Neutral Silver Research Articles

Measurement of core electron binding energies of silver nanoparticles and their modeling with electron propagator calculations of silver clusters

Silver nanoparticles were synthesized by ionic exchange with zeolites and further reduction with hydrogen flux. Core electron binding energies were determined by X-ray photoelectron spectroscopy at different times of the reduction process. Electron propagator calculations of core electron binding energies were performed including scalar relativistic effects using effective core potentials and zero order regular approximation. Theoretical results were compared to the experiment to get insight into the origin of the experimental signals for carbon, oxygen, silicon, aluminum and silver. Small model molecules and zeolite fragments were used for the calculation of core electron binding energies. It is evidenced that although binding energies tend to converge, fluctuations of more than 1 eV are found for non-symmetric structures in neutral and cationic silver clusters. Detailed analysis shows that these fluctuations originate on the different coordination numbers of ionized silver atoms and charge fluctuations.

Synthesis and Lewis Acid Properties of Neutral Silver(III) Adducts Containing the AgIII(CF3)3 Moiety.

The acetonitrile AgIII complex [AgIII(CF3)3(NCCH3)] (2) has been reported independently by Eujen and Naumann in the last century, albeit with intriguing NMR discrepancy. In their reports, 2 was claimed to be obtained starting from either [AgIII(CF3)3Cl]- (3⋅Cl) or [AgIII(CF3)4]- (1) via halide abstraction using AgNO3 or acidic treatment, resp. These two synthetic routes are herein reinvestigated. The feasibility of Naumann's method is demonstrated, thus providing 2 yet accompanied by its s-triazinyl derivative [AgIII(CF3)3(C6H9N3)] (2'). The formation of 2' is unprecedented and was thereby investigated. Both 2 and 2' were isolated in pure fashion and fully characterized. In turn, halide extraction from 3⋅Cl leads to the AgIII-ONO2 anion 5 instead of 2, as evidenced by NMR spectroscopy, EA and Sc-XRD.

Impact of sodium fluoride and nano silver fluoride-based varnishes on remineralisation of enamel caries: an in-vitro study

Background: The aim of this study was to perform a comparative evaluation of 5% Sodium fluoride varnish, neutral nano silver fluoride (NSF) varnish and acidulated nano silver fluoride varnish in remineralising artificially induced enamel caries of primary teeth. Methods: 39 primary anterior teeth were sectioned 2mm below the cemento-enamel junction (CEJ) and mounted in acrylic resin blocks. Incipient enamel caries were induced on the samples artificially and primary Vicker’s surface microhardness (SMH) was assessed. Samples were divided equally and applied varnishes; Group 1: 5% Sodium fluoride varnish; Group 2: Neutral NSF varnish, and Group 3: Acidulated NSF varnish. A pH cycling protocol of 7 days was followed, and second Surface microhardness (SMH) testing was carried out. One sample from each group was observed for Scanning electron microscopy and Energy Dispersive Spectroscopy (SEM EDS). Statistical analysis was conducted using HSD Tukey and one way ANOVA tests. Results: There was a statistically significant difference between the pre-treatment and post-treatment values of all three groups. The difference in SMH after applying 5% Sodium fluoride varnish and acidulated NSF varnish was statistically significant (p<0.01). Similarly, neutral NSF varnish and acidulated NSF varnish also showed statistical significance (p<0.01). However, SMH after application of 5% Sodium fluoride varnish and neutral NSF varnish was statistically not significant. The SEM EDS analysis revealed the presence of an even fine granular layer of minerals on the surface of treated enamel in the acidulated NSF group whereas other groups showed uneven deposits of minerals. EDS showed fluoride and silver in groups containing NSF. Conclusions: Acidulated NSF varnish has the highest efficacy followed by neutral NSF varnish and 5% Sodium fluoride in remineralisation of enamel caries in primary teeth.

Impact of sodium fluoride and nano silver fluoride-based varnishes on remineralisation of enamel caries: an in-vitro study

