Removal of heavy metals from wastewater using magnetic nanocomposites: Analysis of the experimental conditions

This contribution provides insight on the elimination of heavy metals from water resources using magnetic separation. Nanocomposites based on magnetite and chitosan were prepared. An exhaustive characterization of the magnetic adsorbents was developed. Adsorption assays were performed in batch using Cu, Zn, Cd, and Cr as model heavy metals. The efficiency of magnetic adsorbents followed the order: Cu > Cd > Zn > Cr, with maximum values of 188, 159, 72, and 46 mg of Me/g of nanocomposite, respectively. Kinetics and mechanistic issues were studied. The magnetic materials were efficient for five to eight cycles using Cu(II),Cd(II), and Cr(VI).     

Nanoindentation Creep,Nano-Impact,and Thermal Properties of Multiwall Carbon Nanotubes–Polypropylene Nanocomposites Prepared via Melt Blending

Morphological analysis of the nanocomposites showed that multi-wall carbon nanotubes were uniformly distributed in polypropylene. Nanoindentation creep and nano-impact tests were carried out. Several equations/models were used to analyze creep data. From creep test, hardness of the nanocomposites increased by 18 and 36% for C150P and C70P, respectively, compared to polypropylene, whereas elasticity also increased by 20 and 34%. From nano-impact test, hardness of the nanocomposites was also higher than that of neat polypropylene. However, hardness (dynamic/impact) values were slightly higher than the (quasi-static) hardness resulted from creep test. In addition, degree of crystallinity of nanocomposites also increased by 12.6 and 14.3%.     

POSS-based hybrid thermosets via photoinduced copper-catalyzed azide–alkyne cycloaddition click chemistry

An efficient approach for the preparation of inorganic/organic hybrid thermosets via photoinduced copper-catalyzed azide–alkyne cycloaddition click chemistry is established. Highly cross-linked thermoset polymers have been practically obtained by this technique using multifunctional compounds, tri-alkyne (1,1,1-tris[4-(2-propynyloxy) phenyl]-ethane) with octakis-azido-POSS or tri-azide (3,3′-((2-((3-azido-2-hydroxypropoxy)methyl)-2-ethylpropane-1,3-diyl)bis(oxy))bis(1-azidopropan-2-ol)) in the presence of Cu(II)Br₂/N,N,N′,N″,N?-pentamethyldiethylenetriamine/2-dimethoxy-2-phenyl acetophenone. The homogeneously distributed POSS nanoparticles are clearly detected in the TEM micrographs; whereas the TGA analysis shows that the obtained hybrid thermosets are thermally stable up to 360 °C and begin to lose weight at higher temperatures with a char yield of 23–50% at 800 °C.     

Reactive Extrusion Strategies to Fabricate Magnetite–Polyethylene Nanocomposites with Enhanced Mechanical and Magnetic Hyperthermia Properties

Biofouling is a major problem in water filtration units, which leads to premature system failure. Conventional treatment methods involving the use of chemicals or high‐pressure hydraulics exert mechanical strain on filter materials, leading to shortened service lifetimes. In this study, a novel magnetic polymer nanocomposite is fabricated using a blend of high density/ultrahigh molecular weight polyethylene with magnetite nanoparticle (MNP) fillers. The resulting magnetite–polyethylene nanocomposite (MPE‐NC) is mechanically robust and can be externally actuated with an alternating magnetic field to generate localized heating that is effective in eradicating bacterial biofilms. The MNPs are functionalized with silane‐based coupling agents and crosslinked onto the polyethylene backbone via a reactive extrusion approach, which results in a twofold enhancement in mechanical properties of the polymer matrix. Furthermore, the magnetic hyperthermia performance of the MPE‐NC is improved eightfold by replacing undoped magnetite nanospheres with zinc‐doped magnetite nanocube fillers, and the magnetic hyperthermia treatment approach is shown to be 12 times more effective in destroying bacterial biofilms compared to a direct heat‐treatment method. During hyperthermia treatment, the mechanical integrity of the MPE‐NC is preserved, thereby validating the potential of the MPE‐NC as a new filter material with high efficiency in biofilm removal and extended durability.

     

粉末冶金法制备Cu/SiO2纳米复合材料的组织与性能

采用粉末冶金法制备Cu／SiO2纳米复合材料，研究SiO2含量对复合材料性能的影响。结果表明，在烧结过程中．Cu／SiO2复合材料的体积收缩。密度增加，并且随SiO2含量提高，Cu／SiO2纳米复合材料的电导率降低，维氏硬度和机械性能明显升高。退火温度曲线表明，Cu／SiO2复合材料的软化温度为750℃，高于纯铜的软化温度150℃，具有很好的热稳定性。     

Magnetically controlled shape-memory effects of hybrid nanocomposites from oligo(ω-pentadecalactone) and covalently integrated magnetite nanoparticles

