Structure-controlled Synthesis Research Articles

An Overview of Nanoparticle Properties and Their Bioactivity

The term “nanoparticles” being expressed in microbiology is coined from the Greek word “nano” meaning “dwarf”. Nanoparticles range in size from 1-100nm. Nanoparticles vary in size, shape, and other properties and can exist with capping agents present after structure-controlled synthesis with starting materials like metals with or without organic agents. This systematic literature review article discusses current opinions on the properties of nanoparticles including the size and shape, surface area and surface charge, surface chemistry and reactivity and their magnetic properties. We also discuss the mechanisms of bioactivity of nanoparticles in reference to their interactions with microorganisms, penetration into microorganisms, disruption of cellular processes and their effects on microbial growth. We also discuss specifically, their antibacterial, antifungal and antiviral properties. This is followed by a review of their diagnostic and therapeutic applications, the factors affecting nanoparticle bioactivity (exposure time and other intrinsic physicochemical properties) and how the intrinsic properties of microorganisms such as strain selection and growth conditions are affected by the activity of nanoparticles. In this review, we also compare nanoparticle research in the new world with activities in third world countries. We conclude by discussing the toxicity and safety concerns in the use of nanoparticles including the environmental impact and regulatory guidelines in the use of nanoparticles followed by a recommendation on future guidelines for research.

Uncovering Origin of Chirality of Gold Nanoparticles Prepared through the Conventional Citrate Reduction Method

Chiral nanoparticles are one of the research hotspots in the field of materials science, chemistry, and biology. Understanding and controlling the chirality of nanoparticles is one key step toward their use, but the origin of nanoparticles' chirality and its determinative factor are not well understood. In this work, we studied the chirality of gold nanoparticles (AuNPs) prepared through the conventional citrate reduction method. Unexpectedly, it was found that small AuNPs (∼13 nm) exhibited opposite chirality to the large AuNPs (>30 nm). The origin of the AuNPs chirality was revealed by comparing the crystal structure between small AuNPs and large AuNPs. It was proposed that the lattice orientation of fivefold-twinned AuNPs may be responsible for the intrinsic chirality of AuNPs. This work provides a deep mechanistic understanding of the intrinsic chirality of the AuNPs and will boost the development of the structure-controlled synthesis and application of chiral AuNPs and other chiral nanomaterials. Furthermore, based on the unexpected size effect, chiral AuNP probes were rationally constructed to improve the precision of chiral recognition.

Advances in the One-Step Approach of Polymeric Materials Using Enzymatic Techniques.

The formulation in which biochemical enzymes are administered in polymer science plays a key role in retaining their catalytic activity. The one-step synthesis of polymers with highly sequence-controlled enzymes is a strategy employed to provide enzymes with higher catalytic activity and thermostability in material sustainability. Enzyme-catalyzed chain growth polymerization reactions using activated monomers, protein-polymer complexation techniques, covalent and non-covalent interaction, and electrostatic interactions can provide means to develop formulations that maintain the stability of the enzyme during complex material processes. Multifarious applications of catalytic enzymes are usually attributed to their efficiency, pH, and temperature, thus, progressing with a critical structure-controlled synthesis of polymer materials. Due to the obvious economics of manufacturing and environmental sustainability, the green synthesis of enzyme-catalyzed materials has attracted significant interest. Several enzymes from microorganisms and plants via enzyme-mediated material synthesis have provided a viable alternative for the appropriate synthesis of polymers, effectively utilizing the one-step approach. This review analyzes more and deeper strategies and material technologies widely used in multi-enzyme cascade platforms for engineering polymer materials, as well as their potential industrial applications, to provide an update on current trends and gaps in the one-step synthesis of materials using catalytic enzymes.

A non-iterative approach to Linear Quadratic Static Output Feedback

This paper considers the problem of static output feedback (SOF) synthesis for linear time-invariant (LTI) systems. Static output feedback, and more generally structured controller synthesis, is of special interest to any industrial application where a reduced-order controller is desired, e.g., high-order systems, or a specific structure is to be imposed, i.e., distributed/decentralised control. A simple two-step process is proposed, solving one Riccati equation and one optimisation problem with linear matrix inequality (LMI) constraints, enabled via a dilation using the distance to the full-state feedback optimum gain. Numerical analysis shows considerable computational savings, with negligible differences in the performance, when compared to current iterative methods.

