Tunable Nanostructures Research Articles

Fabrication of porous silk fibroin/cellulose nanofibril sponges with hierarchical structure using a lithium bromide solvent system

Porous silk fibroin (SF) sponges have been widely used in biomaterials due to their excellent biocompatibility and tunable degradability. However, it remains a challenge to construct porous SF materials with 3D nanofibrous structure mimicking extracellular matrix. In this study, a novel strategy was developed to fabricate SF/cellulose sponges with micro-nano hierarchical structure through using a lithium bromide aqueous solution system. It was found that the cellulose can be partially dissolved by lithium bromide solution to form abundant cellulose nanofibrils (CNFs). Therefore, the porous SF/CNF sponge was directly prepared after dissolving SF/cellulose blend in lithium bromide solution. The structure and performance of sponges can be regulated by adjusting SF/cellulose ratio. Raising the cellulose ratio enhanced the compression strength and water swelling ratio of sponges, but restrained the 3D spatial distribution of CNFs in the pore space. As SF content increased to 50%, CNFs homogeneously dispersed and formed the porous sponges with micro-nano hierarchical structure. FTIR and XRD results showed cellulose II and silk II structure in composites, and suggested the presence of intermolecular interaction between SF and cellulose. The enzymatic degradation results showed that the degradation rate of sponges could be regulated by the SF component, which significantly promoted degradability. The results provide promising scaffold candidate with tunable nanostructure and degradability.

Recent developments in fabrication and structure regulation of visible-light-driven g-C3N4-based photocatalysts towards water purification: A critical review

Graphitic carbon nitride (g-C3N4), a conjugated polymer semiconductor, has drawn increasing attention in environmental photocatalysis over the past decade, owing to its highly chemical stability, low cost and suitable electronic structure with a mild energy gap (∼ 2.7 eV). Whereas, its practical applications in wastewater purification are still faced with huge challenges, such as insufficient visible light absorption, low electronic conductivity, poor surface area and fast recombination of photoinduced charge carriers. The modification of g-C3N4 by coupling with other nanomaterials or forming unique nanostructures have been confirmed as valuable strategies. In this review, we give a comprehensive introduction about the recent developments in engineering g-C3N4 by constructing heterostructures or diverse morphologies to improve its photodegradation performance for the photocatalytic degradation of persistent organic pollutants. Such heterojunctions contain metal/g-C3N4, g-C3N4/C-based material and many other binary or ternary composites, and these special morphologies normally include nanorods, nanowires, nanotubes, nanosheets, porous architectures and other different tunable nanostructures. Several enhanced photocatalytic mechanisms for these nanohybrids under visible light irradiation have been explicated in detail, and future perspectives are also concluded in this review.

Hierarchical Assembly of l-Phenylalanine-Terminated Bolaamphiphile with Porphyrin Show Tunable Nanostructures and Photocatalytic Properties.

Demands related to clean energy and environmental protection promote the development of novel supramolecular assemblies for photocatalysis. Because of the distinctive aggregation behaviors, bolaamphiphiles with two hydrophilic end groups could be theoretically the right candidates for the fabrication of high-performance photocatalysis. However, photocatalytic applications based on bolaamphiphilic assemblies were still rarely investigated. Especially, the relationship between diverse assembled nanostructures and the properties for different applications is urgently needed to be studied. Herein, we demonstrate that using the hierarchical assembly of bolaamphiphiles could correctly induce the porphyrin supramolecular architectures with much better photocatalytic performances than the aggregations containing 450 times of the porphyrin molecules, even though both molecular structures as well as the J-aggregations of porphyrin building blocks are same in two different systems. Thus, the co-assembly of l-phenylalanine terminated bolaamphiphile (Bola-F) and the porphyrin containing four hydroxyl groups (tetrakis-5,10,15,20-(4-hydroxyphenyl)porphyrin) can form microtube in methanol and forms fibers/spheres in methanol/water mixture. For catalyzing the photodegradation of rhodamine B, the small amount of J-aggregated porphyrin within Bola-F microtubes show much better photocatalytic performance comparing with that of huge porphyrin J-aggregations in fibers/spheres. The supramolecular assemblies as well as the photocatalysis were thoroughly characterized by different spectroscopies and electron microscopy. It is demonstrated that the co-assembly with bolaamphiphiles could inhibit the energy transfer of porphyrin aggregation and subsequently benefit the electron transfer and corresponding photocatalysis under photo-irradiation. This work is not only useful for further understanding the hierarchically supramolecular assembly but also provides a new strategy for making novel functional supramolecular architectures based on the assembly of bolaamphiphiles and porphyrins.

