Complexation behavior of poly(acrylic acid) and lanthanide ions

Chitosan/Poly(maleic acid-alt-vinyl acetate) Hydrogel Beads for the Removal of Cu2+ from Aqueous Solution

Covalent cross-linked hydrogels based on chitosan and poly(maleic acid-alt-vinyl acetate) were prepared as spherical beads. The structural modifications of the beads during the preparation steps (dropping in liquid nitrogen and lyophilization, thermal treatment, washing with water, and treatment with NaOH) were monitored by FT-IR spectroscopy. The hydrogel beads have a porous inner structure, as shown by SEM microscopy; moreover, they are stable in acidic and basic pH due to the covalent crosslinking. The swelling degree is strongly influenced by the pH since the beads possess ionizable amine and carboxylic groups. The binding capacity for Cu2+ ions was examined in batch mode as a function of sorbent composition, pH, contact time, and the initial concentration of Cu2+. The kinetic data were well-fitted with the pseudo-second-order kinetic, while the sorption equilibrium data were better fitted with Langmuir and Sips isotherms. The maximum equilibrium sorption capacity was higher for the beads obtained with a 3:1 molar ratio between the maleic copolymer and chitosan (142.4 mg Cu2+ g-1), compared with the beads obtained using a 1:1 molar ratio (103.7 mg Cu2+ g-1). The beads show a high degree of reusability since no notable decrease in the sorption capacity was observed after five consecutive sorption/desorption cycles.

Multiresponsive Self-Healing Lanthanide Fluorescent Hydrogel for Smart Textiles

Lanthanide organometallic complexes exhibit strong luminescence characteristics, owing to their antenna effects. The f-d energy level transition causes this phenomenon, which occurs when ligands and the external electrons of lanthanide metals coordinate. Based on this phenomenon, we used two lanthanide metals, europium (Eu) and terbium (Tb), in the present study as the metal center for iminodiacetic acid ligands. Further, we developed the resulting fluorescent organometallic complex as a smart material. The ligand-metal bond in the material functioned as a metal chelating agent and a cross-linking agent in a dynamically coordinated form, thereby prompting the material to self-heal. Temperature-sensitive poly-N-isopropylacrylamide was incorporated into the material as the polymer backbone. Afterward, we combined it with water-soluble poly(vinyl alcohol) and an additional ligand from poly(acrylic acid) to fabricate a high-performance hydrogel composite material. The shrinkage and expansion of the polymer form a grid between the materials. Because of the different coordination stabilities of Eu3+ and Tb3+, the corresponding material exhibits environmental responses toward excitation wavelength, temperature, and pH, thus generating different colors. When used in fabrics, the cross-linking mechanism of the material effectively looped the material between fabric fibers; furthermore, the temperature sensitivity of the polymer adjusted the size of pores between fabric fibers. At relatively higher temperatures (>32 °C), the polymer structure shrank, fiber pores expanded, and air permeability improved. Thus, this material appears to be promising for use in smart textiles.

Poly(acrylic acid)-mediated synthesis of cerium oxide nanoparticles with variable oxidation states and their effect on regulating the intracellular ROS level

Cerium oxide nanoparticles (CeNPs) possess multiple redox enzyme mimetic activities in scavenging reactive oxygen species (ROS) as a potential biomedicine. These enzymatic activities of CeNPs are closely related to their surface oxidation state. Here we have reported a synthetic method to modify CeNPs' surface oxidation state by changing the conformation of the poly(acrylic acid) (PAA) polymers adsorbed onto the CeNP surface. The synthesized PAA-CeNPs exhibited the same core size, morphology, crystal structure, and colloidal stability, with the only variation being their surface oxidation state (Ce³⁺ percentage). The modification mechanism can be attributed to the polymers chemisorbed onto the metal oxide surface forming a metal complexation structure. Such adsorption further modified CeNPs' surface oxidation state in a temperature-dependent manner. The series of PAA-CeNPs exhibited multiple redox enzyme mimetic activities (superoxide dismutase, catalase, peroxidase, and oxidase) directly related to their surface oxidation state. In vitro experiments showed no cytotoxic effect of these PAA-CeNPs on the osteoblastic cell line SAOS-2 at high loadings. Microscopic images confirmed the internalization of PAA-CeNPs in the cells. All tested PAA-CeNPs can reduce the basal and hydrogen peroxide-induced intracellular ROS level in the cells, indicating their effective intracellular ROS scavenging effect. However, we did not observe a positive correlation between the CeNP surface oxidation state and their capacities to reduce the intracellular ROS levels. We propose that CeNPs can maintain a dynamic state of Ce³⁺/Ce⁴⁺ during their catalytic activities, exhibiting a non-linear correlation between the CeNP surface oxidation state and their effect on regulating the intracellular ROS level.

