Synthesis of Nitrogen-Doped Mesoporous Carbon Spheres with Extra-Large Pores through Assembly of Diblock Copolymer Micelles

Tunable Hierarchically Structured Meso-Macroporous Carbon Spheres from a Solvent-Mediated Polymerization-Induced Self-Assembly

Herein, we report a versatile solvent-mediated polymerization-induced self-assembly (PISA) strategy to directly synthesize highly N-doped hierarchically porous structured carbon spheres with a tunable meso-macroporous configuration. The introduction of intermolecular hydrogen bonds is verified to enhance the interfacial interactions between block copolymers, oil droplets, and polyphenols. Moreover, the dominant hydrogen-bond-driven interactions can be systematically manipulated by selecting different cosolvent systems to generate diverse porous structures from the transformation of micellar and precursor co-assembly. Impressively, hierarchically structured meso-macroporous N-doped carbon spheres present simultaneously tunable sphere sizes and mesopores and macropores, ranging from 1.2 μm, 9/50 and 227 nm to 1.0 μm, 40, and 183 nm and 480, 24, and 95 nm. As a demonstration, dendritic-like N-doped hierarchically meso-macroporous carbon spheres manifest excellent enzyme-like activity, which is attributed to the continuous mass transport from the multiordered porosity. The current study provides a new platform for the synthesis of novel well-defined porous materials.

Progress in the application of sustained-release drug microspheres in tissue engineering

Sustained-release drug-loaded microspheres provide a long-acting sustained release, with targeted and other effects. There are many types of sustained-release drug microspheres and various preparation methods, and they are easy to operate. For these reasons, they have attracted widespread interest and are widely used in tissue engineering and other fields. In this paper, we provide a systematic review of the application of sustained-release drug microspheres in tissue engineering. First, we introduce this new type of drug delivery system (sustained-release drug carriers), describe the types of sustained-release drug microspheres, and summarize the characteristics of different microspheres. Second, we summarize the preparation methods of sustained-release drug microspheres and summarize the materials required for preparing microspheres. Third, various applications of sustained-release drug microspheres in tissue engineering are summarized. Finally, we summarize the shortcomings and discuss future prospects in the development of sustained-release drug microspheres. The purpose of this paper was to provide a further systematic understanding of the application of sustained-release drug microspheres in tissue engineering for the personnel engaged in related fields and to provide inspiration and new ideas for studies in related fields.

Superhydrophobic Ru Catalyst for Highly Efficient Hydrogenation of Phenol under Mild Aqueous Conditions

Selective hydrogenations of lignin-derived phenolic compounds represent essential processes in the chemical industry, especially for production of a multitude of fine chemicals. However, selective hydrogenation of phenolic compounds in water phase suffers from low conversion. Here we report a catalyst of well-dispersed Ru clusters fixed in N-doped mesoporous hollow carbon spheres (Ru@N-CS) for enhanced cyclohexanol productivity in phenol hydrogenation at mild aqueous condition. This superhydrophobicity carbon spheres appear to selectively allow diffusion of phenol and hydrogen molecules to the electron-rich coordination unsaturated Ru active sites, while confining the reactants there to enhance its reaction probability. The Ru@N-CS catalyst can selectively hydrogenate phenol at 80 °C and 0.5 MPa of H2 in 30 min in aqueous medium with phenol conversions of 100% and ~100% cyclohexanol selectivity, corresponding to cyclohexanol productivity up to 471 per g of Ru per minute. The TOF value is up to 9980 h−1, which 14 times more than Ru nanoparticles supported on N-doped carbon hollow spheres (Ru/N-CS). This work provides an important catalytic system for upgrading of bio-oil into value-added chemicals under mild aqueous-phase.

Anisotropic Self-Assembly of Asymmetric Mesoporous Hemispheres with Tunable Pore Structures at Liquid-Liquid Interfaces

Asymmetric materials have attracted tremendous interest because of their intriguing physicochemical properties and promising applications, but endowing them with precisely controlled morphologies and porous structures remains a formidable challenge. Herein, a facile micelle anisotropic self-assembly approach on a droplet surface is demonstrated to fabricate asymmetric carbon hemispheres with a jellyfish-like shape and radial multilocular mesostructure. This facile synthesis follows an interface-energy-mediated nucleation and growth mechanism, which allows easy control of the micellar self-assembly behaviors from isotropic to anisotropic modes. Furthermore, the micelle structure can also be systematically manipulated by selecting different amphiphilic triblock copolymers as a template, resulting in diverse novel asymmetric nanostructures, including eggshell, lotus, jellyfish, and mushroom-shaped architectures. The unique jellyfish-like hemispheres possess large open mesopores (∼14 nm), a high surface area (∼684 m² g^-1), abundant nitrogen dopants (∼6.3 wt %), a core-shell mesostructure and, as a result, manifest excellent sodium-storage performance in both half and full-cell configurations. Overall, our approach provides new insights and inspirations for exploring sophisticated asymmetric nanostructures for many potential applications.

