Generation of Copper Oxide Nanoparticles from Discarded Printed Circuit Boards: Microscopy Characterization and Surface Impact with Electrolytes

This study extracted copper from discarded printed circuit board (PCB) to improve the electrolyte variations on biosensing surfaces. A mixture of concentrated hydrochloric and nitric acids in volume ratios of 2:1, 1:2, and 1:1 was prepared for Sample A, Sample B, and Sample C, respectively, to examine copper recovery. Ultraviolet-visible spectrometry revealed an absorbance peak at 230 nm representing the formation of copper oxide nanoparticles (CuONPs). X-ray diffraction revealed the monoclinic structure of CuONPs with high crystallinity and an average size of 36–40 nm (n=3). Fourier transform infrared spectroscopy showed that Sample B had high CuONP purity. At the same time, a high-power microscope and 3D profiler revealed the 2D and 3D views of the electrode surface and gap distance with and without the attachment of CuONPs. Scanning electron microscopy revealed a 35 μm gap between the electrodes, which was reduced upon attaching CuONPs. Characterization analysis suggested that Samples B and C had the highest CuONP purity among the three samples examined; hence, these were selected for subsequent electrolyte scouting carried out on the electrode surface at pH 1 to 12 to determine the current variations of the sensor before and after using CuONPs from different samples with various levels (1, 10, and 100 mg/mL). A linear current curve with the least variation was obtained using 100 mg/mL of CuONPs from samples B and C. These results highlight the possibility of using CuONP attachment to alter the dielectric sensor surface to improve the sensitivity and performance of the device in terms of insensitivity towards electrolytes.