Background: The aim of this study was to perform a comparative evaluation of 5% Sodium fluoride varnish, neutral nano silver fluoride (NSF) varnish and acidulated nano silver fluoride varnish in remineralising artificially induced enamel caries of primary teeth. Methods: 39 primary anterior teeth were sectioned 2mm below the cemento-enamel junction (CEJ) and mounted in acrylic resin blocks. Incipient enamel caries were induced on the samples artificially and primary Vicker’s surface microhardness (SMH) was assessed. Samples were divided equally and applied varnishes; Group 1: 5% Sodium fluoride varnish; Group 2: Neutral NSF varnish, and Group 3: Acidulated NSF varnish. A pH cycling protocol of 7 days was followed, and second Surface microhardness (SMH) testing was carried out. One sample from each group was observed for Scanning electron microscopy and Energy Dispersive Spectroscopy (SEM EDS). Statistical analysis was conducted using HSD Tukey and one way ANOVA tests. Results: There was a statistically significant difference between the pre-treatment and post-treatment values of all three groups. The difference in SMH after applying 5% Sodium fluoride varnish and acidulated NSF varnish was statistically significant (p<0.01). Similarly, neutral NSF varnish and acidulated NSF varnish also showed statistical significance (p<0.01). However, SMH after application of 5% Sodium fluoride varnish and neutral NSF varnish was statistically not significant. The SEM EDS analysis revealed the presence of an even fine granular layer of minerals on the surface of treated enamel in the acidulated NSF group whereas other groups showed uneven deposits of minerals. EDS showed fluoride and silver in groups containing NSF. Conclusions: Acidulated NSF varnish has the highest efficacy followed by neutral NSF varnish and 5% Sodium fluoride in remineralisation of enamel caries in primary teeth.

Sensing Bisphenol A by Means of Surface-Enhanced Raman Spectroscopy and DFT Calculations to Elucidate the Enhancement Mechanism That Dominates the Spectrum

Surface-Enhanced Raman Spectroscopy (SERS) was employed as a spectroscopic tool to detect Bisphenol A (BPA), a building block in polycarbonate and epoxy resins or an additive in other polymer plastics like PVC, which has an endocrine disruptor effect. Silver nanoparticles (AgNPs) synthesized by using different reducing agents such as hydroxylamine (Ag@HX), citrate (Ag@Cit), borohydride (Ag@BH), and β-cyclodextrin (Ag@βCD) were employed, aiming to select the best standard SERS substrate. The lowest limit of quantification was reached at a concentration of 0.01 mM (2.3 μg/mL) of a sonicated aqueous solution by using Ag@Cit NPs and identifying two enhanced bands recorded at about 350 and 460 cm−1. In order to gain insight into the nature of the enhanced bands, and therefore into which mechanism governs the SERS signal, electrochemical spectra recorded at different electrode potentials were acquired and TD-DFT calculations were applied to a neutral silver complex of BPA, Ag2-BPA, and to its monohydroxylated chemical specie, Ag2-BPA(OH), which is present in sonicated solution. The calculated electronic structure and the resonance Raman spectra point out that a surface plasmon-like resonance inside the silver cluster dominates the SERS spectrum corresponding to the physisorbed BPA(OH) species, a charge transfer enhancement mechanism or an intramolecular resonance transition localized in the phenolic framework was then discarded.

Superfluid helium droplet-mediated surface-deposition of neutral and charged silver atomic species.

Experimental and theoretical work has delivered evidence of the helium nanodroplet-mediated synthesis and soft-landing of metal nanoparticles, nanowires, clusters, and single atoms on solid supports. Recent experimental advances have allowed the formation of charged metal clusters into multiply charged helium nanodroplets. The impact of the charge of immersed metal species in helium nanodroplet-mediated surface deposition is proved by considering silver atoms and cations at zero-temperature graphene as the support. By combining high-level ab initio intermolecular interaction theory with a full quantum description of the superfluid helium nanodroplet motion, evidence is presented that the fundamental mechanism of soft-deposition is preserved in spite of the much stronger interaction of charged species with surfaces, with high-density fluctuations in the helium droplet playing an essential role in braking them. Corroboration is also presented that the soft-landing becomes favored as the helium nanodroplet size increases.

Nuclear quantum dynamics on the ground electronic state of neutral silver dimer 107Ag109Ag probed by femtosecond NeNePo spectroscopy.

The nuclear quantum dynamics on the ground electronic state of the neutral silver dimer 107Ag109Ag are studied by femtosecond (fs) pump-probe spectroscopy using the 'negative ion - to neutral - to positive ion' (NeNePo) excitation scheme. A vibrational wave packet is prepared on the X1Σ+g state of Ag2via photodetachment of mass-selected, cryogenically cooled Ag2- using a first ultrafast pump laser pulse. The temporal evolution of the wave packet is then probed by an ultrafast probe pulse via resonant multiphoton ionization to Ag2+. Frequency analysis of the fs-NeNePo spectra obtained for a single isotopologue and pump-probe delay times up to 60 ps yields the harmonic (ωe = 192.2 cm-1), quadratic anharmonic (ωexe = 0.637 cm-1) and cubic anharmonic (ωeye = 3 × 10-4 cm-1) constants for the X1Σ+g state of neutral Ag2. The fs-NeNePo spectra obtained at different pump wavelengths provide insight into the excitation mechanism. At a pump wavelength of 510 nm instead of 1010 nm, resonant excitation of a short-lived electronically excited state of the anion followed by autodetachment results in population of higher-energy vibrational levels of the neutral ground state. In contrast, at 1140 nm dynamics with a slightly shorter beating period and different relative phase are observed. The present study demonstrates that isotopologue-specific fs-NeNePo spectroscopy provides accurate vibrational constants of mass-selected neutral clusters in their electronic ground state in the terahertz spectral region, which remains difficult to obtain directly in the frequency domain with any other type of spectroscopy of comparable sensitivity.