Non-Precious Metal-Doped Carbon Materials Derived From Porphyrin-Based Porous Organic Polymers for Oxygen Reduction Electrocatalysis

The cathodic oxygen reduction reaction (ORR) is important in the development of renewable energy devices, to produce novel and non-precious metal catalysts with high electrocatalytic activity to reduce the consumption of non-renewable platinum (Pt) catalyst. In this work, we developed N-doped and Fe/N dual-doped porous carbons as catalysts for ORR simply by high-temperature pyrolysis of porphyrin-based conjugated microporous polymers (CMPs). By combination of heteroatom doping, highly porous structure and tubular morphology, the as-prepared carbon samples exhibited high electrocatalytic activity with 4-electron transfer mechanism, nearly close to the commercial Pt/C catalyst. In particular, among these samples, the Fe/N-CMP-1000 displayed a higher onset potential (0.95 eV), positive half-wave potential (0.85 eV) and limiting current density value (5.1 mA cm^-2 ) as well as good durability and better methanol tolerance contrasting with Pt/C catalyst, suggesting that the as-prepared metal-free catalysts from porphyrin-based CMPs show great potential for ORR.

The Effect of a Hydrogen Reduction Procedure on the Microbial Synthesis of a Nano-Pd Electrocatalyst for an Oxygen-Reduction Reaction

Noble-metal electrocatalysts supported by biological-organism-derived carbons have attracted attention from the public due to the growing demands for green synthesis and environmental protection. Carbonization at high temperatures and hydrogen reduction are critical steps in this technical route. Herein, Shewanella oneidensis MR-1 were used as precursors, and the effects of the hydrogen-reduction procedure on catalysts were explored. The results showed that the performances of FHTG (carbonization followed by hydrogen reduction) displayed the best performance. Its ECSA (electrochemical surface area), MA (mass activity), and SA (specific activity) reached 35.01 m2 g−1, 58.39 A·g−1, and 1.66 A cm−2, respectively, which were 1.17, 1.75, and 1.50 times that of PHTG (prepared through hydrogen reduction followed by carbonization) and 1.56, 2.26, and 1.44 times that of DHTG (double hydrogen reduction). The high performance could be attributed to its fine particle size and rich N content, and the specific regulation mechanism was also proposed in this paper. This study opens a practical guide for effectively avoiding particle agglomeration during the fabrication process for catalysts.

Large-Pore Ordered Mesoporous Turbostratic Carbon Films Prepared Using Rapid Thermal Annealing for High-Performance Micro-pseudocapacitors

Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V₂O₅ without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm² and 126 F/cm³ (at 0.8 mA/cm² using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V₂O₅ deposition yielded pseudocapacitors with 10-fold increase in energy density (20 μW h cm^-2 μm^-1) without adversely affecting the high power density (450 μW cm^-2 μm^-1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors.

Nanostructured Carbon Electrocatalysts for Energy Conversions

The growing energy demand worldwide has led to increased use of fossil fuels. This, in turn, is making fossil fuels dwindle faster and cause more negative environmental impacts. Thus, alternative, environmentally friendly energy sources such as fuel cells and electrolyzers are being developed. While significant progress has already been made in this area, such energy systems are still hard to scale up because of their noble metal catalysts. In this concept paper, first, various scalable nanocarbon-based electrocatalysts that are being synthesized for energy conversions in these energy systems are introduced. Next, notable heteroatom-doping and nanostructuring strategies that are applied to produce different nanostructured carbon materials with high electrocatalytic activities for energy conversions are discussed. The concepts used to develop such materials with different structures and large density of dopant-based catalytic functional groups in a sustainable way, and the challenges therein, are emphasized in the discussions. The discussions also include the importance of various analytical, theoretical, and computational methods to probe the relationships between the compositions, structures, dopants, and active catalytic sites in such materials. These studies, coupled with experimental studies, can further guide innovative synthetic routes to efficient nanostructured carbon electrocatalysts for practical, large-scale energy conversion applications.

