RESUMO
In situ characterization of materials in their operational state is a highly active field of research. Investigating the structure and response of materials under stimuli that simulate real working environments for technological applications can provide new insight and unique input to the synthesis and design of novel materials. Over recent decades, experimental setups that allow different stimuli to be applied to a sample inside an electron microscope have been devised, built, and commercialized. In this review, we focus on the in situ investigation of optically active materials using transmission electron microscopy. We illustrate two different approaches for exposing samples to light inside the microscope column, explaining the importance of different aspects of their mechanical construction and choice of light source and materials. We focus on the technical challenges of the setups and provide details of the construction, providing the reader with input on deciding which setup will be more useful for a specific experiment. The use of these setups is illustrated using examples from the literature of relevance to photocatalysis and nanoparticle synthesis.
Assuntos
Catálise , Microscopia Eletrônica de TransmissãoRESUMO
Catalysis using gold (Au) nanoparticles has become an important field of chemistry. However, activity loss caused by aggregation or leaching of Au nanoparticles greatly limits their application in catalytic reaction. Herein, we report a facile and green synthesis of a core-shell Au@SnO2 nanocomposite, exhibiting excellent activity toward selective nitroaromatics reduction under mild conditions. The core-shell Au@SnO2 nanocomposite (Au size = â¼50 nm; shell thickness = ca. 16 nm) is conceived and validated by a direct redox reaction between HAuCl4 and SnF2. Optimization of the core size, shell thickness, and dispersion of Au@SnO2 has been introduced by an alkaline surface supported by negatively charged metal oxide Na2Ti4O9. The as-obtained Au-Sn-Na2Ti4O9 catalyst with much smaller Au cores (ca. 5 nm) and thinner SnO2 nondensed shells (ca. 4 nm) exhibits highly improved catalytic activities for nitro reduction compared to most of the known Au-based catalysts. Moreover, the core-shell Au@SnO2 structure inhibits the leaching and agglomeration of Au nanoparticles and thus leads to superior catalytic durability.
RESUMO
In situ and operando techniques can play important roles in the development of better performing photoelectrodes, photocatalysts, and electrocatalysts by helping to elucidate crucial intermediates and mechanistic steps. The development of high throughput screening methods has also accelerated the evaluation of relevant photoelectrochemical and electrochemical properties for new solar fuel materials. In this chapter, several in situ and high throughput characterization tools are discussed in detail along with their impact on our understanding of solar fuel materials.
RESUMO
An in situ atomic level investigation of the surface structure of anatase nanocrystals has been conducted under conditions relevant to gas phase photocatalytic splitting of water. The experiments were carried out in a modified environmental transmission electron microscope fitted with a high intensity broadband light source with an illumination intensity of 1430 mW/cm(2) close to 10 suns. When the titania is exposed to light and water vapor, the initially crystalline surface converts to an amorphous phase one to two monolayers thick. Spectroscopic analyses show that the amorphous layer contains titanium in a +3 oxidation state. The amorphous layer is stable and does not increase in thickness with time and is heavily hydroxylated. This disorder layer will be present on the anatase surface under reaction conditions relevant to photocatalytic splitting of water.
