Controllable Synthesis And Photocatalytic Activity Of Porous TiO₂-based Composite Materials

In recent years,with the emergence of the worldwide energy shortage and environmental pollution,photocatalysis has been widely concerned as an efficient green technology for tackling the above problems.Among a variety of semiconductor photocatalytsts,TiO₂ has been regarded as one of the best photocatalysts because of its high activity,high stability and low cost.However,TiO₂ can only absorb the UV light in the solar spectrum due to its wide band gap?3.2 e V?.Moreover,the specific surface area and porosity of TiO₂ will influence its photocatalytic efficiency.Therefore,exploring an effective porous TiO₂ based photocatalyst which are driven by the sunlight and visible light is urgently needed.In this study,in order to solve the various problems of TiO₂ photocatalyst in the photocatalytic reaction,we prepared porous TiO₂ based composite photocatalysts by various modification strategies to improve its photocatalytic reactivity.The main points were discussed as follows:1. The ternary Ag/AgBr/TiO₂ composite photocatalyst with high photocatalytic activity were prepared by a simple impregnation and photoreduction method using tetrabutyl titanate,Agand Na Br as precursors.The photocatalytic degradation of Rhodamine B was carried out to test the photocatalytic performance of the as-prepared samples under visible light.The experimental results showed that the as-prepared macroporous/mesoporous TiO₂ has good crystallinity,high specific surface area and porous structure.Ag/AgBr particles were deposited on the surface of TiO₂ pore structure.Compared with pure TiO₂,AgBr and AgBr/TiO₂,the ternary composites AAT-x had the higher photocatalytic degradation of Rh B.When the molar ratio of Ag/AgBr to TiO₂ was 1,the rate constant of ternary composite AAT1 is 3.7,2.2 and1.7 times more than those of pure TiO₂,AgBr and binary AgBr/TiO₂ composites,respectively.The trapping experiment results showed that the·O₂^-and the h⁺were the main active species in the decomposition of Rh B.A possible photocatalytic mechanism of Ag/AgBr/TiO₂ heterojunction photocatalysts was proposed.2. Carbon dots were first prepared by a solvothermal reaction by using candle ash as the precursors.Then,the macroporous/mesoporous CO₂ ternary heterojunction composite photocatalysts with high specific surface area was prepared by simple ultrasonic dispersion and calcination method using carbon dots,tetrabutyl titanate and melamine as precursors.The photocatalytic activity of the samples was evaluated by hydrogen production under visible light irradiation.The experimental results showed that loading amounts of C dots greatly influenced photocatalytic activities under visible light irradiation.When 0.05 g of the carbon dots was loaded,the hydrogen evolution rates of the CCT0.05 sample reached 580 mol/h/g,exceeding the pure TiO₂,pureand the binary O₂ composite photocatalyst by a factor of 6.6 times,2.1 times and 1.6 times,respectively.The enhanced photocatalytic activity can be attributed to the synergistic effect between the high specific surface area of carbon dots and the narrow band gap structure of.The trapping experiments showed that the composite photocatalyst of CCT0.05 had the lowest fluorescence intensity.Therefore,we proposed that the possible photocatalytic mechanism of the CO₂ in hydrogen production.3. The unique composite photocatalyst of CdS/TiO₂ nanofiber with porous structure was prepared by simple electrospinning and microwave hydrothermal method using,thiourea and tetrabutyl titanate as the precursors.The experimental results showed that the amount ofand thiourea had a great influence on the grain size,crystallization and photocatalytic activity of the as-obtained CdS/TiO₂samples.When the mass ratio of CdS to TiO₂ in the binary composite is 0.8,the CdS/TiO₂ composite exhibited the highest hydrogen evolution rate,which was 3.2 and2.72 times than those of pure TiO₂ and CdS,respectively.The enhanced photocatalytic hydrogen production performance under the solar light irradiation is mainly attributed to the narrow band gap of CdS and the synergistic effect between CdS and TiO₂ heterojunction structure.In the trapping experiment,the fluorescence intensity of hydroxyl terephthalic acid gradually increases versus time in presence of the binary CdS/TiO₂ photocatalysts under the solar light irradiation.Therefore,we proposed the possible mechanism for enhanced photocatalytic hydrogen production performance of CdS/TiO₂.