Key Engineering Materials Vol. 833

Abstract: The advantages of palm kernel shell (PKS) as a renewable and sustainable material for activated carbon production have been explored for various applications such as water treatment, pollutant, pesticide, and heavy metal adsorption. However, the full promises of this material for energy storage devices have not been duly studied. In this research, PKS is physically activated and the effect of particle size on the physical characteristics of the activated char was investigated. Pellet (3 mm), granules (0.4 mm), and powder (0.0075 mm) are the sizes considered in the experiment. The surface morphology, surface area, porosity and functional group at different sized was analyzed. Finally, a suitable particle size was recommended for the electrode material of supercapacitor based on the physical characteristics of the activated carbon.

Abstract: The prevalent sachet economy in the Philippines has led to the country becoming the third largest polluter of oceans in the world. The sachets used for packaging are made of plastic laminates which typically consist of varying polymeric layers combined with other modifiers to improve barrier properties. In this study, applicability of D-limonene and ethanol as solvent/non-solvent pair for the separation of polyethylene (PE) from vacuum-metallized polyethylene terephthalate (VMPET) and polyethylene terephthalate (PET) was established. PE recovery from LDPE/VMPET/PET laminates were calculated to be 50.79% w/w.

Abstract: Use of quicklime as a sole catalyst for transesterification is limited by poor chemical stability and post-reaction recovery. This study investigates the effect of dry milling time on the transesterification catalytic performance (activity and recovery) of mechanically alloyed MgO, Al₂O₃ and eggshell derived quicklime. Raw chicken eggshells were calcined at 900 °C. The resulting flaking eggshell ash was directly mixed and comminuted with MgO and Al₂O₃ in ball milling (BM) machine for 15, 30, 60, 90, 120 and 150 minutes. Each of the catalyst samples was analyzed for surface morphology and particle size distribution, and then utilized for biodiesel production. Analyses of catalyst samples showed that mean particle size reduced, while powder agglomeration advanced with milling time. Optimum catalytic performance was achieved with the composite alloyed for 120 minutes (Z120) and that resulted in fatty acid methyl ester (FAME) yield of 88.4% and catalyst recovery of 98.3%. Sample Z120 was further characterized by TEM, EDX, XRD and BET. Calcination of the composite catalyst enhanced its activity. Dry high energy BM of oxides can be utilized effectively for synthesis of composite catalysts.

Abstract: In this study, influence of nanoparticles size on optical and dielectric properties of TiO₂ nanoparticles is investigated through thermal treatment of hydrous amorphous titania synthesized by chemical precipitation method at temperatures 300 °C and 600 °C. The average sizes of nanoparticles estimated respectively are ~ 8 nm and ~ 22 nm. Although the optical bandgap energy of both samples remains the same the E_g Raman mode observed at 144 cm^-1 for bulk TiO₂ is shifted to 150 cm^-1 only for nanoparticles calcined at 300 °C. The shift is ascribed to the size as well as higher density of surface defects. Moreover, the presence of surface defects like oxygen vacancies which provide effective sites for catalytic reaction are confirmed by EPR and photoluminescence studies. The oxygen vacancies enhances space charge polarization and consequently results in higher dielectric constant. In addition, the peak shift of loss tangent which determines the mobility of charge carriers is found to be size dependent. Hence calcination temperature has significant influence on defect levels which in turn determine the optical and dielectric properties of TiO₂ nanoparticles.

Abstract: In this paper, an analytical expression of the electron spin-dependent tunneling current through a potential barrier by applying a bias voltage was investigated. An Airy wavefunction was applied to derive the transmittance through the barrier by considering a zinc-blende material, which depends on the spin states indicated as ‘up’ and ‘down’. The obtained transmittance was employed to compute the polarization and spin-dependent tunneling current. The spin-dependent tunneling current was then observed at various bias voltages and temperatures. It was shown that the spin-polarized current increases as the bias voltage increases. It was also shown that the increase of temperature enhances the spin-dependent tunneling current.

Abstract: Germanene, which has the same structure as graphene, is an exciting novel 2D functionalized material that controls its band gap using functionalization. The effects of the Ga atom and hydrogen atoms on the structure of Ga-doped H-passivated germanene were investigated with a density functional theory (DFT) calculation. H-passivated germanene has a direct gap of 2.10 eV. Opening the band gap in the H-passivated germanene is due to transition from sp² to sp³ orbital. Adsorption of the Ga adatom on H-site decrease the band gap to 1.38 eV. No interaction between Ga atoms and Hydrogen atoms was observed. Hence, their effects on the band structure of hydrogenated graphene were independent of each other. Our results suggest that hydrogen passivation combined with adsorption of the Ga adatoms could effectively control the band gap of germanene.

Abstract: Without external magnetic field, the relationship between electric current of ferrofluid (MF) and temperature is discussed. The electric current is increasing linearly with temperature rising in ferrofluid with Fe₃O₄ particles distributed into water (MF-Fe₃O₄-W). Through theory and experiment proved, the carrier liquid only in MF-Fe₃O₄-W could not decide the ability of delivering electric energy of MF-Fe₃O₄-W. The electric current would be contributed to the movement of free electric charges (or ions) and colliding of electric polarized particles in MF-Fe₃O₄-W.

Abstract: We presented here the development of an immunosensor based on graphene nanoplatelets-modified screen printed carbon electrode (SPCE) with incorporated rabbit IgG on the amino functionalized surface area. In order to improve sensitivity of working electrode, graphene-nanoplatelets solution was fabricated onto surface carbon working electrode. The effect of different (3-aminopropyl) triethoxysilane (APTES) concentrations (0.125, 0.5, 2 and 8% (v/v)) and incubation time of silanization (30, 60 and 90 min) were studied and compared. An electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize our immunosensor based. It is showed that the optimum APTES concentration which provides higher surface coverage and electron transfer rate was 2% concentration (v/v) at 60 min of incubation time. The modified surface was then evaluated by measuring immobilized rabbit IgG via indirect assay using horseradish peroxidase labelled secondary antibody. The optimum detection immobilized IgG was 0.05 mg/mL. These results indicate the potential for amino functionalized graphene nanoplatelets-modified SPCE in detecting protein biomarkers.

Abstract: Natural gas is rapidly gaining in geopolitical importance. Gas has grown from a marginal fuel in regionally disconnected markets to an energy source that is transported across great distances for consumption in many different economic sectors. Natural gas is the fuel of choice for consumers seeking for relatively low environmental impacts. As a result, the world’s gas consumption is projected to more than double over the next three decades, rising from 23 – 28 % of the total primary energy demand by 2030 and surpassing coal as the world's number two energy source and potentially overtaking oil's share in many large industrialized economies. This paper is devoted to a short review of materials used in the novel approach to natural gas liquefaction – magnetic cooling process.

Abstract: Fusing of silver (Ag) nanoparticles synthesized in an aqueous system was observed at room temperature using halide solutions. The as-synthesized Ag nanoparticles have an average diameter of about 24 nm. After dispersing the Ag nanoparticles in a halide solution, a significant increase in particle size to about 188-197 nm was observed. The enlargement of particle size was accompanied by the increase in conductivity of the Ag nanoparticle ink. The resistance was reduced from 110 kiloohms to 35 and 9.3 ohms for the as-prepared and sintered Ag nanoparticles using NaBr and NaCl solution, respectively.