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

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Organic Amine-Mediated Synthesis of Polymer and Carbon Microspheres: Mechanism Insight and Energy-related Applications Jitong Wang, Liwen Yao, Cheng Ma , Xuhong Guo, Wenming Qiao, Licheng Ling, and Donghui Long ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b11178 • Publication Date (Web): 29 Jan 2016 Downloaded from http://pubs.acs.org on February 5, 2016

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ACS Applied Materials & Interfaces

Organic Amine-Mediated Synthesis of Polymer and Carbon Microspheres: Mechanism Insight and Energy-related Applications Jitong Wang, Liwen Yao, Cheng Ma, Xuhong Guo, Wenming Qiao, Licheng Ling and Donghui Long*

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

* Corresponding author: Donghui Long, Tel: +86-21-64252924. Fax: +86-21-64252914.

E-mail: [email protected]

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ABSTRACT

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 microsphere 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 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 m2·g-1, high nitrogen contents of 5-6 wt. % and a good CO2 adsorption capacity up to 3.6 mmol·g-1 at 0 oC. 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 m2·g-1 and considerable nitrogen content of 2.2-2.0 wt. %. When used as the electrode materials for supercapacitor, these activated carbon microspheres demonstrate a high capacitance up to 240 F·g-1, an unprecedented rate performance and good cycling performance.

Keywords: polymer microsphere; carbon microsphere; formation mechanism; CO2 adsorption; supercapacitor


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INTRODUCTION

Porous carbon materials have been energetically researched for numerous applications such as gas storage and separation, electrochemical capacitors, drug delivery, catalysis and catalyst supports etc.1-5 In order to extend the range of their applications, numerous strategies have been employed for fine-tuning of physical and chemical properties of these carbonaceous materials.6 While the straightforward path to enhance the performance of these materials involves tailoring the pore structure via physical or chemical activation,

7, 8

recent results indicate that additional improvement can be achieved through surface modification such as the incorporation of nitrogen heteroatoms.9,10 In addition, the morphology and size of the carbons can influence their functionalities, which are also crucial factors for some special applications. For example, a great deal of research has been directed towards the synthesis of porous carbons in the form of microsphere/nanosphere,

11-13

which could combine specific advantages in terms of porosity and colloidal

particles (small size and low viscous effect), thus providing greater pore accessibility and faster molecular diffusion/ transfer. Generally, porous carbon microspheres can be prepared by several approaches including chemical vapor deposition (CVD), emulsion polymerization, hydrothermal carbonization of sugars, templating methodology, and organic-organic self-assembly.14-16 Dong et al. reported a simple polymerization of resorcinol-formaldehyde (RF) using L-lysine as a catalyst to prepare RF polymer.

17

Because of their good

thermal stability and high char yield, these phenolic-type microspheres could be easily converted into carbon microspheres by a simple carbonization. Later, Liu and co-workers reported that the RF polymer microspheres could be obtained using an ammonia catalyst in a water/ethanol solvent.

18

They pointed out

that the polymerization mechanism of RF microspheres was analogous to that described for Stöber synthesis of colloidal silica. Jaroniec et al. further showed that this method could be extended to the preparation of RF 3 ACS Paragon Plus Environment


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microspheres using cysteine, ethylenediamine as the catalysts.19, 20 They found that the nitrogen atoms could be incorporated into the polymer/carbon framework, suggesting the role of the organic amines is beyond providing basic conditions. In our recent work, we found that the co-condensation of melamine (M), resorcinol (R) and formaldehyde (F) could successfully produce homogeneous MRF microspheres with rational ratios of M/R, allowing the tailor of nitrogen content (0-34 wt. %) in the polymer framework.

21,22

So far, many routes based on this modified Stöber synthesis of polymer and carbon microspheres have been investigated towards the precursor molecules, chemical composition, porosity development, and with the aim of specific applications. 23-27 Nevertheless, these basic amines, regardless of their molecular structures played a critical role in the polymer microsphere formation. These amines could serve as the catalysts/precursors to accelerate the polymerization of RF, and may also supply the positive charges that adhere to the outer surface of spheres to prevent the aggregation. Although there exist considerable empirical experience regarding the synthesis of RF polymer microspheres and resultant carbon microspheres,18,28 fundamental understanding of their nanostructure evolution is lacking, and therefore, the ability to rationally tailor their structure for specific applications has been limited. Herein, we systematically studied the effects of organic amine on the formation of polymer/carbon microspheres. Numerous nitrogen-doped polymer microspheres could be successfully prepared by a direct polymerization of resorcinol and formaldehyde in the presence of various organic amines including ethylenediamine (EDA), diethylentriamine (DETA), tetraethylenepentamine (TEPA), hexamethylene diamine (HEDA), piperazidine (PA) and polyethylenimine (PEI). Regard of their molecular structures (linear, branched, ring-shaped, and ultrahigh molecular weight), all these amines could involve into the co-polymerization reaction and induce the formation of polymer microspheres. This confirms that organic


