Preparation And Catalytic Performance Of TiO₂(B)-based Complex Compound Nano-heterojunctions

Na_0.9Mg_0.45Ti_3.55O₈?NMTO?is a new-type of complex semiconductor based on TiO₂?B?,exhibitting high photodegradative ability.But its wide band gap limits the solar energy utilization.In this thesis,heterojunction was employed to improve the photocatalytic performance by introducing intra-band states or increasing the separation efficiency of photoinduced electron-hole pairsThe noble metals Au,Ag and Pt were loaded onto NMTO using a chemical bath deposition method.The photocatalytic activity of composite photocatalysts was further improved due to the Schottky barrier built between NMTO and noble metal.Hot electrons generated during localized surface plasmon processes in metal nanoparticles transfer to the semiconductor,manifesting as a depression of surface potential directly detected by scanning Kelvin probe microscopy.The key factor responsible for the improved ability of semiconductor-based photocatalysts is the charge separation.The most effective weight concentrations of Au,Ag and Pt loaded onto NMTO were 5.00%,12.6%and 5.55%respectively.A possible mechanism for the photodegradation of methylene blue over NMTO loaded with noble metals is proposed.This work highlights the potential application of NMTO-based photocatalysts,and provides an effective method to detect localized surface plasmonsIn order to futher enhance the catalytic activity of NMTO,Ag and Pt were co-loaded on NMTO by chemical bath deposition method.The scanning electron microscopy and transmission electron microscopy results show that Ag and Pt nanoparticles were distributed on the different surfaces of NMTO.The photocatalytic activity is obviously superior to that of pure NMTO after loaded with noble metals The best weight concentrations of Ag and Pt are 9.00%and 3.70%,respectively.The electrostatic field is built in the Schottky barrier between NMTO and noble metals,leading to an energy band bending.The photocatalytic properties of NMTO are improved by effectively inhibiting the composite rate of photoelectrons and holes.The heterojunction is also an effective way to improve photocatalytic performance.Heterojunction SnS₂-NMTO was synthesized by hydrothermal method.The SnS₂-NMTO interface was observed by high resolution transmission electron microscopy.The photocatalytic activity of composites were improved in comparison with that of the pure NMTO and SnS₂ for degradation of methylene blue and Rhodamine B.Electrons were inspired in n-type semiconductors NMTO and SnS₂ under light illumination,and a large part of them moves to the interface,determined with surface potential measured by Scanning Kelvin probe microscopy.The charge distribution in the composite illustrates the formation of an internal electric field between interface and SnS₂-NMTO and the photoinduced electron-hole pairs was separated effectively,as a result,enhancing the photocatalytic performance.Then,a new-type of semiconductor Na_0.23TiO₂?NTO?nanofibers were prepared by a two-step hydrothermal method for the first time.Pure NTO was demonstrated as a direct semiconductor and exhibits strong photodegradative ability for RhB.The noble metal Au or Ag nanoparticles was loaded on NTO by a chemical bath deposition method.The composite photocatalysts exhibit much higher photodegradative ability for degradation of RhB because the photoproduced electronic-hole pairs are effectively separated after Au or Ag was loaded on NTO.Hot electrons are generated in metal nanoparticles through localized surface plasmon process under light illumination and then,transfer to semiconductor,expressed as depression of surface potential detected by scanning Kelvin probe microscopy.The high electronmagnetic field of localized surface plasmon resonance and strong coupling between noble metal and NTO will benefit the plasmon-induced charge transportation and separation,as a result,enhancing the activity of semiconductor-based photocatalysts.This work highlights the potential application of NTO and provides an effective method to detect the localized surface plasmonTiO₂/NTO composite photocatalyst is prepared by a simple hydrothermal method Different morphologies are obtained under different experimental conditions—namely,nanosheets,nanowire,and nanorod.The photocatalytic activity of TiO₂/NTO composites is superior to the raw anatase titanium dioxide for the degradation of methylene blue under UV-visible light irradiation.The best photocatalytic performance is achieved in a composite prepared at an alkali concentration of 1.5 M The photogenerated charge separation is a main factor in enhancing the activity of semiconductor-based photocatalysts.