兰州大学机构库 >材料与能源学院
MoS2基复合光催化剂的制备及析氢性能研究
Alternative TitleStudy on Preparation and Hydrogenation Performance of MoS2 Based Composite Photocatalysts
魏学刚
Subtype博士
Thesis Advisor祁菁
2023-08-27
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name理学博士
Degree Discipline凝聚态物理
KeywordMoS2 MoS2 光催化分解水 Photocatalytic water splitting 结构调控 Structure modulation 析氢性能 Hydrogen evolution performance 催化活性机理 Catalytic activity mechanism
Abstract

自工业革命以来,随着煤炭、石油、天然气等传统化石能源不断消耗,引发了能源危机和生态环境恶化等问题,寻求可持续绿色能源势在必行。氢能作为新型绿色能源,有望改善能源短缺和环境恶化问题。目前光催化析氢技术能够利用半导体光催化剂将太阳能转变为绿色环保的氢能,但是传统光催化剂存在光谱响应范围窄,激发后电子-空穴对易复合,活性位点缺失及催化析氢效率低等问题。针对光催化剂存在的问题,研究者常选用离子掺杂、异质结构构建和附着助催化剂等方式对其进行改性。其中,助催化剂主要起提高光催化剂的电荷分离效率和增加催化活性位点的作用,在光催化领域其同样属于光催化剂范畴。

MoS2光催化剂拥有合适的光学带隙和易暴露的边缘S原子催化活性位点,有望解决析氢光催化剂吸光效率低和活性位点缺失的问题。但是MoS2存在自身催化活性位点数目少和激发后电子-空穴对易复合问题。为增加催化活性位点和提高电荷分离效率,本工作首先采用非金属(P,N)掺杂和与WO3复合构建异质结构的方法对MoS2光催化剂进行改性研究。但是研究发现MoS2作为助催化剂相较直接作为光催化剂能够展现出更加优异的催化性能。因此,本工作随后通过调控非金属N掺杂浓度、碳插层及界面构筑等改性策略设计了一系列具有更高催化活性的MoS2基助催化剂,并探究了MoS2基助催化剂与g-C3N4光催化剂复合后用于光催化分解水析氢的性能。主要研究结论如下:

1、通过两步水热反应制备了P-MoS2@WO3异质结构复合光催化剂,研究结果表明非金属P掺杂和Z-scheme异质结构构建可提高MoS2光催化剂析氢性能。这主要是因为掺杂到MoS2基面内的P原子为H+还原提供了丰富的催化活性位点,异质结构的构建使得WO3导带电子与P-MoS2价带空穴发生Z-scheme转移,从而有效地降低了P-MoS2光催化剂中导带电子的回迁几率。制备的非金属P掺杂和异质结构构建两种改性策略实施后的P-MoS2@WO3复合光催化剂具有良好的光催化析氢性能(73.8 μmolh-1g-1)和持久的循环稳定性(16 h)。

2、采用水热反应和溶胶-凝胶法制备了N-MoS2@WO3异质结复合光催化剂,研究结果表明掺杂的非金属N原子有效地提高了电子的吸引能力和激发了MoS2基面内催化活性,且Z-scheme异质结构的构建使得N-MoS2中电子-空穴对的复合几率得到了有效降低,从而提升了N-MoS2@WO3复合光催化剂的析氢性能。制备的0.5N-MoS2@0.5WO3复合光催化剂析氢效率为102.5 μmolh-1g-1。此外,理论计算表明非金属N掺杂(DGH*»0.19 eV)相较P掺杂(DGH*»0.25 eV)为MoS2提供了更加优异的催化活性。

3、通过固相还原法制备了N掺杂的MoS2助催化剂(MoN1.2xS2-1.2x),发现其与g-C3N4光催化剂复合后有效地提升了N-MoS2@g-C3N4复合光催化剂析氢性能。这主要是因为g-C3N4光催化剂导带电子经过异质结构转移至MoN1.2xS2-1.2x助催化剂导带中,使得g-C3N4光催化剂中电子-空穴对发生有效分离。另外MoN1.2xS2-1.2x助催化剂中掺入的N原子为催化反应提供了活性位点,使得H+还原效率得到提高。制备的5 wt% MoN1.2xS2-1.2x@g-C3N4复合光催化剂析氢效率为360.4 μmolh-1g-1约为0.5N-MoS2@0.5WO3复合光催化剂的3.5倍,且循环性良好(16 h)。该研究结果间接说明MoS2基材料更为适合作助催化剂。

