PEROVSKITE PHOTOCATALYSTS FOR THE DECOMPOSITION OF ODOR MOLECULES

In this work, innovative materials were synthesized and investigated for the decontamination of air matrix. In more detail, this project primarily focuses on the photocatalytic decomposition of propionic acid (PA), an organic molecule responsible for odorous environment. Additionally, the photodecomposition of ethanol was studied as a model molecule of VOCs and one of the transformation products (TPs) of propionic acid photodegradation. The primary goal is to optimize an innovative photocatalyst capable of decomposing these two organic VOC pollutants (PA and ethanol) under LED irradiation, with a focus on indoor environments and in line with the importance of indoor air quality. To broaden the potential applications of the synthesized photocatalysts, they were also tested for the degradation of Nitrogen Oxides (NOx), which are one of the main contributors to poor air quality in industrial and urban areas. The investigation began with the benchmark TiO2 due to its wide applications in industry, and a series of micro-sized TiO2-based photocatalysts was synthesized. Given the restrictions of this photocatalyst, such as its wide bandgap energy that mainly makes it active under UV irradiation, surface modification with noble metals was proposed as a strategy to expand its photoactivity under indoor light sources. Nevertheless, noble metals' high prices and resource shortage limit their applications. In fact, many studies aim to find alternatives based on cheaper and more abundant materials. However, to date, noble metals recovery from wastewater from particular manufacturing processes has not been given much credit, although this approach should be considered a valid progressive approach to obtain the precursors of noble metal NPs at a low cost. In this regard, in line with the global perspectives to enhance the efforts towards circular economy processes, this research aimed to synthesize multiple noble metals-modified micrometric TiO2-based photocatalysts through a sustainable perspective toward the valorization of wastewaters, as all the noble metal sources came from metal-enriched wastewaters. In this step, three noble metals (Ag, Au, and Pt) were individually decorated on micrometric commercial TiO2 (1077, Kronos) with different quantities. (between 1 and 8% (wt.) of Ag NPs, and between 0.1 to 1% (wt.) of Au and/or Pt NPs). The most performant single metal photocatalyst (8%Ag/TiO2) was selected to be further decorated with Au, and/or Pt NPs with their optimized performant quantity (0.1% (wt.)), aiming to investigate multistep decorated samples’ photoactivity. The photocatalytic activity of these samples was tested for PA and NOx under both LED and UV irradiations. Tuning properly the noble metal decoration steps, two separate photocatalysts were optimized for the degradation of each pollutant. This work was published in Catalysis Communications Journal in July 2023. As part of the main objective of this Ph.D. project, a range of advanced, innovative SrTiO3 (STO) perovskite materials were synthesized and analyzed. The high thermal stability of STO makes it ideal for applications that involve high surface thermal treatments, such as in the ceramic industry. In such applications, TiO2 needs to be replaced with a material that has higher thermal stability, as anatase TiO2 above 600 °C undergoes a phase transition to rutile, resulting in a significant loss of photoactivity. In this step, the photocatalytic activity of different STO-based catalysts for the photocatalytic degradation of PA and ethanol, was studied. Starting with commercial micrometric STO (particle size ~ 100 nm) and the nanometric one (particle size ~ 30 nm), a series of STO- based material were synthesized. In this regard, STO was synthesized with a previous optimized condition by solgel method with H2O/ethanol (1:3) as solvent. Modified STO was prepared using two different methods with the goal of enhancing its activity under visible light: the first involved a multistep synthesis, where Ag⁰ NPs were initially synthesized through chemical reduction and then applied to the previously synthesized STO sample. The second approach involved incorporating the Ag NPs directly during the STO synthesis process from the beginning. The photocatalytic performance of these series of photocatalyst was evaluated by PA and ethanol degradation under both UV and LED light. In the final phase of this project, an alternative approach was explored to enhance the photoactivity of the perovskite STO photocatalyst. This approach involved doping STO with non-noble metals, and to improve the efficiency of the doping process, an ultrasound-assisted method was employed for synthesis. The materials were synthesized in collaboration with the Università degli Studi di Perugia and Clausthal University of Technology, Germany. For this step, non-noble metals such as Bi, Fe, Ni, and Cu were selected as dopants. The synthesized materials were tested for PA, ethanol, and NOx photodegradation under LED and UV irradiation. When the photocatalytic VOCs abatement tests were performed under LED irradiation, the low intensity of the light source caused an energy insufficiency for the initiation of charges separation and the start of photocatalytic processes, while the synthesized perovskites exhibited outstanding photocatalytic activity when exposed to UV irradiation.