Guang-Ping Hao

Rapid synthesis of nitrogen-doped porous carbon monolith for CO2 capture.

M M U Rapid Synthesis of Nitrogen-Doped Porous Carbon Monolith for CO2 Capture N IC By Guang-Ping Hao, Wen-Cui Li, Dan Qian, and An-Hui Lu* A T IO N The development of novel materials and new technologies for CO2 capture and storage has gained great attention over the past decades. The necessity for reducing the concentration of CO2 in the atmosphere is a very important issue, since CO2 is considered as a greenhouse gas causing global warming. In addition, higher concentrations of CO2 are toxic for humans, especially in space-limited chambers like submarines and space ships. Traditional technologies for CO2 capture including absorption and adsorption-coupled membrane separation along with the corresponding sorbents such as aqueous amines, microporous coordination polymers (MCPs), zeolitic imidazolate frameworks (ZIFs), different types of nitrogen-doped zeolite, mesoporous silica, and activated carbons have been widely explored. However, MCPs and ZIFs synthesized with nitrogen-containing organic compounds as the crosslinker often suffer from structural instability and inefficiency for CO2 selectivity in the presence of water and thus are limited in their widespread use. For aminemodified solids, the main drawback is the possible loss of ammonia associated with the temperature needed for regeneration and the energy-intensive nature of the regeneration process. For instance, amine-surface-modified or amineimpregnated porous silica (e.g., MCM-41, MCM-48, SBA-15, SBA-16) and zeolite 13X materials fail to capture CO2 effectively, require high temperature and long regeneration times and lack stability over many cycles. It should be pointed out that amine-modified silica-based solids are usually prepared by a post-treatment, which is a time-consuming and costly procedure and often involves the use of toxic and corrosive reagents. Porous carbon materials have many specific features such as high surface area, thermal and chemical stability, and hydrophobic surface properties. The incorporation of basic nitrogen groups into the carbon framework ensures an improved adsorption/absorption for acidic gases. Up to date, porous carbon materials used for CO2 capture were mostly prepared by post-synthetic amine modification or ammonia treatment, which again leads to materials lacking stability and, in addition, the reagents are corrosive, which brings the same disadvantages as for modified silica and zeolites. Alternatively, nitrogencontaining porous carbons can be prepared directly from

Structurally Designed Synthesis of Mechanically Stable Poly(benzoxazine-co-resol)-Based Porous Carbon Monoliths and Their Application as High-Performance CO2 Capture Sorbents

Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO(2) capture and separation capacities, high selectivity, and facile regeneration at room temperature. At ~1 bar, the equilibrium capacities of the monoliths are in the range of 3.3-4.9 mmol g(-1) at 0 °C and of 2.6-3.3 mmol g(-1) at 25 °C, while the dynamic capacities are in the range of 2.7-4.1 wt % at 25 °C using 14% (v/v) CO(2) in N(2). The carbon monoliths exhibit high selectivity for the capture of CO(2) over N(2) from a CO(2)/N(2) mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO(2) release in an argon stream at 25 °C, indicating a good regeneration capacity.

Ionic liquid C16mimBF4 assisted synthesis of poly(benzoxazine-co-resol)-based hierarchically porous carbons with superior performance in supercapacitors

Hierarchically porous carbons with variable pore sizes at multi-length-scale, a nitrogen and boron co-doped and local graphitized framework, and high mechanical strength were synthesized through the self-assembly of poly(benzoxazine-co-resol) with ionic liquid C16mimBF4 and a carbonization process. In this synthesis, the ionic liquid acts both as a structure directing agent and a heteroatom precursor. The obtained porous carbons have a specific surface area lower than 376 m2 g−1 and thus a high skeleton density. With such heteroatom doped skeleton structures and fully interconnected macropores, mesopores and micropores, the hierarchically porous carbon shows outstanding electrochemical performance, e.g. a superior high gravimetric capacitance (Cg) of 247 F g−1, an interfacial capacitance (CS) of 66 μF cm−2 (calculated based on the discharge curve with a constant current density of 0.5 A g−1), whilst a high volumetric capacitance (Cv) of 101 F cm−3 compared to those reported in the literature. Cycling stability tests indicate that the carbon exhibits a capacitance retention of ∼96.2% after 4000 charge–discharge cycles, strongly reflecting an excellent long-term cyclability of the electrode. Due to its unique skeleton structure and high conductivity, such hierarchically porous carbon shows promise as an electrode material for supercapacitors.

