【作者】 张海燕；

【导师】 李佑稷；

【作者基本信息】 吉首大学 ， 化学， 2023， 硕士

【摘要】 能源危机是人类社会可持续发展必然面临和亟待解决的重大课题。光催化工程技术是直接利用低密度的太阳能转换成为化学反应所需的能量,还原再生新物质的先进技术,是解决能源危机问题的有效方式。为此,太阳能光催化分解水制氢技术由于无能耗、无污染,而成为最有前景的能源开发技术。半导体材料是光解水制氢技术的关键,它需要最大限度地利用光能,高的光生电子空穴分离效率以及稳定性。氧化镉（Cd O）由于具有合适的带隙、高载流子迁移率、化学稳定性和低成本等特性被用作可见光驱动的光催化剂。然而,其光生载流子的快速复合和太阳光的光利用率低,也严重制约了实际应用。因此,提高Cd O半导体材料的电荷分离效率以及对太阳光的利用率是增强其光催化性能的关键。本论文以Cd O纤维为基体材料,通过复合、掺杂合成出了三种高效、稳定的三元异质结复合光催化材料,并探究材料的光吸收、光生电荷的分离、转移与传输等性质与光催化析氢性能的关系,以期揭示光催化制氢反应的微观机理。本工作的主要研究内容包括以下三个方面:（1）以硝酸镉、硝酸铟、硫脲为原料,通过静电纺丝技术首先制备出纳米纤维前驱体材料,然后经过热处理合成出一种新型的硫掺杂氧化镉和氧化铟（S/Cd O@In₂O₃）三元异质结纳米复合纤维,并对其光解水制氢性能进行分析。在可见光照射下,所构建的S/Cd O@In₂O₃三元异质结具有很高催化活性,其中In₂O₃和Cd O的摩尔比为0.25时,S/Cd O@In₂O₃-25表现出最优异的光催化析氢性能(析氢速率可高达4564.5μmol·g^-1·h^-1),是样品S/In₂O₃和S/Cd O析氢性能的1261.0和22.0倍。该材料突出光催化析氢活性,主要归因于S/Cd O@In₂O₃纳米纤维形成三元异质结,有丰富的氧空位,低的H*原子的吸收能,促进了光生电荷的分离与迁移。另外,S/Cd O@In₂O₃纳米材料表现出较好的光催化析氢稳定性,经过连续4次循环反应后,S/Cd O@In₂O₃-25的光催化活性仍能保持初始活性的85%左右,这归功于复合催化剂化学结构稳定性好。（2）以硝酸镉、氯铂酸为反应原料,通过静电纺丝-热处理技术首先制得一种Pt-Cd O前驱体复合纳米纤维;通过热缩合法制备出g-C₃N₄纳米片;然后,将Pt-Cd O复合纳米纤维和g-C₃N₄纳米片进行研磨混合,之后将所得混合物在N₂氛围下进行煅烧处理,成功制备出一种g-C₃N₄/Pt-Cd O三元异质结复合光催材料,并对其光解水制氢性能进行分析。在模拟太阳光照射下,g-C₃N₄/Pt-Cd O三元异质结复合体具有很高的催化活性,当Pt和Cd O的摩尔比为1.5%,Pt-Cd O与g-C₃N₄的质量比为0.4时,所获得的g-C₃N₄/1.5Pt-Cd O-4复合材料的析氢速率可以高达200.8μmol·g^-1·h^-1,该性能明显优于g-C₃N₄(69.3μmol·g^-1·h^-1)和Pt-Cd O(77.8μmol·g^-1·h^-1)的光催化析氢效率。这归功于g-C₃N₄/Pt-Cd O纳米复合体形成三元异质结具有低阻抗效应和高的光电流响应,助催化剂Pt可以有效地俘获Cd O的光生电子,向g-C₃N₄价带传递,促进电子-空穴对的分离,实现更有效地光催化析氢反应。基于半导体的能带结构,提出了基于三元异质结的Z型电荷载流子转移机制。经过连续3次循环稳定性测试后,g-C₃N₄/Pt-Cd O复合光催化剂材料的活性还能够保持最初光催化析氢性能的80%,这归功于复合催化剂化学结构稳定性好。（3）以硝酸镉盐为镉源,采用静电纺丝法和热处理法先制备出Cd O纳米纤维;以硫粉和硝酸镍为反应原料,利用光沉积技术在所制备的Cd O纳米纤维上生成Cd S和Ni S₂,成功合成出Cd O/Cd S/Ni S₂三元异质结纳米复合材料,在模拟太阳光照射下,并对其光解水制氢性能进行研究。Cd O/Cd S/Ni S₂复合体具有很高的可见光催化活性,当Cd S-Ni S₂负载量为3wt%,相比于Cd S(519.5μmol·g^-1·h^-1)和Cd O/Cd S(578.5μmol·g^-1·h^-1),Cd O/Cd S/Ni S₂三元异质结光催化材料产生H₂的反应速率可高达1085.0μmol·g^-1·h^-1。这归功于Cd O/Cd S/Ni S₂纳米复合体形成三元异质结具有低阻抗效应和高的光电流响应,Ni S₂作为助催化剂,俘获Cd S的光生电子,增强电荷转移,提高光催化析氢反应效率。基于半导体的能带结构,提出了基于三元异质结的Z型电荷载流子转移机制。同时,经过3次循环反应之后,该复合材料的光催化反应活性仍然能够维持最初光催化析氢性能的84%。这归功于复合催化剂化学结构稳定性好。更多还原

【Abstract】 The energy crisis is a significant challenge for human society,and it requires urgent attention to achieve sustainable development.Photocatalytic engineering technology enables the direct conversion of low-density solar energy into the energy needed for chemical reactions,making it an advanced technology for the regeneration of new substances and an effective solution to the energy crisis.Therefore,solar photocatalytic water splitting hydrogen production technology has become the most promising energy development technology due to its zero energy consumption and lack of pollution.Semiconductor materials are crucial for photocatalytic water splitting hydrogen production technology,and they must maximize light energy utilization,have high efficiency in separating photogenerated electrons and holes,and