Structured controller synthesis through block-diagonal factorization and parameter space optimization

Constraints on the feedback structure arise in many control systems due to implementing cost, hardware limitations and operational reliability. The parameter space method aims to solve the robust structured controller design problems based on a convex reformulation technique. Despite its attractiveness, the structural constraints are limited to be either decentralized or linear dependence among entries within the same row or column in the current literature. And the global optimal solution is yet to be guaranteed, since a non-convex constraint is introduced in the parameter space after reformulating it as the output feedback synthesis problem. In this paper, we extend the parameter space method to a more generalized structured optimal control problem, such that the linear dependence can occur among its arbitrary entries. A bilinear factorization to the feedback gain matrix is proposed by a special Kronecker product decomposition. Subsequently, an equivalent transformation is proposed to convert this structured control design problem to a controller synthesis problem under decentralized full-state feedback. Thereby, the prior non-convex constraint in the parameter space is removed and the globally optimal structured controller is synthesized by convex programming. Examples such as integrated design and formation control demonstrate its practical appeals.

Atomic-Scale Evidence of Catalyst Evolution for the Structure-Controlled Growth of Single-Walled Carbon Nanotubes.

ConspectusKnowing how nanomaterials nucleate and dynamically evolve at the nanoscale is crucial to understanding and in turn controlling the structure and properties of a wide variety of materials, among which single-walled carbon nanotubes (SWCNTs) with chirality-dependent properties is a typical example. Catalyst takes a central role in guiding the SWCNT growth. An in-depth understanding of the growth mechanism of SWCNTs requires knowledge of the catalyst dynamic behavior during the chemical vapor deposition process, where real-time atomic-scale observations are needed. The high spatial, temporal, and energy resolution makes the state-of-the-art aberration-corrected environmental transmission electron microscope (ETEM) a superior tool for tracking the catalyst evolution and the SWCNT growth.Several key factors and processes, including the catalyst stability, carbon diffusion pathway, nucleation site, and growth modes of nanotubes, greatly influence the structure of SWCNTs. This Account summarizes our recent progress in the ETEM investigation of the dynamic catalyst behavior and nucleation of SWCNTs. We first compare the different growth modes of SWCNTs on two types of catalyst-stable solid intermetallic Co7W6 and unstable monometallic catalysts. Then we address the origin of different growth modes and chirality selectivity by revealing the atomic-scale stability and evolution of catalysts under carbon feed conditions and the observation of the in situ growth of SWCNTs on catalysts. We also discuss the catalyst-support interaction and the possible influence on SWCNT growth. In the end, we summarize the present achievements and future challenges.We carefully compare the difference in the ordinary Co catalyst and Co7W6 catalyst which has shown great chirality selectivity in SWCNT growth. Direct imaging by ETEM demonstrated that solid catalysts initiated the growth of SWCNTs with diameters smaller (dNT) than those of the catalyst particles (dNP) (dNT < dNP), whereas molten catalyst nanoparticles produced SWCNTs with similar diameters (dNT ≈ dNP). ETEM combined with in situ synchrotron X-ray absorption spectroscopy demonstrated that the Co7W6 catalyst maintained a solid stable structure under carbon feed conditions at 700-1000 °C, demonstrating the feasibility in acting as a structure template to grow SWCNTs. By contrast, the state and composition of the Co catalyst were changing during SWCNT growth. The near-surface lattice spacings of Co7W6 remained unchanged under carbon feed condition with carbon diffusion on the surface, whereas the solid Co catalyst underwent dynamic expansion and contraction due to carbon penetration into and precipitation out of Co nanoparticles. These two different pathways of carbon diffusion on or in catalysts indicate the distinctly different growth mechanisms of SWCNTs: the epitaxial growth of SWCNTs with specified chirality on the facets of Co7W6 nanocrystals and the nonselective growth of SWCNTs by the Co catalyst with Co/CoC3 as the active species. Besides the SWCNT-catalyst interface, the catalyst-support interface is also of importance in SWCNT growth. The atomic-scale information on catalyst dynamics provides a deep mechanistic understanding of SWCNT growth and will boost the development of the structure-controlled synthesis of SWCNTs and other nanomaterials.

Electro-assisted Molecular Assembly Giving Atomic-Scale Catalytic Active-Site Detection.

The artificially accurate design of nonmetal electrocatalysts' active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom.

