Evaluation of structural and photocatalytic properties of g-C₃N₄/ZnO/carbon xerogel composites synthesized with different types of tannin

ABSTRACT

The influence of different carbonaceous precursors on the development of g-C₃N₄/carbon xerogel/ZnO photocatalysts was explored. The coupling between zinc oxide and graphitic carbon nitride is suitable for boosting the degradation of organic pollutants. The function of carbon xerogel is to improve charge transfer and increase catalyst activity under visible radiation. Different commercial tannins (PHENOTAN AP, AG and BS) were used to evaluate the precursor effect on the composite’s properties. X-ray diffractometry showed that the materials have the hexagonal crystal structure of zinc oxide. Diffuse reflectance spectra obtained exhibited the characteristic behavior of zinc oxide (λ<420nm). Furthermore, the material prepared with PHENOTAN AP had a superior visible light absorption capacity. The scanning electron microscopy analysis showed that the materials are composed of clusters of particles similar to spheres and the materials in particle size. The dispersive energy spectroscopy analysis was performed only for the material prepared with PHENOTAN AP and evidenced that all elements are well distributed in g-C₃N₄/carbon xerogel/ZnO matrix. The nitrogen adsorption isotherms of the materials showed that the isotherms characteristics (type IV-H3), whereas the material synthesized with PHENOTAN AP has the largest specific surface area. The pore distribution of the materials showed that the materials had most developed porous structure, with pores ranging from 20 nm to 40 nm. Through thermogravimetry analysis it is possible to observe that the PHENOTAN AP has superior thermal stability. It was observed that the precursor used in the synthesis of composites significantly influences the photocatalytic activity of the materials. The composite with the highest photodegradation efficiency of 4-Chlorophenol under solar radiation was prepared with PHENOTAN AP, since it has a superior visible radiation absorption, greater amount of carbon, greater surface area and greater volume of pores. It is also worth noting that there was no significant adsorption of 4-chlorophenol in the materials synthesized, as well as no leaching of the photocatalysts during the process.

Keywords
ZnO; Carbon xerogel; Photocatalysis; Tannin