Chiral Thin Films of Metal Oxide

Enhanced Replenishment of Active Lattice Oxygen Using Chiral Copper Oxide

Effective catalytic performance of the transition metal oxide is attributed to high specific surface areas, abundant surface oxygen atoms, and balanced valence ratios. Although the chirality of the transition metal has attracted attention, most studies have focused on optical application. A few chiral transition metal oxides were used as electrocatalysts and photocatalysts. The influence of the chiral catalysts on the thermal catalysis process has been less explored. In this study, Mn-loaded chiral (M/l-CuO and M/d-CuO) and achiral CuO (M/a-CuO) were synthesized and compared in the catalytic oxidization of toluene. Spectrally analyzed Mn was well-dispersed on both chiral and achiral CuO. l-CuO and d-CuO showed nanoflower-like chirality. The angles between each (001) plane of CuO were the source of chirality. The toluene turnover frequency (TOF) of the samples was in the order of Mn/d-CuO (5.6 × 10-5 s-1) > Mn/l-CuO (4.4 × 10-5 s-1) > Mn/a-CuO (3.2 × 10-5 s-1) at 240 °C, consistent with the order of the oxygen replenishment rate. The as-prepared catalysts had similar ratios of lattice oxygen/surface adsorbed oxygen, Mn3+/Mn4+, and Cu+/Cu2+. A higher TOF was attributed to chirality, which increased the lattice oxygen replenishment speed from the gaseous phase to the solid surface. Our study indicates gas-solid catalysis from a structure-activity viewpoint.

Chiral Inorganic Nanomaterials for Photo(electro)catalytic Conversion

Chiral inorganic nanomaterials due to their unique asymmetric nanostructures have gradually demonstrated intriguing chirality-dependent performance in photo(electro)catalytic conversion, such as water splitting. However, understanding the correlation between chiral inorganic characteristics and the photo(electro)catalytic process remains challenging. In this perspective, we first highlight the chirality source of inorganic nanomaterials and briefly introduce photo(electro)catalysis systems. Then, we delve into an in-depth discussion of chiral effects exerted by chiral nanostructures and their photo-electrochemistry properties, while emphasizing the emerging chiral inorganic nanomaterials for photo(electro)catalytic conversion. Finally, the challenges and opportunities of chiral inorganic nanomaterials for photo(electro)catalytic conversion are prospected. This perspective provides a comprehensive overview of chiral inorganic nanomaterials and their potential in photo(electro)catalytic conversion, which is beneficial for further research in this area.

Design of surface nanostructures for chirality sensing based on quartz crystal microbalance

Quartz crystal microbalance (QCM) has been widely used for various sensing applications, including chirality detection due to the high sensitivity to nanogram or picogram mass changes, fast response, real-time detection, easy operation, suitability in different media, and low experimental cost. The sensing performance of QCM is dependent on the surface design of the recognition layers. Various strategies have been employed for studying the relationship between the structural features and the specific detection of chiral isomers. This review provides an overview of the construction of chiral sensing layers by various nanostructures and materials in the QCM system, which include organic molecules, supermolecular assemblies, inorganic nanostructures, and metal surfaces. The sensing mechanisms based on these surface nanostructures and the related potentials for chiral detection by the QCM system are also summarized.

Chiral Porous Carbon Surfaces for Enantiospecific Synthesis

Chiral surfaces, developed in the last decade, serve as media for enantioselective chemical reactions. Until today, they have been based mostly on developments in silica templating, and are made mainly from imprints of silicate materials developed a long time ago. Here, a chiral porous activated carbon surface was developed based on a chiral ionic liquid, and the surface chemistry and pore structure were studied to lay a new course of action in the field. The enantioselectivities of surfaces are examined by using variety of methods such as circular dichroism, linear sweep voltammetry and catalysis. These techniques revealed a 28.1% preference for the D enantiomer of the amino acid proline, and linear sweep voltammetry confirmed chirality recognition by another probe. An aldol surface chiral catalytic reaction was devised and allowed to determine the root of the enantiomeric excess. These results affirm the path toward a new type of chiral surface.

