Preparation and characterization of natural melanin and its nanocomposite formed by copper doping

Abstract Natural Melanins have received great interest due to their structural, thermostability, electrochemical and paramagnetic properties. Pure melanin (Mel) is extracted from Nigella Sativa seeds and doped with Copper (Cu‐Mel) to form nano‐composite melanin using wet chemical methods. Several analytics techniques are utilized to evaluate the effects of cop‐per doping on the characteristics of melanin. Thermogravimetric analysis (TGA) is employed to measure the thermal stability of Cu‐Mel relative to Mel. The morphological characterization is explored using Transmission Electron Microscopy (TEM) while X‐Ray Diffraction (XRD) is used to probe the samples’ structure. Vibrating Sample Magnetometer (VSM) is employed to study the magnetic properties of the prepared samples at 10 and 300K. Chemical properties are determined by Spectroscopic techniques such as UV–Vis spectroscopy, RAMAN spectroscopy, Fourier‐Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) spectroscopy, and Electron Paramagnetic Resonance (EPR) spectroscopy. The results show that Mel and Cu‐Mel are non‐crystalline with different structural, optical, and magnetic properties. The EPR analysis provided evidence of copper coordination with herbal Mel and the copper doping improved the magnetic properties of Mel from diamagnetic to paramagnetic at low temperature (10K). Overall, this investigation shows that Mel and Cu‐Mel are non‐crystalline with different structural and magnetic properties.