Merging Biological Self-Assembly with Synthetic Chemical Tailoring: The Potential for 3-D Genetically Engineered Micro/Nano-Devices (3-D GEMS)

Appreciable global efforts are underway to develop processes for fabricating three-dimensional (3-D) nanostructured assemblies for advanced devices. Widespread commercialization of such devices will require: (i) precise 3-D fabrication of chemically tailored structures on a fine scale and (ii) mass production of such structures on a large scale. These often-conflicting demands can be addressed with a revolutionary new paradigm that couples biological self-assembly with synthetic chemistry: B ioclastic a nd S hape-preserving I norganic C onversion (BaSIC). Nature provides numerous examples of microorganisms that assemble biominerals into intricate 3-D structures. Among the most spectacular of these microorganisms are diatoms (unicellular algae). Each of the tens of thousands of diatom species assembles silica nanoparticles into a microshell with a distinct 3-D shape and pattern of fine (nanoscale) features. The repeated doubling associated with biological reproduction enables enormous numbers of such 3-D microshells to be generated (e.g., only 40 reproduction cycles can yield >1 trillion 3-D replicas!). Such genetic precision and massive parallelism are highly attractive for device manufacturing. However, the natural chemistries assembled by diatoms (and other microorganisms) are rather limited. With BaSIC processes, biogenic assemblies can be converted into a wide variety of new functional chemistries, while preserving the 3-D morphologies. Ongoing advances in genetic engineering promise to yield microorganisms tailored to assemble nanoparticle structures with device-specific shapes. Large-scale culturing of such genetically tailored microorganisms, coupled with shape-preserving chemical conversion (via BaSIC processes), would then provide low-cost 3-D G enetically E ngineered M icro/nano-devices (3-D GEMs).     

Chitosan scaffolds formation by a supercritical freeze extraction process

A crucial step of Tissue Engineering (TE) approach is the fabrication of 3-D biodegradable scaffolds. It has been achieved using various techniques, such as gas foaming, fiber bonding, solvent casting/particulate leaching, phase separation and 3D-printing. Each technique presents specific advantages and disadvantages; but, all of them share the difficulty to obtain simultaneously the macro, micro and nanostructure. In this work, a Supercritical Freeze Extraction Process (SFEP) is proposed for the formation of chitosan structures suitable for TE applications. We showed that it is possible to produce chitosan scaffolds characterized by a micrometric cellular structure, nanofibrous sub-structure and porous surfaces. The low process temperature allows to obtain 3-D solids, whose structure is preserved during supercritical drying. Preliminary results on cell cultivation confirmed that the generated chitosan scaffolds are characterized by a morphology that is potentially suitable for TE applications. A good cell adhesion was obtained and a large percentage of living cells was observed. This result can depend on the micrometric morphology of the scaffolds, that assures a good nutrient diffusion, and on the nanometric sub-structure that allows an adequate cells adhesion.     

Intumescent char structures and flame‐retardant mechanism of expandable graphite‐based halogen‐free flame‐retardant linear low density polyethylene blends

The structures of the intumescent charred layers formed from expandable graphite (EG)‐based intumescent halogen‐free flame retardant (HFFR) linear low‐density polyethylene (LLDPE) blends and their flame‐retardant mechanism in the condensed phase have been studied by dynamic Fourier transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), scanning electron microscopy (SEM), differential thermal analysis (DTA) and thermal conductivity (TC) measurements. The dynamic FTIR, XPS and LRS data show that the carbonaceous structures of intumescent charred layers consist of EG and various numbers of condensed benzene rings and/or phosphocarbonaceous complexes attached by the P? O? C and P? N bonds or quaternary nitrogen products. The addition of EG can hasten the formation of these phosphocarbonaceous structures. The above results show that the flame‐retardant mechanism in the condensed phase is that the compact char structures, as observed by SEM, slow down heat and mass transfer between the gas and condensed phase and prevent the underlying polymeric substrate from further attack by heat flux in a flame. The DTA and TC data show that carbonaceous charred layers are good heat‐insulating materials, the TC value of which is only about one‐tenth of that of the corresponding blend and that they increase the oxidization temperature and decrease thermal oxidization heat of the LLDPE/EG/HFFR systems. © 2003 Society of Chemical Industry     

The nature of the carbonaceous layer formed on a MoO3 model catalyst during propylene metathesis

The carbonaceous layer formed on the surface of a MoO₃ model catalyst during propylene metathesis is examined using Auger electron spectroscopy and ex situ laser Raman spectroscopy. Auger spectroscopy confirms the formation of a carbonaceous layer similar to that found after catalysis performed by Mo metal and MoO₂. Raman spectroscopy indicates that the carbonaceous layer is primarily composed of surface-bound hydrocarbon fragments and small graphitic particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct patterning of polystyrene–polymethyl methacrylate copolymer by means of laser interference lithography using UV laser irradiation

