Photocalytic conversion of CO2 to hydrocarbons via modified titania nano-materials (Doctoral thesis)

Μουστάκας, Νικόλαος Γ.

Global warming and increased energy demand are considered two of the most critical problems humanity has faced over the last decades. The increased energy needs cannot be sustainably covered using existing fossil fuel stocks. Anthropogenic emissions of greenhouse gases, and especially carbon dioxide (CO2), are mainly responsible for the climate change causing extreme weather phenomena. An alternative and environmentally friendly energy conversion method, combating both these critical problems, is artificial photosynthesis. In the same way that natural photosynthesis in plants uses water, CO2 and sunlight for the production of glucose in the chloroplasts, artificial photosynthesis converts CO2 to hydrocarbons which can be reused as fuels (solar fuels). In artificial photosynthesis, the role of chloroplasts is played by semiconductive nanostructured materials called photocatalysts. TiO2-based nanomaterials are good candidates for the photocatalytic conversion of CO2 to hydrocarbons, as it is abundant in nature, non-toxic and environmentally friendly. The main drawback of TiO2 is its limited to the UV light absorption capacity. In this dissertation, the synthesis of TiO2 modified photocatalysts, active in the visible range, is achieved using the sol-gel combustion method using urea as fuel. The photocatalysts are optimized in terms of added mass of urea and annealing temperature with the optimal material (m-TiO2) exhibiting increased absorption (at 566nm) in the visible part of the solar spectrum. The m-TiO2 material is characterized using a variety of techniques (UV-Vis, FT-IR, micro-Raman, TEM, SEM, XPS, XRD) and is found to consist of an inorganic crystalline TiO2 core covered by an organic shell (inorganic/organic core-shell formation). Additional characterization methods (elemental analysis, nitrogen porosimetry, contact angle measurement, cyclic voltammetry, temperature programmed desorption) provide important information for the determination of the material’s properties. The photocatalytic properties of m-TiO2 are initially examined (in powder form) for the degradation of the dye Methylene Blue (MB) using different irradiation sources, demonstrating high efficiency even under visible irradiation. In a subsequent step the material is immobilized in γ-alumina ceramic tubular membranes in a hybrid photocatalytic / ultrafiltration process. These membranes are placed in a specially designed photocatalytic water treatment reactor and tested in the degradation of Methylene Blue (MB) and Methyl Orange (MO) dyes. This hybrid process is of high performance under both UV and visible irradiation with low energy consumption. Finally, the m-TiO2 material is used for the photocatalytic conversion (reduction) of CO2 into hydrocarbons. The experimental process takes place in a photocatalytic reactor with controlled parameters and in a high purity environment. The material exhibited a high yield in methane (CH4) production and a high selectivity for the final products. Finally, based on the experimental results and the latest literature publications, a possible mechanism for the conversion of CO2 to hydrocarbons is proposed, based on the carbene pathway.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
Subject classification: Φωτοκατάλυση
Keywords: Διοξείδιο του τιτανίου,Φωτοκατάλυση,Υδρογονάνθρακες,Τροποποίηση διοξειδίου του τιτανίου,Διοξείδιο του άνθρακα,Υδρογονάνθρακες,Ηλιακά καύσιμα,Τεχνητή φωτοσύνθεση,Κεραμικές μεμβράνες υπερδιήθησης αργιλία,Μεθάνιο,Νανοτεχνολογία,Καθαρισμός νερού,Photocatalysis,Titanium dioxide modification,Carbon dioxide,Hydrocarbons,Solar fuels,Artificial photosynthesis,Alumina ceramic ultrafiltration membranes,Methane,Nanotechnology,Water purification
Appears in Collections:Διδακτορικές Διατριβές

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