Xiang-Qian Zhang

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.

Engineering of Hollow Core–Shell Interlinked Carbon Spheres for Highly Stable Lithium–Sulfur Batteries

We report engineered hollow core-shell interlinked carbon spheres that consist of a mesoporous shell, a hollow void, and an anchored carbon core and are expected to be ideal sulfur hosts for overcoming the shortage of Li-S batteries. The hollow core-shell interlinked carbon spheres were obtained through solution synthesis of polymer spheres followed by a pyrolysis process that occurred in the hermetical silica shell. During the pyrolysis, the polymer sphere was transformed into the carbon core and the carbonaceous volatiles were self-deposited on the silica shell due to the blocking effect of the hermetical silica shell. The gravitational force and the natural driving force of lowering the surface energy tend to interlink the carbon core and carbon/silica shell, resulting in a core-shell interlinked structure. After the SiO2 shell was etched, the mesoporous carbon shell was generated. When used as the sulfur host for Li-S batteries, such a hierarchical structure provides access to Li(+) ingress/egress for reactivity with the sulfur and, meanwhile, can overcome the limitations of low sulfur loading and a severe shuttle effect in solid carbon-supported sulfur cathodes. Transmission electron microscopy and scanning transmission electron microscopy images provide visible evidence that sulfur is well-encapsulated in the hollow void. Importantly, such anchored-core carbon nanostructures can simultaneously serve as a physical buffer and an electronically connecting matrix, which helps to realize the full potential of the active materials. Based on the many merits, carbon-sulfur cathodes show a high utilization of sulfur with a sulfur loading of 70 wt % and exhibit excellent cycling stability (i.e., 960 mA h g(-1) after 200 cycles at a current density of 0.5 C).

Converting biowaste corncob residue into high value added porous carbon for supercapacitor electrodes.

In this report, corncob residue, the main by-product in the furfural industry, is used as a precursor to prepare porous carbon by a simple and direct thermal treatment: one-step activation without pre-carbonization. As a consequence, the corncob residue derived porous carbon achieves a high surface area of 1210 m(2) g(-1) after ash-removal. The carbon material has the advantages of low cost and low environmental impact, with a superior electrochemical performance compared to those polymer-based synthetic carbons as electrode material for a supercapacitor. The carbon electrode exhibits a high capacitance of 314 F g(-1) in 6M KOH electrolyte. The corresponding sample also shows a superb cycling stability. Almost no capacitance decay was observed after 100,000 cycles. The excellent electrochemical performance is due to the combination of a high specific surface area with a fraction of mesopores and highly stable structure.

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.

Using Hollow Carbon Nanospheres as a Light-Induced Free Radical Generator to Overcome Chemotherapy Resistance

Under evolutionary pressure from chemotherapy, cancer cells develop resistance characteristics such as a low redox state, which eventually leads to treatment failures. An attractive option for combatting resistance is producing a high concentration of produced free radicals in situ. Here, we report the production and use of dispersible hollow carbon nanospheres (HCSs) as a novel platform for delivering the drug doxorubicine (DOX) and generating additional cellular reactive oxygen species using near-infrared laser irradiation. These irradiated HCSs catalyzed sufficiently persistent free radicals to produce a large number of heat shock factor-1 protein homotrimers, thereby suppressing the activation and function of resistance-related genes. Laser irradiation also promoted the release of DOX from lysosomal DOX@HCSs into the cytoplasm so that it could enter cell nuclei. As a result, DOX@HCSs reduced the resistance of human breast cancer cells (MCF-7/ADR) to DOX through the synergy among photothermal effects, increased generation of free radicals, and chemotherapy with the aid of laser irradiation. HCSs can provide a unique and versatile platform for combatting chemotherapy-resistant cancer cells. These findings provide new clinical strategies and insights for the treatment of resistant cancers.

Controlled hydrothermal synthesis of 1D nanocarbons by surfactant-templated assembly for use as anodes for rechargeable lithium-ion batteries

In this study, we have developed a facile and controllable hydrothermal synthesis assisted by surfactant-templating and subsequent carbonization for low dimensional nanocarbons, particularly 1D rods/fibers. In this synthesis, resorcinol and hexamethylene tetramine (HMT) were used as the monomers and the surfactant Pluronic F127 as the structural directing agent. The nanostructures and morphologies of the as-synthesized carbon can be simply tailored by changing the concentrations of F127 and HMT. The obtained 1D nanocarbon structures with BET surface areas in the range of 570–585 m2 g−1, markedly varied in shape from rods to fibers. When using these nanocarbon structures as the anode material for lithium ion batteries, it was found that carbon nanofibers demonstrated good rate performance (a high reversible capacity of 160 mA h g−1 at a current density of 1500 mA g−1 (ca. 4C)), which is much higher than that of the commercial artificial graphite. This high rate capability is attributed to the unique morphology of the carbon nanofibers with an average diameter of ∼45 nm. Such thin and porous carbon fibers allow fast lithium ion transportation.

