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This study reports on synthesis of ZnO nanostructures using Zinc chloride (ZnCl2) as precursors and Potassium hydroxide (KOH) as alkaline source in a solvothermal process with varying molar concentrations (Zn2+/OH-) of 1:1, 1:3 and 1:5 for temperatures of 30 °C and 50 °C. The synthesized nanostructures were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FT-IR) Spectroscopy, and Ultraviolet Visible (UV-Vis) spectroscopy. ZnO nanostructures synthesized at lower ratios (1:1) exhibited wurtzite hexagonal shapes. However, as the concentration ratios increases in both cases, spherical structures were formed with the emergence of some rod-like structures dominating, and finally aggregated to form flower-like structures at 30 °C temperature. The average crystallite size for nanostructures from XRD (30-50 °C) were in the range 15-21 nm whereas the average particle size from TEM analysis (30-50 °C) were in the range 39-76 nm. Increase in temperature and molar concentration of the alkaline source generally decreased the crystallite and particle size of the as well as a decrease in the wavelength of ZnO nanostructures as a result of blue-shifting of the absorption peak. FT-IR spectra of ZnO NSs prepared from concentration ratios of Zn2+: OH- (1:1, 1:3 and 1:5) at 30 °C and 50 °C showed characteristic peak bands at 461-467 cm-1 and 460-462 cm-1 respectively.

In this study, sorption efficiency of coated (C-) and uncoated (U-) zinc oxide nanoparticles (ZnO-NPs) in aqueous solution onto raw sago hampas (RSH) and acetylated sago hampas (ACSH) was studied. Physical and chemical characteristics of both the sorbate and sorbents were analysed using various characterization techniques. The mechanism of the sorption process was evaluated using equilibrium isotherms, kinetic and thermodynamic studies. From the study, maximum percentage removal of both sorbate ions were achieved at an equilibration time of 100 minutes with an optimum sorbate mass of 2.0 g per 50 ml. The study recorded a maximum % removal of 85.1% & 87.6% for C-and U-ZnO-NPs (< 50 nm) onto RSH and 90.0% & 91.1% onto ACSH. Langmuir isotherm fitted well for the sorption process with the highest efficiency of 0.793 mg/g recorded for C-ZnO-NPs onto RSH. Pseudo-second model best described the sorption process. An exothermic and non-spontaneous sorption process was realised in all the sorption studies except that of U-ZnO-NPs (< 50 nm) onto ACSH which became spontaneous as temperature increased. Based on the findings from the multiple approaches employed, both sorbents could be proposed as viable alternatives to act as a green sorbent in the removal of ZnO-NPs from water and wastewater.

This work reports utilised of RGO from Sengon wood biomass to support Fe–N–C noble-free catalyst (Fe–N-RGO), while also attempt to investigate the effect of pyrolysis stage on Fe–N-RGO catalysts with four different nitrogen precursors towards the ORR activity in acidic medium. One- and two-step pyrolysis were performed at 900 °C for 1 h and 2 h respectively to produce Fe–N-RGO. This work revealed that two-step pyrolysis was able to remove the volatile components and hence forming more graphitised, stable graphitic-N and Fe-Nx, synergistically improve the ORR activity with highest onset potential of 0.83 V vs RHE and limiting current density of 5.33 mA cm−2 reported on Fe-Pani-RGO 2py. An increase in the kinetic on Fe-Pani-RGO 2py with Tafel slope of 74 mV/dec operated at 80 °C was reported. The mesoporous structure on RGO increases the stability by 8% and better methanol tolerance when compared to a benchmark Pt/C catalyst.

Single phase ZnO nanostructures were synthesized by simple and low temperature solvothermal process from two different alkaline sources; Potassium hydroxide (KOH) and Sodium hydroxide (NaOH) with zinc acetate dihydrate (Zn(CH3COO)2∙2H2O) as precursor. This facile and rapid synthesis technique achieve high purity of Zinc oxide (ZnO) nanostructures on large scale negating the use of complex and high temperature routes. The synthesized particles were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared (FT-IR) Spectroscopy, Ultraviolet Visible (UV-Vis) spectroscopy and Brunauer-Emmett-Teller (BET) analysis. ZnO synthesized using KOH and NaOH exhibit wurtzite hexagonal and flake-like nanostructures with average crystallite size of 11.0 nm and 14.9 nm respectively. Surface area of 59.50 m2/g and 31.43 m2/g were determined for KOH and NaOH sources respectively. The optical absorption spectra of the two samples showed absorption bands of 367.70 and 365.30 nm. The results showed the effect of alkaline sources on the surface morphology, structural and optical properties of ZnO.

