Choon Yian Haw

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.

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.

SnO2 Nanoparticles Decorated 2D Wavy Hierarchical Carbon Nanowalls with Enhanced Photoelectrochemical Performance

Two-dimensional carbon nanowall (2D-CNW) structures were prepared by hot wire assisted plasma enhanced chemical vapor deposition (hw-PECVD) system on silicon substrates. Controlled variations in the film structure were observed with increase in applied rf power during deposition which has been established to increase the rate of dissociation of precursor gases. The structural changes resulted in the formation of wavy-like features on the 2D-CNW, thus further enhancing the surface area of the nanostructures. The FESEM results confirmed the morphology transformation and conclusively showed the evolution of the 2D-CNW novel structures while Raman results revealed increase in ratio indicating increase in the presence of disordered domains due to the presence of open edges on the 2D-CNW structures. Subsequently, the best 2D-CNW based on the morphology and structural properties was functionalized with tin oxide (SnO2) nanoparticles and used as a working electrode in a photoelectrochemical (PEC) measurement system. Intriguingly, the SnO2 functionalized 2D-CNW showed enhancement in both Mott-Schottky profiles and LSV properties which suggested that these hierarchical networks showed promising potential application as effective charge-trapping medium in PEC systems.

3D hyperbranched heterostructures of Ag nanocrystals-decorated ZnO nanopillars: controlled growth and characterization of the optical properties

Herein, the synthesis along with the structural and optical characterization of 3D hyperbranched ZnO nanopillars (NPLs) decorated with Ag nanocrystals (NCs) is reported. This hyperbranched heterostructure, displaying broccoli-like morphology, was prepared via two-step synthesis method, in which freestanding ZnO NPLs were hydrothermally grown onto a Zn foil substrate, followed by scrupulous decoration with Ag NCs using a similar approach. FESEM observations revealed that the reaction time highly influenced the crystallization mechanism, whereby the as-deposited Ag NCs could serve as a catalyst to induce secondary nucleation sites that promote the sprouting of secondary ZnO NPLs branches that grow along the edges of the upper half of the primary ZnO NPLs. HRTEM analysis was conducted to investigate the crystallography structure at the interfaces and elemental mapping was used to probe the elemental distribution. These results were further complemented with both XRD and Raman spectroscopy. Finally, diffuse reflectance and photoluminescence analysis were employed to elucidate the optical behaviour. A possible growth mechanism for obtaining such a unique broccoli-like morphology with a complicated nanoarchitecture is proposed. The present study could assist the development of a crystal engineering process for the preparation and analysis of hybrid nanostructures.