Controllable proton and CO2 photoreduction over Cu2O with various morphologies

Simultaneous photocatalytic reduction of water to H2 and CO2 to CO was observed over Cu2O photocatalyst under both full arc and visible light irradiation (>420 nm). It was found that the photocatalytic reduction preference shifts from H2 (water splitting) to CO (CO2 reduction) by controlling the exposed facets of Cu2O. More interestingly, the low index facets of Cu2O exhibit higher activity for CO2 photoreduction than high index facets, which is different from the widely-reported in which the facets with high Miller indices would show higher photoactivity. Improved CO conversion yield could be further achieved by coupling the Cu2O with RuOx to form a heterojunction which slows down fast charge recombination and relatively stabilises the Cu2O photocatalyst. The RuOx amount was also optimised to maximise the junction's photoactivity

Dimensionally and compositionally controlled growth of calcium phosphate nanowires for bone tissue regeneration

Nanostructured biomaterials with controlled morphology and composition are of high interest for bone tissue regeneration. As resorbable and biocompatible materials for bone tissue engineering, calcium phosphate nanowires and nanoneedles with different aspect ratios and compositions have been first synthesized without the use of any toxic surfactants via an energy efficient microwave assisted process. Correlation between solvent composition, mixing methodology and reagent stoichiometric ratios was investigated with the aim of producing orientated growth and varied biphasic composition, resulting in dimensionally controlled growth of materials containing varying hydroxyapatite (HA)/monetite quantities. It was observed that the HA/monetite content and dimensionality could be manipulated by changing the initial ethanol (EtOH) volume in the H2O/EtOH solvent mixture. Three dimensional particles with minute amounts of HA were produced when a H2O/EtOH volumetric ratio of 20/80 was used. Conversely, high aspect ratio (ca. 54) nanowires containing ca. 38 wt% HA were obtained with a 60/40 H2O/EtOH volumetric ratio. Importantly, the quantity of HA in the high aspect ratio nanowires/needles was controlled by varying the stoichiometric ratio of the reactants, demonstrating that one-dimensional materials with close to 100% HA can be achieved when the Ca/P ratio is increased to 1.67. Additionally, significant correlation between the extent of orientated growth of the materials and the point of EtOH addition during the mixing method was observed. The findings highlight that solvent composition, reactant stoichiometric ratio and mixing procedure can be used in tandem to tailor the morphology and composition of calcium phosphate materials, which are of very high importance in developing excellent materials suitable for bone tissue regeneration

Highly Efficient Photocatalytic H2 Evolution from Water using Visible Light and Structure-Controlled Graphitic Carbon Nitride.

The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low-cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3 N4 ) from a low-cost precursor, urea, is reported. The g-C3 N4 exhibits an extraordinary hydrogen-evolution rate (ca. 20 000 μmol h(-1)  g(-1) under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3 N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced

Transition-Metal-Doped alpha-MnO2 Nanorods as Bifunctional Catalysts for Efficient Oxygen Reduction and Evolution Reactions

Nano‐sized α‐MnO2 nanorods doped with Co or Ru were directly synthesized using a continuous hydrothermal synthesis process (production rate 10 g h−1) and investigated as relatively inexpensive (due to the small Ru content) bifunctional catalysts for both the Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER). The materials were extensively characterized using a range of analytical methods; these including Extended X‐Ray Absorption Fine Structure (EXAFS) spectroscopy measurements, which was accompanied by density functional theory studies, in order to elucidate the role of dopants in α‐MnO2 structure. Electrochemical ORR and OER investigations of the as‐prepared doped α‐MnO2 nanomaterials were compared to more expensive Pt/C or RuO2 catalysts. The doped manganese oxide nanomaterials were used as bifunctional catalysts in the positive electrode of zinc air batteries (with oversized zinc metal negative electrode and limited density of discharge window) and displayed excellent performance (the overpotential was 0.77 and 0.68 V for α‐MnO2 modified with 7.6 at% Co and 9.4 at% Ru, respectively). Overall, as a result of doping, this study achieved improved bifunctional catalytic activities of metal oxide catalysts, which was comparable to more expensive alternatives

Probing the electronic and geometric structures of photoactive electrodeposited Cu2O films by X-ray absorption spectroscopy

Cu2O is an attractive photocathode for important renewable energy reactions such as water splitting and CO2 reduction. Electrodeposition is commonly used to deposit Cu2O films on conductive substrates due to its simplicity and consistency. However, structural descriptors, linking electrodeposition parameters, film structure and the catalytic properties are elusive. A variety of Cu2O films reported by many research groups would often display vastly different electronic properties and catalytic activity, while appear indistinguishable under common characterisation tools. In this work, we take a systematic look into electrochemically deposited Cu2O and investigate the impact of deposition parameters towards the bulk and surface chemistry of the deposited film. Specifically, we employ high resolution XANES for thorough quantitative analysis of the Cu2O films, alongside more common characterisation methods like XRD, SEM and Raman spectroscopy. Photoelectrochemical (PEC) studies reveal an unexpected trend, where the highest PEC activity appears to correlate with the amount of Cu2+ content. Other factors which also affect the PEC activity and stability are film thickness and crystallite grain size. Our study shows that the use of high resolution XANES, though not perfect due to possible self-absorption issue, is apt for extracting compositional descriptor in concentrated thin film samples from the pre-edge energy position analysis. This descriptor can serve as a guide for future development of more active Cu2O based films for wide range of PEC processes as well as for solar cell applications