The Preparation,Properties And Photocatalytic Activityof New Structural TiO₂ Based Visible Light Photocatalysts

Recent years,TiO₂ has been investigated by many researchers,due to its high performance,stability,inexpensive and non-toxic properties,which has been applied in many fields,such as photodegradation of organic pollutant,photo-reduction of CO₂and H₂O into CH₄.However,because of its large band gap?anatase:3.2 e V;rutile:3.0e V?,Ti O2 shows nbo reponse to the visible light and the recombination rate is quite low,impeding the efficient usage of solar light and limiting the photocatalytic activity.Therefore,in this work,TiO₂ is modified by doping and compositing techniques and the photocatalytic mechanism is also investigated in details.The main points could be summarized as follows:1.Indium and boron co-doped TiO₂ photocatalysts were prepared by a sol–gel method.The structure and properties of photocatalysts were characterized by XRD,BET,XPS,UV–vis DRS and PL techniques.It is found that boron is mainly doped into the lattice of TiO₂ in interstitial mode,while indium is present as unique chemical species of O–In–Cl_x?x=1 or 2?on the surface.Compared with pure TiO₂,the narrowness of band gap of TiO₂ doped with indium and boron is due to the mixed valence band formed by B2p of interstitial doped B ions hybridized with lattice O2p.And the surface state energy levels of O–In–Cl_x?x=1 or 2?and B₂O₃ species were located at about 0.4 and 0.3 e V below the conduction band respectively,which could lead to significant absorption in the visible-light region and facilitated the effectually separation of photogenerated carriers.Therefore,indium and boron co-doped TiO₂showed the much higher photocatalytic activities than pure TiO₂,boron doped TiO₂?TiO₂-B?and indium doped TiO₂?TiO₂-In?under visible and UV light irradiation.2.A new type of heterostructured photocatalysts?N-Ti O2/In BO₃?were synthesized by coupling nitrogen-modified TiO₂?N-TiO₂?with indium borate?In BO₃?via a one-step sol-gel method.It was revealed that N-Ti O2/In BO₃exhibited an improved photocatalytic performance compared with TiO₂,N-TiO₂,and In BO₃ under both UV and visible light irradiation because of the formation of a heterostructure at the interface as well as the introduction of surface NO_xspecies and In BO₃.These results may provide a paradigm to fabricate and design the optoelectronic functional materials with high efficiency and performance.3.Density functional theory?DFT?calculation is carried out to access the band structure and density of states?DOS?based on the models of TiO₂ nanoparticle,nanotube,and nanosheet,predicting the order of the photocatalytic activity for three different nanostructures.Sol-gel method and hydrothermal method are used to achieve desired morphologies:nanoparticles,nanotubes,and nanosheets?fragmentized nanotubes?.The photocatalytic activity ranks in the order of nanosheets>nanotubes>nanoparticles,which is consistent with theoretical prediction.It was revealed that the enlargement of band gap is caused by the quantum confinement effect;the prolonged lifetime of photogenerated electrons and increased specific surface areas are dependent on the morphology of the nanostructure.All these factors contribute to the improvement of the photocatalytic activity for nanostructures.4.We theoretically forecasted the narrowness of band gap for the nitrogen doped ZrO₂,implying a possible energy level matching at the interfacebetween TiO₂ and ZrO₂.Inspired by the theoretical simulation,thecorresponding experiment was carried out and the band gap of ZrO₂ isnarrowed by doping nitrogen in substitutional mode.The TiO₂-N/ZrO_2-xN_xcomposite photocatalyst exhibited an excellent photocatalytic performanceunder visible-light irradiation.The enhancement is caused by the introduction ofdoping energy level as well as the electrons'transition at interface,which wouldenhance the visible absorption of composite photocatalyst and separate thephotogenerated charge carriers efficiently.These results suggest that theselection of materials and dopants and the matching of energy levels at interfaceare of great importance to design and fabricate photocatalysts with high efficiency and performance.5.Different approaches like doping and sensitization have been used to develop photocatalysts that can lead to high reactivity under visible light illumination,which would allow efficient utilization of solar irradiation and even interior lighting.We demonstrated a conceptually different approach by changing reaction route via introducing the idea of conventional Pd catalysis uased in cross-coupling reactions into photocatalysis.The O-Pd-Cl surface species modified on Ni doped TiO₂ can play a role the same as that in chemical catalysis,resulting in remarkably enhanced photocatalytic activity under visible light irradiaton.For instance,Pd/Ni-TiO₂ has much higher activity than N-TiO₂?about 3?9 times for all of the 4-XP systems?upon irradiation with wavelength of 420 nm.The catalytically active Pd?0?is achieved by reduction of the photogenerated electrons from Ni-TiO₂.Given high efficient,stable Pd catalysts or other suitable chemical catalysts,this concept may enable realization of the pratical applications of photocatalysis.