Highly efficient and selective removal of anionic dyes from aqueous solutions using polyacrylamide/peach gum polysaccharide/attapulgite composite hydrogels with positively charged hybrid network.

To avoid the weakness (lower adsorption rate and selectivity) of peach gum polysaccharide (PGP) and improve the adsorption performance of polyacrylamide (PAAm) hydrogel (lower adsorption capacity), in the present work, the PGP was chemically tailored to afford ammoniated PGP (APGP) and quaternized PGP (QPGP), and attapulgite (ATP) was bi-functionalized with cation groups and carbon­carbon double bond. Then, PAAm/APGP and PAAm/QPGP/ATP hydrogels were synthesized via redox polymerization. The synthesis procedure and properties of hydrogels were traced by FTIR, SEM, XPS, TGA, TEM, and BET methods, and the dye adsorption performance of the hydrogels was evaluated using the new coccine (NC) and tartrazine (TTZ) aqueous solutions as the model anionic dyes. Effects of initial dye concentration, pH, and ionic strength on the adsorption were investigated. Compared with PAAm/APGP hydrogel, PAAm/APGP/ATP hydrogel exhibits higher adsorption rate, superior adsorption capacity, stability, and selectivity towards anionic dye. The adsorption process of PAAm/QPGP/ATP hydrogel reached equilibrium in about 20 min and followed the pseudo-second-order kinetic model and Langmuir isotherm. The adsorption capacities towards NC and TTZ of PAAm/QPGP/ATP hydrogel were calculated as 873.235 and 731.432 mg/g. This hydrogel adsorbent originating from PAAm, PGP, and ATP shows great promise for application in practical water treatment.

Construction of a Self-Assembled Polyelectrolyte/Graphene Oxide Multilayer Film and Its Interaction with Metal Ions.

In this study, a composite multilayer film onto gold was constructed from two charged building blocks, i.e., negatively charged graphene oxide (GO) and a branched polycation (polyethylenimine, PEI) via layer-by-layer (LbL) self-assembly technology, and this process was monitored in situ with quartz crystal microbalance (QCM) under different experimental conditions. This included the differences in frequency (Δf) as well as the changes in dissipation to yield information on the absorbed mass and viscoelastic properties of the formed PEI/GO multilayer films. The experimental conditions were optimized to obtain a high amount of the adsorbed mass of the self-assembled multilayer film. The surface morphology of the PEI/GO multilayer film onto gold was studied with atomic force microscopy (AFM). It was found that the positively charged PEI chains were combined with the oppositely charged GO to form an assembled film on the QCM sensor surface, in a wrapped and curled fashion. Raman and UV-vis spectra also showed that the intensities of the GO-characteristic signals are almost linearly related to the layer number. To explore the films for their use in divalent ion detection, the frequency response of the PEI/GO multilayer-modified QCM sensor to the exposure of aqueous solutions solution of Cu2+, Ca2+, Zn2+, and Sn2+ was further studied using QCM. Based on the Sauerbrey equation and the weight of different ions, the number of metal ions adsorbed per unit area on the surface of QCM sensors was calculated. For metal ion concentrations of 40 ppm, the adsorption capacities per unit area of Cu2+, Zn2+, Sn2+, and Ca2+ were found to be 1.7, 3.2, 0.7, and 4.9 nmol/cm2, respectively. Thus, in terms of the number of adsorbed ions per unit area, the QCM sensor modified by PEI/GO multilayer film shows the largest adsorption capacity of Ca2+. This can be rationalized by the relative hydration energies.

Facile preparation of polyacrylamide/chitosan/Fe3O4 composite hydrogels for effective removal of methylene blue from aqueous solution.

