The Other Dimension—Tuning Hole Extraction via Nanorod Width

Solar-to-hydrogen generation is a promising approach to generate clean and renewable fuel. Nanohybrid structures such as CdSe@CdS-Pt nanorods were found favorable for this task (attaining 100% photon-to-hydrogen production efficiency); yet the rods cannot support overall water splitting. The key limitation seems to be the rate of hole extraction from the semiconductor, jeopardizing both activity and stability. It is suggested that hole extraction might be improved via tuning the rod’s dimensions, specifically the width of the CdS shell around the CdSe seed in which the holes reside. In this contribution, we successfully attain atomic-scale control over the width of CdSe@CdS nanorods, which enables us to verify this hypothesis and explore the intricate influence of shell diameter over hole quenching and photocatalytic activity towards H2 production. A non-monotonic effect of the rod’s diameter is revealed, and the underlying mechanism for this observation is discussed, alongside implications towards the future design of nanoscale photocatalysts

Multi-Modal Nano Particle Labeling of Neurons

The development of imaging methodologies for single cell measurements over extended timescales of up to weeks, in the intact animal, will depend on signal strength, stability, validity and specificity of labeling. Whereas light-microscopy can achieve these with genetically-encoded probes or dyes, this modality does not allow mesoscale imaging of entire intact tissues. Non-invasive imaging techniques, such as magnetic resonance imaging (MRI), outperform light microscopy in field of view and depth of imaging, but do not offer cellular resolution and specificity, suffer from low signal-to-noise ratio and, in some instances, low temporal resolution. In addition, the origins of the signals measured by MRI are either indirect to the process of interest or hard to validate. It is therefore highly warranted to find means to enhance MRI signals to allow increases in resolution and cellular-specificity. To this end, cell-selective bi-functional magneto-fluorescent contrast agents can provide an elegant solution. Fluorescence provides means for identification of labeled cells and particles location after MRI acquisition, and it can be used to facilitate the design of cell-selective labeling of defined targets. Here we briefly review recent available designs of magneto-fluorescent markers and elaborate on key differences between them with respect to durability and relevant cellular highlighting approaches. We further focus on the potential of intracellular labeling and basic functional sensing MRI, with assays that enable imaging cells at microscopic and mesoscopic scales. Finally, we illustrate the qualities and limitations of the available imaging markers and discuss prospects for in vivo neural imaging and large-scale brain mapping

Modular design of solar-powered photocathodic metal protection device

Abstract Metal corrosion leads to severe economic losses and safety hazards to human society. As an energy-efficient and sustainable anticorrosion technique, photocathodic protection (PCP) systems have received growing attention in the past two decades. However, the existing PCP devices barely meet the requirements of adequate metal protection in real-world scenarios. This perspective aims to provide some constructive insights into the rational design of PCP devices and propose “functional module integration” as a new concept for future PCP systems. Similarly to multi-layered solar cells, PCP systems may incorporate multiple modules based on the corresponding functions. These include photoabsorber module (PAM), electron transfer module (ETM), hole transfer module (HTM), hole consumption module (HCM), and electron storage module (ESM). With such a modular design, improved capture of sunlight and fast charge separation, directional transportation, and effective utilization of the photogenerated carriers might be attained. Consequently, the solar-to-electric energy conversion efficiency and operation consistency of PCP devices can be significantly boosted, paving the way for practical application of solar-powered metal protection technology. Graphical Abstract This perspective analyses the key issues of current photocathodic protection systems and proposes a unified design composed of functional modules for the next generation systems inspired by the architecture of solar cells. This modular design allows the breaking-down of all reaction steps of the solar-to-electric conversion process onto various modules, which may bring about breakthroughs for green cathodic metal protection

Selective Growth of Ni Tips on Nanorod Photocatalysts

Selective Growth of Ni Tips on Nanorod Photocatalyst

Luminescence Studies of Individual Quantum Dot Photocatalysts

Using far-field optical microscopy we report the first measurements of photoluminescence from single nanoparticle photocatalysts. Fluence-dependent luminescence is investigated from metal-semiconductor heterojunction quantum dot catalysts exposed to a variety of environments, ranging from gaseous argon to liquid water containing a selection of hole scavengers. The catalysts each exhibit characteristic nonlinear fluence dependence. From these structurally and environmentally sensitive trends, we disentangle the separate rate-determining steps in each particle across the very wide range of time scales, which follow the initial light absorption process. This information will significantly benefit the design of effective artificial photocatalytic systems for renewable direct solar-to-fuel energy conversion

Photocatalytic Hydrogen Production with Tunable Nanorod Heterostructures

We report the design of a multicomponent nanoheterostructure aimed at photocatalytic production of hydrogen. The system is composed of a platinum-tipped cadmium sulfide rod with an embedded cadmium selenide seed. In such structures, holes are three-dimensionally confined to the cadmium selenide, whereas the delocalized electrons are transferred to the metal tip. Consequently, the electrons are now separated from the holes over three different components and by a tunable physical length. The seeded rod metal tip samples studied here facilitate efficient long-lasting charge carrier separation and minimize back reaction of intermediates. By tuning the nanorod heterostructure length and the seed size, we were able to significantly increase the activity for hydrogen production compared to that of unseeded rods. This structure was found to be highly active for hydrogen production, with an apparent quantum yield of 20% at 450 nm, and was active under orange light illumination and demonstrated improved stability compared to CdS rods without a CdSe seed

Lateral Charge Migration in 1D Semiconductor-Metal Hybrid Photocatalytic Systems

Colloidal nanorods based on CdS or CdSe functionalized with metal particles have proven to be efficient catalysts for light driven hydrogen evolution. Seeded CdSe@CdS nanorods have shown increasing performance with increasing rod length. This observation was rationalized by the increasing lifetime of the separated charges, as a large distance between holes localized in the CdSe seed and electrons localized at the metal tip decreases their recombination rate. However, the impact of nanorod length on electron-to-tip localization efficiency or pathway remained an open question. Therefore, we investigated the photo-induced electron transfer to the metal in a series of Ni tipped CdSe@CdS nanorods with varying length. We find that the transfer processes occurring from the region close to the semiconductor-metal interface, the rod region, and the CdSe seed region depend in different ways on the rods length. The rate of the fastest process from excitonic states generated directly at the interface is independent of the rod length but the relative amplitude decreases with increasing rod length as the weight of the interface region is decreasing. The transfer of electrons to the metal tip from excitons generated in the CdS rod region depends strongly on the length of the nanorods which indicates an electron transport limited process, i.e., electron diffusion towards the interface region followed by fast interface crossing. The transfer originating from CdSe excitonic states again shows no significant length dependence in its time constant as it is probably limited by the rate of overcoming the shallow confinement in the CdSe seed