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amine-mediated method is very universal for the synthesis of polymer microspheres. We further addressed the molecular weight effects of branched polyethylenimine (PEI) on the morphology and size of polymer microspheres using Dynamic Light Scattering, to monitor formation of primary clusters and subsequent structure development. A possible self-assembled aggregation mechanism of microsphere formation was provided, which is different with the conventional Stöber process. Furthermore, the nitrogen-doped carbon microspheres were prepared by the carbonization of these nitrogen-enriched polymer microspheres, which demonstrated a good CO2 adsorption capacity. For the further enhancement of the functionality of the carbon microspheres, the KOH activation was employed to develop the porous texture. The resulting activated carbon microspheres were evaluated as electrode materials in supercapacitors exhibiting high specific capacitance, excellent rate performance and good long-term cycling stability. METHODS

Synthesis of Polymer and Carbon Micropheres

Nitrogen containing polymer spheres (PMSs) were synthesized through an organic-amine mediated co-polymerization method, using resorcinol and formaldehyde as carbon source in the presence of different amine compounds. In a typical synthetic procedure, desired amount of amine was dissolved in an aqueous-alcoholic solution (mixing 64 mL of ethanol and 160 mL of distilled water). Subsequently, 4.8 g resorcinol (R) was added in the above solution with consecutive agitation. Next, 7.2 g 37 wt. % formaldehyde (F) was added and stirred for 24 h at a room temperature. The obtained reaction mixture was transferred to a sealed bottle and heated at 80 °C thermostatic water bath for 24 h. Then, the upper liquor of the obtained mixture was removed and the remains were directly dried at 50 °C oven in an ambient condition.



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In this work, the nitrogen-doped polymer spheres were synthesized with different amine compounds: ethylenediamine, diethylentriamine, tetraethylenepentamine, hexamethylene diamine, piperazidine and polyethylenimine, which will be referred to EDA, DETA, TEPA, HEDA, PA and PEI, respectively. Meanwhile, the effect of molecular weight of PEI (average molecular weight of 600 g·mol-1, 1200 g·mol-1, 1800 g·mol-1 and 10000 g·mol-1) on the morphologies and structure of the resulting nitrogen-doped polymer spheres were investigated in detail. The resulting PMS was labelled as PMS-x, where “PMS” refers to polymer microsphere, “x” denotes the molecular mass of amine (1, 2, 3 and 4 refer to the molar weight of PEI used, which are 600 g·mol-1, 1200 g·mol-1, 1800 g·mol-1 and 10000 g·mol-1, respectively). For example, in the case of the PMS-3 sample, PMS and 3 refer to polymer sphere and the molecular weight of PEI used is 1800 g·mol-1. In order to obtain nitrogen-contained carbon microspheres (CMSs), the obtained N-doped PMSs were pyrolyzed at 800 °C for 2 h with a heating rate of 3 °C/min under nitrogen flow. The resulting carbon microspheres were labelled as CMS-x, whereas “CMS” refers to carbon microspheres, the remaining pare of the sample notation is the same as in the case of PMS (see above). To further develop pore structure, the activation of carbon spheres was performed by placing a quartz boat with moderate CMSs mixed with KOH in a tube furnace under flowing nitrogen with a heating rate of 3 °C/min up to 800 °C and retained for 2h. The obtained activated materials are denoted as ACMS-x-y, where “ACMS” refers to activated carbon microspheres, “x” denotes the molecular mass of amine (see above), “y” denotes the mass ratios of KOH to carbon.

Characterization of PMS, CMS and ACMS

The morphology and microstructure of the synthesized microspheres were characterized by scanning electron microscopy (SEM, JEOL-6300F) and Transmission Electron Microscopy (TEM, JEOL-2100F). 6 ACS Paragon Plus Environment

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The porosity was measured with nitrogen adsorption-desorption isotherm at liquid nitrogen temperature (77 K) using a surface area analyser (Quadrasorb SI). Prior to the measurements, the samples were degassed in vacuum at 473 K for 12 h. Pore size distributions (PSD) were calculated from nitrogen adsorption data by the QS-DFT method. Elemental analysis was carried out using an Elemental Vario EL III. The carbon (C), hydrogen (H), and nitrogen (N) contents of the carbons were determined directly using the thermal conductivity detector. FT-IR spectra were collected on a Bruker-Vertex 70 FTIR spectrometer in the frequency range of 4000-500 cm-1, using KBr pellets of the solid samples. XPS (X ray Photoelectron Spectroscopy) measurements were carried out on a VG Microtech ESCA 2000 using a monochromic Al X-ray source (97.9 W, 93.9 eV). The N 1s XPS signals were fitted with mixed Lorentzian-Gaussian curves, and a Shirley function was used to subtract the background using an XPS peak processing software. In Dynamic Light Scattering (DLS) experiments, the prepared solutions were poured into cleaned glass cells with PTFE caps. The cells were settled in the light scattering apparatus (ALV/CGS-5022F) at 25 oC during the measurement. The hydrodynamic sizes of colloidal particles were measured using a digital correlator. The wavelength of incident laser light was k = 632.8 nm and the scattering angle θ was 90 o. The Zeta potential of the solutions was measured by the Zeta sizer (Nano-ZS) from Malvern Instruments and analyzed by Dispersion Technology Software (DTS). Before testing, the solution was stirred using magnetic stirrer for 30 min. Subsequently, the homogeneous solution were injected into the folded capillary cells and analyzed for zeta potential. All measurements were conducted at 273 K. CO2 adsorption isotherms at 273 K under dry conditions were evaluated with a Quadrasorb SI analyser. Before each adsorption experiment, the materials were degassed at 473 K for 12 h to remove the guest molecules in the pores. The CO2 adsorption capacity was recorded in terms of mmol·g-1.

