Preparation And Properties Of Novel Binary Heterojunction Photocatalysts

Energy crisis and environmental pollution are the two major crises in the current world.Photocatalytic degradation technology has become an effective way to degrade various organic pollutants in waste water due to its low cost and high safety.Many semiconductors have been developed as photocatalysts,such as transition metal oxides,metal sulfides,and metal oxysalts,etc.However,the high recombination rate of photogenerated carriers（electrons and holes）and the low photo-generated current and the wide band gap of traditional semiconductors make the photocatalytic efficiency poor.In order to suppress the recombination of electrons and holes,improve the photocurrent and enhance the effective absorption of light,different technologies have been adopted,in which to build heterostructures is one of the most promising approaches.In this paper three different heterostructure photocatalysts were constructed by difference materials to suppress the recombination of photogenerated carriers,boost the photocurrent,increase the utilization rate of sunlight and improve the photocatalytic performance of the photocatalyst.The main researches are as follows:（1）The CeO₂/graphene composite photocatalyst.The CeO₂/graphene heterojunction photocatalyst was obtained by a single-step ultrasonic way at room temperature.The samples were characterized by XRD,TEM,TPC and EIS.The photocatalytic properties of CeO₂/graphene heterojunction photocatalysts were investigated by using rhodamine B（Rh B）as a simulated pollutant under UV light irradiation.The results showed that CeO₂ nanoparticles were uniformly distributed on the surface of graphene,which increases the separation efficiency of electron-hole pairs and boosts the photocurrent.Under the optimal loading conditions,the photocatalytic degradation extent can reach90%within 5 minutes and the degradation efficiency was greatly improved.（2）The Cd（OH）₂/Bi₁₀Cd₃O₂₀（CBDO）binary type II heterostructure photocatalyst.Binary n-n type heterojunction photocatalyst CBDO were synthesized by a one-step hydrothermal way.The samples were characterized by XRD,SEM,TEM,UV-Vis,TPC and EIS.The n-n binary heterojunction was formed by loading BDO nanorods on Cd（OH）₂ hexagonal micro-block.The photocatalytic degradation performance of Rhodamine B（Rh B）was investigated under UV light irradiation.The results showed that under the condition of p H=10,at 200℃and in 24h,the photocatalytic degradation efficiency was the highest,and Rh B can be completely degraded within 30 minutes.The photocatalytic performance of CBDO mainly depends on superoxide radicals（·O₂^-）,followed by hydroxyl radicals（·OH）and holes（h⁺）.Photocatalytic reaction mechanism has also been proposed.（3）Preparation of binary type IIα-Bi₂O₃/Bi₁₂TiO₂₀（BBTO）cross-shaped heterojunction with enhanced visible light photocatalytic performance.The binary type IIα-Bi₂O₃/Bi₁₂TiO₂₀ heterojunction composite was successfully obtained by a simple hydrothermal process.The p H value and the Bi/Ti molar ratio were the key to form theα-Bi₂O₃/Bi₁₂TiO₂₀ heterojunction.Theα-Bi₂O₃ nanobelts intertwined with the Bi₁₂TiO₂₀nanobelts to form a cross-shaped structure in the composite.The obvious red-shift can be detected in Raman spectra.UV-vis DRS also revealed that the effectively reduced band gap of the heterojunction composite led to sunlight absorption in a larger range.Meanwhile,the photocurrent responses and the EIS demonstrated that the combination of Bi₁₂TiO₂₀ andα-Bi₂O₃ significantly promoted the separation of photogenerated electron-hole pairs and suppressed their recombination,which was also confirmed by PL analysis.Furthermore,photocatalytic degradation experiments proved that the BBTO heterojunction composite had excellent catalytic performance under visible light,whose rate constant value（k）was about 2.0 times that of pureα-Bi₂O₃ and4.5 times that of pure Bi₁₂TiO₂₀samples.A possible photocatalytic mechanism of BBTO was also proposed based on p-p and type II heterojunction.It was concluded that the heterojunction structure markedly promoted the migration and separation of carriers to enhance its photoactivity.