Optimization of Copper Stain Removal from Marble through the Formation of Cu(II) Complexes in Agar Gels

Abstract

Copper complexes with different ligands (ethylenediaminetetraacetic acid, EDTA, ammonium citrate tribasic, TAC, and alanine, ALA) were studied in aqueous solutions and hydrogels with the aim of setting the optimal conditions for copper stain removal from marble by agar gels, with damage minimization. The stoichiometry and stability of copper complexes were monitored by ultraviolet-visible (UV-Vis) spectroscopy and the symmetry of Cu(II) centers in the different gel formulations was studied by electron paramagnetic resonance (EPR) spectroscopy. Cleaning effectiveness in optimized conditions was verified on marble laboratory specimens through color variations and by determining copper on gels by inductively coupled plasma-mass spectrometry (ICP-MS). Two copper complexes with TAC were identified, one having the known stoichiometry 1:1, and the other 1:2, Cu(TAC)2, never observed before. The stability of all the complexes at different pH was observed to increase with pH. At pH 10.0, the gel’s effectiveness in removing copper salts from marble was the highest in the presence of ALA, followed by EDTA, TAC, and pure agar gel. Limited damage to the marble surface was observed when gels with added EDTA and TAC were employed, whereas agar gel with ALA was determined to be the most efficient and safe cleaning material.

Poly (Amidehydrazide) Hydrogel Particles for Removal of Cu2+ and Cd2+ Ions from Water

“…The maximum swelling ratio is 1414% of SDH-PAMH 1. 25 , reflecting the hydrophilic nature of the PAMH hydrogel particles.…”

“…Adsorption is a promising method of removing heavy metal ions from water on the basis of its energyefficiency in the removal of pollutants [13]. Among the materials that are employed for adsorption, polymer gel adsorbents such as chitosan, alginate, agarose, polyethyleneimine (PEI), and poly(amidoamine) (PAMAM) have been actively investigated due to their high sorption performance, stemming from their functional group-rich nature [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Among these materials, dendritic PAMAM shows a high sorption capacity because abundant amine and amide groups with dendritic structures facilitate the binding of heavy metal ions.…”

Non-Invasive Assessment of PVA-Borax Hydrogel Effectiveness in Removing Metal Corrosion Products on Stones by Portable NMR

“…In particular, all these agents continuously endanger the life of stone artworks exposed to outdoor. When a stone building, statue or monument under atmospheric conditions is in contact with metallic parts, such as clamps, pivots, or plaques [ 1 ], corrosion of the latter may be induced and the corrosion products may hinder the correct readability of the artwork [ 2 , 3 , 4 ]. In particular, in the case of copper and its alloys, corrosion is a chemical attack mainly promoted by the affinity of metals and pollutants (i.e., sulfur, carbon dioxide, chlorides).…”

“…So, the atmospheric exposure of copper produces the oxidation-reduction reactions leading to different corrosion products: copper(I) oxide which is red, copper(II) oxide which is black, black copper sulfide, various colored salts and nantokite, green-blue atacamite and clinoatacamite [ 6 ]. These corrosion products are responsible for the discoloration of the stone [ 1 , 11 ].…”

“…In the case of iron in contact with a stone artwork and in the presence of oxygen and water, it will corrode depending on the pH value of the surrounding environment [ 1 , 4 , 11 ]. Generally, corrosion is activated by acidic conditions, but it can also take place in an alkaline environment [ 11 ].…”