be stable.Cadmium oxide（Cd O）is a promising visible light-driven photocatalyst due to its appropriate bandgap,high carrier mobility,chemical stability,and low cost.However,the rapid recombination of its photogenerated carriers and low utilization of solar energy severely limit its practical application.Therefore,improving the charge separation efficiency of Cd O semiconductor materials and the utilization efficiency of solar energy is key to enhancing its photocatalytic performance.In this paper,three efficient and stable ternary heterojunction composite photocatalytic materials were synthesized by composite and doping,using Cd O fibers as the matrix material.The relationship between the properties of light absorption,separation,transfer,and transmission of photogenerated charges and the photocatalytic hydrogen production performance of the materials was explored to reveal the micro-mechanism of photocatalytic hydrogen production.The primary research content of this work includes the following three aspects:（1）Starting with cadmium nitrate,indium nitrate,and thiourea as raw materials,a precursor material of nanofibers was first prepared through electrospinning technology.Subsequently,a novel sulfur-doped cadmium oxide and indium oxide（S/Cd O@In₂O₃）ternary heterojunction nanocomposite fiber was synthesized through heat treatment.The photocatalytic hydrogen production performance of this material was then analyzed.Under visible light irradiation,the constructed S/Cd O@In₂O₃ternary heterojunction exhibited high catalytic activity.Specifically,when the molar ratio of In₂O₃to Cd O was0.25,S/Cd O@In₂O₃-25 showed the best photocatalytic hydrogen production performance with a hydrogen evolution rate of 4564.5μmol·g^-1·h^-1,which was 1261.0and 22.0 times higher than that of S/In₂O₃and S/Cd O samples,respectively.The exceptional photocatalytic hydrogen evolution activity of this material is mainly attributed to the formation of the ternary heterojunction structure of S/Cd O@In₂O₃nanofibers.This structure has abundant oxygen vacancies and a low absorption energy for H*atoms,promoting the separation and migration of photo-generated charges.Furthermore,the S/Cd O@In₂O₃nanomaterial showed good photocatalytic hydrogen evolution stability.After four consecutive reaction cycles,the photocatalytic activity of S/Cd O@In₂O₃-25 could still maintain around 85%of its initial activity,thanks to the good chemical stability of the composite catalyst structure.