Hierarchically Porous Single Nanocrystals of Bimetallic Metal–Organic Framework for Nanoreactors with Enhanced Conversion

Nanoreactors constructed by encapsulation of catalytic species in hierarchically porous metal–organic framework (HPMOF) nanostructures have emerged as a type of promising catalysts that deliver enhanced conversion and excellent selectivity/stability. However, the controlled synthesis of small HPMOF nanocrystals with tunable size and nanostructures remains challenging. Here, by coupling external ultrasonication with the inherent binding competitions between the metal ions of bimetallic Co/Zn-ZIF, we design and develop a new strategy, dynamic growth, for the facile synthesis of small (down to ca. 95 nm), single-crystalline and structure-/size-tunable HPMOF nanocrystals through a one-pot, additive-free procedure. Benefiting from the combined structure/size regulation, nanoreactors based on our small nanocrystals of meso-HP-Co/Zn-ZIF-50% are able to deliver exceptional conversion while keeping their excellent selectivity and stability. Insights gained from this work opens a new avenue for the development of c...

Peptide-based hydrogels with tunable nanostructures for the controlled release of dyes

Hydrogels with different microstructures including nanoribbons, stiff nanofibers, helical ribbons and nanotubes were observed by varying the concentration of oxidized glutathione (OGH) with a fixed concentration of sodium deoxycholate (SD). The self-assembled nanostructures were characterized in detail by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Random coil structures and β-sheets play important roles in the constructed nanostructures, which were verified by Fourier-transform infrared (FT-IR) spectroscopy and circular dichroism (CD), as well as small angle X-ray diffraction (SXRD) measurements. We proposed a mechanism for these nanostructural transformations. The "weak hydrogels" exhibited irreversible responses to heating and shaking and a reversible response to pH. Furthermore, the hydrogel could be used for the controlled release of dyes. Due to the strong electrostatic attraction between the positively charged dye methylene violet (MV) and the negatively charged nanofibers, methylene violet is released more slowly than the negatively charged dye, methyl orange (MO).

Two-dimensional porous carbon nanosheets from exfoliated nanopaper-like biomass

Two-dimensional porous carbon nanosheet materials are of increasing importance. Many examples for their synthesis exist, but they generally show some common requirements, such as rigid reaction conditions, high cost and complicated multiple synthetic steps. Here we report a facile and cost-effective way to prepare porous carbon nanosheets by using an exfoliated nanopaper-like biomass, i.e., melaleuca bark as precursor. It is found that just after a simple carbonization treatment, the nanopaper-like barks can be directly transformed into two-dimensional carbon nanosheets with a unique hierarchical porous structure. A high BET surface area of 1397 m2/g can be reached for the obtained carbon materials without any extra activation process. Tuning of nanostructures could be facilely accomplished by varying carbonization treatment conditions. The as-prepared porous carbon nanosheet serves well as the sulfur host materials for lithium-sulfur battery.

Hierarchical Assemblies of Supramolecular Coordination Complexes.

