Magnesiothermic Reduction of Thin Films: Towards Semiconducting Chiral Nematic Mesoporous Silicon Carbide and Silicon Structures

There is a growing demand for new methods to prepare porous Si‐based materials for applications in optoelectronic and microelectronic devices. In this work, the preparation of SiC and Si from magnesiothermic reduction of chiral nematic SiO₂/C composites and mesoporous SiO₂, respectively, is reported. The SiO₂/C composites are prepared by cocondensing SiO₂ with cellulose nanocrystals (CNCs) followed by pyrolysis. The magnesiothermic reduction of the composites produces SiC after prolonged solid‐state reaction, with mixed MgC₂/SiC intermediates. Iridescent mesoporous tetragonal MgC₂/SiC structures that retain the long‐range twisted organization of the starting composites transform to mesoporous cubic SiC with a chiral nematic hierarchical structure, but with some loss of order. On the other hand, the magnesiothermic reduction of the chiral nematic mesoporous SiO₂ templated from CNCs affords mesoporous Si materials with a layered hierarchical structure. The structural properties and the conductivity of the products, as well as the reaction pathways by analysis of the materials at intermediate stages, are investigated. These experimental results show that the magnesiothermic reduction is a promising way to obtain new porous semiconducting materials with chiral nematic structures.     

Photonic Hydrogels from Chiral Nematic Mesoporous Chitosan Nanofibril Assemblies

Iridescence in animals and plants often arises from structural coloration, which involves hierarchical organization of minerals and biopolymers over length scales of the visible spectrum, leading to diffraction of light. In this work, discarded crustacean shells that are not known for their structural colors are used to produce photonic nanostructures of large, freestanding chiral nematic mesoporous chitosan membranes with tunable iridescent color. Bioinspired by colorful nanostructures in nature, photonic hydrogels with Bouligand‐type organization are fabricated from the twisted mesoporous membranes, where the chitosan nanofibrils are a novel precursor for surface acetylation and are also a biotemplate for polymerizing methyl methacrylate. The colors of the hydrogels can be tailored by swelling as they show large volume changes in response to changes in solvent environment.     

介孔组装半导体量子点的研究进展

近年来,由于主客体效应,以多孔二氧化硅作为反应容器组装单分散的半导体量子点引起了人们很大的兴趣。本文主要介绍了介孔二氧化硅的基本概念及其制备方法、机理以及介孔组装半导体量子点这一新学科的研究状况,并展望了它的发展前景。     

Black Phosphorus Quantum Dots Encapsulated Biodegradable Hollow Mesoporous MnO2: Dual-Modality Cancer Imaging and Synergistic Chemo-Phototherapy

To achieve an accurate diagnosis and efficient tumor treatment, developing a facile and powerful strategy to build multifunctional nanotheranostics is highly desirable. Benefiting from the distinct characteristics of black phosphorus quantum dots (BPQDs), herein, a versatile nanoprobe (H-MnO₂/DOX/BPQDs) is constructed for dual-modality cancer imaging and synergistic chemo-phototherapy. The hollow mesoporous MnO₂ (H-MnO₂) nanoparticles are sequentially decorated with a cationic polymer poly (allylamine hydrochloride) (PAH) and an anionic polymer poly (acrylic acid) (PAA). The obtained H-MnO₂-PAH-PAA is covalently grafted with BPQDs-PEG-NH₂ via a carbodiimide cross-linking reaction and then loaded with anti-cancer drug DOX to form final nanoprobe H-MnO₂/DOX/BPQDs. Under the tumor microenvironment, H-MnO₂/DOX/BPQDs is degraded to release encapsulated functional molecules DOX and BPQDs. DOX acts as the chemotherapy and fluorescence imaging agent, and BPQDs endows the nanoprobe with photodynamic therapy (PDT) and photothermal therapy (PTT) abilities under dual laser irradiation of 630 and 808 nm. H-MnO₂ offers contrasts for magnetic resonance imaging (MRI) and facilitates conversion of endogenous H₂O₂ to oxygen, thereby relieving tumor hypoxia and enhancing PDT efficacy. All in vitro and in vivo results demonstrate that the designed nanoprobe displays dual-modality MRI/FL imaging and synergistic chemotherapy/PDT/PTT, which ultimately enhances the accuracy of cancer diagnosis and therapeutic performance.     

