Formation of native point defects in semiconductor and their behaviors play a crucial role in material properties. Although native defects of V2O5 include vacancies, self-interstitials, and antisites, only oxygen vacancy...

Novel behavior has been observed at the interface of LaAlO3/SrTiO3 heterostructures such as two dimensional metallic conductivity, magnetic scattering and superconductivity. However, both the origins and quantification of such behavior have been complicated due to an interplay of mechanical, chemical and electronic factors. Here chemical and strain profiles near the interface of LaAlO3/SrTiO3 heterostructures are correlated. Conductive and insulating samples have been processed, with thicknesses respectively above and below the commonly admitted conductivity threshold. The intermixing and structural distortions within the crystal lattice have been quantitatively measured near the interface with a depth resolution of unit cell size. A strong link between intermixing and structural distortions at such interfaces is highlighted: intermixing was more pronounced in the hetero-couple with conductive interface, whereas in-plane compressive strains extended deeper within the substrate of the hetero-couple with the insulating interface. This allows a better understanding of the interface local mechanisms leading to the conductivity.

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The formation of complexes between copper ions and biomolecules plays important roles in biological systems. In this work, the structures and electrochemical properties of copper-creatinine complexes were investigated by both experimental and computational approaches. DFT calculation revealed the possible structures of copper-creatinine complexes and provided the data of formation energies, bond lengths, and charge distribution. The properties of the complexes were further investigated by cyclic voltammetry, UV-visible spectrophotometry, X-ray absorption spectroscopy, and scanning electron microscopy. The combination of experimental and computational findings revealed that CuII binds with creatinine via the endocyclic nitrogen. In aqueous environment, the [Cu(creatinine)2(H2O)2]2+ complex is formed. The reduction of [Cu(creatinine)2(H2O)2]2+ formed a stable 1:4 complex between CuI and creatinine. Importantly, the understanding of the electrochemical behaviors of copper-creatinine complexes leads to the development of a novel sensor for the detection of creatinine, a biomarker for kidney diseases. Although creatinine itself is not electroactive, the complex formation with copper allows the species to be detected electrochemically with the sensitivity of 6.09 ± 0.13 µA mM−1 and the limit of detection (3sB/m) of 35 µM.

A newly-isolated Lysinibacillus sp. strain WH could precipitate CaCO3 using calcium acetate (Ca(C2H3O2)2), calcium chloride (CaCl2) and calcium nitrate (Ca(NO3)2) via non-ureolytic processes. We developed an algorithm to determine CaCO3 crystal structures by fitting the simulated XRD spectra to the experimental data using the artificial neural networks (ANNs). The biogenic CaCO3 crystals when using CaCl2 and Ca(NO3)2 are trigonal calcites with space group R3c, while those when using Ca(C2H3O2)2 are hexagonal vaterites with space group P6522. Their elastic properties are derived from the Voigt–Reuss–Hill (VRH) approximation. The bulk, Young's, and shear moduli of biogenic calcite are 77.812, 88.197, and 33.645 GPa, respectively, while those of vaterite are 67.082, 68.644, 25.818 GPa, respectively. Their Poisson’s ratios are ~ 0.3–0.33, suggesting the ductility behavior of our crystals. These elastic values are comparable to those found in limestone cement, but are significantly larger than those of Portland cement. Based on the biocement experiment, the maximum increase in the compressive strength of Portland cement (27.4%) was found when Ca(NO3)2 was used. An increased strength of 26.1% was also found when Ca(C2H3O2)2 was used, implying the transformation of less-durable vaterite to higher-durable calcite. CaCO3 produced by strain WH has a potential to strengthen Portland cement-based materials.

Electron−hole recombination is one of the major issues inhibiting practical use of photocatalysts for water splitting to generate clean hydrogen energy. Engineering a heterostructure with an S-scheme heterojunction has been reported to promote e−h separation and maximize potential of photogenerated charge carriers, which, in turn, dramatically improve photocatalytic activity. Herein, based on density functional calculations, we proposed a design of a 2D/2D g-C 3 N 4 /ZnO heterostructure to achieve an S-scheme heterojunction with high catalytic activity toward the overall water splitting reaction. We find that the heterostructure constructed from high tensile strain of the ZnO monolayer and the equilibrium g-C 3 N 4 monolayer exhibits an S-scheme heterojunction. The built-in electric field generated at the interface effectively separates electrons to locate at the g-C 3 N 4 side and holes at the ZnO side leading to lower e−h recombination. The heterostructure improves sunlight utilization where its absorption edge is red-shifted into the visible-light region with a higher absorption coefficient when compared to that of individual monolayers. In addition, the mechanistic study reveals that potential of holes at the valence band of the ZnO side can overcome the potential limiting step of the oxygen evolution reaction, while the hydrogen evolution reaction prefers to occur at the g-C 3 N 4 side, which is also where the electrons are accumulated. Our study demonstrates how we can rationally design high-performance 2D/2D heterostructure photocatalysts for overall water splitting based on first-principles modeling.

Phosphorus (P)-doped BiVO4 has been proposed as a promising photoanode for water splitting as it exhibits significant improvement of photocurrent density and photocatalytic O2 evolution rate. Previous findings suggest that substitution of V with P induces lattice polarization, which facilitates electron–hole separation. However, little attention has been paid to the mechanism underlying the observed changes in electronic conductivity due to oxygen vacancies. In this work, we carry out first-principles calculations to study the effect of P doping on the stability of oxygen vacancies and charge transport properties of BiVO4 photocatalysts. Our computations reveal improved reducibility of P-doped BiVO4 as reflected in the lower energies of oxygen vacancy formation. The generated oxygen vacancy yields two electron polarons localized at the two nearest V centers, where one polaron is always trapped at the defect site. The calculated polaron hopping barriers and their mobilities obtained from kinetic Monte Carlo simulations indicate that the P impurity by itself does not significantly alter the behavior of polaron transport. Hence, P doping improves reducibility of the material, which, in turn, increases the number of charge carriers and improves the electronic conductivity, which could lead to superior photocatalytic activity. These results can explain the experimentally observed higher concentration of oxygen vacancies and the enhancement of photocurrent density of P-doped BiVO4. This study provides valuable insights for designing doping strategies to improve the photocurrent density of photocatalysts.