42 research outputs found
Reading performance with various lamps in age-related macular degeneration
The purpose of this study was to determine if there was an objective difference in reading between four commonly available lamps, of varying spectral radiance, for 13 subjects with age-related maculopathy (ARM) or non-exudative age-related macular degeneration (AMD) - logMAR visual acuity between 0.04 and 0.68. At a constant illuminance of 2000 lux, there was no interaction between ARM and AMD subgroups and no statistically significant difference between the lamps: standard (clear envelope) incandescent, daylight simulation (blue tint envelope) incandescent, compact fluorescent and halogen incandescent, for any reading outcome measure (threshold print size p = 0.67, critical print size p = 0.74, acuity reserve p = 0.84 and mean reading rate p = 0.78). For lamps typically used in low-vision rehabilitation, a clinically significant effect of spectral radiance on reading for people with ARM or non-exudative AMD is unlikely. © 2007 The College of Optometrists
Continuous production of iron oxide nanoparticles via fast and economical high temperature synthesis
From all of the iron oxide nanoparticle (IONP) syntheses, thermal decomposition methods are the most developed for controlling particle properties, but suffer from poor reproducibility at larger scale. An alternative solution for large scale production is continuous synthesis, where the production volume can be increased with longer operation times. However, continuous thermal decomposition synthesis is not trivial as it requires oxygen and water removal from the precursor solution, reaction temperatures above 230 °C, and the formation of particles is likely to cause reactor fouling. This work presents a continuous thermal decomposition synthesis of IONPs using a tubular flow reactor, which provides inert reaction conditions at temperatures of up to 290 °C, and heating/cooling at rates which cannot be achieved in standard batch systems. This makes it possible to define the start and endpoint accurately, hence, allowing for a well-controlled and scalable thermal decomposition synthesis. A simple synthetic protocol was chosen using only ferric acetylacetonate, oleylamine, and 1-octadecene as a solvent, but no additives to minimise costs. In this flow reactor residence times of less than 10 min were shown to be sufficient to synthesise monodisperse IONPs of 5â7 nm and achieve precursor conversion between 10â70% depending on the reaction temperature. For all synthesis conditions tested, there was no indication of reactor fouling. Since the precursor conversion correlated to the residence time and reaction temperature, but particle sizes were comparable for all reaction conditions studied, the particle formation is proposed to follow mechanisms other than classical nucleation and growth. To examine possible economic advantages of such a continuous thermal decomposition process as compared to a conventional batch synthesis, a cost analysis, comparing costs assigned to chemicals, reactor equipment, energy and labour, was performed
Room-temperature emitters in wafer-scale few-layer hBN by atmospheric pressure CVD
Hexagonal boron nitride (hBN) is a two-dimensional, wide band gap semiconductor material suitable for several technologies. 2D hBN appeared as a viable platform to produce bright and optically stable single photon emitters (SPEs) at room temperature, which are in demand for quantum technologies. In this context, one main challenge concerns the upscaling of 2D hBN with uniform spatial and spectral distribution of SPE sources. In this work we optimized the atmospheric-pressure chemical vapor deposition (APCVD) growth and obtained large-area 2D hBN with uniform fluorescence emission properties. We characterized the hBN films by a combination of electron microscopy, Raman and X-ray photoelectron spectroscopy techniques. The extensive characterization revealed few-layer, polycrystalline hBN films (âŒ3 nm thickness) with balanced stoichiometry and uniformity over 2âł wafer scale. We studied the fluorescence emission properties of the hBN films by multidimensional hyperspectral fluorescence microscopy. We measured simultaneously the spatial position, intensity, and spectral properties of the emitters, which were exposed to continuous illumination over minutes. Three main emission peaks (at 538, 582, and 617 nm) were observed, with associated replica peaks red-shifted by âŒ53 nm. A surface emitter density of âŒ0.1 emitters/ÎŒm2 was found. A comparative test with pristine hBN nanosheets produced by liquid-phase exfoliation (LPE) was performed, finding that CVD and LPE hBN possess analogous spectral emitter categories in terms of peak position/intensity and density. Overall, the line-shape and wavelength of the emission peaks, as well as the other measured features, are consistent with single-photon emission from hBN. The results indicate that APCVD hBN might proficiently serve as a SPE platform for quantum technologies
Trapping shape-controlled nanoparticle nucleation and growth stages via continuous-flow chemistry
Continuous flow chemistry is used to trap the nucleation and growth stages of platinum-nickel nano-octahedra with second time resolution and high throughputs to probe their properties ex-situ. The growth starts from poorly crystalline particles (nucleation) at 5 seconds, to crystalline 1.5 nm particles bounded by the {111}-facets at 7.5 seconds, followed by truncation and further growth to octahedral nanoparticles at 20 seconds
