Computational Modeling for the Ag Nanoparticle Coalescence Process: A Case of Surface Plasmon Resonance

Motivated by recent transmission electron microscopy (TEM) experiments on α-Ag2WO4, the coalescence process of Ag nanoparticles (NPs) is investigated using molecular dynamics (MD) simulations. These Ag NPs are formed by irradiation of α-Ag2WO4 crystals by electrons from a TEM gun. This behavior can be considered as a clear example of surface plasmon resonance (SPR), in which Ag NP coalescence processes are controlled by dipole–dipole interaction forming larger clusters. The interactions between Ag NPs along the coalescence processes are studied using MD simulations with embedded atom method (EAM) effective potentials for Ag. With these choices of methods, coalescence is studied by addressing different scenarios for the interacting NPs, which all could possibly occur in experiments

Vanadium doping effect on multifunctionality of SnO2 nanoparticles

In the present study, tin oxide (SnO2) nanoparticles were synthesized by a precursor polymeric method. The obtained nanoparticles were doped with vanadium. The samples were characterized by powder XRD, TEM, optical UV and EPR studies. XRD and TEM showed the rutile crystal structure and its revealed that the lattice cell parameters and particles size were decreased with dopant level. Optical and EPR data confirmed that the doped V enters into SnO2 and distorted the host material symmetry. The films sensing characteristics have been studied from the aspect of doping level of sensing material and microstructure. It is found that V doping on SnO2 enhance sensor sensitivity towards CO gas. The results demonstrated that V doping can improving numerous applications which the SnO2 response is maximized.Fil: Alvarez Roca, Roman. Universidade Federal do São Carlos; BrasilFil: Desimone, Paula Mariela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: da Silva, Mitchell. Universidade Federal do São Carlos; BrasilFil: Ponce, Miguel Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Longo, Elson. Universidade Federal do São Carlos; Brasi

Vanadium Doping Effect on Multifunctionality of SnO2 Nanoparticles

 In the present study, tin oxide (SnO2) nanoparticles were synthesized by a precursor polymeric method. The obtained nanoparticles were doped with vanadium. The samples were characterized by powder XRD, TEM, optical UV and EPR studies. XRD and TEM showed the rutile crystal structure and its revealed that the lattice cell parameters and particles size were decreased with dopant level. Optical and EPR data confirmed that the doped V enters into SnO2 and distorted the host material symmetry. The films sensing characteristics have been studied from the aspect of doping level of sensing material and microstructure. It is found that V doping on SnO2 enhance sensor sensitivity towards CO gas. The results demonstrated that V doping can improving numerous applications which the SnO2 response is maximized

Relationship between Crystal Shape, Photoluminescence, and Local Structure in SrTiO3 Synthesized by Microwave-Assisted Hydrothermal Method

This paper describes the effect of using different titanium precursors on the synthesis and physical properties of SrTiO3 powders obtained by microwave-assisted hydrothermal method. X-ray diffraction measurements, X-ray absorption near-edge structure (XANES) spectroscopy, field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HRTEM) were carried out to investigate the structural and optical properties of the SrTiO3 spherical and cubelike-shaped particles. The appropriate choice of the titanium precursor allowed the control of morphological and photoluminescence (PL) properties of SrTiO3 compound. The PL emission was more intense in SrTiO3 samples composed of spherelike particles. This behavior was attributed to the existence of a lower amount of defects due to the uniformity of the spherical particles

Biocompatibility and inflammatory response of silver tungstate, silver molybdate, and silver vanadate microcrystals

Silver tungstate (α-Ag2WO4), silver molybdate (β-Ag2MoO4), and silver vanadate (α-AgVO3) microcrystals have shown interesting antimicrobial properties. However, their biocompatibility is not yet fully understood. Cytotoxicity and the inflammatory response of silver-containing microcrystals were analyzed in THP-1 and THP-1 differentiated as macrophage-like cells, with the alamarBlue™ assay, flow cytometry, confocal microscopy, and ELISA. The present investigation also evaluated redox signaling and the production of cytokines (TNFα, IL-1β, IL-6, and IL-8) and matrix metalloproteinases (MMP-8 and -9). The results showed that α-AgVO3 (3.9 μg/mL) did not affect cell viability (p > 0.05). α-Ag2WO4 (7.81 μg/mL), β-Ag2MoO4 (15.62 μg/mL), and α-AgVO3 (15.62 μg/mL) slightly decreased cell viability (p ≤ 0.003). All silver-containing microcrystals induced the production of O2 − and this effect was mitigated by Reactive Oxygen Species (ROS) scavenger and N-acetylcysteine (NAC). TNFα, IL-6 and IL-1β were not detected in THP-1 cells, while their production was either lower (p ≤ 0.0321) or similar to the control group (p ≥ 0.1048) for macrophage-like cells. The production of IL-8 by both cellular phenotypes was similar to the control group (p ≥ 0.3570). The release of MMP-8 was not detected in any condition in THP-1 cells. Although MMP-9 was released by THP-1 cells exposed to α-AgVO3 (3.9 μg/mL), no significant difference was found with control (p = 0.7). Regarding macrophage-like cells, the release of MMP-8 and -9 decreased in the presence of all microcrystals (p ≤ 0.010). Overall, the present work shows a promising biocompatibility profile of, α-Ag2WO4, βAg2MoO4, and α-AgVO3 microcrystals

