Boosting Photocatalytic Hydrogen Production by MOF-Derived Metal Oxide Heterojunctions with a 10.0 % Apparent Quantum Yield.

Photocatalytic hydrogen production offers an alternative pathway to establish a sustainable energy economy, utilizing the Earth's natural sunlight and water resources to address environmental concerns associated with fossil fuel combustion. While numerous photoactive materials exhibit high potential for generating hydrogen from water, the synergy achieved by combining two different materials with complementary properties in the form of heterojunctions can significantly enhance the rate of hydrogen production and quantum efficiency. Our study describes the design and generation of the metal-organic framework-derived (MOF) metal oxide heterojunction herein referred to as RTTA, composed of RuO2/N,S-TiO2. The RuO2/N,S-TiO2 is generated through the pyrolysis of MOFs, Ru-HKUST-1, and the amino-functionalized MIL-125-NH2 in the presence of thiourea. Among the various RTTA materials tested, RTTA-1, characterized by the lowest RuO2 content, exhibited the highest hydrogen evolution rate, producing 10,761 µmol ⋅ hr-1 ⋅ g-1 of hydrogen with an apparent quantum yield of 10.0 % in pure water containing glycerol. In addition to RTTA-1, we generated two other MOF-derived metal oxide heterojunctions, namely ZTTA-1 (ZnO/N,S-TiO2) and ITTA-1 (In2O3/N,S-TiO2). These heterojunctions were tested for their photocatalytic activity, leading to apparent quantum yields of 0.7 % and 0.3 %, respectively. The remarkable photocatalytic activity observed in RTTA-1 is thought to be attributed to the synergistic effects arising from the combination of metallic properties inherent in the metal oxides, complemented by the presence of suitable band alignment, porosity, and surface properties inherited from the parent MOFs. These properties enhance electron transfer and restrict hole movement. The photocatalytic efficiency of RTTA-1 was further demonstrated in actual water samples, producing hydrogen with a rate of 8,190 µmol ⋅ hr-1 ⋅ g-1 in tap water, and 6,390 µmol ⋅ hr-1 ⋅ g-1 in river water.

The Microstructure of Cellulose Nanocrystal Aerogels as Revealed by Transmission Electron Microscope Tomography.

The microstructure of highly porous cellulose nanocrystal (CNC) aerogels is investigated via transmission electron microscope (TEM) tomography. The aerogels were fabricated by first supercritically drying a carboxylated CNC organogel and then coating via atomic layer deposition with a thin conformal layer of Al2O3 to protect the CNCs against prolonged electron beam exposure. A series of images was then acquired, reconstructed, and segmented in order to generate a three-dimensional (3D) model of the aerogel. The model agrees well with theory and macroscopic measurements, indicating that a thin conformal inorganic coating enables TEM tomography as an analysis tool for microstructure characterization of CNC aerogels. The 3D model also reveals that the aerogels consist of randomly orientated CNCs that attach to one another primarily in three ways: end to end contact, "T″ contact, and "X″ contact.

Particle size distributions by transmission electron microscopy: an interlaboratory comparison case study.

This paper reports an interlaboratory comparison that evaluated a protocol for measuring and analysing the particle size distribution of discrete, metallic, spheroidal nanoparticles using transmission electron microscopy (TEM). The study was focused on automated image capture and automated particle analysis. NIST RM8012 gold nanoparticles (30 nm nominal diameter) were measured for area-equivalent diameter distributions by eight laboratories. Statistical analysis was used to (1) assess the data quality without using size distribution reference models, (2) determine reference model parameters for different size distribution reference models and non-linear regression fitting methods and (3) assess the measurement uncertainty of a size distribution parameter by using its coefficient of variation. The interlaboratory area-equivalent diameter mean, 27.6 nm ± 2.4 nm (computed based on a normal distribution), was quite similar to the area-equivalent diameter, 27.6 nm, assigned to NIST RM8012. The lognormal reference model was the preferred choice for these particle size distributions as, for all laboratories, its parameters had lower relative standard errors (RSEs) than the other size distribution reference models tested (normal, Weibull and Rosin-Rammler-Bennett). The RSEs for the fitted standard deviations were two orders of magnitude higher than those for the fitted means, suggesting that most of the parameter estimate errors were associated with estimating the breadth of the distributions. The coefficients of variation for the interlaboratory statistics also confirmed the lognormal reference model as the preferred choice. From quasi-linear plots, the typical range for good fits between the model and cumulative number-based distributions was 1.9 fitted standard deviations less than the mean to 2.3 fitted standard deviations above the mean. Automated image capture, automated particle analysis and statistical evaluation of the data and fitting coefficients provide a framework for assessing nanoparticle size distributions using TEM for image acquisition.

Anatomy of a nanoscale conduction channel reveals the mechanism of a high-performance memristor.

By employing a precise method for locating and directly imaging the active switching region in a resistive random access memory (RRAM) device, a nanoscale conducting channel consisting of an amorphous Ta(O) solid solution surrounded by nearly stoichiometric Ta(2) O(5) is observed. Structural and chemical analysis of the channel combined with temperature-dependent transport measurements indicate a unique resistance switching mechanism.