Tuning the physicochemical features of titanium oxide nanomaterials by ultrasound: Elevating photocatalytic selective partial oxidation of lignin-inspired aromatic alcohols
The research for âgreenâ and economically feasible approaches such as (photo)catalysis especially for biomass valorization such as selective oxidation of biomass derived compounds like aromatic alcohols to corresponding aldehyde by avoiding the harsh reaction conditions and the addition of reagents concentrate the focus of attention the last years. Hence, design and development of novel photocatalyst for the partial selective oxidation is highly desirable. In this research work, ultrasonication of different frequencies (22, 40, 80Â kHz) and different amplitudes was utilized as synthesis tool in order to obtain novel materials by precipitation method. The synthesized samples were characterized by using different techniques such as N2 sorption, TEM, XPS, XRD, thermal analysis, and diffuse reflectance spectroscopy. The synthesized sample by using low ultrasound frequency (22Â kHz) and amplitude showed a mixed morphological and structural nature consisting of asymmetric 1-dimensional (nanorods-like), layered nano-structures and not well-defined areas, leading to elevate for metal oxide specific surface areas up to 155Â m2/g. The observed 1-D nanostructures have diamentions in the range of 20â60Â nm. This sample revealed the highest photo-oxidation efficiency for the selective conversion of two biomass-derived, and more specifically lignin-inspired model compounds, benzyl alcohol and cinnamyl alcohol to benzaldehyde and cinnamyl aldehyde, respectively, and hence the highest yield towards the desired aldehydes. The selective photo-oxidation activity was retained even after 5 photocatalytic cycles, while no leaching of Ti was recorded
Controlling Fluorescence Wavelength in the Synthesis of TGA-Capped CdTe Quantum Dots
Quantum dots (QDs) are semiconductor materials, with a size range between 1â10 nm, showcasing unique size-dependent physical and chemical properties. Such properties have potentiated their use in areas like medical imaging and biosensing. Herein, we present an open-air approach for synthesis of QDs, reducing the need for controllable atmospheric conditions. Furthermore, we present a predictive mathematical model for maximum emission wavelength (λmax) control. Through a straightforward microwave-based aqueous synthesis of TGA-CdTe QDs, we investigated the influence of time, temperature, and Te:Cd and TGA:Cd molar ratios on λmax, using a chemometric experimental design approach. CdTe-QDs were characterized by UV-Vis and fluorescence spectroscopies. Additionally, Fourier-Transform Infrared spectroscopy, X-ray photoelectron spectroscopy, Transmission Electron Microscopy, and Energy Dispersive X-ray were conducted. Stable QDs with fluorescence ranging from green to red (527.6 nm to 629.2 nm) were obtained. A statistical analysis of the results revealed that time and temperature were the most significant factors influencing λmax. After fine-tuning the variables, a mathematical model with 97.7% of prediction accurately forecasted experimental conditions for synthesizing TGA-CdTe QDs at predefined λmax. Stability tests demonstrated that the QDs retained their optical characteristics for over a month at 4 °C, facilitating diverse applications
IridiumâIron Diatomic Active Sites for Efficient Bifunctional Oxygen Electrocatalysis
Diatomic catalysts, particularly those with heteronuclear active sites,
have recently attracted considerable attention for their advantages over single-atom
catalysts in reactions involving multielectron transfers. Herein, we report bimetallic
iridiumâiron diatomic catalysts (IrFeâNâC) derived from metalâorganic frameworks
in a facile wet chemical synthesis followed by postpyrolysis. We use various advanced
characterization techniques to comprehensively confirm the atomic dispersion of Ir and
Fe on the nitrogen-doped carbon support and the presence of atomic pairs. The asobtained
IrFeâNâC shows substantially higher electrocatalytic performance for both
oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) when
compared to the single-atom counterparts (i.e., IrâNâC and FeâNâC), revealing
favorable bifunctionality. Consequently, IrFeâNâC is used as an air cathode in zincâ
air batteries, which display much better performance than the batteries containing
commercial Pt/C + RuO2 benchmark catalysts. Our synchrotron-based X-ray
absorption spectroscopy experiments and density functional theory (DFT) calculations suggest that the IrFe dual atoms
presumably exist in an IrFeN6 configuration where both Ir and Fe coordinates with four N atoms and two N atoms are shared by the
IrN4 and FeN4 moieties. Furthermore, the Fe site contributes mainly to the ORR, while the Ir site plays a more important role in the
OER. The dual-atom sites work synergistically, reducing the energy barrier of the rate-determining step and eventually boosting the
reversible oxygen electrocatalysis. The IrFeâNâC catalysts hold great potential for use in various electrochemical energy storage and
conversion devices.info:eu-repo/semantics/publishedVersio