"I hope our work inspires others to think of new rules to design functional nanomaterials for new applications. "Our study fills in the gap for nanomaterial transformations that can't be predicted by traditional theory." Zheng said, who pioneered LC-TEM at Berkeley Lab in 2009 and is a leading expert in the field. The microscope's high-vacuum environment keeps the liquid sample intact. The researchers observed the liquid sample through ThemIS, a specialized electron microscope at the Molecular Foundry that is capable of recording atomic-scale changes in liquids at a speed of 40-400 frames per second. The advance-monitoring how nanoparticles ripen in solution in real time-was enabled by a custom-made, ultrathin "liquid cell" that secures a tiny amount of liquid between two carbon-film membranes on a copper grid. The researchers say that their work is the highest resolution LC-TEM video ever recorded. "The finding was very unexpected, but we're very happy with the results," said Qiubo Zhang, first author and postdoctoral researcher in the Materials Sciences Division.
However, the direction of growth was guided not by a difference in size but by a crack defect in the shell of the initially larger CSNP. In one key experiment, an LC-TEM video shows a small Cd-CdCl 2 core-shell nanoparticle merging with a large Cd-CdCl 2 CSNP to form a larger Cd-CdCl 2 CSNP. By using the PEI of higher molar mass, core shell gold nanoparticles of about 3.6 nm size with a more narrow size distribution and special fluorescence behavior could be synthesized. Using a technique called high-resolution liquid cell transmission electron microscopy (LC-TEM) at the Molecular Foundry, the researchers captured real-time, atomic-scale LC-TEM videos of Cd-CdCl 2 CSNPs ripening in solution. Therefore, in the subsequent reduction process a gold polymer hybrid shell is formed. They are unique because of their easily modular properties, which are a result of their size. New video footage captured by Berkeley Lab scientists reveals for the first time that nanoparticle growth is directed not by difference in size, but by defects. Coreshell semiconducting nanocrystals are a class of materials which have properties intermediate between those of small, individual molecules and those of bulk, crystalline semiconductors. The researchers exposed the solution with an electron beam to produce Cd-CdCl 2 core-shell nanoparticles (CSNPs)-which look like flat, hexagonal discs-where cadmium atoms form the core, and cadmium chloride forms the shell. We are rewriting textbook chemistry, and it's very exciting," said senior author Haimei Zheng, a senior scientist in Berkeley Lab's Materials Sciences Division and an adjunct professor of materials science and engineering at UC Berkeley.įor the study, the researchers suspended a solution of cadmium sulfide (CdS) nanoparticles with cadmium chloride (CdCl 2) and hydrogen chloride (HCl) in a custom liquid sample holder. The scientists recently reported their findings in the journal Nature Communications. When a sufficient amount of K 2CrO 4 was used as the precursor and the solution pH ranged from 3 to 7.5, Cr 2O 3 was successfully formed with a constant shell thickness (≈2 nm) on metallic Rh nanoparticles, which resulted in an effective promoter for overall water splitting.According to this theory, small particles dissolve and redeposit onto the surface of large particles, and the large particles continue to grow until all of the small particles have dissolved.īut now, new video footage captured by Berkeley Lab scientists reveals that nanoparticle growth is directed not by difference in size, but by defects. In addition, the morphology of the Cr 2O 3 photodeposits was significantly affected by the valence state of Rh and the pH at which the photoreduction of K 2CrO 4 was conducted. The activity for visible-light water splitting on GaN:ZnO modified with an Rh/Cr 2O 3 core–shell configuration was dependent on both the dispersion of Rh nanoparticles and the valence state. Among the core materials examined, Rh species exhibited relatively high performance for this application. This enhancement in activity was primarily due to the suppression of undesirable reverse reactions (H 2–O 2 recombination and/or O 2 photoreduction) and/or protection of the core component from chemical corrosion, depending on the core type.
Photodeposition of Cr 2O 3 on GaN:ZnO modified with a noble metal (Rh, Pd and Pt) or metal oxide (NiO x, RuO 2 and Rh 2O 3) co-catalyst resulted in enhanced photocatalytic activity for overall water splitting under visible light ( λ>400 nm). Core nanoparticles were loaded by impregnation, adsorption or photodeposition onto a solid solution of gallium nitride and zinc oxide (abbreviated GaN:ZnO), which is a particulate semiconductor photocatalyst with a band gap of approximately 2.7 eV, and a Cr 2O 3 shell was formed by photodeposition using a K 2CrO 4 precursor. Core–shell-structured nanoparticles, consisting of a noble metal or metal oxide core and a chromia (Cr 2O 3) shell, were studied as promoters for photocatalytic water splitting under visible light.