On the nature of noble gas - metal bond in silver aggregates.

The aim of this paper is to extend the study of the nature of the bond between noble gas to nano- and sub nanoscale silver aggregates. In the framework of DFT-PAW calculations implemented in the abinit package, we carried out a thorough investigation on the nature of the bond between the six noble gases NG (He, Ne, Ar, Kr, Xe and Rn) and numerous neutral silver aggregates Agn from the single atom Ag1 to the nanoparticle Ag147 using atoms-in-molecules (AIM) dual functional analysis,. We evaluated the impact of the silver aggregate size, the adsorption site and of the noble gas on the Ag-NG bond. Our study concluded on the favored adsorption of heavier noble gases (Kr, Xe and Rn) over that of lighter noble gases (He, Ne and Ar) on any aggregate size due to an enhanced chemical contribution in the bond. For these heavier noble gases, in accordance with studies carried out on surfaces, we noted their preferential adsorption on on-top sites rather than on hollow sites, which further evidences the chemical contribution to the bond. Moreover, the slight positive Bader charge on these heavier noble gases implies an electron transfer from the noble gas to the silver atom. Noble gas adsorption is favored on smaller, few-atom, two-dimensional clusters rather than on larger three-dimensional nanoparticles. Finally, we identified a universal power law with a unique exponent linking bond length and electronic density at the bond critical point for all aggregate sizes, noble gases and adsorption sites.

Synthesis of Two Neutral Silver Alkynyl Nanoclusters by a Single Divalent Tetrahedral Anion Template and a Study of Their Optical Features.

The synthesis of nanoclusters from simple structural units is usually a challenging process because of the complexity and unpredictability of the self-assembly process of these types of compounds. Herein, two new neutral 19-nuclearity silver nanoclusters based on alkynyl ligands with the formulas [(CrO4)@Ag19(C≡CtBu)8(Ph2PO2)6(tfa)3(CH3OH)2] (1) and [(SO4)@Ag19(C≡CtBu)8(Ph2PO2)6(tfa)3(CH3OH)2] (2), in which tfa = trifluoroacetate, were synthesized, and their structures were investigated by single-crystal and powder X-ray diffraction, electrospray ionization mass spectrometry, elemental analyses, and Fourier transform infrared spectroscopy. The surface ligands of Ph2PO2H and trifluoroacetate were assembled through hydrogen bonding, metal-aromatic interactions, and coordination bonding around 19 silver atoms as the metal skeletons of the nanoclusters. Sulfate and chromate anions, as a template within the metal skeleton of clusters through bonding with silver atoms, stabilized the structure. In addition, the UV-vis absorption spectroscopy, luminescence properties, and thermal stability of the nanoclusters were investigated.

Temporal analysis of self-reversed Ag I resonant lines in LIBS experiment at different laser pulse energy and in different surrounding media

In this work we studied the temporal evolution of the resonant emission lines of neutral silver (Ag I) at wavelengths 328.9 nm and 338.2 nm, in different surrounding media (He, Ar, Xe and air) and at different laser pulse energy (15 mJ, 30 mJ and 60 mJ), using a frequency triplicated Nd:YAG laser (355 nm).We observed that the self-reversal of the Ag lines, caused by the combined effect of self-absorption and plasma inhomogeneity, is strong when the plasma expands in molecular gases (N2 and O2 in air) while is negligible in atomic noble gases (He, Ar, Xe), independently on the mass of the atoms. From the experimental data, we also conclude that the shock wave generated during the breakdown may play an important role in generating the plasma inhomogeneities which are essential conditions for the occurrence of the self-reversal effect.

