Adsorption of cesium from aqueous solution using agricultural residue--walnut shell: equilibrium, kinetic and thermodynamic modeling studies

BTXs removals by modified clay during mitigation of Karenia brevis bloom: Insights from adsorption and transformation

Harmful algal blooms (HABs), especially those caused by toxic dinoflagellates, are spreading in marine ecosystems worldwide. Notably, the prevalence of Karenia brevis blooms and potent brevetoxins (BTXs) pose a serious risk to public health and marine ecosystems. Therefore, developing an environmentally friendly method to effectively control HABs and associated BTXs has been the focus of increasing attention. As a promising method, modified clay (MC) application could effectively control HABs. However, the environmental fate of BTXs during MC treatment has not been fully investigated. For the first time, this study revealed the effect and mechanism of BTX removal by MC from the perspective of adsorption and transformation. The results indicated that polyaluminium chloride-modified clay (PAC-MC, a typical kind of MC) performed well in the adsorption of BTX2 due to the elevated surface potential and more binding sites. The adsorption process was a spontaneous endothermic process that conformed to pseudo-second-order adsorption kinetics (k2 = 6.8 × 10-4, PAC-MC = 0.20 g L-1) and the Freundlich isotherm (Kf = 55.30, 20 °C). In addition, detailed product analysis using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) indicated that PAC-MC treatment effectively removed the BTX2 and BTX3, especially those in the particulate forms. Surprisingly, PAC-MC could promote the transformation of BTX2 to derivatives, including OR-BTX2, OR-BTX3, and OR-BTX-B5, which were proven to have lower cytotoxicity.

Tuning microscopic structure of La-MOFs via ligand engineering effect towards enhancing phosphate adsorption

The selection of different organic ligands when synthesizing metal organic framework (MOFs) can change their effects on the adsorption performance. Here, four La-MOFs adsorbents (La-SA, La-FA, La-TA and La-OA) with different organic ligands and structures were synthesized by solvothermal method for phosphate adsorption, and the relationship between their adsorption properties and structures was established. Among four La-MOFs, their phosphate adsorption capacities and adsorption rates followed La-SA > La-FA > La-TA > La-OA. The results indicated that average pore diameter played a key role in phosphate adsorption and there was a positive correlation between average pore diameter and adsorption capacity (R2 = 0.86). Coexisting ion experiments showed that phosphate adsorptions on three La-MOFs (La-SA, La-FA and La-TA) were inhibited in the presence of CO32- and HCO3-. The inhibition of CO32- was the most pronounced and the results of redundancy analysis pointed out that it was mainly due to the change of pH value. In contrast, La-OA showed enhanced phosphate adsorption in the presence of CO32- and HCO3-, and the combination of pH experiments showed that phosphate adsorption by La-OA was increased under alkaline conditions. Further combined with FT-IR, XRD, high resolution energy spectra of XPS (La 3d, P 2p and O 1s) and XANES, the adsorption mechanisms were derived electrostatic attraction, chemical precipitation and inner sphere complexation, and the last two were identified as the main mechanisms. Moreover, it can be identified from XPS 2p that the phosphate adsorption on La-FA and La-OA were mainly in the LaPO4 state, while La-SA and La-TA mainly existed in the form of LaPO4·xH2O crystals and inner sphere complexes. From the perspective of material morphology, this work provides a thought for the rational design of MOFs with adjustable properties for phosphate adsorption.

Magnetic Prussian blue nanoshells are controllable anchored on the surface of molybdenum disulfide nanosheets for efficient separation of radioactive cesium from water

The rapid development of nuclear energy in China has led to increased attention to the treatment of radioactive wastewaters. Herein, a novel magnetic adsorbent, magnetic Prussian blue‑molybdenum disulfide (PB/Fe3O4/MoS2) nanocomposite, was prepared by a simple in-situ fixation of ferric oxide nanoparticles (Fe3O4 NPs) and Prussian Blue (PB) shell layers on the surface of molybdenum disulfide (MoS2) nanosheets carrier. The prepared PB/Fe3O4/MoS2 nanocomposites adsorbent displayed excellent fast magnetic separation and adsorption capacity of Cs+ (Qm = 80.51 mg/g) from water. The adsorption behavior of Cs+ by PB/Fe3O4/MoS2 conformed to Langmuir isothermal and second-order kinetic model, which belonged to chemical adsorption and endothermic reaction. The equilibrium adsorption capacity of PB/Fe3O4/MoS2 to Cs+ has reached 90 % in less than 110 min. Moreover, the adsorption properties of PB/Fe3O4/MoS2 remained good in the pH range of 2-7. Based on this, PB/Fe3O4/MoS2 complex was a fast and high selectivity adsorption material for Cs+, which was expected to be used in the practical treatment of cesium-containing radioactive wastewater.

Zein-enhanced sodium alginate/thiostannate microsphere adsorbent Zein@SA/KBS for efficient removal of cesium from wastewater

Although efficient removal of Cs from wastewater is of great importance because of the nuclear energy sustainable development and public health, removing cesium is challenging for the high concentrations of sodium and potassium ions coexist. In this work, we synthesized the first novel bismuth-doped layered tin sulfide (KBS) and applied it to the efficient green adsorption of liquid cesium resources. KBS could reach the adsorption equilibrium for Cs+ within only 2 min with a theoretical adsorption capacity of 425.55 mg/g. Furthermore, the adsorption performance remained reliable after 10 cycles of use. The structure and properties of KBS were explained at the molecular level by DFT calculations, and the calculated results were in sound agreement with the experimental data. Meanwhile, in this study, the material was reinforced and shaped by the electrostatic interaction of Zein and sodium alginate hydrogel, and finally, Zein@SA/KBS spherical composite adsorbent was obtained. The problem of the difficult recovery of adsorbent and the secondary contamination was solved. The adsorption performance of Zein@SA/KBS on Cs+ was better than most composite adsorbents and showed reliable stability. Therefore, the new microspherical adsorbent (Zein@SA/KBS) has great potential for industrial application in removing radioactive cesium from wastewater.

