A Comparative Analysis of Structural, Morphological and Optical Features of α-MnO₂/SnO₂ and β-MnO₂/SnO₂ Composites

INTRODUCTION

Manganese dioxide exists in several polymorphic forms, including α-MnO₂, β-MnO₂, γ-MnO₂, and δ-MnO₂. Among these, the α, β, and γ phases exhibit tunnel structures, while the δ phase possesses a layered structure. Due to its distinctive crystal framework, high surface area, rich oxygen content, and inherent catalytic properties, nanostructured MnO₂ is widely regarded as a promising gas sensing material. This study emphasizes the synthesis of MnO₂-based composites and explores their structural, optical, and morphological characteristics using XRD, UV-Visible, FT-IR, and FE-SEM, respectively.

METHOD

The α-MnO₂ phase is synthesized via a facile co-precipitate route while the β-MnO₂ phase is synthesized using the hydrothermal technique. Composites with SnO₂ areobtained via a solid state reaction method wherein α and β MnO₂ is grinded (1:1 ratio by weight), respectively, with SnO₂ using an agate mortar and pestle, followed by annealing at 400 °C for 2 hours.

RESULTS

The structural analysis reveals the formation of tetragonal α and β MnO_2. The average crystallite sizes of α-MnO₂-SnO₂ and β-MnO₂-SnO₂ are 19.33 nm and 22.58 nm, respectively. The crystallinity of α-MnO₂-SnO₂ and β-MnO₂-SnO₂, respectively, is 94.75% and 88.18%. The optical band gaps of 3.4 eV and 3.58 eV are obtained for α-MnO₂-SnO₂ and β-MnO₂-SnO₂, respectively. The morphology discloses the formation of nanorods of α-MnO₂, nanothreads of β-MnO₂, and granules of SnO₂.

CONCLUSION

Gas sensing performance can be significantly improved by developing nanocomposites that feature small crystallite sizes, high crystallinity, narrow optical band gaps, and porous structures. Such composites are well-suited for the detection of hazardous gases.