Water-dispersible, sulfonated hyperbranched poly(ether-ketone) grafted multiwalled carbon nanotubes as oxygen reduction catalysts

Growth, Properties, and Applications of Branched Carbon Nanostructures

Nanomaterials featuring branched carbon nanotubes (b-CNTs), nanofibers (b-CNFs), or other types of carbon nanostructures (CNSs) are of great interest due to their outstanding mechanical and electronic properties. They are promising components of nanodevices for a wide variety of advanced applications spanning from batteries and fuel cells to conductive-tissue regeneration in medicine. In this concise review, we describe the methods to produce branched CNSs, with particular emphasis on the most widely used b-CNTs, the experimental and theoretical studies on their properties, and the wide range of demonstrated and proposed applications, highlighting the branching structural features that ultimately allow for enhanced performance relative to traditional, unbranched CNSs.

Silica-Coated Fe3O4 Nanoparticles as a Bifunctional Agent for Magnetic Resonance Imaging and ZnII Fluorescent Sensing

Bifunctional magnetic/fluorescent core-shell silica nanospheres (MNPs) encapsulated with the magnetic Fe₃O₄ core and a derivate of 8-amimoquinoline (N-(quinolin-8-yl)-2-(3-(triethoxysilyl) propylamino) acetamide) (QTEPA) into the shell were synthesized. These functional MNPs were prepared with a modified stöber method and the formed Fe₃O₄@SiO₂-QTEPA core-shell nanocomposites are biocompatible, water-dispersible, and stable. These prepared nanoparticles were characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), thermoelectric plasma Quad II inductively coupled plasma mass spectrometry (ICP-MS), superconducting quantum interference device (SQUID), TG/DTA thermal analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR). Further application of the nanoparticles in detecting Zn²⁺ was confirmed by the fluorescence experiment: the nanosensor shows high selectivity and sensitivity to Zn²⁺ with a 22-fold fluorescence emission enhancement in the presence of 10 μM Zn²⁺. Moreover, the transverse relaxivity measurements show that the core-shell MNPs have T2 relaxivity (r2) of 155.05 mM^-1 S^-1 based on Fe concentration on the 3.0 T scanner, suggesting that the compound can be used as a negative contrast agent for MRI. Further in vivo experiments showed that these MNPs could be used as MRI contrast agent. Therefore, the new nanosensor provides the dual modality of magnetic resonance imaging and optical imaging.

Nitrogen-rich graphitic-carbon@graphene as a metal-free electrocatalyst for oxygen reduction reaction

The metal-free nitrogen-doped graphitic-carbon@graphene (Ng-C@G) is prepared from a composite of polyaniline and graphene by a facile polymerization following by pyrolysis for electrochemical oxygen reduction reaction (ORR). Pyrolysis creates a sponge-like with ant-cave-architecture in the polyaniline derived nitrogenous graphitic-carbon on graphene. The nitrogenous carbon is highly graphitized and most of the nitrogen atoms are in graphitic and pyridinic forms with less oxygenated is found when pyrolyzed at 800 °C. The electrocatalytic activity of Ng-C@G-800 is even better than the benchmarked Pt/C catalyst resulting in the higher half-wave potential (8 mV) and limiting current density (0.74 mA cm^-2) for ORR in alkaline medium. Higher catalytic performance is originated from the special porous structure at microscale level and the abundant graphitic- and pyridinic-N active sites at the nanoscale level on carbon-graphene matrix which are beneficial to the high O₂-mass transportation to those accessible sites. Also, it possesses a higher cycle stability resulting in the negligible potential shift and slight oxidation of pyridinic-N with better tolerance to the methanol.

Improvement of Catalytic Activity of Platinum Nanoparticles Decorated Carbon Graphene Composite on Oxygen Electroreduction for Fuel Cells

High-performance platinum (Pt)-based catalyst development is crucially important for reducing high overpotential of sluggish oxygen reduction reaction (ORR) at Pt-based electrocatalysts, although the high cost and scarcity in nature of Pt are profoundly hampering the practical use of it in fuel cells. Thus, the enhancing activity of Pt-based electrocatalysts with minimal Pt-loading through alloy, core−shell or composite making has been implemented. This article deals with enhancing electrocatalytic activity on ORR of commercially available platinum/carbon (Pt/C) with graphene sheets through a simple composite making. The Pt/C with graphene sheets composite materials (denoted as Pt/Cx:G10−x) have been characterized by several instrumental measurements. It shows that the Pt nanoparticles (NPs) from the Pt/C have been transferred towards the π-conjugated systems of the graphene sheets with better monolayer dispersion. The optimized Pt/C8:G2 composite has higher specific surface area and better degree of graphitization with better dispersion of NPs. As a result, it shows not only stable electrochemical surface area but also enhanced ORR catalytic activity in respect to the onset potential, mass activity and electron transfer kinetics. As shown by the ORR, the Pt/C8:G2 composite is also better resistive to the alcohol crossover effect and more durable than the Pt/C.