Layered metal sulfides with MaSbc- framework (M = Sb, In, Sn) as ion exchangers for the removal of Cs(Ⅰ) and Sr(Ⅱ) from radioactive effluents: a review

Nuclear power has emerged as a pivotal contributor to the global electricity supply owing to its high efficiency and low-carbon characteristics. However, the rapid expansion of the nuclear industry has resulted in the production of a significant amount of hazardous effluents that contain various radionuclides, such as 137Cs and 90Sr. Effectively removing 137Cs and 90Sr from radioactive effluents prior to discharge is a critical challenge. Layered metal sulfides exhibit significant potential as ion exchangers for the efficient uptake of Cs+ and Sr2+ from aqueous solutions owing to their open and exchangeable frameworks and the distinctive properties of their soft S2- ligands. This review provides a detailed account of layered metal sulfides with MaSb c- frameworks (M = Sb, In, Sn), including their synthesis methods, structural characteristics, and Cs+ and Sr2+ removal efficiencies. Furthermore, we highlight the advantages of layered metal sulfides, such as their relatively high ion exchange capacities, broad active pH ranges, and structural stability against acid and radiation, through a comparative evaluation with other conventional ion exchangers. Finally, we discuss the challenges regarding the practical application of layered metal sulfides in radionuclide scavenging.

Fracture Resistance Biomechanisms of Walnut Shell with High-Strength and Toughening

Walnut shell is lightweight material with high-strength and toughening characteristics, but it is different from other nut shells' microstructure with two or three short sclerotic cell layers and long bundle fibers. It is essential to explore the fracture resistance biomechanism of lightweight walnut shell and how to prevent damage of bionic structure. In this study, it is found that the asymmetric mass center and geometric center dissipated impact energy to the whole shell without loading concentration in the loading area. Diaphragma juglandis is a special structure improved walnut shell's toughening. The S-shape gradient porosity/elastic modulus distribution combined with pits on single auxetic sclerotic cells requires higher energy to crack expansion, then decreases its fracture behavior. These fantastic findings inspire to design fracture resistance devices including helmets, armor, automobile anti-collision beams, and re-entry capsule in spacecraft.

The latest research trends in the removal of cesium from radioactive wastewater: A review based on data-driven and visual analysis

The widespread adoption of nuclear energy has increased the amount of radioactive cesium (Cs) that is discharged into waste streams, which can have environmental risks. In this paper, we provide a comprehensive summary of current advances in aqueous Cs removal by employing a bibliometric analysis. We collected 1580 articles related to aqueous Cs treatment that were published on the Web of Science database between 2012 and 2022. By applying bibliometric analysis combined with network analysis, we revealed the research distribution, knowledge base, research hotspots, and cutting-edge technologies in the field of aqueous Cs removal. Our findings indicate that China, Japan, and South Korea are the most productive countries with respect to Cs removal research. In addition, both historic events and environmental threats might have contributed to research in Asian countries having a higher focus on Cs removal as well as strong international cooperation between Asian countries. A detailed keyword analysis reveals the main knowledge base for aqueous Cs removal and highlights the potential of the adsorption-based method for treating Cs contamination. Furthermore, the results reveal that exploration of functional materials is a popular research topic in the field of Cs removal. Since 2012, novel materials, including Prussian blue, graphene oxide, hydrogel and nanocomposites, have been widely investigated because of their high capacity for Cs removal. On the basis of the detailed information, we report the latest research trends on aqueous Cs removal, and propose future research directions and describe the challenges related to effective Cs treatment. This scientometric review provides insights into current research hotspots and cutting-edge trends in addition to contributing to the development of this crucial research field.

Adsorption and separation of Cs(I) and Ba(II) from aqueous solution using zinc ferrite-humic acid nanocomposite

Reclaimable adsorbents have an essential role in removing radionuclides from waste streams. Herein, zinc ferrite-humic acid ZFO/HA nanocomposite was synthesized for effective cesium and barium adsorption. The prepared ZFO/HA nanocomposite was analyzed using analytical techniques including XRD, FTIR, EDX, and SEM. From kinetic studies, the mechanism adsorption process follows the second model. The isotherm studies clarified that the Langmuir model fit the adsorption of both ions onto the prepared sample, and the monolayer capacities are equal to 63.33 mg/g and 42.55 mg/g for Ba(II) and Cs(I), respectively. The temperature parameter was also studied, and the adsorption reaction was spontaneous and endothermic. The maximum separation between two ions was achieved at pH 5 (αCs/Ba = 3.3).

Comparative study of ZIF-8-materials for removal of hazardous compounds using physio-chemical remediation techniques

The inherent toxicity, mutagenicity and carcinogenicity of dyes that are discharged into aquatic ecosystems, harming the health of humans and animals. ZIF-8 based composites are regarded as good adsorbents for the breakdown of dyes in order to remove or degrade them. In the course of this research, metal-organic framework materials known as ZIF-8 and its two stable composites, ZIF-8/BiCoO₃ (MZBC) and ZIF-8/BiYO₃ (MZBY), were produced via a hydrothermal process and solvothermal process, respectively, for the dangerous Congo red (CR) dye removal from the solution in water using adsorption method. According to the findings, the most significant amount of CR dye that could be adsorbed is onto MZBC, followed by MZBY and ZIF-8. The pseudo-second-order kinetic model was used effectively to match the data for adsorption behavior and was confirmed using the Langmuir isotherm equation. There is a possibility that the pH and amount of adsorbent might influence the adsorption behavior of the adsorbents. According to the experiment results, the technique featured an endothermic adsorption reaction that spontaneously occurred. The higher adsorption capability of MZBC is because of the large surface area. This results in strong interactions between the functional groups on the surface of MZBC and CR dye molecules. In addition to the electrostatic connection between functional group Zn-O-H on the surface of ZIF-8 in MZBC and the -NH₂ or SO₃ functional group areas in CR molecules, it also includes the strong π-π interaction of biphenyl rings.

