Defect-rich porous graphitic phase carbon nitride layer grafted MXene as desolvation promoter for efficient sulfur conversion in extremely harsh conditions.

Lithium-sulfur (Li-S) batteries exhibit superior theoretical capacity and energy density but are still hindered by the sluggish redox conversion kinetic of lithium polysulfides arising from the significant desolvation barrier, especially under high current density or low-temperature environments. Herein, a two-dimensional (2D) porous graphitic phase carbon nitride/MXene (CN-MX) heterostructure with intrinsic defects was designed via electrostatic adherence and in-situ thermal polycondensation. In the design, the defect-rich CN with abundant catalytic activity and porous structure could efficiently facilitate the lithium polysulfides capture, the dissociation of solvated lithium-ion (Li+), and fast Li+ diffusion. Concurrently, 2D MXene nanosheets with high electronic conductivity could act as charge transport channels and provide electrochemical active sites for sulfur redox reactions. The Li-S cells with CN-MX heterostructure modified separator demonstrated uncommon rate performance (945 mAh/g at 4.0 C) and satisfactory areal capacity (5.5 mAh cm-2 at 0.2 C). Most remarkably, even at 0 °C, the assembled Li-S batteries performed favorable cycle stability (91.6% capacity retention after 100 cycles at 0.5 C) and outstanding rate performance (695 mAh/g at 2.0 C), and superior high loading performance (5.1 mAh cm-2 at 0.1 C). This work offers exciting new insights to enable Li-S batteries to operate in extreme environments.

Controlled Construction of Cobalt-Doped Carbon Nanofiber-Carbon Nanotubes as a Freestanding Interlayer for Advanced Lithium-Sulfur Batteries.

The major challenges for the realistic application of lithium-sulfur batteries (LSBs) lie in the great difficulties in breaking through the obstacles of the sluggish kinetics and polysulfides shuttle of the sulfur cathode at high sulfur loading for continuous high sulfur utilization during prolonged charge-discharge cycles. Herein, cobalt-doped carbon nanofibers containing carbon nanotubes (Co@CNF-CNT) were prepared via electrospinning and chemical vapor deposition (CVD) methods while using polyacrylonitrile (PAN) as the carbon source and cobalt nanoparticles as the catalyst. The obtained uniform thickness film with high mechanical strength can be cut and used directly as a functional freestanding interlayer for LSBs. The appearance of one-dimensional "dendritic" carbon nanotubes on the surface of carbon nanofibers not only enhanced the capture ability of lithium polysulfide (LPSs) but also further improved the conductivity of the materials and increased the electron transport path for Li2S deposition. The results show that under the synergistic effect of porous structure, nitrogen doping, cobalt nanoparticles, and high-conductivity carbon nanotubes, the Co@CNF-CNT interlayer can effectively raise the polysulfide adsorption and conversion efficiency, and provide remarkable rate performance and excellent cycling stability even at high sulfur mass loading. The LSBs with Co@CNF-CNT interlayer have a discharge capacity of 656 mAh g-1 at a high rate of 3C, and the capacity decay rate at 1C after 1000 cycles was only 0.045% per cycle. When fitted with a high sulfur loading cathode of 5.3 mg cm-2, the battery could still maintain a discharge capacity as high as 0.045% mAh g-1 after 70 cycles at 0.2C.

Vanadium as Auxiliary for Fe-V Dual-Atom Electrocatalyst in Lithium-Sulfur Batteries: "3D in 2D" Morphology Inducer and Coordination Structure Regulator.