Practical use of polymer brushes in sustainable energy applications: interfacial nanoarchitectonics for high-efficiency devices

The discovery and development of novel approaches, materials and manufacturing processes in the field of energy are compelling increasing recognition as a major challenge for contemporary societies. The performance and lifetime of energy devices are critically dependent on nanoscale interfacial phenomena. From the viewpoint of materials design, the improvement of current technologies inevitably relies on gaining control over the complex interface between dissimilar materials. In this sense, interfacial nanoarchitectonics with polymer brushes has seen growing interest due to its potential to overcome many of the limitations of energy storage and conversion devices. Polymer brushes offer a broad variety of resources to manipulate interfacial properties and gain molecular control over the synergistic combination of materials. Many recent examples show that the rational integration of polymer brushes in hybrid nanoarchitectures greatly improves the performance of energy devices in terms of power density, lifetime and stability. Seen in this light, polymer brushes provide a new perspective from which to consider the development of hybrid materials and devices with improved functionalities. The aim of this review is therefore to focus on what polymer brush-based solutions can offer and to show how the practical use of surface-grafted polymer layers can improve the performance and efficiency of fuel cells, lithium-ion batteries, organic radical batteries, supercapacitors, photoelectrochemical cells and photovoltaic devices.

Surface coating of UF membranes to improve antifouling properties: A comparison study between cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs)

The inherent properties of hydrophilicity and environmental preferability of cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) make them great candidates for application in water-treatment membranes. In this study, the antifouling properties of CNCs and CNFs, modified ultrafiltration (UF) membranes, were directly compared. A facile modification method was conducted by coating CNCs and CNFs on the surface of polyethersulfone (PES) membranes to prepare CNC-coating membranes and the CNF-coating membranes. Membrane surface morphology was characterized by atomic force microscopy (AFM), and the results showed that the CNF-coating membranes exhibited greater surface roughness than the CNC-coating membranes. Pure water flux measurements demonstrated that the flux of the CNC-coating membranes was slightly lower than that of the CNF-coating membranes. Antifouling properties were evaluated and compared for the two types of membranes by filtration of NOM foulant models, humic acid (HA) and bovine serum albumin (BSA). The results showed that the antifouling properties of the modified membranes were enhanced through the coating of either CNCs or CNFs to a control PES membrane. The CNC-coating membranes outperformed the CNF-coating membranes in alleviating both reversible fouling and irreversible fouling caused by HA and BSA. In addition, the antifouling performance of the coating membranes was enhanced with increased coating content.

Enhancement mechanism of sulfur dopants on the catalytic activity of N and P co-doped three-dimensional hierarchically porous carbon as a metal-free oxygen reduction electrocatalyst

A sulfur, nitrogen and phosphorus ternary-doped cattle-bone-derived hierarchically porous carbon metal-free electrocatalyst was synthesized, exhibiting superior oxygen reduction performance compared to Pt/C.

Defects on carbons for electrocatalytic oxygen reduction

The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production costs is still the bottleneck to realize the large-scale commercialization of fuel cells. In recent years, remarkable progress has been achieved in fabricating effective non-precious metal based ORR catalysts. In particular, modified carbon materials have aroused extensive research interest because of their excellent performance and low cost. In this review, we present an overview on recent advancements in developing defective carbon based materials for catalyzing the ORR. In particular, three general kinds of defective carbon electrocatalysts will be summarized. They are non-metal induced defective carbons (modified by heteroatoms), intrinsic defective carbons (defects created by a physical or chemical method), and atomic metal species induced/coordinated defective carbons (metal-macrocycle complexes with different coordination environments). The common configurations of various defective carbons will be discussed, with typical examples on recently developed both metal-free and precious/non-precious metal species coordinated carbons. Finally, the future research directions of the defective carbon materials are proposed. The newly established defect promoted catalysis mechanism will be beneficial for the design and fabrication of highly effective electrocatalysts for practical energy storage and conversion applications.