（2）Cadmium nitrate and chloroplatinic acid were used as reaction materials to prepare a Pt-Cd O precursor composite nanofiber by electrospinning and heat treatment.Graphitic carbon nitride（g-C₃N₄）nanosheets were prepared by thermal condensation.Then,the Pt-Cd O composite nanofiber and g-C₃N₄nanosheets were mixed by grinding and calcined under N₂atmosphere to obtain a g-C₃N₄/Pt-Cd O ternary heterojunction composite photocatalyst.The photocatalytic performance for hydrogen evolution from water splitting was analyzed.Under simulated solar light irradiation,the g-C₃N₄/Pt-Cd O ternary heterojunction composite photocatalyst exhibited high catalytic activity.When the molar ratio of Pt and Cd O was 1.5%,and the mass ratio of Pt-Cd O to g-C₃N₄was0.4,the hydrogen evolution rate of the g-C₃N₄/1.5Pt-Cd O-4 composite material could reach 200.8μmol·g^-1·h^-1,which was significantly higher than the photocatalytic hydrogen evolution efficiency of g-C₃N₄(69.3μmol·g^-1·h^-1)and Pt-Cd O(77.8μmol·g^-1·h^-1).This was due to the formation of a ternary heterojunction in the g-C₃N₄/Pt-Cd O nanocomposite,which had a low impedance effect and a high photoelectric current response.The catalytic agent Pt can effectively capture the photo-generated electrons of Cd O,transfer them to the conduction band of g-C₃N₄,promote the separation of electron-hole pairs,and achieve a more efficient photocatalytic hydrogen evolution reaction.Based on the band structure of semiconductors,a Z-scheme charge carrier transfer mechanism based on the ternary heterojunction was proposed.After three continuous stability tests,the activity of the g-C₃N₄/Pt-Cd O composite photocatalyst material could still maintain about 80%of the initial photocatalytic hydrogen evolution performance,which was due to the good chemical structural stability of the composite catalyst.（3）Cadmium oxide（Cd O）nanofibers were first prepared using electrospinning and heat treatment methods,with cadmium nitrate as the cadmium source.Cd S and Ni S₂were then synthesized on the Cd O nanofibers using sulfur powder and nickel nitrate as reaction materials,respectively,via a photodeposition technique.The resulting Cd O/Cd S/Ni S₂ternary heterostructure nanocomposite was investigated for its photocatalytic hydrogen production performance under simulated sunlight irradiation.The Cd O/Cd S/Ni S₂composite exhibited high visible-light photocatalytic activity,with a reaction rate of up to 1085.0μmol·g^-1·h^-1,compared to Cd S(519.5μmol·g^-1·h^-1)and Cd O/Cd S(578.5μmol·g^-1·h^-1)when the Cd S-Ni S₂loading amount was 3 wt%.This was attributed to the formation of a ternary heterostructure with low impedance and high photocurrent response,as well as the use of Ni S₂as a co-catalyst that captured the photo-generated electrons of Cd S,enhanced charge transfer,and improved the efficiency of photocatalytic hydrogen evolution.Based on the semiconductor band structure,a Z-scheme charge carrier transfer mechanism based on the ternary heterostructure was proposed.After three cycles of reaction,the photocatalytic activity of the composite material was still able to maintain 84%of its initial performance.This was attributed to the good chemical stability of the composite catalyst.更多还原