Highly Luminescent ZnO Quantum Dots Made in a Nonthermal Plasma

Nonthermal plasmas allow the preparation of ligand‐free quantum dots combining high production rates with superior crystalline quality and luminescence properties. Here, ZnO quantum dots are produced in a radiofrequency capacitively‐coupled plasma, exhibiting size dependent photoluminescent quantum yields up to 60% after air exposure—the highest reported to date for any compound semiconductor quantum dots prepared in the gas phase. Systematic studies indicate the importance of the surface for the observed luminescence behavior. The high luminescent quantum yields in the visible range of the spectrum and the ligand‐free, scalable synthesis make these quantum dots good candidates for light emitting applications.     

Metal Species–Encapsulated Mesoporous Silica Nanoparticles: Current Advancements and Latest Breakthroughs

Despite their advantageous morphological attributes and attractive physicochemical properties, mesoporous silica nanoparticles (MSNs) are merely supported as carriers or vectors for a reason. Incorporating various metal species in the confined nanospaces of MSNs (M‐MSNs) significantly enriches their mesoporous architecture and diverse functionalities, bringing exciting potentials to this burgeoning field of research. These incorporated guest species offer enormous benefits to the MSN hosts concerning the reduction of their eventual size and the enhancement of their performance and stability, among other benefits. Substantially, the guest species act through contributing to reduced aggregation, augmented durability, ease of long‐term storage, and reduced toxicity, attributes that are of particular interest in diverse fields of biomedicine. In this review, the first aim is to discuss the current advancements and latest breakthroughs in the fabrication of M‐MSNs, emphasizing the pros and cons, the confinement of various metal species in the nanospaces of MSNs, and various factors influencing the encapsulation of metal species in MSNs. Further, an emphasis on potential applications of M‐MSNs in various fields, including in adsorption, catalysis, photoluminescence, and biomedicine, among others, along with a set of examples is provided. Finally, the advances in M‐MSNs with perspectives are summarized.     

Biopolymer Templated Glass with a Twist: Controlling the Chirality,Porosity, and Photonic Properties of Silica with Cellulose Nanocrystals

A detailed investigation of the formation and properties of mesoporous silica templated by the chiral nematic liquid crystal phase of cellulose nanocrystals (CNCs) is presented. Under appropriate conditions, CNCs co‐assemble with silica up to loadings of ≈60 wt% to give composite films with periodic chiral nanostructures. The periodicity of these films can be readily controlled to obtain materials that selectively reflect light with wavelengths ranging from ≈400–1400 nm. The co‐assembly of CNCs and silica into ordered chiral nematic structures is demonstrated to occur within a narrow window of pH and is affected by aging: a slow rate of silica condensation appears to be vital for the formation of well‐ordered materials. CNCs can be removed from the composite films by calcination or acid hydrolysis to give high surface area chiral nematic mesoporous silica (CNMS) with tunable pore diameters. The combination of mesoporosity and chiral nematic ordering in CNMS enables it to be used in a unique way for refractometric sensing applications. It is shown that, when using circular dichroism (CD) signals to monitor the chiral photonic properties of CNMS, variations in refractive index can be detected based on changes of both CD signal intensity and peak position with good sensitivity.     

二氧化硅壳层对CdS:Mn/ZnS量子点的光稳定性影响研究

在量子点表面包覆二氧化硅壳层,能够有效的保护纳米粒子核不受外界环境的影响,使得它在光电子器件和生物标记等领域中有着广泛的应用前景。通过一锅法制备高质量CdS:Mn/ZnS量子点,然后利用反相微乳液方法在量子点的表面继续包覆SiO2层,得到CdS:Mn/ZnS@SiO2多层核壳结构量子点材料。化学性质稳定的ZnS及SiO2材料的包覆使CdS量子点材料的毒副作用降低并有效提高其稳定性,然而CdS:Mn/ZnS量子点的大部分性能在包覆SiO2后都保持不变,因此CdS:Mn/ZnS@SiO2量子点在光学应用中有很大的应用潜力。     

Photosensitization of TiO2 Nanostructures with CdS Quantum Dots: Particulate versus Tubular Support Architectures

TiO₂ nanotube arrays and particulate films are modified with CdS quantum dots with an aim to tune the response of the photoelectrochemical cell in the visible region. The method of successive ionic layer adsorption and reaction facilitates size control of CdS quantum dots. These CdS nanocrystals, upon excitation with visible light, inject electrons into the TiO₂ nanotubes and particles and thus enable their use as photosensitive electrodes. Maximum incident photon to charge carrier efficiency (IPCE) values of 55% and 26% are observed for CdS sensitized TiO₂ nanotube and nanoparticulate architectures respectively. The nearly doubling of IPCE observed with the TiO₂ nanotube architecture is attributed to the increased efficiency of charge separation and transport of electrons.     

