. Accordingly, this research states that the system Ag-MPs/H₂O₂ can remove up to 67.01% of Br^- ions and 56.92% of Cl^- ions from water (pH = 7, [Ag-MPs]₀ = 100 mg L^-1, [H₂O₂]₀ = 0.2 mM); it is reusable, regenerated by radiation and can be easily removed by applying a magnetically assisted chemical separation process.

Removal of iodide from water using silver nanoparticles-impregnated synthetic zeolites

Synthetic zeolite-based Ag-nanocomposites were synthesized, characterized and used to remove iodide from aqueous solutions. The results showed high removal efficiency (up to 94.85%) and the formation silver iodide which is stable into the material. The maximum achieved adsorption capacity of the nanocomposites was between 19.54 and 20.44mg/g. The removal mechanism was meticulously studied by taking into account both water chemistry and surface interactions backed by multiple characterization techniques, such as XRD, XRF, SEM/EDX, TEM and BET. The qualitative and quantitative examination of pre- and post-adsorption of nanocomposite samples proved that the anchored silver iodide was formed via oxidation of initial silver nanoparticles followed by reaction with iodide to form a stable crystalline precipitate on the surface of the materials. A diffusion-based adsorption model indicated that the controlling mechanism is a slow intraparticle surface diffusion with diffusion coefficients in the range of 0.37-1.72×10^-13cm²/s. The investigation of competing and co-existing anions (Cl^-, Br^-, CO₃^2-, and CrO₄^2-) on the removal efficiency of iodide demonstrated a negligible effect showing a kinetically favorable precipitation reaction of iodide over other anions.

Visualization of Iodine Chemisorption Facilitated by Aryl C-H Bond Activation

The ability to chemisorb iodine is important for the safe long-term storage of fission products from nuclear reactors. Herein, we successfully used single-crystal X-ray diffraction analysis to crystallographically visualize I₂ binding sites in two isostructural metal-organic frameworks, viz. Co₂(m-DOBDC) (m-DOBDC^4- = 4,6-dioxo-1,3-benzenedicarboxylate) and Co₂(p-DOBDC) (p-DOBDC^4- = 2,5-dioxo-1,4-benzenedicarboxylate), with increasing I₂ loading. Interestingly, the C-H bond at the electron-rich carbon (C5) of m-DOBDC^4- is activated toward electrophilic aromatic substitution, forming an aryl C-I bond and I^- or I₃^- that coordinates to unsaturated open Co sites. Cooperation between the ligand and the open Co sites leads to rapid chemisorption of I₂ even under mild adsorption conditions, such as room temperature. In contrast, molecular I₂ coordinates to the open Co sites of Co₂(p-DOBDC). Owing to the chemisorption of I₂, I₂@Co₂(m-DOBDC) decomposes at a much higher temperature than I₂@Co₂(p-DOBDC), as revealed by thermogravimetric analysis.

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.

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.

Magnetite nanoparticles supported on organically modified montmorillonite for adsorptive removal of iodide from aqueous solution: Optimization using response surface methodology

Magnetite nanoparticles supported on organically modified montmorillonite (MNP-OMMTs) were successfully synthesized by a facile coprecipitation method. The surface of natural clay was modified using a cationic surfactant, hexadecyltrimethylammonium. The synthesized MNP-OMMTs were used as an adsorbent to remove iodide from aqueous solutions. The maximum adsorption capacity of the adsorbent was 322.42mg/g, which is much higher than other previously reported adsorbents for removing iodide in aqueous solution. The experimental data were well fitted to a pseudo-second-order kinetic model, and the adsorption behavior followed the Langmuir isotherm. A thermodynamic study indicated that iodide adsorption was spontaneous and endothermic. The individual and combined effects of key process parameters (pH, temperature, and initial iodide concentration) were studied using a response surface methodology. The maximum iodide removal efficiency of 93.81% was obtained under the optimal conditions of pH3.9, a temperature of 41.3°C, and an initial iodide concentration of 113.8mg/L.

Novel N-rich porous organic polymers with extremely high uptake for capture and reversible storage of volatile iodine

The imino group-contained porous organic polytriphenylamine, which originated from diphenylamine and 1,3,5-tris(4-bromophenyl)benzene, was designedly synthesized though Buchwald-Hartwig coupling reaction. The basic properties including morphologies, structure and thermal stability of the resulting POPs were investigated by scanning electron microscope(SEM), thermo gravimeter analysis (TGA), ¹³C CP/MAS solid state NMR and Fourier transform infrared spectroscope (FTIR). The pore size distribution of POPs present uniform mesoporous of sizes less than 50nm. Scanning electron microscope images show that the resulting POPs formed as an aggregation composed of nanospheres. The POPs were employed as a physicochemical stable porous medium for removal of radioactive iodine and an iodine uptake of up to 382wt% was obtained. To our knowledge, this is one of the highest adsorption value reported to date. Based on these findings, the resulting POPs shows great potential in the removal of radioactive iodine at different states, through a green, environmentally friendly, and sustainable way.

