Agar and Chitosan Hydrogels’ Design for Metal-Uptaking Treatments

Abstract

In the field of cultural heritage, the use of natural gels is rising for the application of active agents. Here, two natural polymers are assessed: agar, a pioneer hydrogel for conservation treatments, and chitosan, a rather novel and metal-binding gel. For chitosan, a state-of-the-art based formulation (CS–ItA–LCys) is evaluated as it was reported for silver-complexing properties. It is evaluated whether these polymers can withstand the addition of the chelating compound deferoxamine, which is a bacterial siderophore. This allows for the obtainment of completely bio-sourced gel systems. A Fourier-transformed (FT) infrared spectroscopy characterization is performed, completed with rheological measurements and Cryo-Scanning Electron Microscopy (cryo–SEM) to investigate the physico–chemical properties of the gels, as well as their interaction with deferoxamine. Both polymers are also tested for their inherent complexing ability on silver ions using FT–Raman spectroscopy. A multi-analytical comparison shows different microstructures, in particular, the presence of a thick membrane for chitosan and different mechanical behaviors, with agar being more brittle. Neither hydrogel seems affected by the addition of deferoxamine; this is shown by similar rheological behavior and molecular structures in the presence or absence of the chelator. The intrinsic abilities of the chitosan formulation to make silver complex are demonstrated with the observation of two peaks characteristic of Ag–S and Ag–O bonds. Agar and chitosan are both proven to be reliable gels to act as carriers for bio-based active agents. This paper confirms the potential asset of the chitosan formulation CS–ItA–LCys as a promising gel for the complexation of soluble silver.

Pickering Emulsion Gel Based on Funori Biopolymer and Halloysite Nanotubes: A New Sustainable Material for the Cleaning of Artwork Surfaces

“…The pH of the composite gel was 6.7. Within this, literature reports neutral pH values should be selected for cleaning gels based on several biopolymers (agar, chitosan, gellan gum, and xanthan gum) because they guarantee safe and controlled conditions. , …”

The Cleaning of Corroded Lacquered Brass with Complexing Agents: A Comparative Study

“…The use of innovative bio-based solutions in gelled form has also been explored more recently in the framework of the HELIX project (investigating metal bioremediation for the preservation of historical metal artworks) [30,[37][38][39]. N,N -ethylenediaminedisuccinic acid (EDDS) and siderophores like deferoxamines (DFOs) were investigated for the cleaning of different metal alloys, including brass [40].…”

Efficacy of Chitosan-Carboxylic Acid Hydrogels in Reducing and Chelating Iron for the Removal of Rust from Stone Surface

“…In fact, thanks to the large number of hydroxyl groups, the active ammino groups, and the flexible polymeric structure, chitosan is generally suitable for the adsorption of heavy metal ions. To enhance the complexing ability of the hydrogel in the removal of silver from aqueous solutions, promising results have been obtained using chemically crosslinked chitosan encapsulating a siderophore [ 38 ]. In addition, physical chitosan hydrogel dissolved in an acid solution and added with thiourea dioxide as a reducing agent has been effective in removing manganese stains from both glass and marble [ 39 ].…”