Effect of temperature, and immersion time on the inhibition performance of Q235 steel using spent coffee grounds derived carbon quantum dots: Electrochemical, spectroscopic and surface studies

This study investigates the anticorrosive properties of undoped, and zinc and nitrogen-doped carbon quantum dots derived from spent coffee grounds referred to as CCDs and Zn,N-CCDs respectively, for the protection of Q235B steel corrosion in a 5 % HCl solution. The synthesized carbon quantum dots (CDs) were characterized using Transmission Electron Microscope (TEM), X-ray diffraction (XRD), zeta potential, Fourier Transform Infrared (FTIR), UV–vis and fluorescence spectroscopy. Their anticorrosive performance was assessed through weight loss measurements, Open circuit potential (OCP), Electrochemical impedance spectroscopy (EIS), Potentiodynamic polarization (PDP), Scanning Electron Microscopy/Energy dispersive Spectroscopy (SEM/EDS), and X-ray Photoelectron Spectroscopy (XPS) analysis. The results demonstrated that Zn,N-CCDs exhibit better inhibition efficiency i.e., 94.65 % at 150 ppm compared to CCDs which show 90.90 % at 300 ppm and 298 K. Moreover, 150 ppm of Zn,N-CCDs at a longer immersion time of up to 72 h at 313 K exhibited an inhibition performance of 98.33 % proving it as an efficient corrosion inhibitor to be used in acid pickling conditions. PDP analysis suggested that the Zn,N-CCDs reduce both anodic and cathodic dissolution processes. XPS and FTIR analyses confirmed the adsorption of CDs through heteroatoms present in the coffee grounds. Furthermore, surface morphological studies indicated significant adsorption of the Zn,N-CCDs on the metal surface, enhancing surface smoothness as compared to CCDs.