Modification Of Nano-photocatalyst Material For Organic Dye Wastewater Treatment

At present, wastewater, especially organic dye wastewater, is a challenging and pressing topic that attracts concern from all over the world. More efficient ways and methods were explored to address the deteriorating serious water pollution issue. Traditional pollution control methods includesphysical treatment, chemical treatment and biological treatment methods, but these methods can not completely degrade organic pollutants, and are likely to cause secondary pollution. In order to avoid the disadvantages of traditional methods, photocatalytic degradation technology was explored. In this thesis, the synthesis of TiO₂, ZnO and ZnO/C₃N₄ was investigated, and the degradation efficiencyof RhB and the degradation mechanism of photocatalytic materials were explored. This work focused on synthesizt strategies of photocatalytic materials to improve the degradation of organic dye wastewater and the degradation mechanism of photocatalytic material. The content of this thesis contains the following three parts.1. The study on the photocatalytic activity of themodified TiO₂The template method and hydrothermal method, which use titanium tetrachloride as titanium source, show advantageous features, such as small particle size, uniform particle distribution.Through Scherrer's formula, particle size was derived to be below 10 nm, and the degradation efficiency was 99.2 % and 98.7 % respectively under the illumination of simulated sunlight for 2 h. In addition, compared with the rutile and brookite phase TiO₂, the anatase phase can promote the photocatalytic degradation efficiency. This shows that both particle size and crystal structure influence the photocatalytic efficiency of TiO₂.2. The study on the preparation of ZnO materialsThrough refluxing process, rods like Zn O with wurtzite structure was synthesed. The crystal size became bigger with increasing reaction temperature, and the crystal growth along?100? direction was promoted and the growth along?002? direction was suppressed. After illumination with mercury lamp for 2h, the degradation efficiency of 99.3 % can be achieved for samples prepared by refluxing at 105 ?for 4 h. This can be attributed to the best combination of?002? and?100? crystal facets that are most suitable for photocatalytic degradation, as it can suppress the recombination of electrons and holes during photocatalytic degradation. The photocatalytic degradation efficiency is closely related to the oxygen vacancies in the crystal lattice, with best photocatalytic performance at medium defects concentrations, while the recombination of electrons and holes would undermine the performance at higher defects concentration.3. The study on the systhesis of ZnO/C₃N₄ compound by ball millingAfter high-speed ball milling, C₃N₄ transformedto layer by layer flake-like morphology, and demonstrated the degradation efficiency of 86.9% after illuminating with visible light for 1 h, which is comparable to the degradation efficiency after 2 h illumination for C₃N₄ materials before milling. This can be attributed to the extended C₃N₄ light response range and improve the photo sensitivity of C₃N₄. Thus high-speed ball mill was also used to modify C₃N₄ / ZnO mixture. After milling it shows similar thin layer flake-like morphology. Compared with the pure ZnO after milling, the milled composite materials showed improved degradation efficiency with increasing ratio of C₃N₄. The highest catalytic efficiency can be achieved with ZnO/C₃N₄ ratio of 1:0.1 after illuminating with visible light for 2 h, but the efficiency started to decrease with excess C₃N₄ due to enhanced recombination ratio of electrons and holes in the compound. The mechanism ofphotocatalytic degradation was investigated, and it was found that holes play a major role in the photocatalytic reaction, and the electrons played a minor role for dye degradation.