Abdullah Mikrajuddin

Preparation of Polyacrylonitrile Nanofibers with Controlled Morphology Using a Constant-Current Electrospinning System for Filter Applications

Polyacrylonitrile (PAN) fibers with average diameters in the range 100 nm with beaded morphology were prepared by a constant current electrospinning system. The fiber morphology could be easily varied by controlling the flow rate and electric current during the electrospinning process without changing the precursor solution. It was found that the use of lower flow rates resulted in more beaded fibers while the number of beads increases. The electric current could control the fiber morphology in which the beaded number (the number of beads or the beaded fibers) decreased as the electric current increased. It was also found that diameter and length of the beaded fibers increases as the electric current increases. Therefore, these results are able to be applied to find optimal conditions in obtaining high performance filter media.

Enhancement Performance of Dye-Sensitized Solar Cells from Black Rice as Dye and Black Ink as Counter Electrode with Inserting Copper on the Space between TiO2 Particle’s by Using Electroplating Method

In this study, we report well performance of Dye Sensitized Solar Cell (DSSC) coated with copper (Cu) by using the electroplating method. The Cu nanoparticle was impregnated into the pore of the titanium dioxide (TiO2) thin film. Particle contact between Cu and TiO2 plays important role to reduce the recombination effect of the electron and also lead to increase the electron transport in DSSC cell. Here, we used natural dye extracted from black rice and carbon from black ink as counter electrode. It is found that efficiency of DSSC coated with Cu nanoparticle is higher than pure DSSC which is obtained from I-V characterization. It shows that efficiency of DSSC is about 0.019% without coating Cu and enhanced about 0.105% after coating Cu. The analysis of internal resistance of DSSC was measured from Electrochemical Impedance Spectroscopy (EIS) characterization.

Syntheses of Hematite (α-Fe2O3) Nanoparticles Using Microwave-Assisted Calcination Method

Hematite (α-Fe2O3) nanoparticles were synthesized from the solution of FeCl3.6H2O and NaOH in water using microwave-assisted calcination method. The syntheses were initially carried out by microwave heating and completed by a calcination process using a simple heating method. The effect of microwave heating time, calcination temperature, and calcination time were investigated. The XRD patterns demonstrated that the obtained nanoparticles are pure hematite. Using the Scherrer method, the average crystallite sizes of hematite nanoparticles were in the range of 35.6 to 54.4 nm. The obtained hematite nanoparticles were spherical with the average particle sizes ranging from 91 to 116 nm as confirmed by the SEM images.

Microwave-Assisted Solid State Synthesis of Red-Emitting BCNO Phosphor and its Characteristics

Red-emitting BCNO phosphor has been synthesized by a microwave-assisted solid state reaction using a low-cost boric acid, urea and polyethylene glycol (PEG-20k) as the starting materials. The effects of reaction parameters: temperature, carbon and nitrogen content on material composition and photoluminescence properties were investigated. Nearly multi-phase hexagonal boron nitride, boron oxide, boron carbide and carbon graphite was observed, indicating the BCNO were successfully synthesized. The photoluminescence spectra of the phosphor excited by a UV light (365 nm) showed a broad emission band at 460 - 620 nm.

Photocatalytic Activities of Electrospun TiO2/Styrofoam Composite Nanofiber Membrane in Degradation of Waste Water

TiO2/Styrofoam composite fiber membranes were synthesized by using an electrospinning system for water purification applications. Composite fiber membrane was fabricated from precursor solution prepared by dissolving Styrofoam in the mixture of tetrahydrofuran (THF), citronella oil and cajuput oil. The precursor solutions is mixed with TiO2 powder with three variations based on the concentration (1:15,1:20 and 1:40). Textile dye with 50 ppm of concentration was performed as a model of waste water. The structure and morphology of each membrane were characterized by using scanning electron microscopy (SEM). The photocatalytic activity was investigated under the bulb light with 60 watt of power in the box of photocatalytic test. Observation of photocatalytic process were performed for 30 hours. The quantitative data of the decrease in the concentration of wantex solution were measured by using UV-Vis spectrometer and simple spectrometer which was developed recently. It was shown that there are significant decrease of the concentration of wantex solutions performed by each membrane. As many as 69% of wantex solution have been successfully degraded for 30 hours under the bulb light.