Bimetallic AgCu/Cu2O hybrid for the synergetic adsorption of iodide from solution

To further improve the capacity of Cu₂O to absorb I^- anions from solution, and to understand the difference between the adsorption mechanisms of Ag/Cu₂O and Cu/Cu₂O adsorbents, bimetallic AgCu was doped into Cu₂O through a facile solvothermal route. Samples were characterized and employed to adsorb I^- anions under different experimental conditions. The results show that the Cu content can be tuned by adding different volumes of Ag sols. After doping bimetallic AgCu, the adsorption capacity of the samples can be increased from 0.02 mmol g^-1 to 0.52 mmol g^-1. Moreover, the optimal adsorption is reached within only 240 min. Meanwhile, the difference between the adsorption mechanisms of Ag/Cu₂O and Cu/Cu₂O adsorbents was verified, and the cooperative adsorption mechanism of the AgCu/Cu₂O hybrid was proposed and verified. In addition, the AgCu/Cu₂O hybrid showed excellent selectivity, e.g., its adsorption efficiencies are 85.1%, 81.9%, 85.9% and 85.7% in the presence of the Cl^-, CO₃^2-, SO₄^2- and NO₃^- competitive anions, respectively. Furthermore, the AgCu/Cu₂O hybrid can worked well in other harsh environments (e.g., acidic, alkaline and seawater environments). Therefore, this study is expected to promote the development of Cu₂O into a highly efficient adsorbent for the removal of iodide from solution.

Synthesis of Cu/Cu2O hydrides for enhanced removal of iodide from water

In order to improve the removal capacity of Cu₂O for I^- anions from water, Cu/Cu₂O hybrids have been synthesized through a facile hydrothermal route, characterized by using SEM, XRD, XPS, and applied to remove I^- anions under different experimental environments. The results demonstrate that the Cu content and morphology of samples can be tuned by the adding amount of ammonia. Meanwhile, the possible crystalline mechanism, Cu₂O formed firstly and then metallic Cu generated, was presented. With the increasing of Cu doped amount, the removal capacity of Cu/Cu₂O hybrids increased significantly from 0.02mmolg^-1 to 0.18mmolg^-1. Furthermore, a reaction mechanism of I^- anions and Cu₂O, which generated from the disproportionation reaction of metallic Cu and CuO, has been proposed according to the characterization analyses of the composites before and after adsorption, explaining the highly efficient removal of I^- anions. In addition, Cu/Cu₂O hybrids showed excellent selectivity for I^- anions in the presence of large concentrations of competitive anions such as SO₄^2- and NO₃^- and could work in an acidic and neutral environment. This study is hopefully to prompt Cu₂O to grow up to be a new and highly efficient adsorbent for the removal of iodide from solutions.

Enhanced uptake of iodide on Ag@Cu2O nanoparticles

In order to improve the uptake capacity of Cu₂O for I^- anions from water, Ag loaded Cu₂O composites have been synthesized through a facile method, characterized using SEM, XRD, XPS and applied to remove I^- anions under different experimental environments. The results show that the uptake capacity of Ag@Cu₂O increased with the increasing Ag doped amount. Meanwhile, the uptake capacity (0.20 mmol g^-1) of 1.0%-Ag@Cu₂O for the removal of I^- anions is ten times higher than that of pure Cu₂O (0.02 mmol g^-1). Furthermore, a mechanism explaining the highly efficient removal of I^- anions has been proposed according to characterization analyses of the composites after adsorption and subsequently been verified by adsorption under visible light experiments. 1.0%-Ag@Cu₂O (0.5%-Ag@Cu₂O, 0.2%-Ag@Cu₂O) shows a high iodide uptake efficiency of 98.5% (77.6%, 37.8%) in the visible light, much higher than that under the darkness (86.3%, 69.7% and 30.8%). In addition, the adsorbent showed excellent selectivity for I^- anions in the presence of large concentrations of competitive anions, eg. uptake efficiencies are 78.2%, 62.8%, 70.2% and 77.9% in the presence of the Cl^-, CO₃^2-, SO₄^2- and NO₃^- competitive anions, respectively, and could work in a wide pH range of 3-11. This study is hopefully to prompt Cu₂O to become a new and highly efficient adsorbent for iodide adsorb from solutions.