4、通过水热合成和高温碳化处理方法制备了C插层MoS2助催化剂(C-MoS2),发现其与g-C3N4光催化剂复合后有效地提升了C-MoS2@g-C3N4复合光催化剂析氢性能。研究结果表明C层的插入提高了C-MoS2助催化剂的导电性能,加快了g-C3N4中激发后的电子向C-MoS2助催化剂转移速率,并且C层的插入有效地扩大了夹层间距和抑制了MoS2沿c轴方向的堆叠,从而增强了边缘S原子催化活性。制备的5 wt% C-MoS2@g-C3N4复合光催化剂析氢效率为157.1 μmolh–1g–1,且具有良好的循环稳定性(16 h)。

5、在高温条件下利用NH3分解的N离子与MoS2局部位置处的S离子发生替换反应制备了MoN/MoS2助催化剂,发现其与g-C3N4复合后有效地提升了MoN/MoS2@g-C3N4复合光催化剂析氢性能。研究结果表明MoN/MoS2的构建有效地增强了助催化剂的催化活性和导电性,使得MoN/MoS2助催化剂中电子还原H+的催化速率得到提高,并且提升了g-C3N4光催化剂中电子-空穴对的分离效率。制备的5 wt% MoN/MoS2@g-C3N4复合光催化剂析氢效率为545.8 μmolh–1g–1,其效率为5 wt% MoN1.2xS2-1.2x@g-C3N4 (360.4 μmolh–1g–1)的1.5倍,为5 wt% C-MoS2@g-C3N4 (157.1 μmolh–1g–1)的3.5倍,且循环性良好(12 h)。该结果说明双功能协同改性后的MoN/MoS2异质结构助催化剂具有更加优异的催化析氢性能。

Other Abstract

Since the beginning of the industrial revolution, the traditional fossil energy of coal, oil, and natural gas has been gradually consumed. The high consumption brought severe energy crisis problems and ecological environment deterioration, which led to seeking new sustainable green energy. Recently, hydrogen has been considered the favorite green energy and is expected to solve these problems. At present, Photocatalytic hydrogen production technology is a feasible method. However, it has encountered problems, such as a narrow spectrum response range, easy recombination of excited electron-hole pairs, absence of active sites, and low catalytic hydrogen evolution rate. In view of the existing problems of photocatalysts, researchers often use ion doping, heterostructure construction and adhesion of cocatalysts to modify them. Therein, cocatalyst mainly plays the role of improving the charge separation efficiency of photocatalyst and increasing the catalytic active site, which also belongs to the category of photocatalyst.

MoS2 photocatalyst with the suitable optical bandgap and the facile exposed S edges activity is a hope to overcome the difficulties encountered. However, the MoS2 photocatalyst still has problems with few active sites and high recombination of electron-hole pairs. Firstly, the MoS2 photocatalyst was modified by doping non-metallic (P, N) and constructing a heterostructure with a WO3 semiconductor to increase the catalytic activity and improve the charge separation efficiency. However, it has been found that MoS2 as a cocatalyst can show better catalytic performance than that it as the photocatalyst. Secondly, a series of MoS2 based cocatalysts with high catalytic activity was designed by doping different N concentrations, carbon intercalation, and interface construction. Finally, the hydrogen performance of their combination with g-C3N4 photocatalyst for photocatalytic water splitting has been explored. The main results of this dissertation are as follows:

1. The P-MoS2@WO3 heterogeneous photocatalyst was prepared by a two-step hydrothermal reaction and the results show that non-metallic P doping and Z-scheme heterostructure improve the hydrogen evolution performance of the MoS2 photocatalyst. The analysis reveals that the P doped atoms provide the active sites for H+ reduction, and the heterostructure constructs a direct Z-scheme transfer channel. The conduction band electrons of WO3 have been transferred to the valence band of P-MoS2 through the heterostructure, reducing the electron back migration of the conduction band in the P-MoS2 photocatalyst. The prepared P-MoS2@WO3 composite has good photocatalytic hydrogen evolution performance (73.8 μmolh–1g–1) and cycle stability (16 h).

