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Identifier

000359421

Title

Χημική σύνθεση οξειδίου του βολφραμίου (WO3) και μελέτη της φωτοκαταλυτικής του απόδοσης για τη διάσπαση αζωχρωμάτων

Alternative Title

Chemical composition of tungsten oxide (WO3) and study of its photocatalytic efficiency for the degradation of azodyes

Author

Βαμβασάκης, Ιωάννης Ευάγγελου

Thesis advisor

Τρικαλίτης, Παντελής

Abstract

This MSc dissertation studies the synthesis of micro- and nanostructure tungsten trioxide (WO₃) catalytic powders from aqueous solutions of tungstic acid (H₂WO₄) and sodium tungstate (Na₂WO₄) precursors and examines the adsorption and photocatalytic ability of the commercial and synthetic WO₃ catalysts for the discoloration and degradation of aqueous standard dye solutions in a variety of pH values: 5 (natural pH), 7, 9 and 12. For the composition of the catalyst powders, the simple and environmental friendly sol-gel and deposition-precipitation growth techniques were used, combined with hydrothermal treatments at low temperatures (95°C) and drying of the resultant samples at 110°C, or annealing at various temperatures, 300, 500 and 700°C. The synthetic samples and the commercial WO₃ were studied regarding their structural and morphological characteristics, based on the known characterization techniques of FT-IR, Raman and SEM. The surface area of the samples was also examined using the BET method. The characterizations of the composite WO₃ samples by simple drying at 110°C (dried powders), showed that the materials was mainly hydrated forms of WO₃ (WO₃,xH₂O), with a low degree of crystallinity and high porous morphology. The annealing, however, seemed to lead to higher crystallinity of the samples, which at high temperatures ≥500°C achieved the monoclinic form of m-WO₃, which is also the form of the commercial WO₃ catalyst. The studies of adsorption and photocatalysis examined - the structural factors such as crystallinity, BET surface area and morphology - and the effect of experimental conditions such as catalyst concentration, pH and type of irradiation - which affect the performance of the WO₃ catalysts in discoloration and degradation of the dye solutions. Finally, the photocatalytic studies at pH ≥ 9 using visible light irradiation gave quite encouraging results, with high discoloration rates (96%) of the Methylene Blue dye solution, using the main WO₃ samples of this work.

Language

Greek

Subject

Methylene Blue

Na2WO4

Tungsten trioxide

Visible light photocatalysis

WO3

Η2WO4

Τριοξείδιο του βολφραμίου

Φωτοκατάλυση ορατής ακτινοβολίας

Issue date