Hierarchical self-assembly (HAS) is a multilevel organization process that first assembles elementary molecular units into ordered secondary structures via noncovalent interactions, which further act as the building blocks to form more complex multifunctional superstructures at the next level(s). The HAS strategy has been used as a versatile method for the preparation of soft-matter nanoarchitectures of defined size and morphologies, tunable luminescence, and biological importance. However, such preparation can be greatly simplified if well-defined dynamic structures are employed as the cores that upon linking form the desired nanoarchitectures. Discrete supramolecular coordination complexes (SCCs) with well-defined shapes, sizes, and internal cavities have been widely employed to construct hierarchical systems with functional diversity. This Account summarizes the prevailing strategies used in recent years in the preparation of SCC-based HASs and illustrates how the combination of dynamic metal-ligand coordination with other interactions was used to obtain hierarchical systems with interesting properties. HASs with dual orthogonal interactions involving coordination-driven self-assembly and hydrogen bonding/host-guest interaction generally result in robust and flexible supramolecular gels. Likewise, hybridization of SCCs with a suitable dynamic covalent network via a hierarchical strategy is useful to prepare materials with self-healing properties. The intrinsic positive charges of the SCCs also make them suitable precursors for the construction of HASs via electrostatic interactions with negatively charged biological/abiological molecules. Furthermore, the interplay between the hydrophilic and lipophilic characters of HASs by varying the number and spacial orientation of alkyl/oxyethylene chains of the SCC is a simple yet controllable approach to prepare ordered and tunable nanostructures. Certain SCC-cored hierarchical systems exhibit reversible polymorphism, typically between micellar, nanofiber, and vesicular phases, in response to various external perturbations: heat, photoirradiation, pH-variance, redox-active agents, etc. At the same time, multiple noncovalent interaction mediated HASs are growing in numbers and are promising candidates for obtaining functionally diverse materials. The photophysical properties of SCC-based HASs have been used in many analytical applications. For example, embedding tetraphenylethene (TPE)-based pyridyl ligands within metallo-supramolecular structures partially restricts the molecular rotations of its phenyl rings, endowing the resultant SCCs with weak emissions. Further aggregation of such HASs in suitable solvents results in a marked enhancement in emission intensity along with quantum yields. They act as sensitive sensors for different analytes, including pathogens, drugs, etc. HASs are also useful to develop multidrug systems with cooperative chemotherapeutic effects. Hence, the use of HASs with theranostic SCCs combining cell-imaging agents and chemotherapeutic scaffolds is a promising drug delivery strategy for cancer theranostics. At the same time, their responsiveness to stimuli, oftentimes due to the dynamic nature of the metal-ligand interactions, play an important role in drug release via a disassembly mechanism.

High-contrast switching and high-efficiency extracting for spontaneous emission based on tunable gap surface plasmon

Controlling spontaneous emission at optical scale lies in the heart of ultracompact quantum photonic devices, such as on-chip single photon sources, nanolasers and nanophotonic detectors. However, achiving a large modulation of fluorescence intensity and guiding the emitted photons into low-loss nanophotonic structures remain rather challenging issue. Here, using the liquid crystal-tuned gap surface plasmon, we theoretically demonstrate both a high-contrast switching of the spontaneous emission and high-efficiency extraction of the photons with a specially-designed tunable surface plasmon nanostructures. Through varying the refractive index of liquid crystal, the local electromagnetic field of the gap surface plasmon can be greatly modulated, thereby leading to the swithching of the spontaneous emission of the emitter placed at the nanoscale gap. By optimizing the material and geometrical parameters, the total decay rate can be changed from 103γ0 to 8750γ0, [γ0 is the spontaneous emission rate in vacuum] with the contrast ratio of 85. Further more, in the design also enables propagation of the emitted photons along the low-loss phase-matched nanofibers with a collection efficiency of more than 40%. The proposal provides a novel mechanism for simultaneously switching and extracting the spontaneous emitted photons in hybrid photonic nanostructures, propelling the implementation in on-chip tunable quantum devices.

Tunable Fabrication of SERS-Active Noble Metal Nanoarrays

This work demonstrates the fabrication of uniform gold nanoarrays by utilizing self-assembled block copolymer (BCP) template, which enables us to finely tune the gold nanostructures by simply adjusting reaction time. We fabricated a series of evolutional gold nanostructures with different reaction time, and investigated their corresponding SERS effects. Results show that the nanostructures have strong size-dependent Raman signal enhancement. This work provides a fast, simple and reproducible way to fabrication of SERS-active substrate with tunable nanostructures.

