Fabrication And Photocatalytic Performance Of Wide Band Gap Semiconductors Modified By Red Phosphorus Nanostructure

In recent years,the world is facing serious environmental pollution and energy shortage crisis,developing semiconductor photocatalytic technology is an effective way to solve the current problem.TiO₂ has been most intensively and the earliest studied because of its high stability,non-toxic,low cost and environmental friendliness.More interestingly,SrTiO₃ has a band gap of 3.2e V comparable to TiO₂,which been proved to be favorable energy for photocatalysis,since its conduction band edge is 200 m V more negative than TiO₂.However,these photocatalysts are only effective under UV light irradiation（only 5%）,and greatly restricts its practical application for solar spectrum rang.As well known,coupling two semiconductors with different band gaps together to form hybrid composites can effectively prohibit the recombination of photogenerated electron-hole pairs.A build-in internal electric field would be generated across the heterojunction interface which can force electrons and holes to transfer towards opposite direction across the interface,and therefore prolonged the survival lifetime of photogenerated carriers.The red phosphorus has a band gap of 1.8e V,which ensures a wide visible light absorption band extending to 700 nm.However,suffering from a rapid recombination of photogenerated electron-hole pairs,the photocatalytic activity for H2 formation over red P is very limited.Recently,we developed a novel technique to synthesize highly crystalline fibrous P nanostructures coupled with P doped Cr2O3 和 P@P-g-C3N4 via vacuum-sealed quartz tube method and this composite exhibited very efficient photocatalytic performance under visible and near infer red light illumination.Motivated by their results,we prepared red phosphorus nanostructures composited with TiO₂ or STO nanoparticles by the same method.The obtained heterostructured composite photocatalysts exhibit outstanding photodegradation and H2 production activities under the visible light irradiation.These work show a useful insight to exploit elemental P based on heterostructured photocatalysts for environment and clean energy source application.Master’s reseanch work has the following contents:1.A facile calcination approach was used to synthesize red phosphorus nanostructures/TiO₂ and red phosphorus nanostructures/STO heterostructured composites.The Results show that by carefully adjusting the synthesis temperatures and the molar ratio of precursors,the crystal quality and morphology of composite materials has changed.The calcination temperature of 700℃ and precursors suitable proportion can form the larger specific surface area and intimate contact heterojunction.Finally,the optimized RP1.0/TiO₂-700 ℃ and RP2.0/SrTiO₃-700 ℃ composites has excellent photocatalytic performance.2.The photocatalytic properties performance testing and mechanism analysis of nanostructures RP/TiO₂ compositesBy carefully adjusting the synthesis temperatures and the molar ratio of precursors,the hydrogen yield for the optimum RP1.0/TiO₂-700°C reaches 276μmolh-1g-1 improving 12.7 times compared with pure RP,and the composite photocatalysts highlight excellent photocatalytic degradation efficiency under visible light irradiation,improving 7.4 times.The composites were characterized for crystal structure,morphology,thermal stability and optical properties.Thin nanorod-like RP nanostructures with a large exposed surface and a good surface contacting with TiO₂ were obtained.The synergetic effect of heterostructured RP/TiO₂ composites leads to an enhanced charge separation and transfer,and a better utilization of visible-light.In addition,we research the charge transfer dynamics of heterostructured photocatalyst.3.The photocatalytic properties and mechanism study of the nanorods RP/STO compositesWe prepared red phosphorus nanostructures composited with STO nanoparticles by the same method.Various structural characterizations,including XRD,Raman,UV-vis,SEM-EDX and FT-IR,indicate that nanorod-like RP nanostructures with a large exposed surface and a good surface contacting with STO.The photocatalytic performance of RP/STO composites were evaluated,photocatalytic degradation efficiency of RP2.0/SrTiO₃-700 ℃ increasing 6.8 times,and hydrogen production efficiency of RP2.0/SrTiO₃-70℃ reaching 169.95mmolh-1g-1.In order to study the superior photoactivity of mechanism of RP/STO composites,the photo-induced I-t curves and EIS curves of pure STO,bare P and RP2.0/STO-700°C composites were measured,indicating a more effective separation of photogenerated electron-hole pairs and faster interface charge transfer in the RP/TiO₂ composites.In addition,the reactive oxygen species（ROS）were tested,which shows that h+,OH,.O2-act as main reactive species in RP/STO photocatalyst reaction system.On the basis of the above experimental results,the efficient photocatalytic mechanism for RP/STO composite is tentatively proposed.