Wee Siong Chiu

Citric acid modified kenaf core fibres for removal of methylene blue from aqueous solution.

Chemically modified kenaf core fibres were prepared via esterification in the presence of citric acid (CA). The adsorption kinetics and isotherm studies were carried out under different conditions to examine the adsorption efficiency of CA-treated kenaf core fibres towards methylene blue (MB). The adsorption capacity of the kenaf core fibres increased significantly after the citric acid treatment. The values of the correlation coefficients indicated that the Langmuir isotherm fitted the experimental data better than the Freundlich isotherm. The maximum adsorption capacity of the CA-treated kenaf core fibres was found to be 131.6mg/g at 60°C. Kinetic models, pseudo-first-order, pseudo-second-order and intraparticle diffusion, were employed to describe the adsorption mechanism. The kinetic data were found to fit pseudo-second-order model equation as compared to pseudo-first-order model. The adsorption of MB onto the CA-treated kenaf core fibres was spontaneous and endothermic.

Facile synthesis of a Ag/MoS2 nanocomposite photocatalyst for enhanced visible-light driven hydrogen gas evolution

The current study reports the facile synthesis of a Ag/MoS2 nanocomposite photocatalyst for visible-light driven hydrogen gas evolution. The MoS2 nanoflakes were hydrothermally prepared and then decorated with Ag nanoparticles (NPs) by a simple chemical reduction process at room temperature. Detailed characterizations were carried out to probe the physical structure and properties of the as-synthesized nanocomposite. The nanocomposite shows enhanced visible-light absorption and pronounced quenching of photoluminescence intensity as compared to that of pure MoS2. The photocatalytic hydrogen gas evolution experiments reveal that the Ag NPs can act as an efficient co-catalyst for the MoS2 nanoflakes and subsequently improve the hydrogen gas evolution rate. Ag-loading dependent photocatalytic tests indicate that the 20 wt%-Ag/MoS2 nanocomposite exhibits the highest photocatalytic activity with a hydrogen gas evolution of 179.5 μmol H2 gcat−1, which is enhanced by 95% compared to that of commercial MoS2 nanopowder (92.0 μmol H2 gcat−1). The possible mechanisms that contribute to the improvement of the visible-light driven photocatalytic performance for the nanocomposite are proposed.

A REVIEW OF METAL OXIDE COMPOSITE ELECTRODE MATERIALS FOR ELECTROCHEMICAL CAPACITORS

With the emerging technology in the 21st century, which requires higher electrochemical performances, metal oxide composite electrodes in particular offer complementary properties of individual materials via the incorporation of both physical and chemical charge storage mechanism together in a single electrode. Numerous works reviewed herein have identified a wide variety of attractive metal oxide-based composite electrode material for symmetric and asymmetric electrochemical capacitors. The focus of the review is the detailed literature data and discussion regarding the electrochemical performance of various metal oxide composite electrodes fabricated from different configurations including binary and ternary composites. Additionally, projection of future development in hybrid capacitor coupling lithium metal oxides and carbonaceous materials are found to obtain significantly higher energy storage than currently available commercial electrochemical capacitors. This review describes the novel concept of l...

Improved Synthesis of Reduced Graphene Oxide-Titanium Dioxide Composite with Highly Exposed 001 Facets and Its Photoelectrochemical Response

Crystal facet engineering has attracted worldwide attention, particularly in facet manipulation of titanium dioxide (TiO2) surface properties. An improved synthesis by solvothermal route has been employed for the formation of TiO2 with highly exposed facets decorated on reduced graphene oxide (RGO) sheets. The RGO-TiO2 composite could be produced with high yield by following a stringently methodical yet simple approach. Field emission scanning electron microscope and high resolution transmission electron microscope imaging reveal that the structure consists of TiO2 nanoparticles covered with TiO2 nanosheets of exposed facets on a RGO sheet. The photocurrent response of the RGO-TiO2 composite was discovered to outperform that of pure TiO2, as a ~10-fold increase in photocurrent density was observed for the RGO-TiO2 electrodes. This may be attributed to rapid electron transport and the delayed recombination of electron-hole pairs due to improved ionic interaction between titanium and carbon.