The covalent integration of inorganic nanoparticles in polymer matrices has gained significance for improving the structural properties of polymer-based materials. Here we report on the performance of poly(ω-pentadecalactone) networks with magnetite nanoparticles as netpoints in their magnetically-controlled shape-memory capability. Hybrid nanocomposites with magnetite nanoparticle content ranging from 5 to 11 wt% were prepared by reacting two types of oligo(ω-pentadecalactone) (OPDL) based precursors with terminal hydroxy groups, a three arm OPDL (³AOPDL, M_n = 6000 g mol⁻¹) and an OPDL (M_n = 3300 g mol⁻¹) coated magnetite nanoparticle (∅ = 10 nm), with a diisocyanate. Homogenous hybrid nanocomposites were obtained independent from the weight content of the OPDL decorated nanoparticles in the samples. At 100 °C (T > T_m-OPDL) the covalent integration of the nanoparticles increased the mechanical strength with increasing weight content whereby the elasticity remained almost constant. In magnetically-controlled one-way dual-shape experiments the shape fixity decreased from 95% to 90% but the shape recovery increased slightly from 95% to 97% when the nanoparticle content was increased. In magnetically-controlled reversible dual-shape experiments the nanoparticles had a restraining effect and the maximum shape-change of 65% for hybrid nanocomposites with 5 wt% magnetite nanoparticles was reduced to 36% when the particle content was increased to 11 wt%. These results show that the performance of hybrid nanocomposites can be tailored by nanoparticle content, however in terms of their applicability either mechanical strength or actuation capability should be focussed in the material selection.     

Influence of a cyclic butylene terephthalate oligomer on the processability and thermoelectric properties of polycarbonate/MWCNT nanocomposites

The thermoelectric properties of melt-processed nanocomposites consisting of a polycarbonate (PC) thermoplastic matrix filled with commercially available carboxyl (–COOH) functionalized multi-walled carbon nanotubes (MWCNTs) were evaluated. MWCNTs carrying carboxylic acid moieties (MWCNT-COOH) were used due the p-doping that the carboxyl groups facilitate, via electron withdrawing from the electron-rich π-conjugated system. Preliminary thermogravimetric analysis (TGA) of MWCNT-COOH revealed that the melt-mixing was limited at low temperatures due to thermal decomposition of the MWCNT functional groups. Therefore, PC was mixed with 2.5 wt% MWCNT-COOH (PC/MWCNT-COOH) at 240 °C and 270 °C. In order to reduce the polymer melt viscosity, a cyclic butylene terephthalate (CBT) oligomer was utilized as an additive, improving additionally the electrical conductivity of the nanocomposites. The melt rheological characterization of neat PC and PC/CBT blends demonstrated a significant decrease of the complex viscosity by the addition of CBT (10 wt%). Optical and transmission electron microscopy (OM, TEM) depicted an improved MWCNT dispersion in the PC/CBT polymer blend. The electrical conductivity was remarkably higher for the PC/MWCNT-COOH/CBT composites compared to the PC/MWCNT-COOH ones. Namely, the PC/MWCNT-COOH/CBT processed at 270 °C exhibited the best values with electrical conductivity; σ = 0.05 S/m, Seebeck coefficient; S = 13.55 μV/K, power factor; PF = 7.60 × 10⁻⁶μW/m K⁻², and thermoelectric figure of merit; ZT = 7.94 × 10⁻⁹. The PC/MWCNT-COOH/CBT nanocomposites could be ideal candidates for large-scale thermal energy harvesting, even though the presently obtained ZT values are still too low for commercial applications.     

Effect of silane structure on the properties of silanized multiwalled carbon nanotube-epoxy nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were functionalized with aminosilanes via an aqueous deposition route. The size and morphology of siloxane oligomers grafted to the MWCNTs was tuned by varying the silane functionality and concentration and their effect on the properties of a filled epoxy system was investigated. The siloxane structure was found to profoundly affect the thermo-mechanical behavior of composites reinforced with the silanized MWCNTs. Well-defined siloxane brushes increased the epoxy T_g by up to 19 °C and significantly altered the network relaxation dynamics, while irregular, siloxane networks grafted to the MWCNTs had little effect. The addition of both types of silanized MWCNTs elicited improvements in the strength of the nanocomposites, but only the well-defined siloxane brushes engendered dramatic improvements in toughness. Because the silanization reaction is simple, rapid, and performed under aqueous conditions, it is also an industrially attractive functionalization route.     

Influence of injection molding on the electrical properties of polyamide 12 filled with multi-walled carbon nanotubes

Microinjection-molded and compression-molded polyamide (PA12) matrix composites filled with 0.67, 1.33, 2 and 4 wt% multi-walled carbon nanotubes (MWNTs) were prepared from twin-screw extruded pellets. The compression molded samples have an electrical percolation threshold close to 1.2 wt%. Coupled rheological and electrical measurements show that their electrical properties start decreasing as soon as shear begins and are partially restored during flow, suggesting successively breakage and reconstruction of a percolating network. On the other hand, the electrical properties of the microinjection molded composites are close to the matrix ones, showing that cooling is too fast for the MWNTs to form a network. There is some electrical anisotropy in these composites, as evidenced by a greater conductivity measured in the flow direction. However polarized Raman spectroscopy analysis does not reveal a significant orientation of the MWNTs.