Bizmut-volframát és bizmut-vanadát alakformált fotokatalizátorok előállítása és alkalmazhatóságának vizsgálata

Abstract

While in the developed countries the wastewater treatment is mostly solved, in the developing countries the major problem is even the production of water suitable for human consumption. In most of these cases, conventional water purification processes are irrelevant, so it is necessary to find another alternative purification method to remove the pollutants that cause this problem. Heterogeneous photocatalysis among advanced oxidation processes (AOP’s) may be a good solution, which is one of the most dynamically developing recent water purification method. Heterogeneous photocatalysis is based on a semiconductor material, a photocatalyst, which can be activated with light irradiation to initiate the degradation of organic pollutants. If the electron- and band structure of the semiconductor allows, the excitation can be induced by visible light, a lower energy irradiation, which is more advantageous for the utilization of sunlight than the higher energy UV light excitation. Consequently, the development of visible light active photocatalysts such as bismuth tungstate and bismuth vanadate are a major priority. It is well-known that the photocatalytic efficiency highly depends on the physical-chemical properties of the photocatalyst, such as particle size, morphology, band-gap, etc. Among these properties, the photocatalyst (micro)morphology and hierarchical organization levels have a prominent role, making possible a fine-tuning of the properties by during their synthesis. This is the so-called controlled crystallization, i.e. shape-tailoring, which favors the development of such morphological properties which are favorable to a specific application. During my research, I aimed to shape control bismuth tungstate and bismuth vanadate semiconductor photocatalysts. In case of bismuth tungstate, the effect of the synthesis time, the calcination, and the additives on the physical-chemical properties of the microcrystals and as well the photocatalytic activity were intensively investigated. Considering the results, a morphological series was sought, which was obtained by changing the used additives systematically during the synthesis, in order to explore a clear relationship between the produced morphological series, the used additives and the photocatalytic activities. In the second part of my work, the synthesis of specific crystal facet dominated bismuth vanadate microparticles were targeted by solvothermal crystallization fine-tuned by the change of the pH of the synthesis mixture. The relationship between the amount of photocatalytically active (040) crystal facet and the photocatalytic degradation of two model pollutants, the rhodamine B and the oxalic acid was targeted. However, the crucial role of (040) crystal facet in other chemical reaction was also planned .