Synthesis and characterization of a novel core–shell magnetic nanocomposite via surface-initiated RAFT polymerization for highly efficient and selective adsorption of uranium(VI)

Unlocking the potential of biochar: an iron-phosphorus-based composite modified adsorbent for adsorption of Pb(II) and Cd(II) in aqueous environments and response surface optimization of adsorption conditions

In this work, iron-phosphorus based composite biochar (FPBC) was prepared by modification with potassium phosphate and iron oxides for the removal of heavy metal ions from single and mixed heavy metal (Pb and Cd) solutions. FTIR and XPS characterization experiments showed that the novel modified biochar had a greater number of surface functional groups compared to the pristine biochar. The maximum adsorption capacities of FPBC for Pb(II) and Cd(II) were 211.66 mg·g-1 and 94.08 mg·g-1 at 293 K. The adsorption of Pb(II) and Cd(II) by FPBC followed the proposed two-step adsorption kinetic model and the Freundlich isothermal adsorption model, suggesting that the mechanism of adsorption of Pb(II) and Cd(II) by FPBC involved chemical adsorption of multiple layers. Mechanistic studies showed that the introduction of -PO4 and -PO3 chemisorbed with Pb(II) and Cd(II), and the introduction of -Fe-O increased the ion exchange with Pb(II) and Cd(II) during the adsorption process and produced precipitates such as Pb3Fe(PO4)3 and Cd5Fe2(P2O7)4. Additionally, the abundant -OH and -COOH groups also participated in the removal of Pb(II) and Cd(II). In addition, FPBC demonstrated strong selective adsorption of Pb(II) in mixed heavy metal solutions. The Response Surface Methodology(RSM) analysis determined the optimal adsorption conditions for FPBC as pH 5.31, temperature 26.01 °C, and Pb(II) concentration 306.30 mg·L-1 for Pb(II). Similarly, the optimal adsorption conditions for Cd(II) were found to be pH 5.66, temperature 39.34 °C, and Cd(II) concentration 267.68 mg·L-1. Therefore, FPBC has the potential for application as a composite-modified adsorbent for the adsorption of multiple heavy metal ions.

A fungal-modified material with high uranium (VI) adsorption capacity and strong anti-interference ability

With open-chain polyether as the bridge chain, a new fungal-modified material with diamidoxime groups was prepared by a series of uncomplex synthesis reaction. The orthogonal experiment obtained its optimized adsorption conditions as follows: the initial pH value of 6.5, the initial uranyl concentration of 40 mg L^-1, the contact time of 130 min, and the a solid-liquid ratio of 25 mg L^-1. The maximum adsorption capacity of target material was 446.20 mg g^-1, and it was much greater than that of the similar monoamidoxime material (295.48 mg g^-1). The linear Langmuir (R² = 0.9856) isotherm models and the linear pseudo-second-order kinetic model (R² = 0.9931) fit the experimental data of uranium (VI) adsorption better, indicating the adsorption mechanism should mainly be the monolayer adsorption and chemical process. In addition, the relevant experiments exhibited the prepared material had the good reusability, which reached 84.25% of the maximum capacity after five cycles, and the excellent anti-interference performance. The above features suggest the modified fungus material will have the good application prospect in the future.

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.

Ultra-high mechanical property and multi-layer porous structure of amidoximation ethylene-acrylic acid copolymer balls for efficient and selective uranium adsorption from radioactive wastewater

Adsorption uranium [U(VI)] from U-containing radioactive wastewater (URW) is a critical strategy for solving the resource shortage and environmental pollution in pace with the sustainable development of nuclear energy. However, the URW universally exhibits acidity and contains co-existing metal ions with high concentration. Herein, the amidoximation ethylene-acrylic acid copolymer balls (EAA-AO) with aciduric and super-high mechanical property were successfully synthesized through grafting diaminomaleonitrile and further treatment of amidoximation. Significantly, the mechanical properties of EAA-AO were not affected by the grafting process and maintained super-high mechanical properties. Furthermore, the -NH₂ and unreacted -CN groups in diaminomaleonitrile adjusted the pK_a to make the optimal pH be 4. In addition, the microstructure of EAA-AO was transformed from the original dense to multi-layer porous structure, which promoted the mass transfer process and the contact between uranyl ions (UO₂²⁺) and internal adsorption active sites. The adsorption capacity of EAA-AO was about 1.78 times that of EAA at pH = 4, and the adsorption capacity for U(VI) was about 8.17 times that of Ba²⁺ with the second highest adsorption capacity. Therefore, the EAA-AO exhibited ultra-high adsorption performance (q_e = 3.196 mg g^-1) in the artificial radioactive wastewater, laying a good foundation for subsequent large-scale industrial adsorption of U(VI) in nuclear industrial wastewater.