In this study, Fe3O4 magnetic nanoparticles were synthesized in situ in the polyacrylamide/chitosan (PAAm/CS) hydrogel networks. The obtained hydrogels are characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The results confirm that the three-dimensional network structure of the hydrogels is incorporated with Fe3O4 nanoparticles. The adsorption properties of PAAm/CS/Fe3O4 hydrogels for methylene blue (MB) in aqueous solution were studied using Ultraviolet and visible spectrophotometry (UV-vis). The results show that when compared to PAAm/CS hydrogels, PAAm/CS/Fe3O4 hydrogels can adsorb MB with higher adsorption capacities of approximately 1603 mg/g, and the kinetics and isotherm models of the adsorption process could be better described by the pseudo-first order model and Langmuir isotherm model, respectively. Due to the facile preparation, high adsorption capacity, and low cost, the PAAm/CS/Fe3O4 hydrogels are good adsorbents for MB and exhibit significant potential in the treatment of sewage.

Facile Fabrication of High-Contrast and Light-Colored Marking on Dark Thermoplastic Polyurethane Materials.

In this work, using ferroferric oxide (Fe3O4) and zirconium oxide (ZrO2) as laser-sensitive particles and thermoplastic polyurethane (TPU) as the matrix resin, a series of TPU/Fe3O4/ZrO2 composites were prepared by melt blending, and the effect of the laser marking additive content, composition, and laser marking parameters on the laser marking properties of composites was investigated. The laser marking mechanism of Fe3O4/ZrO2 additives and the role of each component in TPU laser marking were studied by metallographic microscopy, color difference test, scanning electron microscopy, and Raman spectroscopy. Fe3O4 nanoparticles as a laser sensitizer component, on the one hand, can act as a pigment to make the TPU substrate black and, on the other hand, can absorb laser energy to contribute to the formation of laser markings on TPU composite surfaces. In addition, the introduction of ZrO2 nanoparticles can help absorb the laser energy, while the contrast can be improved to enhance the laser marking performance of the TPU composite. Through thermogravimetric analysis, the changes in the thermally stable properties of TPU composites before and after laser marking were investigated, and the results indicated that Fe3O4/ZrO2 nanoparticles can absorb the laser energy, causing melting and pyrolysis of the TPU backbone at a high temperature, to produce a gaseous product resulting in foaming. Finally, the high-contrast and light-colored markings were formed on the black TPU composite surface. This work provides a facile method for producing high-contrast and light-colored markings on the dark TPU composite surface.

Preparation of near-infrared laser responsive hydrogels with enhanced laser marking performance.

Polystyrene modified bismuth oxide particles (PS@Bi2O3) were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Using acrylamide (AM) as a monomer, and PS@Bi2O3 as laser sensitive additives, PAM/PS@Bi2O3 hydrogels were fabricated and treated by a 1064 nm near-infrared laser. The laser responsive properties of PAM/PS@Bi2O3 hydrogels were investigated at different current intensities and loading content of PS@Bi2O3 by visual observation, optical microscopy, and SEM, and the mechanism of laser response was analyzed by XRD and Raman spectroscopy. The results indicate that the PAM hydrogel with added PS@Bi2O3 particles showed excellent response to the laser, and high contrast and resolution text and pattern marks on the hydrogel surface can be obtained. The selection of suitable laser current intensity is key to the laser response of the PAM/PS@Bi2O3 composite hydrogel. Through analysis of XRD, Raman spectroscopy, and TGA data, the laser marking of the PAM/PS@Bi2O3 hydrogels originates from the generation of both bismuth metal and amorphous carbonized materials. After adding PS@Bi2O3 with a loading content from 1% to 3%, the mechanical properties of the hydrogels were improved, but the swelling properties were finally decreased.

The effect of chain structures on the crystallization behavior and membrane formation of poly(vinylidene fluoride) copolymers.

The crystallization behaviors of two copolymers of PVDF were studied, and the effect of copolymerized chains on the crystallization behavior was investigated. The results indicated that both copolymers had a lowered crystallization temperature and crystallinity. The crystallization rate was improved by the copolymer with symmetrical units in PVDF chains, but hindered by asymmetrical units, compared with the neat PVDF. The symmetrical units in PVDF chains favored the ß-crystals with fiber-like structures. According to the solubility parameter rule, methyl salicylate (MS) can be chosen as a diluent for PVDF copolymers. Both diluted systems had liquid-liquid (L-L) regions in the phase diagrams, which was due to the lowered crystallization temperature.