A Solvent-Polarity-Induced Interface Self-Assembly Strategy towards Mesoporous Triazine-Based Carbon Materials

Triazine-based materials with porous structure have recently received numerous attentions as a fascinating new class because of their superior potential for various applications. However, it is still a formidable challenge to obtain triazine-based materials with precise adjustable meso-scaled pore sizes and controllable pore structures by reported synthesis approaches. Herein, we develop a solvent polarity induced interface self-assembly strategy to construct mesoporous triazine-based carbon materials. In this method, we employ a mixed solvent system within a suitable range of polarity (0.223≤Lippert-Mataga parameter (Δf) ≤0.295) to induce valid self-assembly of skeleton precursor and surfactant. The as-prepared mesoporous triazine-based carbon materials possess uniform tunable pore sizes (8.2-14.0 nm), high surface areas and ultrahigh nitrogen content (up to 18 %). Owing to these intriguing advantages, the fabricated mesoporous triazine-based carbon materials as functionalized porous solid absorbents exhibit predominant CO₂ adsorption performance and exceptional selectivity for the capture of CO₂ over N₂ .

Hollow mesoporous polydopamine nanospheres: synthesis, biocompatibility and drug delivery

Various polydopamine (PDA) nanospheres were synthesized by utilizing triblock copolymer Pluronic F127 and 1,3,5-trimethylbenzene (TMB) as soft templates. Precise morphology control of polydopamine nanospheres was realized from solid polydopamine nanospheres to hollow polydopamine nanospheres, mesoporous polydopamine nanospheres and hollow mesoporous polydopamine nanospheres (H-MPDANSs) by adjusting the weight ratio of TMB to F127. The inner diameter of the prepared H-MPDANSs can be controlled in the range of 50-100 nm, and the outer diameter is about 180 nm. Furthermore, the thickness of hollow mesoporous spherical shell can be adjusted by changing the amount of dopamine (DA). The H-MPDANSs have good biocompatibility, excellent photothermal properties, high drug loading capacity, and outstanding sustainable drug release properties. In addition, both NIR laser irradiation and acid pH can facilitate the controlled release of doxorubicin (DOX) from H-MPDANSs@DOX.

Phenolic-enabled nanotechnology: versatile particle engineering for biomedicine

Phenolics are ubiquitous in nature and have gained immense research attention because of their unique physiochemical properties and widespread industrial use. In recent decades, their accessibility, versatile reactivity, and relative biocompatibility have catalysed research in phenolic-enabled nanotechnology (PEN) particularly for biomedical applications which have been a major benefactor of this emergence, as largely demonstrated by polydopamine and polyphenols. Therefore, it is imperative to overveiw the fundamental mechanisms and synthetic strategies of PEN for state-of-the-art biomedical applications and provide a timely and comprehensive summary. In this review, we will focus on the principles and strategies involved in PEN and summarize the use of the PEN synthetic toolkit for particle engineering and the bottom-up synthesis of nanohybrid materials. Specifically, we will discuss the attractive forces between phenolics and complementary structural motifs in confined particle systems to synthesize high-quality products with controllable size, shape, composition, as well as surface chemistry and function. Additionally, phenolic's numerous applications in biosensing, bioimaging, and disease treatment will be highlighted. This review aims to provide guidelines for new scientists in the field and serve as an up-to-date compilation of what has been achieved in this area, while offering expert perspectives on PEN's use in translational research.

Direct Access to Bowl-Like Nanostructures with Block Copolymer Anisotropic Truncated Microspheres

Bowl-like nanostructures have attracted significant scientific and technological interest due to their favorable characteristics, such as high specific surface area, interconnected porous channels, and conductivity. However, tailored synthesis of bowl-like nanostructures with well-defined and uniform morphology is still a challenge. Herein, we report a versatile microemulsion assembly approach to prepare bowl-like nanostructures of three different materials: polymer, carbon, and platinum. To this end, polystyrene-block-poly(4vinylpyridine), PS-b-P4VP, block copolymer (BCP) microparticles with truncated-sphere shape and composed of stacks of parallel lamellae were used because those anisotropic microparticles play an important role in the design of bowl-like nanostructures. To form nanolamellae-within-microparticle morphology, a designed PS-b-P4VP/chloroform/CTAB microemulsion can be facilely obtained in the aqueous medium, where the morphology can be tailored by the interplay between macro-phase separations, BCP self-assembly, and interfacial energies of three phases in the presence of cetyltrimethylammonium bromide (CTAB). Finally, protonation or combination of cross-linking and pyrolysis of those truncated microparticles enables formation of polymer or carbon bowl-like nanostructures, respectively. Upon selective adsorption of Pt precursor salt ions with the pyridyl moieties followed by chemical reduction, subsequent calcination permits the synthesis of Pt bowl-like nanostructures. The microemulsion assembly approach opens up new ways to direct and template bowl-like nanostructures.

