Fabrication And Photocatalytic Property Of Titanium-based Composite Nanofibers

Titanium-based semiconductors have been widely studied and used inphotocatalysis. With the potential application in organic degradation and H2production, there still existed several major issues: Firstly, Titanium-basedsemiconductors with wide bandgap suffer from lower sunlight utilization rate, such asTiO2, ZnxTiyOzetc. Secondly, the rapid recombination of photoinduced electrons andholes greatly lowers the quantum efficiency. Thirdly, in the practice application, thephotocatalysts with nanosize are difficult to separate and recycle. Thus, the paperfocuses on the intrinsic problem and the practical application of titanium-basedsemiconductors photocatalytic, a series of nano-photocatalysts from binary to ternarywere fabricated by combining the electrospinning technique, hydrothermal methodand an in situ reduction approach. Such structure with titanium-based semiconductornanofiber as a template to construct heterojunction, shows the concept of "junction" inthe micro-nano-composite structure. And, the super long one-dimensionalnanostructures and unique fiber network structure could improve photocatalyst'sperformance of separation and reuse. The main researches are list as follow:(1) The TiO2@carbon core/shell nanofibers were fabricated by combining theelectrospinning technique and hydrothermal method. The results showed that auniform graphite carbon layer (2-8nm) was formed around the electrospun TiO2nanofiber via C-O-Ti bonds. By adjusting the hydrothermal fabrication parameters,the thickness of carbon layer could be easily controlled. The photocatalytic studiesrevealed that the TiO2@C NFs exhibited enhanced photocatalytic efficiency ofphotodegradation of Rhodamine B (RB) compared with the pure TiO2nanofibersunder visible light irradiation, which might be attributed to high separation efficiencyof photogenerated electrons and holes based on the existence of carbon as a sensitizer.Notably, the photocatalytic mechanism was confirmed by the hydroxyl radicalsscavenger experiment.(2) Based on TiO2@carbon core/shell nanofibers, Ag nanoparticles werefabricated by an in situ reduction approach. The results showed that a uniformgraphite carbon layer of approximately8nm in thickness was formed around theelectrospun TiO2nanofiber and small Ag nanoparticles (Ag NPs) were dispersed wellinside the carbon layer. And, the TiO2@C/Ag NFs had remarkable light absorption inthe visible region. The photocatalytic studies revealed that the TiO2@C/Ag NFsexhibited enhanced photocatalytic efficiency of photodegradation of Rhodamine B(RB) and Methyl orange (MO) compared with the pure TiO2nanofibers,TiO2@carbon core/shell nanofibers and TiO2/Ag nanofibers under visible lightirradiation, which might be attributed to the good light absorption capability and high separation efficiency of photogenerated electron-hole pairs based on thephotosynergistic effect among the three components of TiO2, carbon and Ag. And, theTiO2@C/Ag NFs could be easily recycled due to their one-dimensional nanostructuralproperty.(3) We firstly highlight a water-solution synthesis approach at low temperatureto prepare the carbon-rich graphitic carbon nitride nanosheets (CCN). Compared withthe bulk CN prepared by solid-state synthesis at high temperature, the as-obtainedultrathin CCN nanosheets show enhancement of photocurrent and photocatalyticactivity, which could be ascribed to its improved electron transport ability along thein-plane direction, and increased lifetime of photoexcited charge carriers.Three-dimensional (3D) free-standing network composed of TiO2@g-C3N4core/shellnanofibers was fabricated by combining the electrospinning technique and an in situcatalytic approach. The results showed that a uniform g-C3N4layer of approximately1nm in thickness was formed around the electrospun TiO2nanofiber. What's more,it's interesting to note that the g-C3N4layer with high quality was formed by an in situcatalytic reaction under a mild condition. And, the as-prepared TiO2@g-C3N4networkexhibited enhancement of photocurrent and photocatalytic activity. The enhancementin performance under UV irradiation was induced by the high separation efficiency ofphotoinduced holes from TiO2to the HOMO of C3N4. Under visible light irradiation,the electron excited from the HOMO to the LUMO of C3N4could inject into the CBof TiO2, making TiO2@g-C3N4present visible light photocatalytic activity. Notably,the free-standing3D nanofibrous network structure could improve photocatalyst'sperformance of separation and reuse.(4) The TiO2/ZnO nanofibers embedded by Au nanoparticles were fabricated bycombining the electrospinning technique (for TiO2/ZnO nanofibers) and an in situreduction approach (for Au nanoparticles). The results showed that small Aunanoparticles (Au NPs) were dispersed well on the TiO2/ZnO nanofibers (TiO2/ZnONFs). And, the TiO2/ZnO/Au nanofibers showed high charge separation efficiencyunder ultraviolet excitation, as evidenced by photoluminescence spectra. Thephotocatalytic studies revealed that the TiO2/ZnO/Au NFs exhibited enhancedphotocatalytic efficiency of photodegradation of Methyl orange (MO) and4-nitrophenol (4-NP) compared with the pure TiO2nanofibers, ZnO nanofibers andTiO2/ZnO NFs under ultraviolet excitation, which might be attributed to the highseparation efficiency of photogenerated electron-hole pairs based on thephotosynergistic effect among the three components of TiO2, ZnO and Au. And, theTiO2/ZnO NFs could be easily separated and recycled due to their one-dimensionalnanostructural property.(5) Zn2TiO4@carbon core/shell nanofibers (Zn2TiO4@C NFs) with differentthinkness of carbon layers (from2to8nm) were fabricated by combining theelectrospinning technique and hydrothermal method. The results showed that a uniform carbon layer was formed around the electrospun Zn2TiO4nanofiber (Zn2TiO4NFs). By adjusting the hydrothermal fabrication parameters, the thickness of carbonlayer varied linearly with the concentration of glucose and was, thus, able to becontrolled with a resolution in the nanometer range. Furthermore, the core/shellformed between Zn2TiO4and carbon enhanced the charge separation of pure Zn2TiO4under ultraviolet excitation, as evidenced by photoluminescence spectra. Thephotocatalytic studies revealed that the Zn2TiO4@C NFs exhibited enhancedphotocatalytic efficiency of photodegradation of Rhodamine B (RB) compared withthe pure Zn2TiO4NFs under ultraviolet excitation, which might be attributed to highseparation efficiency of photogenerated electrons and holes based on the synergisticeffect between carbon and Zn2TiO4. Notably, the Zn2TiO4@C NFs could be easilyrecycled due to their one-dimensional nanostructural property.(6) The3D open Bi2MoO6/ZnTiO3hierarchical heterostructures with Bi2MoO6ultrathin nanosheets grown on hexagonal-phase ZnTiO3nanofibers were fabricated bycombining the electrospinning technique and solvothermal method. The hierarchicalheterostructures synergistic system exhibited exceptional visible-light photocatalyticactivity, which might be attributed to the synergistic system with excellent chargeseparation characteristics and the unique morphology of Bi2MoO6nanosheets. What'smore, the3D open structure supported on nanofibrous candidates could be easilyrecycled easily by sedimentation without a decrease of the photocatalytic activity.