Preparation of ZnNiAl-LDHs microspheres and their adsorption behavior and mechanism on U(VI)

Kinetics, isotherm, mechanism, and recyclability of novel nano-sized Ce4+-doped Ni-Al layered double hydroxide for defluoridation of aqueous solutions

Excessive fluoride removal from aqueous solutions is of utmost importance as it has an adverse impact on human health. This study investigates the defluoridation efficiency of a novel nano-sized Ce+4-doped Ni/Al layered double hydroxide (Ni-Al-Ce LDH) for aqueous solutions. The synthesized Ni-Al-Ce LDH exhibited a well-defined nanoscale plate-like morphology and a high surface area with an average size of 11.51 nm, which contributed to its enhanced fluoride adsorption capacity. XRD, SEM, HRTEM, and BET studies confirmed these characteristics. XPS analysis confirmed the presence of Ce4+ ions within the Ni-Al LDH. The experimental results indicated that the process of defluoridation followed a pseudo-second-order model of kinetics, suggesting a chemisorption mechanism. The fluoride adsorption isotherms demonstrated well fits to the Freundlich, Langmuir, and Jovanovic models, indicating both monolayer and multilayer fluoride adsorption on the Ce-doped Ni-Al LDH. The maximum adsorption capacity was found to be 238.27 mg/g (Langmuir) and 130.73 mg/g (Jovanovic) at pH 6.0 and 25 °C. The proposed mechanisms for fluoride adsorption on the LDH include ion exchange, surface complexation, hydrogen bonding, and ligand exchange. The Ni-Al-Ce LDH nanomaterial exhibited good recyclability, maintaining 71% of the fluoride adsorption efficiency even after four consecutive cycles. This study highlights the significant role of Ce doping in improving the performance of Ni-Al LDH as a defluoridation adsorbent.

High efficiency electrochemical separation of uranium(VI) from uranium-containing wastewater by microbial fuel cells with different cathodes

As an emerging versatile technology for separating uranium from uranium-containing wastewater (UCW), microbial fuel cell (MFC) offers a novel approach to UCW treatment. Its cathode is essential for the treatment of UCW. To thoroughly investigate the efficacy of MFC in treating UCW, investigations were conducted using MFCs with five materials (containing iron sheet (IP), stainless steel mesh (SSM), carbon cloth (CC), carbon brush (CB), and nickel foam (NF)) as cathodes. The results revealed that each MFC system performed differently in terms of carbon source degradation, uranium removal, and electricity production. In terms of carbon source degradation, CB-MFC showed the best performance. The best uranium removal method was NF-MFC, and the best electricity production method was carbon-based cathode MFC. Five MFC systems demonstrated stable performance and consistent difference over five cycles, with CC-MFC outperforming the others. Furthermore, SEM and XPS characterization of the cathode materials before and after the experiment revealed that a significant amount of U(IV) was generated during the uranium removal process, indicating that uranium ions were primarily removed by electrochemical reduction precipitation. This study confirmed that abiotic cathode MFC had a high UCW removal potential and served as a good guideline for obtaining the best cathode for MFC.

Bio-functionalized magnetic nanoparticles for cost-effective adsorption of U(vi): experimental and theoretical investigation

U(vi) removal using cost-effective (production cost: $14.03 per kg), biocompatible, and superparamagnetic Cinnamomum tamala (CT) leaf extract-coated magnetite nanoparticles (CT@MNPs or CT@Fe₃O₄ nanoparticles) from water resources was studied. From pH-dependent experiments, the maximum adsorption efficiency was found to be at pH 8. Isotherm and kinetic studies were performed and found to follow Langmuir isotherm and pseudo-second order kinetics, respectively. The maximum adsorption capacity of CT@MNPs was calculated to be 45.5 mg of U(vi) per g of nanoparticles (NPs). Recyclability studies suggest that over 94% sorption was retained even after four consecutive cycles. The sorption mechanism was explained by the point of the zero-charge experiment and the XPS measurement. Additionally, calculations using density functional theory (DFT) were carried out to support the experimental findings.

