Preparation And Catalytic Properties Of One-Dimensional Nanotubular Photocatalysts

Photocatalysis uses light to stimulate electrons to cause chemical reactions,which can break and recombine chemical bonds under mild conditions.Photocatalysis has many advantages,such as green,clean,safe,environmental friendly and easy control.Many researchers have tried to use photocatalytic methods to achieve various organic reactions,such as reduction coupling of nitroaromatic compounds,Suzuki-Miyaura cross-coupling reaction,cyclohexane oxidation,and photocatalytic degradation of organic compounds.However,many factors,such as low photocatalytic efficiency,low universality,unclear mechanism and low visible light utilization efficiency,are still the bottlenecks restricting the further development of photocatalytic field.This thesis aims to improve photocatalytic efficiency of one-dimensional photocatalysts,by means of noble metal doping semiconductors,construction of heterojunction and multi-component heterojunction.Several one-dimensional tubular photocatalysts such as Au/CuCo₂O₄ binary photocatalyst,Au/CuO/Co₃O₄and Pd/CuO/Co₃O₄ ternary photocatalyst were fabricated and their photocatalytic properties were studied.Considering the cost of the noble metals such as Au and Pd,we also synthesized Au/Fe₃O₄/PEI/rGO nanocomposite catalysts,which can be reused at a simple and low cost way while maintaining the catalytic activity of noble metals.This thesis is categorized into five chapters.Chapter 1:Firstly,a literature survey is provided summarizing the principles of photocatalysis,the progress of semiconductor photocatalysis,the factors affecting the photocatalytic activity,and the ways to improve the photocatalytic efficiency.Secondly,we introduce the method of preparing one-dimensional nanomaterials by electrospinning technology.Chapter 2:Au/CuCo₂O₄ binary photocatalyst was synthesized and its catalytic performance in the selective hydrogenation of?,?-unsaturated aldehydes under visible light irradiation was studied.In this work,CuCo₂O₄,a one-dimensional tubular semiconductor photocatalyst,was synthesized by a simple and low-cost electrospinning method.Then a semiconductor/noble metal heterojunction was constructed by introducing noble metal nanoparticles through photo-induced method.The binary catalyst utilizes the advantages of surface plasmon resonance of gold nanoparticles.Meanwhile,it also utilize the charge separation characteristics of gold nanoparticles/semiconductor interface.Compared with single semiconductor CuCo₂O₄,the binary catalyst can achieve a more efficient photocatalytic selective hydrogenation of?,?-unsaturated aldehydes.Taking 5-hydroxymethyl furfural as an example,after 60 minutes of reaction,the conversion and selectivity of Au/CuCo₂O₄binary photocatalyst reached 93%and 100%.The application of semiconductor-based photocatalysts in organic reactions is of great significance for expanding the scope of photocatalysis,and understanding of the catalytic reaction mechanism.Chapter 3:Au/CuO/Co₃O₄ ternary photocatalyst was synthesized and its catalytic performance in visible light photocatalytic water oxygen release reaction was studied.In this work,a suitable heterojunction was firstly designed and synthesized by simple and low-cost electrospinning method.Then this heterojunction was applied to the photocatalytic oxygen release reaction.On this heterojunction,noble metals are then introduced to construct a three-component heterojunction.This three-component heterojunction structure combines the advantages of heterojunction and surface plasmon resonance.In the visible spectrum range,the light response can be greatly enhanced,and the electron/hole recombination can be effectively prevented,thereby improving the catalytic efficiency.The rate of oxygen release reached 2.92 mmol h^-1g^-1.Compared with the binary photocatalyst CuO/Co₃O₄,its catalytic efficiency was improved by 47%.Chapter 4:Pd/CuO/Co₃O₄ ternary photocatalyst was synthesized.The photocatalytic activity of Pd/CuO/Co₃O₄ ternary photocatalyst was evaluated by the photocatalytic degradation of methylene blue?MB?.The catalyst was synthesized by a simple,low-cost electrospinning and photo-induced method.The advantages of multi-component heterojunction were utilized to achieve high photodegradation of methylene blue.At the same time,it is hoped to take advantage of multi-components heterojunction to widen the scope of degradable substrates,broaden the light absorption and improve the efficiency of photocatalytic degradation.Modification of CuO/Co₃O₄ photocatalyst with different noble metals may help to understand the catalytic mechanism.Chapter 5:Au/Fe₃O₄/PEI/rGO nanocomposite catalyst was synthesized,and the catalytic activity for the reduction of 4-nitrophenol was studied.The rate constant was found to reach 0.429 min^-1.The good catalytic properties can be attributed to the well-dispersed gold nanoparticles,which is chemically bound to graphene.The presence of ferriferrous oxide enables the recycling of the catalyst.