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<p>This study presents the development of a sustainable carbon quantum dot (CQD)/titanium dioxide (TiO₂) nanocomposite designed for the photocatalytic degradation of antibiotic pollutants in water through advanced oxidation processes (AOPs). CQDs were synthesized via a green, one-step hydrothermal method using lemon peel waste and subsequently integrated with TiO₂ nanoparticles. Comprehensive structural and surface characterizations—including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED)—confirmed the presence of functional groups such as carboxyl (–COOH), ether (C–O–C), and titanium-oxygen (Ti–O) bonds. The analyses also verified the anatase/rutile crystalline phase of TiO₂ structure, with consistent results across imaging and diffraction techniques. Ultraviolet–visible (UV–vis) spectroscopy revealed a π–π* transition peak at 280&#xa0;nm and determined the bandgap energy to be 2.8&#xa0;eV. Zeta potential measurements indicated a negatively charged surface, attributed to the carboxyl groups on CQDs, suggesting moderate colloidal stability and a propensity for adsorbing positively charged pollutants. Photocatalytic experiments demonstrated efficient degradation of ciprofloxacin (concentration range: 5–20&#xa0;ppm) under visible light irradiation. Optimal conditions were identified at a catalyst loading of 1.5&#xa0;mg·L⁻<sup>1</sup>, neutral pH (7), and a reaction time of 50&#xa0;min. The adsorption behavior conformed well to both Freundlich and Langmuir isotherm models (R<sup>2</sup> = 0.95) and followed pseudo-first-order kinetics. Under these conditions, the CQD/TiO₂ nanocomposite achieved a 97.3% degradation efficiency for ciprofloxacin within 50&#xa0;min, outperforming pure TiO₂. Furthermore, the composite retained 93% of its photocatalytic activity after four successive cycles, indicating excellent reusability. Brunauer–Emmett–Teller (BET) surface area analysis revealed a high specific surface area of 197 m<sup>2</sup>·g⁻<sup>1</sup>, enhancing adsorption capacity and providing abundant reactive sites. The significant retention of material (93%) after extended use suggests the potential applicability of the CQD/TiO₂ nanocomposite as an electrode material in future energy storage devices such as batteries and supercapacitors.</p>

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Hydrothermal Synthesis and Photocatalytic Performance of CQDs/TiO₂ Nanocomposites for CIP Removal

  • 期刊论文

  • 发表日期：

    2025年11月17日

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  • Qurtulen Qurtulen,
  • Asrar Ahmad,
  • Mohammad Mujahid,
  • Omar Al-Hartomy,
  • Prince Mufti Ziaul Hasan

摘要

This study presents the development of a sustainable carbon quantum dot (CQD)/titanium dioxide (TiO₂) nanocomposite designed for the photocatalytic degradation of antibiotic pollutants in water through advanced oxidation processes (AOPs). CQDs were synthesized via a green, one-step hydrothermal method using lemon peel waste and subsequently integrated with TiO₂ nanoparticles. Comprehensive structural and surface characterizations—including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED)—confirmed the presence of functional groups such as carboxyl (–COOH), ether (C–O–C), and titanium-oxygen (Ti–O) bonds. The analyses also verified the anatase/rutile crystalline phase of TiO₂ structure, with consistent results across imaging and diffraction techniques. Ultraviolet–visible (UV–vis) spectroscopy revealed a π–π* transition peak at 280 nm and determined the bandgap energy to be 2.8 eV. Zeta potential measurements indicated a negatively charged surface, attributed to the carboxyl groups on CQDs, suggesting moderate colloidal stability and a propensity for adsorbing positively charged pollutants. Photocatalytic experiments demonstrated efficient degradation of ciprofloxacin (concentration range: 5–20 ppm) under visible light irradiation. Optimal conditions were identified at a catalyst loading of 1.5 mg·L⁻1, neutral pH (7), and a reaction time of 50 min. The adsorption behavior conformed well to both Freundlich and Langmuir isotherm models (R2 = 0.95) and followed pseudo-first-order kinetics. Under these conditions, the CQD/TiO₂ nanocomposite achieved a 97.3% degradation efficiency for ciprofloxacin within 50 min, outperforming pure TiO₂. Furthermore, the composite retained 93% of its photocatalytic activity after four successive cycles, indicating excellent reusability. Brunauer–Emmett–Teller (BET) surface area analysis revealed a high specific surface area of 197 m2·g⁻1, enhancing adsorption capacity and providing abundant reactive sites. The significant retention of material (93%) after extended use suggests the potential applicability of the CQD/TiO₂ nanocomposite as an electrode material in future energy storage devices such as batteries and supercapacitors.