| Semiconductor photocatalysis offers many advantages over traditional technologies in degradation of organic pollutants in water. Nowadays, fabrication of visible-light responsive photocatalysts with highly activity and exploration of novel synthetic methods are two hot topics in the field of research and development. Zinc ferrite (ZnFe2O4), a kind of semiconductor which can absorb visible light over a wide range of wavelengths, owns a poor photocatalytic activity due to the low separation efficiency of photo-generated electrons and holes. Because polyaniline (PANI) is a conducting polymer with properties such as high electrical conductivity and chemical stability, modification of ZnFe2O4nanocrystals with PANI may arouse rapid photoinduced charge separation and therefore improve the photocatalytic activity. Moreover, cadmium sulfide (CdS) is a kind of visible-light-driven photocatalyst with high photoelectric conversion efficiency. As it is deposited on surfaces of magnetic polymer particles, catalyst dispersion in aqueous system can potentially be improved and the recovery will be convenient and quick by using an external magnetic field. Therefore, two kind of inorganic/organic hybrid photocatalysts were synthesized and their performance on photocatalytic dye degradation in water was investigated in the dissertation. Also the photosynthetic methods for the composites were explored. The research contents are as follows: Firstly, using ZnFe2O4nanocrystals prepared by co-precipitation method as the core and aniline as the monomer, ZnFe2O4/PANI core-shell composites with different PANI contents were prepared by chemical oxidation polymerization, and the composition, structure, morphology, absorption and magnetic properties of these composites were also characterized. The results show that the morphology of ZnFe2O4/PANI turns into micron-sized irregular conglomerates from spherical particles with mean diameter of about20nm as the weight percent of PANI in ZnFe2O4/PANI increases. Meanwhile, the photocatalyst with a higher PANI percentage shows enhanced visible light adsorption and improved adsorbability for rhodamine B (RhB). However, the photocatalytic activity initially increases and then declines with increasing the proportion of PANI. The obtained catalyst had the maximum activity that could degrade RhB over90%under UV and visible light irradiation in150min when the proportion got to6.6%.Secondly, a novel photochemical approach was explored to synthesize ZnFe2O4/PANI core-shell nanocomposite. Results show that the resulting material in the size range from15nm to35nm has thinner shell of PANI and shows a better dispersion than the above analogue. Additionally, it has a PANI percentage of about9.8%and a specific surface area of54.99m2/g. It is found that the doping level of HCl on PANI in the sample is higher than that of the product prepared by chemical oxidation polymerization in aqueous system with the same pH value. But its adsorption capacity and photocatalytic degradation activity for RhB are lower than the latter. It should be noted that polymerization of aniline on the surface of ZnFe2O4can be done at much low acidic solution, even at pH5. It is assumed that holes of excited zinc ferrite play a significant role to oxidize aniline during the polymerization process.Finally, poly(acrylic acid)-modified magnetic nanoparticle (Fe3O4/PAA) was synthesized by photopolymerization of acrylic acid in the presence of Fe3O4nanoparticle. In a following photochemical reaction, CdS was deposited on the carboxyl-functionalized surface of Fe3O4/PAA to construct Fe3O4/PAA/CdS core-shell composite microspheres. The microspheres are luminescent and quasi- superparamagnetic and exhibit excellent visible light photocatalytic activity for RhB decomposition, by which the RhB decomposition efficiency is54.2%higher than that by TiO2(P25). Besides, the magnetic composite microspheres can be recovered by a magnet from aqueous solution within2min and be reused directly. |
PDF Full Text Request