Optimization Strategies of Preparation of Biomass-Derived Carbon Electrocatalyst for Boosting Oxygen Reduction Reaction: A Minireview

Oxygen reduction reaction (ORR) has attracted considerable attention for clean energy conversion technologies to reduce traditional fossil fuel consumption and greenhouse gas emissions. Although platinum (Pt) metal is currently used as an electrocatalyst to accelerate sluggish ORR kinetics, the scarce resource and high cost still restrict its further scale-up applications. In this regard, biomass-derived carbon electrocatalysts have been widely adopted for ORR electrocatalysis in recent years owing to their tunable physical/chemical properties and cost-effective precursors. In this minireview, recent advances of the optimization strategies in biomass-derived carbon electrocatalysts towards ORR have been summarized, mainly focusing on the optimization of pore structure and active site. Besides, some current challenges and future perspectives of biomass-derived carbon as high-performance electrocatalysts for ORR have been also discussed in detail. Hopefully, this minireview will afford a guideline for better design of biomass-derived carbon electrocatalysts for ORR-related applications.

Hierarchically Porous Carbon Materials from Self-Assembled Block Copolymer/Dopamine Mixtures

Hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores are desirable for electrochemical applications in biosensors, electrocatalysis, and supercapacitors. In this study, we report a facile synthetic route to fabricate hierarchically porous carbon materials by controlled macro- and mesophase separation of a mixture of polystyrene-block-poly(ethylene) and dopamine. The morphology of mesopores is tailored by controlling the coassembly of PS-b-PEO and dopamine in the acidic tetrahydrofuran-water cosolvent. HCl addition plays a critical role via enhancing the charge-dipole interactions between PEO and dopamine and suppressing the clustering and chemical reactions of dopamine in solution. As a result, subsequent drying can produce interpenetrated PS-b-PEO/DA mixtures without forming dopamine microsized crystallites. Dopamine oxidative polymerization induced by solvent annealing in NH₄OH vapor enables the formation of percolating macropores. Subsequent pyrolysis to selectively remove the PS-b-PEO template from the complex can produce hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores when pyrolysis is implemented at a low temperature or when DA is a minor component.

A Mechanochemical-Assisted Synthesis of Boron, Nitrogen Co-Doped Porous Carbons as Metal-Free Catalysts

A green and convenient solid-state method assisted by mechanical energy is employed for the synthesis of boron (B) and nitrogen (N) co-doped porous carbons (B,N-Cs). Glutamic acid (Glu) and boric acid (H₃ BO₃ ) are used as the N-containing carbon precursor and boron source, respectively. This method is easy to perform and proved to be efficient towards co-doping B and N into the carbon matrix with high contents of B (7 atom %) and N (10 atom %). By adjusting the molar ratio of H₃ BO₃ to Glu, the surface chemical states of B and N could be readily modulated. When increasing H₃ BO₃ dosage, the pore size of B,N-Cs could be tuned ranging from micropores to mesopores with a Brunauer-Emmett-Teller (BET) surface area up to 940 m²  g^-1 . Finally, the B,N-Cs were applied as metal-free catalysts for the cycloaddition of CO₂ to epoxides, which outperform the N-doped carbon catalyst (NC-900) and the physically mixed catalyst of NC-900/B₄ C. The enhanced activity is attributed to the cooperative effect between B and N sites. X-ray photoelectron spectroscopy (XPS) analysis reveals that BN₃ in the B,N-Cs serves as a critical active site for the cooperative catalysis.

Catalytically-active porous assembly with dynamic pulsating motion for efficient exchange of products and reagents

Despite recent advances in the use of porous materials as efficient heterogeneous catalysts which operate through effectively trapping reagents in a well-defined space, continuously uptaking reagents to substitute products in the cavity for efficient product turnover still remains challenging. Here, a porous catalyst is endowed with 'breathing' characteristics by thermal stimulus, which can enable the efficient exchange of reagents and products through reversible stacking from inflated aromatic hexamers to contracted trimeric macrocycles. The contracted super-hydrophobic tubular interior with pyridine environment exhibits catalytic activity towards a nucleophilic aromatic substitution reaction by promoting interactions between concentrated reagents and active sites. Subsequent expansion facilitates the exchange of products and reagents, which ensures the next reaction. The strategy of mesoporous modification with inflatable transition may provide a new insight for construction of dynamic catalysts.