Dynamic Chiro-Optics of Bio-Inorganic Nanomaterials via Seamless Co-Assembly of Semiconducting Nanorods and Polysaccharide Nanocrystals

This study demonstrates a novel chiral organization of multi-materials from semiconducting quantum nanorods (QNRs) co-assembled into chiral nematic polysaccharide (cellulose) nanocrystals for active manipulation of chiro-optical light emission properties in elastomeric materials. Highly emissive anisotropic QNRs with dimensions and surface chemistry commensurate with those of biological nanocrystals facilitate seamless co-assembly into an integrated chiral nematic organization due to preferable enthalpic interactions and pairing processes. The resulting freestanding highly emissive bio-inorganic elastomeric materials exhibit vivid iridescence and emission with a strong optical activity that manifests itself in active and tunable chiral photoluminescence with unusually large asymmetry. Intriguingly, large-strain reversible mechanical deformation of physically crosslinked elastomers endows fully reversible alternation of helical structural configuration and corresponding linearly and circularly polarized photoluminescence. This study provides a platform to render dynamic optical functionality with reconfigurable light propagation/emission in bio-inorganic elastomers for futuristic applications in chiral lasing, biosensing, optical gauges, and holographic display.     

Mn2+‐Doped CdSe Quantum Dots: New Inorganic Materials for Spin‐Electronics and Spin‐Photonics

Recent advances in the chemistry of colloidal semiconductor nanocrystal doping have led to new materials showing fascinating physical properties of potential technological importance. This article provides an overview of efforts to dope one of the most widely studied colloidal semiconductor nanocrystal systems, CdSe quantum dots, with one of the most widely studied transition‐metal dopant ions, Mn²⁺, and describes the major new physical properties that have emerged following successful synthesis of this material. These properties include spin‐polarizable excitonic photoluminescence, magnetic circular dichroism, exciton storage, and excitonic magnetic polaron formation. A brief survey of parallel advances in the characterization of analogous self‐assembled Mn²⁺‐doped quantum dots grown by molecular beam epitaxy is also presented, and the physical properties of the colloidal quantum dots are shown to compare favorably with those of the self‐assembled quantum dots. The rich variety of physical properties displayed by colloidal Mn²⁺‐doped CdSe quantum dots highlights the attractiveness of this material for future fundamental and applied research.     

Ultrabright Fluorescent Silica Mesoporous Silica Nanoparticles: Control of Particle Size and Dye Loading

The synthesis of ultrabright fluorescent mesoporous silica nanoparticles (UFSNPs) of various sizes loaded with different amounts of fluorescent dye (Rhodamine 6G) is reported here. The dye is physically entrapped inside the nanochannels of the silica matrix created during templated sol–gel self assembly. Due to the specific nanoenvironment, the fluorescence of the encapsulated dye molecules remains unquenched up to very high concentrations, which results in relatively high fluorescence. The particle size (ranging from 20–50 nm) and dye loading (0.8–9.3 mg dye per g particles) are controlled by the timing of the synthesis and the concentration of several organotriethoxysilanes, which are coprecursors of silica. The quantum yields of the encapsulated dye range from 0.65 to 1.0. The relative brightness of a single particle is equivalent to the fluorescence of 30–770 free nondimerized R6G dye molecules in water, or to that of 1.5–39 CdSe/ZnS quantum dots. Despite the presence of some hydrophobic groups on the particles' surfaces, colloidal suspensions of the particles are relatively stable (as monitored for 120 days).     

Design and Synthesis of Multifunctional Drug Carriers Based on Luminescent Rattle‐Type Mesoporous Silica Microspheres with a Thermosensitive Hydrogel as a Controlled Switch