Electrochemical Measurements 7 ACS Paragon Plus Environment


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To prepare the capacitor electrodes, the ACMS and CMS powder (85 wt. %) were mixed with poly(tetrafluoroethlyene) (PTFE, 5 wt. %) and acetylene black (10 wt. %) homogenized in a mortar and pestle, then rolled into a thin film of uniform thickness, and finally punched into pellets. Each electrode has a thickness of ~70 µm with a mass loading of 6-8 mg·cm-2. Electrochemical experiments were carried out with traditional two-electrode configuration in 3 M H2SO4. The cyclic voltammetry in a potential window between 0 and 0.9 V and electrochemical impedance spectroscopy in a frequency range from 100 kHz to 10 mHz were performed with an electrochemical working station PCI4/300 (Gamry Instrument). The galvanostatic charge-discharge test was conducted using an Arbin battery cycler (Arbin BT2000).

RESULTS AND DISCUSSION

Preparation of polymer microspheres

A series of nitrogen-containing phenolic polymer microspheres were synthesized by co-polymerization of resorcinol, formaldehyde and various organic amines (EDA, DETA, TEPA, HEDA, PA and PEI) using ethanol-water as a mixed solvent at 30 °C. Figure 1 shows the typical molecular structure of organic amines and resultant SEM images of these polymer microspheres synthesized at same molar ratio of amine group/resorcinol (A/R=1.4). In all cases, spherical particles with relatively narrow particle size distribution are observed. Particle size distribution of selected polymer microspheres (PEI-1800) is shown in Figure S1. It reveals that the particle size distribution is narrow with an average size of 122 nm. The CHN elemental results of these polymer microspheres are listed in Table S1, which reveal the obtained nitrogen contents in the microspheres are very close to the theoretical values that designed by the precursor chemistry. Therefore,


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all these organic amines should be well involved in the polymerization reaction and induce the formation of microspheres, despite their apparently different molecular structures.

Figure 1. Molecular structure of organic amines used (a) and resultant SEM images of PMSs synthesized with different amines; (b) EDA, (c) PEI-1800, (d) PA, (e) HEDA, (f) DETA and (g) TEPA. Among these organic amines, PEI (Mw 1800 g·mol-1) with branched polymeric structure seems to be the best choice due to the formation of relatively small and well-dispersed microspheres. To further illuminate the influence of different parameters in the formation of PEI-mediated microspheres, the effects of the molar ratio of the amine group in PEI/resorcinol (PEI/R), reaction concentration and reaction temperature are investigated. The SEM images of these PMSs are shown in Figure S2, which demonstrate that well dispersed PMSs can be obtained at a reaction temperature ranging from 25 to 70 °C and with a relatively wide reactant concentration (3-7 wt.%) and a wide precursor composition (PEI/R=0.5-1.5). It is interesting 9 ACS Paragon Plus Environment


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to note that the experimental parameters mentioned above have slight effects on the morphology, which means relatively homogeneous microspheres can be obtained in a wide range of experimental operations.

Figure 2. SEM images of PMSs synthesized with branched PEI; (a) PMS-1, (b) PMS-2, (c) PMS-3 and (d) PMS-4.

To facile the study of the formation mechanism of microspheres, we focused on polymeric PEI which have branched structure with adjustable molecular weights. Four forms of branched PEI, with the molecular weight of 600 g·mol-1, 1200 g·mol-1, 1800 g·mol-1 and 10000 g·mol-1 were evaluated. These PEI are polymers with repeating unit composed of primary, secondary and tertiary amino groups. The SEM images of the as-obtained PEI-mediated polymer microspheres (PMSs) are shown in Figure 2. Except for PEI-10000, all samples show nano-spherical morphology with good dispersion. An increase in the PEI molecular weight from 600 to 1200 and 1800 g·mol-1 causes a gradual decrease in the average particle size 10 ACS Paragon Plus Environment

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of 280, 190 and 120 nm, respectively. A further increase in the PEI molecular weight of 10000 g·mol-1 result in colloid-like polymer particles with sizes only around 20-30 nm. Table 1. Chemical composition of PEI-mediated PMSs obtained from elemental analysis and XPS results

Elements analysis

XPS analysis

Samples N (wt.

C (wt.

O (wt.

N/C

N

C

O

N/C

%)

%)

%)

(at./at.)

