Roong Jien Wong

Combined electrophoretic deposition-anodization method to fabricate reduced graphene oxide-TiO2 nanotube films

We directly constructed reduced graphene oxide–titanium oxide nanotube (RGO–TNT) film using a single-step, combined electrophoretic deposition–anodization (CEPDA) method. This method, based on the simultaneous anodic growth of tubular TiO2 and the electrophoretic-driven motion of RGO, allowed the formation of an effective interface between the two components, thus improving the electron transfer kinetics. Composites of these graphitic carbons with different levels of oxygen-containing groups, electron conductivity and interface reaction time were investigated; a fine balance of these parameters was achieved.

Interfacing BiVO4 with Reduced Graphene Oxide for Enhanced Photoactivity: A Tale of Facet Dependence of Electron Shuttling

Efficient interfacial charge transfer is essential in graphene-based semiconductors to realize their superior photoactivity. However, little is known about the factors (for example, semiconductor morphology) governing the charge interaction. Here, it is demonstrated that the electron transfer efficacy in reduced graphene oxide-bismuth oxide (RGO/BiVO4 ) composite is improved as the relative exposure extent of {010}/{110} facets on BiVO4 increases, indicated by the greater extent of photocurrent enhancement. The dependence of charge transfer ability on the exposure degree of {010} relative to {110} is revealed to arise due to the difference in electronic structures of the graphene/BiVO4 {010} and graphene/BiVO4 {110} interfaces, as evidenced by the density functional theory calculations. The former interface is found to be metallic with higher binding energy and smaller Schottky barrier than that of the latter semiconducting interface. The facet-dependent charge interaction elucidated in this study provides new aspect for design of graphene-based semiconductor photocatalyst useful in manifold applications.

Reduced Graphene Oxide: Control of Water Miscibility, Conductivity, and Defects by Photocatalysis

A TiO2‐based photocatalytic reaction is demonstrated to synthesize water miscible reduced graphene oxide (RGO) sheets with conductivity comparable to that of bulk graphite. Unlike the conventional chemical/thermal reduction pathways which effectively deoxygenated the oxidized graphite, the photocatalytic method removes oxygen functional groups selectively to afford excellent conductivity restoration yet maintaining its water miscibility. The controlled redox capabilities of the photocatalyst serve as an effective modulation tool to tune the conductivity restoration and suppression of hydrophobicity. Moreover, the evolution of defect minimization/generation in a two‐step pattern is monitored throughout the photocatalytic process and its association with the conductivity of RGO is established. The insights of defect engineering at the initial stage of graphene oxide (GO) to RGO transformation provides useful information in developing optimum chemical methods to produce large domain and small defect density graphene.

Investigating the effect of UV light pre-treatment on the oxygen activation capacity of Au/TiO2

The potential for applying UV light pre-treatment to enhance the oxygen activation capacity of Au/TiO2 under ambient conditions was examined. Catalytic formic acid oxidation in an aqueous environment was employed as the test reaction. Pre-illuminating Au/TiO2 with UV light can amplify the catalytic formic acid oxidation rate by up to four times with the degree of enhancement governed by system parameters such as Au loading, pre-illumination time, and initial formic acid loading. X-ray photoelectron spectroscopy, photoluminescence spectroscopy and electrochemical assessment of the Au/TiO2 indicated light pre-illumination invokes photoexcited electron transfer from the TiO2 support to the Au deposits. The Au deposits then utilise the additional electrons to catalyse molecular oxygen activation and promote the oxidation reaction. Scanning tunneling spectroscopy analysis and first principle calculations indicated the Au deposits introduced new electronic states above the TiO2 valence band. The new electronic states were most intense at the Au–TiO2 interface suggesting the Au deposit:TiO2 perimeter may be the key region for oxygen activation. The current study has demonstrated that pre-illuminating Au/TiO2 with light can be used to augment reactions where oxygen activation is a critical component, such as for the oxidation of organic pollutants and for the oxygen reduction reaction in fuel cells or energy storage systems.

Enhancing bimetallic synergy with light: the effect of UV light pre-treatment on catalytic oxygen activation by bimetallic Au–Pt nanoparticles on a TiO2 support

UV light pre-treatment was examined as a means of enriching the catalytic activation of oxygen by bimetallic AuPt deposits loaded on TiO2. The rate of catalytic oxygen activation was assessed by monitoring the rate of formic acid oxidation in an aqueous system. A catalytic synergy was observed to exist for the bimetallic AuPt on TiO2 and was governed by the Au–Pt structure and ratio. The extent of the synergy was further enhanced upon UV light pre-treatment. Exceptional improvements in bimetallic catalysts are often simply attributed to a synergy effect, which is not necessarily well-understood. The Au–Pt bimetallic synergy and UV light pre-illumination phenomena were probed using high-end characterisation tools in conjunction with first principle calculations with the effects attributed to a combined influence of work-function difference and lattice mismatch between Au and Pt. Understanding the origin of bimetallic synergism is a critical step toward developing advanced catalysts.

Promoting catalytic oxygen activation via localised surface plasmon resonance: effect of visible light pre-treatment and bimetallic interaction

Visible light pre‐treatment has been found to be capable of enhancing the catalytic oxygen activation on AuPt/TiO2 by up to seven times. Visible light pre‐treatment exploits the localized surface plasmon resonance effect of Au to generate free electrons, which are transferred to the Pt active sites. The electron transfer was evident from a change in Pt speciation observed from X‐ray photoelectron spectroscopy, showing the presence of PtO after visible light pre‐treatment. Photoluminescence spectroscopy was used to reveal the bimetallic synergistic enhancement, as indicated by an overall decrease in the charge recombination rate. Further examination revealed that a good bimetallic interaction is necessary to achieve the enhancement by visible light pre‐treatment. Weak bimetallic interaction, such as the occurrence of element segregation in the bimetallic alloy, inhibits electron transfer from the Au to the Pt and increases electron recombination rates, diminishing the degree to which visible light pre‐treatment improves catalytic performance.