Temperature-Programmed Precise Control over the Sizes of Carbon Nanospheres Based on Benzoxazine Chemistry

On the basis of benzoxazine chemistry, we have established a new way to synthesize highly uniform carbon nanospheres with precisely tailored sizes and high monodispersity. Using monomers including resorcinol, formaldehyde, and 1,6-diaminohexane, and in the presence of Pluronic F127 surfactant, polymer nanospheres are first synthesized under precisely programmed reaction temperatures. Subsequently, they are pseudomorphically and uniformly converted to carbon nanospheres in high yield, due to the excellent thermal stability of such polybenzoxazine-based polymers. The correlation between the initial reaction temperature (IRT) and the nanosphere size fits well with the quadratic function model, which can in turn predict the nanosphere size at a set IRT. The nanosphere sizes can easily go down to 200 nm while retaining excellent monodispersity, i.e., polydispersity <5%. The particle size uniformity is evidenced by the formation of large areas of periodic assembly structure. NMR, FT-IR, and elemental analyses prove the formation of a polybenzoxazine framework. As a demonstration of their versatility, nanocatalysts composed of highly dispersed Pd nanoparticles in the carbon nanospheres are fabricated, which show high conversion and selectivity, great reusability, and regeneration ability, as evidenced in a selective oxidation of benzyl alcohol to benzaldehyde under moderate conditions.

Novel porous solids for carbon dioxide capture

The development of novel materials for CO2 capture has received much attention during the past decade. Herein, we focus on the latest advances in novel porous solids as highly effective adsorbents for CO2 capture. The advantages and existing barriers of each porous material and their future perspectives will be discussed.

Stretchable and Semitransparent Conductive Hybrid Hydrogels for Flexible Supercapacitors

Conductive polymers showing stretchable and transparent properties have received extensive attention due to their enormous potential in flexible electronic devices. Here, we demonstrate a facile and smart strategy for the preparation of structurally stretchable, electrically conductive, and optically semitransparent polyaniline-containing hybrid hydrogel networks as electrode, which show high-performances in supercapacitor application. Remarkably, the stability can extend up to 35,000 cycles at a high current density of 8 A/g, because of the combined structural advantages in terms of flexible polymer chains, highly interconnected pores, and excellent contact between the host and guest functional polymer phase.

Porous carbon nanosheets with precisely tunable thickness and selective CO2 adsorption properties

We report the wet-chemistry synthesis of a new type of porous carbon nanosheet whose thickness can be precisely controlled over the nanometer length scale. This feature is distinct from conventional porous carbons that are composed of micron-sized or larger skeletons, and whose structure is less controlled. The synthesis uses graphene oxide (GO) as the shape-directing agent and asparagine as the bridging molecule that connects the GO and in situ grown polymers by electrostatic interaction between the molecules. The assembly of the nanosheets can produce macroscopic structures, i.e., hierarchically porous carbon monoliths which have a mechanical strength of up to 28.9 MPa, the highest reported for the analogues. The synthesis provides precise control of porous carbons over both microscopic and macroscopic structures at the same time. In all syntheses the graphene content used was in the range 0.5–2.6 wt%, which is significantly lower than that of common surfactants used in the synthesis of porous materials. This indicates the strong shape-directing function of GO. In addition, the overall thickness of the nanosheets can be tuned from 20 to 200 nm according to a fitted linear correlation between the carbon precursor/GO mass ratio and the coating thickness. The porous carbon nanosheets show impressive CO2 adsorption capacity under equilibrium, good separation ability of CO2 from N2 under dynamic conditions, and easy regeneration. The highest CO2 adsorption capacities can reach 5.67 and 3.54 CO2 molecules per nm3 pore volume and per nm2 surface area at 25 °C and ∼1 bar.