In situ growth of Ag nanoparticles on alpha-Ag2WO4 under electron irradiation: probing the physical principles

Exploiting the plasmonic behavior of Ag nanoparticles grown on α-Ag2WO4 is a widely employed strategy to produce efficient photocatalysts, ozone sensors, and bactericides. However, a description of the atomic and electronic structure of the semiconductor sites irradiated by electrons is still not available. Such a description is of great importance to understand the mechanisms underlying these physical processes and to improve the design of silver nanoparticles to enhance their activities. Motivated by this, we studied the growth of silver nanoparticles to investigate this novel class of phenomena using both transmission electron microscopy and field emission scanning electron microscopy. A theoretical framework based on density functional theory calculations (DFT), together with experimental analysis and measurements, were developed to examine the changes in the local geometrical and electronic structure of the materials. The physical principles for the formation of Ag nanoparticles on α-Ag2WO4 by electron beam irradiation are described. Quantum mechanical calculations based on DFT show that the (001) of α-Ag2WO4 displays Ag atoms with different coordination numbers. Some of them are able to diffuse out of the surface with a very low energy barrier (less than 0.1 eV), thus, initiating the growth of metallic Ag nanostructures and leaving Ag vacancies in the bulk material. These processes increase the structural disorder of α-Ag2WO4 as well as its electrical resistance as observed in the experimental measurements.The authors are grateful to Generalitat Valenciana (Spain) for PrometeoII/2014/022 and ACOMP/2014/270 projects, Ministerio de Economia y Competitividad (Spain), CTQ2012-36253-C03-02, and to the Spanish Brazilian Program (PHB2009-0065-PC), CAPES (203038 009607/2013- 56 088/2013), INCTMN (2008/57872-1), FAPESP (2013/ 07296-2; 2012/14468-1; 2010/16970-0) and CNPq (147001/2013-7; 573636/2008-7) for financially supporting this research. Most of the calculations were performed using IFGW-UNICAMP computer facilities and the National Center for High Performance Computing in São Paulo (CENAPAD- SP)

The role of counter-ions in crystal morphology, surface structure and photocatalytic activity of ZnO crystals grown onto a substrate

In this contribution, we present an experimental and theoretical investigation of the role of counter-ions in the crystal morphology, surface structure, and photocatalytic activity of hierarchical ZnO nanostructures. The effect of zinc precursor (nitrate, acetate and, sulfate) along the synthesis of ZnO nanostructures grown directly onto a substrate by means of a simple hydrothermal method was analyzed in detail. Scanning electron microscopy images showed a preferential growth of ZnO nanostructures along the c-axis, with a slight reduction in the orientation depending on the choice of the Zn source. Theoretical calculations based on the Wulff theory allowed us to better understand the morphological changes and directly relate the photocatalytic performance at the different exposed surfaces of the as-observed crystal shapes. Our results showed that photocatalytic activities in the discoloration of organic dyes became superior for hierarchical ZnO nanostructures obtained from zinc nitrate. This finding was explained by X-ray photoelectron and photoluminescence spectroscopies, which revealed that in addition to, the attached counter-ions and the abundance of carboxylate groups and organic residuals on ZnO surfaces, the presence of surface defects are determinant to enhance the photocatalytic performance of the material

Increasing the photocatalytic and fungicide activities of Ag3PO4 microcrystals under visible-light irradiation

