Supramolecular association induced by Fe(III) in low molecular weight sodium polyacrylate

Stabilization of low-cost phase change materials for thermal energy storage applications

Sodium sulfate decahydrate (Na₂SO₄^.10H₂O, SSD), a low-cost phase change material (PCM), can store thermal energy. However, phase separation and unstable energy storage capacity (ESC) limit its use. To address these concerns, eight polymer additives-sodium polyacrylate (SPA), carboxymethyl cellulose (CMC), Fumed silica (SiO₂), potassium polyacrylate (PPA), cellulose nanofiber (CNF), hydroxyethyl cellulose (HEC), dextran sulfate sodium (DSS), and poly(sodium 4-styrenesulfonate) (PSS)-were used to explore several stabilization mechanisms. The ESC of PCMs deteriorated when thickeners, SPA, PPA, and CNF, were added. DSS-modified PCMs exhibited greater stability up to 150 cycles. Rheology measurements indicated that DSS did not impact SSD viscosity significantly during stabilization. Dynamic light scattering showed that DSS reduces SSD particle size and electrostatically suspends salt particles in a stable homogeneous solution, avoiding phase separation. This study proposes a promising method to improve the thermal stability of salt hydrate PCMs by utilizing polyelectrolyte-salt hydrate mixture for thermal energy storage applications.

Confining polyacrylic acid on the surface of nanoscale zero-valent iron by aluminum hydroxide for in-situ anti-passivation

Aggregation and surface passivation of nanoscale zero-valent iron (NZVI) particles have limited their reactivity and application for environmental remediation. In this study, an aluminum hydroxide/polyacrylic acid (Al(OH)₃/PAA) hybrid shell was homogeneously coated on the NZVI surface to overcome the limitations. PAA molecules were confined onto the NZVI surface by hydration of Al(III) cations. The Al(OH)₃/PAA coating shell provided more electrostatic repulsion forces between NZVI particles to hinder the particle aggregation and preserve the NZVI reactivity. On the other hand, the surface-anchored PAA provided a thickened reactive layer for Cr(VI) reduction. Besides, XPS and TEM results showed that the surface carboxylic groups bound produced Cr(III) and Fe(III) cations and inhibited the precipitation of hydroxides on the NZVI surface. The reduced passivation layer increased the longevity of NZVI for surface reactions. As a result, the 24-h Cr(VI) reduction capacity of NZVI particles was improved from 49.4 to 92.6 mg/g with a 2 wt% (Al/Fe) Al(OH)₃/PAA coating shell. Overall, this study presented a promising strategy to effectively tune the surface properties of nanoparticles and improve the feasibility of NZVI for environmental remediation.

Coprecipitation of Fe/Cr Hydroxides with Organics: Roles of Organic Properties in Composition and Stability of the Coprecipitates

Iron hydroxides are important scavengers for dissolved chromium (Cr) via coprecipitation processes; however, the influences of organic matter (OM) on Cr sequestration in Fe/Cr-OM ternary systems and the stability of the coprecipitates are not well understood. Here, Fe/Cr-OM coprecipitation was conducted at pH 3, and Cr hydroxide was undersaturated. Acetic acid (HAc), poly(acrylic acid) (PAA), and Suwannee River natural organic matter (SRNOM) were selected as model OMs, which showed different complexation capabilities with Fe/Cr ions and Fe/Cr hydroxide particles. HAc had no significant effect on the coprecipitation, as the monodentate carboxyl ligand in HAc did not favor complexation with dissolved Fe/Cr ions or Fe/Cr hydroxide nanoparticles. Contrarily, PAA and SRNOM with polydentate carboxyl ligand had strong complexation with Fe/Cr ions and Fe/Cr hydroxide nanoparticles, leading to significant amounts of PAA/SRNOM sequestered in the coprecipitates, which caused the structural disorder and fast aggregation of the coprecipitates. In comparison with that of PAA, preferential complexation of Cr ions with SRNOM resulted in higher Cr/Fe ratios in the coprecipitates. This study advances the fundamental understanding of Fe/Cr-OM coprecipitation and mechanisms controlling the composition and stability of the coprecipitates, which is essential for successful Cr remediation and removal in both natural and engineered settings.