The fabrication of functionalized surfaces on polymeric substrates is of importance in chemistry, biology, physics, and material science. Examples of functional surfaces are micro/nano periodic arrays that can be fabricated using different methods. However, many of these techniques require several fabrication steps. In this communication, we report the fabrication of advanced architectures in poly(methylmethacrylate)–polystyrene (PMMA–PS) copolymers using direct laser interference patterning. Because of the mixed optical properties of the copolymers, a different type of periodic architectures could be fabricated when compared with traditional pure polymers. This new type of periodic structures results from the local swelling of the copolymer due to the formation of gaseous products induced by the laser radiation. Additionally, relatively low laser fluences are necessary to initiate the ablation process of the copolymers. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Synthesis of crystalline and amorphous,particle-agglomerated 3-D nanostructures of Al and Si oxides by femtosecond laser and the prediction of these particle sizes

We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide.     

The versatile synthesis method for hierarchical micro‐ and mesoporous zeolite: An embedded nanocarbon cluster approach

In this work, we are reporting for the first time the synthesis of hierarchical micro‐ and mesoporous zeolite using silica–carbon (SiO₂/C) composites prepared by pyrolysis of carbonaceous gases in the presence of silica gel. The pyrolysis effectively yielded carbon deposited onto the raw silica material. The obtained SiO₂/C composites were utilised as a bifunctional material, mesoporous template and silica source, for the zeolite synthesis. Tetrapropylammonium hydroxide (TPAOH) was used as a microporous template. The combination of the obtained composites and the TPAOH for the hydrothermal synthesis resulted in the formation of hierarchical micro‐ and mesoporous ZSM‐5. The results from the SEM, TEM, and N₂ adsorption/desorption isotherms, and ²⁷Al MAS NMR characterisations of the synthesised samples obtained after the removal of the templates confirmed the successful formation of the micro‐ and mesoporous zeolites. The mesoporosity of the zeolites could be controlled by adjusting the carbon content in the SiO₂/C composites while the carbon content could be controlled by varying the deposition time and the concentration of the carbonaceous gases used. This controllable and efficient synthesis method is considered to be a promising method for creating hierarchical micro‐ and mesoporous zeolites. © 2011 Canadian Society for Chemical Engineering     

New approaches to the analysis of high connectivity materials: design frameworks based upon 4(4)- and 6(3)-subnet tectons

Coordination framework polymers derived from lanthanide metal ions with N,N'-dioxide ligands (4,4'-bipyridine-N,N'-dioxide, pyrazine-N,N'-dioxide, 1,2-bis(pyridin-4-yl)ethane-N,N'-dioxide, trans-1,2-bis(pyridin-4-yl)ethene-N,N'-dioxide) exhibit such intricate architectures that a new strategy is required to appreciate and understand their structures. Rather than analyzing the overall structure in terms of the connectivity of individual metal nodes, which can lead in some cases to extremely complex topological treatments, our new strategy is based on the visualization of the structures as combinations of interconnected layered 2-D sheets or subnet tectons. Despite the diversity and relative complexities of many of the structures discussed here, they can all be described by the interconnection of just two types of 2-D subnet tectons, 4(4) square grids or 6(3) hexagonal grids. The interconnection of these layered sheets with bridging N,N'-dioxide molecules gives rise to both 2-D bilayer and 3-D network extended structures depending upon the relative dispositions of the interconnecting N,N'-dioxide ligands. Thus, 2-D bilayers result when the N,N'-dioxide ligands that bridge two subnet tectons are located on the same side of the sheet, while 3-D networks are formed when the bridging N,N'-dioxide ligands are located on both sides of the sheet. This analysis allows ready identification and interpretation of some of the most highly connected and complex architectures yet observed in materials chemistry.     

3D microfabrication of single-wall carbon nanotube/polymer composites by two-photon polymerization lithography

We present a method to develop single-wall carbon nanotube (SWCNT)/polymer composites into arbitrary three-dimensional micro/nano structures. Our approach, based on two-photon polymerization lithography, allows one to fabricate three-dimensional SWCNT/polymer composites with a minimum spatial resolution of a few hundreds nm. A near-infrared femtosecond pulsed laser beam was focused onto a SWCNT-dispersed photo resin, and the laser light solidified a nanometric volume of the resin. The focus spot was three-dimensionally scanned, resulting in the fabrication of arbitrary shapes of SWCNT/polymer composites. SWCNTs were uniformly distributed throughout the whole structures, even in a few hundreds nm thick nanowires. Furthermore, we also found an intriguing phenomenon that SWCNTs were self-aligned in polymer nanostructures, promising improvements in mechanical and electrical properties. Our method has great potential to open up a wide range of applications such as micro- and nanoelectromechanical systems, micro/nano actuators, sensors, and photonics devices based on CNTs.     

