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<p>Malachite Green (MG) is a toxic and persistent organic dye that causes serious environmental problems due to its resistance to conventional wastewater treatment processes. Malachite Green has been reported to exhibit acute toxicity to aquatic organisms with LC50 values in the range of mg/L, and its use has been restricted or banned in many countries due to its carcinogenic and mutagenic effects. This study aimed to develop an efficient La-doped TiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub> composite photocatalyst for MG removal and to clarify the effects of operational parameters using statistical optimization. The TiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub> composite was synthesized through a co-precipitation method, followed by La impregnation to obtain the La-doped TiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub> photocatalyst. The prepared catalyst was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, UV–Vis diffuse reflectance spectroscopy, and Brunauer–Emmett–Teller analysis. A central composite design coupled with response surface methodology was applied to evaluate the effects of pH, irradiation time, and temperature on photocatalytic performance under visible light irradiation using a 500&#xa0;W mercury lamp equipped with a UV cut-off filter (λ &gt; 420&#xa0;nm). The prepared La/TiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub> composite exhibited a crystallite size of 17.02&#xa0;nm and a specific surface area of 110.13&#xa0;m<sup>2</sup>&#xa0;g<sup>−1</sup> with mesoporous characteristics. The highest experimentally observed MG degradation efficiency reached 97.07% at pH 7, 40&#xa0;°C, and 35&#xa0;min irradiation time. In contrast, RSM-based numerical optimization provided a model-predicted optimum response within the experimental design space, highlighting the statistical interactions among variables rather than a single experimental maximum. The analysis confirmed that pH and irradiation time had the most significant influence on photocatalytic performance, along with their interaction effects. The catalyst retained approximately 93% of its initial activity after five consecutive cycles, demonstrating good stability. These results indicated that the La-doped TiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub> composite provided an effective photocatalytic platform for organic dye removal and wastewater remediation applications.</p>

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Optimization of Malachite Green photodegradation using a La-doped TiO2–Fe2O3 composite photocatalyst: characterization, photocatalytic performance, and response surface methodology approach

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • Nastaran Parsafard

摘要

Malachite Green (MG) is a toxic and persistent organic dye that causes serious environmental problems due to its resistance to conventional wastewater treatment processes. Malachite Green has been reported to exhibit acute toxicity to aquatic organisms with LC50 values in the range of mg/L, and its use has been restricted or banned in many countries due to its carcinogenic and mutagenic effects. This study aimed to develop an efficient La-doped TiO2–Fe2O3 composite photocatalyst for MG removal and to clarify the effects of operational parameters using statistical optimization. The TiO2–Fe2O3 composite was synthesized through a co-precipitation method, followed by La impregnation to obtain the La-doped TiO2–Fe2O3 photocatalyst. The prepared catalyst was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, UV–Vis diffuse reflectance spectroscopy, and Brunauer–Emmett–Teller analysis. A central composite design coupled with response surface methodology was applied to evaluate the effects of pH, irradiation time, and temperature on photocatalytic performance under visible light irradiation using a 500 W mercury lamp equipped with a UV cut-off filter (λ > 420 nm). The prepared La/TiO2–Fe2O3 composite exhibited a crystallite size of 17.02 nm and a specific surface area of 110.13 m2 g−1 with mesoporous characteristics. The highest experimentally observed MG degradation efficiency reached 97.07% at pH 7, 40 °C, and 35 min irradiation time. In contrast, RSM-based numerical optimization provided a model-predicted optimum response within the experimental design space, highlighting the statistical interactions among variables rather than a single experimental maximum. The analysis confirmed that pH and irradiation time had the most significant influence on photocatalytic performance, along with their interaction effects. The catalyst retained approximately 93% of its initial activity after five consecutive cycles, demonstrating good stability. These results indicated that the La-doped TiO2–Fe2O3 composite provided an effective photocatalytic platform for organic dye removal and wastewater remediation applications.