Order of magnitude increase in photocatalytic rate for hierarchically porous anatase thin films synthesized from zinc titanate coatings

In this paper we report on the use of aerosol assisted chemical vapour deposition (AACVD) to form thin films of the zinc titanate phases using zinc acetate and titanium isopropoxide as precursors in methanol solution. Analysis by XRD and XPS found that through variation in experimental conditions we have been able to synthesize films of zinc titanate with composition of Zn2TiO4 or Zn0.3Ti2.7O4.94, which adopt the spinel and pseudobrookite structure respectively. In addition, we have also formed hybrid films of Zn2TiO4 with either ZnTiO3 or ZnO. Using a technique previously reported with powders, the mixed ZnO and Zn2TiO4 films were treated with acid to produce porous Zn2TiO4 which, through reduction and vapour leaching of zinc, were converted to hierarchically porous thin films of anatase TiO2. This conversion was monitored by XRD. Analysis of photocatalytic activity of the hierarchically porous titania, using dye and stearic acid degradation tests, found a factor of 12 to 14 increase in rates of photocatalysis over conventional TiO2 thin films. Finally we are able to report a maximum formal quantum efficiency for stearic acid degradation of 1.76 × 10−3 molecules per photon

Heterometallic Coordination Polymer Gels Supported by 2,4,6-Tris(pyrazol-1-yl)-1,3,5-triazine

Complexes of type [M(tpt)2]X2 (M2+ = Fe2+, Co2+, Ni2+; tpt = 2,4,6-tri{pyrazol-1-yl}-1,3,5-triazine; X– = BF4– or ClO4–) crystallize in a cubic lattice, with the metal ion and ligand conformation showing unusual symmetry-imposed disorder. Addition of 1 equiv AgX to the corresponding preformed [M(tpt)2]X2 salt in concentrated MeNO2 solution affords thixotropic gels. Gelation was not observed in analogous reactions using [Mn(tpt)2][ClO4]2, or from reactions in other, more donating solvents. Scanning electron microscopy (SEM) images from dilute solutions of the reagents confirmed the fibrous microstructure of the gels and their homogeneous elemental composition. However, energy-dispersive X-ray data show a reduced Fe/Ag ratio compared to the Co/Ag and Ni/Ag gels, where a 1:1 ratio of metals is evident. More concentrated gels decomposed to silver nanoparticles during SEM sample preparation. Mass spectrometry and 1H NMR indicate that silver induces partial ligand displacement reactions in [Fe(tpt)2]2+ and [Co(tpt)2]2+, but not in [Ni(tpt)2]2+. Hence, the strength of the gels, which follows the order M = Mn (no gel) < Fe < Co < Ni, correlates with the stability of octahedral [M(tpt)2]2+ under gelation conditions. Iron(II) complexes of the related ligands 2,4,6-tri{pyrazol-1-yl}pyridine (tpp) and 2,4,6-tri{pyrazol-1-yl}pyrimidine (tpym) did not undergo gelation with silver salts under the above conditions. The unique properties of tpt as a gelator in this work may reflect the crystallographically observed ability of metal-coordinated tpt to chelate to exogenous silver ions, through its pendant pyrazolyl group and triazinyl N donors. In contrast, the pendant azolyl substituents in silver complexes of the nongelators tpp and tpym only bind exogenous silver in monodentate fashion

A Quantitative Evaluation of Electron Beam Sensitivity in Calcite Nanoparticles

We present analysis and quantification of electron beam sensitivity in calcite in order to identify damage thresholds under which bright field TEM imaging, selected area electron diffraction and scanning TEM should be performed. A large reduction in damage under TEM was found when operating at 300 kV rather than 200 kV, suggesting that the irradiation induced degradation of calcite to calcium oxide is dominated by radiolysis. At 300 kV, bright field STEM imaging was able to retain lattice information at higher fluences than was possible using TEM and, although damage was still seen to occur, there was no observation of the formation of crystalline calcium oxide

Physical Confinement Promoting Formation of Cu2O−Au Heterostructures with Au Nanoparticles Entrapped within Crystalline Cu2O Nanorods

Building on the application of cuprite (Cu2O) in solar energy technologies and reports of increased optical absorption caused by metal-to-semiconductor energy transfer, a confinement-based strategy was developed to fabricate high aspect ratio, crystalline Cu2O nanorods containing entrapped gold nanoparticles (Au nps). Cu2O was crystallized within the confines of track-etch membrane pores, where this physical, assembly based method eliminates the necessity of specific chemical interactions to achieve a well-defined metal−semiconductor interface. With high-resolution scanning/transmission electron microscopy (S/TEM) and tomography, we demonstrate the encasement of the majority of Au nps by crystalline Cu2O and show crystalline Cu2O−Au interfaces that are free of extended amorphous regions. Such nanocrystal heterostructures are good candidates for studying the transport physics of metal/semiconductor hybrids for optoelectronic applications

