Growth of BiVO₄ Nanoparticles on a Bi₂O₃ Surface: Effect of Heterojunction Formation on Visible Irradiation-Driven Catalytic Performance

Heterostructured materials composed of different semiconductors can be used to decrease rapid charge carrier recombination in photocatalysts, but the development of efficient synthesis methods for these materials remains a challenge. This work describes a novel strategy for tailoring heterostructures that is based on the solubility difference between two semiconductors with at least one metal in common. The growth of BiVO₄ on a preformed Bi₂O₃ particle was used as a model for heterojunction formation. The number of Bi₂O₃/​BiVO₄ heterojunctions was tuned using synthesis variables (temperature and V concentration) and the particle size of the preformed Bi₂O₃. The synthesis of the Bi₂O₃/​BiVO₄ heterostructures using Bi₂O₃ nanoparticles resulted in a larger quantity of heterojunctions due to the higher solubility of the nanoparticles compared to micrometric Bi₂O₃, which led to a classical heterogeneous precipitation on the preformed surfaces. The proposed growth mechanism was effective for obtaining heterostructured Bi₂O₃/​BiVO₄ semiconductors with enhanced photocatalytic performances compared to the isolated phases. The greater photoactivity of the heterostructures could be explained by the increased spatial separation in the photogenerated electron/hole pairs due to the formation of a type-II heterostructure and was observed by time-resolved photoluminescence analysis. In this case, the photogenerated electrons were transferred from the conduction band of the p-type semiconductor (Bi₂O₃) to the n-type (BiVO₄) semiconductor, while the photogenerated holes were transferred from the valence band of the n-type semiconductor to the p-type semiconductor

Smart Fertilization Based on Sulfur–Phosphate Composites: Synergy among Materials in a Structure with Multiple Fertilization Roles

Sulfur is currently a bottleneck for agronomic productivity. Many products are based on the application of elemental sulfur (S°), but the ability of the soil to oxidize them is variable and dependent on the presence of oxidizing microorganisms. In this work, a composite was designed based on a matrix of S° prepared by low-temperature extrusion, reinforced by rock phosphate particles acting as P fertilizer, and with encapsulation of <i>Aspergillus niger</i> as an oxidizing microorganism. This structure was shown to be effective in significantly increasing S° oxidation while providing P by rock phosphate dissolution in an acid environment. X-ray absorption near-edge structure (XANES) spectra provided information about P fixation in the soil after dissolution, showing that the composite structure with <i>A. niger</i> modified the nutrient dynamics in the soil. This fully integrated material (a smart fertilizer) is an innovative strategy for eco-friendly agronomic practices, providing high nutrient delivery with minimal source preprocessing

Quantum Mechanics Insight into the Microwave Nucleation of SrTiO₃ Nanospheres

An extensive investigation of strontium titanate, SrTiO₃ (STO), nanospheres synthesized via a microwave-assisted hydrothermal (MAH) method has been conducted to gain a better insight into thermodynamic, kinetic, and reaction phenomena involved in STO nucleation and crystal growth processes. To this end, quantum-chemical modeling based on the density functional theory and periodic super cell models were done. Several experimental techniques were employed to get a deep characterization of structural and optical features of STO nanospheres. A possible formation mechanism was proposed, based on dehydration of titanium and strontium clusters followed by mesoscale transformation and a self-assembly process along an oriented attachment mechanism resulting in spherical-like shape. Raman and XANES analysis renders a noncentrosymmetric environment for the octahedral titanium, while infrared and first-order Raman modes reveal OH groups which are unsystematically incorporated into uncoordinated superficial sites. These results seem to indicate that the key component is the presence of distorted TiO₆ clusters to engender a luminescence property. Analysis of band structure, density of states, and charge map shows that there is a close relationship among local broken symmetry, polarization, and energy split of the 3d orbitals of titanium. The interplay among these electronic and structural features provides necessary conditions to evaluate its luminescent properties under two-energy excitation

Potentiated Electron Transference in α‑Ag₂WO₄ Microcrystals with Ag Nanofilaments as Microbial Agent

This study is a framework proposal for understanding the antimicrobacterial effect of both α-Ag₂WO₄ microcrystals (AWO) synthesized using a microwave hydrothermal (MH) method and α-Ag₂WO₄ microcrystals with Ag metallic nanofilaments (AWO:Ag) obtained by irradiation employing an electron beam to combat against planktonic cells of methicillin-resistant Staphylococcus aureus (MRSA). These samples were characterized by X-ray diffraction (XRD), FT-Raman spectroscopy, ultraviolet visible (UV–vis) measurements, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). The results reveal that both AWO and AWO:Ag solutions have bacteriostatic and bactericidal effects, but the irradiated sample is more efficient; i.e., a 4-fold of the MRSA planktonic cells as compared to the nonirradiated sample was observed. In addition, first principles calculations were performed to obtain structural and electronic properties of AWO and metallic Ag, which provides strong quantitative support for an antimicrobacterial mechanism based on the enhancement of electron transfer processes between α-Ag₂WO₄ and Ag nanoparticles