Adding a recyclable amendment to facilitate sewage sludge biodrying and reduce costs

Finding an economical amendment, available in a steady supply, is needed to support the biodrying industrialization. This research developed a recyclable biodrying amendment (RBA) to condition the biodrying of sewage sludge. The pilot-scale treatment (T_R), which included the addition of equivalent weights of RBA and sawdust as amendments, resulted in a higher pile temperature and longer thermophilic phase compared to the control (T_C), which used only sawdust as an amendment. The final moisture content levels were below 50% with both T_R and T_C. The heat use efficiency for water evaporation was 72.2% and 73.0% in T_R and T_C, respectively. The activity of α-amylase and cellulose 1,4-β-cellobiosidase increased during the thermophilic phase, while the activity of endo-1,4-β-glucanase and endo-1,4-β-xylanase decreased during the thermophilic phase with both T_R and T_C. The fourier-transform infrared spectra indicated that adding the RBA resulted in good biodegradability of the lipids, proteins, and polysaccharides. The humic acid to fulvic acid ratio in T_R and T_C increased from 0.33 (T_R) and 0.35 (T_C) on day 0-0.46 (T_R) and 0.45 (T_C) on day 21, indicating the humification process. The RBA recovery rate was 95.6% and can be reused. These findings highlight that adding RBA showed satisfactory biodrying performance, reduced the amendment cost, and the biodrying product could be incinerated without energy deficit.

Modifying alginate beads using polycarboxyl component for enhanced metal ions removal

Designing desirable adsorbent for highly efficient removal of heavy metal ions is of practical significance, given the cost-effectiveness, environmental benign, natural abundance and easy-handling collection features. Herein, a bead-like adsorbent with high adsorption capacity was prepared by modifying alginate beads using polyacrylate with high density of carboxyl groups. The developed alginate/polyacrylate beads were collaboratively characterized by FT-IR, TGA, SEM, XPS, etc., and various adsorption conditions were tested including the pH of the solution, contact time and the initial concentration. The experimental data were fitted well by the Freundlich isotherm model, and the maximum adsorption capacity was obtained from the Langmuir model was 611.0 mg/g, and adsorption process followed the Pseudo-second-order kinetic model. The adsorption mechanisms conformed to multi-layer adsorption, and mainly dominated by chemical interactions. The bead-like adsorbent exhibited excellent reusability after eight sequential cycles and displayed higher adsorption capacity towards lead ions. This type of adsorbent might possess promising role in treating heavy metals from water by virtue of degradable, cost-effective component and high adsorption efficiency.

Homogeneous and Real Super Tough Multi-Bond Network Hydrogels Created through a Controllable Metal Ion Permeation Strategy

Poly(acrylic acid) (PAA) hydrogels with a multi-bond network composed of sparse chemical cross-links and carboxyl-Fe³⁺ coordination are prepared through a controllable permeation strategy utilizing ferric citrate (FeCA). The existing strategies that directly soak PAA hydrogels in Fe³⁺ solutions usually induce an inhomogeneous network with densely cross-linked shells and uncertain water content of the hydrogels, which brings about ambiguity when investigating strengthening mechanisms because water content significantly affects the mechanical properties of hydrogels. Herein, the controllable permeation of Fe³⁺ into PAA networks based on the competition between citric acid (CA)-Fe³⁺ chelation and PAA-Fe³⁺ coordination guarantees sustained release of Fe³⁺, facilitating homogeneous distribution of ionic cross-links and a certain water content. The obtained hydrogels exhibit excellent and balanced mechanical properties (high tensile strength of 3.28 to 6.95 MPa with large elongations at break of 1400 to 780% when water content decreases from 80 to 50 wt %). The real robust tensile strength of this hydrogel originates from the effective energy dissipation of the homogeneous PAA-Fe³⁺ cross-links, and the high water content ensures a large elongation at break. Furthermore, the hydrogel also has pH-responsive and shape-memory properties.

