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<p>The rational design of defect-rich transition-metal oxides through sustainable synthesis remains a significant challenge in photocatalysis. A photothermal-assisted biogenic strategy was employed for defect engineering of birnessite-type MnO₂ nanoparticles, utilizing bamboo leaf (BL) extract as a dual-functioning phytochemical reductant and stabilizing agent. The photothermal process, driven by localized photon-to-heat conversion, accelerated Mn²⁺ oxidation and promoted defect formation, yielding MnO₂ nanocrystals with an average crystallite size of ~11 nm and expanded interlayer spacing (0.85 nm). Nitrogen adsorption–desorption analysis revealed a mesoporous architecture with a pore size distribution centered at ~3.1 nm, a DFT-mode pore width of 4.7 nm, and a total pore volume of 0.00885 cc g⁻¹. The defect-rich structure exhibited high oxygen-vacancy density and surface-bound organic residues, collectively narrowing the optical band gap to ~1.87 eV and enhancing visible-light absorption and charge separation efficiency. Under natural sunlight, the optimized BL–MnO₂ achieved 90% degradation of methylene blue within 40 min (k = 0.0507 min⁻¹), following pseudo-first-order kinetics. Reactive species trapping experiments identified superoxide radicals (O₂•⁻) as the dominant oxidative species, with minor contributions from •OH and h⁺. The photocatalyst retained &gt;87% efficiency after five consecutive cycles, demonstrating excellent stability. This study establishes a green photothermal route for defect engineering in MnO₂, providing mechanistic insight into the synergistic coupling of biogenic chemistry and photothermal activation for solar-driven wastewater remediation applications.</p><p></p>

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Defect-engineered birnessite MnO₂ via photothermal biogenic synthesis for solar dye mineralization

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月9日

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  • G. Kavitha,
  • Moganesh Govindhan

摘要

The rational design of defect-rich transition-metal oxides through sustainable synthesis remains a significant challenge in photocatalysis. A photothermal-assisted biogenic strategy was employed for defect engineering of birnessite-type MnO₂ nanoparticles, utilizing bamboo leaf (BL) extract as a dual-functioning phytochemical reductant and stabilizing agent. The photothermal process, driven by localized photon-to-heat conversion, accelerated Mn²⁺ oxidation and promoted defect formation, yielding MnO₂ nanocrystals with an average crystallite size of ~11 nm and expanded interlayer spacing (0.85 nm). Nitrogen adsorption–desorption analysis revealed a mesoporous architecture with a pore size distribution centered at ~3.1 nm, a DFT-mode pore width of 4.7 nm, and a total pore volume of 0.00885 cc g⁻¹. The defect-rich structure exhibited high oxygen-vacancy density and surface-bound organic residues, collectively narrowing the optical band gap to ~1.87 eV and enhancing visible-light absorption and charge separation efficiency. Under natural sunlight, the optimized BL–MnO₂ achieved 90% degradation of methylene blue within 40 min (k = 0.0507 min⁻¹), following pseudo-first-order kinetics. Reactive species trapping experiments identified superoxide radicals (O₂•⁻) as the dominant oxidative species, with minor contributions from •OH and h⁺. The photocatalyst retained >87% efficiency after five consecutive cycles, demonstrating excellent stability. This study establishes a green photothermal route for defect engineering in MnO₂, providing mechanistic insight into the synergistic coupling of biogenic chemistry and photothermal activation for solar-driven wastewater remediation applications.