Synthesis, Characterizations, and 9.4 Tesla T2 MR Images of Polyacrylic Acid-Coated Terbium(III) and Holmium(III) Oxide Nanoparticles

Polyacrylic acid (PAA)-coated lanthanide oxide (Ln2O3) nanoparticles (NPs) (Ln = Tb and Ho) with high colloidal stability and good biocompatibility were synthesized, characterized, and investigated as a new class of negative (T2) magnetic resonance imaging (MRI) contrast agents at high MR fields. Their r2 values were appreciable at a 3.0 T MR field and higher at a 9.4 T MR field, whereas their r1 values were negligible at all MR fields, indicating their exclusive induction of T2 relaxations with negligible induction of T1 relaxations. Their effectiveness as T2 MRI contrast agents at high MR fields was confirmed from strong negative contrast enhancements in in vivo T2 MR images at a 9.4 T MR field after intravenous administration into mice tails.

Binary Pectin-Chitosan Composites for the Uptake of Lanthanum and Yttrium Species in Aqueous Media

Rare-earth elements such as lanthanum and yttrium have wide utility in high-tech applications such as permanent magnets and batteries. The use of biopolymers and their composites as adsorbents for La (III) and Y (III) ions were investigated as a means to increase the uptake capacity. Previous work has revealed that composite materials with covalent frameworks that contain biopolymers such as pectin and chitosan have secondary adsorption sites for enhanced adsorption. Herein, the maximum adsorption capacity of a 5:1 Pectin-Chitosan composite with La (III) and Y (III) was 22 mg/g and 23 mg/g, respectively. Pectin-Chitosan composites of variable composition were characterized by complementary methods: spectroscopy (FTIR, ¹³C solids NMR), TGA, and zeta potential. This work contributes to the design of covalent Pectin-Chitosan biopolymer frameworks for the controlled removal of La (III) and Y (III) from aqueous media.

Effect of Copolymer Structure on Rare-Earth-Element Chelation Thermodynamics

Rare-earth elements (REEs) are crucial to modern technology, leading to a high demand for materials capable of REE extraction and purification. Metal-chelating polymers (e.g., polycarboxylic acids, polyamines, and others) are particularly useful in these applications due to their synthetic accessibility and high selectivity. Copolymers with varied mole fractions of acrylic acid and methyl acrylate are synthesized and isothermal titration calorimetry (ITC) to measure the thermodynamics of REE binding for each material is used. Across a series of copolymer compositions, entropically driven binding thermodynamics (∆G, ∆H, and ∆S) that appear to be independent of χ_{Acrylic Acid} are found. ITC stoichiometry data reveal that each copolymer requires between four and five repeat units to bind each REE. These data suggest that alterations in the copolymer structure do not affect the overall binding thermodynamics of REEs to these copolymers.

Polymer Complex Fiber for Linear Actuation with High Working Density and Stable Catch-State

Fiber-based linear actuators (FLAs) are a key module in microrobots and biomimetic devices. It has been a great challenge to develop linear actuators that can balance output stress and output strain and hence provide high working density. Herein, we report the preparation and performance of a FLA system made from commercially available materials and allowed mass production at relatively low cost. The FLAs can lift up or lay down objects more than 1000 times of its own weight during active contraction and expansion under environmental stimuli. The contraction ratio and output stress can reach 30% and 0.24 MPa, respectively, and the sustainable work density is about 80 J/kg, which is 10 times the typical value of human skeletal muscles. Especially, the FLAs show stable catch-state (lock-up state) with no creeping and no further energy consumption.