One-Pot Structure-Controlled Synthesis of Hyperbranched Polymers by a "Latent" Inimer Strategy Based on Diels-Alder Chemistry.

An efficient "one-pot" strategy for the structure-controlled synthesis of hyperbranched polymers (HBPs) based on a "latent" inimer (LI-Br), containing a furan-protected maleimide monomer and a haloalkane initiator, is presented. At high temperatures, the "latent" inimer is converted to a "real" inimer after releasing maleimide (MI) via a retro-Diels-Alder (r-DA) reaction and then copolymerized with methyl methacrylate by self-condensing vinyl copolymerization. Due to the dynamic characteristic of the r-DA reaction, the release of naked MI and the subsequent copolymerization can be regulated by the temperature or stereochemistry of Diels-Alder (DA) adducts. Thus, the "one-pot" structure-controlled synthesis of HBPs with various degrees of branching was achieved. By further implementation of a programmable temperature change, some valuable hyperbranched topologies such as star-shaped and long-chain hyperbranched polymers can be constructed avoiding sophisticated synthetic routes.

Multi-step chemical vapor synthesis reactor based on a microplasma for structure-controlled synthesis of single-walled carbon nanotubes

To address the need for the high precision synthesis of nanomaterials with the potential for high productivity, we present a novel design of a multi-step chemical vapor synthesis (CVS) reactor, which centers on the use of an atmospheric, continuous flow microplasma. Based on computational fluid dynamic gas flow simulations, the CVS reactor was designed to provide abrupt interaction steps to provide a well-defined and highly controlled start and stop to the nanomaterial (e.g., nanoparticle) growth. By applying this framework to gas-phase single-walled carbon nanotube (SWCNT) synthesis, the precise start and stop of the catalyst nanoparticle nucleation process can be done using the microplasma reactor (start) and carbon reactant gas to suppress further aggregation/promote SWCNT growth (stop), respectively. In so doing, we demonstrated the generation of controlled size of catalyst nanoparticles and SWCNTs despite high particle densities. We envision that our approach demonstrates the feasibility of fine structural control of nanomaterials through a multi-step CVS process with precisely regulating the aggregation time for high density particle flow, which overcomes the obstacle of both structural control and productivity.

Route to the Structure-Controlled Synthesis of Fe Nanobelts and Their Oxygen Evolution Reaction Application.

Belt-shaped metal-organic frameworks (MOFs) have received extensive attention because of their unique structure. In this Communication, Fe-MOF nanobelts were synthesized by a solvothermal method with Fe2+ as the metal source and could not be obtained by using Fe3+ as the metal source. The final result shows that Fe2+ played a transitional role in the process of achieving belt-shaped and cubelike structural changes. Our work provides an idea for the synthesis of belt-shaped MOFs and promotes the development of electrocatalysts.

Characterization on the formation mechanism of Fe0/Fe3C/C nanostructure and its effect on PMS activation performance towards BPA degradation

Fe3C/C nanohybrid has a wide application in many fields due to its versatility in numerous scenarios, however, the need for precise control of nanostructure is the obstacle during high-temperature pyrolysis of iron–nitrogen precursor. The purpose of this study was to explore the formation process and formation dynamic of Fe3C/C nanohybrid via pyrolysis. Based on in-situ (TGA-MS, TGA-FTIR) and ex-situ characterization (XRD, Raman, HR-TEM, Mössbauer, XAFS), the self-assembled ‘laminated template CxNy’ involved nucleation was crucial for the formation of Fe3C/C nanostructure. It enabled the dispersion of iron atoms at the molecular level and the nucleation of Fe(NCN) at the nanoscale. Moreover, the effects of temperature programming were evaluated by the peroxymonosulfate (PMS) activation efficiency towards bisphenol A (BPA) degradation. Fe0/Fe3C/C prepared with a heating rate of 3.5 °C/min during nucleation was proven to have the optimum PMS activation performance (1O2 and ·OH pathway), owing to Fe3C mediator is able to modulate the electronic structure of carbon as well as the corrosion rate of Fe0. This finding of nucleation and growth process would be valuable for the structure-controlled synthesis of Fe0/Fe3C/C in the large-scale.

