By grafting small amounts of iron ions onto TiO2, the rate of photocatalytic oxidation of NO2 is increased by a factor of 9.

It is the unique electronic structure of the f-block elements that is responsible for their desirable catalytic, magnetic and photophysical properties. These phosphors can be broadly classified into two groups, based on the desired electronic transition and emission band width required; namely, broad band 5d → 4f interelectronic transitions possessing a short radiative lifetime (cf. 1 µs) and sharp emission bands arising from 4f → 4f intraelectronic transitions, that are La-Porte forbidden, possessing a longer radiative lifetime (cf. 1 ms). [10] The 4f subshell is relatively insensitive to the local environment, due to the screening of occupied 5s and 5p subshells which reduce the electrostatic potential of the ligand field. Therefore, the sharp f-f band transitions are usually weakly affected by an external bias, although the relative intensities can be perturbed significantly. The relative energy and degeneracy of the 5d orbitals are in contrast significantly influenced by the crystal field. Consequently, the relative energy between the 4f and 5d states, and thus the corresponding emissive wavelength, is readily tuned by the coordination environment. After the Coulombic and crystal field effects, other important considerations include dopant concentration, particle size distribution, crystallinity and concentration of defects or impurities within the material which may compete with the lanthanide activator. As a result, the specific luminescent intensity of the broad band may be reduced via interaction with these impurities, either by competition for incident optical absorption, energy transfer processes, or quenching of luminescent emission at the desired wavelength. [11,12] The luminescent efficiency of phosphors is also highly dependent on the relaxation properties of the activator during absorption and emission, i.e., the amount of energy lost to the lattice as heat, [9] which must be minimized to preserve the overall quantum yield. Eu 2+-doped calcium sulfide (labeled hereafter as CaS:Eu) phosphors have in particular recently generated considerable interest as solid state light sources for algae growth, owing to the broad band red emission near λ = 645 nm. Eu is readily found in the divalent oxidation state due to a half-filled 4f subshell and resulting stabilization energy. Over 300 Eu 2+ compounds in different host matrices have been reported to date, where the emission color of the 5d-4f transition has been tuned A series of commercial and prepared CaS:Eu 2+ rare earth activated phosphors are investigated following different post-synthetic treatments. A number of species directly related to the function of the material are characterized using electron paramagnetic resonance (EPR) spectroscopy. Isolated Eu 2+ sites are identified and associated with the substitutional doping for Ca 2+ in the lattice which are responsible for the 645 nm emission of interest. Another inactive Eu 2+ site based within a "EuO" type phase aggregated on the surface of the material is also identified, as well as competitive F + ...

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Species bearing unpaired electrons, including paramagnetic redox metal centres, surface defect centres, reactive oxygen species, adsorbed radical anions, are often involved in catalytic reactions. These species can be readily and thoroughly interrogated using Electron Paramagnetic Resonance (EPR) spectroscopy, providing information on the identity, chemical composition and even the dynamics of the centres themselves, thereby helping to elucidate the involvement of the radicals in the reaction cycles. This review will summarise and highlight the applications of EPR in heterogeneous, homogeneous, photocatalytic and microporous materials, all of which are of vital importance to the field of catalysis.

Chelating exchange resins (CERs) are now widely used for metal extraction in aqueous acidic media. Many of these CERs contain surface N-donor ligands, such as di(2-picolylamine) (BPA) and picolylamine (PA), which are highly selective for Cu(II) uptake. Two such widely used resins are Dowex M4195 and CuWRAM. Surprisingly, very little is known about the Cu(II) binding environments on the exchange resins, particularly at variable concentrations and pH's, and therefore we used EPR spectroscopy to investigate this binding. The broad EPR spectra of the Cu(II) loaded resins are quite complex, indicating the presence of multiple Cu(II) binding environments. By preparing a series of well-defined [Cu II (PA) x ] and [Cu II (BPA) x ] complexes and studying their EPR and UV−vis spectra, the individual Cu(II) species contributing to the broad and overlapping EPR spectra of the loaded resins were identified. For Dowex M4195, [Cu II (BPA)](H 2 O) m and [Cu II (BPA) 2 ] complexes are most dominant, whereas for CuWRAM two dominant species including [Cu II (PA) 2 ](H 2 O) m and [Cu II (PA) 3 ] were identified. Notably, [Cu II (PA)](H 2 O) m was not present in this sample. The experimental spin Hamiltonian parameters for all these species were in good agreement with the density functional theory derived values. Additional intermolecular Cu(II) species were identified on both resins, labeled [Cu II (BPA) x (BPA) y (H 2 O) n ] and [Cu II (PA) x (PA) y (H 2 O) n ]. The presence of coordinated water in these intermolecular anchored sites was confirmed in a series of dehydration−rehydration experiments. Furthermore, a series of acid elution experiments also confirmed that these species are less strongly coordinated to the resins compared to the intramolecular species [Cu II (BPA)](H 2 O) m , [Cu II (BPA) 2 ], [Cu II (PA) 2 ](H 2 O) m , and [Cu II (PA) 3 ]. Finally, while equilibrium batch uptake measurements revealed that the CuWRAM material had a much lower Cu(II) capacity compared to the polymeric Dowex material, the adsorbed copper can be recovered more efficiently using acid elution.