A novel approach for the fabrication of multifunctional microspheres integrating several advantages of mesoporous, luminescence, and temperature responses into one single entity is reported. First, the hollow mesoporous silica capsules are fabricated via a sacrificial template route. Then, Gd₂O₃:Eu³⁺ luminescent nanoparticles are incorporated into the internal cavities to form rattle‐type mesoporous silica nanocapsules by an incipient‐wetness impregnation method. Finally, the rattle‐type capsules serve as a nanoreactor for successfully filling temperature‐responsive hydrogel via photoinduced polymerization to form the multifunctional composite microspheres. The organic–inorganic hybrid microspheres show a red emission under UV irradiation due to the luminescent Gd₂O₃:Eu³⁺ core. The in vitro cytotoxicity tests show that the samples have good biocompatibility, which indicates that the nanocomposite could be a promising candidate for drug delivery. In addition, flow cytometry and confocal laser scanning microscopy (CLSM) confirm that the sample can be effectively taken up by SKOV3 cells. For in vitro magnetic resonance imaging (MRI), the sample shows the promising spin‐lattice relaxation time (T₁) weighted effect and could potentially apply as a T₁‐positive contrast agent. This composite drug delivery system (DDS) provides a positive temperature controlled “on‐off”drug release pattern and the drug, indomethacin (IMC), is released fast at 45 °C (on phase) and completely shut off at 20 °C (off phase). Meanwhile Gd₂O₃:Eu³⁺ plays an important role as the luminescent tag for tracking the drug loading and release process by the reversible luminescence quenching and recovery phenomenon. These results indicate that the obtained multifunctional composite has the potential to be used as a smart DDS for biomedical applications.     

Chiroptical Resolution and Thermal Switching of Chirality in Conjugated Polymer Luminescence via Selective Reflection using a Double‐Layered Cell of Chiral Nematic Liquid Crystal

An optically resolvable and thermally chiral‐switchable device for circularly polarized luminescence (CPL) is first constructed using a light‐emitting conjugated polymer film and a double‐layered chiral nematic liquid crystal (N*‐LC) cell. The double‐layered N*‐LC cell with opposite handedness at each layer is fabricated by adding each of two types of N*‐LCs into each of the cells, and the N*‐LCs consist of nematic LCs and chiral dopants with opposite chirality and different mole concentrations. The selective reflection band due to the N*‐LC is thermally shifted so that the band wavelength is close to the luminescence band of the racemic conjugated polymer, such as disubstituted polyacetylene (diPA), yielding CPL with opposite handedness and high dissymmetry factor values (|g_lum|) of 1.1–1.6 at low and high temperatures. The double‐layered N*‐LC cell bearing the temperature‐controlled selective reflection is useful for generating CPLs from racemic fluorescent materials and for allowing thermal chirality‐switching in CPLs, which present new possibilities for optoelectronic and photochemical applications.     

GaN／AIN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发，采用有限元方法计算了GaN／AIN量子点结构中的应变分布，研究了其自发极化、压电极化以及极化电荷密度．结果表明，应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化，使电子聚集在量子点顶部，空穴聚集在量子点下面的湿润层中，在量子点结构中产生显著的极化电场，并讨论了电场的存在对能带带边的形状以及能级分布的影响．     

GaN/AlN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发,采用有限元方法计算了GaN/AlN量子点结构中的应变分布,研究了其自发极化、压电极化以及极化电荷密度.结果表明,应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化,使电子聚集在量子点顶部,空穴聚集在量子点下面的湿润层中,在量子点结构中产生显著的极化电场,并讨论了电场的存在对能带带边的形状以及能级分布的影响.     

GaN/AlN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发,采用有限元方法计算了GaN/AlN量子点结构中的应变分布,研究了其自发极化、压电极化以及极化电荷密度.结果表明,应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化,使电子聚集在量子点顶部,空穴聚集在量子点下面的湿润层中,在量子点结构中产生显著的极化电场,并讨论了电场的存在对能带带边的形状以及能级分布的影响.     

Cancer‐Targeting Graphene Quantum Dots: Fluorescence Quantum Yields,Stability, and Cell Selectivity

Folic acid, due to its high affinity toward folate receptors (FR), is recognized as one of the most promising cancer targeting vectors. However, the inherent defects of low water solubility (1.6 µg mL^?1), high sensitivity toward photo‐bleaching, low fluorescent quantum yields (QYs, <0.5%) seriously limit its practical application. Herein, ultrastable, highly luminescent graphene quantum dots (GQDs) that selectively target diverse cancer cells are prepared and tested. The new GQDs present step changes compared to common folic acid through an ≈6250 times increase in water solubility (to ≈10 mg mL^?1), more than 150 times in QYs (up to ≈77%), while maintaining luminescence stability up to 98% when subjected to UV, visible light, and heating over 360 min. It is shown that the suppression of nonradiative transitions by amino groups pyrolyzed from pterin plays a key role in the mechanism of high QYs and excellent stability. The functional groups that are likely responsible for the selective targeting of cancer cells with different levels of folate receptor expression on the surface are identified. Collectively with these promising properties, the new functional graphene quantum dots may open a new avenue for cancer diagnosis, drug delivery, and therapies.