Hyperbranched Macromolecules: From Synthesis to Applications

Hyperbranched macromolecules (HMs, also called hyperbranched polymers) are highly branched three-dimensional (3D) structures in which all bonds converge to a focal point or core, and which have a multiplicity of reactive chain-ends. This review summarizes major types of synthetic strategies exploited to produce HMs, including the step-growth polycondensation, the self-condensing vinyl polymerization and ring opening polymerization. Compared to linear analogues, the globular and dendritic architectures of HMs endow new characteristics, such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility. After discussing the general concepts, synthesis, and properties, various applications of HMs are also covered. HMs continue being materials for topical interest, and thus this review offers both concise summary for those new to the topic and for those with more experience in the field of HMs.

Metal-Free Carbon Materials for CO2 Electrochemical Reduction

The rapid increase of the CO₂ concentration in the Earth's atmosphere has resulted in numerous environmental issues, such as global warming, ocean acidification, melting of the polar ice, rising sea level, and extinction of species. To search for suitable and capable catalytic systems for CO₂ conversion, electrochemical reduction of CO₂ (CO₂ RR) holds great promise. Emerging heterogeneous carbon materials have been considered as promising metal-free electrocatalysts for the CO₂ RR, owing to their abundant natural resources, tailorable porous structures, resistance to acids and bases, high-temperature stability, and environmental friendliness. They exhibit remarkable CO₂ RR properties, including catalytic activity, long durability, and high selectivity. Here, various carbon materials (e.g., carbon fibers, carbon nanotubes, graphene, diamond, nanoporous carbon, and graphene dots) with heteroatom doping (e.g., N, S, and B) that can be used as metal-free catalysts for the CO₂ RR are highlighted. Recent advances regarding the identification of active sites for the CO₂ RR and the pathway of reduction of CO₂ to the final product are comprehensively reviewed. Additionally, the emerging challenges and some perspectives on the development of heteroatom-doped carbon materials as metal-free electrocatalysts for the CO₂ RR are included.

Novel fluorinated hyperbranched polyimides with excellent thermal stability, UV-shielding property, organosolubility, and low dielectric constants

A novel fluorinated aromatic triamine, named 1,3,5-tris (4-(2-trifluoromethyl-4-aminophenoxy)phenyl) benzene (TTFAPOPB), with several –CF3 groups, prolonged chain segments, and ether bonds was first successfully synthesized via a three-step reaction. Then a series of fluorinated hyperbranched polyimides (FHBPIs) with terminal amino or anhydride groups were prepared by condensation polymerization, which were derived from three commercial dianhydrides and the obtained triamine. The prepared FHBPIs showed excellent optical properties with the transmittance reaching 94.5% at 800 nm, favorable ultraviolet (UV)-shielding property with only 27% photodegradation of methylene blue solution after intense UV irradiation for 50 min, good thermal stability with glass transition temperature between 225°C and 264°C, and 10% weight loss temperature of 520–555°C and 509–541°C, respectively, in nitrogen and air atmosphere. They also exhibited relatively good mechanical properties with tensile strength, tensile modulus, and elongation at break values of 64.2–84.2 MPa, 1.2–1.5 GPa, and 6–10%, respectively. Moreover, the introduction of –CF3 and hyperbranched architecture reduced the dielectric constants of the FHBPIs to 2.69–2.92 and increased the surface contact angles to more than 98°. Thus, the FHBPIs are promising dielectric or UV-shielding materials.

Defect/Edge-Selective Functionalization of Carbon Materials by "Direct" Friedel-Crafts Acylation Reaction

Popularly utilized oxidation media, via nitric acid/sulfuric acid mixtures, are too corrosive and oxidizing to preserve structural integrity of highly ordered graphitic materials (carbon nanotubes (CNTs) and graphene). Here, for the most commonly used oxidation method, the important advantages of defect/edge-selective functionalization of carbon materials (CNTs/graphene/graphite) in a polyphosphoric acid (PPA)/phosphorous pentoxide (P₂ O₅ ) medium are elucidated. The optimized PPA/P₂ O₅ medium is a mild acid that is not only less corrosive than popularly utilized oxidation media, but also has a strong capability to drive Friedel-Crafts acylation by covalently modifying carbon materials. With a broader spectrum of functional groups accessible, the PPA/P₂ O₅ -driven Friedel-Crafts acylation offers more options for tailoring the properties and processing of carbon materials.

Noncovalent immobilization of pyrene-terminated hyperbranched triazole-based polymeric ionic liquid onto graphene for highly active and recyclable catalysis of CO2/epoxide cycloaddition

Combination of bifunctional HBP and rGO for highly active, selective and recyclable catalysis for CO₂/epoxide cycloaddition.

