Rosiyah Yahya

The removal of heavy metal ions from wastewater/aqueous solution using polypyrrole-based adsorbents: a review

Water pollution caused by heavy metal ions is becoming a serious threat to human and aquatic lives day by day. Therefore, the treatment of heavy metal ions is of special concern for environmental scientists and engineers. Historically, various methods, such as physical and chemical precipitation, ion-exchange, reverse osmosis, membrane filtration, electrochemical treatment, solvent extraction, and adsorption, have been widely studied for the removal of these metal ions from aqueous/wastewater. However, over the past few decades, conducting polymer-based adsorbents have received considerable attention owing to their potential applications for different heavy metal ions especially Cr(VI), Zn(II), and Pb(II). Among the various conducting polymers, polypyrrole (PPy) based adsorbents play a major role for the removal of various heavy metal ions due to their ease of synthesis, biocompatibility and redox properties. The current review has mainly focused on the physico-chemical properties, adsorption characteristics and mechanism of different polypyrrole-based adsorbents, including PPy/biosorbents, PPy/Fe3O4 nanocomposites, PPy–polyaniline nanofibers, PPy–graphene nanocomposites, exfoliated PPy-organically modified clay nanocomposites, and hierarchical porous PPy-nanoclusters, as well as their applications towards the removal of heavy metal ions.

Tensile, Impact and Fiber Length Properties of Injection-Molded Short and Long Glass Fiber-Reinforced Polyamide 6,6 Composites

Injection molding of fiber-reinforced polymer composites is associated with the problem of fiber breakage. If the fiber length retained in the finish product is too short, it will limit the expected improvement in the property. Extrusion and pultrusion are two methods normally employed for the melt compounding of polymer composite feedstock for the injection molding and produced short- and long-fiber composites (SFCs and LFCs), respectively. In this work, short- and long-glass fiber-reinforced polyamide 6,6 composites were injection molded at different fiber loading and tested for the tensile properties, impact properties and fiber length characteristics. It was found that both tensile strength and tensile modulus of LFCs improved compared to the SFCs counterpart despite reduction in fracture strain, while pultrusion compounded composites also showed superior fiber characteristics, in terms of fiber length distribution, Ln, Lw, etc. compared to the extrusion compounded composites counterpart. Fiber length characteristics were also in agreement with the improvement in tensile strength and tensile modulus of LFCs over the SFCs. Impact properties of LFCs also show some improvement compared to the SFCs counterpart with equivalent composition, despite longer fiber retained in composites.

ATR-FTIR studies on ion interaction of lithium perchlorate in polyacrylate/poly(ethylene oxide) blends

The interaction behaviours between components of polyacrylate (PAc)/poly(ethylene oxide) (PEO) and lithium perchlorate (LiClO(4)) were investigated in detail by Attenuated Total Reflectance (ATR)-Fourier Transformed Infrared (FTIR) spectroscopy. Solution cast films of the PAc/PEO and PAc/PEO/LiClO(4) were examined. No obvious shifting of the characteristic ether and ester group stretching modes of PEO and PAc was observed, indicating incompatibility of the binary PAc/PEO blend. The spectroscopic studies on the PAc/PEO/LiClO(4) blends reveal that Li(+) ions coordinate individually to the polymer components at the ether oxygen of PEO and the C-O of the ester group of PAc. Frequency changes observed on the nu(C-O-C) and omega(CH(2)) of PEO confirm the coordination between PEO and Li(+) ions resulting in crystallinity suppression of PEO. The absence of experimental evidence on the formation of PEO-Li(+)-PAc complexes suggests that LiClO(4) does not enhance the compatibility of PAc/PEO blend.

Structural and Optical Characterization of Metal Tungstates (MWO4; M=Ni, Ba, Bi) Synthesized by a Sucrose-Templated Method

BackgroundMetal tungstates have attracted much attention due to their interesting structural and photoluminescence properties. Depending on the size of the bivalent cation present, the metal tungstates will adopt structures with different phases. In this work, three different phases of metal tungstates MWO4 (M= Ba, Ni and Bi) were synthesized via the sucrose templated method.ResultsThe powders of BaWO4 (tetragonal), NiWO4 (monoclinic) and Bi2WO6 (orthorhombic) formed after calcination temperatures of 750, 650 and 600°C for 4 h respectively are found to be crystalline and exist in their pure phase. Based on Scherrer estimation, their crystallite size are of nanosized. BET results showed NiWO4 has the highest surface area. BaWO4 exhibited less Raman vibrations than the NiWO4 because of the increased lattice symmetry but Bi2WO6 showed almost the same Raman vibrations as BaWO4. From the UV-vis spectra, the band gap transition of the metal tungstates are of the order of BaWO4 > Bi2WO6 > NiWO4. Broad blue-green emission peaks were detected in photoluminescence spectra and the results showed the great dependence on morphology, crystallinity and size of the metal tungstates.ConclusionThree different phases of metal tungstates of BaWO4 (scheelite), NiWO4 (wolframite) and Bi2WO6 (perovskite layer) in their pure phase were successfully prepared by the simple and economical sucrose-templated method. The highest surface area is exhibited by NiWO4 while largest band gap is shown by BaWO4. These materials showed promising optical properties.

pH Sensitive Hydrogels in Drug Delivery: Brief History, Properties, Swelling, and Release Mechanism, Material Selection and Applications

Improving the safety efficacy ratio of existing drugs is a current challenge to be addressed rather than the development of novel drugs which involve much expense and time. The efficacy of drugs is affected by a number of factors such as their low aqueous solubility, unequal absorption along the gastrointestinal (GI) tract, risk of degradation in the acidic milieu of the stomach, low permeation of the drugs in the upper GI tract, systematic side effects, etc. This review aims to enlighten readers on the role of pH sensitive hydrogels in drug delivery, their mechanism of action, swelling, and drug release as a function of pH change along the GI tract. The basis for the selection of materials, their structural features, physical and chemical properties, the presence of ionic pendant groups, and the influence of their pKa and pKb values on the ionization, consequent swelling, and targeted drug release are also highlighted.

