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Abstract <p>Water pollution from synthetic dyes poses a persistent environmental challenge, demanding sustainable and efficient remediation strategies. In this paper, a novel Cu-Co doped ZnO/D-carvone modified biochar composite was synthesized from citrus fruit waste via sol–gel synthesis. It was further explored for simultaneous photocatalytic-adsorptive elimination of methylene blue (MB) dye under UV irradiation. The average crystallite size for biochar (6.17&#xa0;nm), photocatalyst (39.79&#xa0;nm), and composite (33.64&#xa0;nm) was calculated by the Debye–Scherrer equation from XRD data. Structure morphology from SEM analysis revealed a porous, irregular, and heterogeneous architecture of the composite with an average particle size of ~ 0.52&#xa0;µm. The optical studies confirmed the formation of a composite with an energy band gap of ~ 1.25&#xa0;eV (Tauc’s plot), favoring enhanced photocatalytic activity. FTIR spectra exhibited characteristic Zn–O stretching vibrations at 623 and 570&#xa0;cm⁻<sup>1</sup>, validating successful incorporation of metal oxides within the biochar framework. The adsorption behavior was evaluated using the Langmuir and the Freundlich adsorption isotherm models under varying pH conditions, with a moderate MB dye removal efficiency of 63.02% achieved at neutral pH and 10&#xa0;ppm as initial concentration. Kinetic investigations revealed that the pseudo-first-order model best described the adsorption process, which was supported by higher correlation coefficients and lower error values. The composite demonstrated effective MB dye degradation through a Type-II heterojunction mechanism under UV light with simultaneous adsorption. These findings highlight the potential of waste-derived, green-engineered composites as cost-effective and eco-friendly alternatives for wastewater treatment. This contributes to both the circular economy and sustainable environmental remediation.</p> Highlights <p>• A novel Cu-Co doped ZnO/D-carvone modified biochar composite was derived from citrus fruit waste, tested for photocatalytic removal and simultaneous adsorption of MB dye.</p> <p>• Bimetallic Cu-Co doping effectively narrowed ZnO band gap from its conventional value, significantly improving charge carrier separation, minimizing recombination losses, and enhancing photocatalytic activity.</p> <p>• D-carvone surface modification enriched the biochar with electron-donating groups and aromatic functionalities, which facilitated abundant adsorption sites, π–π stacking interactions, and enhanced MB dye uptake.</p> <p>• Adsorption rate kinetics revealed that dye removal predominantly followed the pseudo-first-order model, indicating physisorption as the dominant mechanism.</p> Graphical Abstract <p></p>

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Green Synthesized Cu-Co Doped ZnO/D-Carvone Modified Biochar for Dual Photocatalytic-Adsorptive Elimination of Methylene Blue under UV Irradiation

  • 期刊论文

  • 发表日期：

    2026年6月30日

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  • Eksha Guliani,
  • Vinayak V. Pathak,
  • Sangita Banga,
  • Sudhish K. Shukla,
  • Shailendra K. Singh,
  • Amit Awasthi,
  • Sumanta Das,
  • Malini Roy Choudhury

摘要

Abstract

Water pollution from synthetic dyes poses a persistent environmental challenge, demanding sustainable and efficient remediation strategies. In this paper, a novel Cu-Co doped ZnO/D-carvone modified biochar composite was synthesized from citrus fruit waste via sol–gel synthesis. It was further explored for simultaneous photocatalytic-adsorptive elimination of methylene blue (MB) dye under UV irradiation. The average crystallite size for biochar (6.17 nm), photocatalyst (39.79 nm), and composite (33.64 nm) was calculated by the Debye–Scherrer equation from XRD data. Structure morphology from SEM analysis revealed a porous, irregular, and heterogeneous architecture of the composite with an average particle size of ~ 0.52 µm. The optical studies confirmed the formation of a composite with an energy band gap of ~ 1.25 eV (Tauc’s plot), favoring enhanced photocatalytic activity. FTIR spectra exhibited characteristic Zn–O stretching vibrations at 623 and 570 cm⁻1, validating successful incorporation of metal oxides within the biochar framework. The adsorption behavior was evaluated using the Langmuir and the Freundlich adsorption isotherm models under varying pH conditions, with a moderate MB dye removal efficiency of 63.02% achieved at neutral pH and 10 ppm as initial concentration. Kinetic investigations revealed that the pseudo-first-order model best described the adsorption process, which was supported by higher correlation coefficients and lower error values. The composite demonstrated effective MB dye degradation through a Type-II heterojunction mechanism under UV light with simultaneous adsorption. These findings highlight the potential of waste-derived, green-engineered composites as cost-effective and eco-friendly alternatives for wastewater treatment. This contributes to both the circular economy and sustainable environmental remediation.

Highlights

• A novel Cu-Co doped ZnO/D-carvone modified biochar composite was derived from citrus fruit waste, tested for photocatalytic removal and simultaneous adsorption of MB dye.

• Bimetallic Cu-Co doping effectively narrowed ZnO band gap from its conventional value, significantly improving charge carrier separation, minimizing recombination losses, and enhancing photocatalytic activity.

• D-carvone surface modification enriched the biochar with electron-donating groups and aromatic functionalities, which facilitated abundant adsorption sites, π–π stacking interactions, and enhanced MB dye uptake.

• Adsorption rate kinetics revealed that dye removal predominantly followed the pseudo-first-order model, indicating physisorption as the dominant mechanism.

Graphical Abstract