High Sensitivity pH Sensor Based on Porous Silicon (PSi) Extended Gate Field-Effect Transistor

In this study, porous silicon (PSi) was prepared and tested as an extended gate field-effect transistor (EGFET) for pH sensing. The prepared PSi has pore sizes in the range of 500 to 750 nm with a depth of approximately 42 µm. The results of testing PSi for hydrogen ion sensing in different pH buffer solutions reveal that the PSi has a sensitivity value of 66 mV/pH that is considered a super Nernstian value. The sensor considers stability to be in the pH range of 2 to 12. The hysteresis values of the prepared PSi sensor were approximately 8.2 and 10.5 mV in the low and high pH loop, respectively. The result of this study reveals a promising application of PSi in the field for detecting hydrogen ions in different solutions.

The design of new magnetic-photocatalyst nanocomposites (CoFe2O4–TiO2) as smart nanomaterials for recyclable-photocatalysis applications

The current study reports the synthesis and characterisation of a new magnetic-photocatalyst (CoFe2O4–TiO2) and tests its feasibility to be used as smart magnetically-recoverable nanomaterial in the photodegradation of methylene blue (MB). 3D urchin-like TiO2 microparticles are hydrothermally prepared and decorated with CoFe2O4 magnetic nanoparticles (NPs) through a co-precipitation method. The as-prepared CoFe2O4–3D TiO2 nanocomposites show an enhancement in the photodegradation of MB as compared to the commercial rutile-phase TiO2 and the pure urchin-like TiO2 (3D TiO2) microparticles. Such an enhancement could be accredited to the lower recombination rate of the photoexcited charge carriers of the CoFe2O4–3D TiO2 nanocomposites. Furthermore, the CoFe2O4–3D TiO2 nanocomposite is magnetically-retrievable for sequential recycling, and the results indicate that the nanocomposite shows a relatively consistent photocatalytic performance with negligible degradation. Thus, the current study would offer a potential route for the design and processing of a value-added photocatalyst nanocomposite that will contribute to the advancement of photocatalysis studies.

Temperature-Driven Structural and Morphological Evolution of Zinc Oxide Nano-Coalesced Microstructures and Its Defect-Related Photoluminescence Properties

In this paper, we address the synthesis of nano-coalesced microstructured zinc oxide thin films via a simple thermal evaporation process. The role of synthesis temperature on the structural, morphological, and optical properties of the prepared zinc oxide samples was deeply investigated. The obtained photoluminescence and X-ray photoelectron spectroscopy outcomes will be used to discuss the surface structure defects of the prepared samples. The results indicated that the prepared samples are polycrystalline in nature, and the sample prepared at 700 °C revealed a tremendously c-axis oriented zinc oxide. The temperature-driven morphological evolution of the zinc oxide nano-coalesced microstructures was perceived, resulting in transformation of quasi-mountain chain-like to pyramidal textured zinc oxide with increasing the synthesis temperature. The results also impart that the sample prepared at 500 °C shows a higher percentage of the zinc interstitial and oxygen vacancies. Furthermore, the intensity of the photoluminescence emission in the ultraviolet region was enhanced as the heating temperature increased from 500 °C to 700 °C. Lastly, the growth mechanism of the zinc oxide nano-coalesced microstructures is discussed according to the reaction conditions.

