Synthesis And Photocatalytic Properties Of A/M/SrSO₄?A=TiO₂,Bi₂WO₆;M=Ag,Pt? Double-heterojunction Nanomaterials

With the development of science and technology,the rapid changes have taken place in people's lives.Science and technology has provided the new ways to facilitate the human beings convenience,at the same time,brought environmental pollution and a lot of hidden crisis.At present,the energy crisis and environmental pollution have become two major problems restricting the development of human society.Titanium dioxide?TiO₂?with good stability and high catalytic activity has succeeded in capturing the attention of scientists.However,there are some critical issues which cannot be ignored for the practical applications of TiO₂ as a photocatalysts,which include the poor quantum efficiency,narrow range of photo-response and recycling issues,which restrict the development of TiO₂.In order to enhance the photocatalytic activity of nano materials,plenty of work has been carried out to decrease the band gap and inhibiting the recombination of photo-generated electron-hole pairs,including doping metallic ions or nonmetallic ions and deposition of noble metals.Heterojunction has been widely used in many aspects such as in electronic devices,electrode materials for supercapacitor,thermoelectric materials.Heterojunction is also widely used for the photodegradation of pollutants and production of hydrogen.In order to enhance the photocatalytic activity,we designed several double-heterojunction structured materials.In this thesis,we mainly focus on the synthesis and catalytic performance of several double-heterojunction structure materials.There are seven main parts in this thesis:1)The TiO₂/M/SrSO₄?M=Ag,Pt?double-heterostructured catalysts were synthesized by modified Composite-Hydroxide-Mediated Approach and UV irradiation reduction method.The degradation of methylene blue?MB?in the presence of TiO₂ nanoparticles,Ag/TiO₂ heterojunction,Sr SO₄/TiO₂ heterojunction and TiO₂/Ag/SrSO₄ double-heterojunction catalysts under the simulated solar light illumination were investigated.The degradation of NO in presence of the TiO₂/Ag/SrSO₄ double-heterojunction catalysts was also investigated.From the experimental results and theoretical calculations,in the TiO₂/Ag/SrSO₄ double heterojunction structure,where TiO₂ nanoparticles work as light harvester to generate electron-hole pairs,Ag nanoparticles conduct as electron trapped and accumulated sites,and SrSO₄ nanoparticles are used to build coherent electron transportation paths and consumption sites.The accumulated electrons in Ag nanoparticles greatly promotes the localized surface plasmon resonance effect,which pumps electrons to SrSO₄,and the high valence band potential and strong adsorption of SrSO₄ ensures the good electron consumption sites and promotes photocatalysis.The holes in TiO₂ react with adsorbed OH-and produce H2 O and OH,while and electrons on SrSO₄ react with adsorbed O₂ to produce O₂-,HO₂ and OH.The electron flow path forms as ECB?TiO₂??Ef?Ag??ECB?Sr SO₄?and then photogenerated electron-hole pairs can be successfully separated,holes on TiO₂ and electrons on SrSO₄.2)The Sr SO₄/Ag/Bi₂WO₆ double-heterostructured catalysts were synthesized by hydrothermal method and UV irradiation reduction method.The degradation of MB in presence of Ag/Bi₂WO₆ heterojunction catalysts using different weight ratio under the simulated solar light illumination was investigated.The SrSO₄/Ag/Bi₂WO₆ double-heterostructures display the higher activity for the degradation of MB under simulated sunlight irradiation.In the SrSO₄/Ag/Bi₂WO₆ double heterojunction structure,Bi₂WO₆ nanoparticles work as light harvester to generate electron-hole pairs,Ag nanoparticles conducted as electron trapped and accumulated sites,and SrSO₄ nanoparticles are used to adsorb O₂ and OH-ions on different exposed facets.3)The TiO₂/Pt/SrSO₄ double-heterostructured catalysts were synthesized by modified Composite-Hydroxide-Mediated Approach and UV irradiation reduction method.The photocatalytic H2 evolution using TiO₂/M/SrSO₄?M=Ag,Pt?and double-heterostructured catalysts were investigated in details.TiO₂/M/SrSO₄?M=Ag,Pt?displayed high activity for H2 evolution with the catalytic activity and morphologic stability in 20% methanol solution,which is about 2100 ?mol/h/g.The high activity of H2 evolution is due to that photogenerated electron-hole pairs,which can be successfully separated.On the other hand,the good adsorption ability of SrSO₄ ensures the good electron consumption sites for photodecomposition of water.