(wt.%)

(wt.%)

(wt.%)

(at./at.)

PMS-1

9.6

58.2

25.1

0.14

2.9

73.7

23.4

0.03

PMS-2

9.7

58.0

26.1

0.14

3.4

74.2

22.7

0.04

PMS-3

9.8

57.7

26.6

0.15

4.5

74.1

21.4

0.05

PMS-4

9.9

58.7

25.2

0.14

6.9

72.7

20.3

0.08

The chemical structure of these PEI-mediated microspheres could be revealed using CHN analysis, FTIR spectroscopy and XPS spectra. The element compositions of these PEI-mediated PMSs are listed in Table 1. All samples have similar CHN composition with nitrogen content of 9.7 wt. %, being close to the calculated amount. This suggests that all the reactants are involved into the polymerization reaction. Figure S2 (a) shows the FTIR spectra for these PMSs, which show similar IR peaks, particularly the stretch peaks of N-H and C-N species regardless of PEI molecular weight. The surface chemistry compositions of these PMSs are analyzed from XPS survey spectra (Figure S3 b-e), which demonstrate the present of C1s, N1s and O1s peak without any undesirable elemental compositions. The surface N contents of these microspheres, however are only 2.5-6.9 wt. % (shown in Table 1), significantly lower than these from CHN analysis. Generally, XPS is a surface-sensitive analysis technique that measures the elemental



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composition from the top 0 to 10 nm of the material.29 This suggests a formation of heterogeneous structure in the microspheres, where the surface should contain fewer nitrogen content than in the bulk. TEM observation could confirm the formation of a core-shell heterogeneous structure. As shown in Figure 3, all polymer microspheres are separated from each other without obvious agglomeration. Moreover, high resolution images clearly demonstrate that each microsphere is consisted of a dark irregular-spherical core in contrast to the relatively bright shell, indicating the core has a higher projected mass density. Combined with XPS results, there is reason to believe that the core is PEI-phenolic phase and the shell is nitrogen-poor phenolic phase.

Figure 3. TEM images of PMSs synthesized with branched PEI; (a-c) PMS-1, (d-f) PMS-3.

Formation mechanism of PEI-mediated polymer microspheres

To understand the chemical processes that take place in the earliest stages of microsphere formation, DLS measurements were used to monitor the formation of primary clusters and development of subsequent 12 ACS Paragon Plus Environment

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structure. The polymeric PEI with branched structure has relatively large hydrodynamic diameter in aqueous solutions, with a mean value of 2.4, 3.0, 4.4 and 7.2 nm for the molecular weight of 600, 1000, 1800 and 10000 g·mol-1 respectively, as list in Table 2. However, the hydrodynamic diameter of a resorcinol molecule cannot be directly measured using our DLS instrument, which is about 0.8 nm according to the molecular simulation calculation.30 After adding the resorcinol into PEI solution (PEI/R mass ratio is fixed), interestingly, the measured hydrodynamic diameters increase regularly to 1.5-3.4 nm, responding to 1-2 layer of resorcinol molecules binding on the surface of a PEI molecule. The results were further verified by the change of Zeta potential of PEI molecule, as shown in Table S2. It can be seen that the Zeta potential change from negative to positive charge, indicating that the resorcinol molecules could link with PEI molecules. Table 2. Hydrodynamic diameter of PEI and R-PEI solution with different molecular weights

hydrodynamic diameter (nm)

molecular weight (Mw) 600

1200

1800

10000

PEI

2.4

3.1

4.4

7.2

R-PEI

3.9

5.0

6.4

10.6



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Figure 4. Transient changes of the size of colloidal particles synthesized with different branched PEI; (a) PMS-1, (b) PMS-2, (c) PMS-3 and (d) PMS-4.

After adding formaldehyde into R-PEI solution, the polymerization reaction was very fast even under a room temperature. As shown in Figure S4, the reaction solution immediately becomes creamy white within 5 s, suggesting the formation of colloidal particles. A series of in-situ DLS experiments were performed to investigate the apparent mean hydrodynamic diameter of primary clusters in more detail. Since experimental preparation and autocorrelation functions of DSL need some time, the initial data can only be recorded from the third minute of the reaction. Figure 4 shows the mean hydrodynamic diameters of the colloidal clusters as a function of reaction time during the early state of microsphere formation. Clearly, the hydrodynamic diameter is essentially dependent on the molecular weight of PEI, which is in good agreement with the SEM 14 ACS Paragon Plus Environment

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results. However, an abnormal shrinkage-growth phenomenon is observed for the microsphere formation. The primary clusters are formed instantaneously after adding formaldehyde and then gradually decrease: e.g. for PEI-600, the diameter reaches 300 nm at 3 min and to a minimum of 200 nm at 17 min, and then follows an increase in size over time. The PEI 1200 and PEI 1800 have a similar variation tendency, but the time to minimal size prolongs gradually with the increase of PEI molecular weight. It needs ca. 27 min for PEI-1200 and 35 min for PEI-1800, and even no inflexion time is observed for PEI-10000 to reach the minimal size. The shrinkage-growth phenomenon can also be observed for other organic amines. As shown in Figure S5, the diameter of colloidal particles synthesized with TEPA gradually decreases to reach a minimum of 429 nm at 18 min, and then increases in size over time. In a controlled experiment, the colloidal silica prepared by a classical Stöber synthesis

31

experience a gradual increase in size with the time (Figure S6), which is

obviously different with the PEI-mediated polymerization process.