Hydrodynamic behaviors of amphiphilic dendritic polymers with different degrees of amidation

This work highlights the structure evolution and the response to solvent quality of ADPs.

Sugar-functionalized triptycenes used for dispersion of single-walled carbon nanotubes in aqueous solution by supramolecular interaction

Two water-soluble sugar-functionalized triptycene derivatives were synthesized and used for dispersion of SWCNTs in aqueous solution via supramolecular interaction.

Covalent entrapment of cobalt-iron sulfides in N-doped mesoporous carbon: extraordinary bifunctional electrocatalysts for oxygen reduction and evolution reactions

To alleviate the kinetic barriers associated with ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) in electrochemical systems, efficient nonprecious electrocatalysts are urgently required. Here we report a facile soft-template mediated approach for fabrication of nanostructured cobalt-iron double sulfides that are covalently entrapped in nitrogen-doped mesoporous graphitic carbon (Co0.5Fe0.5S@N-MC). Notably, with a positive half-wave potential (0.808 V) and a high diffusion-limiting current density, the composite material delivers unprecedentedly striking ORR electrocatalytic activity among recently reported nonprecious late transition metal chalcogenide materials in alkaline medium. Various characterization techniques, including X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, are conducted to elucidate the correlation between structural features and catalytic activities of the composite. Moderate substitution and well-dispersion of iron in bimetallic sulfide composites are believed to have positive effect on the adsorption and activation of oxygen-containing species, thus leading to conspicuous ORR and OER catalytic enhancement compared to their monometallic counterparts. Besides, the covalent bridge between active sulfide particles and mesoporous carbon shells provides facile pathways for electron and mass transport. Beneficially, the intimate coupling interaction renders prolonged electrocatalytic performances to the composite. Our results may possibly lend a new impetus to the rational design of bi- or multimetallic sulfides encapsulated in porous carbon with improved performance for electrocatalysis and energy storage applications.

Impact of dendritic polymers on nanomaterials

Primary/secondary covalent/non-covalent interactions between dendritic polymers and nanomaterials can change the physicochemical properties, such as shape, of the obtained hybrid nanomaterials.

Hydrophilic non-precious metal nitrogen-doped carbon electrocatalysts for enhanced efficiency in oxygen reduction reaction

The role of surface hydrophilicity of non-precious metal N-doped carbon electrocatalysts is found to be positive in enhancing catalysis efficiency for oxygen reduction reaction.

Solution-processed PEDOT:PSS/graphene composites as the electrocatalyst for oxygen reduction reaction

Composites of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and reduced graphene oxide (rGO) have been prepared by solution mixing and applied as electrocatalysts for oxygen reduction reaction (ORR) after treatment with concentrated H2SO4. The blending of rGO induces the conformational change of PEDOT chains from benzoid to quionoid structure and charge transfer from rGO to PEDOT. H2SO4 post-treatment can remove part of insulating PSS from the surface of the PEDOT:PSS/rGO composite film, resulting in a significant conductivity enhancement of the composite. This synergistic effect makes the H2SO4-treated PEDOT:PSS/rGO composite a promising catalyst for ORR. It exhibits enhanced electrocatalytic activity, better tolerance to a methanol crossover effect and CO poisoning, and longer durability than those of the platinum/carbon catalyst.

Large-scale production of edge-selectively functionalized graphene nanoplatelets via ball milling and their use as metal-free electrocatalysts for oxygen reduction reaction

Edge-selectively functionalized graphene nanoplatelets (EFGnPs) with different functional groups were efficiently prepared simply by dry ball milling graphite in the presence of hydrogen, carbon dioxide, sulfur trioxide, or carbon dioxide/sulfur trioxide mixture. Upon exposure to air moisture, the resultant hydrogen- (HGnP), carboxylic acid- (CGnP), sulfonic acid- (SGnP), and carboxylic acid/sulfonic acid- (CSGnP) functionalized GnPs readily dispersed into various polar solvents, including neutral water. The resultant EFGnPs were then used as electrocatalysts for oxygen reduction reaction (ORR) in an alkaline electrolyte. It was found that the edge polar nature of the newly prepared EFGnPs without heteroatom doping into their basal plane played an important role in regulating the ORR efficiency with the electrocatalytic activity in the order of SGnP > CSGnP > CGnP > HGnP > pristine graphite. More importantly, the sulfur-containing SGnP and CSGnP were found to have a superior ORR performance to commercially available platinum-based electrocatalyst.