Ultrahigh Surface Area N-Doped Hierarchically Porous Carbon for Enhanced CO2 Capture and Electrochemical Energy Storage

Facile synthesis of ultrahigh surface area porous carbons with well-defined functionalities such as N-doping remains a formidable challenge as extensive pore creation results in significant damage to the active sites. Herein, an ultrahigh surface area, N-doped hierarchically porous carbon was prepared through a multicomponent co-assembly approach. The resultant N-doped hierarchically porous carbon (N-HPC) possessed an ultrahigh surface area (≈1960 m²  g^-1 ), a uniform interpenetrating micropore (≈1.3 nm) and large mesopore (≈7.6 nm) size, and high N-doping in the carbon frameworks (≈5 wt %). The N-HPC exhibited a high specific capacitance (358 F g^-1 at 0.5 A g^-1 ) as a supercapacitor electrode in aqueous alkaline electrolyte with a stable cycling performance after10 000 charge/discharge cycles. Moreover, as a CO₂ absorbent, N-HPC displayed an adsorption capacity of 29.0 mmol g^-1 at 0 °C under a high pressure of 30 bar.

Catalyst-Free One-Step Preparation of Self-Crosslinked pH-Responsive Vesicles

The fabrication of block copolymer (BCP) vesicles with controlled membrane permeability and promising stability remains a considerable challenge. Herein, a new type of pH-responsive and self-crosslinked vesicle based on a hydrolytically hindered urea bond is reported. This kind of vesicle is formed by the self-assembly of a pH-responsive and hydrolytically self-crosslinkable copolymer poly(ethylene glycol)-block-poly[2-(3-(tert-butyl)-3-ethylureido)ethyl methacrylate-co-2-(diethylamino)ethyl methacrylate] (PEG-b-P(TBEU-co-DEA)). The BCP can be easily synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(3-(tert-butyl)-3-ethylureido)ethyl methacrylate (TBEU) and 2-(diethylamino)ethyl methacrylate (DEA) using PEG-based macro-chain transfer agent. The copolymer could self-assemble into stable vesicles by the hydrophobic interaction and in situ cross-linking between amines and isocyanates after the hydrolysis of the hindered urea bonds without any catalyst. Dynamic light scattering (DLS) studies show that the vesicles exhibit enhanced stability against the dilution of organic solvent, and the size can be adjusted through the change of pH values. Moreover, the alkaline phosphatase-loaded vesicles can act as nano-reactor and enable free diffusion of small molecules into the vesicles, followed by the significantly improved fluorescence intensity of phosphate-caged fluorescein. This self-crosslinking and pH-sensitive vesicles may serve as a smart platform in controlled drug delivery and molecular reactor.

Dual-Porosity Hollow Carbon Spheres with Tunable Through-Holes for Multi-Guest Delivery

Dual-porosity hollow carbon spheres (DPHCs) with small mesopores (2-4 nm) and large through-holes (20-30 nm) in shells were successfully synthesized using colloidal silica as the template, small silica nanoparticles as nanomasks, and nontoxic dopamine as the carbon precursor followed by post-carbonization and etching. The synthesized DPHCs were further oxidized to be hydrophilic and then used to simultaneously deliver the protein bovine serum albumin (21 × 4 × 14 nm³) and the small molecule doxorubicin (<1 nm), which exhibited a high loading capacity of 689.4 and 1421.2 mg/g, respectively. The release of these two guest molecules can be controlled independently under the stimuli of heat and acidity. In vitro and in vivo experiments also proved that the DPHCs are promising for the co-delivery of multiple cargoes of different sizes.

Self-Assembled Structures of Diblock Copolymer/Homopolymer Blends through Multiple Complementary Hydrogen Bonds

A poly(styrene-b-vinylbenzyl triazolylmethyl methyladenine) (PS-b-PVBA) diblock copolymer and a poly(vinylbenzyl triazolylmethyl methylthymine) (PVBT) homopolymer were prepared through a combination of nitroxide-mediated radical polymerizations and click reactions. Strong multiple hydrogen bonding interactions of the A···T binary pairs occurred in the PVBA/PVBT miscible domain of the PS-b-PVBA/PVPT diblock copolymer/homopolymer blend, as evidenced in Fourier transform infrared and 1H nuclear magnetic resonance spectra. The self-assembled lamellar structure of the pure PS-b-PVBA diblock copolymer after thermal annealing was transformed to a cylinder structure after blending with PVBT at lower concentrations and then to a disordered micelle or macrophase structure at higher PVBT concentrations, as revealed by small-angle X-ray scattering and transmission electron microscopy.