Juglans regia Linn.: A Natural Repository of Vital Phytochemical and Pharmacological Compounds

Juglans regia Linn. is a valuable medicinal plant that possesses the therapeutic potential to treat a wide range of diseases in humans. It has been known to have significant nutritional and curative properties since ancient times, and almost all parts of this plant have been utilized to cure numerous fungal and bacterial disorders. The separation and identification of the active ingredients in J. regia as well as the testing of those active compounds for pharmacological properties are currently of great interest. Recently, the naphthoquinones extracted from walnut have been observed to inhibit the enzymes essential for viral protein synthesis in the SARS-CoV-2. Anticancer characteristics have been observed in the synthetic triazole analogue derivatives of juglone, and the unique modifications in the parent derivative of juglone have paved the way for further synthetic research in this area. Though there are some research articles available on the pharmacological importance of J. regia, a comprehensive review article to summarize these findings is still required. The current review, therefore, abridges the most recent scientific findings about antimicrobial, antioxidant, anti-fungal, and anticancer properties of various discovered and separated chemical compounds from different solvents and different parts of J. regia.

One-Step Pyrolysis of Nitrogen-Containing Chemicals and Biochar Derived from Walnut Shells to Absorb Polycyclic Aromatic Hydrocarbons (PAHs)

The pyrolysis of biomass is an efficient means of utilizing biomass resources. Biomass can be converted into various high-performance chemicals and functional materials through pyrolysis. However, current pyrolysis technologies suffer from low conversion rates and single products, so the preparation of nitrogen compounds with high economic value remains a challenge. The walnut shell was soaked in three nitrogen-containing compound solutions before carbonization to produce high-value-added nitrogen-containing chemicals (with a nitrogen content of 59.09%) and biochar for the adsorption of polycyclic aromatic hydrocarbons (PAHs). According to biochar analysis, biochar has a porous structure with a specific surface area of 1161.30 m²/g and a high level of rocky desertification. The surface forms a dense pyrrole structure, and the structure produces π-π interactions with naphthalene molecules, exhibiting excellent naphthalene adsorption with a maximum capacity of 214.98 mg/g. This study provides an efficient, rapid, and environmentally friendly method for producing nitrogen-containing chemicals with high-added value and biochar.

Designer biochar with enhanced functionality for efficient removal of radioactive cesium and strontium from water

Radioactive elements released into the environment by accidental discharge constitute serious health hazards to humans and other organisms. In this study, three gasified biochars prepared from feedstock mixtures of wood, chicken manure, and food waste, and a KOH-activated biochar (40% food waste + 60% wood biochar (WFWK)) were used to remove cesium (Cs⁺) and strontium (Sr²⁺) ions from water. The physicochemical properties of the biochars before and after adsorbing Cs⁺ and Sr²⁺ were determined using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, extended X-Ray absorption fine structure (EXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). The WFWK exhibited the highest adsorption capacity for Cs⁺ (62.7 mg/g) and Sr²⁺ (43.0 mg/g) among the biochars tested herein. The removal of radioactive ¹³⁷Cs and ⁹⁰Sr exceeded 80% and 47%, respectively, in the presence of competing ions like Na⁺ and Ca²⁺. The functional groups present in biochar, including -OH, -NH₂, and -COOH, facilitated the adsorption of Cs⁺ and Sr²⁺. The Cs K-edge EXAFS spectra revealed that a single coordination shell was assigned to the Cs-O bonding at 3.11 Å, corresponding to an outer-sphere complex formed between Cs and the biochar. The designer biochar WFWK may be used as an effective adsorbent to treat radioactive ¹³⁷Cs- and ⁹⁰Sr-contaminated water generated during the operation of nuclear power plants and/or unintentional release, owing to the enrichment effect of the functional groups in biochar via alkaline activation.

A Review of the Role of Extracellular Polymeric Substances (EPS) in Wastewater Treatment Systems

A review of the characterization and functions of extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems is presented in this paper. EPS represent the complex high-molecular-weight mixture of polymers excreted by microorganisms generated from cell lysis as well as adsorbed inorganic and organic matter from wastewater. EPS exhibit a three-dimensional, gel-like, highly hydrated matrix that facilitates microbial attachment, embedding, and immobilization. EPS play multiple roles in containments removal, and the main components of EPS crucially influence the properties of microbial aggregates, such as adsorption ability, stability, and formation capacity. Moreover, EPS are important to sludge bioflocculation, settleability, and dewatering properties and could be used as carbon and energy sources in wastewater treatment. However, due to the complex structure of EPS, related knowledge is incomplete, and further research is necessary to understand fully the precise roles in biological treatment processes.

Treatment of nitrate containing wastewater by adsorption process using polypyrrole-modified plastic-carbon: Characteristic and mechanism

Polypyrrole-modified plastic-carbon (PET-PPy) composite was prepared by using high porosity plastic-carbon materials and a special doping mechanism of polypyrrole to remove nitrate from water to achieve waste recycling. As a result, PET-PPy-500 showed remarkable nitrate adsorption in both acidic and alkaline wastewater. The pseudo-second-order kinetic and Langmuir isotherm models were fit for the nitrate adsorption by PET-PPy-500, and the maximum adsorption capacity predicted by the Langmuir model was 10.04 mg NO₃-N/g (45.18 mg NO₃^-/g) at 30 °C. The ion exchange and electrostatic attraction were the main mechanisms of removing NO₃^- by PET-PPy-500, which was demonstrated by the interface characterization and theoretical calculation. The doped ions (Cl^-) and/or other anions produced by charge transfer interaction were the main exchange ions in the process of NO₃^- adsorption. The main binding sites in the electrostatic adsorption process were nitrogen-containing functional groups, which can be confirmed by the results of XPS and density functional theory (DFT). Furthermore, DFT results also showed that the adsorption of nitrate by PET-PPy was a spontaneous exothermic process, and the adsorption energy at the nitrogen site was the lowest. The findings of this study provide a feasible strategy for the advanced treatment of nitrate containing wastewater.