Pyrene tags for the detection of carbohydrates by label‐assisted laser desorption/ionisation mass spectrometry

Matrix‐assisted laser desorption/ionisation mass spectrometry (MALDI‐MS) is widely used for the analysis of biomolecules. Label‐assisted laser desorption/ionisation mass spectrometry (LALDI‐MS) is a matrix‐free variant of MALDI‐MS, in which only analytes covalently attached to a laser desorption/ionisation (LDI) enhancer are detected. LALDI‐MS has shown promise in overcoming the limitations of MALDI‐MS in terms of sample preparation and MS analysis. In this work, we have developed a series of pyrene‐based LDI reagents (LALDI tags) that can be used for labelling and LALDI‐MS analysis of reducing carbohydrates from complex (biological) samples without the need for additional chemical derivatisation or purification. We have systematically explored the suitability of four pyrene‐based LDI enhancers and three aldehyde‐reactive handles, optimised sample preparation, and demonstrated the use of LALDI tags for the detection of lactose. We have also exemplified the potential of LALDI tags for labelling carbohydrates in biological samples by direct detection of lactose in cow's milk. These results demonstrate that LALDI‐MS is a promising technique for the analysis of reducing carbohydrates in biological samples, and pave the way for the development of LALDI‐MS for glycomics and diagnostics

Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates

3D Visualisation of Additive Occlusion and Tunable Full-Spectrum Fluorescence in Calcite

From biomineralization to synthesis, organic additives provide an effective means of controlling crystallisation processes. There is growing evidence that these additives are often occluded within the crystal lattice, where this promises an elegant means of creating nanocomposites and tuning physical properties. Here, we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in calcite (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in crystal shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy was then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates calcite nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required

Direct observation of mineral-organic composite formation reveals occlusion mechanism

Manipulation of inorganic materials with organic macromolecules enables organisms to create biominerals such as bones and seashells, where occlusion of biomacromolecules within individual crystals generates superior mechanical properties. Current understanding of this process comes from entrapment of micron-size particles in cooling melts. Here, by studying micelle incorporation in calcite with atomic force microscopy (AFM) and micromechanical simulations, we show that different mechanisms govern nanoscale occlusion. By simultaneously visualizing the micelles and propagating step edges, we demonstrate that the micelles experience significant compression during occlusion, which is accompanied by cavity formation. This generates local lattice strain, leading to enhanced mechanical properties. These results give new insight into the formation of occlusions in natural and synthetic crystals, and will facilitate the synthesis of multifunctional nanocomposite crystals

Oral health knowledge and behavior among male health sciences college students in Kuwait

BACKGROUND: Health auxiliary personnel have an important role in oral health promotion when they graduate and start working in the health care system. This study aims to find out oral health knowledge and oral health behavior of male Health Sciences College students. METHODS: A questionnaire was distributed to all students at the male Health Sciences College in Kuwait (N = 153) during the academic year 2001/2002. The students filled the anonymous questionnaire in the class after the lecture. The response rate was 84% (n = 128). The questions consisted information on the general background, oral health behavior and oral health knowledge. RESULTS: Oral health knowledge seemed to be limited and very few background factors were associated with it. More than half of the students had visited a dentist during the previous 12 months, but only one third of students were brushing twice a day or more often. CONCLUSIONS: It may be concluded that the male Health Sciences College students seemed to have appropriate knowledge on some oral health topics, but limited knowledge on the others. Their toothbrushing practices are still far behind the international recommendation (twice a day) and also the knowledge, why it should be done so frequently also very limited

Anionic block copolymer vesicles act as Trojan horses to enable efficient occlusion of guest species into host calcite crystals

We report a versatile ‘Trojan Horse’ strategy using highly anionic poly(methacrylic acid)–poly(benzyl methacrylate) vesicles to incorporate two types of model payloads, i.e. either silica nanoparticles or an organic dye (fluorescein), within CaCO3 (calcite). Uniform occlusion of silica-loaded vesicles was confirmed by scanning electron microscopy, while thermogravimetry studies indicated extents of vesicle occlusion of up to 9.4% by mass (∼33% by volume). Efficient dye-loaded vesicle occlusion produces highly fluorescent calcite crystals as judged by fluorescence microscopy. In control experiments, silica nanoparticles alone are barely occluded, while only very weakly fluorescent calcite crystals are obtained when using just the fluorescein dye. This new ‘Trojan Horse’ strategy opens up a generic route for the efficient occlusion of various nanoparticles and organic molecules within inorganic host crystals