Linear-Polyethyleneimine-Templated Synthesis of N-Doped Carbon Nanonet Flakes for High-performance Supercapacitor Electrodes

Novel N-doped carbon nanonet flakes (NCNFs), consisting of three-dimensional interconnected carbon nanotube and penetrable mesopore channels were synthesized in the assistance of a hybrid catalytic template of silica-coated-linear polyethyleneimine (PEI). Resorcinol-formaldehyde resin and melamine were used as precursors for carbon and nitrogen, respectively, which were spontaneously formed on the silica-coated-PEI template and then annealed at 700 °C in a N2 atmosphere to be transformed into the hierarchical 3D N-doped carbon nanonetworks. The obtained NCNFs possess high surface area (946 m2 g-1), uniform pore size (2-5 nm), and excellent electron and ion conductivity, which were quite beneficial for electrochemical double-layered supercapacitors (EDLSs). The supercapacitor synthesized from NCNFs electrodes exhibited both extremely high capacitance (up to 613 F g-1 at 1 A g-1) and excellent long-term capacitance retention performance (96% capacitive retention after 20,000 cycles), which established the current processing among the most competitive strategies for the synthesis of high performance supercapacitors.

Preparation of thick silica coatings on carbon fibers with fine-structured silica nanotubes induced by a self-assembly process

A facile method to coat carbon fibers with a silica shell is presented in this work. By immobilizing linear polyamines on the carbon fiber surface, the high catalytic activity of polyamines in the sol-gel-processing of silica precursors is used to deposit a silica coating directly on the fiber's surface. The surface localization of the catalyst is achieved either by attaching short-chain polyamines (e.g., tetraethylenepentamine) via covalent bonds to the carbon fiber surface or by depositing long-chain polyamines (e.g., linear poly(ethylenimine)) on the carbon fiber by weak non-covalent bonding. The long-chain polyamine self-assembles onto the carbon fiber substrate in the form of nanoscopic crystallites, which serve as a template for the subsequent silica deposition. The silicification at close to neutral pH is spatially restricted to the localized polyamine and consequently to the fiber surface. In case of the linear poly(ethylenimine), silica shells of several micrometers in thickness can be obtained and their morphology is easily controlled by a considerable number of synthesis parameters. A unique feature is the hierarchical biomimetic structure of the silica coating which surrounds the embedded carbon fiber by fibrillar and interconnected silica fine-structures. The high surface area of the nanostructured composite fiber may be exploited for catalytic applications and adsorption purposes.

Polycondensation and carbonization of phenolic resin on structured nano/chiral silicas: reactions, morphologies and properties

Diversely shaped and chiral nano-carbonaceous materials were obtained using bioinspired polyethyleneimine (PEI)–silica hybrids as catalytic templates and chiral sources.

Constructing Biopolymer-Inorganic Nanocomposite through a Biomimetic Mineralization Process for Enzyme Immobilization

Inspired by biosilicification, biomimetic polymer-silica nanocomposite has aroused a lot of interest from the viewpoints of both scientific research and technological applications. In this study, a novel dual functional polymer, NH₂-Alginate, is synthesized through an oxidation-amination-reduction process. The "catalysis function" ensures the as-prepared NH₂-Alginate inducing biomimetic mineralization of silica from low concentration precursor (Na₂SiO₃), and the "template function" cause microscopic phase separation in aqueous solution. The diameter of resultant NH₂-Alginate micelles in aqueous solution distributed from 100 nm to 1.5 μm, and is influenced by the synthetic process of NH₂-Alginate. The size and morphology of obtained NH₂-Alginate/silica nanocomposite are correlated with the micelles. NH₂-Alginate/silica nanocomposite was subsequently utilized to immobilize β-Glucuronidase (GUS). The harsh condition tolerance and long-term storage stability of the immobilized GUS are notably improved due to the buffering effect of NH₂-Alginate and cage effect of silica matrix.