A study of the interaction of atomic oxygen with various carbonaceous materials

A variety of techniques have been used to examine the manner by which atomic oxygen species interact with various carbonaceous solids. In addition, the effect of such a treatment on the physical and surface chemical properties of the carbons has been determined. In situ electron microscopy studies have enabled us to establish that graphite is probably the most reactive form of carbon for this reaction. This behavior is rationalized according to the notion that atomic oxygen reacts preferentially with the delocalized π electrons in the graphite basal plane to create micro-pits. It is shown that careful control of the reaction of atomic oxygen with a carbonaceous surface can lead to certain beneficial effects when such structures are used in a reinforcement application.     

炭质催化剂上乙苯氧化脱氢制苯乙烯

炭质催化剂在乙苯氧化脱氢制苯乙烯及应中的应用是近年来发现的炭质催化剂的又一应用途径,结合炭质催化剂结构特点,对炭质催化剂上乙苯氧化肥氢制苯乙烯的机理、影响因素进行了初步的阐述。     

Spherical silica micro/nanomaterials with hierarchical structures: synthesis and applications

This paper reviews the progress made recently in synthesis and applications of spherical silica micro/nanomaterials with multilevel (hierarchical) structures. The spherical silica micro/nanomaterials with hierarchical structures are classified into four main structural categories that include (1) hollow mesoporous spheres, (2) core-in-(hollow porous shell) spheres, (3) hollow spheres with multiple porous shells and (4) hierarchically porous spheres. Due to the complex structures and being focused on spherical silica micro/nanomaterials, some novel methods based on the combination of two routine methods or two surfactants, and some special synthetic strategies are proposed to produce the spherical silica micro/nanomaterials with hierarchical structures. Compared with the same-sized solid, porous or hollow silica spheres, these fantastic spherical silica micro/nanomaterials with hierarchical structures exhibit enhanced properties which may enable them to be used in broad and promising applications as ideal scaffolds (carriers) for biological, medical, and catalytic applications.     

Construction and evaluation of a three-dimensional structure of cytochrome P450choP enzyme (CYP105C1)

The purpose of this work was to develop and carefully evaluateimproved strategies for constructing reliable 3-D models ofP450 isozymes. To this end, a unique combination of steps forbuilding and evaluating a model structure was used to builda homology model of the P450choP isozyme, based on knowledgeof the X-ray structures of P450cam, P450terp, P450BM-3 and P450eryF.Specifically, the reliability of this model was examined bysystematic comparisons of its conformational, energetic, environmentaland packing properties and those of the four reference proteinswith corresponding properties from the database of proteinswith known structures. The results showed that the examinedproperties of this model structure are well within the criteriaestablished for reliable structures and are of nearly as goodquality as those of the reference proteins. In addition, theresult from a 120 ps unconstrained MD simulation of the modelwith structural waters provided evidence that the model is stableat room temperature. This 3-D model can now be reliably usedfor explicit characterization of substrate and inhibitor complexes.Most importantly, although it is envisioned that building modelsfor mammalian P450s will be even more challenging, the stepsdescribed here should be very useful in future constructionof 3-D models of mammalian P450 isozymes.     

Hierarchical self‐assembly of Y‐shaped amphiphilic triblock polyurethane/poly(acrylic acid) complexes: Giant vesicles,vesicles, 3D network,and bulk structures

A simple and effective approach to induce hierarchical self‐assembly of Y‐shaped amphiphilic triblock polyurethane/poly(acrylic acid) complexes system in aqueous media is reported here. Hydrogen bonding interactions and electrostatic repulsive forces, which can be controlled by regulating the pH condition of complexes solution, were the main driving forces to induce morphological transitions. With the gradual decrease of pH value, a variety of micro‐/nanostructures including giant vesicles, small vesicles, multi‐layer three‐dimensional (3D) porous network structures and “bulk” structures were successively obtained. Among these structures, the micron‐scale multi‐layer 3D porous network structure formed from block copolymer/homopolymer complexes was rarely reported. Therefore, this research demonstrates that the hierarchical self‐assembly of polymers complexes in aqueous media is a viable approach to construct different interesting micro‐/nanostructure assemblies, and supplies a new clue for the fabrication of multi‐layer 3D porous network structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46503.     