Synthesis of Fe2O3/C Nanocomposite Using Microwave Assisted Calcination Method

Fe2O3/C nanocomposites were successfully synthesized using microwave assisted calcination method. Ferric (III) chloride hexahydrate (FeCl36H2O), sodium hydroxide (NaOH), and dextrose monohydrate (C6H12O6H2O) were used as precursors. A microwave oven of 2.445 GHz with a power of 600 W for 20 minutes was employed during the syntheses. Calcination was performed in a simple furnace at 350 °C for 30 min. The molar ratio of C:Fe is the only process parameter. From Scanning Electron Microscope images, the average particle size were 199 nm and 74 nm for the samples with molar ratio of C:Fe of 1:2 and 1:1, respectively. X-ray diffractometer spectra showed that the obtained samples have γ-Fe2O3 (maghemite) crystal structure. Using the Scherrer method, the crystallite size were 61.7, 58.8, 52.5, and 48.8 nm for the samples with the molar ratios of C:Fe of 1:3, 1:2, 1:1, and 2:1, respectively. It means that the crystallite size of the nanocomposite decreases with the increase of the molar ratio of carbon to iron (C:Fe). The Brunauer-Emmett-Teller characterization showed that the surface area as high as 255.6 m2/g is achieved by of the Fe2O3/C nanocomposite with the molar ratio of C:Fe of 1:1.

A Theoretical Study on the Performance of SnO2/SiO2/n-Si Solar Cells

The performance of SnO2/SiO2/n-Si solar cells was studied by considering various transport mechanisms including minority-carrier diffusion, carrier recombination, and tunneling through insulating layer. The tunneling current through the SiO2 layer was obtained by employing the Airy-wavefunction approach. The efficiency was calculated to determine the performance of the cells under AM1 illumination for different values of insulating layer thickness, interface state density, hole life-time, doping density of silicon substrate, and cell thickness. It was shown that the efficiency increases as the insulating layer becomes thinner due to the decrease of short-circuit current. It was also shown that the efficiency increases as the doping density increases up to 6x1022/m3 and it then decreases for higher doping densities. As the interface state density decreases, the efficiency becomes higher. In addition, the increases in the hole lifetime and cell thickness enhance the efficiency of the solar cell.

Photocatalytic Degradation of C.I. Reactive Red 2 by Using TiO2-Coated PET Plastic under Solar Irradiation

The synthetic dyes are a refractory and poisonous material. Most of industrial textile today used the synthetic dyes that can be dangerous to the environment because of the colored wastewater produced from their processes. This study concentrates on the application of Advanced Oxidation Processes (AOPs) for synthetic dyes wastewater treatment. Photocatalysis process as one of AOPs was applied for the degradation of organic content of synthetic dyes wastewater. The reactive dye, C.I. Reactive Red 2 (RR 2) was used as the organic pollutant model at the concentration of 100 mg/l. The TiO2 concentration of 0.05-0.4 g/ml was used as the photocatalyst. The bulk and nanosize of TiO2 were coating on the PET plastic and the degradation of organic content was examined in the term of color and COD within 0-12 hrs under solar irradiation. By using 0.4 g/ml of bulk TiO2, the color degradation of 88% and COD removal of 46% was achieved. Furthermore, by using 0.4 g/ml of nanosize TiO2, the enhancement of color degradation and COD removal was observed, that is 98% and 56%, respectively.

Effect of Heating Time on Atrazine-Based MIP Materials Synthesized via the Cooling-Heating Method

Molecular imprinting is a technique to produce a polymer called as molecularly imprinted polymer (MIP) that provides cavities to form a particular space generated by removing the template when the polymer has been formed. It will recognize a target that has the shape and physico-chemical properties similar or identical with those of template molecule. In this study, MIPs using atrazine as template have been made via the cooling-heating method. Initially the pre-polymer solution was cooled at a refrigerator for 1 h. Next, the polymerization was carried out at 70 °C for heating times of 90, 120, and 150 min. without nitrogen flow which is generally done for polymerization process. Characterizations were performed by employing a reversed-phase high performance liquid chromatograph (HPLC) and scanning electron microscope (SEM). From Scatchard plots, it was found that the equilibrium dissociation constant KD and the apparent maximum number of binding sites Bmax, which are written as (KD, Bmax), are (4.69 μM, 9.87 mmol/g), (4.54 μM, 9.56 mmol/g) and (3.52 μM, 7.44 mmol/g) for the heating times of 150, 120, and 90 min., respectively. This is verified by their SEM images showing that the broadest pore size distribution with the highest number of pores is in the MIP prepared under the heating time of 150 min. The MIPs therefore could be applied as an atrazine sensor and the MIP prepared under the heating time of 150 min. would give its best characteristics compared to the others.

A Theoretical Study on Electron Tunneling Current in Isotropic High-κ Dielectric Stack-Based MOS Capacitors with Charge Trapping

Electron tunneling current in an isotropic metal-oxide-semiconductor (MOS) capacitor with a high-κ dielectric stack has been studied by considering the effect of charge trapping. The transmittance was analytically calculated by employing an Airy-wavefunction approach and including a coupling term between the transverse and longitudinal kinetic energies which is represented by an electron phase velocity in the gate. The transmittance was then applied to obtain tunneling currents in isotropic n+poly-Si/HfSiOxN/trap/SiO2/Si (100) MOS capacitors for different electron gate phase velocities and trap depths and widths. The calculated results show that the transmittance and tunneling current increase as the electron gate velocity decreases. In addition, the increase in the trap depth and width enhances the tunneling current.