Sustainable corrosion inhibition of Copper-based alloys by smart Beta-Cyclodextrin/Benzotriazole complexes

Environmental and safety issues are a global concern for the use of corrosion inhibitors in important fields of interest, such as industrial applications and conservation of Cultural Heritage. The development of safe and reliable long-term methods and strategies for the conservation of metals is nowadays a mandatory demand, since the presently used hazardous materials and processes need to be replaced. "Bronze disease" is the most dangerous form of active corrosion of a copper-based alloy, due to a cyclic reaction that involves chlorine as the aggressive agent. The method commonly used to cure "bronze disease" requires the use of a 1-H benzotriazole (BTA) alcoholic solution (3-6 wt. %) at t = 60°C. Unfortunately, despite its widely application as reference copper corrosion inhibitor, BTA is toxic and a suspected carcinogen. In order to reduce BTA toxicity and to develop new and safe protection systems to be offered as alternative choices to conservation/restoration professionals, suitable nanocontainers of corrosion inhibitors can be used. In this work, beta-Cyclodextrins (beta-CD) were investigated as nanocontainer of BTA for a controlled release on a metallic surfaces. Complexes of beta-Cyclodextrin and benzotriazole were prepared in a 1:1 and 1:10 (beta-CD/BTA adduct) molar ratio. The efficiency of the BTA loading was determined by UV-VIS spectroscopy, confirming the formation of the inclusion complex. The kinetics of release was investigated by UV-VIS spectroscopy in an aqueous NaCl solution (3% w/w) at room temperature in order to simulate a marine environment. Different beta-CD/BTA systems were prepared as nanostructured films on Cu-based alloy supports by a casting procedure. The corrosion inhibition performances were tested in the chloride solution by electrochemical techniques (dynamic polarization and EIS) as a function of the immersion time at room temperature. The surface chemical composition of the samples was investigated by X-ray Photoemission Spectroscopy (XPS), both before and after the corrosive attack. Results were compared with the corresponding data for the pure BTA films. A potential use of the smart beta-CD/BTA system as a non-toxic, self-healing and long-lasting corrosion inhibitor of Cu-based alloys was ascertained. Acknowledgements Financial support by the PON03PE_00214_1 TECLA Project: "Nanotecnologie e Nanomateriali per i Beni Culturali", Distretto di Alta Tecnologia per l'Innovazione nel settore dei Beni Culturali della Regione Sicilia, is gratefully acknowledged.