Factors affecting the relation between stretching frequencies and bond lengths. Diatomic and polyatomic species without adjustable fitting parameters

Rational Design of W-Doped Ag3PO4 as an Efficient Antibacterial Agent and Photocatalyst for Organic Pollutant Degradation

Bacterial and organic pollutants are major problems with potential adverse impacts on human health and the environment. A promising strategy to alleviate these impacts consists in designing innovative photocatalysts with a wider spectrum of application. In this paper, we report the improved photocatalytic and antibacterial activities of chemically precipitated Ag3PO4 microcrystals by the incorporation of W at doping levels 0.5, 1, and 2 mol %. The presence of W directly influences the crystallization of Ag3PO4, affecting the morphology, particle size, and surface area of the microcrystals. Also, the characterization via experimental and theoretical approaches evidenced a high density of disordered [AgO4], [PO4], and [WO4] structural clusters due to the substitution of P5+ by W6+ into the Ag3PO4 lattice. This leads to new defect-related energy states, which decreases the band gap energy of the materials (from 2.27 to 2.04 eV) and delays the recombination of e'-h• pairs, leading to an enhanced degradation process. As a result of such behaviors, W-doped Ag3PO4 (Ag3PO4:W) is a better visible-light photocatalyst than Ag3PO4, demonstrated here by the photodegradation of potential environmental pollutants. The degradation of rhodamine B dye was 100% in 4 min for Ag3PO4:W 1%, and for Ag3PO4, the obtained result was 90% of degradation in 15 min of reaction. Ag3PO4:W 1% allowed the total degradation of cephalexin antibiotic in only 4 min, whereas pure Ag3PO4 took 20 min to achieve the same result. For the degradation of imidacloprid insecticide, Ag3PO4:W 1% allowed 90% of degradation, whereas Ag3PO4 allowed 40%, both in 20 min of reaction. Moreover, the presence of W-dopant results in a 16-fold improvement of bactericidal performance against methicillin-resistant Staphylococcus aureus. The outstanding results using the Ag3PO4:W material demonstrated its potential multifunctionality for the control of organic pollutants and bacteria in environmental applications.

Peculiar magnetism in Eu substituted BiFeO3 and its correlation with local structure

We have systematically investigated the effects of Eu substitution on chemical pressure, bond lengths, microstrain, bond angles, octahedral tilting, vibrational modes and phase transformation, in BiFeO₃. Correlation between concentration, phase, local structure and magnetism has been explained. Substitution of Eu ions with contrasting magnetic moment and dissimilar size, affects the local structure by changing bond angles and hence modifies spin structure through weakening of Dzyaloshinsky-Moriya (DM) interaction which lead to destruction of spiral spin configuration. Intriguing as well as anomalous magnetic response such as weak ferromagnetism with high coercivity, stair step like loops with significant drop in coercivity and systematic decrease in the magnetic coercivity at low temperatures has been observed as a function of Eu concentration (x). These results are explained on the basis of weakening of DM interaction, field induced melting of antiferromagnetic clusters and modification in effective magnetic anisotropy including contribution of magnetoelectric coupling, for various values of x. These results were used to generate the magnetic phase diagram.