Unpredictable Dynamics of Polymeric Reacting Flow by Comparison between Pre- and Post-Reaction Fluid Properties: Hydrodynamics Involving Molecular Diagnosis via ATR-FTIR Spectroscopy

In reacting flows, changes in fluid properties induced by the chemical reaction can alter the flow dynamics. Generally, these changes in fluid properties are evaluated by comparison between their pre- and post-reaction properties. If a fluid property such as viscosity decreases between pre- and post-reaction, we expect a decrease in viscosity to occur in the reacting flow. However, this study demonstrates a reacting polymeric liquid flow where a remarkable increase in the viscoelasticity temporally occurs despite the viscosity slightly decreasing after the reaction. We elucidated the underlying reaction mechanism, which involves a structural change in the side functional group (carboxyl) in polyacrylamide at ultrahigh molecular weights ( M_w > 10⁶) with ultralow concentrations ([polymer] < 1 wt %) by using ATR-FTIR spectroscopy. This study demonstrates the existence of a reacting flow in which examination of microscopic molecular structure is required to understand the macroscopic flow dynamics. The findings will be valuable not only for industrial application such as reactor designs and rheology control but also for opening a new research area: chemically reacting flow involving the diagnosis of molecule structure.

Evaluation of Single Hydrogel Nanofiber Mechanics Using Persistence Length Analysis

Polyelectrolyte hydrogel fibers can mimic the extracellular matrix and be used for tissue scaffolding. Mechanical properties of polyelectrolyte nanofibers are crucial in manipulating cell behavior, which metal ions have been found to enable tuning. While metal ions play an important role in manipulating the mechanical properties of the fibers, evaluating the mechanical properties of a single hydrated hydrogel fiber remains a challenging task and a more detailed understanding of how ions modulate the mechanical properties of individual polyelectrolyte polymers is still lacking. In this study, dark-field microscopy and persistence length analysis help directly evaluate fiber mechanics using electrospun fibers of poly(acrylic acid) (PAA), chitosan (CS), and ferric ions as a model system. By comparing the persistence length and estimated Young's modulus of different nanofibers, we demonstrate that persistence length analysis is a viable approach to evaluate mechanical properties of hydrated fibers. Ferric ions were found to create shorter and stiffer nanofibers, with Young's modulus estimated at a few kilopascals. Ferric ions, at low concentration, reduce the Young's modulus of PAA and PAA/CS fibers through the interaction between ferric ions and carboxylate groups. Such interaction was further supported by nanoscale infrared spectroscopy studies of PAA and PAA/CS fibers with different concentrations of ferric ions.

DNA binding and cytotoxicity studies of magnetic nanofluid containing antiviral drug oseltamivir

In this work, the possibility of preparing a nanoparticle with improved treatment properties was investigated. In this regard, synthesis, characterization, in vitro cytotoxicity and DNA binding of Fe₃O₄@oleate/oseltamivir magnetic nanoparticles (MNPs) were investigated. Fe₃O₄ nanoparticles were synthesized via chemical co-precipitation and coated by oleate bilayers. Then, Fe₃O₄@OA MNPs were functionalized with an antiviral drug (oseltamivir), for better biological applications. The MNPs were subsequently characterized by zeta sizer and Zeta potential measurements, Fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM) analyses. The TEM image demonstrated that average sizes of Fe₃O₄@OA/oseltamivir MNPs were about 8 nm. The in vitro cytotoxicity of Fe₃O₄@OA/oseltamivir MNPs was studied against cancer cell lines (MCF-7 and MDA-MB-231) and compared with oseltamivir drug. The results illustrated that Fe₃O₄@OA/oseltamivir magnetic nanoparticles have better antiproliferative effects on the mentioned cell lines as compared with oseltamivir. Also, in vitro DNA binding studies were done by UV-Vis, circular dichroism, and Fluorescence spectroscopy. The results indicated that Fe₃O₄@OA/oseltamivir MNPs bound to DNA via groove binding. Moreover, this magnetic nanofluid has potential for magnetic hyperthermia therapy due to magnetic core of its nanoparticles. Communicated by Ramaswamy H. Sarma.