A novel self-heating hydrogen gas sensor based on zinc oxide nanorods coated on indium tin oxide was fabricated. This sensor utilizes Joule heating effect of indium tin oxide to generate heat, while ZnO acts as a variable resistor to regulate the amount of electric current that passes through indium tin oxide layer upon exposure to oxygen and hydrogen gas. The gas sensor was capable of detecting very low concentration of H2 in air. Hence, for the first time, a new way of gas detection based on sensor temperature variation as the sensing mode was demonstrated.

In this study, single phase of nickel oxides was synthesized using a feasible precipitation technique. The sample was irradiated by argon ion beams with pulsed plasma of kilojoules energy to induce microstructural changes in the materials before it was assembled on a graphene support as electrocatalyst for oxygen reduction reactions in fuel cell. Physical and electrochemical characterizations have been carried out to study the structure-property relationship of the electrocatalyst. Irradiated graphene supported nickel oxides demonstrated improved catalytic performance for the oxygen reactions due to the increased exposed surface area available as active sites resulting from the structural modification induced by the plasma radiation, apart from the high synergistic effect with graphene.

A study on the levels of uranium (U) in urban soils of Samarahan was conducted to assess the contamination of uranium in the soil. Uranium was extracted from soil samples using aqua regia and extract was analyzed using ICP-OES. Results showed that acidic soils influence the absorption of uranium in soils and the binding of uranium due to the presence of organic matter. The highest concentration of uranium obtained from UM2 with 60 mg kg-1 and the lowest from UM3 with < 0.01 mg kg-1. Based on the contamination factors (CF) and geo-accumulation index (Igeo) calculations, the locations presented from low to high contamination of uranium and fall in Class 0 to Class 3. Most of the concentrations of the studied areas are within the tolerable value which was 23 mg kg−1 for residential lands and 33 mg kg−1 for commercial lands except for UM2 based on the soil quality guidelines. In conclusion, the current U concentrations in soil of Kota Samarahan do not pose any hazardous effect towards the environment and human health.

Solvothermal synthesis has shown to have a great potential to synthesize Zinc Oxide nanoparticles (ZnO NPs) with less than 10 nm size. In this study, we present a rapid synthesis of ZnO NPs in which ZnO NPs with more uniform shape and highly dispersed were synthesized using zinc acetate dihydrate (Zn(CH 3 COO) 2 ∙2H 2 O) and potassium hydroxide (KOH) as a precursor and absolute ethanol as solvent via solvothermal method. Few techniques were exploited to characterize synthesized ZnO NPs including X-ray diffraction (XRD), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), energy-dispersive X-ray spectroscopy (EDX), fourier transform infrared (FT-IR) spectroscopy, and ultraviolet visible (UV-Vis) spectroscopy. Synthesized ZnO NPs that were prepared via solvothermal synthesis method at 60 o C for 3 hours exhibited a wurtzite structure with a crystalline size of 10.08 nm and particle size of 7.4 ± 1.2 nm. The UV-vis absorption spectrum has shown peak at 357 nm indicate the presence of ZnO NPs. Hence, better quality with uniform size ZnO NPs can be easily synthesized with reduced amount of time via solvothermal synthesis method rather than using other complicated and lengthy synthesis methods.

In this study, we have demonstrated the humidity sensitivity of graphite pencil marks sensing material drawn on paper. The fabricated sensing devices (sensors) were characterized for their humidity sensitivity by measuring the resistance changes across the pencil marks. In order to improve the humidity sensitivity of the sensing material, ethanol chemical treatment was applied on the pencil marks to increase their surface hydrophilicity. Sensors with different levels of intrinsic resistances were also prepared and tested. Results showed that the ethanol-treated sensors have better humidity sensitivities and the intrinsic resistances of the sensors were directly proportional to their humidity sensitivity. To evaluate this carbon-based sensing material, the humidity sensing characteristics of the pencil graphite were gauged with other forms of carbon materials that have been reported in previous studies, such as carbon quantum dots film, carbon nanoparticles, carbon nanotubes, graphene oxide and graphene.