Tunable, Hybrid 1D ZnO Nanostructures Obtained by Using Bio‐renewable Ferulic Acid as Support and its Applications

AbstractInorganic oxides such as titanium dioxide (TiO2) and zinc oxide (ZnO) are desired as ultraviolet (UV) filters. Such UV‐filters derived from naturally occurring oxides are promising components for formulating personal care products sustainably. However, UV‐filters based on inorganic oxides pose challenges to formulators and users in terms of strong adherence to skin and high photocatalytic activity. As a means to influence the morphology of such functional oxides, a simple one‐dimensional (1D) ZnO nanorod was synthesized via solvothermal technique assisted by the seed‐growth method. Thus bio‐renewable ferulic acid (FA) was used as a capping and structure‐directing agent to obtain tunable nanostructures such as spheres, sheets, and rods. SEM and TEM analyses revealed the self‐assembled elongated morphology with increased aspect ratio. Based on these as well as other analyses the growth mechanism of zinc oxide functionalized ferulic acid (ZnO@FA) was investigated. ZnO@FA also exhibited broad absorption in the UV−B and A regions, unique antioxidant behavior along with a highly suppressed photocatalytic activity. The ZnO@FA are sustainable, functional materials. These materials are potentially useful in areas such as cosmetics, functional coatings, sensors and solar cells.

Tunable quantum criticality and super-ballistic transport in a "charge" Kondo circuit.

Quantum phase transitions (QPTs) are ubiquitous in strongly correlated materials. However, the microscopic complexity of these systems impedes the quantitative understanding of QPTs. We observed and thoroughly analyzed the rich strongly correlated physics in two profoundly dissimilar regimes of quantum criticality. With a circuit implementing a quantum simulator for the three-channel Kondo model, we reveal the universal scalings toward different low-temperature fixed points and along the multiple crossovers from quantum criticality. An unanticipated violation of the maximum conductance for ballistic free electrons is uncovered. The present charge pseudospin implementation of a Kondo impurity opens access to a broad variety of strongly correlated phenomena.

Constrained-volume assembly of organometal confined in polymer to fabricate multi-heteroatom doped carbon for oxygen reduction reaction

The design and preparation of non-precious metal and carbon-based nanocomposites are critical to the development of efficient catalysts for technologies ranging from water splitting to fuel cell. Here, we present a constrained-volume self-assembly process for the one-step continuous precipitation-induced formation of soft colloidal particles, in which hydrophobic organoferrous compound, (Ph3P)2Fe(CO)3, is encapsulated within poly(styrene-co-acrylonitrile) nanoparticles (NPs). The protective and confining polymer matrix ensures uniform carbonization and dispersion of (Ph3P)2Fe(CO)3 within a carbon matrix after a pyrolysis process. The obtained carbon NPs are successfully co-doped with Fe, P and N with a relatively high surface area of ~380 m2 g−1. The Fe-P-N-doped carbon catalyst exhibits high catalytic performance and stability toward oxygen reduction reaction in both alkaline and acidic electrolytes via a favorable four-electron pathway. Meanwhile, the catalytic capability of Fe-P-N-doped carbon can be tailored by the tunable nanostructures.

Lifetime-Encoded Infrared-Emitting Nanoparticles for in Vivo Multiplexed Imaging.

Advanced diagnostic procedures are required to satisfy the continuously increasing demands of modern biomedicine while also addressing the need for cost reduction in public health systems. The development of infrared luminescence-based techniques for in vivo imaging as reliable alternatives to traditional imaging enables applications with simpler and more cost-effective apparatus. To further improve the information provided by in vivo luminescence images, the design and fabrication of enhanced infrared-luminescent contrast agents is required. In this work, we demonstrate how simple dopant engineering can lead to infrared-emitting rare-earth-doped nanoparticles with tunable (0.1-1.5 ms) and medium-independent luminescence lifetimes. The combination of these tunable nanostructures with time-gated infrared imaging and time domain analysis is employed to obtain multiplexed in vivo images that are used for complex biodistribution studies.

