兰州大学机构库 >物理科学与技术学院
两种典型光催化剂的形貌控制合成及其用于构筑复合界面提升反应活性的研究
Alternative TitleMorphology controlled synthesis of two kinds of typical photocatalysts to fabricate heterostructure interface with enhanced photocatalytic activity
马新龙
Thesis Advisor王育华
2018-03-20
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword光催化 晶面 复合界面 助催化剂 异质结 光腐蚀 选择性
Abstract

光催化技术由于在环境治理和清洁能源等方面具有独特的优势和应用前景,近年来得到了广泛的关注和研究。光催化的核心关键问题逐渐清晰,包括光子吸收、载流子分离与转移和表面反应活化等,相应的有效策略被提出和验证,如能带调控、晶面控制、异质结构筑和助催化剂负载。其中,很多关键因素,如晶面、助催化剂和异质结等,在光催化反应过程中的角色表现出多重化且相互关联。大量基础研究表明,活性晶面是单组分光催化剂活性提升的关键因素;在多组分光催化剂中,异质结与助催化剂的存在,在复合界面处起到驱动载流子分离和转移及表面反应活化的作用,使得复合界面的晶面表现出不同的性质。反过来,复合界面处的载流子定向驱动和活化作用也依赖于界面处的晶面特性。因此,研究复合界面处的晶面是探索载流子分离与转移和活化效率提升的关键途径。 本工作选取典型光催化剂ZnO和Ag3PO4作为研究对象,分别通过界面位点选择性和界面晶面选择性两方面系统研究了晶面控制在复合界面的调控作用及对反应活性的提升效率。 第一方面,选取ZnO多孔纳米片作为研究对象,通过水热合成形貌控制来理解其晶面生长演变规律及对应光催化活性差异,接着通过研究其选择性光腐蚀对ZnO活性和稳定性的影响,进而通过吸附和降解过程研究选择性腐蚀产生的内在原因,探究活性晶面在选择性光腐蚀中的内在作用,建立腐蚀位点与活性晶面的关系,并在六角片状等其它形貌的ZnO中验证关联的普适性。研究表明,光催化降解活性优异的ZnO多孔纳米片存在选择性光腐蚀现象,能够造成单位质量活性的明显降低,归因于活性晶面的损失。同时,相同电性染料分子对ZnO的吸附位点和反应位点都存在类似的竞争关系,表明这种选择性腐蚀是染料分子选择性吸附和活性晶面损失共同作用下的结果,其根本原因归因于ZnO纳米片中的孔周围(002)晶面为极性晶面和活性晶面的双重角色。六角片状和六角碗状的ZnO在罗丹明B溶液中的选择性腐蚀,证实了(002)晶面是既是吸附位点的极性晶面,也是降解反应发生的位点。 在活性晶面认识的基础上,通过负载双助催化剂,探索两种助催化剂在ZnO纳米片上的沉积位点规律,研究其沉积位点的自主选择性,并对比分析这种选择性对空间载流子分离效率的影响,揭示不同沉积位点界面处的ZnO晶面对光催化反应活性的影响差异。结果表明,助催化剂在二维ZnO纳米片上的自主选择性沉积仍具挑战,主要有分布规律的影响因素众多、降解活性并没有体现出优势、未能在气相光催化反应中测试活性等问题。与此同时,在ZnO多孔纳米片的研究基础上,设计并合成了选择性复合和随机复合的ZnO/CdS,测试了光电性质和产氢效率。通过对比两者之间的差别,阐述选择性构筑异质结的优势所在。结果表明,ZnO/CdS-S2表现出了最优的光催化产氢活性,产氢速率达到384 µmol·g-1·h-1,高出纯CdS(25 µmol·g-1·h-1)的14倍,且ZnO/CdS-S2的产氢效率要比ZnO/CdS-R2的高,表明异质结的选择性构筑较随机分布表现出更高的产氢活性,揭示了异质结界面处的晶面对光催化反应效率具有重要作用。 第二方面,选取Ag3PO4为另一种研究对象,集中探究影响其形貌的因素,通过控制变量,对这些因素进行逐个系统研究。研究表明,Ag3PO4的形貌受动力学和热力学两方面影响。动力学方面的影响因素有滴加方式(滴加速率和滴加顺序)、离子浓度比、离子总浓度、体系饱和度和pH等,而热力学方面主要是温度导致的离子浓度比和饱和度变化。当然,以上这些影响因素背后的本质原因不尽相同,却又相互交叉。研究发现,一些生成条件可以相互耦合而无明显相互干扰,如温度与离子浓度比等,为不同Ag3PO4晶面构筑复合界面的研究提供了条件和思路。 基于不同条件下晶面生长的规律,通过一步混合、离子交换法复合及异相成核法复合三种方式制备了Ag3PO4的复合物。通过一步混合制备的Ag3PO4/TiO2混合物在黑暗中存在自腐蚀现象,其中Ag的化学环境发生的变化不同于光腐蚀,在紫外光下降解活性不随自腐蚀而变化,却表现出较差的可见降解活性。通过离子交换法复合制备的Ag3PO4/AgBr和Ag3PO4/Ag2CN2复合物中,Ag3PO4形貌特定,另一组分形貌却不受合成条件控制,分别为颗粒状和刺状。通过异相成核法复合制备的异质结Ag3PO4/Ag2CN2和同质结Ag3PO4(1)/Ag3PO4(2)复合物中,由于各自形貌对应的生长条件可以无干扰耦合,两种组分的特定形貌可以实现复合,形成特定晶面构筑的复合界面,为研究Ag3PO4不同晶面在复合界面处的调控规律提供了可能。