Sulfur-modified chitosan derived N,S-co-doped carbon as a bifunctional material for adsorption and catalytic degradation sulfamethoxazole by persulfate

N,S-co-doped carbons were synthesized through the calcination of sulfur-modified chitosan for the first time, and utilized as persulfate activators for sulfamethoxazole (SMX) remediation in water. The chitosan and sulfonyl chloride underwent one-step sulfonylation reaction to generate S-modified chitosan. The catalyst NSC-3 showed both excellent adsorption and catalytic oxidation efficiency, corresponding 98.62% removal and 81.34% mineralization rate within 90 min. The rate constant (k_obs) was up to 0.0578 min^-1, with 75.60-folders higher than that of sulfur-free catalyst NC (7.6580 ×10^-4 min^-1). The synergy of N and S contributed to the improvement of removal efficiency. The adsorption and oxidation performance were highly depended on the S/N atomic ratio. At the S/N ratio of 0.18, the maximum adsorption and oxidation capability were obtained. The NSC-3/PS system exhibited outstanding adaptability at the wide pH range from 3.07 to 9.28, while the inhibitory effect occurred at strong basic conditions (pH = 11.01). The thiophene sulfur and structural defects were identified as the catalytic sites in activating PS. Both radical and non-radical pathways were responsible for degradation process, where ¹O₂ played a major role, SO₄^·-exerted a minor contribution, and O₂^·- acts as the precursor for the production of ¹O₂. Another source of ¹O₂ was assigned to the activation of PS by structure defects. This work indicates that N,S-co-doped carbon at an optimal S/N atomic ratio effectively catalyzes persulfate, and provides an innovative method to construct bifunctional carbon materials of adsorption and oxidization.

Chitin/egg shell membrane@Fe3O4 nanocomposite hydrogel for efficient removal of Pb2+ from aqueous solution

The development of adsorbents by using the byproducts or waste from large-scale industrial and agricultural production is of great significance, and is considered to be an economic and efficient strategy to remove the heavy metals from polluted water. In this work, a novel chitin/EM@Fe₃O₄ nanocomposite hydrogel was obtained from a NaOH/urea aqueous system, where the proteins of egg shell membrane and Fe₃O₄ nanoparticles were chemically bonded to chitin polymer chains with the help of epichlorohydrin. Due to the existence of a large number of –NH₂, –OH, –CONH–, –COOH and hemiacetal groups, the adsorption efficiency for Pb²⁺ into the absorbent was dramatically enhanced. The experimental results revealed that the adsorption behavior strongly depends on various factors, such as initial pH, initial Pb²⁺ concentration, incubation temperature and contact time. The kinetic experiments indicated that the adsorption process for Pb²⁺ in water solution agreed with the pseudo-second-order kinetic equation. The film diffusion or chemical reaction is the rate limiting process in the initial adsorption stage, and the adsorption of Pb²⁺ into the nanocomposite hydrogel can well fit the Langmuir isotherm. Thermodynamic analysis demonstrated that such adsorption behaviors were dominated by an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

A novel kind of chitin/EM@Fe₃O₄ nanocomposite hydrogel derived from the biowastes of egg shell membrane and chitin was successfully prepared for efficient removal of Pb²⁺ from wastewater solution.

Rapid Cs+ Capture via Multiple Supramolecular Interactions in Anionic Metal-Organic Framework Isomers

Metal-organic frameworks (MOFs) provide an ideal platform for ion exchange due to their high porosity and structural designability; however, developing MOFs that have the essential characteristics for ion exchange remains a challenge. These crucial features include fast kinetics, selectivity, and stability. We present two anionic isomers, DGIST-2 (2D) and DGIST-3 (3D), comprising distinctly arranged 5-(1,8-naphthalimido)isophthalate ligands and In³⁺ cations. Interestingly, in protic solvents, DGIST-2 transforms into a hydrolytically stable crystalline phase, DGIST-2'. DGIST-2' and DGIST-3 exhibit rapid Cs⁺ adsorption kinetics, as well as high Cs⁺ affinity in the presence of competing cations. The mechanism for rapid and selective sorption is explored based on the results of single-crystal X-ray diffraction analysis of Cs⁺-incorporated DGIST-3. In Cs⁺-containing solutions, the loosely incorporated dimethylammonium countercation of the anionic framework is replaced by Cs⁺, which is held in the hydrophobic cavity by supramolecular ion-ion and cation-π interactions.

Preparation and characterization of a newly constructed multifunctional Co(ii)–organic framework: proton conduction and adsorption of Congo red in aqueous medium

The efficient adsorption of CR over Co-MOF 1 as well as the pH-dependent proton-conducting mechanism of the composite Co-MOF–Nafion membrane.

Rapid and selective harvest of low-concentration phosphate by La(OH)3 loaded magnetic cationic hydrogel from aqueous solution: Surface migration of phosphate from -N+(CH3)3 to La(OH)3