The undesirable shuttling behavior, the sluggish redox kinetics of liquid-solid transformation, and the large energy barrier for decomposition of Li2S have been the recognized problems impeding the practical application of lithium-sulfur batteries. Herein, inspired by the spectacular catalytic activity of the Fe/V center in bioenzyme for nitrogen/sulfur fixation, we design an integrated electrocatalyst comprising N-bridged Fe-V dual-atom active sites (Fe/V-N7) dispersed on ingenious "3D in 2D" carbon nanosheets (denoted as DAC), in which vanadium induces the laminar structure and regulates the coordination configuration of active centers simultaneously, realizing the redistribution of the 3d-orbital electrons of Fe centers. The high coupling/conjunction between Fe/V 3d electrons and S 2p electrons shows strong affinity and enhanced reactivity of DAC-Li2Sn (1 ≤ n ≤ 8) systems. Thus, DAC presents strengthened chemisorption ability toward polysulfides and significantly boosts bidirectional sulfur redox reaction kinetics, which have been evidenced theoretically and experimentally. Besides, the well-designed "3D in 2D" morphology of DAC enables uniform sulfur distribution, facilitated electron transfer, and abundant active sites exposure. Therefore, the assembled Li-S cells present outstanding cycling stability (637.3 mAh g-1 after 1000 cycles at 1 C) and high rate capability (711 mAh g-1 at 4 C) under high sulfur content (70 wt %).

Understanding structure-performance relationships of CoOx/CeO2 catalysts for NO catalytic oxidation: Facet tailoring and bimetallic interface designing.

Crystalline structure and bimetallic interaction of metal oxides are essential factors to determine the catalytic activity. Herein, three different CoOx/CeO2 catalysts, employing CeO2 nanorods (predominately exposed {110 facet), CeO2 nanopolyhedra ({111} facet) and CeO2 nanocubes ({100} facet) as the supports, are successfully prepared for investigating the effect of exposed crystal facets and bimetallic interface interaction on NO oxidation. In comparison with the {111} and {100} facets, the exposed crystal facet {110} exists the best superiority to anchor and stabilize Co species. Moreover, ultra-small CoOx clusters composed of strong Co-O coordination shells with minor Co-O-Ce interaction are formed and uniformly dispersed on the CeO2 nanorods. Structural characterizations reveal that the active exposed crystal facet {110} and the strong bimetallic interface interaction in CoOx/CeO2-nanorods (R-CC) result in more structural defect, endowing it with abundant oxygen vacancies, excellent reducibility and strong adsorption capacity. The DRIFTs spectra further indicate that the exposed crystal facet {110} has a significant promoting effect on the strength of nitrates compared with {111} and {100} facets. The bimetallic interface interaction not only significantly facilitates the formation of nitrate species at lower temperature, but also effectively suppresses the generation of sulfate and lower the sulphation rate. Therefore, R-CC catalyst exhibits the maximum NO oxidation activity with the conversion of 86.4 % at 300 °C and still sustains its high activity under cyclic condition or 50 ppm SO2. The provided crystalline structure and interaction-enhanced strategy sheds light on the design of high-activity NO oxidation catalysts.

Low-Temperature Selective Catalytic Reduction of NO x with NH3 over Mn-Ce Composites Synthesized by Polymer-Assisted Deposition.

The Mn x Ce y binary catalysts with a three-dimensional network structure were successfully prepared via a polymer-assisted deposition method using ethylenediaminetetraacetic acid and polyethyleneimine as complexing agents. The developed pore structure could facilitate the gas diffusion and accelerate the catalytic reaction for NH3 selective catalytic reduction (SCR). Moreover, the addition of Ce is beneficial for the exposure of active sites on the catalyst surface and increases the adsorption of the NH3 and NO species. Therefore, the Mn1Ce1 catalyst exhibits the best catalytic activity for NO x removal with a conversion rate of 97% at 180 °C, superior water resistance, and favorable stability. The SCR reaction over the Mn1Ce1 catalyst takes place through the E-R pathway, which is confirmed by the in situ diffuse reflectance Fourier transform analysis. This work explores a new strategy to fabricate multimetal catalysts and optimize the structure of catalysts.

Construction of mesoporous carbon microsphere/polyaniline composites as high performance pseudocapacitive electrodes.

