Wen-Cui Li

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.

Carbon aerogels derived from cresol-resorcinol-formaldehyde for supercapacitors

Abstract The objective of the present paper is to demonstrate the possibility to synthesize mixed carbon aerogels (denoted CmRF) from cresol (Cm), resorcinol (R) and formaldehyde (F), as an alternative economic route to the classical RF synthesis. These porous carbon aerogels can be used as electrode materials for supercapacitors with a high volume-specific capacitance. Organic precursor gels were synthesized via polycondensation of a mixture of resorcinol and cresol with formaldehyde in an aqueous alkaline (NaOH) solution. After gelation and aging the solvent was removed via drying at ambient pressure to produce organic aerogels. Upon pyrolysis of the organic aerogels at 1173 K, monolithic carbon aerogels can be obtained. By controlling the catalyst (Cat) molar ratio (Cm+R/Cat) in the range 200–500, up to 70% of the resorcinol can be replaced with the cheap cresol. The resulting homogeneous organic aerogels exhibit a drying shrinkage below 15% (linear). The shrinkage and mass loss upon pyrolysis of the mixed aerogels increase with increasing cresol content. Nitrogen adsorption at 77 K was employed to characterize the microstructure of the carbon aerogels. The data show that the porous structure of mixed carbon aerogels is similar to that of RF carbon aerogels. Cyclic voltammetry measurements show that the as-prepared CmRF carbon aerogels exhibit a high volume-specific capacitance of up to 77 F/cm3.

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.

High Sulfur Loading Cathodes Fabricated Using Peapodlike, Large Pore Volume Mesoporous Carbon for Lithium–Sulfur Battery

Porous carbon materials with large pore volume are crucial in loading insulated sulfur with the purpose of achieving high performance for lithium-sulfur batteries. In our study, peapodlike mesoporous carbon with interconnected pore channels and large pore volume (4.69 cm(3) g(-1)) was synthesized and used as the matrix to fabricate carbon/sulfur (C/S) composite which served as attractive cathodes for lithium-sulfur batteries. Systematic investigation of the C/S composite reveals that the carbon matrix can hold a high but suitable sulfur loading of 84 wt %, which is beneficial for improving the bulk density in practical application. Such controllable sulfur-filling also effectively allows the volume expansion of active sulfur during Li(+) insertion. Moreover, the thin carbon walls (3-4 nm) of carbon matrix not only are able to shorten the pathway of Li(+) transfer and conduct electron to overcome the poor kinetics of sulfur cathode, but also are flexible to warrant structure stability. Importantly, the peapodlike carbon shell is beneficial to increase the electrical contact for improving electronic conductivity of active sulfur. Meanwhile, polymer modification with polypyrrole coating layer further restrains polysulfides dissolution and improves the cycle stability of carbon/sulfur composites.

Fabrication of superior-performance SnO2@C composites for lithium-ion anodes using tubular mesoporous carbon with thin carbon walls and high pore volume

A tubular composite, including ultrafine SnO2 particles encapsulated in ordered tubular mesoporous carbon with thin walls and high pore volume, is fabricated through the in situ hydrolysis method. It is observed that up to 80 wt% of SnO2 particles with size between 4–5 nm are highly dispersed and homogeneously encapsulated in the mesopore channels and no bulky aggregates are visible. The tubular composite exhibits a considerably high reversible capacity of 978 mA h g−1 and a high initial efficiency of 71% at a current density of 200 mA g−1 between 0.005–3 V. Its reversible capacity even increases up to 1039 mA h g−1 after 100 cycles, which is much higher than the conventional theoretical capacity of SnO2 (782 mA h g−1), meanwhile, it also displays fast discharge/charge kinetics at a high current density of 1500 mA g−1. The excellent electrochemical performance is ascribed to its unique mesostructure by recruiting tubular mesoporous carbon with thin carbon walls (∼2 nm) and high pore volume (2.16 cm3 g−1). This tubular nanostructure provides confined nanospace for hosting immobilized ultrafine SnO2 with high loading, compensates volume expansion of SnO2, warrants efficient contact between nanoparticles and carbon matrix before and after Li+ insertion. We believe this special structure model might be extended for the fabrication of other cathode and anode electrode materials, to achieve high performance LIBs.

Synthesis of Discrete and Dispersible Hollow Carbon Nanospheres with High Uniformity by Using Confined Nanospace Pyrolysis

In recent years, hollow carbon nanospheres (HCSs) have attracted a great deal of attention because of their unique properties such as high surface-to-volume ratios, and excellent chemical and thermal stabilities. In this regard, HCSs are superior to polymerand metal-based hollow nanospheres. 3] HCSs are promising materials in a variety of applications such as adsorption, lithium ion batteries, fuel cells, and catalysis, and can also serve as building blocks for complex structures. The success of HCSs in these applications relies strongly on the availability of HCSs with carefully controlled diameter and shell thickness, surface properties, crystallinity of the carbon shell, and dispersibility in media. Much effort has been devoted to the synthesis of HCSs by a nanocasting approach. However, most previous reports on HCSs have the sole aim of obtaining hollow structural units, and little attention has been paid to addressing the issue of particle conglutination. In fact, an inevitable tendency of all carbon nanostructures during high-temperature annealing is the incidental condensing and sintering. Consequently, the end results are often nondispersible and conglutinated bulky materials. This challenge becomes even greater when the carbon particles are smaller, for example, below 200 nm. Discrete and dispersible HCSs are of critical importance for both the fundamental study of carbon colloids and for many practical applications such as colloidal catalysts, drug carriers, nanodevices, and inks. However, to the best of our knowledge, no feasible solution has been reported to date that can satisfactorily resolve the issue of conglutination for carbon nanoparticles. Thus, it remains a great challenge to develop a simple and effective strategy to overcome the barrier and to produce discrete and dispersible HCSs with high uniformity. Herein, we describe a new method referred to as “confined nanospace pyrolysis” for the synthesis of discrete and highly dispersible HCSs that have both tailorable shell thickness and cavity size. This idea is inspired from nature, in particular the structure of an egg, which consists of an inorganic outer shell (eggshell), organic inner shell (egg white), and core (yolk). The presence of the inorganic outer shell is an essential element that ensures that eggs retain their original shape, and remain discrete. A designed synthesis of HCSs that was inspired by the egg structure is illustrated in Figure 1a. Firstly, monodisperse polystyrene nanospheres (PS) with a specific particle size are prepared as the seed;

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.

Characterization of the microstructures of organic and carbon aerogels based upon mixed cresol–formaldehyde

Abstract Organic aerogels were synthesized via the sol–gel polycondensation of mixed cresol with formaldehyde in a slightly basic aqueous solution followed by supercritical drying with carbon dioxide. Carbon aerogels are generated by pyrolysis of organic aerogels in inert atmosphere at high temperature. Obvious chemical and physical changes can take place within aerogel microstructures during the pyrolysis process. IR combined with TGA, TEM, and nitrogen adsorption is employed to study these changes in detail. Appreciable transformation of aerogel structure occurs during 250–600°C, which results from the release of water,organic groups and simultaneous rearrangement of aromatic rings. A new band occurring at 874 cm −1 in IR spectra after 400°C is associated with the IR-active vibration states of graphitic structure. With the increase of pyrolysis temperature, the density, surface area and total volume of aerogels keep increasing; on the contrary, the pore size distribution becomes narrower and the pore size decreases. The carbon aerogel microspheres are smaller than their organic aerogel precursors as a result of shrinkage during pyrolysis, as seen from TEM results.