Comparing the catalytic mechanisms of different surface terminations of strontium titanate for the degradation of organic pollutants.

Senthilmurugan, Balasurya (2024). Comparing the catalytic mechanisms of different surface terminations of strontium titanate for the degradation of organic pollutants. Mémoire. Québec, Maitrise en sciences de l'énergie et des matériaux, Université du Québec, Institut national de la recherche scientifique, 112 p.

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Résumé

In the past decades, environmental water pollution has emerged as a major challenge that calls for scalable water treatment as water scarcity adversely affects more than 40% of the world population. Semiconductor-based nanomaterials have been widely deployed as photocatalysts as they are effective in making use of the high-energy portion of the solar spectrum. In this context, strontium titanate, a wide-band-gap semiconductor, offers a noticeable catalytic efficiency for waste water remediation. While the bulk properties have been subject to substantial investigation, research on the impact of the surface still remains in its infancy. Nanoparticles of strontium titanate provide for surfaces with different Miller indices but as these particles grow larger, two surface orientations prevail: (100) and (110). We focus on the (100) surface that has mixed terminations under otherwise arbitrary conditions of production: (100) planes have vicinal surfaces that are either SrO- or TiO2-terminated. With two possible terminations, the question arises as to whether these surface terminations affect the catalytic performance. We implement a strategy to control the surface terminations of SrTiO3: (1) Hydrothermal etching removes the SrO layer, resulting in pure TiO2-terminated SrTiO3 and (2) Annealing above 1000°C under ambient atmosphere results in pure SrO-terminationed SrTiO3. Raman spectroscopy shows the signature of a carbonate (CO₃^2-) contamination that selectively chemisorbs onto an SrO-terminated surface while it is not observed in a TiO2-terminated SrTiO3 surface. This carbonate signature is attributed to the adsorption of CO2 onto SrO terraces causing the formation of SrCO3. The photocatalytic activity of surface-engineered SrTiO₃ was evaluated to study the effects of surface terminations and the impact of SrCo₃ on the degradation of toxic pollutants. A combination of catalytic processes (sono-, photo-catalysis) was employed to determine whether different catalytic mechanisms may be combined to accelerate the degradation of methyl orange as a model pollutant. Considering that strontium titanate is neither piezo-, nor pyroelectric, the focus of the investigation was on the effect of sono-catalysis, often attributed to cavitation under sonification. A relevant question of this MSc thesis relates to the nature of the rate limiting step in catalytic reactions. Compared to their photovoltaic counterparts, where photogenerated charges deliver energy in an external circuit, commonly achieving energy conversion efficiencies of 0.1 (10%), the energy conversion efficiency of photocatalysts is roughly 4 to 5 orders of magnitude lower. This cannot be explained by any aspect of the light-induced charge transport inside the catalyst as it is exactly the same for photovoltaics and photocatalysts. We identify the mass transport at the catalyst’s surface as the rate limiting step and discuss the effect of sonification in terms of a positive contribution to mass transport.

Type de document:	Thèse Mémoire
Directeur de mémoire/thèse:	Ruediger, Andreas Peter
Mots-clés libres:	Photocatalysis; sono-catalysis; waste-water remediation; light-induced charge transport; photocatalyse; sono-catalyse; assainissement des eaux usées; transport de charge induit par la lumière
Centre:	Centre Énergie Matériaux Télécommunications
Date de dépôt:	24 avr. 2025 13:58
Dernière modification:	24 avr. 2025 15:23
URI:	https://espace.inrs.ca/id/eprint/16467

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