A Multi-Analytical Approach on Silver-Copper Coins of the Roman Empire to Elucidate the Economy of the 3rd Century A.D.

In this study, 160 silver-copper alloy denarii and antoniniani from the 3rd century A.D. were studied to obtain their overall chemical composition. The approach used for their characterisation is based on a combination of physical, chemical, and chemometric techniques. The aim is to identify and quantify major and trace elements in Roman silver-copper coins in order to assess changes in composition and to confirm the devaluation of the currency. After a first cataloguing step, µ-EDXRF and SEM-EDX techniques were performed to identify the elements on the coins' surface. A micro-destructive sampling method was employed on a representative sample of the coins to quantify the elements present in the bulk. The powder obtained from drilling 12 coins (keeping the two categories of coins separate) was dissolved in an acidic medium; heated and sonicated to facilitate dissolution; and then analysed by ICP-AES and ICP-MS. The two currencies had different average alloy percentages; in particular, the % difference of Ag was about 8%. The other elements were found in concentrations <1 wt%. Of these, the element highest in concentration were Pb and Sn, which is in agreement with the literature. The multivariate analysis performed on the data acquired revealed two groups of coins, corresponding to the two currencies.

Chemical analysis and computed tomography of metallic inclusions in Roman glass to unveil ancient coloring methods.

This paper describes the analysis of two near-spherical metallic inclusions partially incorporated within two Roman raw glass slags in order to elucidate the process that induced their formation and to determine whether their presence was related to ancient glass colouring processes. The theory of metallic scraps or powder being used in Roman times for glass-making and colouring purposes is widely accepted by the archaeological scientific community, although the assumption has been mainly based on oral traditions and documented medieval practices of glass processing. The analysis of the two inclusions, carried out by X-ray computed tomography, electrochemical analyses, and scanning electron microscopy, revealed their material composition, corrosion and internal structure. Results indicate that the two metallic bodies originated when, during the melting phase of glass, metal scraps were added to colour the material: the colloidal metal-glass system reached then a supersaturation condition and the latter ultimately induced metal expulsion and agglomeration. According to the authors' knowledge, these two inclusions represent the first documented and studied finds directly associated with the ancient practise of adding metallic agents to colour glass, and their analysis provides clear insights into the use of metallic waste in the glass colouring process.

Confined-Melting-Assisted Synthesis of Bismuth Silicate Glass-Ceramic Nanoparticles: Formation and Optical Thermometry Investigation.

Bismuth-based (nano)materials have been attracting increasing interest due to appealing properties such as high refractive indexes, intrinsic opacity, and structural distortions due to the stereochemistry of 6s2 lone pair electrons of Bi3+. However, the control over specific phases and strategies able to stabilize uniform bismuth-based (nano)materials is still a challenge. In this study, we employed the ability of bismuth to lower the melting point of silica to introduce a new synthetic approach able to confine the growth of bismuth-oxide-based materials into nanostructures. Combining in situ temperature-dependent synchrotron radiation X-ray powder diffraction (XRPD) with high-resolution transmission electron microscopy (HR-TEM) analyses, we demonstrate the evolution of a confined Bi2O3-SiO2 nanosystem from Bi2SiO5 to Bi4Si3O12 through a melting process. The silica shell acts as both a nanoreactor and a silicon source for the stabilization of bismuth silicate glass-ceramic nanocrystals keeping the original spherical shape. The exciton peak of Bi2SiO5 is measured for the first time allowing the estimation of its real energy gap. Moreover, based on a detailed spectroscopic investigation, we discuss the potential and the limitations of Nd3+-activated bismuth silicate systems as ratiometric thermometers. The synthetic strategy introduced here could be further explored to stabilize other bismuth-oxide-based materials, opening the way toward the growth of well-defined glass-ceramic nanoparticles.

Redesigning an Electrochemical MIP Sensor for PFOS: Practicalities and Pitfalls.

There is a growing interest in the technological transfer of highly performing electrochemical sensors within portable analytical devices for the in situ monitoring of environmental contaminants, such as perfluorooctanesulfonic acid (PFOS). In the redesign of biomimetic sensors, many parameters should be taken into account from the working conditions to the electrode surface roughness. A complete characterization of the surface modifiers can help to avoid time-consuming optimizations and better interpret the sensor responses. In the present study, a molecularly imprinted polymer electrochemical sensor (MIP) for PFOS optimized on gold disk electrodes was redesigned on commercial gold screen-printed electrodes. However, its performance investigated by differential pulse voltammetry was found to be poor. Before proceeding with further optimization, a morphological study of the bare and modified electrode surfaces was carried out by scanning electron microscopy-energy-dispersive X-ray spectrometry (SEM-EDS), atomic force microscopy (AFM) and profilometry revealing an heterogeneous distribution of the polymer strongly influenced by the electrode roughness. The high content of fluorine of the target-template molecule allowed to map the distribution of the molecularly imprinted polymer before the template removal and to define a characterization protocol. This case study shows the importance of a multi-analytical characterization approach and identify significant parameters to be considered in similar redesigning studies.

Bi2SiO5@g-SiO2 upconverting nanoparticles: a bismuth-driven core-shell self-assembly mechanism.

Core-shell systems have attracted increasing interest among the research community in recent years due to their unique properties and structural features, and the development of new synthetic strategies is still a challenge. In this work, we have investigated lanthanide-doped Bi2SiO5 nanocrystal formation inside mesoporous silica nanoparticles (MSNs). The role of both synthesis temperature and concentration of the bismuth precursor impregnated into the MSNs is discussed, showing an unprecedented strategy for the simultaneous stabilization of a crystalline core and a glassy shell. Temperature dependent synchrotron radiation X-ray powder diffraction (SR-XRPD) and high resolution transmission electron microscopy (HR-TEM) analyses allow one to follow the crystalline core growth. A mechanism for the formation of a Bi2SiO5@g-SiO2 core-shell nanosystem is proposed. In addition, the easy tunability of the color output of the upconverting system is demonstrated by means of suitable doping lanthanide ions with potential applications in several fields.

Design of Carbon Dots for Metal-free Photoredox Catalysis.

The photoreduction potential of a set of four different carbon dots (CDs) was investigated. The CDs were synthesized by using two different preparation methods-hydrothermal and pyrolytic-and two sets of reagents-neat citric acid and citric acid doped with diethylenetriamine. The hydrothermal syntheses yielded amorphous CDs, which were either nondoped (a-CDs) or nitrogen-doped (a-N-CDs), whereas the pyrolytic treatment afforded graphitic CDs, either non-doped (g-CDs) or nitrogen-doped (g-N-CDs). The morphology, structure, and optical properties of four different types of CDs revealed significant differences depending on the synthetic pathway. The photocatalytic activities of the CDs were investigated as such, that is, in the absence of any other redox mediators, on the model photoreduction reaction of methyl viologen. The observed photocatalytic reaction rates: a-N-CDs ≥ g-CDs > a-CDs ≥ g-N-CDs were correlated with the presence/absence of fluorophores, to the graphitic core, and to quenching interactions between the two. The results indicate that nitrogen doping reverses the photoredox reactivity between amorphous and graphitic CDs and that amorphous N-doped CDs are the most photoredox active, a yet unknown fact that demonstrates the tunable potential of CDs for ad hoc applications.