Synthesis of superior carbon nanofibers with large aspect ratio and tunable porosity for electrochemical energy storage

Porous carbon nanofibers (CNFs) are regarded as essential components of high-performance energy storage devices in the development of renewable and sustainable resources, due to their high surface areas, tunable structures, and good conductivities. Herein, we report new synthesis methods and applications of two types of porous carbon nanofibers, i.e., colloidal mesoporous carbon nanofibers as electrode materials for supercapacitors, and microporous carbon nanofibers as substrate media for lithium–sulfur (Li-S) batteries. These carbon nanofibers can be synthesized either by confined nanospace pyrolysis or conventional pyrolysis of their polymeric precursors. The supercapacitor electrodes which are fabricated via a simple dipping and rinsing approach exhibit a reversible specific capacitance of 206 F g−1 at the current density of 5 A g−1 in 6.0 mol L−1 aqueous KOH electrolyte. Meanwhile, the Li-S batteries composed of microporous carbon nanofiber-encapsulated sulfur structures exhibit unprecedented electrochemical performance with high specific capacity and good cycling stability, i.e., 950 mA h g−1 after 50 cycles of charge–discharge. The excellent electrochemical performance of CNFs is attributed to their high-quality fiber morphology, controlled porous structure, large surface area, and good electrical conductivity. The results show that the carbon nanofibers represent an alternative promising candidate for an efficient electrode material for energy storage and conversion.

Porous Carbons for Carbon Dioxide Capture

Porous carbons play an important role in CO2 adsorption and separation due to their developed porosity, excellent stability, wide availability, and tunable surface chemistry. In this chapter, the synthesis strategies of porous carbon materials and evaluation of their performance in CO2 capture are reviewed. For clarity, porous carbons are mainly classified into the following categories: conventional activated carbons (ACs), renewable-resources-derived porous carbons, synthetic polymer-based porous carbons, graphitic porous carbons, etc. In each category, macroscopic and microscopic morphologies, synthesis principles, pore structures, composition and surface chemistry features as well as their CO2 capture behavior are included. Among them, porous carbons with targeted functionalization and a vast range of nanostructured carbons (carbon nanofibers, CNTs, graphene, etc.) for CO2 capture are being created at an increasing rate and are highlighted. After that, the main influence factors determining CO2 capture performance including the pore features and heteroatom decoration are particularly discussed. In the end, we briefly summarize and discuss the future prospectives of porous carbons for CO2 capture.

Designed porous carbon materials for efficient CO2 adsorption and separation

Abstract The emission of CO 2 from industry and power plants has become a worldwide problem with a strong link to global warming. The development of novel materials for efficient CO 2 capture and utilization is attracting worldwide attention as a hot topic in materials sciences. Among various CO 2 adsorbents, porous carbons have proven competitive by virtue of their high specific surface area, tunable pore and surface structures, moderate heat of adsorption, and less sensitivity to humidity than other CO 2 -philic materials. In this review, we summarize the recent significant advances in porous carbon materials for CO 2 adsorption and separation. Strategies to increase the CO 2 capture capability are highlighted. We also briefly discuss the future prospects of porous carbons for CO 2 capture.

Hollow carbon nanofibers with dynamic adjustable pore sizes and closed ends as hosts for high-rate lithium-sulfur battery cathodes

Designing a better carbon framework is critical for harnessing the high theoretical capacity of Li-S batteries and avoiding their drawbacks, such as the insulating nature of sulfur, active material loss, and the polysulfide shuttle reaction. Here, we report an ingenious design of hollow carbon nanofibers with closed ends and protogenetic mesopores in the shell that can be retracted to micropores after sulfur infusion. Such dynamic adjustable pore sizes ensure a high sulfur loading, and more importantly, eliminate excessive contact of sulfur species with the electrolyte. Together, the high aspect ratio and thin carbon shells of the carbon nanofibers facilitate rapid transport of Li+ ions and electrons, and the closed-end structure of the carbon nanofibers further blocks polysulfide dissolution from both ends, which is remarkably different from that for carbon nanotubes with open ends. The obtained sulfur-carbon cathodes exhibit excellent performance marked by high sulfur utilization, superior rate capability (1,170, 1,050, and 860 mA·h·g−1 at 1.0, 2.0, and 4.0 C (1 C = 1.675 A·g−1), respectively), and a stable reversible capacity of 847 mA·h·g−1 after 300 cycles at a high rate of 2.0 C.