Highly efficient removal of Cr(III)-poly(acrylic acid) complex by coprecipitation with polyvalent metal ions: Performance, mechanism, and validation

The Cr(III)-organic complexes formed between Cr(III) and multifunctional group ligands, such as polyacrylate, are highly water soluble and difficult to be removed from wastewater by common treatments. A novel strategy for efficiently removing Cr(III)-poly (acrylic acid) complex (Cr(III)-PAA) from wastewater without introducing secondary pollution is proposed using a coprecipitation method with polyvalent metal ions. Al(III), Fe(III), Zr(IV), and Ti(IV) were combined with the carboxyl of Cr(III)-PAA to decrease hydrophilia and achieve fast and efficient coprecipitation. Cr(III)-PAA was efficiently removed from wastewater by using these polyvalent metal ions, especially at low pH, where the ions exist as monomer. The residual concentration of Cr(III) in treated wastewater under the optimized experimental condition was less than 1.0 mg/L. No Cr(VI) and negligible amount of polyvalent metal ions were detected in the treated wastewater, indicating that almost all of the ions coprecipitated with Cr(III)-PAA. No secondary pollution also occurred. The high reactivity between the polyvalent metal ions and Cr(III)-PAA and the sharp decrease in the hydrophilia of the complex contributed to its highly efficient removal from wastewater. Actual tannery wastewater containing Cr(III)-organic complexes with high solubility and stability was treated through coprecipitation with Al(III). A high Cr(III) removal efficiency of 99.0% was obtained. This work provides new insights into the removal of soluble Cr(III)-organic complexes from wastewater by using an environment-friendly and cost-effective method.

Luminescent Properties of Lanthanoid-Poly(Sodium Acrylate) Composites: Insights on the Interaction Mechanism

The interaction between polyelectrolytes and metal ions is governed by different types of interactions, leading to the formation of different phases, from liquid state to weak gels, through an appropriate choice of metal ion/polyelectrolyte molar ratio. We have found that lanthanide ions, europium(III) and terbium(III), are able to form polymer composites with poly(sodium acrylate). That interaction enhances the luminescent properties of europium(III) and terbium(III), showing that Eu³⁺/poly(sodium acrylate) (PSA) and Tb³⁺/PSA composites have a highly intense red and green emission, respectively. The effect of cations with different valences on the luminescent properties of the polymer composites is analyzed. The presence of metal ions tends to quench the composite emission intensity and the quenching process depends on the cation, with copper(II) being by far the most efficient quencher. The interaction mechanism between lanthanoid ions and PSA is also discussed. The composites and their interactions with a wide range of cations and anions are fully characterized through stationary and non-stationary fluorescence, high resolution scanning electronic microscopy and X-ray diffraction.

Structural Study of Polystyrene-b-poly(acrylic acid) Micelles Complexed with Uranyl: A SAXS Core-Shell Model Analysis

The interactions between natural colloidal organic matter and actinides in solutions are complex and not fully understood. In this work, a crew-cut polystyrene-b-poly(acry1ic acid) (PS-b-PAA) micelle is proposed as a model particle for humic acid (HA) colloid with the aim to better understand the sequestration, aggregation, and mobility of HA colloids in the presence of uranyl ions. The effects of uranyl ions on the structure of PS_29k-b-PAA_5k micelles in aqueous solution were mainly investigated by synchrotron small-angle X-ray scattering. A core-shell model, accounting for the thickness and contrast changes of the PAA corona induced by the adsorption of uranyl, was employed to analyze the scattering data. A combination of transmission electron microscopy, dynamic light scattering, and zetametry showed a strong affinity of uranyl ions to PAA segments in water at pH 4-5 that resulted in the shrinkage and improved contrast of the PAA corona, as well as colloidal destabilization at a high uranyl concentration.

Fast-Response and Reusable Oxytetracycline Colorimetric Strips Based on Nickel (II) Ions Immobilized Carboxymethylcellulose/Polyacrylonitrile Nanofibrous Membranes

Driven by economic interests, the abuse of antibiotics has become a significant concern for humans worldwide. As one of the most commonly used antibiotics, oxytetracycline (OTC) residue in animal-derived foods occurs occasionally, which has caused danger to humanity. However, there is still no simple and efficient solution to detect OTC residue. Here, an easily-operated colorimetric strategy for OTC detection was developed based on nickel ions (Ni2+) immobilized carboxymethylcellulose/polyacrylonitrile nanofibrous membranes (Ni@CMC/PAN NFMs). Owing to numerous O- and N-containing groups OTC has a strong tendency to complex with Ni2+ on the strips, inducing a color change from light green to yellow visible to the naked eye. The NFMs structural features, CMC functionalization process, and Ni2+ immobilization amount was carefully regulated to assure OTC detection whilst maintaining the inherent characteristics of NFMs. With the benefits of the large specific surface area (SSA) and small pore size of NFMs, the strips not only exhibited a rapid response (2 min), and low detection limit (5 nM) but also performed with good reversibility and selectivity concerning OTC detection over other antibiotics. The successful development of such enchanting nanofibrous materials may provide a new comprehension into the design and improvement of colorimetric strips.