Figure 5. Illustration of the preparation of the PMSs synthesized with branched PEI.



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On the basis of the above results, a possible mechanism by which the PEI-mediated microsphere formation is proposed as illustrated in Figure 5. Colloidal microspheres are usually prepared via precipitation reactions, a process that often involves two sequential steps: nucleation and growth of the nuclei.32, 33 The branched PEI molecules into the solution could be regarded as positively charged ellipsoids which are highly dispersed by electrostatic repulsion. The introduction of electronegative resorcinol into PEI causes an increase in hydrodynamic diameters, suggesting the self-assembly of R-PEI driven by electrostatic interaction between them. After adding formaldehyde in to the R-PEI system, resorcinol can react quickly with formaldehyde to form numerous (simply, doubly or triply) substituted hydroxymethyl resorcinol, which can position at the surface of the PEI molecules owing to the electrostatic interaction. This primary RF-PEI self-assembled structure can be regarded as the nuclei, which could immediately aggregate together to form a colloidal particle. The aggregation process is spontaneous and very fast as evidenced by a change in color immediately after adding formaldehyde. Then, the as-formed colloidal particles undergo two different reaction pathways: cross-linking inside the particles and step-growth polymerization of substituted resorcinol on the surface of the particles. The former reaction results in the shrinkage and dense of the microspheres, which may issues both from the condensation of substituted resorcinol between primary structures and the desolvation of hydrated PEI molecules. The latter reaction can induce the step-growth of the microspheres, via an epitaxial condensation of hydroxymethyl substituted resorcinol from solution. Thus, the obtained microspheres exhibit a core-shell structure, in which RF-PEI self-assembled structure as core and step-growth RF as shell. This could be confirmed by TEM observation and also evidenced by the fact that surface N contents from XPS data are much lower than these of CHN results. The shrinkage-growth is a simultaneous process of dynamic equilibrium, in which shrinkage is majorly dominate in the initial stage. It should be noted that the PEI molecular weight (more specially, molecular size) play an important


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role on the microsphere size. Larger molecular size is used, smaller microsphere size is achieved. This should be due to the small primary particles having higher surface activity which could grow more easily and rapidly than larger ones. Therefore, the PEI-mediated polymer microspheres should be the result of aggregation of RF-PEI primary nucleis, rather than the conventional Stöber process of continuous growth by diffusion of species from the solution towards the surface of nuclei.33 In the case of PEI-10000, the larger RF-PEI structure could form immediately Brownian particles, which then subsequently coalesce to form a space-filling gel network of interconnected clusters, rather than aggregate together to form a microsphere.

Preparation of carbon microspheres and CO2 adsorption performance

Because of their good thermal stability and high carbon yield, these PEI-mediated phenolic-microspheres could be easily converted into carbon microspheres (CMSs) by a simple carbonization. The SEM images of the carbonized samples are shown in Figure 6 a-d. It is shown that the obtained CMSs possess spherical morphology with relatively narrow particle size distribution and average diameter of 150, 105 and 85 nm for CMS-1, CMS-2 and CMS-3 respectively. The smaller particle sizes of CMSs as compared to PMSs are mainly caused by the structure shrinkage during thermal treatment, which is common in carbonization process.34 TEM images of CMS-3 (Figure 6 e-f) also show that the original spherical morphology could be retained with slight structural collapse. It should be noted that the core-shell structure is still discerned after the carbonization, although the colour contrast between the core and shell region becomes shallow. Even in some cases (Figure 6 f), spherical mesopores with ordered array can be observed inside the carbon microspheres. Some mesoporous structure was formed from the decomposition of PEI molecules with high hydrodynamic diameter which could collapse during the carbonization process, resulting in mesopores only observed in some cases. In case of CMS-4, the polymeric nanoparticles are melted into condensed solid



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without obvious porosity, and no core-shell structure could be found both in the polymeric and carbon samples (see TEM images in Figure S7).

Figure 6. SEM images of CMSs synthesized with branched PEI; (a) CMS-1, (b) CMS-2, (c) CMS-3, and (d) CMS-4 and TEM images of CMS-3 (e, f).


