XPS characterization of (copper-based) coloured stains formed on limestone surfaces of outdoor Roman monuments

The Chemistry of Chelation for Built Heritage Cleaning: The Removal of Copper and Iron Stains

Chelators are widely used in conservation treatments to remove metal stains from marble, travertine, and limestone surfaces. In the current review the chemical aspects underlying the use of chelators for the removal of copper and iron stains from built heritage are described and clear criteria for the selection of the most efficient stain removal treatment are given. The main chelator structural features are outlined and the operating conditions for effective metal stain removal (pH, time of application, etc.) discussed, with a particular emphasis on the ability to form stable metal complexes, the high selectivity towards the metal that should be removed, and the high sustainability for the environment. Dense matrices often host chelators for higher effectiveness, and further research is required to clarify their role in the cleaning process. Then, relevant case studies of copper and iron stain removal are discussed. On these bases, the most effective chelators for copper and stain removal are indicated, providing chemists and conservation scientists with scientific support for conservation operations on stone works of art and opening the way to the synthesis of new chelators.

Sulfonated Zinc Phthalocyanine Coating as an Efficient and Ecofriendly Corrosion Inhibitor for Copper Surfaces: An In Silico Led Design and Its Experimental Validation

The current study highlights the successful integration of an in silico design with experimental validation to create a highly effective corrosion inhibitor for copper (Cu) surfaces. The synthesized sulfonated zinc phthalocyanine (Zn-Pc) is electrochemically characterized and demonstrates an impressive 97% inhibition efficiency, comparable to the widely used industrial corrosion inhibitor, BTA, for Cu surfaces. The corrosion inhibition is comprehensively analyzed through potentiodynamic polarization and impedance spectroscopy techniques, supported by their respective equivalent circuits. Furthermore, the sample undergoes thorough characterization using scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, contact angle measurements, and atomic force microscopy. Density functional theory calculations reveal that sulfonated Zn-Pc exhibits the highest interaction energy, underscoring its exceptional inhibition properties. These results open possibilities for utilizing computational methods to design and optimize corrosion inhibitors for protection of Cu surfaces.

Looking for Novel Natural Gels to Improve Cleaning Methods for Bronze Leachates on Marble

Marble is one of the materials most susceptible to copper leaching, resulting in easily identifiable turquoise stains on the marble. This problem is particularly relevant when we are talking about marble structures of heritage value. For this reason, conservators look for cleaning materials that are specific to the structure to be treated without damaging the original surface. Materials such as agar have been studied for a long time. Agar creates a controlled water release system that adapts to the needs of conservators who seek the greatest possible cleanliness without damaging the material to be treated. To improve the cleaning, chelating agents such as EDTA are added to the agar composition. However, the microbiological growth and the damage it produces to the original material are disadvantages to take into account. In order to solve these problems, other natural materials with cleaning potential such as kudzu and konjac gels were studied in combination with other chelating agents such as citrate, oxalate, and gluconic acid. For the characterization and evaluation of copper cleaning, various analytical techniques were used, including Raman spectroscopy, colorimetry, X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). In this study, both konjac and kudzu emerged as promising alternatives to agar, revealing distinctive features such as simplified preparation methods and inherent antimicrobial properties. The EDTA chelator was found to be the most harmful for marble surfaces, as it extracted a greater amount of calcium from the marble during application of the gels doped with it. Citrate and gluconic acid have been identified as a promising substitute to prepare doped gels for the removal of copper stains. These compounds exhibit comparable or potentially superior cleaning capabilities than EDTA, with no negative side effects.

Analytical Investigation of Iron-Based Stains on Carbonate Stones: Rust Formation, Diffusion Mechanisms, and Speciation

In cultural heritage, unaesthetic stains on carbonate stones due to their close contacts with metals are of concern for the preservation of sculptures, monumental facades and archeological finds of various origin and antiquities. Rust stains made up of various oxidized iron compounds are the most frequent forms of alteration. The presence of ferric iron on rust-stained marble surfaces was confirmed in previous studies and oriented the choice of the best cleaning method (based on complexing agents specific for ferric ions). However, the composition of rust stains may vary along their extension. As the corrosion of the metallic iron proceeds, if the oxygen levels in the surroundings are low and there are no conditions to favor the oxidation, ferrous ions can also diffuse within the carbonate structure and form a variety of intermediate compounds. In this study, the iron stains on archeological marbles were compared with those artificially produced on Carrara marbles and Travertine samples. The use of integrated techniques (optical and scanning electron microscopy as well as Mössbauer and XPS spectroscopy) with complementary analytical depths, has provided the overall information. Rust formation and diffusion mechanisms in carbonates were revealed together with the evolution of iron speciation and identification of phases such as ferrihydrite, goethite, maghemite, nanomagnetite, and hematite.

An advanced Ca/Zn hybrid battery enabled by the dendrite-free zinc anode and a reversible calcification/decalcification NASICON cathode

The proposal of hybrid ion batteries, which can integrate the advantages of the single ion battery, opens up a new route for developing high-performance secondary batteries. Herein, we successfully constructed an aqueous hybrid battery comprised of polyanionic-type cathode material (Na3V2(PO4)3, NVP), Zn metal anode, and aqueous Ca2+/Zn2+ hybrid electrolyte. This exciting combination gives full play to not only the excellent diffusion dynamics of Ca2+ in the NASICON (sodium super ion conductors) structure but also the electrostatic shielding effect of Ca2+ with low reduction potential that inhibits the formation of zinc dendrites. As results, the NVP//Zn Zn/Ca hybrid battery delivers favorable specific capacity with outstanding rate performance (85.3 mAh g-1 capacity at 1 C, 60.5 mAh g-1 capacity at 20 C), and excellent cycle stability (74 % capacity retention after 1300 cycles).

