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Construction and Modification of Ternary Metal Sulfide for Efficient Photocatalytic CO₂ Reduction
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| Title: | Construction and Modification of Ternary Metal Sulfide for Efficient Photocatalytic CO₂ Reduction |
| Other Titles: | 三元系金属硫化物の組成および表面構造制御による効率的な光触媒CO₂還元に関する研究 |
| Authors: | 王, 琦 Browse this author |
| Issue Date: | 23-Mar-2023 |
| Publisher: | Hokkaido University |
| Abstract: | Photocatalytic carbon dioxide reduction is one of the most promising strategies to solve the energy crisis and achieve the global carbon cycle. Developing and designing highly efficient photocatalysts for photocatalytic CO₂ reduction under visible light has become a hot topic over the world. Metal sulfide-based materials have been widely used in photocatalytic CO₂ reduction due to their low cost, high stability, and suitable band structure. However, the metal sulfide photocatalysts still suffer obvious drawbacks, such as high photogenerated electron-hole pairs recombination rate, less reactive sites, and so on. To overcome these drawbacks, two fundamental strategies can be considered: the construction of suitable electronic structures and abundant reaction sites. Therefore, this thesis focuses on the rational design of metal sulfide photocatalysts with appropriate electronic structures by modifying the elemental ratio and constructing more reactive sites on the catalyst surface through surface engineering.
In chapter 1, a general background about semiconductor-based photocatalytic CO₂ reduction and the concept of photocatalysts were introduced. Then, the key factors and common strategies for enhancing photocatalytic activity were discussed. In the end, the ongoing research beyond ternary metal sulfide was summarized.
In chapter 2, the facile fabrication of Cd-In-S (CIS) colloidal nanocrystals was constructed as an efficient visible light-responsive photocatalyst for the conversion of CO₂ to CO. Both experimental and theoretical investigations reveal the importance of Cd to In ratio, which positively influences not only the charge carrier separation rate but also the electronic structures of the CIS samples. In particular, the light absorption ability, redox potential of photo-induced electrons, and charge transfer ability from CIS to the cobalt-based cocatalyst were effectively modulated, endowing the optimized sample with a high CO evolution rate of 22.9 μmol h⁻¹ and selectivity up to 80% under visible light irradiation. This work's findings provide guidance for designing and constructing ternary metal sulfide materials for CO₂ conversion by modulating elemental ratio.
In chapter 3, the non-stoichiometric Ag-In-S quantum dots (QDs) was constructed as highly efficient and robust photocatalysts for visible-light-driven photocatalytic reduction of CO₂ to syngas at atmospheric pressure and room temperature. The introduction of Co(bpy)₃²⁺ (bpy = 2’2-bipyridine) cocatalyst can promote the conversion of CO₂ to CO reaction and meanwhile improve the photo-stability of Ag-In-S QDs. The photocatalytic activity and selectivity of Ag-In-S QDs are strongly dependent on the Ag to In molar ratios, and the optimized sample exhibits the highest CO evolution rate of 9.20 μmol h⁻¹, and H₂ evolution rate of 3.13 μmol h⁻¹, corresponding to the CO selectivity of 74.61%, outperforming most of the reported QDs based photocatalysts. This work provides a new example of Cd and Pb free QDs photocatalysts for efficient and stable CO₂ photoreduction.
In chapter 4, a CdS₀.₈CdSe₀.₂ colloidal quantum dot was prepared by a simple method as an excellent visible light reactive photocatalyst for the reduction of CO₂ to carbon monoxide. In addition, vacancy defects were created on the quantum dot surface by a simple acidic solution etching method to enhance the photocatalytic carbon dioxide reduction activity. The optimal sample exhibited the highest CO production rate of 19.79 μmol h⁻¹ and selectivity of up to 77%. It can be demonstrated that the surface vacancy defects contribute to the outstanding performance of photocatalytic CO₂ reduction. In this paper, the role of the introduction of Cd vacancies in the photocatalytic CO₂ reduction activity is presented and discussed. This work provides guidance and theoretical insight for vacancy construction on QDs for potential photocatalytic CO₂ reduction.
In chapter 5, an overall summary of this dissertation work was presented. This thesis presents a systematic study on the elemental ratio modification of metal sulfides and their surface defects construction for efficient photocatalytic CO₂ reduction. By adjusting the proportion of metal elements in the ternary metal sulfide, the electronic structure of the catalyst can be effectively tuned, which is an effective way to improve photocatalytic performance. The construction of more reactive sites on the catalyst surface by surface etching can directly affect surface catalysis. The relevant findings of this study deepen the understanding of metal sulfide photocatalysts for CO₂ reduction. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第15409号 |
| Degree Level: | 博士 |
| Degree Discipline: | 理学 |
| Examination Committee Members: | (主査) 教授 村越 敬, 教授 上野 貢生, 教授 忠永 清治, 客員教授 葉 金花, 客員教授 白幡 直人 |
| Degree Affiliation: | 総合化学院（総合化学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/91500 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 総合化学院(Graduate School of Chemical Sciences and Engineering)
学位論文 (Theses) > 博士 （理学）
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