Phosphate is an important factor for the occurrence of surface water eutrophication, and is also a non-renewable resource which faces a potential depletion crisis. In this study, La(OH)₃ loaded magnetic cationic hydrogel composite MCH-La(OH)₃-EW was used to absorb low strength phosphate in simulated water and real water. The adsorption amount of MCH-La(OH)₃-EW was 39.14 ± 0.31 mg P/g and the equilibrium time was 120 min at the initial phosphate concentration of 2.0 mg P/L. The adsorption process was a spontaneous endothermic reaction. MCH-La(OH)₃-EW exhibited a high selectivity towards phosphate within pH of 4.0-10.0 or in the presence of co-existing ions (including Cl^-, SO₄^2-, NO₃^-, HCO₃^-, SiO₃^2-) and humic acid. After 10 cycles of adsorption-desorption, the adsorption amount of regenerated MCH-La(OH)₃-EW still remained at 63.4% of its maximum value. For the real water sample with phosphate concentration of 2.0 mg P/L, the phosphate removal efficiency could achieve 97.65-98.90% and the effluent turbidity was 2.10-4.27 NTU at the MCH-La(OH)₃-EW dosage of 0.04 g/L. The adsorption mechanism analysis showed that both quaternary amine groups (-N⁺(CH₃)₃) and La(OH)₃ of MCH-La(OH)₃-EW were involved in the process of phosphate adsorption. The electrostatic interaction between phosphate and -N⁺(CH₃)₃ rapidly occurred at the initial stage of adsorption process, then the electrostatic absorbed phosphate migrated to La(OH)₃ on the surface of MCH-La(OH)₃-EW via ligand exchange to form inner-sphere complex. This phenomenon was conducive to phosphate adsorption kinetics by MCH-La(OH)₃-EW.

Efficient Removal of Pb(II) from Aqueous Medium Using Chemically Modified Silica Monolith

The adsorptive removal of lead (II) from aqueous medium was carried out by chemically modified silica monolith particles. Porous silica monolith particles were prepared by the sol-gel method and their surface modification was carried out using trimethoxy silyl propyl urea (TSPU) to prepare inorganic–organic hybrid adsorbent. The resultant adsorbent was evaluated for the removal of lead (Pb) from aqueous medium. The effect of pH, adsorbent dose, metal ion concentration and adsorption time was determined. It was found that the optimum conditions for adsorption of lead (Pb) were pH 5, adsorbent dose of 0.4 g/L, Pb(II) ions concentration of 500 mg/L and adsorption time of 1 h. The adsorbent chemically modified SM was characterized by scanning electron microscopy (SEM), BET/BJH and thermo gravimetric analysis (TGA). The percent adsorption of Pb(II) onto chemically modified silica monolith particles was 98%. An isotherm study showed that the adsorption data of Pb(II) onto chemically modified SM was fully fitted with the Freundlich and Langmuir isotherm models. It was found from kinetic study that the adsorption of Pb(II) followed a pseudo second-order model. Moreover, thermodynamic study suggests that the adsorption of Pb(II) is spontaneous and exothermic. The adsorption capacity of chemically modified SM for Pb(II) ions was 792 mg/g which is quite high as compared to the traditional adsorbents. The adsorbent chemically modified SM was regenerated, used again three times for the adsorption of Pb(II) ions and it was found that the adsorption capacity of the regenerated adsorbent was only dropped by 7%. Due to high adsorption capacity chemically modified silica monolith particles could be used as an effective adsorbent for the removal of heavy metals from wastewater.

Selective Separation of Radiocesium from Complex Aqueous Matrices Using Dual Solid-Phase Extraction Systems

The release of radiocesium (r-Cs) into natural aqueous systems is of concern because of its extended solubility as an alkaline metal ion and its facile incorporation into living beings. A technique for the selective separation of Cs from an aqueous matrix using dual solid-phase extraction (SPE) systems in a series is proposed in this paper. The SPEs equipped with chelates (Nobias Chelate-PA1 and Nobias Chelate-PB1), an ion-exchange resin (Nobias Ion SC-1), or macrocycles (MetaSEP AnaLig Cs-01 and MetaSEP AnaLig Cs-02) were evaluated in terms of selectivity and retention/recovery behavior toward Cs and other potentially competing ions (Li, Na, K, Rb, Ba, Ca, Mg, and Sr). The simulated solution of ¹³³Cs, a chemical analog of r-Cs, was used to optimize the separation process. Operating parameters such as pH (3-13), flow rate (0.2-5.0 mL min^-1), and elution behavior (HCl, 0.1-5.0 mol L^-1) were optimized to ensure maximum removal of Cs from the aqueous matrices. The dual SPE system comprised Nobias Chelate-PB1 that minimized the competing impact of ions, while selective Cs retention was attained with MetaSEP AnaLig Cs-02. The proposed process was verified using real r-Cs-contaminated water from Fukushima, Japan, to observe the quantitative separation and preconcentration of r-Cs from the complex matrices.

Novel One-Pot Solvothermal Synthesis of High-Performance Copper Hexacyanoferrate for Cs+ Removal from Wastewater

Efficient removal of radioactive cesium from complex wastewater is a challenge. Unlike traditional precipitation and hydrothermal synthesis, a novel vast specific surface area adsorbent of copper hexacyanoferrates named EA-CuHCF was synthesized using a one-pot solvothermal method under the moderate ethanol media characterized by XRD, SEM, EDS, BET, and FTIR. It was found that the maximum adsorption capacity towards Cs+ was 452.5 mg/g, which is far higher than most of the reported Prussian blue analogues so far. Moreover, EA-CuHCF could effectively adsorb Cs+ at a wide pH range and low concentration of Cs+ in geothermal water within 30 minutes, and the removal rate of Cs+ was 92.1%. Finally, the separation factors between Cs+ and other competitive ions were higher than 553, and the distribution coefficient of Cs+ reached up to 2.343 × 104 mL/g. These properties suggest that EA-CuHCF synthesized by the solvothermal method has high capacity and selectivity and can be used as a candidate for Cs+ removal from wastewater.

Prussian blue analogs-based layered double hydroxides for highly efficient Cs+ removal from wastewater

In this work, novel Prussian blue analogs-based layered double hydroxide (PBA@ZnTi-LDH) was in situ synthesized and used for radioactive Cs⁺ removal from wastewater. The results suggested that this PBA@ZnTi-LDH prepared using LDH as skeleton and transition metal source showed higher adsorption capacity (243.9 mg/g) and water stability than conventional PBAs, and promising application in scale-up Cs⁺ removal. Thus, it was granulated by calcium alginate and the PBA@ZnTi-LDH/CaALG exhibited favorable post-separation and fixed-bed adsorption ability at different Cs⁺ concentrations and flow rates, highlighting its application perspective on Cs⁺ removal from various kinds of wastewater. Moreover, the real-world Cs⁺ removal was preliminarily explored using natural complex Cs⁺-containing water. As a result, this stable and easily separated PBA@ZnTi-LDH/CaALG showed high removal efficiency, selectivity and good reusability, which was promising in scale-up Cs⁺ removal from the real-world wastewater.