Measuring the effective density, porosity, and refractive index of carbonaceous particles by tandem aerosol techniques

The physical properties of carbonaceous aerosol particles are often of interest but are difficult to determine from a single measurement. In this study, we used tandem aerosol measurement techniques to measure the effective physical properties, namely the effective density, porosity, and effective complex refractive index of spheroid aggregated and porous carbonaceous aerosol particles. An in-flight measurement system, composed of a differential mobility analyzer (DMA) followed by either an aerosol particle mass analyzer (APM) or a laser particle counter-pulse height analyzer (LPC–PHA), was constructed and used to examine shape-controlled and porosity-controlled carbonaceous particles produced by a spray-drying process. The effective density and porosity were inferred from tandem measurements in which particles were first mobility-classified by the DMA and subsequently mass classified in the APM. The effective refractive index of the particles was inferred from tandem DMA–LPC–PHA measurements in conjunction with Mie Theory. The measured effective density and porosity of the carbonaceous particles ranged from 695.0 to 1399.9 kg/cm³ and 15.2% to 64.3%, respectively. Furthermore, the real and imaginary parts of the effective complex refractive index were between 1.430 and 1.736 and between 0.035 and 0.125, respectively. Both the real and imaginary parts decreased with increasing particle porosity.     

Three-dimensional alumina nanotemplate

Cylindrically and pentagonally shaped three-dimensional (3-D) alumina nanotemplates were fabricated by electrochemical anodization of high purity aluminum. Crack-free 3-D nanotemplates were achieved by anodizing various aluminum pre-formed structures through their concave surfaces. A critical parameter for obtaining crack-free 3-D nanotemplates was manipulating the stress at the aluminum/aluminum-oxide interface, because tensile stress at this interface can cause radial cracks. Two different cathode configurations were used to produce 3-D nanotemplates: inner and outer cathode configuration. The outer cathode configuration allowed fabrication of 3-D alumina templates with smaller diameters (<500 μm) and the inner cathode configuration allowed fabrication of 3-D alumina templates with larger diameters (>500 μm). A larger pore density was observed at the inner surface of 3-D template than at the outer surface due to the curvature of the template. The pore diameter of alumina nanotemplate was strongly depended on the applied current density. No defect was observed independent of anodizing solutions and applied current density. This cost-effective and manufacturable method can be utilized for preparation of hierarchical nanostructures.     

含碳添加剂对大同烟煤压块活性炭性能的影响

采用焦煤、1 /3焦煤、硬质煤沥青和木炭 4种含碳添加剂 ,考察了它们对大同煤质压块成型活性炭性能的影响程度 .研究表明 :添加硬质沥青能提高活性炭的中孔率、强度、水容量、焦糖脱色率、四氯化碳吸附率和亚甲兰值 ,而对碘值几乎无影响 ;添加焦煤能使活性炭的微孔容积、中孔容积和 BET表面积同时提高 ,且显著增加试样的焦糖脱色率 ;添加 1 /3焦煤可提高活性炭的微孔容积、总孔容积和 BET表面积 ,但中孔容积会降低 ;添加木炭除使试样强度明显降低外 ,其他性能均大幅提高 .     

Investigation of carbonaceous compounds deposited on NiMo catalyst used for ultra-deep hydrodesulfurization of gas oil by means of temperature-programmed oxidation and Raman spectroscopy

NiMo/Al₂O₃ catalyst used for ultra-deep HDS of several gas oils at various conditions was characterized by both temperature-programmed oxidation combined with mass spectroscopy (TPO–MS) and/or gas chromatography (TPO–GC), and Raman spectroscopy to make clear how the catalyst was deactivated. TPO–MS showed the presence of carbonaceous compounds containing H and N atoms on the used catalysts. TPO–GC showed that the combustive property of the carbonaceous compounds sensitively changes depending on the HDS reaction conditions and the position of the catalyst charged in the HDS reactor. A curve fitting analysis of TPO–GC profiles indicated that the carbonaceous compounds combusted below 680 K during TPO were observed on all the spent catalysts examined here whereas more refractory carbonaceous compound (combusted at around 690 K during TPO) was observed on the catalyst that had experienced severe HDS reaction conditions. More refractory carbonaceous compound was preferentially observed on the catalyst charged near the outlet of the HDS reactor. Raman spectra of the carbonaceous compounds indicated that the carbonaceous compounds combusted below 680 K during TPO has an amorphous-like structure whereas the refractory carbonaceous compound has a graphite-like one. Raman spectra also indicated that the graphite-like carbonaceous compound possesses a greater lateral size than the amorphous-like one, implying that the refractory carbonaceous compound can cover the catalyst surface more effectively. The carbonaceous compound having a graphite-like structure is one of main reasons for the catalyst deactivation. It is suggested that the precursor for this type of carbonaceous compound is not formed directly from the feed, but indirectly formed during the HDS of gas oil, because of its preferential deposition on the catalyst charged near the outlet of the HDS reactor.