Direct Z-scheme mediated SmVO4/UiO-66-NH2 heterojunction nanocomposite for the degradation of antibiotic tetracycline hydrochloride molecules under sunlight.

The use of tetracycline hydrochloride (TCH) for veterinary, human therapy, and agriculture has risen in the past few decades, making it to become one of the most exploited antibiotics. However, TCH residue in the environment is causing issues related to the evolution of antibiotic-resistant bacteria. To address such a problem, photodegradation offers a potential solution to decompose these pollutants in wastewater and thereby mitigates negative environmental impacts. In this context, the research focuses on the use of the rare-earth metal oxide samarium orthovanadate (SmVO4) with nanorod structure, coupled with UiO-66-NH2 for the photocatalytic degradation. Their photocatalytic activity to degrade antibiotic TCH molecules is explored under simulated solar light irradiation. The integration of UiO-66-NH2 with SmVO4 enhanced the light absorption, recombination resistance, carrier lifetime (from 0.382 to 0.411 ns) and specific surface area (from 67.17 to 246 m2/g) of the composite system as confirmed from multiple analyses. The obtained results further indicated that SmVO4/UiO-66-NH2 nanocomposites could form a direct Z-scheme based heterojunction. Such mechanism of charge transfer leads to the effective degradation of TCH molecules up to 50% in 90 min under solar light, while it is degraded only 30% in the case of bare-SmVO4 nanorods. In this work, the incorporation of UiO-66-NH2 positively influences photoelectrochemical properties and improves the overall photoredox properties of SmVO4 for the degradation of complex compounds like antibiotic TCH molecules. Therefore, UiO-66-NH2 can be proposed as an effective material to sensitize the rare-earth based photocatalytic material.

Machine-Learning Assisted Screening of Energetic Materials.

In this work, machine learning (ML), materials informatics (MI), and thermochemical data are combined to screen potential candidates of energetic materials. To directly characterize energetic performance, the heat of explosion ΔHe is used as the target property. The critical descriptors of cohesive energy, averaged over all constituent elements and the oxygen balance, are found by forward stepwise selection from a large number of possible descriptors. With them and a theoretically labeled ΔHe training data set, a satisfactory surrogate ML model is trained. The ML model is applied to large databases ICSD and PubChem to predict ΔHe. At the gross-level filtering by the ML model, 2732 molecular candidates based on carbon, hydrogen, nitrogen, and oxygen (CHNO) with high ΔHe values are predicted. Afterward, a fine-level thermochemical screening is carried out on the 2732 materials, resulting in 262 candidates with TNT equivalent power index Pe(TNT) greater than 1.5. Raising Pe(TNT) further to larger than 1.8, 29 potential candidates are found from the 2732 materials, all are new to the current reservoir of well-known energetic materials.

A DFT theoretical study of heats of formation and detonation properties of nitrogen-rich explosives.

We present density-functional theory predictions and analysis of some properties of synthesized high-nitrogen compounds 3,6-diazido-1,2,4,5-tetrazine (DiAT) and N-oxides of 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO) together with 3,6-di(hydrazino)-1,2,4,5-tetrazine (DHT) and 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAAT) for which experimental data are available. In this work the reference molecules DHT and DAAT have been studied in order to validate the theoretical approach and facilitate further progress developments for the molecules of interest such as DiAT and DAATO. Geometries of all compounds have been optimized employing the B3LYP density-functional method in conjunction with 6-311++G(3d,3p) basis sets. The energy content of the molecules in the gas phase is evaluated by calculating standard enthalpies of formation, using isodesmic reaction paths. We also include estimates of the condensed-phase heats of formation and heats of sublimation in the framework of the Politzer approach. The obtained results show that DiAT compound has the highest heat of formation (231 kcal/mol) in comparison with those of DHT, DAAT and DAATO molecules. The detonation velocity and pressure have also been estimated for these molecules using the Stine method.

Nanoscale high energetic materials: a polymeric nitrogen chain N(8) confined inside a carbon nanotube.

We present a theoretical study of a new hybrid material, nanostructured polymeric nitrogen, where a polymeric nitrogen chain is encapsulated in a carbon nanotube. The electronic and structural properties of the new system are studied by means of ab initio electronic structure and molecular dynamics calculations. Finite temperature simulations demonstrate the stability of this nitrogen phase at ambient pressure and room temperature using carbon nanotube confinement. This nanostructured confinement may open a new path towards stabilizing polynitrogen or polymeric nitrogen at ambient conditions.