The present study reports for the first time the performance of silver phosphate (Ag3PO4) microcrystals as photocatalyst (degradation of Rodamine B-RhB) and antifungal agent (against Candida albicans–C. albicans) under visible-light irradiation (455 nm). Ag3PO4 microcrystals were synthesized by a simple co-precipitation (CP) method at room temperature. The structural and electronic properties of the as-synthetized Ag3PO4 have been investigated before and after 4 cycles of RhB degradation under visible light using X-ray diffraction (XRD), micro-Raman spectroscopy, UV–Vis spectrophotometer and field emission scanning electron microscopy (FE-SEM) images. The antifungal activity was analyzed in planktonic cells and 48h-biofilm of C. albicans by colony forming units (CFU) counting, confocal laser and FE-SE microscopies. Statistical analysis was carried out using SPSS software. Morphological and structural modifications of Ag3PO4 were observed upon recycling. After 4 recycles, the material maintained its photodegradation property; an eightfold increase in the efficiency of Ag3PO4 was observed in planktonic cells and a two fold increase in biofilm when irradiated under visible light. Thus, higher antifungal effectiveness against C. albicans was obtained when associated with visible-light irradiation.Funding for open access charge: CRUE-Universitat Jaume

An Experimental and Computational Study of β-AgVO3: Optical Properties and Formation of Ag Nanoparticles

This article aims to gather together in one place and for first time the formation process of Ag nanoparticles (NPs) on β-AgVO3 crystals, driven by an accelerated electron beam from an electronic microscope under high vacuum. Synthesis and optical properties of β-AgVO3 are reported, and the relationship between structural disorder and photoluminescence emissions is discussed. First principle calculations, within a QTAIM framework, have been carried out to provide a deeper insight and understanding of the observed nucleation and early evolution of Ag nanoparticles (NPs) on β-AgVO3 crystals. The Ag nucleation and formation is a result of structural and electronic changes of the [AgO5] and [AgO6] clusters, consistent with Ag metallic formation.The authors are grateful to PrometeoII/2014/022 and ACOMP/2014/270 (GeneralitatValenciana), Ministerio de Economia y Competitividad (Spain), CTQ2012-36253-C03-02 and PRX15/00261, Spanish Brazilian program (PHBP14-00020), FAPESP (FAPESP-CDMF: 2013/07296-2), CNPq and CAPES (for financially supporting this research), and special thanks to Dr. Alan Silva de Menezes of Department of Physics of Universidade Federal do Maranhão for the by Rietveld refinement. L.G. acknowledges Banco Santander (Becas Iberoamérica: Jóvenes profesores e investigadores). J.A. acknowledges Ministerio de Economia y Competitividad, “Salvador Madariaga” program, PRX15/00261. We also acknowledge Servei Informática, Universitat Jaume I, for the generous allotment of computer time

Fingerprints of Short-Range and Long-Range Structure in BaZr1−xHfxO3 Solid Solutions: An Experimental and Theoretical Study

A microwave-assisted hydrothermal method was applied to synthesize BaZr1xHfxO3, (BZHO) solid solutions at a low temperature, 140 1C, and relatively short times, 160 min. The detailed features of the crystal structure, at both short and long ranges, as well as the crystal chemistry doping process, are extensively analysed. X-ray diffraction measurements and Raman spectroscopy have been used to confirm that pure and Hf-doped BZO materials present a cubic structure. Extended X-ray absorption fine structure (EXAFS) spectra indicate that Hf4+ ions have replaced the Zr4+ ions on the 6-fold coordination and a subsequent change on the Ba2+ 12-fold coordination can be sensed. X-ray absorption near-edge structure (XANES) spectroscopy measurements reveal a local symmetry breaking process, associated to overlap of the 4d–2p and 5d–2p orbitals of Zr–O and Hf–O bonds, respectively. Field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM) show the mesocrystalline nature of self-assembled BZHO nanoparticles under a dodecahedron shape. In addition first principle calculations were performed to complement the experimental data. The analysis of the band structures and density of states of the undoped BZO and doped BZHO host lattice allow deep insight into the main electronic features. The theoretical results help us to find a correlation between simulated and experimental Raman modes and allow a more substantial interpretation of crystal structure.Brazilian research funding institution FAPESP. 2009/17752-0 FAPERGS. 2031-2551/13-9SIAS CNPq (MCT/CNPq). 458452/2014-9 Generalitat Valenciana. Prometeo/2009/053 Ministerio de Ciencia e Innovacion. CTQ-2012-36253-C03-01 Programa de Cooperacion Cientificacon Iberoamerica (Brazil), Ministerio de Educacion. PHB2009-0065-P