Mesoporous carbon microspheres (MCMs), as a supercapacitor electrode material, have good gravimetric capacitance and rate performance; however, their low volumetric capacitance, which results from their low density, restricts their application as a micro power source. Herein, polyaniline was introduced into the channels of MCMs to achieve a synergistic effect and significantly increase the volumetric capacitance. MCMs with a high surface area and pore volume allowed the uniform dispersion of PANI within their channels in nanoscale dimensions. The interconnected carbon framework could provide excellent electrical conductivity and alleviate the structural collapse of PANI. Moreover, PANI could function not only as an active pseudocapacitive material that facilitated energy storage but also as a proton transport media that promoted a rapid protonation/deprotonation process during the redox reaction in the internal channels. As a result, PANI/MCM composites, even with a poor pore structure, delivered a high volumetric capacitance of 539F cm-3 at 1 A g-1 and an excellent rate performance of 83% at current densities ranging from 0.5 to 20 A g-1. In addition, PANI/MCM composites exhibited good cycling stability, retaining 84% of the capacitance after 1000 charge/discharge cycles at 1 A g-1, owing to the high mechanical strength of the MCMs. Therefore, this synthesis strategy could provide an efficient and scalable solution for the development of supercapacitor electrode materials.

Preparation of Mesoporous Mn-Ce-Ti-O Aerogels by a One-Pot Sol-Gel Method for Selective Catalytic Reduction of NO with NH3.

Novel Mn-Ce-Ti-O composite aerogels with large mesopore size were prepared via a one-pot sol-gel method by using propylene oxide as a network gel inducer and ethyl acetoacetate as a complexing agent. The effect of calcination temperature (400, 500, 600, and 700 °C) on the NH3-selective catalytic reduction (SCR) performance of the obtained Mn-Ce-Ti-O composite aerogels was investigated. The results show that the Mn-Ce-Ti-O catalyst calcined at 600 °C exhibits the highest NH3-SCR activity and lowest apparent activation energy due to its most abundant Lewis acid sites and best reducibility. The NO conversion of the MCTO-600 catalyst maintains 100% at 200 °C in the presence of 100 ppm SO2, showing the superior resistance to SO2 poisoning as compared with the MnOx-CeO2-TiO2 catalysts reported the literature. This should be mainly attributed to its large mesopore sizes with an average pore size of 32 nm and abundant Lewis acid sites. The former fact facilitates the decomposition of NH4HSO4, and the latter fact reduces vapor pressure of NH3. The NH3-SCR process on the MCTO-600 catalyst follows both the Eley-Rideal (E-R) mechanism and the Langmuir-Hinshelwood (L-H) mechanism.

Insights into the promotion role of phosphorus doping on carbon as a metal-free catalyst for low-temperature selective catalytic reduction of NO with NH3.

The catalytic reduction of NO with NH3 (NH3-SCR) on phosphorus-doped carbon aerogels (P-CAs) was studied in the temperature range of 100-200 °C. The P-CAs were prepared by a one-pot sol-gel method by using phosphoric acid as a phosphorus source followed by carbonization at 600-900 °C. A correlation between catalytic activity and surface P content is observed. The P-CA-800vac sample obtained via carbonization at 800 °C and vacuum treatment at 380 °C shows the highest NO conversion of 45.6-76.8% at 100-200 °C under a gas hourly space velocity of 500 h-1 for the inlet gas mixture of 500 ppm NO, 500 ppm NH3 and 5.0 vol% O2. The coexistence of NH3 and O2 is essential for the high conversion of NO on the P-CA carbon catalysts, which can decrease the spillover of NO2 and N2O. The main Brønsted acid sites derived from P-doping and contributed by the C-OH group at edges of carbon sheets are beneficial for NH3 adsorption. In addition, the C3-P[double bond, length as m-dash]O configuration seems to have the most active sites for favorable adsorption and dissociation of O2 and facilitates the formation of NO2. Therefore, the simultaneous presence of acidic groups for NH3 adsorption and the C3-P[double bond, length as m-dash]O active sites for NO2 generation due to the activation of O2 molecules is likely responsible for the significant increase in the NH3-SCR activity over the P-CAs. The transformation of C3-P[double bond, length as m-dash]O to C-O-P functional groups after the reaction is found, which could be assigned to the oxidation of C3-P[double bond, length as m-dash]O by the dissociated O*, resulting in an apparent decrease of catalytic activity for P-CAs. The C-O-P based functional groups are also active in the NH3-SCR reaction.

