Synthesis and characterization of cryptomelane (α-MnO₂) nanoparticles: Influence of phthalic acid adsorption and oxidation on the mineral structure

Abstract

Cryptomelane (α-MnO₂) nanoparticles synthesis was achieved via a Sol-Gel route in mild conditions. XRD analysis showed that the α-MnO₂ phase was of high purity and crystallized in the monoclinic space group I2/m, with 12 nm average crystallite size (D). After interaction with an organic pollutant (Phthalic acid, PA), excepting the pronounced decrease in β angle, α-MnO₂ cell parameters slightly changed, probably resulting from leaching of K⁺ cations. Adsorption isotherm of PA on α-MnO₂ nanoparticles was fitted in L2 type Langmuir model. Accordingly, an outer-sphere PA-Mn surface complex was suggested. Further, the mineral oxide exerted a low activity in the decarboxylation of PA. Raman analysis illustrated the major bands, of α-MnO₂, and their evolution after adsorption indicated the effect of PA on the phase structure, as revealed by the XRD Rietveld refinement. AFM analysis showed stick shaped nanoparticles with D = 15 nm, but the interaction with PA induced aggregation.

KEYWORDS:

• α-MnO₂
• phthalic acid
• adsorption
• XRD
• Raman spectroscopy
• AFM

Acknowledgments

We thank Prof. B. Boudine for XRD diffractograms and Mr. D. Daoudi for Raman spectra, as well as Prof. A. Zertal for his dedication and help for the facilities.

Conflict of interest

All the authors have no conflict of interest.

Additional information

Funding

This study was supported by the General Direction of Research in Science and Technology (GDRST), Ministry of Higher Education and Scientific Research (MHESR), Algeria.