Efficient Removal of Uranium(VI) from Aqueous Solutions by Triethylenetetramine-Functionalized Single-Walled Carbon Nanohorns

In the present study, SWCNH-COOH and SWCNH-TETA were fabricated using single-walled carbon nanohorns (SWCNHs) via carboxylation and grafting with triethylenetetramine (TETA) for uranium (VI) ion [U(VI)] removal. The morpho-structural characterization of as-prepared adsorbing materials was performed by transmission electron microscopy, X-ray diffractometry, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Several parameters including the pH value of the aqueous solutions, contact time, temperature, and U(VI) concentration were used to evaluate the sorption efficiency of SWCNH-COOH and SWCNH-TETA. The Langmuir isotherm model could well represent the as-obtained adsorption isotherms, and the kinetics was successfully modeled by pseudo-second-order kinetics in the adsorption process. The maximum adsorption capacity of SWCNH-TETA was calculated as 333.13 mg/g considering the Langmuir isotherm model. Thermodynamic studies showed that adsorption proved to be a spontaneous endothermic process. Moreover, SWCNH-TETA exhibited excellent recycling performance and selective adsorption of uranium. Furthermore, the possible mechanism was investigated by XPS and density functional theory calculations, indicating that the excellent adsorption was attributed to the cooperation capability between uranium ions and nitrogen atoms in SWCNH-TETA. This efficient approach can provide a strategy for developing high-performance adsorbents for U(VI) removal from wastewater.

Transport of uranium(VI) in red soil in South China: influence of initial pH and carbonate concentration

Uranium-contaminated wastewater associated with uranium (U) mining and processing inevitably releases into soil environment. In order to assess the risk of U wastewater contamination to groundwater through percolation, U adsorption and transport behavior in a typical red soil in South China was investigated through batch adsorption and column experiments, and initial pH and carbonate concentration were considered of the high-sulfate background electrolyte solution. Results demonstrated that U adsorption isotherms followed the Freundlich model. The adsorption of U to red soil significantly decreased with the decrease of the initial pH from 7 to 3 in the absence of carbonate, protonation-deprotonation reactions controlled the adsorption capacity, and lnC_s had a linear relationship with the equilibrium pH (pH_eq). In the presence of carbonate, the adsorption was much greater than that in the absence of carbonate owing to the pH_eq values buffered by carbonate, but the adsorption decreased with the increase of the carbonate concentration from 3.5 to 6.5 mM. Additionally, the breakthrough curves (BTCs) obtained by column experiments showed that large numbers of H⁺ and CO₃^2- competed with the U species for adsorption sites, which resulted in BTC overshoot (C/C₀ > 1). Numerical simulation results indicated that the BTCs at initial pH 4 and 5 could be well simulated by two-site chemical non-equilibrium model (CNEM), whereas the BTCs of varying initial carbonate concentrations were suitable for one-site CNEM. The fractions of equilibrium adsorption sites (f) seemed to correlate with the fractions of positively charged complexes of U species in solution. The values of partition coefficients (k_d^') were lower than those measured in batch adsorption experiments, but they had the same variation trend. The values of first-order rate coefficient (ω) for all BTCs were low, representing a relatively slow equilibrium between U in the liquid and solid phases. In conclusion, the mobility of U in the red soil increased with the decrease of the initial pH and with the increase of the initial carbonate concentrations.

Facile preparation of low-cost HKUST-1 with lattice vacancies and high-efficiency adsorption for uranium

In this work, we prepared HKUST-1 and HKUST-1 with lattice vacancies (HLV) using benzoic acid (BA) as a low-cost modulator to replace part of the traditional trimesic acid ligand (H3BTC). The structure and morphology of the products were characterized by FTIR, XRD, SEM and XPS. The adsorption performance of the products for uranium from aqueous solutions was investigated. The results showed that the sorption of U(vi) on HKUST-1 and HLV agreed with the Langmuir isotherm model (R HKUST-1 2 = 0.9867 and R HLV 2 = 0.9828) and the maximum adsorption capacity was 430.98 mg g-1 and 424.88 mg g-1, respectively. According to kinetics studies, the adsorption fitted better with a pseudo-second-order model (R HKUST-1 2 = 1.0000 and R HLV 2 = 0.9978). The as-prepared adsorbents were used for the removal of uranium from real water samples as well. The results showed that HLV with lower cost is a promising adsorbent for uranium from aqueous solutions.