Gradient Methods for Fixed Structure Controller Synthesis and System Identification of Decomposable Systems

In this letter we are considering the problem of fixed structure controller synthesis and system identification for large scale systems. The systems considered are referred to as decomposable systems and can be seen as resulting from the interconnection of a large number of identical subsystems. Combining recent results from nonsmooth controller synthesis with the special structure of decomposable systems, we show that the computational complexity of the controller synthesis and system identification procedure scale linearly with the size of the system. Employing results from robust control, the computational complexity of the controller synthesis can be reduced further, however, at the cost of additional conservatism. Using numerical examples we demonstrate that the proposed method can reduce the conservatism compared to existing LMI methods for full order decomposable controllers.

Molecular structure-controlled synthesis of sulfur-containing polymers for rechargeable Li–S batteries

Strategies for the molecular structure-controlled synthesis of sulfur polymers used in Li–S batteries are summarized, thus presenting the opportunities and challenges for the development of sulfur polymers in the future.

Robust structured controller synthesis for interleaved boost converters using an H∞ control method

The regulation of output voltage and equivalent distribution of phase currents of multi-phase converters which have non-minimum phase characteristic are still challenges, especially in the presence of uncertainties in real parameters, duty cycle, input voltage, and load disturbances. However, in classical third-order integral-lead (Type-III) controller design methodologies, the controller is synthesized considering only the nominal performance conditions. This paper proposes a structured [Formula: see text] synthesis framework based on an optimization methodology to the design of a robust Type-III controller for interleaved boost converters. The structured [Formula: see text] control approach is adapted for optimization of Type-III feedback and feedforward controllers in two-degree-of-freedom (2-DOF) control system configuration. The robust stability of the closed-loop interleaved boost converter system against model uncertainties is ensured via the classical [Formula: see text]-analysis technique. Numerical comparisons are made among the classical, i.e. unstructured or full order, [Formula: see text]-based controller design method, a dual-loop PI controller, and proposed 1-DOF and 2-DOF structured controller synthesis approaches on an interleaved boost converter model. Simulation results verify the effectiveness and advantages of the proposed approach from the viewpoint of the output voltage regulation under different disturbance points.

Structure-controllable synthesis of ZnO nanowires using water vapor in an atmospheric-pressure microwave plasma system

Although the use of atmospheric-pressure microwave plasma to synthesize ZnO nanowires addresses various issues associated with conventional synthesis methods, it is difficult to obtain nanowires with controlled diameters and lengths. Herein, we investigated the effects of microwave input power and water vapor on the structure of ZnO nanowires grown using an atmospheric-pressure microwave plasma system. It was found that the aspect ratio of ZnO nanowires could be controlled by adjusting the plasma temperature and the amount of OH radicals. This method successfully produced ZnO nanowires in a structure-controllable manner with a wide range of aspect ratios from 10 to 340. Interestingly, we found that the sensitivity of the ZnO nanowires to UV irradiation was closely related to the morphology. In particular, the ZnO nanowires with high aspect ratios and densities showed excellent sensing characteristics.

Rational Design and Mechanical Understanding of Three-Dimensional Macro-/Mesoporous Silicon Lithium-Ion Battery Anodes with a Tunable Pore Size and Wall Thickness.

Silicon is regarded as one of the most promising next generation lithium-ion battery anodes due to its exceptional theoretical capacity, appropriate voltage profile, and vast abundance. Nevertheless, huge volume expansion and drastic stress generated upon lithiation cause poor cyclic stability. It has been one of the central issues to improve cyclic performance of silicon-based lithium-ion battery anodes. Constructing hierarchical macro-/mesoporous silicon with a tunable pore size and wall thickness is developed to tackle this issue. Rational structure design, controllable synthesis, and theoretical mechanical simulation are combined together to reveal fundamental mechanisms responsible for an improved cyclic performance. A self-templating strategy is applied using Stöber silica particles as a templating agent and precursor coupled with a magnesiothermic reduction process. Systematic variation of the magnesiothermic reduction time allows good control over the structures of the porous silicon. Finite element mechanical simulations on the porous silicon show that an increased pore size and a reduced wall thickness generate less mechanical stress in average along with an extended lithiation state. Besides the mechanical stress, the evolution of strain and displacement of the porous silicon is also elaborated with the finite element simulation.