Enhanced reactivity of nZVI embedded into supermacroporous cryogels for highly efficient Cr(VI) and total Cr removal from aqueous solution

Novel supermacroporous PSA-nZVI composites with nanoscale zero-valent iron particles (nZVI) embedded into poly (sodium acrylate) (PSA) cryogels were synthesized through ion exchange followed by in-situ reduction. The magnetic composites were evaluated for material characterizations and their efficiency for Cr(VI) and total Cr removal from aqueous medium in batch experiments. PSA-nZVI composites with high nZVI loading capacity up to 128.70 mg Fe/g PSA were obtained, and the interconnected macroporous structure of PSA cryogel remained unaltered with nZVI uniformly distributed on PSA cryogel as determined by TGA, SEM, TEM, XRD and XPS analyses. PSA-nZVI composites showed faster reaction rate than free nZVI both for Cr(VI) and total Cr removal, suggesting no mass transfer resistance and the enhanced reactivity of nZVI in PSA carrier. PSA-nZVI composites exhibited much more remarkable performance for Cr(VI) and total Cr removal than free nZVI particles in high removal capacity and broad pH application range (pH 4-10). The reaction mechanisms were also elucidated with XPS analyses before and after Cr(VI) reduction reactions. These results demonstrate that PSA cryogel acts as an excellent carrier and shows multiple functions in nZVI particle dispersion, pH buffering and oxidation resistance in addition to immobilizing nZVI particles from release.

Designed polyelectrolyte shell on magnetite nanocore for dilution-resistant biocompatible magnetic fluids

Magnetite nanoparticles (MNPs) coated with poly(acrylic acid-co-maleic acid) polyelectrolyte (PAM) have been prepared with the aim of improving colloidal stability of core-shell nanoparticles for biomedical applications and enhancing the durability of the coating shells. FTIR-ATR measurements reveal two types of interaction of PAM with MNPs: hydrogen bonding and inner-sphere metal-carboxylate complex formation. The mechanism of the latter is ligand exchange between uncharged -OH groups of the surface and -COO(-) anionic moieties of the polyelectrolyte as revealed by adsorption and electrokinetic experiments. The aqueous dispersion of PAM@MNP particles (magnetic fluids - MFs) tolerates physiological salt concentration at composition corresponding to the plateau of the high-affinity adsorption isotherm. The plateau is reached at small amount of added PAM and at low concentration of nonadsorbed PAM, making PAM highly efficient for coating MNPs. The adsorbed PAM layer is not desorbed during dilution. The performance of the PAM shell is superior to that of poly(acrylic acid) (PAA), often used in biocompatible MFs. This is explained by the different adsorption mechanisms; metal-carboxylate cannot form in the case of PAA. Molecular-level understanding of the protective shell formation on MNPs presented here improves fundamentally the colloidal techniques used in core-shell nanoparticle production for nanotechnology applications.

Simultaneous Presence of Diverse Molecular Patterns in Humic Substances in Solution

The chemical and structural nature of humic substances (HS) is the object of an intense debate in the literature involving two main theoretical positions: the classical view defending the macromolecular pattern, and the new, more recent, view proposing a supramolecular pattern. In this study, we observe that both molecular patterns are present in different whole humic systems in solution. We also identify these molecular patterns with a specific fraction of HS. Thus, the HS family formed by the gray humic acids studied presented a clear macromolecular pattern, whereas the HS family formed by the fulvic acids studied presented the coexistence of supramolecular assemblies and individual molecules. The third HS family studied, the brown humic acids, presented both the macromolecular pattern and the supramolecular pattern. We also find that molecular aggregation-disaggregation has a strong influence in the fluorescence pattern of HS, thus indicating that the current concepts of HS structure derived from fluorescence studies need revision.