Modification Of Metal Oxide Nanosheets And Investigation On Their Synergetic Effects

There has been an increase in the use of clean and renewable energy due to the growing concern about energy shortage and environmental pollution.Hence,it is inevitable to exploit highly efficient functional nanomaterials with desirable activity and high selectivity.Recently,the rapid development in two-dimensional(2D)nanomaterials brings about new breakthroughs in designing of new-generation multifunctional nanocomposites with fascinating properties and potential applications.2D metal oxide nanosheets exhibit unique electronic structure and distinctive physicochemical properties arising from their molecular thickness and extremely high 2D anisotropy.The fully exposed surface atoms render them easy to hybridize with other nanomaterials to create novel assemblies and hierarchical structures.The hybridization can not only tailor their physicochemical properties,but also create unexpected functionality via a synergetic coupling between the components.In this thesis,we intend to reorganize metal oxide nanosheets with graphene,ionic liquids(ILs),and metal elements to fabricate novel 2D nanocomposites.The synergetic effects of hybridization on the physicochemical properties(such as morphology,crystal structure,electronic structure,energy band structure,and acidity)of nanosheets were fully investigated.These functional 2D composites were also applied into energy and environmental fields to clearly probe the relationships between the microstructures of nanohybrids and their performances.The main results are summarized below:1.Layered HNb3O8/graphene hybrids with numerous heterogeneous interfaces and hierarchical pores were fabricated via the alternative stacking of HNb3O8 nanosheets with graphene nanosheets.When applied in the photocatalytic conversation of CO2 into renewable fuels,the optimized HNb3O8/G hybrids yielded 8.0-fold and 8.6-fold improvements in CO evolution amounts than that of commercial P25 and HNb3O8 bulk powders.The improved photocatalytic performance is attributed to the exotic synergetic effects via the combination of enhanced specific BET surface area,narrowed band gap energy,depressed electron-hole recombination rate,as well as increasing strong acid sites and strong acid amounts.This work demonstrates that rational design and controllable synthesis of layered nanohybrids based on metal oxide nanosheets can not only tune the physicochemical properties and photocatalytic performance of the nanohybrids,but provide a better understanding of the relationships between the microstructures of nanohybrids and their synergetic performances at the molecular level.2.Fe-doped HTaWO6 nanotubes as highly active solid acid catalysts were prepared via an exfoliation-exchange process.Doping Fe ions into the nanotubes endowed them with an improved structural and thermal stability due to the stronger interaction between intercalated Fe ions and the host layer.This interaction also preserved the effective Br(?)nsted acid sites of nanotubes upon calcination and facilitated the generation of new acid sites.The integration of these functional roles resulted in Fe-doped nanotubes with high acidic catalytic activities in the Friedel-Crafts alkylation of anisole and the esterification of acetic acid.Due to their improved catalytic activity and stability,Fe-doped nanotubes can be used as solid acid catalyst in harsh conditions.Moreover,Mn,Co,Ni,Cu,and Zn were doped into HTaWO6 nanotubes to investigate the effect of doped metal species on the acid properties and acidic catalytic performance of nanotubes.This can shed new lights on rationally designing solid acid nanohybrids with superior catalytic performance.3.Layered inorganic-organic TiO2-ILs hybrids were fabricated through intercalating imidazolium-based ILs into 2D titanate nanosheets.The effects of cation sizes on the interfacial properties and CO2 uptake capacity of hybrids were comprehensively investigated.The results indicated that the length of carbon chain can modify the interlayer spacing of the hybrids by regulating the interaction strength between ILs and the host nanosheets,thus leading to the variation in morphology,physicochemical properties and CO2 uptake capacity.As a result,TiO2-ILs compounds displayed enhanced CO2 absorption capacity with the increasing carbon chain length,owing to the synergistically interfacial effects induced by water contents and free space in interlayer region,as well as diverse interactions of ILs with inorganic nanosheets.The structural integration and interfacial regulation of 2D inorganic nanosheets with ILs will provide a protocol to develop novel layered nanocomposites for energy and environmental applications.