Other Abstract

Photocatalysis technology has been widely concerned and studied in recent years due to its unique advantages in environmental governance and clean energy. The key problems in this field gradually get clear, including the photon absorption, charge carrier separation and transfer, and surface reaction activity. Meanwhile, the corresponding effective strategies have been proposed and verified, such as band structure engineering, crystal facets control, heterostructure fabrication and cocatalyst loading. Among them, several key factors, such as facets, cocatalysts and heterostructure, play multiple and interrelated roles during the photocatalytic reaction. Extensive basic researches show that the active facet is the key factor to improve the activity for the monocomponent of photocatalyst. In multicomponent system, the heterostructure and cocatalysts can separate the charge carrier at the interface and activate the reaction on the surface, respectivily, which lead to the change of properties at interfacial facets. In turn, the carrier driving force and activation function also depend on the crystal facets at the interface. Therefore, the research on the crystal facets at multicomponent interface is the key approach to enhance the separation and transfer of carrier and activation efficiency. This work focus on the facets control at multicomponent interface to enhance the reactive efficiency. Two kinds of methods, selectivity of sites and facets at multicomponent interface, are proposed to investigate two kinds of photocatalysts, ZnO and Ag3PO4, respectively. In the first part, the morphology evolution of porous ZnO nanosheets synthesized by hydrothermal reaction and the corresponding photocatalytic activity are investigated. Then relation between the selective photocorrosion and the stability is presented, followed by the revelation of its reason through the process of adsorption and degradation. Based on the function of active facets during the selective photocorrosion, the correlation between the active facets and the corroded sites is established, which can be validated in the hexagonal sheets and other morphology of ZnO. It is found that the selective photocorrosion of porous ZnO nanosheets with excellent photocatalytic activity can be observed, which results in a significant decease of the unit activity attributed to the loss of the active crystal facets. At the same time, the similar competitive relationship between the same kinds of dye molecules are exhibited in the adsorption and reaction process. It indicates that the selective adsorption and the specific active facets loss make the jointly efforts on the selective photocorrosion, due to the (002) crystal plane in ZnO acts as polar crystal face and active face. It is also verified that the selective photocorrosion of ZnO with hexagonal and hexagonal bowl-like morphology in the Rhodamine B solution take place on the (002), where the polarity results in the selective adsorption and activity leads to the degradation reaction. Following the investigation of active facets, two kinds of cocatalysts are loaded on porous ZnO nanosheets to observe the deposition sites, explore their selectivity, analyze the influence of the selectivity on spacial charge separation efficiency and reveal the different impacts of ZnO facets at the deposited interface on photocatalytic activity. The results turn out to be challenging, including the numerous factors-induced distribution, disadvantage on degradation activity, undiscovered properties in oxygen evolution, and so on. Meanwhile, based on the porous ZnO nanosheets, the selectively and randomly distributed ZnO/CdS heterostructures are designed and synthesized, followed by the measurement of photoelectrical properties and hydrogen evolution activity. Then, the above results are compared to present the advantage of selective heterostructure. It shows that the H2 evolution rate of ZnO/CdS-S2 reaches 384 µmol·g-1·h-1, which is 14 times higher than that (25 µmol·g-1·h-1) of CdS. More importantly, the H2 evolution rate of ZnO/CdS-S2 is higher than that of ZnO/CdS-R2, which indicates more efficient charge separation and higher hydrogen evolution are achieved for ZnO/CdS-S compared with ZnO/CdS-R. Thus, the facets at the heterostructure interface are revealed to be vital and significant for the photocatalytic reaction efficiency. In the second part, the factors related to morphology of Ag3PO4 are mainly studied on by on with controlled variables. It is found that the morphology of Ag3PO4 is both influenced by dynamics and thermodynamics. In detail, the dynamic factors include adding approach (adding rate and order), ionic concentration ratio, total ionic concentration, saturation and pH, etc. in the system, while thermodynamics mainly rely on temperature change induced the ionic concentration ratio and saturation. Of course, these factors determine the morphology via various way but not individually. It is noted that some growth conditions can be coupling without obvious disturbance to morphology, such as temperature and ionic concentration ratio. Thus, it can provide the chance and approach to fabricate the multicomponent interface with different facets of Ag3PO4 crystal. According to how these factors determine facets growth, three methods are used to synthesize Ag3PO4-based heterostructures, including one-step mixing, ion exchange and heterogeneous nucleation. In Ag3PO4/TiO2 compound prepared by one-step mixing, the self-corrosion in dark is observed and the corresponding chemical environment change of Ag differs from that in photocorrosion. It is revealed that the self-corrosion attributes to the deceased degradation activity under visible light but no obvious effect under ultraviolet light. In Ag3PO4/AgBr and Ag3PO4/Ag2CN2 heterojunctions synthesized through ion exchange, AgBr nanoparticles and Ag2CN2 nanosheets are both out control during synthesis. In Ag3PO4/Ag2CN2 heterojunction and Ag3PO4(1)/Ag3PO4(2) homojunction, the growth condition of each component can be coupled without obvious disturbance to morphology. Thus, two components with specific morphology can be coupled to form heterostruture interface with corresponding facets through heterogeneous nucleation, which give a chance to explore the function of specific facets at heterostruture interface for Ag3PO4.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229611
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
马新龙. 两种典型光催化剂的形貌控制合成及其用于构筑复合界面提升反应活性的研究[D]. 兰州. 兰州大学,2018.
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