CO2 Adsorption by Carbon Quantum Dots/Metal Ferrites (M = Co2+, Ni2+, and Zn2+): Electrochemical and Theoretical Studies Academic Article in Scopus uri icon

abstract

  • In this study, we investigated the adsorption of CO2 by carbon quantum dot-based ferrites (MFe2O4, M = Co2+, Ni2+, and Zn2+) in the context of industrial CO2 emissions and global warming. The ferrites have been characterized using various analytical techniques [X-ray powder diffraction, FTIR, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS)], showing cubic spinel for CoFe2O4, reverse cubic spinel for NiFe2O4, and typical spinel for ZnFe2O4. A TGA study revealed a significant weight loss around 740-780 °C, indicating structural change occurred with increasing temperature. SEM and TEM images displayed spherical particles with sizes ranging from 10 to 50 nm. XPS confirmed the presence of C, O, and Fe atoms with specific cations (Co2+, Ni2+, and Zn2+). Electrochemical impedance Nyquist diagrams suggest a linear relationship between Z¿ (ohm) and Z¿ (ohm) at low frequencies, but the semicircular loop obtained was significantly increased at higher frequencies. This suggests that the charge transfer resistance (RCT) at the electrode boundaries (interface) is much higher than at low frequencies, indicating the resistance per area was 1853 ¿ cm2 for carbon paste electrodes (CPE)/CoFe2O4 and it decreased to 1652 ¿ cm2 for CPE/NiFe2O4 and 1672 ¿ cm2 for CPE/ZnFe2O4. However, improved electron transfer with lower resistance was seen due to the composite nature of the samples (CQDs@MFe2O4), revealing a lower resistance (1163 ¿ cm2) for CQD@MFe2O4-CO2 as compared to 1567 ¿ cm2 for MFe2O4. Thus, the adsorption of CO2 was studied electrochemically, and interaction between ferrates with CO2 was enhanced by the presence of CQDs in the samples. This is consistent with the adsorption of CO2 with the samples as it follows the Langmuir pseudo-second-order kinetics (k = 4.9, qe = 121.93 for CQD@CoFe2O4, k = 2.9, qe = 156.52 for CQD@NiFe2O4, and k = 3.0, qe = 141.71 for CQD@ZnFe2O4), and the data show that the adsorption efficiency has been decreased by around 1.0% after 7-8 cycles. Lastly, density functional theory analysis demonstrated the interaction of CO2 on the surface of the ferrites, deforming the CO2 linearity, which leads to a subsequent C-O interaction to form carbonate. © 2025 The Authors. Published by American Chemical Society.

publication date

  • April 15, 2025