Radioactive cesium ion removal from wastewater using polymer metal oxide composites

Radioactive cesium ion (Cs-137) removal from wastewater was investigated by novel composite adsorbents, chitosan-bone powder (CS-KT) and chitosan-bone powder-iron oxide (CS-KT-M) at 25 and 50 °C. The characterization of adsorbents was performed by Fourier-Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller and Barrett-Joyner-Hallenda (BET-BJH), and Atomic Force Microscopy (AFM) analyses. While BET surface areas of CS-KT and CS-KT-M adsorbents were found to be 131.5 and 144.9 m²/g, respectively, average pore size and pore volume values were 4.69 nm/0.154 cm³/g and 7.49 nm/0.271 cm³/g, respectively. Amongst Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models, Langmuir model fits well for Cs⁺ ion sorption by these adsorbents. The maximum adsorption capacity obtained from Langmuir adsorption isotherm was 0.98 × 10^-4 mol/g at 25 °C, and 1.16 × 10^-4 mol/g at 50 °C for CS-KT; it was found to be 1.79 × 10^-4 mol/g at 25 °C and 2.24 × 10^-4 mol/g at 50 °C for CS-KT-M. FT-IR analyses showed that Cs⁺ sorption occurs by its interaction with CO₃^2-, PO₄^3- and -NH₂ groups. The average adsorption energy "E" was calculated as ca.11 kJ/mol from D-R adsorption isotherm. The adsorption kinetics was interpreted well by pseudo-second order model.

Prediction and optimization of adsorption properties for Cs+on NiSiO@NiAlFe LDHs hollow spheres from aqueous solution: Kinetics, isotherms, and BBD model

In this work, novel NiSiO@NiAlFe layered double hydroxides (LDHs) hollow spheres were prepared by hydrothermal method. It was worth noting that LDHs' grafting towards NiSiO hollow spheres could avoid the LDHs' aggregation, and thus enhanced the material's adsorption capacity. Furthermore, adsorption kinetics, adsorption isotherms, and Box-Behnken Design (BBD) model were conducted. Results indicated that NiSiO@NiAlFe LDHs hollow spheres had sufficient adsorption capability towards Cs⁺. The adsorption kinetics satisfied the pseudo-second-order adsorption model, Temkin model and Langmuir isotherm model. The adsorption process was efficient at the alkaline condition (pH = 10). The adsorption kinetics indicated that the adsorption process could reach the equilibrium in only 20 min. The maximum adsorption capacity of Cs⁺ towards NiSiO@NiAlFe LDHs hollow spheres was estimated to be 61.5 mg g^-1. Moreover, the adsorption thermodynamics indicated that the adsorption process was exothermal, feasible and spontaneous. Thus, NiSiO@NiAlFe LDHs hollow spheres presented a broad potential for treating cesium containing wastewater.

Dual-functional micro-adsorbents: Application for simultaneous adsorption of cesium and strontium

In current work, Prussian blue (PB)- and hydroxyapatite (HAp)-embedded micro-adsorbents (PB-HAp-MAs) were rationally fabricated through an easy and flexible custom-made micronozzle system as a novel bifunctional adsorbent. The adsorption performance of the as-prepared samples was conducted based on the removal of cesium (Cs⁺) and strontium (Sr²⁺) ions. Adsorption behaviors of the PB-HAp-MAs were also evaluated as function extrusion dimensions and adsorbate concentration. The adsorption isotherm was well fitted by the Langmuir model with adsorption capacities of 24.688 mg g^-1 and 29.254 mg g^-1 for Cs⁺ and Sr²⁺, respectively. Specially, the enhanced adsorption activity can be synergistically attributed to the porous nature of the developed alginate backbone with a high surface area of encapsulated functional nanoparticles, thus leading to rapid saturation within 1 min. In addition, the as-synthesized PB-HAp-MAs were successfully separated from the aqueous solution within 10 s by applying a magnetic field. We expect that our findings will provide valuable guidelines towards developing highly efficient adsorbents for environmental remediation.

Efficient cesium encapsulation from contaminated water by cellulosic biomass based activated wood charcoal

In this study, cost-effective cellulosic biomass based activated wood charcoal was developed from Japanese Sugi tree (Cryptomeria japonica) by concentrated nitric acid modification for adsorption of Cs from contaminated water. The physicochemical properties of specimens were investigated using N₂ adsorption-desorption isotherms (BET method), FESEM, FTIR, and XPS spectra analysis. The experimental results revealed that the surface area of the raw wood charcoal was significantly decreased after boiling nitric acid modification. However, several oxygen-containing acidic function groups (-COOH, -CO) were introduced on the surface. The adsorption study confirmed that the equilibrium contact time was 1 h, the optimum adsorption pH was neutral to alkaline and the suitable adsorbent dose was 1:100 (solid: liquid). The maximum Cs was removed when the concentration of Na and K were lower (5.0 mM) with Cs in solution. The Cs adsorption processes well approved by the Langmuir isotherm and pseudo-second-order kinetic models and the maximum adsorption capacity was 35.46 mgg^-1. The Cs adsorption mechanism was clearly described and it was assumed that the adsorption was strongly followed by chemisorptions mechanism based on the adsorbent surface properties, kinetic model and Langmuir isotherm model. Most importantly, about 98% of volume reduction was obtained by burning (500 °C) the Cs adsorbed charcoal, which ensured safe storage and disposal of radioactive waste. Therefore, this study can offer a guideline to produce a functional adsorbent for effective Cs removal and safe radioactive waste disposal.