Synthesis of Er3+ doped KNbO3 nanocrystals and nanoceramics with outstanding up-conversion luminescence behaviors

Rare earth doped perovskite has become one of the most attractive multifunctional materials benefiting from the unique ferro-/piezoelectric, photocatalytic and photoluminescence properties. In this contribution, a series of Er3+ doped KNbO3 nanocrystals with distinctive morphologies, i.e., nanocubes, nanocuboids, and quasi-nanospheres, were prepared via a facile molten salt synthesis method. Furthermore, using the as-synthesized nanocrystals, the Er3+ doped KNbO3 ceramics with homogeneous nanograins were obtained. The growth mechanism of the nanocrystals with different morphologies and sintering process of the nanoceramics were rationally proposed, respectively. It was demonstrated that the morphology of the nanocrystals could be controlled by adjusting the doping amount of Er3+ and the structure of the as-sintered nanoceramics strongly depends on the morphology of the pristine nanocrystals. Impressively, the Er3+-KNbO3 nanocrystals and nanoceramics exhibited excellent up-conversion photoluminescence (UC PL) properties. This work may pave a new way to the structure-controlled synthesis of rare earth doped perovskite oxides and related nanoceramics, which show large potential in applications of novel multifunctional devices.

Facile synthesis of NiS2–MoS2 heterostructured nanoflowers for enhanced overall water splitting performance

Although MoS2 materials are known as the efficient catalysts in acidic solution toward hydrogen evolution reaction, it remains a challenging issue for improving catalytic activity of MoS2 materials toward electrochemical splitting of water in alkaline solution. Herein, we developed NiS2–MoS2 heterostructured nanoflowers with 430–810 nm in diameter using a simple one-pot hydrothermal method. The resultant catalysts required the potential of 1.5 V to afford 10 mA/cm2 toward the oxygen evolution reaction, lower than that of MoS2 nanoflowers. Hydrogen evolution reaction was enhanced by the introduction of Ni into MoS2 nanoflowers with 194 mV at the current density of 10 mA/cm2. Moreover, the cell assembled by the NiS2–MoS2 heterostructured nanoflowers could drive the voltage of 1.67 V at 10 mA/cm2 using two-electrode system in 1.0 mol/L KOH solution toward overall water splitting. Structure-controlled synthesis of NiS2–MoS2 nanoflowers, directing the construction of heterointerfaces with the exposure of the abundant active sites, greatly altered the electron distribution due to synergistic effect between Ni–S and Mo–S. Due to the unique structure, NiS2–MoS2 heterostructured nanoflowers could effectively catalyze overall water splitting. NiS2–MoS2 heterostructured nanoflowers exhibited the enhanced overall water splitting activity in alkaline media due to more positive charges for Ni atoms and more surplus electrons for S.

Organic Cathode Materials for Rechargeable Zinc Batteries: Mechanisms, Challenges, and Perspectives.

Energy and environmental issues have given rise to the development of advanced energy-storage devices worldwide. Electrochemical energy technologies, such as rechargeable batteries, are considered to be the most reliable and efficient candidates. Compared with other batteries, zinc-based batteries seem promising due to their advantages, including inherent safety, cost-effectiveness, and environmentally friendliness. As potential alternatives to conventional inorganic cathodes, organic cathodes for Zn-organic batteries have become a hot topic for research, owing to their favorable characteristics, such as easy structure design, controllable synthesis, and environmental benignancy. Herein, a systematic overview on the fundamentals of organic cathode materials for zinc batteries, including material design, electrochemical mechanisms, technical advances, and challenging analysis, is provided. Furthermore, perspectives and corresponding research directions are offered to facilitate the future development of organic cathode materials for zinc batteries toward practical applications.

Structure-controlled synthesis of palladium concave nanocubes via CTAB-assisted reduction for methanol electro-oxidation

Structure-controlled synthesis of Pd nanocrystals has received much attention recently due to their remarkable catalytic performance. To get deep insight into the mechanism of kinetically controlled overgrowth and the relationship between structure and electrocatalytic performance, palladium concave nanocubes (PdCNs) with high-index facets were synthesized through a facile none-seeded routine induced by hexadecylpyridinium bromide (CTAB). The structural changes of PdCNs along with the concentration of CTAB, reaction time and temperature were investigated by transmission electron microscopy and X-ray diffraction. It was indicated that Pd nanocubes first grew into larger size with numerous interstices inside the PdCNs, and then the inner interstices were filled along with oxidative etching on the surface. The electrocatalytic activities of PdCNs with different structures were evaluated toward the electro-oxidation of methanol. The result showed that the electrocatalytic activity weakened with the decrease in interstices, which demonstrated that interstices played a more crucial role than the concave structures.