Local structure and photocatalytic property of mechanochemical synthesized ZnO doped with transition metal oxides

Co and Mn doped ZnO nanoparticles with up to 5 at% doping level were prepared using a mechanochemical method. The location of dopant ions and the effect of doping on the photocatalytic activity were investigated by Synchrotron X-ray Absorption (XAS) Spectroscopy and photo-degradation of Rhodamine B solution. The XAS results showed that the Co ions substituted the Zn ions in the ZnO wurtzite phase structure. It was revealed that Co-doping strongly reduced the photocatalytic activity, while Mn-doping increased the photocatalytic activity at low doping levels but reduced the activity at high doping levels

Cobalt complexes with tripodal ligands: implications for the design of drug chaperones

Extensive research is currently being conducted into metal complexes that can selectively deliver cytotoxins to hypoxic regions in tumours. The development of pharmacologically suitable agents requires an understanding of appropriate ligand–metal systems for chaperoning cytotoxins. In this study, cobalt complexes with tripodal tren (tris-(2-aminoethyl)amine) and tpa (tris-(2 pyridylmethyl)amine) ligands were prepared with ancillary hydroxamic acid, β-diketone and catechol ligands and several parameters, including: pKa, reduction potential and cytotoxicity were investigated. Fluorescence studies demonstrated that only tpa complexes with β-diketones showed any reduction by ascorbate in situ and similarly, cellular cytotoxicity results demonstrated that ligation to cobalt masked the cytotoxicity of the ancillary groups in all complexes except the tpa diketone derivative [Co(naac)tpa](ClO4)2 (naac = 1-methyl-3-(2-naphthyl)- propane-1,3-dione). Additionally, it was shown that the hydroxamic acid complexes could be isolated in both the hydroxamate and hydroximate form and the pKa values (5.3–8.5) reveal that the reversible protonation/deprotonation of the complexes occurs at physiologically relevant pHs. These results have clear implications for the future design of prodrugs using cobalt moieties as chaperones, providing a basis for the design of cobalt complexes that are both more readily reduced and more readily taken up by cells in hypoxic and acidic environments

Implanting Ni-O-VOx sites into Cu-doped Ni for low-overpotential alkaline hydrogen evolution

Nickel-based catalysts are most commonly used in industrial alkaline water electrolysis. However, it remains a great challenge to address the sluggish reaction kinetics and severe deactivation problems of hydrogen evolution reaction (HER). Here, we show a Cu-doped Ni catalyst implanted with Ni-O-VOx sites (Ni(Cu)VOx) for alkaline HER. The optimal Ni(Cu) VOx electrode exhibits a near-zero onset overpotential and low overpotential of 21 mV to deliver -10 mA cm−2, which is comparable to benchmark Pt/C catalyst. Evidence for the formation of Ni-O-VOx sites in Ni(Cu)VOx is established by systematic X-ray absorption spectroscopy studies. The VOx can cause a substantial dampening of Ni lattice and create an enlarged electrochemically active surface area. First-principles calculations support that the Ni-O-VOx sites are superactive and can promote the charge redistribution from Ni to VOx, which greatly weakens the H-adsorption and H2 release free energy over Ni. This endows the Ni(Cu)VOx electrode high HER activity and long-term durability.This research was undertaken with the assistance of resources provided by the National Computational Infrastructure (NCI) facility at the Australian National University; allocated through both the National Computational Merit Allocation Scheme supported by the Australian Government and the Australian Research Council grant (LE190100021). C.Z. is grateful for the award of a Future Fellow from Australian Research Council (FT170100224)

Towards hydrogen energy: progress on catalysts for water splitting

This article reviews some of the recent work by fellows and associates of the Australian Research Council Centre of Excellence for Electromaterials Science (ACES) at Monash University and the University of Wollongong, as well as their collaborators, in the field of water oxidation and reduction catalysts. This work is focussed on the production of hydrogen for a hydrogen-based energy technology. Topics include: (1) the role and apparent relevance of the cubane-like structure of the Photosystem II Water Oxidation Complex (PSII-WOC) in non-biological homogeneous and heterogeneous water oxidation catalysts, (2) light-activated conducting polymer catalysts for both water oxidation and reduction, and (3) porphyrin-based light harvesters and catalysts

Ligand field and molecular orbital theories of transition metal X-ray absorption edge transitions

Carl Ballhausen made a wide range of seminal contributions to ligand field theory and its application to ground state and ligand field excited state spectroscopies. These provided a fundamental basis for probing the nature of transition metal complexes using their visible spectra and a range of magnetic spectroscopies. The advent of synchrotrons provided access to high flux electromagnetic radiation that could be tuned across a wide range of energies including X-ray. This expanded the scope of spectroscopic techniques available to inculde X-ray Absorption Edge Spectroscopies. Paralleling a visible absorption experiment, X-ray spectra (metal K-edge, i.e. 1s→3d and metal L-edge, i.e. 2p→3d) taken at a synchrotron are dominated by ligand field splittings, electron repulsion effects and covalency. These can be used to obtain important insight into the properties of a diverse range of materials from solar cells to the catalytic centers of metalloenzymes. Herein we systematically consider applications of ligand field theory to X-ray absorption edge transitions

Co-doped ZnO nanopowders : Location of cobalt and reduction in photocatalytic activity

The location of dopant ions and the effect of doping level on the photocatalytic activity have been investigated on Co-doped ZnO nanopowders. A co-precipitation method was used to prepare ZnO nanoparticles of <50 nm in diameter doped with up to 5 at% of Co. The crystal structure of nanoparticles and local atomic arrangements around dopant ions were analysed by X-ray diffraction and extended X-ray absorption fine structure spectroscopy using synchrotron radiation. The results showed the Co ions substituted the Zn ions in ZnO crystal lattice and induced lattice shrinkage. The photocatalytic activity under simulated sunlight irradiation was characterised by the decomposition of Rhodamine B dye molecules, which revealed the successful reduction of photocatalytic activity by Co-doping