| Nanotubular titanic acid?NTA?is the promising materials in photocatalytic field due to its one-dimensional tubular morphology and larger specific surface area.NTA can be transformed into novel anatase Ti O2 with large single electron trapped oxygen vacancies?SETVOs,VO·?in the bulk phase.The lattice defects VO·form a sub-band within the band gap of novel anatase TiO2,which results in obvious visible light absorption.However,this novel TiO2 has not any photocatalytic activity under visible light irradiation due to high recombination rate of photo-generated electron and hole.It is important to obtain higher visible light photocatalytic activity by modifying the novel TiO2.An effective strategy is to modify the surface of novel anatase TiO2 with visible-light-absorbing conjugated materials.Conjugated materials,with extending?-conjugated electron system,are efficient electron donors and good hole transporters.It is well-known that the electron transfer on the interface between the conjugation and TiO2 is of great significance to the photocatalytic efficiency.In conjugation/TiO2 system,the strong interaction could speed up the electron transfer on the interface,then cause a rapid photo-generated charge separation,and hence improve the visible light photocatalytic efficiency.In this paper,g-C3N4/TiO2 and PVAD/TiO2 nanohybrid photocatalysts were obtained with polyvinyl alcohol?PVA?,melamine and NTA.The influence of conjugated?materials on the photocatalytic activity and charge separation mechanism of novel Ti O2 was studied.The specific work is as follows:?1?A series of g-C3N4/TiO2 photocatalysts were prepared by one-step calcination method with melamine and NTA.The effect of melamine content on the photocatalytic activity of g-C3N4/TiO2 was studied.It can be seen that the melamine is formed sheet structure of g-C3N4 by calcinations and the g-C3N4was coated on the surface of TiO2 from the transmission electron microscope?TEM?.The result of X-ray photoelectron spectroscopy?XPS?shows that g-C3N4 formed by calcination of melamine in the g-C3N4/TiO2 system.The shift of Ti and O binding energy in g-C3N4/TiO2 photocatalysts showed a strong interaction between TiO2 and g-C3N4.The result of UV-vis diffuse reflectance?UV-vis?indicated that the absorption of novel TiO2 has obvious red shift compared with the P25,this is due to the bulk VO·in the novel TiO2.As shown in the electron spin resonance spectroscopy?ESR?,all samples have a signal at g=2.003,which is assigned to SETOVs.I-t curve indicated that the photocurrent response of g-C3N4/TiO2photocatalysts significantly enhanced,which hints the enhanced photoinduced charge separation efficiency and improved photocatalytic activity.The photocatalytic activity of propylene removal was significantly improved for g-C3N4/TiO2 nanocomposites.At the optimal melamine content?2%?,the apparent photocatalytic activity of 2%g-C3N4-TiO2 was 9 times higher than that of pure Ti O2 under visible-light illumination.In order to investigate the combination pattern of g-C3N4 and TiO2,the experiment of fluorescence hydroxyl detection was carried out.The results show that g-C3N4/TiO2 Z-scheme photocatalytic system is formed,which results in efficient space separation of photo-generated charge carriers.In the same time,the photo-generated electrons and holes are enriched on the conduction band of g-C3N4 and the valence band of TiO2,respectively,which exhibit the strongest redox ability.?2?In this part,the metal-contained g-C3N4/Pd/TiO2 photocatalytic Z-scheme was obtained by the deposition of metal Pd nanoparticles as an electron mediator.The effect of Pd content and location on the visible light photocatalytic activity was investigated for g-C3N4/Pd/TiO2 samples.It can be seen that two kinds of photocatalysts?g-C3N4/Pd/TiO2 and Pd/g-C3N4/TiO2?were formed when Pd nanoparticles were deposited at different positions through TEM.The one is Pd located at the interface between g-C3N4 and TiO2,the other one is Pd on the surface of g-C3N4/TiO2.The XPS also indicated that Pd exists in the state of zero valence in the g-C3N4/Pd/TiO2 samples.From the spectrum of UV-vis it can be seen that the absorption of the g-C3N4/Pd/Ti O2 catalysts was enhanced with Pd as a mediator due to surface plasmon resonance.The content of Pd has a great influence on the absorption visible light,2%g-C3N4-?1%Pd-NTA?exhibits the strongest absorption in visible light region.It can be seen from i-t curve that the photocurrent significantly increased with the deposition of Pd nanoparticles.After deposition of Pd?1wt%?at the contact interface between g-C3N4 and TiO2,the 2%g-C3N4-?1%Pd-TiO2?nanocomposites demonstrated the highest visible-light-driven photocatalytic activity for the degradation of gaseous propylene,which was 16-and2-fold higher activity than pure TiO2 and 2%g-C3N4-TiO2,respectively.In order to investigate the photocatalytic mechanism of g-C3N4/Pd/TiO2 photocatalyst,the hydroxyl radical was evaluated by fluorescence detection.The results show that the metal-contained g-C3N4/Pd/TiO2 Z-scheme photocatalytic system is formed,Pd can further enhance the separation efficiency of photogenerated electrons and holes as electron transfer mediator,the ability of generate·OH was also increased.?3?In the third part PVAD/TiO2 nanohybrid photocatalysts were obtained by calcining with polyvinyl alcohol?PVA?and NTA used as precursor.The effects of NTA's pretreatment temperature and the mass ratio between PVAD and NTA on the photocatalytic activity of PVAD/TiO2 were investigated.The infrared spectrum?IR?and XPS analysis showed that the C=C conjugate structure was obtained after calcination,and the Ti-O-C bond formed between TiO2 and PVAD in the composite photocatalyst.The absorption edge of PVAD/TiO2 has a red shift compared to P25,and the visible light absorption was also significantly enhanced.The results of impedance?EIS?showed that the PVAD/TiO2 composite has the smallest impedance radius under visible-light irradiation,indicating a decrease in the resistance of the solid-state interface and in the charge transfer resistance at the surface.The Ti-O-C can accelerate the charge separation as transmission channel of electrons.Therefore,PVAD/TiO2 exhibited excellent photocatalytic activity in the photocatalytic degradation of methyl orange under visible light irradiation. |
PDF Full Text Request