| Energy crisis and environmental pollution are the two major challenges that human beings are facing today. How to solve the above two problems posed a challenge for scientific researchers. Because of the large diversity of composition and structure, layered materials exhibit a wide range of intriguing physical and chemical properties and have been widely applied in sensing, catalysis and energy storage. Recently, exfoliation of various layered materials to yield unilamellar two-dimensional (2D) nanosheets has become an area at the forefront of intensive research. And extensive research efforts have been devoted to construct2D composites by using exfoliated2D nanosheets as a building block. As an important category in layered materials, layered hydroxides (especially the layered double hydroxides, LDHs) have earn much attention and intensive research in recent years because of their diversity of composition and properties. In the past few years, there has been a rapid growth in the synthesis and application of layered hydroxides nanosheets as a building block to develop nanocomposites. Especially, a variety of types of layered hydroxides-based materials can be obtained by different synthetic pathways, such as calcination to convert layered hydroxides to metal oxides and assembly of layered hydroxide with graphene nanosheets. These materials have a wide range of properties and are significant for both fundamental and application research in the fields of environment and energy. This dissertation focus on the basic research for application of layered hydroxides in three aspects of photocatalytic energy conversion, environmental electrochemical analysis and water treatment:1. The earth-abundant cobalt complexes have been demonstrated to act as catalysts for photocatalytic CO2reduction. Although promising, the homogeneous systems still face obstacle of extracting and recycling, we try to choose Co(OH)2and CO3O4as a heterogeneous catalyst to substitute homogeneous cobalt complexes. By calcining the layered Co(OH)2precursors, Co3O4hexagonal platelets exposed (112) facets were synthesized to achieve efficent solar CO2conversion. We found that the crystal plane structure of CO3O4hexagonal platelets has a significant influence on the photocatalytic properties for CO2reduction. The density-functional theory (DFT) calculations and experimental results both demonstrate that the (112) plane is a more favorable plane than (111) plane for CO2reduction. Our combined experimental and theoretical studies provide a solid hint to get deeper insight into the relationship between the facet effect and the photocatalytic properties for CO2reduction. On the other hand, Co(OH)2has been demonstrated to be an effective water oxidation catalysts. We expect to develop a highly efficient Co-based layerd hydroxides water oxidation catalyst. We try to further improve the catalyst performance through exploration the exfoliated Co(OH)2and Co-based LDHs as water oxidation catalyst. We found that α-Co(OH)2and β-Co(OH)2give different catalytic performance as water oxidation catalyst.2. In the present study, for the first time, AlOOH-reduced graphene oxide (RGO) nanocomposites with excellent electrochemical properties have been successfully and directly synthesized from graphene oxide (GO) through a green, facile, effective, and scalable hydrothermal method. The AlOOH nanoplates were homogeneously attached on the graphene sheets and effectively prevented the graphene sheets from aggregating together. In combination of the advantages of both AlOOH and graphene sheets, the AlOOH-RGO nanocomposites are a promising material which possesses good sensitivity, high stability, excellent practical applicability, and long-term usage possibility in electrochemical detecting heavy metal ions. On the basis of this work, we prove the new bridge between adsorption and electrochemical behavior. More significantly, as a new material, the AlOOH-RGO nanocomposites may possess many unknown properties waiting to be explored. Furthermore, based on AlOOH-RGO nanocomposites, we got a new structure of graphene decorated with Al2O3nanoplates through a subsequent calcining process. Through further optimization, Al2O3-RGO nanocomposites is expected to be applied in the electrochemical analysis of organophosphorus pesticides in drinking water.3. In this study, Mg-Al LDHs nanoflake impregnated magnetic alginate beads (LDH-n-MABs) were prepared for fluoride removal. The objective of this work is to investigate whether alginate is an effective material for the immobilization of Mg-Al LDHs. As Mg-Al LDHs has a greater affinity for F-compared to NO3-interlayer anions, so it is expected to adsorption F-in the water by ion exchange. Through encapsulating Fe3O4nanoparticles, the prepared beads had a high magnetic sensitivity to an external magnetic field providing an easy and efficient way to separate them from aqueous solution. We also want to demonstrate the feasibility of fluoride removal using LDH-n-MABs by systematically evaluating them under various operating conditions such as pH, time, temperature, initial fluoride concentration and co-existing substances. The potential use of this bio-based sorbent for fluoride removal from real contaminated groundwater was also investigated. |
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