Synergistic Adsorption and Oxidation of Ciprofloxacin by Biochar Derived from Metal-Enriched Phytoremediation Plants: Experimental and Computational Insights

Biochar is a promising candidate for the adsorptive removal of organic/inorganic pollutants, yet its role in metal-free catalyzed advanced oxidation processes still remains ambiguous. In this work, five biochar samples (PPBKx, where x represents the pyrolysis temperature) were prepared by using metal-enriched phytoremediation plant residue as the feedstock. Notably, PPBK exhibited a high specific surface area (as high as 1090.7 m² g^-1) and outstanding adsorption capacity toward ciprofloxacin (CIP, as much as 1.51 ± 0.19 mmol g^-1). By introducing peroxymonosulfate (PMS, 5 mM) as the chemical oxidant, over 2 mmol g^-1 CIP was synergistically adsorbed and oxidized within 30 min although PMS itself could not oxidize CIP efficiently, suggesting the formation of reactive oxidative species. Theoretical calculations revealed that PMS anions preferentially adsorbed on the activated C atoms adjacent to the graphitic N dopant, where the carbon matrix served as the electron donor, instead of as an electron mediator. The adsorbed PMS possessed a smaller molecular orbital energy gap, indicating that it was much easier to be activated than free PMS anions. Surface-bound reactive species were elucidated to be the dominant contributor through chemical quenching experiments and electrochemical characterizations. The catalytic activity of PPBK700 could be greatly retained in repeated oxidations because of the stable N species, which serve as the active catalytic sites, while the CIP adsorption was greatly deteriorated because of the diminishing active adsorption sites (carbon matrix edge) caused by the partial oxidation of PMS. This work not only provides a facile and low-cost approach for the synthesis of functional biochar toward environmental remediation but also deepens the understanding of biochar-catalyzed PMS activation and nonradical oxidation.

Effective removal of radioactive cesium from contaminated water by synthesized composite adsorbent and its thermal treatment for enhanced storage stability

A composite adsorbent for the removal of radioactive cesium (¹³⁷Cs) was synthesized by immobilizing potassium cobalt ferrocyanide in the micro pores of the zeolite chabazite. The synthetically optimized composite adsorbent demonstrates a rapid cesium adsorption rate under both salt-free and high-salt conditions with a high distribution coefficient of cesium (≥10⁵ mL/g). Although both components have the same ion-exchange reaction between potassium and cesium, the reaction by ferrocyanide component was predominant, which derived hundred times higher distribution coefficient of the composite adsorbent than that of pure chabazite. A thermal stabilization process was studied for improving the storage and/or disposal stability of the spent adsorbent. The formation of a eutectic system within the spent adsorbent reduced the stabilization temperature to 1000 °C from 1200 °C. Accordingly, the leaching of cesium was remarkably reduced by the remineralization to the stable pollucite. The stable impregnation of ferrocyanide component in the chabazite pores derived the reduction of cesium volatility enabling the high temperature stabilization method. Our experimental results provide evidence that the composite adsorbent has clear advantages on the cesium removal from contaminated water and its stabilization via thermal-treatment.

Isolation and characterization of micro and nanocrystalline cellulose fibers from the walnut shell, corncob and sugarcane bagasse

The present study aims to extract and characterize the microcrystalline cellulose (MCC) present in different agro-industrial wastes such as walnut shells, corncob, and sugarcane bagasse. Moreover, it is also the aim of this study to convert MCCs to nanocrystalline cellulose fiber (NCCF), to demonstrate the difference in morphological, structural, thermal, and chemical natures. Corncob cellulose was observed to possess a loosely bounded linear bundle structure. Nanocrystalline cellulose fiber yield from walnut shell and sugarcane bagasse cellulose were higher than corncob cellulose. The thermal stability of cellulose was noted to be high for walnut shell NCCF. Nanocrystalline cellulose fiber of corncob and sugarcane bagasse was estimated to have a low thermal degradation temperature. All the MCCs and NCCFs produced from investigated cellulose sources were found to have type I cellulose. Functional group compositions of cellulose were observed to be intact for converted agro-based NCCF's.

A potential lignocellulosic biomass based on banana waste for critical rare earths recovery from aqueous solutions

Rare earth elements (REE) present multiple applications in technological devices but also drawbacks (scarcity and water contaminant). The current study aims to valorise the banana wastes - banana rachis (BR), banana pseudo-stem (BPS) and banana peel (BP) as sustainable adsorbent materials for the recovery of REE (Nd³⁺, Eu³⁺, Y³⁺, Dy³⁺ and Tb³⁺). The adsorbent materials were characterized using analytical techniques such as: Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential and scanning electron microscopy with energy dispersive X-ray probe. The adsorption performance and mechanisms were studied by pH dependence, equilibrium isotherms, kinetics, thermodynamics, ion-exchange and desorption evaluation. The results show good adsorption capacities for the three materials, highlighting BR that presents ∼100 mg/g for most of the REE. The adsorption process (100 mg REE/L) reaches the 60% uptake in 8 min and the equilibrium within 50 min. On the other hand, the thermodynamic study indicates that the adsorption is spontaneous and exothermic (ΔH° < 40 kJ/mol). The adsorption mechanism is based on the presence of carboxylic groups that induce electrostatic interactions and facilitate the surface nucleation of REE microcrystals coupled to an ion exchange process as well as the presence of other oxygen containing groups that establish weak intermolecular forces. The recovery of REE from the adsorbent (∼97%) is achieved using EDTA as desorbing solution. This research indicates that banana waste and particularly BR is a new and promising renewable bioresource to recover REE with high adsorption capacity and moderated processing cost.

