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<p>The increasing environmental threat posed by stable and toxic thiocyanate (SCN<sup>−</sup>) in hydrometallurgical wastewater highlights the need for efficient and environmentally friendly removal technologies. Here, a folded carbon nitride (FCN)/TiO<sub>2</sub> (TFCN) composite photocatalyst was synthesized via a sol–gel method and systematically optimized (TiO<sub>2</sub>: FCN = 1:4, 180&#xa0;°C calcination for 18&#xa0;h). The TFCN composite exhibits an outstanding specific surface area (71.77 m<sup>2</sup>/g) and exceptional photocatalytic performance. Under the best tested conditions (initial SCN<sup>−</sup> concentration = 200&#xa0;mg/L, TFCN dosage = 0.5&#xa0;g, pH = 12, LED wavelength = 405&#xa0;nm, LED power = 15 W), 98% SCN<sup>−</sup> degradation efficiency was achieved. Free radical scavenging experiments and electron paramagnetic resonance (EPR) studies indicated that superoxide radicals (·O<sub>2</sub><sup>−</sup>) and holes (h<sup>+</sup>) are the dominant reactive species responsible for the degradation. The enhanced activity is tentatively associated with a proposed Type-II-like interfacial charge-transfer pathway between FCN and TiO<sub>2</sub>, which may facilitate photogenerated charge separation. Intermediate-product analysis showed that SCN<sup>−</sup> was converted mainly into liquid-phase inorganic products, including SO<sub>4</sub><sup>2−</sup>, CO<sub>3</sub><sup>2−</sup>, and NH<sub>4</sub><sup>+</sup>. Meanwhile, total cyanide exhibited a transient rise–fall profile during the reaction, suggesting the formation and subsequent conversion of cyanide-related intermediates under continued irradiation. This result indicates efficient SCN<sup>−</sup> conversion while limiting the accumulation of cyanide-related species in the measured liquid phase. This work presents TFCN as a promising photocatalyst for SCN<sup>−</sup> abatement and provides cautious mechanistic insight into photo-driven SCN<sup>−</sup> conversion in both simulated and real wastewater systems.</p>

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Enhanced Photocatalytic Degradation of Thiocyanate Using an FCN/TiO2 Heterojunction: Performance, Mechanism, and Real Wastewater Application

  • 期刊论文

  • 发表日期：

    2026年6月18日

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  • Lin Qi,
  • Zihui Xu,
  • Hongtao Jing,
  • Mingqing Zhang,
  • Lucheng Zhang,
  • Qi Liu

摘要

The increasing environmental threat posed by stable and toxic thiocyanate (SCN−) in hydrometallurgical wastewater highlights the need for efficient and environmentally friendly removal technologies. Here, a folded carbon nitride (FCN)/TiO2 (TFCN) composite photocatalyst was synthesized via a sol–gel method and systematically optimized (TiO2: FCN = 1:4, 180 °C calcination for 18 h). The TFCN composite exhibits an outstanding specific surface area (71.77 m2/g) and exceptional photocatalytic performance. Under the best tested conditions (initial SCN− concentration = 200 mg/L, TFCN dosage = 0.5 g, pH = 12, LED wavelength = 405 nm, LED power = 15 W), 98% SCN− degradation efficiency was achieved. Free radical scavenging experiments and electron paramagnetic resonance (EPR) studies indicated that superoxide radicals (·O2−) and holes (h+) are the dominant reactive species responsible for the degradation. The enhanced activity is tentatively associated with a proposed Type-II-like interfacial charge-transfer pathway between FCN and TiO2, which may facilitate photogenerated charge separation. Intermediate-product analysis showed that SCN− was converted mainly into liquid-phase inorganic products, including SO42−, CO32−, and NH4+. Meanwhile, total cyanide exhibited a transient rise–fall profile during the reaction, suggesting the formation and subsequent conversion of cyanide-related intermediates under continued irradiation. This result indicates efficient SCN− conversion while limiting the accumulation of cyanide-related species in the measured liquid phase. This work presents TFCN as a promising photocatalyst for SCN− abatement and provides cautious mechanistic insight into photo-driven SCN− conversion in both simulated and real wastewater systems.