The Role of Hydrogen Adsorption Site Diversity in Catalysis on Transition Metal Phosphide Surfaces

Hydrogen production via clean technologies such as water electrolysis, and its use in the synthesis of value-added chemicals (e.g., ammonia production), play a critical role in the pursuit of decarbonization. This realization requires effective earth-abundant catalysts that facilitate making and breaking H—H and H—X bonds. Transition metal phosphides (TMPs), such as nickel phosphide, cobalt phosphide, and molybdenum phosphide, have been historically used as hydro-processing catalysts in the petroleum industry, enabling critical hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) reactions. Over the past two decades, TMPs have been attracting extensive attention for applications in energy conversion due to their exceptional activity towards the hydrogen evolution reaction (HER). The exceptional HER activity of certain TMPs has been attributed to their nearly ideal H binding energy (HBE), similar to Pt, as deduced by first-principles calculations. In contrast to Pt and other noble metals, where HER and the hydrogen oxidation reaction (HOR) activities are usually correlated, TMPs are usually inactive for HOR. This challenges the applicability of HBE theory to describe activity trends for H2 electrocatalysis on TMPs. In this viewpoint, we discuss the structural complexity of TMPs and its impact on the formation of adsorbed H (Had) and catalysis. In light of this we discuss the validity of HBE theory on TMPs and whether a single value of HBE is sufficient to describe TMP activity trends. Lastly, we propose that the presence of diverse adsorption sites on TMP surfaces can be leveraged to design selective and efficient hydrogenation and electrochemical reduction reactions beyond HER

Pathways of Quantum Dot Degradation during Photocatalysis

CdS QDs are widely employed as photocatalysts for reactions such as hydrogen evolution, and its degradation under aerobic, aqueous conditions is well understood. However, despite evidence of aggregation and precipitation of CdS QD photocatalysts under inert conditions, catalyst speciation and degradation are under-explored. In this work, we demonstrate that during a reductive dehalogenation reaction, CdS QDs undergo surface ligand etching, leading to loss of colloidal stability and the formation of micro-crystalline cadmium metal deposits. We hypothesize that this results from the accumulation of electrons on the QD surface. In addition, we demonstrate a high catalytic TOF of 0.67 s-1 and show evidence of mild surface sulfur oxidation and formation of an ammonium salt by-product of the hole quencher. This work adds to our atomic-level understanding of the reactions occurring at the QD surface during photocatalysis and ultimately uncovers design principles that will allow the design of more stable and efficient catalysts

Arthrokinematics of the Distal Radioulnar Joint Measured Using Intercartilage Distance in an In Vitro Model

© 2018 American Society for Surgery of the Hand Purpose: Current techniques used to measure joint contact rely on invasive procedures and are limited to statically loaded positions. We sought to examine native distal radioulnar joint (DRUJ) contact mechanics using nondestructive imaging methods during simulated active and passive forearm rotation. Methods: Testing was performed using 8 fresh-frozen cadaveric specimens that were surgically prepared by isolating muscles involved in forearm rotation. A wrist simulator allowed for the evaluation of differences between active and passive forearm rotation. Three-dimensional cartilage surface reconstructions were created using volumetric data acquired from computed tomography. Using optically tracked motion data, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics. The effects of forearm movement method and rotation angle on centroid coordinate data and DRUJ contact area were examined. Results: The DRUJ contact area was maximal at 10° supination. There was more contact area in supination than pronation for both active and passive forearm rotation. The contact centroid moved volarly with supination, with magnitudes of 10.5 ± 2.6 mm volar for simulated active motion and 8.5 ± 2.6 mm volar for passive motion. Along the proximal–distal axis, the contact centroid moved 5.7 ± 2.4 mm proximal during simulated active motion. These findings were statistically significant. The contact centroid moved 0.2 ± 3.1 mm distal during passive motion (not significant). Conclusions: It is possible to examine cartilage contact mechanics of the DRUJ nondestructively while undergoing simulated, continuous active and passive forearm rotation. The contact centroid moved volarly and proximally with supination. There were higher contact area values in supination compared with pronation, with a peak value at 10° supination. Clinical relevance: This study documented normal DRUJ arthrokinematics using a nondestructive in vitro approach. It further reinforced the established biomechanical and clinical literature on contact patterns at the native DRUJ during forearm rotation

Predicting Indium Phosphide Quantum Dot Properties from Synthetic Procedures Using Machine Learning