Hierarchical honeycomb-patterned polydimethylsiloxane films with tunable nanostructures

The preparation of hierarchical nanoporous films is of great significance for their potential applications, but the development of a facile method to synthesize such films method remains a great challenge. In the current work, hierarchically honeycomb-patterned polydimethylsiloxane (PDMS) films with unique nanostructures were synthesized by simply depositing an acid solution, specifically consisting of a mixture of H2SO4, HNO3, and DI water, on PDMS films displaying regular concave structures. During the post-processing, secondary extrusions were generated on the surfaces of such PDMS films, leading to the formation of highly hierarchical honeycomb-shaped patterns. In the synthesis, the composition of the acid solution played a critical role in the formation and growth of the secondary extrusions. The morphological evolution of the PDMS films during the post-processing proceeded along different pathways depending on the experimental conditions of the process. Based on our results and observations, a plausible mechanism explaining the formation of the hierarchical honeycomb-shaped patterns and the morphological evolution during the synthesis was proposed. The developed approach provides a simple route for fabricating polymer films with unique hierarchical honeycomb-shaped patterns and without the need for any expensive or sophisticated lithographic patterning instruments.

Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma.

Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 μm thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm2.

Highly Tunable Hollow Gold Nanospheres: Gaining Size Control and Uniform Galvanic Exchange of Sacrificial Cobalt Boride Scaffolds.

In principle, the diameter and surface plasmon resonance (SPR) frequency of hollow metal nanostructures can be independently adjusted, allowing the formation of targeted photoactivated structures of specific size and optical functionality. Although tunable SPRs have been reported for various systems, the shift in SPR is usually concomitant with a change in particle size. As such, more advanced tunability, including constant diameter with varying SPR or constant SPR with varying diameter, has not been properly achieved experimentally. Herein, we demonstrate this advanced tunability with hollow gold nanospheres (HGNs). HGNs were synthesized through galvanic exchange using cobalt-based nanoparticles (NPs) as sacrificial scaffolds. Co2B NPscaffolds were prepared by sodium borohydride nucleation of aqueous cobalt chloride and characterized using UV-vis, dynamic light scattering, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Careful control over the size of the Co2B scaffold and its galvanic conversion is essential to realize fine control of the resultant HGN diameter and shell thickness. In pursuit of size control, we introduce B(OH)4- (the final product of NaBH4 hydrolysis) as a growth agent to obtain hydrodynamic diametersrangingfrom ∼17-85 nm with relative standard deviation <3%. The highly monodisperse Co2B NPs were then used as scaffolds for the formation of HGNs. In controlling HGN shell thickness and uniformity, environmental oxygen was shown to affect both the structural and optical properties of the resultant gold shells. With careful control of these key factors, we demonstrate an HGN synthesis that enables independent variation of diameter and shell thickness, and thereby SPR, with unprecedented uniformity. The new synthesis method creates a truly tunable plasmonic nanostructure platform highly desirable for a wide range of applications, including sensing, catalysis, and photothermal therapy.

Tailoring Interfacial Nanoparticle Organization through Entropy.