Electrochemical studies on nanometal oxide-activated carbon composite electrodes for aqueous supercapacitors

In present study, the electrochemical performance of eco-friendly and cost-effective titanium oxide (TiO2)-based and zinc oxide-based nanocomposite electrodes were studied in neutral aqueous Na2SO3 electrolyte, respectively. The electrochemical properties of these composite electrodes were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that these two nanocomposite electrodes achieve the highest specific capacitance at fairly low oxide loading onto activated carbon (AC) electrodes, respectively. Considerable enhancement of the electrochemical properties of TiO2/AC and ZnO/AC nanocomposite electrodes is achieved via synergistic effects contributed from the nanostructured metal oxides and the high surface area mesoporous AC. Cations and anions from metal oxides and aqueous electrolyte such as Ti4+, Zn2+, Na+ and can occupy some pores within the high-surface-area AC electrodes, forming the electric double layer at the electrode–electrolyte interface. Additionally, both TiO2 and ZnO nanoparticles can provide favourable surface adsorption sites for anions which subsequently facilitate the faradaic processes for pseudocapacitive effect. These two systems provide the low cost material electrodes and the low environmental impact electrolyte which offer the increased charge storage without compromising charge storage kinetics.

Structural- and optical-properties analysis of single crystalline hematite (α-Fe2O3) nanocubes prepared by one-pot hydrothermal approach

High quality single crystal hematite (α-Fe2O3) nanocubes with average dimensions of 40 nm were successfully synthesized by a facile one-pot hydrothermal method. Systematic analyses were performed to investigate the morphological-, structural- and optical-properties of the as-synthesized α-Fe2O3 nanocubes. Continuous formation and hourly monitoring towards proper arrangement of single crystal α-Fe2O3 nanocubes was observed throughout the hydrothermal heating process of 180 °C from 4 h to 12 h. The probable growth mechanism on the formation of cubic nanostructures is also proposed. Electron micrographs show the cubic α-Fe2O3 synthesized at the most optimum 8 h hydrothermal heating duration are indeed produced in high-yield with a well-defined cubical shape. The typical rhombohedral structure of cubic α-Fe2O3 was evident from the XRD pattern. The SAED pattern indicates that the α-Fe2O3 nanocubes are single-crystalline in nature, with lattice-fringes and a d-spacing value of 3.6 A. The optical characterization reveals that α-Fe2O3 nanocubes show strong visible-light absorption with a band gap energy of ∼2.1 eV while the photoluminescence emission spectra depicts a mono-peak centered at ∼590 nm. Both the SAED pattern and UV-vis spectra show a strong correlation with the standard α-Fe2O3. The as-synthesized α-Fe2O3 single crystal is of high quality that potentially could be used as a visible-light active nanomaterial in renewable energy device applications.

Sensitivity enhancement of graphene/zinc oxide nanocomposite-based electrochemical impedance genosensor for single stranded RNA detection

An efficient electrochemical impedance genosensing platform has been constructed based on graphene/zinc oxide nanocomposite produced via a facile and green approach. Highly pristine graphene was synthesised from graphite through liquid phase sonication and then mixed with zinc acetate hexahydrate for the synthesis of graphene/zinc oxide nanocomposite by solvothermal growth. The as-synthesised graphene/zinc oxide nanocomposite was characterised with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffractometry (XRD) to evaluate its morphology, crystallinity, composition and purity. An amino-modified single stranded DNA oligonucleotide probe synthesised based on complementary Coconut Cadang-Cadang Viroid (CCCVd) RNA sequence, was covalently bonded onto the surface of graphene/zinc oxide nanocomposite by the bio-linker 1-pyrenebutyric acid N-hydroxysuccinimide ester. The hybridisation events were monitored by electrochemical impedance spectroscopy (EIS). Under optimised sensing conditions, the single stranded CCCVd RNA oligonucleotide target could be quantified in a wide range of 1.0×10-11M to 1.0×10-6 with good linearity (R =0.9927), high sensitivity with low detection limit of 4.3×10-12M. Differential pulse voltammetry (DPV) was also performed for the estimation of nucleic acid density on the graphene/zinc oxide nanocomposite-modified sensing platform. The current work demonstrates an important advancement towards the development of a sensitive detection assay for various diseases involving RNA agents such as CCCVd in the future.