Oxygen vacancies enhance the lithium ion intercalation pseudocapacitive properties of orthorhombic niobium pentoxide.

While orthorhombic niobium pentoxide (T-Nb2O5) is one of the most promising energy storage material with rapid lithium ion (Li+) intercalation pseudocapacitive response, a key challenge remains the achievement of high-rate charge-transfer reaction when fabricated into thick electrodes. Herein, we report a facile method to create intrinsic defects in T-Nb2O5 through a hydrogen (H2) reduction, which is effective to overcome the limitations of electrochemical utilization and rate capability. Due to the high number of active sites introduced, the specific capacity of hydrogenated (H-) Nb2O5 with oxygen vacancies reaches 649 C g-1 at 0.5 A g-1, greatly exceeding that of T-Nb2O5 which is 580 C g-1. In addition, theformation of oxygen vacancies leads to increased donor density and enhanced electrical conductivity, which accelerates charge storage kinetics and enables excellent long-term cycling stability (86% retention after 2000 cycles). The analysis of electrochemical impedance spectroscopy (EIS) plots and the calculation of Li+ diffusion coefficients (DLi) further explains the high rate-performance of H-Nb2O5. When the electrode thickness increased to 150 µm, the H-Nb2O5 still delivers excellent electrochemical properties. Therefore, the introduction of oxygen vacancies provides a new method towards the improvement of the electrochemical properties of various transition metal oxides.

Construction of Mn-Zn binary carbonate microspheres on interconnected rGO networks: creating an atomic-scale bimetallic synergy for enhancing lithium storage properties.

Transition metal carbonates (TMCs), as promising anode materials for high-performance lithium ion batteries, possess the advantages of abundant natural resources and high electrochemical activity; however, they suffer from poor Li+/e- conductivities and serious volume changes during the charge/discharge process. Constructing multicomponent carbonates by introducing binary metal atoms, as well as designing a robust structure at the micro and nanoscales, could efficiently address the above problems. Therefore, single-phase MnxZn1-xCO3 microspheres anchored on 3D conductive networks of reduced graphene oxide (rGO) are facilely synthesized via a one-pot hydrothermal method without any structure-directing agents or surfactants. Due to the well-designed architecture and atomic-scale bimetallic synergy, the MnxZn1-xCO3/rGO composites show superior lithium storage capacity, good rate capability and ultra-long cycling performance. Specifically, the Mn2/3Zn1/3CO3/rGO composites could deliver a high capacity of 1073 mA h g-1 at 200 mA g-1. After 1700 cycles at a high rate of 2000 mA g-1, a stable capacity of 550 mA h g-1 can be maintained with the capacity retention approaching 88.6%. Density functional theory (DFT) calculations indicate that the partial Zn substitution in MnCO3 could significantly decrease the band gap of the crystal, resulting in great improvement of electric conductivity. Moreover, the commercial potential of the MnxZn1-xCO3/rGO composites is investigated by assembling full cells, suggesting good practical adaptability of the composite anodes. This work would provide a feasible and cost-efficient method to develop high-performance anodes and stimulate many more related research studies on TMC-based electrodes.

Controllable synthesis of mesoporous carbon microspheres with renewable water glass as a template for lithium-sulfur batteries.

Mesoporous carbon microspheres (MCMs) were prepared via a spray drying-assisted template method using resorcinol-formaldehyde as the carbon precursor and water glass as the template. The pore structure could be controlled by adjusting the hydrolysis time, hydrolysis temperature, concentration of the water glass and reactant ratio. Water glass could be recycled after use, making this strategy environmentally friendly and cost-effective. MCMs with three-dimensional interconnected networks, high surface area (852-1549 m2 g-1), large pore volume (1.7-2.1 cm3 g-1) and controllable pore diameter (3.8-15.1 nm) were constructed and have good electrical conductivity and a large volume for sulfur loading. The S/MCM composites with abundant residual nanochannels could not only benefit for the diffusion of electrolyte but also improve the utilization of sulfur and buffer the volume expansion of sulfur. The MCMs with relatively small mesopores manifest a high reversible capacity and rate performance owing to the strong confinement effect of polysulfides. MCM-1 delivered an initial capacity of 888.7 mA h g-1 under 0.5C with a capacity retention of 700.5 mA h g-1 after 100 cycles. The good electrochemical performance confirms that mesoporous carbon microspheres can be an excellent host material for sulfur cathodes.