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Elemental analysis and XPS analysis are recorded to analyze the chemical composition of these carbonized CMSs samples. Table 3 summarizes the CHN elemental compositions, which indicate that the nitrogen content is 6.1, 6.0, 6.3 and 5.1 wt. % for CMS-1, CMS-2, CMS-3 and CMS-4, respectively. It is noteworthy that the nitrogen loss during carbonization of the polymer studied is smaller as compared to other nitrogen-containing carbons, 35, 36 possibly due to the confined effect by the phenolic shell during high temperature pyrolysis. What is more, the surface N wt. % for CMS-1 and CMS-3 from XPS analysis are 6.0 and 6.8 (wt. %), respectively (Table 3), being comparable with the CHN data. This result suggests the nitrogen specie decomposed from PEI could diffuse into carbon shell region and further react with carbon framework, leading to a relative uniformity of nitrogen distribution throughout the entire microspheres. The high resolution XPS spectra (N 1s) further reveal the form of nitrogen in the carbon matrix. The N1s spectra (Figure S8) are curve-fitted into three peaks with binding energies of 398.6±0.3, 400.3±0.3 and 401.3±0.3 eV, that correspond to pyridinic N (N1), pyrrolic N (N2) and graphitic N (N3), respectively. The relative contents of these different functionalities in N 1s are similar. The graphitic N representing around 20-25% and almost no N-O is resolved.



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Table 3. Porosity parameters and chemical compositions of the carbon microspheres Elements analysis

XPS analysis

SBET

VTotal

SDFT

VDFT

m2/g

cm3/g

m2/g

cm3/g

N wt.%

C wt.%

N/C at./at.

N wt.%

C wt.%

N/C at./at.

CMS-1

420

0.25

344

0.14

6.1

79.5

0.07

6.0

87.6

0.06

CMS-2

467

0.28

405

0.16

6.4

79.1

0.07

_

_

_

CMS-3

485

0.33

402

0.17

6.3

78.7

0.07

6.8

86.8

0.08

CMS-4

270

0.20

196

0.08

5.1

79.6

0.05

8.4

72.8

0.10

ACMS-3-2

1528

1.03

1348

0.62

2.2

77.1

0.03

2.1.

93.0

0.02

ACMS-3-3

1980

1.10

1774

0.73

2.0

76.2

0.02

1.7

91.8

0.02

Samples

Figure 7. N2 adsorption isotherms at 77 K (a) and pore size distributions (b) of the as prepared carbon microspheres and CO2 adsorption isotherms for the CMSs measured at 273 K (c) and 298 K (d). 20 ACS Paragon Plus Environment

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Figure 7 a, b shows the N2 adsorption–desorption isotherms and the resulting DFT pore size distributions of the CMSs. The curves of these CMSs are type I responding to a typical microporous structure. The calculated porosity values are listed in Table 3. It is worth noting that the surface areas (~400 m2/g) are almost independent of PEI molecular weight, except for the sample CMS-4 which is a condensed solid after the carbonization. The CMSs have relatively narrow microporous size distribution mainly located below 1.0 nm. Considering the co-exist of considerable microporosity and the relatively high nitrogen content, both of which have been reported to be beneficial for acidic CO2 adsorption,37-39 the obtained CMS should be potential adsorbents for CO2 capture. Herein, CO2 adsorption performance on the nitrogen-containing microporous CMSs was investigated at 273K and 298K under atmospheric pressure (1 bar). The CO2 adsorption isotherms for CMSs are shown in Figure 7 c, d, which have a steep rise at low pressure and slowly reach the maximum at 1 bar. The CO2 adsorption capacities at 273K for CMSs are 3.1, 3.4, 3.6 and 2.9 mmol·g-1 for CMS-1, CMS-2, CMS-3, and CMS-4 respectively. It is worthy to note that the CO2 adsorption capacities are in line with the values of BET surface area while these CMSs have similar pore size distributions, suggesting that micropores play a crucial role in CO2 adsorption. What is more, compared to other porous carbon materials35,40, the BET surface area of the CMSs prepared here is not high, however, their CO2 uptake are really impressive, possibly due to the synergistic contributions of narrow micropores centered at 0.6-0.7 nm and appropriate nitrogen doping as well as small microsphere size with short transport distance.

Preparation of KOH-Activated carbon microspheres and their application for supercapacitors

Although direct carbonization of polymer microspheres could produce the CMS with a considerable microporosity and high nitrogen doping, higher BET surface area is generally necessary for carbon materials in adsorption and electrochemical applications where microporosity plays a dominate role.38 For the further 21 ACS Paragon Plus Environment


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enhancement of the functionality, the KOH activation is employed to develop the porous texture of carbon microspheres. Owing to the pre-developed microporous structure of CMSs, KOH could be easily infiltrated into the carbon structure for homogenous dispersion and activation. As shown in Figure 8, SEM and TEM images of the activated CMS-3 prepared by different mass ratios of KOH/carbon (K/C) show spherical structure without obvious structure destruction. The average diameters of ACMS3-2 and ACMS3-3 are only around 75 and 70 nm respectively, significantly smaller than that of carbonized microspheres, 41 which may be caused by peeling off the outer carbon layer during activation with KOH.

42

It should be noted that the

heterogeneous core-shell structure is hardly discerned after the KOH activation, possibly due to low level of nitrogen doping resulting in no obvious contrast between core and shell region.