Synthesis and biological evaluation of fluoro-substituted cationic and neutral antibiotic NHC* silver derivatives of SBC3

Two fluoro-substituted neutral carbene silver acetates and thirteen cationic dicarbene silver complexes were synthesised from the appropriate imidazolium precursors in good to very good yields using batch and flow synthesis. Six of the derivatives were characterised by XRD and showed expected structural aspects in the solid state. Most of these fifteen new silver-based antimicrobial drug candidates showed improved stability as well as comparable biological activity against E. coli and Methicillin-resistant S. aureus when compared against the lead compound 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene silver(I) acetate (SBC3). Fluoro-substitution as well as the use of dicarbene complexes have the potential to develop the field of silver-based antimicrobials further.

Preparation, characterization and stability of silver sulfadiazine nanoliposomes


 
 
 
 Purpose: To prepare, characterize and investigate the stability and drug release profile of silver sulfadiazine (AgSD) nanoliposomes as functions of pH, UV exposure, and/or heat.
 Methods: Silver sulfadiazine (AgSD) nanoliposomes were prepared. The stability and release properties of the free drug and nanoliposomal formulations of AgSD as functions of pH, UV exposure, and/or heat were analyzed. The analyses were performed at different time points.
 Results: The results of characterization showed that acidic, basic and neutral silver sulfadiazine nano-liposomal suspensions (AgSD NLSs) were produced as stable homogenous formulations, as indicated by low polydispersity index (PDI) and high zeta potential. The three AgSD NLSs and AgSD were unstable under different heat and/or UV conditions. The pH tended to shift towards neutrality, starting from day 1. Silver sulfadiazine nanoliposomal suspensions (AgSD NLSs) and free drug (AgSD) exhibited similar release properties (100 % of the drug was released at day 12).
 Conclusion: Incorporation of AgSD into nanoliposomes has no significant effect on the stability and in vitro release properties of the drug. This indicates that NLS did not change the physical characteristics of the drug. Studies that focus only on improving the lipophilicity of silver sulfadiazine may benefit from these results.
 
 
 

Facile N9-Alkylation of Xanthine Derivatives and Their Use as Precursors for N-Heterocyclic Carbene Complexes.

The xanthine-derivatives 1,3,7-trimethylxanthine, 1,3-dimethyl-7-benzylxanthine and 1,3-dimethyl-7-(4-chlorobenzyl)xanthine are readily ethylated at N9 using the cheap alkylating agents ethyl tosylate or diethyl sulfate. The resulting xanthinium tosylate or ethyl sulfate salts can be converted into the corresponding PF6− and chloride salts. The reaction of these xanthinium salts with silver(I) oxide results in the formation of different silver(I) carbene-complexes. In the presence of ammonia, ammine complexes [Ag(NHC)(NH3)]PF6 are formed, whilst with Et2NH, the bis(carbene) salts [Ag(NHC)2]PF6 were isolated. Using the xanthinium chloride salts neutral silver(I) carbenes [Ag(NHC)Cl] were prepared. These silver complexes were used in a variety of transmetallation reactions to give the corresponding gold(I), ruthenium(II) as well as rhodium(I) and rhodium(III) complexes. The compounds were characterized by various spectroscopic methods as well as X-ray diffraction.

Determination of Spectroscopic Parameters of Ag(I) and Ag(II) Emission Lines Using Time-Independent Extended C-Sigma Method.

The knowledge of the spectroscopic parameters of the elemental emission lines is important for diagnostics of laser-induced plasmas and the application of calibration-free/fundamental parameters analytical methods. In this paper, we used the recently proposed time-independent extended C-sigma method for determining, for the first time, the transition probabilities and Stark broadening coefficients of several neutral (TIECS) and ionic silver emission lines. The method allows for a compensation of self-absorption in the plasma, thus providing a measure of the spectroscopic parameters which is not affected by the optical thickness of the plasma.

One-pot green synthesis of Ag@AgCl nanoparticles with excellent photocatalytic performance

Ag@AgCl composites are effective photocatalysts used for degrading organic pollutants, but the limitations of their large-scale production hinder them from having a broad scope of applications. In this study, Ag@AgCl nanoparticles (NPs) with efficient photocatalytic performance were synthesized using a simple and straightforward strategy. Excess chloride (Cl−) ions were added into a silver nitrate (AgNO3)/N,N-dimethylacetamide solution to form [AgCl2]−. The solution of [AgCl2]− was slowly dropped into a 0.5 wt. % polyvinylpyrrolidone solution to obtain silver chloride (AgCl). Neutral silver ions (silver (0) (Ag0)) were produced by the partial decomposition of silver chloride and formed Ag@AgCl under irradiation with visible light. The experimental analysis showed that Ag@AgCl NPs had strong absorption within the range of visible light. They exhibited excellent photocatalytic activity with recyclability for the degradation of methyl orange dyes under visible-light irradiation. The photocatalyst prepared in this study can have practical application in wastewater treatment through the significant degradation of organic pollutants.

