Study On Preparation And Photocatalytic Applications Of Porous Polyvinyl Alcohol Spheres

In this paper, the porous PVA spheres were prepared by phase separation method, and followed by optimization of the structure. Then, these porous PVA spheres were used as carriers to prepare TiO2/PVA, AgCl/PVA, Ag/PVA spheres through impregantion method, precipitation method and reduction method, respectively. Afterwards, these prepared spheres were characterized and applied to the photocatalytic degradation of methyl orange.Firstly, the influence of DMAc and PVP content on the viscosity and gel velocity of PVA/DMAc/PVP solution was studied. And, the diameter distribution, specific surface area and pore diameter distribution were used to characterize the effect of DMAc and PVP content on the structure of spheres. Results indicated that, there was no significant correlation between the DMAc content and the diameter distribution of these spheres. Moreover, the increase of DMAc content resulted in the lower surface area, the bigger pore size, and the obvious contraction of these PVA spheres. On the contrary, the addition of PVP was beneficial to forming the pore structure. With the increase of PVP content, the surface area of these spheres increased at first and then decreased, meanwhile, the pore structure became a mesh structure.Secondly, the porous PVA spheres were immersed into TiO2precursor solution with different aging time to prepare porous TiO2/PVA spheres. XRD results showed that anatase TiO2particles were successfully loaded on PVA spheres. With the increase of the aging time, the TiO2with high crystallinity can be obtained. Then, the photocatalytic degradation of methyl orange was used to evaluate the property of porous TiO2/PVA spheres. It showed that a higher photocativity was obtained by the TiO2/PVA spheres, prepared from the precursor solution with60days aging time.Thirdly, the AgCl/PVA and Ag/PVA spheres were crosslinked by glutaraldehyde and toluene diisocyanate (TDI), respectively. In the case of complexation between PVP and AgNO3, the formation of pore structure was promoted by the increase of DMAc content, which resulted in the increase of the specific surface area. The specific surface area of the spheres from PVA/DMAc/PVP/AgNO3system was lower, compared to that of the pure PVA spheres, and it increased with the increasing of AgNO3content, but the spheres did not form the network structure. Finally, the state change of Ag+during the catalyst preparation process was investigated. During the preparation of solution, the solution was continuously characterizated by UV-Visible spectroscopy, and the absorption peak at about425nm was attributed to the formation of Ag nanoparticles. XRD results showed that after crosslinking the spheres by glutaraldehyde, the Ag+changed to the spherical AgCl particles, which were about50nm. Meanwhile, the catalytic performance of these catalysts was improved with the increase of AgNO3content. On the other hand, after the spheres crosslinked by TDI, the Ag+partly changed to the Ag particles. Howover, The low surface area and the unconspicuous pore structure of these spheres resulted that the degradation rate of methyl orange was only47%.