Figure 8. SEM images of (a) ACMS3-2, (b) ACMS3-3 and TEM images of (c) ACMS3-2, (d) ACMS3-3


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Figure 9 shows the N2 adsorption-desorption isotherms and resulting DFT pore size distributions of the activated ACMS samples. The detailed porosity parameters are also summarized in Table 3. KOH activation could significantly improve the porosity, as the BET surface area could increase to 1500 and 2000 m2·g-1 for K/C=2 and K/C=3, respectively, which are about 1000-1500 m2·g-1 enhancement as compared to the respective non-activated carbon microspheres. Obviously, this enlargement in the surface area is due to the creation of additional micropores during KOH activation process. From Figure 9 b, the KOH activated samples have pore size predominantly ranging from 0.7-2 nm, slightly wider than that of un-activated sample.

Figure 9. N2 adsorption isotherms (a) and pore size distributions (b) of CMS-3 and resultant ACMSs.

The activated samples still maintain a certain amount of nitrogen atoms doped in the porous carbon framework. As listed in Table 3, the nitrogen content of activated microspheres can remain 2.2-2.0 wt. % compared to 6.3 wt. % of un-activated CMS-3. The nitrogen contents decrease a lot owing to the decomposition of nitrogen containing group and the increase of the oxygen-containing groups introduced during the KOH activation process.43 The elemental composition and nitrogen bonding configurations of activated ACMS are further quantified by XPS measurements, as shown in Figure S9. The activated 23 ACS Paragon Plus Environment


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ACMSs possess very similar nitrogen bonding configurations, with a relatively high portion of the pyridinic N and pyrrolic N configurations, and a low content of the graphitic N and N-O configuration.

Figure 10. (a) cyclic voltammetry (CV) testing at 100 mV·s-1; (b) Galvanostatic charge/discharge voltage profiles at 0.1 A·g-1;

(c) Plot of specific capacitances calculated from the discharge curves

versus current density; (d) Cycling ability at 0.1 A·g-1.

Supercapacitors present an attractive new energy storage technology, specifically for high power applications44. The fast diffusion of electrolytes to carbon surfaces is considered a key factor affecting the performance of these devices, especially at high rates.

45

Thus, these activated carbon microspheres should

be very promising electrode materials for supercapacitor, because they bear spherical morphology with short diffusion distance (< 80 nm), well developed porous structures (~ 2000 m2·g-1) and nitrogen-containing functional groups. As a proof-of-concept study, the ACMSs were evaluated with a two-electrode


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symmetrical cell in a 3 M H2SO4 electrolyte solution. The electrochemical performances of CMS-3 were measured for comparison (Figure S 10-12). The cyclic voltammetry (CV) testing (Figure 10 a) shows very rectangular curves from 0-0.9 V even at an ultrahigh scan rate of 100 mV·s-1, indicating the efficient formation of electric double layer and fast charge diffusion within the microspheres for ACMS3-2 and ACMS3-3. The galvanostatic charge/discharge curves at a current density of 0.1 A·g-1 (Figure 10 b) display symmetric triangular profiles with negligible ohmic voltage drops. The specific capacitances of ACMSs are calculated to be 186 and 241 F·g-1 for the samples prepared at the KOH/C ratio of 2 and 3, respectively, in proportion to the BET surface areas of the activated microspheres, while the specific capacitance of CMS-3 is only 129 F·g-1 (Figure S11). The electrochemical impedance spectroscopies of the samples are also shown in Figure S12. The equivalent series resistance (ESR) value of ACMS3-2 and ACMS3-3 is about 0.14 Ohm and 0.25 Ohm, respectively, much lower than CMS-3 of about 0.55 Ohm, suggesting high charging and discharging rate of the activated samples. Moreover, a more vertical nature of the curve for the activated samples at low frequency also indicates near-ideal electric double layer capacitor behaviour. The rate capability as a function of charge/discharge current density is plotted in Figure 10 c. Interestingly, the capacitance of these activated materials does not show much degradation even with 200 time increase of the current density. For the sample ACMS3-2, it can retain 169 F·g-1 at 20 A·g-1 with a capacitance retention ratio of 89 %, while for ACMS3-3 the retention ratio is still up to 80%, both of which are dramatically higher than CMS-3 of 70 % (Figure S11). Such high retention ratios are among the highest values for many other reported high-rate porous carbon electrodes.46, 47

Apparently, this rate performance should be ascribed to the well-developed porous structure and the short

ion diffusion path inside microspheres, as well as improved electrolyte wettability and electrical conductivity by nitrogen doping. In addition, the ACMS3-2 and ACMS3-3 electrodes exhibit very high



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cycle stability with 99 % and 97 % capacitance retention after 5000 cycles, respectively (Figure 10 d), indicating excellent physical stabilities and extraordinary cycling ability for the electrodes. These results indicate that these carbon microspheres have the potential to become a kind of electrode materials, suitable to be used in energy storage and other related areas.

