Mohammad Hafizuddin Haji Jumali

Modified microwave method for the synthesis of visible light-responsive TiO2/MWCNTs nanocatalysts

Recently, TiO2/multi-walled carbon nanotube (MWCNT) hybrid nanocatalysts have been a subject of high interest due to their excellent structures, large surface areas and peculiar optical properties, which enhance their photocatalytic performance. In this work, a modified microwave technique was used to rapidly synthesise a TiO2/MWCNT nanocatalyst with a large surface area. X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller measurements were used to characterise the structure, morphology and the surface area of the sample. The photocatalytic activity of the hybrid nanocatalysts was evaluated through a comparison of the degradation of methylene blue dye under irradiation with ultraviolet and visible light. The results showed that the TiO2/MWCNT hybrid nanocatalysts degraded 34.9% of the methylene blue (MB) under irradiation with ultraviolet light, whereas 96.3% of the MB was degraded under irradiation with visible light.

Influence of TiO 2 nanoparticles on enhancement of optoelectronic properties of PFO-based light emitting diode

Improvement on optoelectronic properties of poly (9,9′-di-n-octylfluorenyl-2.7-diyl)- (PFO-) based light emitting diode upon incorporation of TiO2 nanoparticles (NPs) is demonstrated. The PFO/TiO2 nanocomposites with different weight ratios between 5 and 35wt.% were prepared using solution blending method before they were spin coated onto Indium Tin Oxide substrate. Then a thin Al layer was deposited onto the nanocomposite layer to act as top electrode. The nanocomposites were tested as emissive layer in organic light emitting diodes (OLEDs). The TiO2 NPs played the most crucial role in facilitating charge transport and electrical injection and thus improved device performance in terms of turn-on voltage, electroluminescence spectra (EL), luminance, and luminance efficiency. The best composition was OLED with 5 wt.% TiO2 NPs content having moderate surface roughness and well distribution of NPs. The device performance was reduced at higher TiO2 NPs content due to higher surface roughness and agglomeration of TiO2 NPs. This work demonstrated the importance of optimum TiO2 NPs content with uniform distribution and controlled surface roughness of the emissive layer for better device performance.

Enhanced Optoelectronic Properties of PFO/Fluorol 7GA Hybrid Light Emitting Diodes via Additions of TiO2 Nanoparticles

The effect of TiO2 nanoparticle (NP) content on the improvement of poly(9,9′-di-n-octylfluorenyl-2,7-diyl) (PFO)/Fluorol 7GA organic light emitting diode (OLED) performance is demonstrated here. The PFO/Fluorol 7GA blend with specific ratios of TiO2 NPs was prepared via a solution blending method before being spin-coated onto an indium tin oxide (ITO) substrate to act as an emissive layer in OLEDs. A thin aluminum layer as top electrode was deposited onto the emissive layer using the electron beam chamber. Improvement electron injection from the cathode was achieved upon incorporation of TiO2 NPs into the PFO/Fluorol 7GA blend, thus producing devices with intense luminance and lower turn-on voltage. The ITO/(PFO/Fluorol 7GA/TiO2)/Al OLED device exhibited maximum electroluminescence intensity and luminance at 25 wt % of TiO2 NPs, while maximum luminance efficiency was achieved with 15 wt % TiO2 NP content. In addition, this work proved that the performance of the devices was strongly affected by the surface morphology, which in turn depended on the TiO2 NP content.

Two-dimensional CdS intercalated ZnO nanorods: a concise study on interfacial band structure modification

The controllable growth of metal sulfide–metal oxide based nanomaterials with a tunable band gap structure is vital in the fabrication of new generation optoelectronic devices. In this paper, two-dimensional hierarchical CdS/ZnO nanorod arrays were successfully grown via a low temperature hydrothermal-SILAR method. A concise mechanism related to the surface and band gap modification on the CdS/ZnO nanorods was investigated under various CdS deposition cycles (N). The diameter and surface roughness properties of the sample were found to be linearly dependent on the value of N. A bathochromic shift in the optical energy band gap revealed the quantum size effects of the CdS/ZnO nanorods, as well as the induced interface band state and energy band split in the ZnO band state. An impressive improvement in the crystallinity of the sample was also observed under the CdS treatment. The correlation between the optical band gap and photovoltaic efficiency was evaluated. The results proved that the ZnO nanorod/CdS devices exhibited a threefold higher power conversion efficiency in comparison to a pristine ZnO nanorod device.

One-step formation of TiO2 hollow spheres via a facile microwave-assisted process for photocatalytic activity

Mesoporous TiO2 hollow spherical nanostructures with high surface areas were successfully prepared using a microwave method. The prepared hollow spheres had a size range between 200 and 500 nm. The spheres consisted of numerous smaller TiO2 nanoparticles with an average diameter of 8 nm. The particles had an essentially mesoporous structure, with a pore size in the range of 2-50 nm. The results confirmed that the synthesised of anatase TiO2 nanoparticles with specific surface area approximately 172.3 m2 g-1. The effect of ultraviolet and visible light irradiation and catalyst dosage on the TiO2 photocatalytic activity was studied by measuring the degradation rate of methylene blue. The maximum dye degradation performances with low catalyst loading (30 mg) were 99% and 63.4% using the same duration of ultraviolet and visible light irradiation, respectively (120 min).