2. The N-MoS2@WO3 heterogeneous photocatalyst was prepared by hydrothermal reaction and sol-gel method. The results indicate that the doped non-metallic N atoms improve the electron attraction ability and effectively trigger the base plane's catalytic activity. The construction of the Z-scheme heterostructure reduces the recombination rate of electron-hole pairs in N-MoS2, thus improving the hydrogen evolution performance of the N-MoS2@WO3 composite. The hydrogen evolution rate of prepared 0.5N-MoS2@0.5WO3 composite is 102.5 μmolh–1g–1. In addition, theoretical calculations show that N doping (DGH* » 0.19 eV) provides more excellent catalytic activity for MoS2 than P doping (DGH* » 0.25 eV).

3. The N doped MoS2 cocatalyst (MoN1.2xS2-1.2x) was prepared by the solid-phase reduction method, and the outcomes show that the photocatalytic performance of MoN1.2xS2-1.2x@g-C3N4 composite is improved. The analysis reveals that the constructed heterostructure induces the conduction band electrons of g-C3N4 transfer to the conduction band of MoN1.2xS2-1.2x cocatalyst. The transformation enhances the separation efficiency of electron-hole pairs, and the N doped atoms provide abundant active sites for the H+ reduction. In addition, the hydrogen evolution rate of the prepared 5 wt% MoN1.2xS2-1.2x@g-C3N4 composite exhibits the H2 evolution rate of 360.4 μmolh–1g–1 with good stability (16 h), which is about 3.5 times that of the 0.5N-MoS2@0.5WO3 composite. The result indicates that MoS2-based material is more suitable as the cocatalyst than that it as the photocatalyst.

4. The carbon-intercalated MoS2 cocatalyst (C-MoS2) was prepared through hydrothermal and high-temperature carbonization processes. The results show that the photocatalytic performance of the C-MoS2@g-C3N4 composite is improved. The analysis reveals that the carbon intercalation enhances the conductivity of the C-MoS2 cocatalyst and accelerates the electron separation efficiency from g-C3N4 to C-MoS2 cocatalyst. Furthermore, the intercalation of carbon enlarged the interlayer spacing and inhibited the stacking of MoS2 along the c-axis direction, thus enhancing the catalytic activity of edge S atoms. Additionally, the prepared 5 wt% C-MoS2@g-C3N4 composite exhibits the H2 evolution rate of 157.1 μmolh–1g–1 with excellent cycle stability (16 h).

5. The MoN/MoS2 cocatalyst was prepared by replacing partial S anions in the MoS2 lattice with N anions generated by NH3 decomposition at high temperature. The findings demonstrate that the photocatalytic performance of the MoN/MoS2@g-C3N4 composite is improved. The analysis reveals that the MoN/MoS2 cocatalyst provides abundant active sites and excellent electrical conductivity for H+ reduction and electron transfer and improves the separation efficiency of electron-hole pairs in the g-C3N4 photocatalyst. In addition, the hydrogen evolution rate of the prepared 5 wt% MoN/MoS2@g-C3N4 composite is 545.8 μmolh–1g–1 and exhibits good stability (12 h). The obtained results are about 1.5 and 3.5 times higher than that of 5 wt% MoN1.2xS2-1.2x@g-C3N4 (360.4 μmolh–1g–1) and 5 wt% C-MoS2@g-C3N4 (157.1 μmolh–1g–1) composites, respectively. The results indicate that the MoN/MoS2 heterostructure cocatalyst with dual-function co-modification has better catalytic hydrogen evolution performance.

MOST Discipline Catalogue理学 - 物理学 - 凝聚态物理
URL查看原文
Language中文
Other Code262010_120190906991
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/538082
Collection材料与能源学院
Affiliation
兰州大学材料与能源学院
Recommended Citation
GB/T 7714
魏学刚. MoS2基复合光催化剂的制备及析氢性能研究[D]. 兰州. 兰州大学,2023.
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