Investigation of photocatalytic nitrate reduction over different nanomaterials
Modabber, Zeinab (2025)
Diplomityö
2025
School of Engineering Science, Kemiantekniikka
Kaikki oikeudet pidätetään.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2025061266972
https://urn.fi/URN:NBN:fi-fe2025061266972
Tiivistelmä
Nitrate contamination in water sources poses serious environmental and health risks, such as eutrophication and methemoglobinemia. Conventional nitrate removal technologies often face limitations, including high operational costs and byproduct management challenges, highlighting the need for effective and sustainable alternatives. This study investigates photocatalytic nitrate reduction (PNR) using silver-modified titanium dioxide (Ag/TiO₂) nanomaterials, evaluating their efficiency, selectivity, and reusability under varying conditions, including light intensity, pH, initial nitrate concentration, catalyst loading, and hole scavenger presence.
Seven photocatalysts were screened, with 0.5%, 2%, and 10% Ag/TiO₂ demonstrating the highest nitrate removal efficiencies. Complete nitrate reduction was achieved under optimized conditions, with 0.5% Ag/TiO₂ exhibiting superior performance at lower light intensities (200), while 2% Ag/TiO₂ required higher intensities (600). The results highlight the critical role of an acidic environment in promoting nitrate reduction and show that formic acid, as a hole scavenger, enhances efficiency likely by generating CO₂•⁻ radicals and reducing charge recombination. Dissolved oxygen was found to inhibit the process, emphasizing the importance of argon purging.
Product selectivity varied with experimental parameters: 0.5% Ag/TiO₂ favored nitrogen (N₂) formation (up to 96% selectivity), whereas 2% Ag/TiO₂ produced more ammonium (NH₄⁺) (68%). The 0.5% Ag/TiO₂ retained 70% activity over three reuse cycles. These findings underscore the potential of Ag/TiO₂ photocatalysts for sustainable nitrate removal, balancing high efficiency with minimal harmful byproducts. Future research should explore scalability, competing anion effects, and optimization of higher Ag loadings.
Seven photocatalysts were screened, with 0.5%, 2%, and 10% Ag/TiO₂ demonstrating the highest nitrate removal efficiencies. Complete nitrate reduction was achieved under optimized conditions, with 0.5% Ag/TiO₂ exhibiting superior performance at lower light intensities (200), while 2% Ag/TiO₂ required higher intensities (600). The results highlight the critical role of an acidic environment in promoting nitrate reduction and show that formic acid, as a hole scavenger, enhances efficiency likely by generating CO₂•⁻ radicals and reducing charge recombination. Dissolved oxygen was found to inhibit the process, emphasizing the importance of argon purging.
Product selectivity varied with experimental parameters: 0.5% Ag/TiO₂ favored nitrogen (N₂) formation (up to 96% selectivity), whereas 2% Ag/TiO₂ produced more ammonium (NH₄⁺) (68%). The 0.5% Ag/TiO₂ retained 70% activity over three reuse cycles. These findings underscore the potential of Ag/TiO₂ photocatalysts for sustainable nitrate removal, balancing high efficiency with minimal harmful byproducts. Future research should explore scalability, competing anion effects, and optimization of higher Ag loadings.