Recycling of printed circuit boards (PCBs) using various deep eutectic solvents (DESs) and insights from DFT simulations

In this study, the dissolution of copper present in printed circuit boards (PCBs) was investigated using different choline chloride (ChCl) based deep eutectic solvents (DES) at a temperature of 100 °C for 24 h. According to the results, the two-component combinations ChCl-PTSA (p-toluene sulfonic acid) and ChCl-ACA (acetic acid) achieved nearly complete copper extraction efficiency. In contrast, ChCl-EG (ethylene glycol) showed less than 1% efficiency. The mechanism of copper dissolution in the ChCl-PTSA was examined using DFT simulations. COSMO analysis reveals a hydrogen bond between ChCl's chloride ion (negative potential) and PTSA's hydroxyl group. Mulliken charges show that DES formation causes charge redistribution, increasing polarization within the sulfonate group and stabilizing the DES structure via enhanced electrostatic interactions. In addition, COSMO analysis of DES with Cu(I) and Cu(II) reveals distinct interaction patterns: Cu(I) primarily interacts with chloride and sulfonate groups, disrupting the original hydrogen bonding network, while Cu(II) shows potential coordination with both chloride and sulfonate groups, influencing the electronic properties of the DES.