Preparation of phosphoric-modified aloe vera/chitosan aerogels and their efficient adsorption of U(VI)

The efficient adsorption of radioactive elements from nuclear wastewater is an important research topic in the environmental field. The unique three-dimensional porous structure of aerogels has great potential in the field of adsorption. Phosphoric-modified aloe vera/chitosan aerogel (CS/AL-AP) was prepared from chitosan, phosphoric acid, and aloe powder by vacuum freeze-drying self-assembly. The maximum adsorption of uranyl ions by CS/AL-AP was found to be 322.34 mg/g at pH 6, adsorption time of 120 min, solid-to-liquid ratio of 0.125 g/L, reaction temperature of 303 K, and initial uranyl ion concentration of 50 mg/L. The adsorption process is consistent with the Langmuir isotherm model and the quasi-secondary kinetic model, indicating that the adsorption process is monolayer adsorption. The type of adsorption is mainly chemisorption. FTIR and XPS analyses indicate that the adsorption of U(VI) by CS/AL-AP results from the combined action of coordination or chelation of amino, hydroxyl, and carboxyl groups. In addition, CS/AL-AP shows excellent adsorption capacity in the presence of complex co-existing ions. After five adsorption-desorption experiments, the adsorption capacity of CS/AL-AP for uranyl ions remained at a high level. It indicates that CS/AL-AP has good stability and recoverability. The results indicate that CS/AL-AP has excellent potential in the field of uranium removal.

Preparation of a Bi6O5(OH)3(NO3)5·2H2O/AgBr composite and its long-lasting antibacterial efficacy

A novel Bi₆O₅(OH)₃(NO₃)₅·2H₂O/AgBr (6535BBN/AgBr) composite with long-lasting antibacterial efficacy was prepared. The microstructure of the composite was characterized. AgBr nanoparticles (NPs) were sandwiched in 6535BBN nanosheets (NSs) or loaded on their surfaces. The utilization of 6535BBN as carriers contributed to the long-term lasting antibacterial activity of the composite after storage in water or 0.9% NaCl. The antibacterial activity was evaluated by inhibition zones against E. coli. The inhibition zone diameters of 6535BBN/AgBr stored in water for 0 h, 8 h, 16 h, and 48 h were measured as 22.50, 21.71, 20.43, and 20.29 mm, respectively. The activity of the composite after storage in water for 48 h remained 90.2% of that in the beginning. After storing in 0.9% NaCl for 16 h, the activity was determined to be 90.1% of that in the beginning. In comparison with the rapid decrease in the antibacterial activity of pure AgBr, the slow reduction of 6535BBN/AgBr after storage indicates long-lasting efficacy. The excellent dispersion states of 6535BBN/AgBr powders after storage in solutions were revealed, and the positive relationship between the dispersion state and its long-lasting antibacterial activity was suggested. Based on the unique load-on-carrier (LOC) structure, the long-lasting antibacterial performance was promoted by the synergy of the sharp-edge-cutting effect of 6535BBN NSs, prolonged ROS antibacterial effect, and restrained sterilization effects of silver ions caused by their slow release.

Efficient Adsorption of Tl(I) from Aqueous Solutions Using Al and Fe-Based Water Treatment Residuals

Iron and aluminum water treatment residuals from a water supply plant were used as adsorbents for Tl(I) to treat thallium-containing Tl(I) wastewater and realize the resource utilization of water treatment residuals. The feasibility study results showed that Fe-WTR and Al-WTR reached adsorption equilibria within 120 min. The Langmuir model showed maximum adsorption capacities of Tl(I) on Fe-WTR and Al-WTR as 3.751 and 0.690 mg g−1 separately at an initial concentration of 5 mg L−1. The adsorption capacities of Fe-WTR and Al-WTR positively correlated with pH. The removal of Tl(I) using Fe-WTR exceeded Al-WTR; the adsorbed Tl(I) in Fe-WTR occurred primarily in the reduced state, while the Tl(I) adsorbed in Al-WTR was mainly in acid-extractable and reduced states. FTIR and XPS data showed that Tl(I) and Fe/Al-OH-functional groups formed stable surface complexes (Fe/Al-O-Tl) during adsorption, and there was no redox reaction. This confirmed that WTR is a highly efficient adsorbent for the stable removal of Tl(I), which provides a practical foundation for industrial application in Tl(I)-containing wastewater treatment.