Electrochemical route has been a favorite technique for the fabrication of ZnO as it is relatively cheap and capable of producing abundance amount of materials. In this paper, we investigate the morphologies of hydrothermally synthesized ZnO structures assisted by galvanic process on conducting Au-coated silicon substrate. To induce the galvanic process, the substrate was in contact with aluminum so that the difference in the reduction potentials between the two materials provided the driving force for the formation of the ZnO structures. The galvanic process was found to promote compact and anisotropy growth of ZnO nanorods along the (001) plane. It was also found that substrate orientations in the electrolyte solution had an important bearing on the morphologies of ZnO. Well aligned periodic hexagonal arrays of ZnO nanorods of homogeneous diameters were obtained on gold-coated Si substrate with face-down orientation in the electrolyte solution.

The electrochemical processes in current fuel cell is still relying on high-loading of scarce and expensive precious metals such as Pt as electrocatalysts for device operation which hinder their commercialization Thus, there is a critical need in search of non-precious metal-based electrocatalysts to replace these precious metals. In view of its corrosion resistant advantage and low production cost, non-precious metal oxides have been recognized as the potential candidates for electrocatalysts in fuel cell. In this study, the aim was to develop a stable catalyst based on transition metal oxides using a simple and cheap modified precipitation technique. Three types of transition metal oxides, namely the cobalt oxides, nickel oxides and iron oxides, were synthesized and a systematic study on the physicochemical properties of the materials are carried out using X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM). It was observed that cobalt oxide was grown as porous hexagonal platelets while iron oxides and nickel oxides were grown as nanosized particles. The role of the microstructural properties of these transition metals in enhancing their catalytic performance is discussed.

The capability of zinc oxide (ZnO) as a hydrogen sensing element has been pushed to its limits. Different methods have been explored to extend its sensing capability. In this paper, we report a novel approach which significantly improves the hydrogen sensing capability of zinc oxide by applying a bias voltage to ZnO nanorods as the sensing elements. Zinc oxide in the form of aligned nanorods was first synthesized on an Au-coated Si(111) substrate using a facile method via the galvanic-assisted chemical process. The sensing performance of the zinc oxide nanorods was investigated in response to the applied biasing voltage. It was found that the sensitivity, response time and detection limit of the ZnO sensing elements were dramatically improved with increasing bias voltage. A 100% increment in sensing response was achieved for the detection of 2000 ppm hydrogen gas when the bias voltage was increased from −2 to −6 V with 70% reduction in response and recovery times. This remarkable sensing performance is attributed to the reaction of hydrogen with chemisorbed oxygen ions on the surface of the ZnO nanorods that served as the electron donors to increase the sensor conductance. Higher reverse bias voltages sweep the electrons faster across the electrodes. This shortened the response time and, at the same time, depleted the electrons in the sensor elements and weakens oxygen adsorption. The oxygen ions could then be readily removed by hydrogen, leading to a higher sensitivity of the sensors. This, therefore, envisages a way for high-speed hydrogen gas sensing with high detection sensitivities.

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.

In this work, palladium surface-functionalized single-walled carbon nanotubes (SWNTs) hydrogen gas sensor was fabricated by electrodeposition and its sensing properties were systematically studied under various conditions. The diameter and density of the Pd nanoparticles were optimized by tuning the deposition voltage and time. Using a microfabricated chip consisting of a circular array of 16 individually addressable Pd-functionalised nanosensors, the gas sensing performance for each nanosensor was evaluated sequentially via a customized multiplexer-coupled electronic measurement system with Labview program control. The sensing properties were optimized for high sensitivity and short response time with respect to hydrogen detection. Sensor formed from non-connected chains of Pd particles was found to exhibit excellent sensing properties with resistance change exceeding 60% in 2000 ppm of hydrogen and lowest detection limit of 30 ppm hydrogen. The response time increased from a few minutes to tens of minutes with decreasing hydrogen concentrations.

This paper reports on the process developed to fabricate anodic aluminum oxide (AAO) templates suitable for the fabrication of nanowires arrays. Anodization process has been used to fabricate the AAO templates with pore diameters ranging from 15 nm to 30 nm. Electrodeposition of parallel arrays of high aspect ratio nickel nanowires were demonstrated using these fabricated AAO templates. The nanowires produced were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the orientations of the electrodeposited nickel nanowires were governed by the deposition current and electrolyte conditions.