Predictions of chemical reaction outcomes using machine learning (ML) has emerged as a powerful tool for advancing materials synthesis. However, this approach requires large and diverse datasets, which are extremely limited in the field of nanomaterials synthesis due to inconsistent and non-standardized reporting in the literature and a lack of understanding of synthetic mechanisms. In this study, we extracted parameters of InP quantum dot (QD) syntheses as our inputs, and resultant properties (absorption, emission, diameter) as our outputs from 72 publications. We “filled in” missing outputs using a data imputation method to prepare a complete dataset containing 216 entries for training and testing predictive ML models. We defined the descriptor space in two ways (condensed and extended) based on either chemical identity or the role of reagents to explore the best approach for categorizing input features. We achieved mean absolute errors (MAEs) as low as 20.29, 11.46, and 0.33 nm for absorption, emission, and diameter respectively with our best ML model across diverse synthetic methods. We used these models to deploy an accessible and interactive webapp for designing syntheses of InP (https://share.streamlit.io/cossairt-lab/indium-phosphide/Hot_injection/hot_injection_prediction.py). Using this webapp, we investigated the power of ML to uncover chemical trends in InP syntheses, such as the effects of common additives, like zinc salts and trioctylphosphine. We also designed and conducted new experiments based on extensions of literature procedures and compared our experimentally measured properties to predictions, thus evaluating the “real-life” accuracy of our models. Conversely, we used inverse-design to obtain InP QDs with specific properties. Finally, we applied the same approach to train, test, and launch predictive models for CdSe QDs by expanding a previously published dataset. Altogether, our data pre-processing method and ML implementations demonstrate the ability to design materials with targeted properties and explore underlying reaction mechanisms even when faced with limited data resources

Single Crystal Growth of Sillén–Aurivillius Perovskite Oxyhalides Bi₄NbO₈X (X = Cl, Br)

Sillén–Aurivillius perovskite Bi₄NbO₈X (X = Cl, Br) is a promising photocatalyst for water splitting under visible light, as well as a potential ferroelectric material. In this work, we investigate the crystal growth conditions by mainly varying soak temperature, soak time and cooling rate. Under the optimal conditions, we successfully obtained yellow platelet single crystals with an in-plane distance of several hundred microns. As opposed to conventional crystal growth, a moderate cooling is essential to suppress an evaporation of the Bi–O–Cl species from a melt zone. The single crystals of Bi4NbO8Br were also grown using a similar condition. We suggest that the knowledge obtained in this study can be generally applied to other Sillén–Aurivillius phases and related oxyhalide

The Effect of Dorsally Angulated Distal Radius Deformities on Carpal Kinematics: An In Vitro Biomechanical Study

© 2018 American Society for Surgery of the Hand Purpose: The purpose was to quantify the effect of distal radius dorsal angulation (DA) on carpal kinematics and the relative roles of the radiocarpal and midcarpal joints during wrist motion. Methods: Six cadaveric specimens (69 ± 17 y) were mounted at 90° elbow flexion in a custom wrist motion simulator. The wrist was guided through planar passive flexion and extension motion trials (∼ 5°/s). A custom modular distal radius implant was used to simulate native alignment and 3 distal radius DA deformities (10° 20° 30°). An optical tracking system captured carpal bone motion, from which radiocarpal and midcarpal joint motion was determined. Results: The radiocarpal joint made a greater contribution to wrist motion than the midcarpal joint in flexion, and the midcarpal joint made a greater contribution to motion than the radiocarpal joint in wrist extension. Increasing DA caused the radiocarpal joint contribution to increase throughout the motion arc, with the effect being more pronounced in wrist flexion. Conversely, as DA increased, the midcarpal joint contributed less rotation to the total wrist motion and its overall motion arc decreased; the magnitude of effect was greater in wrist extension. Dorsal angulation resulted in increased lunate flexion with respect to the distal radius. Conclusions: Our findings agree with current literature that suggests that, in an uninjured wrist, the radiocarpal joint predominates flexion, and the midcarpal joint predominates extension. In addition, the radiocarpal joint has an amplified contribution in wrist flexion with greater DA malunion. Clinical relevance: The altered contributions of the radiocarpal and midcarpal joints may contribute to pain, stiffness, and the development of arthritis, which is commonly seen at the radiocarpal joint after malunion of the distal radius