Fabrication of hierarchical carbon nanosheet-based networks for physical and chemical adsorption of CO2.

A hierarchical carbon nanosheet-based networks (GPC) with controllable pore structure are developed for physical adsorption and chemical adsorption of CO2. The synthesis employs graphene oxide (GO) nanosheet as the structure-directing agent, cetyltrimethyl ammonium bromide (CTAB) as the soft template and melamine as the bridging molecule. The individual GO nanosheet is uniformly coated with the in-situ chemical polymerization of resorcinol-formaldehyde-melamine (RMF) polymers via electrostatic interaction with melamine. Thus, micropores with high specific surface area is developed from the cross-linked networks of polymers after carbonation and KOH activation, which is beneficial to the physical adsorption of CO2 at low temperature. CTAB as a soft template could induce the assembly of GO to form a "ring-like" stacking three-dimensional structure, producing macropores and mesopores with high pore volume after carbonization which could act as novel reservoirs to host a high loading amount of amine with good dispersion for CO2 chemical adsorption at elevated temperature. After activation with KOH, the specific surface area is up to 1555.7 m2/g, with CO2 physical adsorption capacity of 4.62 mmol/g under 273 K and 1 bar. After loading PEI of 75%, the CO2 chemical adsorption capacity achieves 5.52 mmol/g under 75 °C. The outstanding advantages of hierarchical carbon nanosheet-based networks, including their macro-meso-microporous structures, fast diffusion kinetics, excellent adsorptivity and easy synthesis, endow them with good potential to be used in a wide range of applications.

Free-standing carbon nanofiber fabrics for high performance flexible supercapacitor.

Free-standing carbon nanofiber fabrics with high surface area and good flexibility were prepared via a combined electrospinning and nanocasting method using low molecular weight phenolic resol as carbon precursor and partial-hydrolyzed tetraethyl orthosilicate as template, followed by carbonization and silica removal. The key to our strategy lies in the formation of a stable electrospinning solution derived from the polycondensation of partial-hydrolyzed TEOS in mild hydrolysis with low molecular phenolic resol and PVB which could decrease the gelation rate to benefit for the steady electrospinning process of preparing large area hybrid nanofiber fabrics. The obtained carbons possess high specific surface area up to 2292 m2/g with a large pore volume of 1.02 cm3/g. As flexible electrodes, these carbon nanofiber fabrics could deliver high specific capacitance up to 274 F/g at 0.1 A/g in H2SO4 electrolyte and 220 F/g at 0.5 A/g in solid-state supercapacitor with good rate and cyclic performance. These outstanding advantages of carbon nanofiber fabrics, including their well-developed microporosity, easily tailored pore structure, good mechanical strength and flexibility, endow them with great potential for application in flexible energy storage devices.

Nanocrystalline celluloses-assisted preparation of hierarchical carbon monoliths for hexavalent chromium removal.

Hierarchical porous carbon monoliths with a 3D framework were synthesized through a facile sol-gel process using resorcinol-melamine-formaldehyde (RMF) as carbon precursors, and nanocrystalline celluloses (NCCs) as the structural inducing agent, followed by ambient pressure drying and carbonization. Polymerization of the RMF resin occurs around the nanorod-like NCCs dispersed homogeneously in water, which is quite beneficial for the formation of an interconnected network and supports the rigid macroporous structure. A hierarchical porous carbon monolith with modest micropores and well-developed macropores was prepared after CO2 activation at 950°C. The microporous structure was generated from the network of RMF polymer chains, while the macroporous structure was formed from the interconnection of polymer networks induced by NCCs. The obtained carbon monolith has a large specific surface area of 1808m2g-1 and shows a high adsorption capacity of 463mgg-1 for toxic Cr(VI) ions. Moreover, the activated carbon monolith exhibits a high selectivity for Cr(VI) in the coexistence of several other metal ions. These outstanding advantages of carbon monoliths, including their micro/macroporous structures, rich functional groups, low cost and easy synthesis, endow them with potential for use in a wide range of applications.

