Key Engineering Materials Vol. 757

Abstract: The trans- and cis-isomers of potassium diaquabis(oxalato)chromate (III) were studied computationally and experimentally. The structures of trans- and cis-configurations of [Cr(H₂O)₂(C₂O₄)₂]^- were optimized by DFT methodology with various functionals namely: B3LYP, CAM-B3LYP, TPSS, PBE, M06-L and ωB97X-D along with the more sophisticated MP2 method. The calculations show that the most stable forms for both isomers are in quartet states. The results from all DFT methods reveal that the cis-isomer is literally more stable than the trans-isomer with the lower average relative energy of 2.1 kcal/mol. These are consistent with the results from MP2 calculation and experimental observation. The absorption wavelengths for the excited states of trans- and cis-structures were calculated by the time-dependent density functional theory (TDDFT) method. For the experiments, the trans- and cis-isomers of potassium diaquabis(oxalato)chromate (III) were synthesized and characterized by UV-Vis spectrophotometry. Both isomers have two maximum absorption wavelengths at 415 and 560 nm.

Abstract: Azo dyes are usually used in textile industry. However, they can cause water contamination, lead to water pollution, damage to aquatic lives and degenerate scenery due to their toxicity. These problems can be overcome by photocatalytic process in which the azo dyes are converted to CO₂ and water. This research concentrates on effect of Bi₂O₃, BiOBr and BiOI contents on titanium dioxide substance (TiO₂) for the photocatalytic process. In the study, photocatalysts were synthesized by sol-gel and wetness impregnation methods. They were studied in surface area by BET technique, chemical composition by FT-IR spectroscopy and optical properties by UV-DRS technique. Increase in bismuth content on TiO₂ results in decreasing surface area. In FT-IR spectra, Ti-O-Ti stretching bands at 400-800 cm^-1 were detected. The band gap energy of these photocatalysts is decreased when bismuth was doped. Since efficiency of CO₂ and water conversion of the photocatalysts can be determined indirectly via determinaiton of decreasing Methyl Orange (MO) concentration, the lowest MO concentration was observed in the 4%Bi₂O₃T photocatalyst after 16 hours when compared to the other photocatalyst samples and Degussa P25. In other words, this photocatalyst efficiently converts the azo dyes to CO₂ and water.

Abstract: Silvernanoshell consisting of Ag coated on SiO₂ core was synthesized and employed as a colorimetric probe for detection of toxic metals ions in water. The SiO₂@Ag Core-Shell preparation method was fine-tuned and adjusted to prepare a mono-dispersed and fully encapsulated Ag nanoshell. Silica core spheres with the average diameter of 100 nm was prepared by Stöber method and subsequently coated with AgNPs by Seed-Mediated Growth Technique using NaBH₄ as a reducing agent and PVA as a stabilizer. The resulting Ag nanoparticles tethered on silica spheres were found to serve as nucleation sites for the further growth of a silver nanoshell overlayers. The SiO₂@Ag was characterized by UV-Visible Spectroscopy and Transmission Electron Microscopy. It was found that the AgNPs was successfully coated on the surface of silica spheres with the average thickness around 20 nm. The adsorptivity of metal ions onto the surface of Ag nanoshell were tested and calibrated using series of Hg²⁺ and Pb²⁺ ions with various concentrations. The changes in the band intensity of the surface plasmonresonance (SPR) band, which correspond to the changes in the concentration of ions in model waste water, were evident.

Abstract: Electrospun shellac nanofibers might be potentially used for wound dressing application due to its natural origin and excellent protective properties. In this study, a full factorial design with three replicated center points was performed in order to investigate the main and interaction effects of shellac content (35-40% w/w), applied voltage (9-27 kV) and flow rate (0.4-1.2 mL/hr) on the morphology of shellac nanofibers. A total of 11 experiments were conducted. The response variables were the diameter of nanofibers, the distribution of diameter and the amount of beads. The results showed that the concentration of shellac was the most significant impact on shellac nanofiber diameter, while applied voltage, interaction between shellac content and voltage, and feed rate were minor factors, respectively. Shellac content and applied voltage had negative relationships with bead amount. When reducing the concentration of shellac and voltage, the amount of beads was increased. However, the influence of these parameters on diameter distribution seemed to be not significant. Based on response surface plot, nanofibers with thinner diameter (~493 nm) and less number of beads (~0.47) could be obtained at the optimum conditions; the shellac content of 38.5% w/w, the voltage of 21 kV and the feed rate of 0.4 mL/hr.

Abstract: Zinc ferrites (ZnFe₂O₄) nanoparticles were successfully prepared by the simple co-precipitation method. The effects of calcination temperature and the amount of surfactant on the microstructure of zinc ferrite products were studied. The products were characterized with X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and UV-Vis diffuse reflectance spectroscopy (DRS). The XRD results confirmed the formation of a cubic spinel structure in all samples. The SEM results revealed that surfactant molecules play a crucial role to control the microstructure of the samples. All samples showed extended absorptions in the visible region. The photocatalytic results indicated that ZnFe₂O₄ enhanced the photocatalytic activity with increased calcination temperature. In addition, the ZnFe₂O₄ prepared by addition of high concentrations of surfactant gave the highest photocatalytic activity. The synthesized ZnFe₂O₄ can be recovered by applying an external magnetic field.