The ability to tailor the interfacial behaviors of nanoparticles (NPs) is crucial not only for the design of novel nanostructured materials with superior properties and of interest for many promising applications such as water purification, enhanced oil recovery, and innovative energy transduction, but also for a better insight into many biological systems where nanoscale particles such as proteins or viruses can interact and organize at certain interfaces. As a class of emerging building blocks, Janus NPs consisting of two compartments of different chemistry or polarity are ideal candidates to generate tunable and stable interfacial nanostructures because of the asymmetric nature. However, precise control over such interfacial nanostructures toward a controllable order and even responses to various external stimuli still remains a great challenge as the interfaces do not simply serve as a scaffold but rather induce complex enthalpic and entropic interactions. In this Account, we focus on our efforts on exploiting entropy strategies based on computational design to tailor the spatial distribution and ordering of NPs at the interfaces of various systems. First, we introduce the physical principle of entropic ordering, being the theoretical basis of entropy-directed interfacial self-assembly. The typical types of entropy, which have been harnessed to manipulate the interfacial NP organization, are then summarized, including conformational entropy, shape entropy, and rotational and vibrational entropy. Next, we describe the emerging pathways in the development of novel environmentally responsive systems which involve the use of entropy to access the stimuli-responsive behaviors of interfacial nanostructures. Taking one step further, how molecular architectures can be tailored to tune the entropic contributions to the interfacial self-assembly is demonstrated, through identifying the effects of various intrinsic properties of block segments, such as chain length and stiffness, on entropy-governed precise organization of Janus NPs at block copolymer interfaces. Finally, we detail some key factors for tailoring interfacial organization through entropy. In summary, entropy strategies offer a promising and abundant framework for precisely programming the structural organization of NPs at interfaces. We discuss future directions to signify the framework in tailoring the interfacial organization of NPs. We hope that this Account will promote further efforts toward fundamental research and the wide applications of designed interfacial assemblies in new types of functional nanomaterials and beyond.

The role of different initial rest times on synthesized buffer layer and UV sensing of ZnO nanorods grown on rotational substrate

ZnO nanorods (NRs) were successfully synthesized on seed layered substrate by a rotational hydrothermal method. The critical role of initial rest time of rotating substrate on the growth and UV photodetecting properties of ZnO NRs was systematically investigated. Moreover, the crystal structure and morphology of as-grown ZnO NRs were characterized by X-ray diffraction and field emission scanning electron microscopy, respectively. The XRD studies showed that the c-oriented (002) peak of ZnO NRs was shifted towards higher values with increasing initial rest time while the grain size decreased. Interestingly, the diameter and length of NRs displayed increasing trend with increasing the initial rest time which makes them tunable nanostructures through facile hydrothermal-based fabrication process. The change in the electrical resistance of the samples was described according to morphological specification of NRs and buffer layer thickness which was ascribed to the transport mechanism of electrons in the synthesized buffer layer. Finally, photosensing properties of ZnO based ultraviolet (UV) detectors were evaluated. Accordingly, it was observed the photodetector with optimal performance (20 min initial time) shows an optimum sensitivity of ~ 1270 and responsivity of ~ 1.18 A/W.

Stimuli-Responsive Multilayers Based on Thiolated Polysaccharides That Affect Fibroblast Cell Adhesion.

Control of the biomaterial properties through stimuli-responsive polymeric platforms has become an essential technique in recent biomedical applications. A multilayer system of thiolated chitosan (t-Chi) and thiolated chondroitin sulfate (t-CS), consisting of five double layers ([t-Chi/t-CS]5), was fabricated here by applying a layer-by-layer coating strategy. To represent a novel class of chemically tunable nanostructures, the ability to cross-link pendant thiol groups was tested by a rise from pH 4 during layer formation to pH 9.3 and a more powerful chemical stimulus by using chloramine-T (ChT). Following both treatments, the resulting multilayers showed stimuli-dependent behavior, as demonstrated by their content of free thiols, wettability, surface charge, elastic modulus, roughness, topography, thickness, and binding of fibronectin. Studies with human dermal fibroblasts further demonstrated the favorable potential of the ChT-responsive multilayers as a cell-adhesive surface compared to pH-induced cross-linking. Because the [t-Chi/t-CS]5 multilayer system is responsive to stimuli such as the pH and redox environment, multilayer systems with disulfide bond formation may help to tailor their interaction with cells, film degradation, and controlled release of bioactive substances like growth factors in a stimuli-responsive manner useful in future wound healing and tissue engineering applications.

Chloride Ion Induced Formation of Size/Shape Tunable Hollow Gold Nanostructures

Chloride Ion Induced Formation of Size/Shape Tunable Hollow Gold Nanostructures