Příprava materiálů na bázi g-C3N4 a jejich analytická charakterizace pro environmentální aplikace

Mgr. Arianit GASHI

Doctoral thesis

Preparation of g-C3N4 based material and analytical characterization for environmental applications

Abstract:

Problems with global energy and environmental pollution have led on finding the alternatives worldwide. Therefore, our objectives were focused on preparation of different composites, like C-rich-g-C3N4, N-rich porous carbon and F-doped-g-C3N4, based on g-C3N4 material, with possible applications in photocatalysis. C-rich graphitic carbonitride materials (CNx) with a large range of composition have been prepared in different ratios thanks to the self-assembly of melamine (M) and a panel of polycarboxylic acid (A) such as oxalic, tartaric and citric acid (Chapter 3). This route required simple precipitation process, using water as a solvent. The thermal conversion of the formed adducts (MAy), led to CNx phases with x ranging from 0.66 to 1.4 (x =1.33 for g-C3N4 for comparison). It appears that the increase of the C content is associated to a disappearance of the long-range order of heptazine units, and to an increase of the subnanometric carbon-rich cluster size within the graphitic g-C3N4 structure. The materials described in the Chapter 3 (calcined under inert atmosphere at 550 °C), were further pyrolized in oxidized atmosphere (air) in order to prepare N-rich porous carbon material. Thermal stability/reactivity with oxygen, of g-C3N4 and C-rich-g-C3N4 samples, with different C/N ratios was investigated under different range of temperature, (470-650 °C). The C-rich-g-C3N4 materials display a distinct thermal behavior in air (or inert atmosphere), compared to the basic g-C3N4. This behavior is explain by lower thermal stability (and decomposition) of g-C3N4 domains compared to C-rich phases within the composite. Controlled oxidation at different temperature, have produced highly porous material with surface area up to 600 m2 g-1. Disorder of materials is increased, evidenced by increase of interlayer distance and D peak. The highly doped g-C3N4 based materials were prepared via pure F2 gas phase method, at room temperature (Chapter 5). The level of fluorine doping depends on the chemical nature and structure of materials. The C-rich-g-C3N4 sample has lower F content compared to g-C3N4, with an increase of atomic ratio from 9 at. % up to 26 at. %. All fluorinated samples have exhibited the narrowing band gap in comparision with pristine materials, from 2.66 eV to 2.57 eV, influencing photocatalytic properties. Visible light was efficient to produce paramagnetic species for fluorinated g-C3N4 samples, in contrast to C-rich-g-C3N4. Thereafter, materials were evaluated in photocatalytic point of view. Methyl orange solution was used as a target pollutant to perform photodegradation experiments under visible light irradiation. The results showed that all fluorinated g-C3N4 based photocatalysts, have enhanced the photocatalytic activities in comparison with the pristine g-C3N4 based samples.

Abstract:

Problems with global energy and environmental pollution have led on finding the alternatives worldwide. Therefore, our objectives were focused on preparation of different composites, like C-rich-g-C3N4, N-rich porous carbon and F-doped-g-C3N4, based on g-C3N4 material, with possible applications in photocatalysis. C-rich graphitic carbonitride materials (CNx) with a large range of composition have been prepared in different ratios thanks to the self-assembly of melamine (M) and a panel of polycarboxylic acid (A) such as oxalic, tartaric and citric acid (Chapter 3). This route required simple precipitation process, using water as a solvent. The thermal conversion of the formed adducts (MAy), led to CNx phases with x ranging from 0.66 to 1.4 (x =1.33 for g-C3N4 for comparison). It appears that the increase of the C content is associated to a disappearance of the long-range order of heptazine units, and to an increase of the subnanometric carbon-rich cluster size within the graphitic g-C3N4 structure. The materials described in the Chapter 3 (calcined under inert atmosphere at 550 °C), were further pyrolized in oxidized atmosphere (air) in order to prepare N-rich porous carbon material. Thermal stability/reactivity with oxygen, of g-C3N4 and C-rich-g-C3N4 samples, with different C/N ratios was investigated under different range of temperature, (470-650 °C). The C-rich-g-C3N4 materials display a distinct thermal behavior in air (or inert atmosphere), compared to the basic g-C3N4. This behavior is explain by lower thermal stability (and decomposition) of g-C3N4 domains compared to C-rich phases within the composite. Controlled oxidation at different temperature, have produced highly porous material with surface area up to 600 m2 g-1. Disorder of materials is increased, evidenced by increase of interlayer distance and D peak. The highly doped g-C3N4 based materials were prepared via pure F2 gas phase method, at room temperature (Chapter 5). The level of fluorine doping depends on the chemical nature and structure of materials. The C-rich-g-C3N4 sample has lower F content compared to g-C3N4, with an increase of atomic ratio from 9 at. % up to 26 at. %. All fluorinated samples have exhibited the narrowing band gap in comparision with pristine materials, from 2.66 eV to 2.57 eV, influencing photocatalytic properties. Visible light was efficient to produce paramagnetic species for fluorinated g-C3N4 samples, in contrast to C-rich-g-C3N4. Thereafter, materials were evaluated in photocatalytic point of view. Methyl orange solution was used as a target pollutant to perform photodegradation experiments under visible light irradiation. The results showed that all fluorinated g-C3N4 based photocatalysts, have enhanced the photocatalytic activities in comparison with the pristine g-C3N4 based samples.

Keywords

graphitic carbon nitride, adducts, fluorination, photocatalysis, photodegradation, oxidation, N-rich porous carbon, methyl orange

Language used: English

Date on which the thesis was submitted / produced: 4. 7. 2022

Accessible from:: 31. 12. 2999

Thesis defence

• Date of defence: 5. 9. 2022
• Supervisor: doc. RNDr. Roman Maršálek, Ph.D., doc. RNDr. Roman Maršálek, Ph.D.

University of Ostrava

Faculty of Science

Doctoral programme / field:
Analytical Chemistry / Analytical chemistry of Heterogenous Systems