Unveiling the different physicochemical properties of M-doped β-NaFeO2 (where M = Ni or Cu) materials evaluated as CO2 sorbents: a combined experimental and theoretical analysis

M-doped beta-NaFeO2 samples (where M = Cu or Ni) were synthesized through the nitrate-pyrolysis method, aiming to enhance the sodium ferrite's CO2 capture properties. For the first time, these doped-ferrites were studied with a combined experimental and theoretical approach, to unveil the modifications in the structural, electronic, and optical properties. Several experimental techniques were employed to perform an in-depth characterization (XRD, XPS, SEM and N-2-ads-des, as well as Raman, FTIR-ATR and UV-vis spectroscopies), while the stable structure configurations of pristine beta-NaFeO2 and different doped ferrites were calculated through density functional theory (DFT) at the DFT + U level. Besides, ab initio molecular dynamics (AIMD) simulations were performed to analyze the temperature effect on the Na-ion diffusion, within the ferrite's crystal structure. Results showed that effective doping was achieved with less than 5 mol% of metal, while the efficiency was higher in the nickel-containing samples, as these systems showed the generation of oxygen vacancies with the insertion of divalent Ni2+ cations into the ferrite structure. These changes were linked to the improved CO2 sorption of the low nickel-doped sodium ferrite (2.5 mol%). On the other hand, time-dependent DFT (TD-DFT) calculations showed significant changes in the structural, electronic and optical properties of both doped systems, which corroborate the characterization performed for the synthesized materials. In addition, AIMD simulations evidence a Na-ion mobility increment based on the obtained diffusion coefficients, due to thermal effects, which favors a better CO2 capture. These theoretical results agree with performances shown experimentally.

Automated summary

In this study, M-doped beta-NaFeO2 samples (where M = Cu or Ni) were synthesized to improve the CO2 capture properties of sodium ferrite. Both experimental and theoretical approaches were used to investigate the structural, electronic, and optical modifications caused by doping. Experimental techniques including XRD, XPS, SEM, and spectroscopies were used for characterization, while DFT and AIMD simulations were employed for theoretical calculations. The results demonstrated effective doping with a small amount of metal and showed that nickel-containing samples exhibited higher efficiency in CO2 sorption.