A General Silica-Templating Synthesis of Alkaline Mesoporous Carbon Catalysts for Highly Efficient H2S Oxidation at Room Temperature.

A general synthesis of alkaline mesoporous carbons (AMCs) is developed based on a simplified silica-templating method for room-temperature catalytic oxidation of H2S. The key to the success relies on dissolving the silica templates to create the interconnected mesoporous structure as well as leaving parts of the alkaline products in the pores; both of them are prerequisites for H2S oxidation. By adjusting the alkaline etching degree and organic/inorganic ratio, the porosity and basicity of the AMC could be simultaneously tuned, allowing the AMCs direct use for H2S catalytic oxidation with an unprecedented removal capacities of 4.49 ± 0.12 g/g. Such excellent catalytic performance should be attributed to the developed pore structure that stores the product sulfur and the strong basicity that promotes the dissociation of H2S into HS- ions. Moreover, this simplified silica-templating method could be easily extended to the preparation of various silica templated mesoporous carbon catalysts. All these AMCs demonstrate a successful combination of low cost with high performance, which may well be the answer for the technical development of industrial H2S removal.

Template-free synthesis of nitrogen-doped hierarchical porous carbons for CO2 adsorption and supercapacitor electrodes.

Nitrogen-doped hierarchical porous carbons (NHPCs) with controllable nitrogen content were prepared via a template-free method by direct carbonization of melamine-resorcinol-terephthaldehyde networks. The synthetic approach is facile and gentle, resulting in a hierarchical pore structure with modest micropores and well-developed meso-/macropores, and allowing the easy adjusting of the nitrogen content in the carbon framework. The micropore structure was generated within the highly cross-linked networks of polymer chains, while the mesopore and macropore structure were formed from the interconnected 3D gel network. The as-prepared NHPC has a large specific surface area of 1150m2·g-1, and a high nitrogen content of 14.5wt.%. CO2 adsorption performances were measured between 0°C and 75°C, and a high adsorption capacity of 3.96mmol·g-1 was achieved at 1bar and 0°C. Moreover, these nitrogen-doped hierarchical porous carbons exhibit a great potential to act as electrode materials for supercapacitors, which could deliver high specific capacitance of 214.0F·g-1 with an excellent rate capability of 74.7% from 0.1 to 10 A·g-1. The appropriate nitrogen doping and well-developed hierarchical porosity could accelerate the ion diffusion and the frequency response for excellent capacitive performance. This kind of new nitrogen-doped hierarchical porous carbons with controllable hierarchical porosity and chemical composition may have a good potential in the future applications.

Catalytic Graphitization of Coal-Based Carbon Materials with Light Rare Earth Elements.

The catalytic graphitization mechanism of coal-based carbon materials with light rare earth elements was investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy. The interface between light rare earth elements and carbon materials was carefully observed, and two routes of rare earth elements catalyzing the carbon materials were found: dissolution-precipitation and carbide formation-decomposition. These two simultaneous processes certainly accelerate the catalytic graphitization of carbon materials, and light rare earth elements exert significant influence on the microstructure and thermal conductivity of graphite. Moreover, by virtue of praseodymium (Pr), it was found that a highly crystallographic orientation of graphite was induced and formed, which was reasonably attributed to the similar arrangements of the planes perpendicular to (001) in both graphite and Pr crystals. The interface between Pr and carbon was found to be an important factor for the orientation of graphite structure.

Nanoarchitectured Nb2O5 hollow, Nb2O5@carbon and NbO2@carbon Core-Shell Microspheres for Ultrahigh-Rate Intercalation Pseudocapacitors.