Universal aqueous synthesis of ultra-small polymer-templated nanoparticles: synthesis optimization methodology for counterion-collapsed poly(acrylic acid)

A long polyelectrolyte chain collapses into a nano-sized particle upon the addition of counterions under appropriate solution conditions. This phenomenon forms the basis for a simple universal method for aqueous synthesis of ultra-small (<10 nm) metal, metal oxide, and other types of nanoparticles in the following manner: the counterion-collapsed polyelectrolyte chains are made stable by crosslinking, effectively trapping the counterions, which are subsequently chemically modified, to form metal nanoparticles via reduction or metal oxides nanoparticles via oxidation, within the collapsed polymer nanoparticle. This highly versatile platform methodology can be applied to almost any polyelectrolyte–counterion pair, making possible the rapid development of syntheses of different nanoparticles within the same chemical environment. Using poly(acrylic acid) as a model system, a methodology for the optimization of conditions for the polyelectrolyte collapse by various mono- and multi-valent metal cations is developed. The optimal counterion concentration did not correlate with ionic strength and metal ion valency and was highly variable from system to system. By monitoring the polyelectrolyte conformation using viscosity and turbidity measurements, the appropriate metal ion concentration for each nanoparticle system was determined.

Electrospun Poly(acrylic acid)/Silica Hydrogel Nanofibers Scaffold for Highly Efficient Adsorption of Lanthanide Ions and Its Photoluminescence Performance

Combined with the features of electrospun nanofibers and the nature of hydrogel, a novel choreographed poly(acrylic acid)-silica hydrogel nanofibers (PAA-S HNFs) scaffold with excellent rare earth elements (REEs) recovery performance was fabricated by a facile route consisting of colloid-electrospinning of PAA/SiO2 precursor solution, moderate thermal cross-linking of PAA-S nanofiber matrix, and full swelling in water. The resultant PAA-S HNFs with a loose and spongy porous network structure exhibited a remarkable adsorption capacity of lanthanide ions (Ln(3+)) triggered by the penetration of Ln(3+) from the nanofiber surface to interior through the abundant water channels, which took full advantage of the internal adsorption sites of nanofibers. The effects of initial solution pH, concentration, and contact time on adsorption of Ln(3+) have been investigated comprehensively. The maximum equilibrium adsorption capacities for La(3+), Eu(3+), and Tb(3+) were 232.6, 268.8, and 250.0 mg/g, respectively, at pH 6, and the adsorption data were well-fitted to the Langmuir isotherm and pseudo-second-order models. The resultant PAA-S HNFs scaffolds could be regenerated successfully. Furthermore, the proposed adsorption mechanism of Ln(3+) on PAA-S HNFs scaffolds was the formation of bidentate carboxylates between carboxyl groups and Ln(3+) confirmed by FT-IR and XPS analysis. The well-designed PAA-S HNFs scaffold can be used as a promising alternative for effective REEs recovery. Moreover, benefiting from the unique features of Ln(3+), the Ln-PAA-S HNFs simultaneously exhibited versatile advantages including good photoluminescent performance, tunable emission color, and excellent flexibility and processability, which also hold great potential for applications in luminescent patterning, underwater fluorescent devices, sensors, and biomaterials, among others.

Dynamics of the layer-by-layer assembly of a poly(acrylic acid)-lanthanide complex colloid and poly(diallyldimethyl ammonium)

Poly(acrylic acid) (PAA) and lanthanide (Ln) ions, such as Ce(3+), Eu(3+), and Tb(3+), were prepared as dispersed complex colloidal particles through three different protocols with rigorous control of the pH value and mixing ratio. The negatively charged PAA-Ln complex particles were layer-by-layer (LbL) assembled with positively charged poly(diallyldimethyl ammonium) (PDDA) to prepare a thin film. The film thickness growth is much quicker than PDDA/PAA film. Due to the incorporation of Ln(3+) ions, the film exhibits fluorescence. During LbL assembly, PDDA-PAA association based on electrostatic force and PAA-Ce association based on coordination are in competition, which leads to the LbL assembly of PDDA and PAA-Ln complex colloidal particles being a complicated dynamic process.