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Johan Andres Vargas Rueda, Speaker at Catalysis Conference
Metropolitan Autonomous University, Mexico
Title : Functional catalytic materials based on prussian blue analog-modified and bismuth vanadate to degradation of cyanide ions

Abstract:

Bismuth vanadate has been reported as a promising active semiconductor for visible light harvesting. However, the rapid recombination of charge carriers has limited its photocatalytic properties. As an alternative route for the treatment of contaminated water containing cyanide ions, latent catalytic Fe-[Fe(CN)]/BiVO4, Fe-[Co(CN)]/BiVO4, and Co-[Co(CN)]/BiVO4 have been investigated. The photocatalytic mechanism of Prussian Blue analog-modified and bismuth vanadate involves the separation of electrons and holes under UV-Visible irradiation. The strong oxidative/reductive potential of both photogenerated holes and electrons are important to oxidize cyanide surrounding the catalyst surface. Cyanate is about 1/100 as toxic as cyanide, with a median lethal dose (LD50 oral for rats) equal to 567 mg/kg, versus 5.7333 mg/kg for cyanide. It is therefore recommended that cyanide be converted to cyanate.

The BiVO4 particles were synthesized by the sol-gel method. Characterization of structural and optical properties indicated that BiVO4 has a monoclinic crystal structure, a direct band gap energy of 2.5 eV, and Urbach energy values around 88 meV. Subsequently, the FeIII-[Fe(CN)]/BiVO4, FeIII-[Co(CN)]/BiVO4, and CoII-[Co(CN)]/BiVO4 composites were obtained by the precipitation method assisted by ultrasonic methods. Structural, optical, and morphological analysis, elemental chemical composition, BET surface area, catalytic tests, and selectivity were carried out.

The photocatalytic activity under UV-Visible light irradiation of the FeIII-[Fe(CN)]/BiVO4, FeIII-[Co(CN)]/BiVO4, and CoII-[Co(CN)]/BiVO4 composites were evaluated by the 4500-CN? D titrimetric method for the quantification of cyanide ions. The reaction performance of the FeIII-[Fe(CN)]/BiVO4 sample in the degradation of cyanide was found to be efficient (96.43% ± 0.05) with a reaction time equal to 5 hours. The cyanide oxidation was confirmed by the analysis of ammonia using the Nessler’s reagent method, which showed a low content of NH4(ac).

The selectivity test with two colorants (methylene blue and methyl red) and two drugs (naproxen and ciprofloxacin) for the Fe4[Fe(CN)6]3/BiVO4 system was conducted. The results indicated that the Fe4[Fe(CN)6]3/BiVO4 catalyst has a greater influence on cyanide ions. So, the high efficiency of the photocatalytic reaction for the removal of free cyanide can be ascribed to the enhanced of catalytic properties of BiVO4, which diminish the recombination of photoinduced charge carriers.

Audience Take Away

  • The synthesis of a new generation of photocatalytic materials based on Fe4[Fe(CN)6]3/BiVO4 for the oxidation reactions of cyanide ions showed high efficiency in removal. Furthermore, its potential application in drug degradation presents a research opportunity to explore the treatment of wastewater containing a mixture of drugs. Therefore, understanding the relationship between the physicochemical properties of the catalyst and its catalytic performance will enable the audience to comprehend that Fe4[Fe(CN)6]3/BiVO4 is a functional material not only for cyanide oxidation but also for drug degradation and potentially other organic pollutants.
  • BiVO4 is an active semiconductor for visible light harvesting. However, the rapid recombination rate of photoinduced electron-hole pairs has limited its photocatalytic properties. As an alternative to improving the photocatalytic properties of BiVO4, composites synthesized with Prussian blue analog-modified coupled with bismuth vanadate were studied. Strategies to enhance charge separation and slow down the recombination rate of charge carriers for cyanide oxidation by the Fe4[Fe(CN)6]3/BiVO4 catalyst have been successfully implemented. For this reason, this research could explore the design of a photoreactor with a solar collector and its catalytic evaluation of Prussian blue analog-modified and bismuth vanadate catalysts for the degradation of cyanide ions originating from the metallurgical industry or for drug degradation, due to modified catalytic, optical, and electrical properties.
  • Cyanide may be found as a contaminant in wastewater from metal processing plants (e.g., metal cleaning, metal coating or electroplating, and steel tempering), mining (e.g., ore leaching), automobile parts manufacturing, photographic processing, pharmaceuticals, and plastics industries among others. One important aspect to consider is that cyanide-bearing wastewaters need to be treated before they react with hydronium ions to form hydrogen cyanide, which is the deadliest form of cyanide. Cyanate is about 1/100 as toxic as cyanide, with a median lethal dose (LD50 oral for rats) equal to 567 mg/kg, versus 5.7333 mg/kg for cyanide. It is recommended, therefore, that cyanide be converted to cyanate. Thus, photocatalytic removal of cyanide waste by Fe4[Fe(CN)6]3/BiVO4 catalyst could be a practical solution to wastewater treatment that contains this organic pollutant.

Biography:

Johan Andrés Vargas Rueda, Metallurgical Engineer at the Universidad Industrial de Santander (UIS), Colombia - Bucaramanga, Master's in Materials Science and Engineering at the Universidad Autónoma Metropolitana (UAM), México - Ciudad de México, and doctoral student in the final year of the Process Engineering program at the same institution. Awarded the Best Master's Thesis by the Mexican Society of Surface and Materials Science and Technology, A.C., in 2021, for the thesis titled "Synthesis and characterization of thin films of Cu2SnS3 (CTS) and ZnS using the chemical bath deposition technique". Currently, I am serving as a co-advisor for two undergraduate research projects at the UAM.

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