TiO2 Modified with C,N Originated from Pyridine Organic Compounds for Photocatalytic Hydrogen Evolution

Author:Xu Xing

Supervisor:song shuang he zhi qiao


Degree Year:2019





The exploration of low cost,high performance,and stable photocatalysts for the highly efficient conversion and storage of solar energy in hydrogen is of great importance.Among various photocatalysts reported to date,TiO2 has been extensively explored due to its low cost,efficiency,long-term stability and eco-friendly features.However,the photocatalytic water splitting performance of pristine TiO2 remains unsatisfactory due to its insufficient light response and poor photogenerated carrier separation efficiency.Therefore,it is extremely important to design TiO2-based photocatalysts to enlarge the light absorption region and improve the charge mobility.Doping TiO2 with different elements,especially co-doping with two(or more)non-metal atoms,is considered to be one of the most efficient ways to develop visible light responsive TiO2 by introducing impurity states in the forbidden region or narrowing the effective band gap.Moreover,loading ofπ-conjugated carbon materials onto TiO2 can induce synergetic effects to enhance the separation of electron-hole pairs.The role of theπ-conjugated carbon structure in storing and shuttling photogenerated electrons from the semiconductor to an acceptor can endow the composite with high photocatalytic activity.In this paper,the novel pyridine-type carbonitrides(CN)-modified surface-disordered C-doped TiO2(PCN/CTiO2@TiO2-x)catalysts were prepared by the method of hydrolysis-calcination using tetrabutyl titanate and pyridine as the precursors.And nitrogen-doped carbon-wrapped C,N-codoped TiO2(C,N-TiO2@CN)was also successfully prepared using the same facile and efficient method using tetrabutyl titanate and 2,6-diaminopyridine as the precursors.To ensure the repeatability of the sample preparation procedures,major operating parameters such as stirring intensity,the drop rate of Ti(OC4H9)4,hydrolysis and calcination time,and solidification and carbonization temperature,etc.were carefully controlled.The catalyst samples were characterized by X-ray diffraction(XRD),Raman,transmission electron microscopy(TEM)and high resolution transmission electron microscopy(HRTEM),X-ray photoelectron spectra(XPS),valence band XPS(VB-XPS),electron paramagnetic resonance(EPR),UV-Vis diffuse reflectance spectra(DRS),Brunauer-Emmett-Teller(BET)surface area,electrochemical impedance spectra(EIS),photoluminescence(PL)spectra and PL decay curves to correlate the physicochemical properties of the catalysts with their performance in photocatalytic hydrogen evolution from water.The optimized PCN/CTiO2@TiO2-x exhibited an impressive hydrogen evolution rate of3743μmol h-1 g-1 under simulated solar light(AM 1.5)and remained stable after five cycles.The maximal quantum efficiency reached 37.5%at 370 nm and 7.0%at 400 nm,which was superior or comparable with several reported relevant TiO2-based catalysts.Benefitting from the pyridine-type CN modification,disordered surface layer(TiO2-x)and increased oxygen vacancies/Ti3+species,the photogenerated electrons moved rapidly from the visible-response C-doped TiO2 to CN to participate in the photoreduction reaction,which led to a marked improvement in the catalytic activity.For C,N-TiO2@CN,XPS and VB-XPS measurements reveal the successful co-doping of interstitial carbon and nitrogen into TiO2,which leads to visible-light absorption up to550 nm in the UV-Vis DRS.Raman spectra and HRTEM results show that N-doped carbon exists on the surface of C,N-TiO2,which gives rise to the efficient separation of photoexcited charge carriers,as determined by PL and EIS.Benefiting from the combined effects of surface coated N-doped carbon layer and C,N-co-doping,the photocatalyst calcined at 450°C exhibits remarkable visible-light activity towards the hydrogen evolution reaction in the water splitting process with a H2 production rate of 833.2μmol h-1 g-1 under visible-light illumination(λ>420 nm).Moreover,the representative C,N-TiO2@CN sample can maintain its activity for at least 40 h.We anticipate that these high activity catalysts prepared using low cost raw materials and easy scale-up method can render versatile applications in solar energy conversion.