Odín Reyes-Vallejo, Rocío Magdalena Sánchez-Albores, José Escorcia-García, Abumale Cruz-Salomón, Pascual Bartolo-Pérez, Ashok Adhikari, Maritza Del Carmen Hernández-Cruz, Héctor Hiram Torres-Ventura, Héctor Armando Esquinca-Avilés
{"title":"Green synthesis of CaO-Fe₃O₄ composites for photocatalytic degradation and adsorption of synthetic dyes.","authors":"Odín Reyes-Vallejo, Rocío Magdalena Sánchez-Albores, José Escorcia-García, Abumale Cruz-Salomón, Pascual Bartolo-Pérez, Ashok Adhikari, Maritza Del Carmen Hernández-Cruz, Héctor Hiram Torres-Ventura, Héctor Armando Esquinca-Avilés","doi":"10.1007/s11356-025-36310-w","DOIUrl":null,"url":null,"abstract":"<p><p>The efficient removal of synthetic dyes, such as methylene blue (MB) and malachite green (MG), continues to pose a significant challenge due to their high stability, toxicity, and resistance to conventional treatment methods. In this study, CaO-Fe₃O₄ compounds were synthesized using a sustainable ball-milling technique, utilizing calcium oxide derived from eggshells and Fe₃O₄. The compounds were calcined at temperatures ranging from 200 to 800 °C to optimize their structural and photocatalytic properties. The sample calcined at 400 °C exhibited the highest surface area (17.86 m<sup>2</sup>/g), the narrowest bandgap (2.10 eV), and the coexistence of CaO, Ca(OH)₂, and γ-Fe₂O₃ phases, making it an ideal candidate for achieving high dye removal efficiency. Under visible light, this sample completely degraded MB at 10 ppm within 30 min, following pseudo-first-order kinetics with a rate constant (kₐₚₚ) of 0.110 min<sup>-1</sup> and a half-life (t₁<sub>/</sub>₂) of 6.30 min. At an MB concentration of 50 ppm, complete degradation was achieved in 90 min. Radical scavenging experiments indicated that superoxide radicals (·O₂<sup>-</sup>) played a key role in the degradation mechanism. For MG (100 ppm), the maximum adsorption capacity (qₑ) was 1111.11 mg/g, fitting the Langmuir model (R<sup>2</sup> = 0.996) with an equilibrium constant (K<sub>L</sub>) of 0.6822 L/mg, indicating a highly favorable process. The adsorption kinetics followed a pseudo-second-order model (R<sup>2</sup> ≈ 0.999), suggesting chemisorption as the rate-limiting step. Thermodynamic parameters confirmed that MG adsorption was spontaneous and endothermic, with negative Gibbs free energy, positive enthalpy, and increased entropy. This study proposes an eco-friendly and efficient approach for dye removal, integrating waste valorization.</p>","PeriodicalId":545,"journal":{"name":"Environmental Science and Pollution Research","volume":" ","pages":""},"PeriodicalIF":5.8000,"publicationDate":"2025-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Environmental Science and Pollution Research","FirstCategoryId":"93","ListUrlMain":"https://doi.org/10.1007/s11356-025-36310-w","RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"0","JCRName":"ENVIRONMENTAL SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
The efficient removal of synthetic dyes, such as methylene blue (MB) and malachite green (MG), continues to pose a significant challenge due to their high stability, toxicity, and resistance to conventional treatment methods. In this study, CaO-Fe₃O₄ compounds were synthesized using a sustainable ball-milling technique, utilizing calcium oxide derived from eggshells and Fe₃O₄. The compounds were calcined at temperatures ranging from 200 to 800 °C to optimize their structural and photocatalytic properties. The sample calcined at 400 °C exhibited the highest surface area (17.86 m2/g), the narrowest bandgap (2.10 eV), and the coexistence of CaO, Ca(OH)₂, and γ-Fe₂O₃ phases, making it an ideal candidate for achieving high dye removal efficiency. Under visible light, this sample completely degraded MB at 10 ppm within 30 min, following pseudo-first-order kinetics with a rate constant (kₐₚₚ) of 0.110 min-1 and a half-life (t₁/₂) of 6.30 min. At an MB concentration of 50 ppm, complete degradation was achieved in 90 min. Radical scavenging experiments indicated that superoxide radicals (·O₂-) played a key role in the degradation mechanism. For MG (100 ppm), the maximum adsorption capacity (qₑ) was 1111.11 mg/g, fitting the Langmuir model (R2 = 0.996) with an equilibrium constant (KL) of 0.6822 L/mg, indicating a highly favorable process. The adsorption kinetics followed a pseudo-second-order model (R2 ≈ 0.999), suggesting chemisorption as the rate-limiting step. Thermodynamic parameters confirmed that MG adsorption was spontaneous and endothermic, with negative Gibbs free energy, positive enthalpy, and increased entropy. This study proposes an eco-friendly and efficient approach for dye removal, integrating waste valorization.
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