Stability and Electronic Properties of TiO2 Nanostructures With and Without B and N Doping

We address one of the main challenges to TiO2-photocatalysis, namely band gap narrowing, by combining nanostructural changes with doping. With this aim we compare TiO2's electronic properties for small 0D clusters, 1D nanorods and nanotubes, 2D layers, and 3D surface and bulk phases using different approximations within density functional theory and GW calculations. In particular, we propose very small (R < 0.5 nm) but surprisingly stable nanotubes with promising properties. The nanotubes are initially formed from TiO2 layers with the PtO2 structure, with the smallest (2,2) nanotube relaxing to a rutile nanorod structure. We find that quantum confinement effects - as expected - generally lead to a widening of the energy gap. However, substitutional doping with boron or nitrogen is found to give rise to (meta-)stable structures and the introduction of dopant and mid-gap states which effectively reduce the band gap. Boron is seen to always give rise to n-type doping while depending on the local bonding geometry, nitrogen may give rise to n-type or p-type doping. For under coordinated TiO2 surface structures found in clusters, nanorods, nanotubes, layers and surfaces nitrogen gives rise to acceptor states while for larger clusters and bulk structures donor states are introduced

Trends in Metal Oxide Stability for Nanorods, Nanotubes, and Surfaces

The formation energies of nanostructures play an important role in determining their properties, including the catalytic activity. For the case of 15 different rutile and 8 different perovskite metal oxides, we find that the density functional theory (DFT) calculated formation energies of (2,2) nanorods, (3,3) nanotubes, and the (110) and (100) surfaces may be described semi-quantitatively by the fraction of metal--oxygen bonds broken and the bonding band centers in the bulk metal oxide

Phylogeny in Aid of the Present and Novel Microbial Lineages: Diversity in Bacillus

Bacillus represents microbes of high economic, medical and biodefense importance. Bacillus strain identification based on 16S rRNA sequence analyses is invariably limited to species level. Secondly, certain discrepancies exist in the segregation of Bacillus subtilis strains. In the RDP/NCBI databases, out of a total of 2611 individual 16S rDNA sequences belonging to the 175 different species of the genus Bacillus, only 1586 have been identified up to species level. 16S rRNA sequences of Bacillus anthracis (153 strains), B. cereus (211 strains), B. thuringiensis (108 strains), B. subtilis (271 strains), B. licheniformis (131 strains), B. pumilus (83 strains), B. megaterium (47 strains), B. sphaericus (42 strains), B. clausii (39 strains) and B. halodurans (36 strains) were considered for generating species-specific framework and probes as tools for their rapid identification. Phylogenetic segregation of 1121, 16S rDNA sequences of 10 different Bacillus species in to 89 clusters enabled us to develop a phylogenetic frame work of 34 representative sequences. Using this phylogenetic framework, 305 out of 1025, 16S rDNA sequences presently classified as Bacillus sp. could be identified up to species level. This identification was supported by 20 to 30 nucleotides long signature sequences and in silico restriction enzyme analysis specific to the 10 Bacillus species. This integrated approach resulted in identifying around 30% of Bacillus sp. up to species level and revealed that B. subtilis strains can be segregated into two phylogenetically distinct groups, such that one of them may be renamed

The stability of halloysite nanotubes in acidic and alkaline aqueous suspensions

The long term stability of natural halloysite nanotubes was studied at room temperature (22 ± 2 ºC) in pure water, acidic and basic aqueous suspensions. The structural and morphological transformations of nanotubes were studied by TEM, SEM, nitrogen adsorption, XRD Raman and FTIR spectroscopy accompanied by monitoring the concentration of dissolved Si(IV) and Al(III) in solution. It has been revealed that, in 1 mol dm-3 H2SO4 solution, the dissolution of halloysite is initiated on the inner surface of nanotubes leading to formation of amorphous spheroidal nanoparticles of SiO2 whereas, in 1 mol dm-3 NaOH solution, dissolution of inner surface of nanotubes is accompanied by formation of Al(OH)3 nanosheets

Application of magic-angle spinning NMR to examine the nature of protons in titanate nanotubes

Systematic MAS 1H-NMR studies of protonated titanate nanotubes (produced by alkaline hydrothermal treatment of TiO2 with NaOH) have revealed that there are several types of protons incorporated into their wall structure, including crystallographic water molecules and ion-exchangeable OH groups.Each type (a) has a characteristic chemical shift and (b) disappears at a different rate during annealing in air. The evolution of protons in titanate nanotubes during crystallographic and morphological transformation in the sequence H2Ti3O7•xH2O, H2Ti3O7, H2Ti6O13, TiO2(B), TiO2(anatase) during calcination, at temperatures from 140 ºC to 500 ºC, has been studied using MAS NMR and Raman spectroscopies together with TGA, XRD and TEM techniques. The irreversible disappearance of ion-exchangeable OH groups has been observed, even under low temperature treatment

Stability of the primary organization of nucleosome core particles upon some conformational transitions.

The sequential arrangement of histones along DNA in nucleosome core particles was determined between 0.5 and 600 mM salt and from 0 to 8 M urea. These concentrations of salt and urea up to 6 M had no significant effect on the linear order of histones along DNA but 8 M urea caused the rearrangement of histones. Conformational changes in cores have been identified within these ranges of conditions by several laboratories 8-21. Also, abrupt structural changes in the cores, apparently their unfolding, were found by gel electrophoresis to occur at urea concentration, between 4 and 5 M. 600 mM salt and 6 M urea were shown to relax the binding of histones to DNA in cores but do not however release histones or some part of their molecules from DNA. It appears therefore that nucleosomal cores can undergo some conformational transitions and unfolding whereas their primary organization remains essentially unaffected. These results are consistent with a model of the core particles in which the histone octamer forms something like a helical "rim" along the superhelical DNA and histone-histone interactions beyond the "rim" are rather weak in comparison with those within the "rim"