Co@C Nanoparticle Embedded Hierarchically Porous N-Doped Hollow Carbon for Efficient Oxygen Reduction

The rational construction of highly active and stable non-noble metal electrocatalysts for the oxygen reduction reaction (ORR) is an ongoing challenge for practical applications of catalysts. Here, we report a novel nanostructured hollow N-doped carbon hybrid through pyrolysis of silica@CoZn-coordinated zeolitic imidazolate frameworks. The carbon layer encased cobalt nanoparticles were embedded in the hierarchically porous carbon catalyst (Co@C-HN-hC). Profiting from the synergistic effect between highly active Co@C NPs and HN-hC, the Co@C-HN-hC catalyst exhibited remarkable catalytic performances as compared to porous N-doped hollow carbon (N-hC) and N-doped carbon encased Co NPs (Co@N-C). The electrochemical measurements show that the performances of the Co@C-HN-hC catalyst is close to that of the Pt/C catalysts, along with an excellent stability and durability in the ORR process. This study provides a guideline for controllable design of carbon-based ORR catalysts for substituting noble metal catalysts.

Assembly of Hollow Carbon Nanospheres on Graphene Nanosheets and Creation of Iron-Nitrogen-Doped Porous Carbon for Oxygen Reduction

Triblock copolymer micelles coated with melamine-formaldehyde resin were self-assembled into closely packed two-dimensional (2D) arrangements on the surface of graphene oxide sheets. Carbonizing these structures created a 2D architecture composed of reduced graphene oxide (rGO) sandwiched between two monolayers of sub-40 nm diameter hollow nitrogen-doped carbon nanospheres (N-HCNS). Electrochemical tests showed that these hybrid structures had better performance for oxygen reduction compared to physically mixed rGO and N-HCNS that were not chemically bonded together. Further impregnation of the sandwich structures with iron (Fe) species followed by carbonization yielded Fe_1.6-N-HCNS/rGO-900 with a high specific surface area (968.3 m² g^-1), a high nitrogen doping (6.5 at%), and uniformly distributed Fe dopant (1.6 wt %). X-ray absorption fine structure analyses showed that most of the Fe in the nitrogen-doped carbon framework is composed of single Fe atoms each coordinated to four N atoms. The best Fe_1.6-N-HCNS/rGO-900 catalyst performed better in electrocatalytic oxygen reduction than 20 wt % Pt/C catalyst in alkaline medium, with a more positive half-wave potential of 0.872 V and the same limiting current density. Bottom-up soft-patterning of regular carbon arrays on free-standing 2D surfaces should enable conductive carbon supports that boost the performance of electrocatalytic active sites.

Magnesium and Nitrogen Co-Doped Mesoporous Carbon with Enhanced Microporosity for CO₂ Adsorption

Mesoporous carbons (MC) have attracted a tremendous amount of interest due to their efficient molecular transport properties. However, the limited number of active sites and low microporosity generally impede their use for practical applications. Herein, we have fabricated Mg and N co-doped mesoporous carbon (Mg-NMC) with high microporosity via one-pot synthetic route followed by further steam activation. In comparison with the parent N-doped mesoporous carbon, Mg-NMC shows partially ordered mesostructure and improved CO₂ adsorption capacity attributed to the introduction of basic site after Mg doping. Upon further steam activation, the microporosity is enhanced to 37.3%, while the CO₂ adsorption capacity is also increased by 70.4% at 273 K and 1.0 bar.

Realization of Walnut-Shaped Particles with Macro-/Mesoporous Open Channels through Pore Architecture Manipulation and Their Use in Electrocatalytic Oxygen Reduction

Herein we report a simple dual-soft-template approach to prepare walnut-shaped macro-/mesoporous polydopamine particles with diameter of ca. 270 nm, highly accessible bicontinuous channels and wide pore size distribution from ca. 20 nm to ca. 95 nm. This approach provides great opportunities to tailor the soft template-directed assembly processes and generate various polydopamine particles with controllable mesophase curvature. Walnut-shaped mesoporous carbon particles with large open mesochannels in the range of ca. 13 nm to ca. 50 nm can be fabricated by subsequent thermal treatment under nitrogen atmosphere. Lastly, we demonstrate that the as-derived walnut-shaped carbon particles manifest enhanced electrocatalytic performance for oxygen reduction reaction in alkaline electrolyte.