Growth of Hybrid Inorganic/Organic Chiral Thin Films by Sequenced Vapor Deposition

One of the many challenges in the study of chiral nanosurfaces and nanofilms is the design of accurate and controlled nanoscale films with enantioselective activity. Controlled design of chiral nanofilms creates the opportunity to develop chiral materials with nanostructured architecture. Molecular layer deposition (MLD) is an advanced surface-engineering strategy for the preparation of hybrid inorganic-organic thin films, with a desired embedded property; in our study this is chirality. Previous attempts to grow enantioselective thin films were mostly focused on self-assembled monolayers or template-assisted synthesis, followed by removal of the chiral template. Here, we report a method to prepare chiral hybrid inorganic-organic nanoscale thin films with controlled thickness and impressive enantioselective properties. We present the use of an MLD reactor for sequenced vapor deposition to produce enantioselective thin films, by embedding the chirality of chiral building blocks into thin films. The prepared thin films demonstrate enantioselectivity of ∼20% and enantiomeric excess of up to 50%. We show that our controlled synthesis of chiral thin films generates opportunities for enantioselective coatings over various templates and 3D membranes.

Chiral Metal-Oxide Nanofilms by Cellulose Template Using Atomic Layer Deposition Process

In this article, we describe an advance approach for the fabrication of chiral metal-oxide nanofilms. Our approach is based on the atomic layer deposition of titania and alumina nanofilms onto cellulose microfibers, used as chiral templates, leading to the formation of chiral nanofilms with a spatial fibrous structure. The chiral nanofilms were extensively characterized by X-ray photoelectron spectroscopy and high-resolution electron microscopy. The chiral property of the produced titania nanofilms was studied by enantioselective adsorption experiments using circular-dichroism spectroscopy and chiral high-performance liquid chromatography. We demonstrate the application of the titania chiral nanofilms for enantioselective crystallization. Overall, the basic principle for the preparation of chiral nanofilms by atomic layer deposition is demonstrated, as well as their uses for several enantioselective applications.

A new approach towards spintronics-spintronics with no magnets

We review a recently discovered phenomenon, the chiral induced spin selectivity (CISS) effect, that can enable a new technology for the injection of spin polarized current without the need for a permanent magnetic layer. The effect occurs in chiral molecules and systems without parity symmetry, i.e. systems that do not have inversion symmetry. The theoretical foundations for the effect are presented first and then followed by several examples of spin-valves that are based on chiral systems. The CISS-based spin valves introduce the possibility to inject spin current without the use of a permanent magnet and to achieve relatively large magnetoresistance at room temperature.

Chiral templating of alumina nanofilms by the atomic layer deposition process

In this communication, we describe the synthesis of new chiral alumina nanofilms and surfaces. Our method is based on chiral templating of alumina nanofilms by cellulose microfibers using the atomic layer deposition process. The chiral nature of the alumina nanofilms was characterized by a variety of techniques, such as quartz crystal microbalance, chiral circular-dichroism adsorption, chiral high-performance liquid chromatography and cyclic voltammetry measurements.

pH-triggered formation of nanoribbons from yeast-derived glycolipid biosurfactants

In the present paper, we show that the saturated form of acidic sophorolipids, a family of industrially scaled bolaform microbial glycolipids, unexpectedly forms chiral nanofibers only at pH below 7.5. In particular, we illustrate that this phenomenon derives from a subtle cooperative effect of molecular chirality, hydrogen bonding, van der Waals forces and steric hindrance. The pH-responsive behaviour was shown by Dynamic Light Scattering (DLS), pH-titration and Field Emission Scanning Electron Microscopy (FE-SEM) while the nanoscale chirality was evidenced by Circular Dichroism (CD) and cryo Transmission Electron Microscopy (cryo-TEM). The packing of sophorolipids within the ribbons was studied using Small Angle Neutron Scattering (SANS), Wide Angle X-ray Scattering (WAXS) and 2D (1)H-(1)H through-space correlations via Nuclear Magnetic Resonance under very fast (67 kHz) Magic Angle Spinning (MAS-NMR).