DFT Study of NO Reduction Process on Ag/γ-Al2O3 Catalyst: Some Aspects of Mechanism and Catalyst Structure

Catalysts based on Ag/γ-Al2O3 are perspective systems for practical implementation of catalytic NO reduction. Nevertheless, the mechanism and regularities of this process have still not been fully investigated. Herein, we present the results of quantum-chemical research of the Ag/γ-Al2O3 catalyst surface and some aspects of the NO reduction mechanism on it. Proposed calculation methods using DFT and cluster models of the catalyst surface are compared and verified. The possibility of existence of small adsorbed neutral and cationic silver clusters on the surface of the catalyst is shown. It is demonstrated that NO adsorption on these clusters is energetically favorable, in the form of both monomers and dimers. The scheme of NO selective catalytic reduction (SCR) that explains increasing of N2O side-product amount on catalysts with silver fraction more than 2 wt % is proposed. The feasibility of this scheme is justified with calculated data. Some recommendations that allow decreasing amounts of N2O are developed.

Cation−π Complexes of Silver Studied with Photodissociation and Velocity-Map Imaging

Ag+(aromatic) ion-molecule complexes of benzene, toluene, or furan are generated in the gas phase by laser vaporization in a supersonic expansion. These ions are mass selected in a time-of-flight spectrometer and studied with ultraviolet laser photodissociation and photofragment imaging. UV laser excitation results in dissociative charge transfer (DCT) for these ions, producing neutral silver atom and the respective aromatic cation as the photofragments. Velocity-map imaging and slice imaging techniques are employed to investigate the kinetic energy release in these photodissociation processes. In each case, DCT produces significant kinetic energy, and evidence is also found for excitation of the internal rovibrational degrees of freedom for the molecular cations. Analysis of the kinetic energy release together with the known ionization energies of silver and the molecular ligands provides new information on the cation-π bond energies.

Comment on: “Measurement of deviations of transition probability of the neutral silver lines at 827.35 and 768.77 nm using OES-technique” by Alhijry et al. [JQSRT (2020) 106922

In this comment we pointed out an error in the identification of the neutral silver line at 768.77 that invalidates some of the results reported in the paper “Measurement of deviations of transition probability of the neutral silver lines at 827.35 and 768.77 nm using OES-technique” by Alhijry et al., recently published on JQSRT.

Hexavalent Octahedral Template: A Neutral High-Nucleus Silver Alkynyl Nanocluster Emitting Infrared Light.

The first silver nanocluster with an octahedral template of TeO66- was synthesized as a neutral 36-nucleus nanocluster, and its structure was demonstrated using single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, electrospray ionization mass spectrometry, and X-ray photoelectron spectroscopy. The peripheral ligands of the cagelike skeleton of the nanocluster are CF3COO- and tBuC≡C-. During the synthesis, the TeO66- template arranged the nanocluster, and a 36-nucleus nanocluster was formed. The effect of the template nature was displayed on the structural features of the nanocluster in comparison with an 8-nucleus cluster, with the same synthesis conditions. The photoluminescence and UV-vis absorption analyses of the nanocluster were also investigated. The nanocluster displayed near-infrared luminescence emission at 690 nm.

Silver diffusion effects in aluminum nitride/silver films on polydimethylsiloxane gratings via nitrogen–argon sputtering

In this study, we present the effect of silver diffusion into a dielectric medium and its consequent effect on the optical spectra on thin metal-dielectric structures. We show that on a grating pattern, reactive sputter deposition of aluminum nitride immediately following the sputter deposition of a thin layer of silver results in a broadening of the absorption peak of the AlN/Ag gratings which is directly related to diffusion of Ag ions into the overlying AlN layer. Time of Flight Secondary Ion Mass spectroscopy shows that the sample with broadened optical absorption has a significant concentration of Ag within the AlN layer and that the concentration profile follows the error function consistent with Fick’s second law of diffusion. Plasma emission spectroscopy reveal that the use of N2/Ar mixture instead of an Ar only plasma during RF sputtering reduces the emission of neutral silver atoms, implying that the density of singly ionized silver increases in a nitrogen-containing plasma. However, sputter deposition of AlN following exposure of the underlying silver grating film to ambient atmosphere does not give rise to the same broadening effect in the optical spectra for the AlN/Ag gratings due to the increased concentration of oxygen within the AlN and Ag layers, indicating that oxidation at the AlN/Ag interface inhibits silver migration into the dielectric.