The Photocatalysis Of Surface Modified TiO₂ Particles And Its Effects On PVC Plastics

The anatase TiO₂ does not show photocatalytic activity under visible light irradiation.In order that TiO₂ can show the visible light photocatalytic activity,TiO₂ must be modified through decreasing its E_bg or doping photosensitizer.A novel visible light active photocatalyst(TiO₂/D-PVA) was prepared in one portion of PVA(polyvinyl alcohol) and Ti(OH)₄ by means of hydrothermal method.The structure,surface composition,lipophilic nature and photocatalytic activity of TiO₂/D-PVA were investigated by XRD,BET,SEM,TGA,XPS,EPR,UV-vis and the degradation of methyl orange(MO).TiO₂/D-PVA-PVC plastics was prepared by mixing and melting of TiO₂/D-PVA,PVC and other necessary additives,and its mechanical properties,rheological behavior and antibacterial properties were studied in detail.PVA was degraded to produce the D-PVA of conjugated C=C accelerated by the synthesized TiO₂ as a Lewis acid under hydrothermal process,and the D-PVA was doped onto the surface of TiO₂.Due to the interaction between D-PVA and TiO₂, TiO₂/D-PVA showed significant visible light photocatalytic activity and could effectively degrade methyl orange under visible light.All the synthesized TiO₂/D-PVA samples consisted of anatase structure with high crystallinity and D-PVA was doped on the surface of TiO₂ particles,which indicated that D-PVA did not exist in the crystal lattice and hardly influenced the crystalline phase of TiO₂.The feed ratio of PVA to TiO₂,hydrothermal reaction temperature and reaction time obviously influenced the crystal size,BET surface area and photocatalytic activity.TiO₂/D-PVA showed less crystal size and bigger BET surface area than pure TiO₂,because D-PVA prohibited TiO₂ from crystallizing and agglomerating.TiO₂ showed the tendency of visible light photocatalytic activity from increasing to decreasing with the increased feed ratio of PVA to TiO₂.The visible light photocatalytic activity also showed the tendency from increasing to decreasing with the increased hydrothermal reaction temperature and reaction time.TiO₂/D-PVA,synthesized at 180℃with the reaction time for 6h and the 1: 10 feed ratio of PVA to TiO₂,exhibited a higher visible light photocatalytic activity. When the suspension system of TiO₂/D-PVA and methyl orange was irradiated under visible light for 40 h,the degradation percentage of methyl orange reached 84.0%, which was 9.2 times than P25.The rate of methyl orange degradation fit the first-order reaction kinetics equition in the form of([MO]₀ /[MO]_t) =0.0461t).The influence of TiO₂/D-PVA on the rheological behavior of PVC plastics was also investigated.The results showed that TiO₂/D-PVA could obviously improve the rheological behavior and decrease the Non-Newtonian parameters.Due to the big particle size,the tensile strength and elongation at break of PVC plastics were all obviously decreased,compared to the PVC plastics without TiO₂/D-PVA particles.The antibacterial rates to Colibacillus and Staphylococcus were 76.3%and 71.4%with the addition of 8 phr TiO₂/D-PVA,respectively.The surface modification of TiO₂/Ag⁺ nanoparticles by grafting the coupling agent of KH-560 and preparation of modified nano-TiO₂/Ag⁺-PVC plastics were performed, and the effect of the modified nano-TiO₂/Ag⁺ content on the mechanical properties, rheological behavior,ageing resistance and antibacterial properties of PVC plastics were investigated.The KH-560 grafted onto the surface of nano-TiO₂/Ag⁺ particles decreased the surface tension of TiO₂/Ag⁺ nanoparticles and prohibited the TiO₂/Ag⁺ nanoparticles from agglomeration,which improved the compatibility of TiO₂/Ag⁺,nanoparticles with PVC plastics and had the TiO₂/Ag⁺ particles be dispersed in plastics with nanometer scale.The content of TiO₂/Ag⁺ nanoparticles,reaction time and reaction temperature all influenced the modified effect of KH-560.The results showed that the optimal modified conditions were 8%contents of KH-560,78.5℃reaction temperature and 5h reaction time.The tensile strength and elongation at break of PVC plastics could all been improved and showed the tendency from increasing to decreasing with the increased content of TiO₂/Ag⁺ nanoparticles.The rheological behavior was also improved because the TiO₂/Ag⁺ nanoparticles reduced the interaction force of PVC molecules,which acted as an internal lubricant.TiO₂/Ag⁺ nanoparticles could absorb the ultraviolet radiation and improve the uvioresistant ageing resistance.The antibacterial rates to Colibacillus and Staphylococcus were exceeded 90%and 99%with the additions of 1 phr(0.63%) and 4 phr(2.5%) modified TiO₂/Ag⁺ nanoparticles,respectively.All the results show that the good application perspective of these new kinds of TiO₂/D-PVA and TiO₂/Ag⁺ additives.