Copper-Binding Properties of Polyethylenimine-Silica Nanocomposite Particles

Increasing demand for copper resources, accompanied by increasing pollution, has resulted in an urgent need for effective materials for copper binding and extraction. Polyethylenimine (PEI) is one of the strongest copper-chelating agents but is not suitable directly (as is) for most applications due to its high solubility in water. PEI-based composite materials show potential as efficient and practical alternatives. In the present work, the interaction of copper ions with PEI-silica nanocomposite particles and precursor PEI microgels (as a reference) is investigated. It is hypothesized that the main driving force of the reaction is chelation of copper ions by amino groups in the PEI network. The presence of silica in the PEI-silica composites was shown to increase the copper-binding capacity in comparison with the parent microgel. The copper-binding behavior of etched (PEI-free "ghost") composite particles in comparison with the original composites and microgel particles shows that silica nanoparticles in the composite structure increase the number of copper-binding sites in the PEI network rather than adsorbing copper themselves. PEI-silica composites can be easily recycled after copper adsorption by simply washing in 1 M nitric acid, which results in complete copper extraction. Employing this recovery method, PEI-silica composite particles can be used for multiple, efficient cycles of copper removal and extraction.

Advanced microscopy and spectroscopy reveal the adsorption and clustering of Cu(ii) onto TEMPO-oxidized cellulose nanofibers

TEMPO (2,2,6,6-tetramethylpiperidine-1-oxylradical)-mediated oxidation nanofibers (TOCNF), as a biocompatible and bioactive material, have opened up a new application of nanocellulose for the removal of water contaminants. This development demands extremely sensitive and accurate methods to understand the surface interactions between water pollutants and TOCNF. In this report, we investigated the adsorption of metal ions on TOCNF surfaces using experimental techniques atthe nano and molecular scales with Cu(ii) as the target pollutant in both aqueous and dry forms. Imaging with in situ atomic force microscopy (AFM), together with a study of the physiochemical properties of TOCNF caused by adsorption with Cu(ii) in liquid, were conducted using the PeakForce Quantitative NanoMechanics (PF-QNM) mode at the nano scale. The average adhesion force between the tip and the target single TOCNF almost tripled after adsorption with Cu(ii) from 50 pN to 140 pN. The stiffness of the TOCNF was also enhanced because the Cu(ii) bound to the carboxylate groups and hardened the fiber. AFM topography, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) mapping and X-ray photoelectron spectroscopy (XPS) indicated that the TOCNF were covered by copper nanolayers and/or nanoparticles after adsorption. The changes in the molecular structure caused by the adsorption were demonstrated by Raman and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). This methodology will be of great assistance to gain qualitative and quantitative information on the adsorption process and interaction between charged entities in aqueous medium.

Cofactor-embedded nanoporous activated carbon matrices for the immobilization of intracellular enzymes and degradation of endocrine disruptor

The mixed intracellular enzyme (MICE) from Citrobacter freundii, capable of degrading o-phenylene diamine (OPD), was extracted and characterized. Cofactors such as zinc and copper ions enhanced the MICE activity. The functionalized nanoporous-activated carbon (FNAC) matrix, zinc-impregnated FNAC matrix (Zn²⁺ -FNAC), copper-impregnated FNAC matrix (Cu²⁺ -FNAC), and zinc- and copper-impregnated FNAC matrix (Zn²⁺ -Cu²⁺ -FNAC) were prepared and characterized to immobilize MICE. The parameters such as time (0-240 Min), pH (1-10), temperature (20-50 ºC), amount of MICE (1-5 mg), particle size of carbon (100-600 μm), and mass of carbon (0.5-2.5 g) were optimized for immobilization of MICE on different FNAC matrices. The carrier matrices in the free and MICE immobilized form were characterized using SEM, FT-IR, XPS, XRD, thermogravimetric analysis (TGA), and DSC analyses. The kinetic and adsorption models for the immobilization of MICE on FNAC matrices were studied. The parameters such as time, pH, temperature, concentration of OPD, and agitation speed were optimized for the degradation of OPD using FNAC-MICE and MICE-immobilized metal-impregnated FNAC matrices. The maximum amount of pyruvic acid formed was found to be 133 μg/mg of OPD using Zn²⁺ -Cu²⁺ -FNAC-MICE matrix. The kinetic models were studied for the formation of pyruvic acid on OPD degradation and confirmed using FT-IR spectroscopy.

An investigation into the use of cuprous chloride for the removal of radioactive iodide from aqueous solutions

Cuprous chloride (CuCl) was examined as a precipitant to remove iodide (I(-)) from aqueous solutions. The effects of the dosage of CuCl, reaction time, initial concentrations of I(-) and bicarbonate (HCO3(-)) on I(-) removal were investigated. The results showed that the optimized removal efficiency of I(-) reached approximately 95.8% when the dosage was 150 mg/L, the initial I(-) concentration ranged from 5 to 40 mg/L and the reaction time was 15 min. The removal efficiency decreased from 95.8% to 76.0% with the addition of HCO3(-) at a concentration in the range of 0-107 mg/L. Furthermore, the dissociation of CuCl, the disproportionation reaction of Cu(+), the precipitation of cuprous iodide (CuI) and cuprous oxide (Cu2O), and the formations of copper sulfide (CuxS, 1≤x<2) were identified as the primary reactions using the PHREEQC software and the measurements of water quality parameters under various conditions. X-rays photoelectron spectroscopy (XPS) analysis was performed before and after the reaction, helping to elucidate the reaction mechanism. This study can provide a promising method to address radioactive I(-) pollution in water.

Solvothermal synthesis of CuO–MgO nanocomposite particles and their catalytic applications

CuO–MgO nanocomposites were prepared by a solvothermal procedure.