Synergistic Effect of Boron Nitride and Carbon Domains in Boron Carbide Nitride Nanotube Supported Single-Atom Catalysts for Efficient Nitrogen Fixation

Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N₂ adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of −0.62 V via associative distal path. This work suggests new opportunities for driving NH₃ production by carbon-based single-atom electrocatalysts under ambient conditions.     

Modern contaminants affecting microscopic residue analysis on stone tools: A word of caution

Residue analysis is a method frequently used to infer the function of stone tools and it is very often applied in combination with use-wear analysis. Beyond its undeniable potential, the method itself has several intrinsic constraints. Apart from the exceptional circumstances necessary for residues to survive, the correct identification of the residue type is a very debatable topic. Before attempting to recognise ancient residues, a proper method should allow analysts to identify possible modern contaminants and exclude them from the final interpretation. Therefore, analysts should not underestimate the presence of modern contaminants and might learn how to discriminate the background noise due to handling.The main aim of this research is to provide some methodological improvements to residue analysis through the characterisation of some modern residues often present on the surface of stone tools (e.g. skin flakes, modelling clay). This characterisation was done by using both optical light microscopy (OLM) and scanning electron microscopy (SEM).Finally, a special care in the post-excavation treatment of stone tools is claimed in order to avoid major contamination of the samples.     

Base‐Stabilized Phosphinidene Boranes by Silylium‐Ion Abstraction

We report the preparation of N‐heterocyclic carbene (NHC)‐stabilized compounds containing P=B double bonds. The reaction of the highly functionalized phosphinoborane Mes*(SiMe₃)P?B(Cl)Cp* with Lewis bases allows access to base‐stabilized phosphinidene boranes Mes*P=B(L)Cp* (L=4‐dimethylaminopyridine (DMAP), NHC) by Me₃SiCl elimination. The formation of these species is shown to proceed through transient borylphosphide anions generated by Me₃Si abstraction.     

Evaluation of Formaldehyde in Foundry Waste Sands Using Liquid Chromatography

Abstract

The industrial manufacturing of metallic objects results in a high level of foundry waste sands that may contain toxic compounds such as formaldehyde. The formaldehyde content of foundry waste sands was evaluated by liquid chromatography. Samples were collected during various steps of the industrial processes. Results showed that the phenolic alkaline process generated waste sands with higher formaldehyde content than the furanic process; the highest value was 7.6 × 10^?3% (w/w). In this work, formaldehyde content decreased with time in all of the samples studied, revealing that most formaldehyde was released to the occupational environment.     

Disclosing the Structure/Activity Correlation in Trivalent Boron‐Containing Compounds: A Tendency Map

Most trivalent boron reagents are electrophiles owing to the vacancy for two electrons to fill the outer orbital of boron; however, interestingly, trivalent boron compounds can change their electrophilic character to a nucleophilic character by only changing the nature of the substituents on the boron atoms. With the help of computational tools, we have analyzed the structural‐ and electronic properties of boryl fragments that were either bonded to main‐group metals or coordinated to transition‐metals/rare‐earth‐metals and we have designed a map that might help to identify certain trends. This trend map will be useful for selecting an appropriate trivalent boron compound, depending on the sought reactivity.