Abstract: The modification of commercial zirconia nanopowder by sulfuric acid and heat treatment was conducted. The aim of this present research was to obtain a stable modified zirconia nanopowder chemically and thermally by studying the effect of sulfuric acid treatment and calcination temperature on commercial zirconia nanopowder. The material was prepared by dispersing the commercial zirconia nanopowder into 0.2, 0.5 and 0.8 M sulfuric acid solutions, followed by calcination at varied temperatures, i.e. 600, 700, 800 and 900 °C. The so called sulfated zirconias then were characterized their physicochemical properties using FT-IR, XRD and SEM-EDX analysis methods. The optimized condition for that modification was obtained by using sulfuric acid of 0.8 M and calcination temperature of 600 °C. The characterization results also revealed that using ammonia adsorption method, the acidity of the catalyst was found to be 1.06 mmol/g.

Abstract: Polypropylene/three-carbon-filler composite bipolar plates (BPs) of direct methanol fuel cell (DMFC) were fabricated by an injection molding. The composite materials were made of polypropylene (PP), carbon black, carbon fiber and graphite. Gas flow channel surfaces on the BPs were subsequently modified by polypyrrole (PPy) using a coating technique in order to improve surface electrical conductivity. This research is a feasibility study to use PPy-coated PP composite as BPs in a DMFC. The surface electrical resistance and performance in a fuel cell containing the composite BPs under DMFC operating conditions were evaluated against conventional graphite BPs. The surface resistance values of PPy-coated PP composites decreased around six orders of magnitude, compared with those values of PP composites. According to the performance results, PPy-coated composite BPs can be used in DMFC if the surface adhesion between a PPy layer and the BP surface was further improved.

Abstract: This study employed statistically based experimental designs to optimize environmental factors for H₂ production from sugarcane bagasse hydrolysate by K. pneumoniae subsp. Pneumonia DSM 30104(T) isolated from wastewater sludge using statistical method. The 12 runs of Plackett-Burman design were used to classify important factors influencing the H₂ production from sugarcane bagasse hydrolysate by K. pneumonia subsp. pneumonia DSM 30104(T). Mutual interaction between the significant factor and their optimal values that brought the maximum H₂ production (mL H₂/L) were further investigated using Box-Behnken design of response surface method. Experimental results indicated that yeast extract, ammonium chloride, potassium chloride, calcium chloride, iron (II) sulfate and total sugar of sugarcane bagasse had an interdependent effect on the maximum H₂ production while only interaction effect between yeast extract and calcium chloride had statistically significant (P≤0.05) influences on the maximum H₂ production. Optimal conditions for the predicted maximal H₂ production were 7.50 g/L yeast extract, 0.50 g/L ammonium chloride, 15.0 g/L potassium chloride, 0.75 g/L calcium chloride, and 10.0 g/L total sugar. At the optimal condition, the maximum H₂ production of 277 mL H₂/L was estimated from Box-Behnken design that more than 9 times compared to Plackett-Burman design. The highest ratio of butyric acid to acetic acid (B/A ratio) of 1.47 was indicated the high performance of H₂ fermentation of sugarcane bagasse hydrolysate by K. pneumoniae subsp. Pneumonia DSM 30104(T) under the optimal condition obtained.

Abstract: Palm fruit bunch (PFB) and palm fruit residue (PFR) are considered as potential raw materials for ethanol production due to their large availability from palm oil industry. However, the presence of lignin can retard the rate of enzymatic hydrolysis. Both PFB and PFR were pretreated with a 10% w/v sodium hydroxide solution. The amounts of their hemicellulose were substantially decreased whereas their lignin contents were slightly reduced. After that, they were hydrolyzed using cellulase from Trichoderma reesei (ATCC 26921) at 50 °C and pH 5. An addition of Tween 80, nonionic surfactant, with 0.25% w/v concentration provided an increase in reducing sugar production about 50.5% at 10 FPU/g PFB cellulase loading, while the addition of Tween 80 with 0.5% w/v concentration increased reducing sugar production by 38.8% at 20 FPU/g PFR cellulase loading. The greater the amount of lignin in the lignocellulosic materials, the higher the dosages of enzyme and surfactant required for the enzymatic hydrolysis. The adsorption of added nonionic surfactant onto the hydrophobic surface of lignin resulted in an increase in the availability of added enzyme to both cellulose and hemicellulose, leading to the enhancement of enzymatic hydrolysis. Additionally, the adsorption of cellulase on PFB and PFR were well fitted with the Freundlich isotherm.

Abstract: An investigation of the effect of the addition of char from agricultural residues on the torrefaction of moist municipal solid waste (MSW) pellets (40 wt.% moisture) was carried out in a microwave oven (500-800 W for 4-12 minutes). Char from agricultural residues, including corncob, palm shell, straw, and bagasse, was used as the microwave absorbers to enhance the absorption of microwave irradiation. It was found that the addition of char from bagasse yielded the lowest remaining mass (or mass yield) and volatile matter (VM) content, but the highest temperature and heating value, of the torrefied MSW pellet. Moisture in the MSW pellet with or without the addition of microwave absorber was completely removed after being torrefied for 8-12 minutes. The VM contents remained in the MSW pellets with the addition of microwave absorbers were lower than that in the MSW pellet without the addition of microwave absorber. The addition of microwave absorbers led to an increase in carbon (C) content but a decrease in oxygen (O) content of the torrefied MSW pellets, compared to those of the raw MSW pellet. The heating values of the torrefied MSW pellets with the addition of microwave absorbers were equivalent to that of sub-bituminous coal, enhanced from that of the raw MSW pellet, which was lower than that of lignite.