Extrusion and injection-molding of glass-fiber/MAPP/polypropylene: Effect of coupling agent on DSC, DMA and mechanical properties

Glass fiber-reinforced PP composites compatibilized with maleic anhydride grafted polypropylene (MAPP) were compounded with a twin-screw extruder and injection molded. The composite specimens were subjected to DSC, DMA, tensile, and flexural property characterizations. DSC results showed that the presence of glass fiber loading and MAPP produced insignificant effect on the melting temperature of the composites. The melting enthalpy was decreased with glass fiber loadings, but no significant change was noted in the crystalline peak temperatures ( T c ). Incorporation of the compatibilizer led to a reduction in T c . Incorporation of glass fiber reduced the crystalline enthalpy of compatibilized and uncompatibilized systems. DMA results showed that composite properties were affected by the presence of the compatibilizer at low fiber loading (≤14% Vf). Tensile and flexural properties also showed sensible improvement of compatibilized against uncompatibilized composite systems.

The influence of novel zinc hydroxystannate-coated fillers on the fire properties of flexible PVC

Zinc hydroxystannate (ZHS), at levels of 2-5 phr, and the hydrated fillers, magnesium hydroxide (MH) and alumina trihydrate (ATH), at levels of 20–50 phr, are effective flame retardants and smoke suppressants for flexible PVC. Novel ZHS-coated hydrated fillers are found to exhibit markedly improved fire-retardant properties, particularly with regard to increasing LOI values, reducing heat release rates and suppressing smoke generation, when compared with conventional uncoated forms. The ZHS coating appears to change the filler particle morphology and there is evidence that the coating is largely retained on the filler surface after melt processing into the PVC. The improved dispersion of the active tin compound in the polymer matrix leads to enhanced fire retardancy and this, in turn, allows significant reductions to be made in overall filler loading, with no loss in flame-retardant or smoke-suppressant performance.

Hydrogenolysis of alkanes. Part 5.—Effect of metal dispersion in ruthenium/alumina catalysts on the hydrogenolysis of propane and of n-butane

Turnover frequencies for the hydrogenolysis of propane and of n-butane decrease with increasing dispersion for a series of Ru/Al2O3 catalysts prepared from Ru(acac)3, having values of H/Ru between 0.07 and 1.05. Activation energies for reactant removal do not vary greatly or systematically with dispersion, but product selectivities found with n-butane do. Thus at 480 K, selectivity to methane (S1) decreases markedly, and those to ethane (S2) and to propane (S3) increase correspondingly, with increasing dispersion; and most notably the very highly dispersed catalyst maintains its high value of S2 to > 520 K, at which temperature the catalyst of lowest dispersion produces almost pure methane.These variations are interpreted in terms of a combination of geometric and electronic factors; an ensemble-size requirement determines the rate, but an increasing electron deficiency with increasing dispersion favours a 2,3-adsorbed C4 intermediate, which preferentially forms ethane. The results are compared with those in the literature for other supported Ru catalysts, and it is concluded that the method of preparation, as well as the kind of support and the particle size, affect turnover frequency.

From crab shell to solar cell: a gel polymer electrolyte based on N-phthaloylchitosan and its application in dye-sensitized solar cells

Chitosan, a biopolymer derived from crab shells which is insoluble in common organic solvents has been converted to the organosoluble N-phthaloylchitosan (PhCh) by reaction with phthalic anhydride in dimethylformamide (DMF). The formation and structure of PhCh was confirmed by the characteristic peaks of phthalimido and aromatic groups observed at 719, 1708 and 1772 cm−1 and two sets of peaks centered at 3.0 and 7.5 ppm obtained from FTIR and 1H NMR analyses respectively. Gel polymer electrolytes consisting of PhCh, ethylene carbonate (EC), and DMF with various amounts of tetrapropylammonium iodide (TPAI) and iodine were prepared. The interaction behavior between polymer–plasticizer–salt was thoroughly investigated using FTIR spectroscopy. The gel polymer electrolyte consisting of PhCh : EC : DMF : TPAI : I2 in a weight ratio (g) of 0.1 : 0.3 : 0.3 : 0.12 : 0.012 showed the highest conductivity of 5.46 × 10−3 S cm−1 at room temperature and exhibited the best performance in DSSCs with efficiency of 5.0%, with JSC of 12.72 mA cm−2, VOC of 0.60 V and fill factor of 0.66.

Polypropylene/glass fiber/nanoclay hybrid composites: morphological, thermal, dynamic mechanical and impact behaviors

Polypropylene/E-glass fiber/nanoclay were compounded with a twin-screw extruder and injection molded. Thermal, dynamic mechanical, and impact tests were carried out. Differential scanning calorimetry investigations showed that the incorporation of nanoclay into polypropylene/glass fiber composite shifted the melting temperature (Tm) to higher values. The degree of crystallinity (Xc) was strongly influenced by the presence of the glass fiber and nanoclay in the matrix. Dynamic mechanical analysis showed an increase in storage modulus (E′); indicating higher stiffness of the hybrid composites when compared to the glass fiber composites and the virgin matrix. From the tan δ curves, a strong influence of glass fiber and nanoclay content on the magnitude of tan δmax value was observed. Impact test showed a reduction in the critical strain energy release rate, Gc for hybrid composites with higher nanoclay loading. The stress intensity factor, Kc values showed insignificant effect with the presence of nanoclay and GF.