Efficient charge transfer mechanism in Polyfluorene/ZnO nanocomposite thin films

The optical properties and charge transfer mechanism of poly (9,9′-di-n-octylfluorenyl-2.7-diyl) (PFO)/ZnO thin films have been investigated. The ZnO nanorods (NRs) were prepared via a microwave technique. The solution blending method was used to prepare the PFO/ZnO nanocomposites. X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) were used to determine the structural properties, while UV-Vis and photoluminescence (PL) were employed to investigate the optical properties of the films. XRD patterns confirmed that there was no variation in the structure of both PFO and ZnO NRs due to the blending process. FE-SEM micrographs displayed that ZnO NRs were well coated by PFO in all nanocomposite films. The absorption spectra of the nanocomposite thin films exhibited a red-shift indicating the increment in conjugation length of the PFO/ZnO nanocomposite. Significant quenching in the emission intensity of PFO was observed in fluorescence spectra of the nanocomposite films. This quenching was attributed to efficient charge transfer in the PFO/ZnO nanocomposites, which was further supported by the shorter PL lifetime of PFO/ZnO than that of the PFO thin film. The continuous decline in PL intensity of these nanocomposites is attributed to homogenous dynamic quenching between PFO and ZnO NRs.

Synthesis of monodisperse CdSe QDs using controlled growth temperatures

This paper reports on the effect of growth temperatures on optical properties of monodisperse CdSe QDs synthesized via wet chemical method. The growth temperature was varied from 260 – 310 °C while growth period was fixed at 60 s. The resulting colloidal was in strong quantum confinement regime and having yield as high as 53%. As the growth temperature increased, the monodispersed CdSe QDs with diameter in the range of 3-7 nm were obtained. Both absorption and PL spectra of the QDs revealed a strong red-shift with the increment of growth temperature. Thus, the size of QDs was enlarged with increment of the wavelength from both the spectra. Consequently, the energy gap of resulting QDs can be tuned by tuning the size of QDs. More importantly, the narrow widths of the PL emissions with different colors make these colloidal to be a potential candidate for different optical and optoelectronic devices.

Development of gas sensor system based on the TiO 2 /Pani composite thin film

Development of organic and inorganic composites has grown in recent years due to a wide range of potential use of these materials. The aim of this research is to investigate the effect of Pani additions on the TiO2 based thin film as VOC gas sensing properties. TiO2 were prepared using sol gel technique. Up to 3 wt% of Pani were directly added to the TiO2 solution. 3 layers of TiO2/Pani solution mixture were deposited onto SiO2 coated silicon substrate using spin coating technique for fabrications of gas sensing device. The microstructures properties of samples were investigated using XRD, TEM and SEM. In addition, all samples were exposed to ethanol for gas sensing performance test. The gas sensing test revealed that all films were responsive towards ethanol vapour exposure with 2 wt% TiO2/Pani film exhibited the best sensitivity. However, over longer exposure cycles, it was observed that 3 wt% TiO2/Pani film have a better stability.

Modification of Optophysical Properties of Poly[(9,9-Di-N-Octylfluorenyl-2,7-Diyl)-Alt-(Benzo[2,1,3]Thiadiazol-4,8-Diyl)] Thin Film via Additions of TiO2 Nanoparticles

The solution of poly [(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo [2,1,3] thiadiazol-4,8-diyl)] (F8BT) F8BT/TiO2 nanocomposites were prepared using solution blending methods. The TiO2 contents were fixed between 0 wt% - 35 wt%. Then, the solutions were spin coated at 1000 rpm for 30 s onto glass substrates to form thin film samples. The optical properties of the nanocomposites were determined using UV-Vis spectroscopy and photoluminescence spectroscopy. The absorption properties of the thin film increased due to existence of intermediate energy band which lead to higher space charge regions for electron insertion. Besides that, the λmax for absorption and emission spectrum were systematically shifted due to incorporation of TiO2 NPs indicating an interaction between nanoparticles and polymer matrix. Furthermore, the intensity of the emission spectrum were enhanced in the presence of TiO2 NPs. This is due to the existence of TiO2 NPs which trapped more electrons at the interface F8BT/TiO2, resulted production of higher number of exciton formation in the nanocomposirte samples.

Controlled growth and alignment of palladium nanowires prepared by template-assisted electrodeposition

Palladium nanowires are good candidates for hydrogen sensing due to the many advantages. In this paper, we discuss the controlled growth of palladium nanowires into the nanopores of anodized alumina oxide (AAO) via template-assisted electrodeposition. This technique provides precise control for the dimensional growth of Pd nanowires. The potential range for electrochemical deposition of palladium nanowires was determined by Linear Sweep Voltammetry (LSV). Crystallinity and microstructural studies of the palladium nanowires were carried out using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) as characterization tools. Systematic study on nanowire alignment across 3 µm-gaps between pairs of microfabricated gold electrodes was carried out using a.c. dielectrophoresis technique. Optimized conditions for good nanowire alignment were reported.