Green Synthesis of Three-Dimensional Hybrid N-Doped ORR Electro-Catalysts Derived from Apricot Sap

Rapid depletion of fossil fuel and increased energy demand has initiated a need for an alternative energy source to cater for the growing energy demand. Fuel cells are an enabling technology for the conversion of sustainable energy carriers (e.g., renewable hydrogen or bio-gas) into electrical power and heat. However, the hazardous raw materials and complicated experimental procedures used to produce electro-catalysts for the oxygen reduction reaction (ORR) in fuel cells has been a concern for the effective implementation of these catalysts. Therefore, environmentally friendly and low-cost oxygen reduction electro-catalysts synthesised from natural products are considered as an attractive alternative to currently used synthetic materials involving hazardous chemicals and waste. Herein, we describe a unique integrated oxygen reduction three-dimensional composite catalyst containing both nitrogen-doped carbon fibers (N-CF) and carbon microspheres (N-CMS) synthesised from apricot sap from an apricot tree. The synthesis was carried out via three-step process, including apricot sap resin preparation, hydrothermal treatment, and pyrolysis with a nitrogen precursor. The nitrogen-doped electro-catalysts synthesised were characterised by SEM, TEM, XRD, Raman, and BET techniques followed by electro-chemical testing for ORR catalysis activity. The obtained catalyst material shows high catalytic activity for ORR in the basic medium by facilitating the reaction via a four-electron transfer mechanism.

Creation of Triple Hierarchical Micro-Meso-Macroporous N-doped Carbon Shells with Hollow Cores Toward the Electrocatalytic Oxygen Reduction Reaction

A series of triple hierarchical micro-meso-macroporous N-doped carbon shells with hollow cores have been successfully prepared via etching N-doped hollow carbon spheres with CO₂ at high temperatures. The surface areas, total pore volumes and micropore percentages of the CO₂-activated samples evidently increase with increasing activation temperature from 800 to 950 °C, while the N contents show a contrary trend from 7.6 to 3.8 at%. The pyridinic and graphitic nitrogen groups are dominant among various N-containing groups in the samples. The 950 °C-activated sample (CANHCS-950) has the largest surface area (2072 m² g^-1), pore volume (1.96 cm³ g^-1), hierarchical micro-mesopore distributions (1.2, 2.6 and 6.2 nm), hollow macropore cores (~91 nm) and highest relative content of pyridinic and graphitic N groups. This triple micro-meso-macropore system could synergistically enhance the activity because macropores could store up the reactant, mesopores could reduce the transport resistance of the reactants to the active sites, and micropores could be in favor of the accumulation of ions. Therefore, the CANHCS-950 with optimized structure shows the optimal and comparable oxygen reduction reaction (ORR) activity but superior methanol tolerance and long-term durability to commercial Pt/C with a 4e^--dominant transfer pathway in alkaline media. These excellent properties in combination with good stability and recyclability make CANHCSs among the most promising metal-free ORR electrocatalysts reported so far in practical applications.

Dendritic and Core-Shell-Corona Mesoporous Sister Nanospheres from Polymer-Surfactant-Silica Self-Entanglement

Mesoporous nanospheres are highly regarded for their applications in nanomedicine, optical devices, batteries, nanofiltration, and heterogeneous catalysis. In the last field, the dendritic morphology, which favors molecular diffusion, is a very important morphology known for silica, but not yet for carbon. A one-pot, easy, and scalable co-sol-gel route by using the triphasic resol-surfactant-silica system is shown to yield the topologies of dendritic and core-shell-corona mesoporous sister nanospheres by inner radial phase speciation control on a mass-transfer-limited process, depending on the relative polycondensation rates of the resol polymer and silica phases. The trick was the use of polyolamines with different catalytic activities on each hard phase polycondensation. The self-entanglement of phases is produced at the {O^- , S⁺ , I^- } organic-surfactant-inorganic interface. Mono- and biphasic mesoporous sister nanospheres of carbon and/or silica are derivatized from each mother nanospheres and called "syntaxic" because of similar sizes and mirrored morphologies. Comparing these "false twins", or yin and yang mesoporous nanospheres, functionalized by sulfonic groups provides evidence of the superiority of the dendritic topologies and the absence of a shell on the diffusion-controlled catalytic alkylation of m-cresol.

Coffee Waste-Derived Hierarchical Porous Carbon as a Highly Active and Durable Electrocatalyst for Electrochemical Energy Applications

Nitrogen-doped porous carbon materials have been highlighted as promising alternatives to high-cost platinum in various electrochemical energy applications. However, protocols to generate effective pore structure are still challenging, which hampers mass production and utilization of carbon materials. Here, we suggest a facile and effective method for hierarchical porous carbon by a single-step carbonization of coffee waste (CW) with ZnCl₂. The CW, which is one of the most earth-abundant organic waste, can be successfully converted to nitrogen-doped porous carbon. It shows outstanding oxygen reduction activity and durability comparable to the state-of-the-art platinum, and the half-wave potential is also comparable to the best metal-free electrocatalysts in alkaline media. Finally, we apply it to counter electrode of dye-sensitized solar cell, whose photovoltaic efficiency surpasses the one made with conventional platinum electrode. We demonstrate the feasibility of our strategies for highly efficient, cheap, and environment-friendly electrocatalyst to replace platinum in various electrochemical energy applications.

