Preparation And Photocatalytic Degradation Performance Of Titanium Niobate-based Composite Materials

Semiconductor-based photocatalysis,which can directly convert solar energy into chemical energy and simultaneously accomplish solar energy conversion and storage objectives,is regarded as one of the most promising strategies in solving energy supply and environmental pollution problems.However,the need for ultraviolet irradiation in most successful photocatalytic processes has limited both the feasibility and environmental benefits of photocatalysis on industrially relevant scale.Therefore,it's important to design and synthesize some novel visible-light-response photocatalysts.At present,layered metal compounds have received extensive attention due to their special structural and physicochemical properties.As a typical layered transition metal oxide,HTi₂NbO₇ shows a band-gap value of 3.35 eV,non-porous structure and small specific surface area.Thus,pure HTi₂NbO₇ has a response only in the ultraviolet light region,and low utilization of sunlight.In this work,some novel nanocomposite photocatalysts were successfully synthesized by the intercalation or facile calcination methods using HTi₂NbO₇ as a starting material.The as-prepared samples were characterized by X-ray diffraction pattern?XRD?,high resolution transmission electron microscopy?HR-TEM?,scanning electron microscopy?SEM?,X-ray photoelectron spectroscopy?XPS?,photoelectrochemicalmeasurements,UV-VisspectroscopyaswellasN₂adsorption-desorption measurements.The photocatalytic performance was evaluated by the degradation of rhodamine B?RhB?under visible light irradiation and the possible photocatalytic mechanism was also discussed in detail.Firstly,layered CsTi₂NbO₇ was prepared by high temperature solid synthesis,and then treated with HNO₃ solution to obtain layered HTi₂NbO₇ by a proton-exchange reaction.The resulted layered HTi₂NbO₇ was well dispersed in tetrabutylammonium hydroxide?TBAOH?solution in order to prepare HTi₂NbO₇ nanosheets by exfoliation reaction.The as-prepared HTi₂NbO₇ nanosheets were dried,and then mixed with urea.Nitrogen-doped HTi₂NbO₇nanosheet photocatalyst were successfully synthesized by heating the above mixture.N-doped HTi₂NbO₇ nanosheets exhibited a good photocatalytic activity for photocatalytic degradation of RhB under visible light irradiation.It was found that nitrogen doping resulted in an intrinsic narrowing bandgap so as to widen light response region.The doped nitrogen atoms were mainly located at the interstitial position of Ti₂NbO₇^-sheets and chemically bonded with hydrogen ions.Compared with N-doped HTi₂NbO₇,N-doped HTi₂NbO₇ nanosheets had a larger specific surface area and richer mesoporous structure due to the relatively loose and irregular arrangement of the titanium niobate nanosheets,so that the N-doped HTi₂NbO₇ nanosheets had a higher visible-light catalytic activity than N-doped HTi₂NbO₇.Secondly,HTi₂NbO₇ nanosheet was used as the host material,and CdS nanoparticle sol was used as the positively charged guest.The formed CdS nanoparticl was pillared to the HTi₂NbO₇layer to prepared CdS/HTi₂NbO₇ composite.It can be found that the composite showed an increased interlayer spacing,a large specific surface area and mesoporous structure.When CdS accounts for 20wt%of HTi₂NbO₇,The prepared CdS/HTi₂NbO₇ composite,with an optimal CdS amount of 20wt%,exhibited the highest photocatalytic activity for degradation of RhB under visible light.The degradation rate can reach 98%in half an hour,which is 9.5 times and 1.3times than that of HTi₂NbO₇ and CdS,respectively.The improvement of photocatalytic activity was attributed to the enlarged specific surface area and the effective separation of photogenerated carriers between the host and guest materials.In addition,the photocorrosion effect of CdS could be greatly reduced by introducing HTi₂NbO₇ nanosheet.Finally,nitrogen-doped nanocomposite based on TiO₂ nanoparticles and HTi₂NbO₇nanosheets was also successfully synthesized by first mixing freeze-dried HTi₂NbO₇ nanosheets with titanium isopropoxide,and then calcinating with urea in air.It was found that anatase TiO₂nanoparticles were well-distributed on the surface of HTi₂NbO₇ nanosheets,resulting in the formation of heterojunction structure between two components.The photocatalytic performance was evaluated by the degradation of RhB under visible light irradiation.It indicated that the resultant N-doped nanocomposite showed a highest photocatalytic activity toward the degradation of RhB,owing to the synergistic effects of nitrogen doping,the formation of heterojunction,increased specific surface area and rich mesoporous structure.