Vacancies-engineering Of Nanostructured Tio₂ And Its Interfacial N-p Effect

Titanium dioxide?TiO₂?,with rich reserves,stable structure and environmental-friendly,is the most widely used semiconductor,especially in photo-/electro-catalytic field.However,its relatively low separation and transfer efficiency of the carriers is a big limitation to its further applications.Interface engineering by constructing interfacial homojunction and heterojunction structures,and vacancy engineering by constructing oxygen vacancies?V_O?with n-type conductivity and titanium vacancies(V_Ti)with p-type conductivity in TiO₂,could greatly improve the separation and transfer efficiency of carriers.Engineering the interfacial VO and VTi in n-type TiO2,is therefore most perfect because of the advantageous combination of both interface engineering and vacancy engineering.This interfacial n-p effect would be beneficial to the specific transfer of carriers and thus enhancing photo/electro performances.High energy treatment is always required to construct the vacancies,and therefore the high migration rate of interface oxygen species has been used to fabricate the homojunction of V_Ti and V_O in nanostructured TiO₂ in a mild condition?calcination at 350°C in an open system?.The homojunction of V_Ti and V_O improves the interfacial n-p transfer of carriers and the influence of interfacial n-p effect to photocatalysis and electrochemical performance is revealed.The detailed contents are as follows:Firstly,we successfully construct p-type structure in n-type TiO₂.By utilizing the oxygen-rich property of titanium glycerate,nanotube assembled TiO₂microspheres with V_Ti and coordinated carbon are obtained.The existence of V_Ti is investigated by electron spin resonance?EPR?and X-ray photoelectron spectroscopy?XPS?,while the coordinated carbon species are characterized by advanced electron microscope technique,XPS and FT-IR.The efficient transfer route of carriers from TiO₂ lattice to V_Ti and then to coordinated carbon is presented.The interfacial V_Ti/C structure shows enhanced activities in photocatalytic performance and electrochemical performance,such as 4.7-fold of TiO₂(V_Ti)mixed C,named as TiO2?VTi-mix-C?and 1.8-fold of commercial TiO2 nanotube mixed with carbon,named as TiO2?Tube-mix-C?in photocatalysis and 2.5-fold of TiO2?VTi-mix-C?in electrochemical performance.The nanoscaled interfacial n-p structure is then designed by a nanocomposing way using n-type TiO₂ with V_O in the synthesis of p-type TiO₂ with V_Ti.Advanced electron microscope technique demonstrates that the n-type and p-type TiO₂ are constructed together by nanofusion in the interface,and the existence of V_O and V_Tii are proved by EPR and XPS.Owing to the efficient transfer path of carriers from V_O to V_Ti and then to carbon,this nanocomposite shows enhanced performance,such as1.8-fold of photocatalytic activity and 1.8-fold of electrochemical activity than n-type TiO2;1.9-fold of photocatalytic activity than commercial anatase TiO2 mixed carbon,named as Ana-TiO₂?mix-C?.Finally,we achieve the homojunction of V_O/V_Ti at atomic-scale in TiO₂.Two-dimensional nuclear magnetic resonance with triple quantum technique,EPR and XPS techniques have been used to characterize titanium vacancies and oxygen vacancies,while advanced electron microscope technique indicates the atomic-scaled nanofusion at the interface of amorphous/crystalline phase.The oxygen vacancies and titanium vacancies at the amorphous/crystalline interface form an interfacial n-p structure.This interfacial n-p effect endows a significant improvement on performance,such as 2-fold of photocatalytic activity and 1.9-fold of electrochemical activity than n-type TiO₂,1.5-fold of photocatalytic activity than commercial TiO₂nanotube.