Co-sorption of Sr2+ and SeO42- as the surrogate of radionuclide by alginate-encapsulated graphene oxide-layered double hydroxide beads

Ions-Induced Alginate Gelation According to Elemental Analysis and a Combinatorial Approach

This study considers the potential of elemental analysis of polysaccharide ionotropic gels in elucidating the junction zones for different divalent cations. The developed algorithm ensures the correct separation of contributions from physically adsorbed and structure-forming ionic compounds, with the obtained results scaled to alginate C12 block. Possible versions of chain association into dimers and their subsequent integration into flat junction zones were analyzed within the framework of the "egg-box" model. The application of combinatorial analysis made it possible to derive theoretical relations to find the probability of various types of egg-box cell occurrences for alginate chains with arbitrary monomeric units ratio μ = M/G, which makes it possible to compare experimental data for alginates of different origins. Based on literature data and obtained chemical formulas, the possible correspondence of concrete biopolymer cells to those most preferable for filling by alkaline earth cations was established. The identified features of elemental composition suggest the formation of composite hydrated complexes with the participation of transition metal cations. The possibility of quantitatively assessing ordered secondary structures formed due to the physical sorption of ions and molecules from environment, correlating with the sorption capabilities of Me2+ alginate, was established.

A study on the adsorption property and mechanism of β-cyclodextrin/polyvinyl alcohol/polyacrylic acid hydrogel for ciprofloxacin

Polyvinyl alcohol (PVA), acrylic acid (AA), and β-cyclodextrin (β-CD) were used as monomers, and ammonium persulfate was used as an initiator. Orthogonal tests were optimized the experimental condition, and aqueous polymerization was used to prepare poly-β-cyclodextrin/polyvinyl alcohol/polyacrylic acid (β-CD/PVA/PAA) hydrogel. The samples were characterized by FT-IR (Fourier transform infrared), SEM (Scanning electron microscopy), and XRD (X-ray diffraction). β-CD/PVA/PAA hydrogel was analyzed, which influenced external environmental factors on the β-CD/PVA/PAA hydrogel adsorption performance, and the kinetic behavior of β-CD/PVA/PAA hydrogel on ciprofloxacin (CIP) adsorption was explored. The results concluded that the prepared β-CD/PVA/PAA hydrogel has a well-defined three-dimensional network structure. The decrease in the pH of the CIP solution and the adsorption temperature reduces the adsorption reaction of β-CD/PVA/PAA hydrogel on CIP. The kinetics of CIP adsorption by β-CD/PVA/PAA hydrogel confirmed the pseudo-second-order kinetic model (R 2 > 0.997), the maximum equilibrium adsorption amounts is 372.12 mg/g, the removal rate reaches 74.42%. The adsorption process was mainly chemisorption, the adsorption isotherm fits the Freundlich adsorption isotherm model (R 2 > 0.946), and the adsorption process was heterogeneous with multi-molecular layer adsorption. The adsorption process inclined more toward the adsorption of inhomogeneous multi-molecular layers. The β-CD/PVA/PAA hydrogel retained 80% adsorption properties after three adsorption-desorption under optimal conditions.

Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

Hydrothermal synthesis and sorption performance to Cs(I) and Sr(II) of zirconia-analcime composites derived from coal fly ash cenospheres

The paper is concerned with (i) the hydrothermal synthesis of hydrous zirconium dioxide (HZD) bearing analcime (HZD-ANA, zirconia-analcime) and (ii) its sorption properties with respect to Cs+ and Sr2+. The HZD-ANA particles were synthesized from coal fly ash cenospheres composed of aluminosilicate glass with (SiO2/Al2O3)wt.=3.1 and characterized by PXRD, SEM-EDS, STA, and low-temperature N2 adsorption. The non-radioactive simulant solutions of different acidity (pH=2–10) and Cs+/Sr2+ content (0.5–50.0 mg/L) were used in the work. The effect of synthesis conditions on the HZD-ANA particle size, zirconia content and localization as well as the sorption behavior with respect to Cs+ and Sr2+ (capacity, KD) were clarified. It was found that the small-sized HZD-ANA composites surpasses the Zr free analcime and large-sized HZD-ANA material in the Cs+ and Sr2+ sorption parameters (KD ~104–106 mL/g). The conditions to synthesize the zirconia-analcime composite of the highly enhanced sorption ability with respect to Sr2+ (KD ~106 mL/g) were determined. The high-temperature solid-phase re-crystallization of Cs+/Sr2+-exchanged HZD-ANA composites was shown to occur at 1000 °C resulting in a polyphase system based on nepheline, tetragonal ZrO2, and glass phase.

A novel modified Fe-Mn binary oxide graphite felt (FMBO-GF) cathode in a neutral electro-Fenton system for ciprofloxacin degradation

A graphite felt (GF) cathode was firstly modified by Fe-Mn binary oxide (FMBO), active carbon (AC), carbon black (CB), and polytetrafluoroethylene (PTFE), which exhibits satisfactory ciprofloxacin (CIP) removal efficiency at neutral pH value in electro-Fenton (EF) system. Morphological data showed that modified cathodes have larger surface area and volume pore as well as more active sites. And electrochemical properties have proved stronger current response after modification. In compassion to the unmodified GF, the FMBO/AC/CB modified GF (FMBO-GF) has wider pH range and higher CIP removal efficiency due to its unique nanoparticles structure. The CIP removal efficiency achieved 95.40% in 30 min, and the removal efficiency of total organic carbon (TOC) achieved 93.77% in 2 h when conditions were optimal (25 mg/L initial CIP concentration, 2 mA/cm² current density, FMBO/AC: CB: PTFE of 1:1:5, and 7 initial pH value) in this study. The results of great degradation and mineralization of CIP in this study indicate that the FMBO-GF cathode has huge potential on antibiotics removals in neutral environment.

FeIIFeIII layered double hydroxide modified carbon felt cathode for removal of ciprofloxacin in electro-Fenton process

The disadvantages of limited working pH range and poor stability have hindered the practical application of traditional electro-Fenton process. In this research, a novel heterogeneous electro-Fenton (HEF) process with Fe^IIFe^III layered double hydroxide/carbon felt (Fe^IIFe^III LDH/CF) as cathode was developed for the rapid destruction of ciprofloxacin (CIP) in bulk solution. Effects of crucial influencing factors (initial pH, current intensity) on CIP degradation were investigated. Results indicated that Fe^IIFe^III LDH/CF cathode was efficient for CIP degradation (88.11%). Furthermore, CIP degradation performance in HEF could remain stable over wide range of pH (pH 3-9). The catalytic degradation of CIP in HEF process might be a combined effect of homogeneous EF reaction, anodic oxidation, and surface catalysis process via≡Fe^II/≡Fe^III cycle. Possible degradation pathways were proposed. The results suggested that Fe^IIFe^III LDH/CF cathode showed great application potential for CIP degradation.