Can Carbon Spheres Be Created through the Stöber Method

Monodisperse colloidal nanospheres, including those composed of silica, polymers, and carbon, have received considerable attention during the past decade because they promise wide applications in drug delivery, active material encapsulation, colloidal catalysts, and particle templates. The success of all these applications strongly depends on the availability of colloidal spheres with tightly controlled sizes and surface properties, and on their ability to self-assemble into ordered superstructures. The classical Stcber method, which usually relies on sol–gel chemistry involving the hydrolysis of tetraalkyl silicates in an alcohol/water solution using ammonia as the catalyst, is a general approach for the synthesis of silica spheres having a size mostly in the range of 150–500 nm. Monodisperse polymer spheres, such as polystyrene, poly(methyl methacrylate), and poly(hydroxyethyl methacrylate) can be prepared by the emulsion polymerization approach. However, these colloidal spheres have failed to be converted into their carbonaceous analogues because of thermal decomposition. Differing from most polymers and silica materials, carbon materials in general show a series of excellent characteristics such as high surface area, high thermal stability (in an inert atmosphere), and acid/ base resistance, and can be applied in harsh reaction conditions. Hence, to integrate the advantages of carbon materials and colloids into one type of material, remains a grand challenge, which could be exploited by the new synthesis of monodisperse colloidal carbon spheres. Phenolic resins derived from the polymerization of phenols (e.g. phenol, resorcinol) and aldehydes (e.g. formaldehyde, furfuraldehyde), are commonly employed as excellent precursors for the production of carbon materials. Although there are several reports regarding the synthesis of carbon microspheres and nanospheres from phenolic resins, it is rather rare to find a report about truly monodisperse phenolic resin nanospheres that can form colloidal crystals by self-assembly. Recently, Liu et al. smartly associated the synthesis of carbon spheres with silica spheres. They considered that the synthesis of silica spheres based on the Stcber method involves the condensation of silicon alkoxides (e.g. tetraethyl orthosilicate (TEOS)) in ethanol/water mixtures under alkaline conditions (e.g. ammonia solution) at room temperature. Coincidentally, the resorcinol-formaldehyde precursors exhibit structural similarities to silanes, i.e. similar coordination sites and tetrahedral geometry, so their condensation behavior should be analogous to the hydrolysis and subsequent condensation of silicon alkoxides. Hence, a curious question arises: can carbon spheres really be created by the Stcber method? The answer is “yes”. Liu et al. have developed methods that are inspired by and exploit the Stcber method for the synthesis of monodisperse resorcinol-formaldehyde (RF) resin polymer colloidal spheres and their carbonaceous analogues (Figure 1). The particle size of the obtained colloidal products can be easily tuned by changing the ratio of alcohol to water, changing the amounts of NH4OH and of the RF precursor, using alcohols with short alkyl chains, and introducing a triblock copolymer surfactant. Critical to the successful synthesis of such polymer spheres is the use of ammonia in the reaction system; its role, they consider, lies in not only accelerating the polymerization of RF, but also supplying the positive charges that adhere to the outer surface of the spheres and thus, prevent the aggregation. Firstly, ammonia molecules catalyze the polymerization of RF inside the emulsion droplets, thus initiating their condensation process. Resorcinol reacts quickly with formaldehyde, forming numerous hydroxymethyl-substituted species. These hydroxymethyl-substituted species are positioned at the surface of the emulsion droplets owing to the electrostatic interaction with the ammonia molecules, and further cross-linking of these species during the hydrothermal treatment results in uniform colloidal spheres. The ammonia, indeed, plays a key role in such a copolymerization system. However, it may serve other functions than that mentioned above, and this ability may lead to a rather different reaction sequence. Early in 1948, Richmond et al. investigated the reaction between formaldehyde and ammonia, and found that a fast reaction occurs after their mixing, thus resulting in cyclotrimethylenetriamine as the intermediate in the eventual formation of hexamine. This was further confirmed by a recent report which shows [*] Prof. A.-H. Lu, G.-P. Hao, Q. Sun State Key Laboratory of Fine Chemicals School of Chemical Engineering, Dalian University of Technology Dalian 116024 (P.R. China) E-mail: anhuilu@dlut.edu.cn

High-defect hydrophilic carbon cuboids anchored with Co/CoO nanoparticles as highly efficient and ultra-stable lithium-ion battery anodes

We propose an effective strategy to engineer a unique kind of porous carbon cuboid with tightly anchored cobalt/cobalt oxide nanoparticles (PCC–CoOx) that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The host carbon cuboid features an ultra-polar surface reflected by its high hydrophilicity and rich surface defects due to high heteroatom doping (N-/O-doping both higher than 10 atom%) as well as hierarchical pore systems. We loaded the porous carbon cuboid with cobalt/cobalt oxide nanoparticles through an impregnation process followed by calcination treatment. The resulting PCC–CoOx anode exhibits superior rate capability (195 mA h g−1 at 20 A g−1) and excellent cycling stability (580 mA h g−1 after 2000 cycles at 1 A g−1 with only 0.0067% capacity loss per cycle). Impressively, even after an ultra-long cycle life exceeding 10000 cycles at 5 A g−1, the battery can recover to 1050 mA h g−1 at 0.1 A g−1, perhaps the best performance demonstrated so far for lithium storage in cobalt oxide-based electrodes. This study provides a new perspective to engineer long-life, high-power metal oxide-based electrodes for lithium-ion batteries through controlling the surface chemistry of carbon host materials.

Synthesis of Hierarchical Porous Carbon Monoliths with Incorporated Metal–Organic Frameworks for Enhancing Volumetric Based CO2 Capture Capability

This work aims to optimize the structural features of hierarchical porous carbon monolith (HCM) by incorporating the advantages of metal-organic frameworks (MOFs) (Cu₃(BTC)₂) to maximize the volumetric based CO₂ capture capability (CO₂ capacity in cm³ per cm³ adsorbent), which is seriously required for the practical application of CO₂ capture. The monolithic HCM was used as a matrix, in which Cu₃(BTC)₂ was in situ synthesized, to form HCM-Cu₃(BTC)₂ composites by a step-by-step impregnation and crystallization method. The resulted HCM-Cu₃(BTC)₂ composites, which retain the monolithic shape and exhibit unique hybrid structure features of both HCM and Cu₃(BTC)₂, show high CO₂ uptake of 22.7 cm³ cm⁻³ on a volumetric basis. This value is nearly as twice as the uptake of original HCM. The dynamic gas separation measurement of HCM-Cu₃(BTC)₂, using 16% (v/v) CO₂ in N₂ as feedstock, illustrates that CO₂ can be easily separated from N₂ under the ambient conditions and achieves a high separation factor for CO₂ over N₂, ranging from 67 to 100, reflecting a strongly competitive CO₂ adsorption by the composite. A facile CO₂ release can be realized by purging an argon flow through the fixed-bed adsorber at 25 °C, indicating the good regeneration ability.