Highly ordered macroporous silica dioxide framework embedded with supramolecular as robust recognition agent for removal of cesium

Owning to highly mechanical strength and non-interference effectivity, silica dioxide is often explored as a stable supporter commonly with mesopore. It is known that a macroporous framework has larger mass transfer channel, possibly beneficial to adsorption process. Herein highly ordered macroporous silica dioxide framework (homogeneous pore size of 194.20 nm) was synthesized and embedded with supramolecular (CC/OMS). Cs cation adsorption onto CC/OMS was explored under different pH (presence or absence of humic acid), initial cesium concentration, shaking time, competing ions. The robust cesium uptake capacity demonstrated by a theory adsorption amount of 150.01 mg/g highlighted unique CC/OMS properties combining large mass transfer channel and superior complex capacity of supramolecular. The adsorption was well fit with Langmuir and pseudo-second-order model. Sodium and potassium at a lower concentration showed little influence on cesium adsorption. The results demonstrated that CC/OMS was an alternative material for cesium capture from acidic aqueous solution.

Electroactive magnetic microparticles for the selective elimination of cesium ions in the wastewater

To improve operability as well as the removal efficiency for cesium ions in the wastewater treatment, a novel electrochemically switched ion exchange (ESIX) technique by using electroactive Prussian-blue(PB)-based magnetic microparticles (PB@Fe₃O₄ microparticle) with different uniform particle sizes in the range of 300-900 nm as the adsorption materials was developed. The obtained PB@Fe₃O₄ microparticle were characterized by Scanning electron microscopy (SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and Thermogravimetric analysis (TGA). It is found that the PB can be well coated on the surface of Fe₃O₄ microsphere, which can be easily adsorbed on the magnetic electrode substrate for the electrochemical adsorption of Cs⁺ ions. Electrochemical adsorption of 97% Cs⁺ on PB/Fe₃O₄ was achieved in less than 10 min, and the maximum adsorption capacity was 16.13 mg/g, and the distribution coefficient (K_D) of Cs⁺ ions reached as high as 3938. In addition, the electrochemical adsorption behavior of PB@Fe₃O₄ microparticle fitted well with the Freundlich adsorption isotherm and the Pseudo-second-order kinetic models. It is expected that such an ESIX technique using PB@Fe₃O₄ microparticle can be applied for the separation and recovery of dilute Cs⁺ ions from cesium-contaminated solution in a practical process.

Hybrid Pectin-Based Sorbents for Cesium Ion Removal

In this paper, beads-shaped hybrid sorbents composed of pectin and Prussian blue were prepared. Various ratios of pectin and Prussian blue in hybrid sorbents were tested. Obtained sorbents had high and roughly constant sorption capacity in a broad pH range (4–10), in which also the swelling index and stability of sorbents were satisfactory. The preliminary sorption studies proved that almost 100% of cesium removal efficiency may be achieved by using the proper sorbent dose. The sorption capacity of the hybrid sorbent with a 1:1 ratio of pectin to Prussian blue equaled q = 36.5 ± 0.8 mg/g (dose 3 g/L, pH = 6, temp. = 22 ± 1 °C, t = 24 h). The obtained results showed that the prepared hybrid pectin-based sorbents are promising for cesium ions removal.

Low-Spin-State Hematite with Superior Adsorption of Anionic Contaminations for Water Purification

Hematite attracts intensive interest as an adsorbent for water purification, but the oversized dimension and inherent high-spin Fe(III) restrict its adsorption capability and kinetics. Herein a spatial-confinement strategy is reported that synthesizes ultrafine α-Fe₂ O₃ benefiting from nanogrids constructed by predeposition of TiO₂ nanodots in the MCM-41 channel, and that tunes the spin-state of Fe(III) from high-spin to low-spin induced by the strong guest-host interaction between the ultrafine Fe₂ O₃ with SiO₂ (MCM-41). The low-spin Fe(III) endorses strong bonding with anionic adsorbates, and significantly facilitates the electrons transfer from Fe₂ O₃ to SiO₂ to form a highly positive charged surface, and thereby shows superior electrostatic multilayer adsorption performance to different kinds of anionic contaminations. Specifically, the maximum uptake, adsorption rate, and distribution coefficient (K_d ) for Rose Bengal dye reach as high as 1810 mg g^-1 , 1644 g (g min)^-1 , and 2.2 × 10⁶ L kg^-1 , which are more than 8, 230, and 3700 times higher than those of commercial activated carbon, respectively. It also shows outstanding purification performance for real field water. It is demonstrated that a strong guest-host interaction can alter the spin-state of transition metal oxides, which may pave a new way to improve their performance in adsorption and other applications like catalysis.

Synthesis of mesoporous MFI zeolite via bacterial cellulose-derived carbon templating for fast adsorption of formaldehyde

Mesoporous ZSM-5 (MFI) zeolite was synthesized by using bacterial cellulose-derived activated carbon (BC-AC500) with a high surface area as a hard template. Different ratios of BC-AC500 and zeolite precursor gel were prepared in a Teflon-lined autoclave and crystallized at 180 °C for 48 h in a rotating oven. The physicochemical properties of the samples were characterized by x-ray diffraction (XRD), scanning/transmission electron microscopies (SEM/TEM), and N₂ physisorption techniques. It was found that the mesoporous ZSM-5 zeolites have a specific surface area of 184-190 m²/g, a high mesopore volume of 0.120-0.956 ml/g and a wide pore size distribution ranging from 5 to 100 nm with a maximum at approximately 25.3 nm. The successfully made mesoporous ZSM-5 was tested as an adsorbent for formaldehyde adsorption in batch mode. The mesoporous ZSM-5 zeolite made from bacterial cellulose-derived activated carbon showed significantly faster adsorption kinetics than conventional ZSM-5 (0.0081 vs. 0.0007 g/mg min, respectively). The prepared material has an adsorption capacity of 98 mg/g and is highly reusable. The reported mesoporous ZSM-5 zeolites can be deployed for the rapid removal of toxic organics from wastewater when urgently needed, e.g., under breakthrough conditions.