Component-Customizable Porous Rare-Earth-Based Colloidal Spheres towards Highly Effective Catalysts and Bioimaging Applications

Multicomponent porous colloidal spheres are of interest because they not only show a combination of the properties associated with all different components, but also usually present synergy effects. However, a combination of different components in a single porous sphere is still greatly challenged due to the different precipitation behaviors of each component. In this work, we have developed a general synthetic route to prepare several categories of porous monodisperse rare-earth (RE)-based colloidal spheres with customizable elemental compositions and a uniform element distribution. The two-step synthetic strategy is based on the integration of coordination chemistry precipitation of RE ions and a subsequent ion-exchange process, which steers clear of obstacles, such as differences in solubility product constant, that are to be found in traditional co-precipitation methods. Our approach provides a new mixing mechanism to realize homogeneous distribution of each element within the porous spheres. An array of binary, ternary, and even senary RE colloidal porous spheres with diameters of 500 nm to 700 nm has been successfully synthesized. Taking advantage of their good dispersibility, porosity, and customizable components, these porous RE oxide spheres show excellent catalytic activity for the reduction of 4-nitrophenol, and promising application in single-phase multifunctional bioprobes.

Block Copolymers: Synthesis, Self-Assembly, and Applications

Research on block copolymers (BCPs) has played a critical role in the development of polymer chemistry, with numerous pivotal contributions that have advanced our ability to prepare, characterize, theoretically model, and technologically exploit this class of materials in a myriad of ways in the fields of chemistry, physics, material sciences, and biological and medical sciences. The breathtaking progress has been driven by the advancement in experimental techniques enabling the synthesis and characterization of a wide range of block copolymers with tailored composition, architectures, and properties. In this review, we briefly discussed the recent progress in BCP synthesis, followed by a discussion of the fundamentals of self-assembly of BCPs along with their applications.

Tailored Design of Bicontinuous Gyroid Mesoporous Carbon and Nitrogen-Doped Carbon from Poly(ethylene oxide-b-caprolactone) Diblock Copolymers

Highly ordered mesoporous resol-type phenolic resin and the corresponding mesoporous carbon materials were synthesized by using poly(ethylene oxide-b-caprolactone) (PEO-b-PCL) diblock copolymer as a soft template. The self-assembled mesoporous phenolic resin was found to form only in a specific resol concentration range of 40-70 wt % due to an intriguing balance of hydrogen-bonding interactions in the resol/PEO-b-PCL mixtures. Furthermore, morphological transitions of the mesostructures from disordered to gyroid to cylindrical and finally to disordered micelle structure were observed with increasing resol concentration. By calcination under nitrogen atmosphere at 800 °C, the bicontinuous mesostructured gyroid phenolic resin could be converted to mesoporous carbon with large pore size without collapse of the original mesostructure. Furthermore, post-treatment of the mesoporous gyroid phenolic resin with melamine gave rise to N-doped mesoporous carbon with unique electronic properties for realizing high CO₂ adsorption capacity (6.72 mmol g^-1 at 0 °C).

Metal-Organic Framework-Derived FeCo-N-Doped Hollow Porous Carbon Nanocubes for Electrocatalysis in Acidic and Alkaline Media

Metal-organic frameworks (MOFs) are ideal precursors/ templates for porous carbons with homogeneous doping of active components for energy storage and conversion applications. Herein, metalloporphyrinic MOFs, PCN-224-FeCo, with adjustable molar ratio of Fe^II /Co^II alternatively residing inside the porphyrin center, were employed as precursors to afford FeCo-N-doped porous carbon (denoted as FeCo-NPC) by pyrolysis. Thanks to the hollow porous structure, the synergetic effect between highly dispersed FeN_x and CoN_x active sites accompanied with a high degree of graphitization, the optimized FeCo₂ -NPC-900 obtained by pyrolysis at 900 °C exhibits more positive half-wave potential, higher diffusion-limited current density, and better stability than the state-of-the-art Pt/C, under both alkaline and acidic media. More importantly, the current synthetic approach based on MOFs offers a rational strategy to structure- and composition-controlled porous carbons for efficient electrocatalysis.