Preparation And Photocatalytic Performance Of Titanium-Based Binary Composite Oxides

Titanium dioxide photocatalytic technology is a promising semiconductor material,which can be used to alleviate the environmental and energy problems,and it has been widely concerned and applied.The development of composite photocatalytic materials has important scientific significance to promote the semiconductor photocatalytic technology in the utilization of solar energy.In this paper,TiO₂ was used as the matrix,and the TiO₂/SiO₂,TiO₂/Bi₂WO₆ and TiO₂/Bi_3.64Mo_0.36O_6.55 photocatalyst were synthesized by template-solventhermal method,solventhermal method and in situ-solventhermal method,and the effects of morphology and microstructure of the composite materials on their photocatalytic performance have also been studied.Through the photocatalytic degradation of pollutant to evaluate the photocatalytic activity of the catalyst,and discussed the free radical trapping experiment,electron spin resonance technique,fluorescence spectrum and photoelectrochemical test,the possible photocatalytic mechanism was proposed.First,the binary composite semiconductor photocatalyst TiO₂/SiO₂ was prepared by template-solventhermal method.Rhodamine B was used as the degradation model to evaluate the photocatalytic degradation of organic pollutants under UV and visible light,and to improve the utilization of solar energy.Under optimized conditions,the apparent rate constant of TS2?TS2 represent the titanium silicon molar ratio of 1:1?is as much as 33 times that of pure TiO₂ and is more than 6 times that of commercial TiO₂?P25?under visible light irradiation.Moreover,the apparent rate constant of TS2 is also as much as 5 times that of pure TiO₂ and is more than 1 times that of P25 under UV light irradiation.It is noteworthy that the TS2 photocatalyst exhibits good photostability under visible light irradiation and its photocatalytic efficiency only reduces by 9% after 5 repeated cycles.Under the condition of 40 min of the visible light,the degradation rate of methyl orange is only 11.6%,the photocatalytic activity of the TS2 composite photocatalyst for RhB is best under visible light irradiation.The composite semiconductor photocatalyst TiO₂/SiO₂ exhibits selective photocatalyticactivity based on the decomposition of RhB.The degradation efficiency of RhB on TS2 decreases to 19.0% and 37.8% when 1,4-benzoquinone?BQ?or ethylenediaminte-traacetic acid disodium?EDTA-2Na?is added into the photocatalytic reaction solution,respectively,confirming that the superoxide radicals?·O₂-?and photogenerated holes?h+?play important role in the photocatalytic degradation of Rh B.The degradation efficiency of RhB decreases to 95.7% when t-butyl alcohol?TBA?is added into the reaction solution.Therefore,it can be assumed that the hydroxyl radicals?·OH?is not the main reactive species.Second,TiO₂/Bi₂WO₆ composite materials have been designed and synthesized through solventhermal method.Through the photocatalytic activity evaluation by the degradation of two different kinds of pollutants?RhB,TC and CIP?under visible light irradiation to broaden the practical application of the composite.The corresponding ln?C0/C?plot has a good linearity,indicating that the visible light-driven photodegradation of RhB solutions in the presence of different photocatalysts follows the first order kinetics.The apparent rate constant of TB2?The molar ratio of TiO₂ to Bi₂WO₆ is 1:1?is 0.1598 min-1,which is much higher than that of Bi₂WO₆?0.0996min-1?,TiO₂?0.0165 min-1?and P25?0.0255 min-1?.The result showed that the TC conversion was 63.3% by TB2 under visible light irradiation within 40 min,while only 33.9% of TC can be degraded by pure Bi₂WO₆,only 56.9% of TC can be degraded by pure TiO₂.The as-prepared composite revealed enhancements in the photocatalytic degradation activity of RhB,TC and CIP under visible-light irradiation due to the effects of low recombination rate of electron–hole pairs in the heterogeneous interface between the two semiconductors.TiO₂/Bi₂WO₆ composite reduced PL intensity more largely than the solely Bi₂WO₆,indicating that the formation of composites restrained the recombination of electron and holes.The photoelectrochemical current measurement has shown largely increased photocurrent and electrochemical impedance spectroscopy which has depicted a lower charge transfer resistance that is composed of un-recombined photogenerated electrons and holes.The ESR results show that ·O₂-is the reactive oxygen species for TB2 in the degradation of RhB,which is in agreement with the trapping experiments for theactive species.On the basis of this,the possible photocatalytic mechanism is proposed.At last,TiO₂/Bi_3.64Mo_0.36O_6.55 composite photocatalyst with various loading amount of TiO₂ to Bi_3.64Mo_0.36O_6.55 was prepared by an in situ-solventhermal method.Bi_3.64Mo_0.36O_6.55 can degrade 85.8% of RhB after irradiation of 30 min.However,the photocatalytic activity of TiO₂?15wt%?/Bi_3.64Mo_0.36O_6.55?denoted as TBMO₃?composite is distinguishing enhanced after the introduction of TiO₂ nanosheets.The photocatalytic degradation of RhB solution fits the first order kinetic reaction.The calculated k value for the TBMO₃ was 0.2068 min-1,which was 4.5,10 and 94 times higher than that of Bi_3.64Mo_0.36O_6.55,P25 and TiO₂,respectively.By making full use of the high specific surface area of TiO₂?134.24 m2·g-1?,the specific surface area and porosity of the composites were studied,and the obvious advantages of the specific surface area in the photocatalytic activity of the composite materials were proved.The result indicated that a slower average lifetime is 4.61 ns of TBMO₃ compared to the Bi_3.64Mo_0.36O_6.55 is 6.77 ns.The higher photocatalytic activity can be attributed to efficient charge transfer and separation.The fluorescence spectra further demonstrate that the synergistic effect between TiO₂ and Bi_3.64Mo_0.36O_6.55 can effectively achieve the separation and transport of the photoinduced charge carriers,which might be attributed to the Z-type photocatalytic mechanism.TiO₂/Bi_3.64Mo_0.36O_6.55 photocatalysts have good stability,suggesting that the composite materials could be an effective strategy for formulating new efficient photocatalyst in water purification and environmental treatment applications.