Influence of the ligand nature on the in situ laser-induced synthesis of the electrocatalytically active copper microstructures

Abstract

In this work we demonstrate the role of a ligand in formation of the conductive and electrocatalytically active copper microstructures produced using the in situ laser-induced metal deposition technique. For this purpose, the alkaline solutions of different concentrations containing copper(II) chloride and Rochelle salt, which is used as the ligand and exhibits both coordination and reduction properties, were studied by ATR-FTIR, UV–Vis, and Raman spectroscopy. According to spectroscopic studies and theoretical considerations, it was observed that at certain concentrations and proportion of copper(II) chloride and sodium potassium tartrate, and also within pH range between 7 and 13 the components of the plating copper solution form the tartrate copper complex, in which copper ion is coordinated by four hydroxyl groups of the ligand and two hydroxyl groups of the environment. As a result, the laser-induced deposition from solutions, where copper coordination occurs via hydroxyls rather than through other functional groups (e.g. carboxylate), results in the synthesis of the sensory active materials. Furthermore, we figured out that the presence of the reducing agents such as polyols in the plating copper solution also enhances the electrical conductivity and electrochemical characteristics of the resulting copper microdeposits, among which sorbitol displays the most attractive results. Thus, it was shown that the regime of copper coordination in an organic ligand and number of hydroxyl groups in a ligand and a reducing agent directly affect the properties of the synthesized copper microstructures. In addition, the overall results obtained in this study are quite useful for better understanding the mechanisms of the laser-induced metal deposition process, and very perspective for development and design of new non-enzymatic electrochemical sensors and biosensors. Keywords: Rochelle salt, ATR-FTIR, Laser-induced copper deposition, Tartrate copper complex, Quantum-chemical calculations