Poly(L-glutamic acid)-decorated hybrid colloidal particles from complex particle-templated silica mineralization

We report the synthesis of polyelectrolyte complex (PEC) particles by mixing the negatively and positively charged polyelectrolytes, poly(L-glutamic acid) (PGA) and poly(2-(N,N-diethylamino) ethylmethacrylate) (PDEAEMA), and the use of negatively charged PEC particles as colloidal templates for silica mineralization under ambient conditions. The structure and property of PEC particles, as well as polypeptide chain conformation, were found to depend on the mixing weight percentage, polymer molecular weight, and solution condition. The negatively charged PEC micelles can be deposited with silica without loss colloid stability, leading to PGA-decorated hybrid particles. These hybrid particles were negatively charged at neutral and basic condition and become positively charged, accompanying the conformational changes of the grafted PGA, upon decreasing pH below isoelectric points due to the protonation/deprotonation of PGA and PDEAEMA. Functional nanoparticles such as gold NPs could be incorporated using polypeptides as the mediating agents. These hybrid particles loaded with drug exhibited noticeable pH-responsive behavior with accelerated release at acidic condition, demonstrating the potential for use as pH-responsive delivery vehicles. This type of polypeptide-decorated hybrid particles represents an interesting class of organic-inorganic hybrids in which the functional properties of polypeptides such as biocompatibility, stimuli responsiveness, and directed growth of metal nanoparticles can be incorporated.

Bioinspired synthesis of a soft-nanofilament-based coating consisting of polysilsesquioxanes/polyamine and its divergent surface control

The synthesis of polysilsesquioxanes coating with controllable one-dimensional nanostructure on substrates remains a major long-term challenge by conventional solution-phase method. The hydrolytic polycondensation of organosilanes in solution normally produces a mixture of incomplete cages, ladderlike, and network structures, resulting in the poor control of the formation of specific nanostructure. This paper describes a simple aqueous process to synthesize nanofilament-based coatings of polysilsesquioxanes possessing various organo-functional groups (for example, thiol, methyl, phenyl, vinyl, and epoxy). We utilized a self-assembled nanostructured polyamine layer as a biomimetically catalytic scaffold/template to direct the formation of one-dimensional nanofilament of polysilsesquioxanes by temporally and spatially controlled hydrolytic polycondensation of organosilane. The surface nanostructure and morphology of polysilsesquioxane coating could be modulated by changing hydrolysis and condensation reaction conditions, and the orientation of nanofilaments of polysilsesquioxanes on substrates could be controlled by simply adjusting the self-assembly conditions of polyamine layer. The nanostructure and polyamine@polysilsesquioxane hybrid composition of nanofilament-based coatings were examined by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The template role of nanostructured polyamine layer for the formation of polysilsesquioxane nanofilament was confirmed by combining thin film X-ray diffraction (XRD) and XPS measurements. Moreover, these nanotextured coatings with various organo-functional groups could be changed into superhydrophobic surfaces after surface modification with fluorocarbon molecule.

Controlled synthesis and tunable properties of ultrathin silica nanotubes through spontaneous polycondensation on polyamine fibrils

This paper describes a facile approach to a biomimetic rapid fabrication of ultrathin silica nanotubes with a highly uniform diameter of 10 nm and inner hollow of around 3 nm. The synthesis is carried out through a spontaneous polycondensation of alkoxysilane on polyamine crystalline fibrils that were conveniently produced from the neutralization of a solution of protonated linear polyethyleneimine (LPEI-H(+)) by alkali compounds. A simple mixing the fibrils with alkoxysilane in aqueous solution allowed for the rapid formation of silica to produce LPEI@silica hybrid nanotubes. These 10-nm nanotubes were hierarchically organized in a mat-like morphology with a typical size of 1-2 micrometers. The subsequent removal of organic LPEI via calcination resulted in silica nanotubes that keep this morphology. The morphology, the structure, the pore properties and the formation mechanism of the silica nanotubes were carefully investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller measurements (BET), and X-ray diffraction (XRD). Detailed studies demonstrated that the formation of the nanotubes depends on the molar ratio of [OH]/[CH2CH2NH] during the neutralization as well as on the basicity of the alkali compound and on the concentration of the silica source. The synthesis of silica nanotubes established here could be easily applied to a fabrication on the kilogram scale. Silica nanotubes that were obtained from the calcination of hybrid nanotubes of LPEI@silica in an N2 atmosphere showed a distinct photoluminescence centered at 540 nm with a maximum excitation wavelength of 320 nm. Furthermore, LPEI@silica hybrid nanotubes were applied to create silica-carbon composite nanotubes by alternative adsorption of ionic polymers and subsequent carbonization.