Synthesis Of Novel Photocatalysts Based On Yeast Cells As Templates/Carriers And Their Application In The Treatment Of Printing And Dyeing Wastewater

As a harmful industrial water body, printing and dyeing wastewater has been a technically refractory pollution. Semiconductor photocatalytic oxidation process is deemed as an ideal treatment technology for printing and dyeing wastewater as it exhibits outstanding superiority such as mild reaction conditions, thorough purification, environmental protection, high economic efficiency, and etc. In this thesis, employing yeast cells as bio-templates and biological carriers, we prepared ZnWO4 hollow microspheres and yeast—zinc sulfide (YC-ZnS).And new photocatalysts were characterized by various means and methods to learn their main physical and chemical properties and to propose probable formation mechanisms. On this basis, we obtained the parameters of photocatalytic process of two photocatalysts in the treatment of low concentrations dyeing wastewater. Main results were summarized as follows:(1) We used yeast cells as biotemplates in the synthesis of ZnWO4 hollow microspheres. Results from characterizations indicated that ZnWO4 hollow microspheres were sphalerite ZnWO4 crystal; particles were in good dispersion which faithfully retained the morphology of yeast templates; and the size was approximate 3.7×2.0μm. Based on the experimental results, the formation mechanism of the ZnWO4 hollow microspheres was proposed into four steps:activation of functional groups on yeast cells—hydration zinc ion level formation on the cell surface through biological adsorption—growth of ZnWO4 nanoparticles on the yeast cellwall—calcinations to elimination yeast templates to form hollow microspheres.(2) Rhodamine B was taken as the degradation goal in the photocatalytic examination of ZnWO4 hollow microspheres. The dye photodecolorization process was studied considering the influence of experimental parameters such as pH,the initial dye concentration and catalyst amount used. The conditions when ZnWO4 with the best photocatalytic activity towards the Rhodamine B wastewater were 2g/L catalyst used, pH 6 and the dye concentration 0.5×10-5mol/L. And the ZnWO4 hollow microspheres displayed stable photocatalytic activity in the photocatalytic circulation experiments.(3) Employing yeast cells as carriers, a novel loaded photocatalyst YC-ZnS was successfully synthesized. Results from characterizations showed that the product particles were in good dispersion with consistent appearance; YC-ZnS particles maintained the morphology of yeast cells fairly well and the size was about 2-3×3-5μm; structurally the particle was consisted of a yeast cell inside covered with nanometer ZnS granule layer of 450-500nm thickness. The loaded ZnS was the sphaleriteβ-ZnS, and fluorescence characterization confirmed the loaded ZnS with fluorescence properties. The study on the preparation mechanism of YC-ZnS proved the successful loading of ZnS onto yeasts relied greatly on the reactive surface provided from the yeast cells.(4) Both the settling property of YC-ZnS in solution and its adsorption performance to the dye methylene blue were studied. Isotherm modeling revealed that Freundlich equations described well the adsorption of methylene blue onto YC-ZnS. The optimized adsorption conditions were:23℃, pH7 and the YC-ZnS amount used was 4.5g/L. Under these conditions, the adsorption capacity of YC-ZnS may reach 471.2μg/g. Compared with ZnS microspheres and yeast cells, the settling properties of YC-ZnS were also examined and simulated. It was found that the suspending performance of YC-ZnS was slightly less than yeast cell, but by far better than the ZnS microspheres.(5) Taking methylene blue as the degradation goal, we studied the photocatalytic process conditions of YC-ZnS. Factors affecting the photocatalysis of YC-ZnS were evaluated in details, such as the pH value, the catalyst amount used, the initial dye concentration, the illumination distance and the reaction temperature. Then we obtained the optimized conditions of photochemical catalysis system as followed:pH 8, the illumination distance is 5cm, and the yeast-ZnS amount used was 3g/LIn this article we prepared two new photocatalysts, blending together both the superiorities of the biological cells and the nanomaterials in the material design. It was proved that the preparation processes were simple and environmentally friendly, and the synthesized products exhibited high photocatalytic efficiency in the treatment of the printing and dyeing wastewater. Hence we might achieve goals in the green solution of environmental pollution and the ecological development of resources as well. This paper has made some attempts in the multidiscipline among nanotechnology, biological science and environmental engineering. And it may be of reference value to the application of other organism-related new material in the research of environmental engineering.