Li-ion intercalation materials with extremely high rate capability will blur the distinction between batteries and supercapacitors. We construct a series of nanoarchitectured intercalation materials including orthorhombic (o-) Nb2O5 hollow microspheres, o-Nb2O5@carbon core-shell microspheres and tetragonal (t-) NbO2@carbon core-shell microspheres, through a one-pot hydrothermal method with different post-treatments. These nanoarchitectured materials consist of small nanocrystals with highly exposed active surface, and all of them demonstrate good Li(+) intercalation pseudocapacitive properties. In particular, o-Nb2O5 hollow microspheres can deliver the specific capacitance of 488.3 F g(-1), and good rate performance of 126.7 F g(-1) at 50 A g(-1). The o-Nb2O5@carbon core-shell microspheres show enhanced specific capacitance of 502.2 F g(-1) and much improved rate performance (213.4 F g(-1) at 50 A g(-1)). Furthermore, we demonstrate for the first time, t-NbO2 exhibits much higher rate capability than o-Nb2O5. For discharging time as fast as 5.9 s (50 A g(-1)), it still exhibits a very high specific capacitance of 245.8 F g(-1), which is 65.2% retention of the initial capacitance (377.0 F g(-1) at 1 A g(-1)). The unprecedented rate capability is an intrinsic feature of t-NbO2, which may be due to the conductive lithiated compounds.

Organic Amine-Mediated Synthesis of Polymer and Carbon Microspheres: Mechanism Insight and Energy-Related Applications.

A general organic amine-mediated synthesis of polymer microspheres is developed based on the copolymerization of resorcinol, formaldehyde, and various organic amines at room temperature. Structure formation and evolution of colloidal microspheres in the presence of polyethylenimine are monitored by dynamic light scattering measurements. It is found that the colloidal clusters are formed instantaneously and then experience an anomalous shrinkage-growth process. This should be caused by two different reaction pathways: cross-linking inside the microspheres and step-growth polymerization of substituted resorcinol on the microsphere surface, leading to the formation of core-shell heterogeneous structures as confirmed by TEM observation and XPS analysis. A formation mechanism of polymer microspheres is provided based on the aggregation of polyethylenimine/resorcinol-formaldehyde (PEI-RF) self-assembled nuclei, which is apparently different from the conventional Stöber process. Furthermore, nitrogen-doped carbon microspheres are prepared by the direct carbonization of these polymer microspheres, which exhibit microporous BET surface areas of 400-500 m(2) g(-1), high nitrogen contents of 5-6 wt %, and a good CO2 adsorption capacity up to 3.6 mmol g(-1) at 0 °C. KOH activation is further employed to develop the porous texture of carbon microspheres without sacrificing the spherical morphology. The resultant activated carbon microspheres exhibit small particle size (<80 nm), high BET surface areas of 1500-2000 m(2) g(-1), and considerable nitrogen content of 2.2-2.0 wt %. When used as the electrode materials for supercapacitors, these activated carbon microspheres demonstrate a high capacitance up to 240 F g(-1), an unprecedented rate performance and good cycling performance.

Effective removal of hexavalent chromium from aqueous solutions by adsorption on mesoporous carbon microspheres.

High-surface-area mesoporous carbon microspheres were successfully synthesized by a spraying method with the purpose of removing Cr(VI) from waste water. Various factors influencing the adsorption of Cr(VI), including pH, adsorption temperature, and contact time were studied. As the adsorption process was pH dependent, it showed maximum removal efficiency of Cr(VI) at pH 3.0. Pseudo-second-order model was found to best represent the kinetics of Cr(VI) adsorption. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models, and Qm value was as high as 165.3mg/g. The thermodynamic parameters including standard Gibb's free energy (ΔG(0)), standard enthalpy (ΔH(0)) and standard entropy (ΔS(0)) were investigated for predicting the nature of adsorption, which suggested the adsorption was an endothermic and a spontaneous thermodynamically process. Furthermore, Fe3O4-loaded MCMs were prepared to rapidly separate the adsorbent from the solution by a simple magnetic process. Fe3O4-loaded MCMs had a high adsorption capacity of 156.3mg/g, and a good regeneration ability with a capacity of 123.9mg/g for the fifth adsorption-desorption cycle.