CONCLUSIONS

Nitrogen-containing polymer microspheres are synthesized through a one-pot organic-amine mediated reaction-induced copolymerization process, using resorcinol, formaldehyde and different organic amine as precursors. The synthesis is universal and very flexible, permitting a facile control of particle size by adjusting the molecular weight of nitrogen source. Besides, formation of primary clusters and their subsequent evolution is monitored by DLS. It is found that the colloidal clusters are formed instantaneously and then experience a unique shrinkage-growth process, which is caused by two different reaction pathways: cross-linking inside the microspheres and step-growth polymerization of substituted resorcinol on the surface of the microspheres. As a result, a core-shell heterogeneous structure is obtained, in which PEI-RF self-assembled structure as core and RF as shell. The polymer microspheres should be formed by the aggregation of nanometer-size PEI-RF self-assembled nuclei, rather than the conventional Stöber-type continuous growth. Such understanding of the chemical processes that take place in the earliest stages of a microsphere formation should provide the potential to better control microstructural evolution of the resulting polymer microspheres. Furthermore, the nitrogen-doped carbon microspheres are prepared by the carbonization of these polymer microspheres, which show a good CO2 adsorption capacity up to 3.6 mmol·g-1 at 0 °C. For the further enhancement of the functionality, the KOH activation is employed to develop the porous texture of carbon microspheres. The resultant activated carbon microspheres exhibit very 26 ACS Paragon Plus Environment

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small particle size, high BET surface areas and excellent capacitive performance. Such unique combination of nano-spherical morphology, highly porous structures and appropriate nitrogen doping may open new opportunities to create a class of novel porous carbon materials for a variety of energy and environment related applications.

ASSOCIATED CONTENT Supporting Information Figures showing the SEM images of PMS-PEI obtained at the different experiment condition, FT-IR spectra and XPS results of PMS-PEI, digital photograph of solution obtained with PEI, DLS results of TEOS and TEPA, the TEM images of CMSs, XPS results of CMSs and ACMSs, electrochemical performances of CMS-3. Table showing the CNH results of PMSs, Zeta potential of PEI and R-PEI solutions, relative contents of different functionalities in N 1s peaks. This material is available free of charge via the Internet at http://pubs.acs.org.

Corresponding Author E-mail: [email protected]. Tel: +86 21 64252924. Fax: +86 21 64252914.

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes

The authors declare no competing financial interest.



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ACKNOWLEDGMENT This work was supported by MOST (2014CB239702) and National Science Foundation of China (No. 21576090, No. 21506061) and Shanghai Municipal Natural Science Foundation (No. 14ZR1410400) and Fundamental Research Funds for the Central Universities and Shanghai Rising-Star Program (15QA1401300).

References: (1)

Inagaki, M.; Konno, H.; Tanaike, O. Carbon Materials for Electrochemical Capacitors. J. Power

Sources 2010, 195, 7880-7903. (2)

Lee, J.; Kim, J.; Hyeon, T. Recent Progress in the Synthesis of Porous Carbon Materials. Adv. Mater.

2006, 18, 2073-2094. (3)

Liu, Z.; Sun, X.; Nakayama-Ratchford N.; Dai, H. Supramolecular Chemistry on Water-Soluble

Carbon Nanotubes for Drug Loading and Delivery. ACS Nano 2007, 1, 50-56. (4)

Zhang, L. L.; Zhao, X. S. Carbon-Based Materials as Supercapacitor Electrodes. Chem. Soc. Rev.

2009, 38, 2520-2531. (5)

Zhu, B.; Li, K.; Liu, J. Nitrogen-Enriched and Hierarchically Porous Carbon Macro-Spheres-Ideal for

Large-Scale CO2 Capture. J. Mater. Chem. A 2014, 2, 5481-5489. (6)

Liang, C.; Li, Z.; Dai, S. Mesoporous Carbon Materials: Synthesis and Modification. Angew. Chem.

Int. Ed. 2008, 47, 3696-3717. (7)

Wang, J. C.; Kaskel, S. KOH Activation of Carbon-Based KOH Activation Materials for Energy

Storage. J. Mater. Chem. 2012, 22, 23710-23725. (8)

Rasines, G.; Macías, C.; Haro, M.; Jagiello, J.; Ania, C. O. Effects of CO2 Activation of Carbon

Aerogels Leading to Ultrahigh Micro-Meso Porosity. Microporous Mesoporous Mater. 2015, 209, 18-22. 28 ACS Paragon Plus Environment

Page 29 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(9)


Hulicova-Jurcakova, D.; Kodama, M.; Shiraishi, S.; Hatori, H.; Zhu, Z. H.; Lu, G. Q.

Nitrogen-Enriched Nonporous Carbon Electrodes with Extraordinary Supercapacitance. Adv. Funct. Mater. 2009, 19, 1800-1809. (10) Wei, J.; Zhou, D.; Sun, Z.; Deng, Y.; Xia, Y.; Zhao, D. A Controllable Synthesis of Rich Nitrogen-Doped Ordered Mesoporous Carbon for CO2 Capture and Supercapacitors. Adv. Funct. Mater. 2013, 23, 2322–2328. (11) Han, J.; Xu, G.; Dou, H.; MacFarlane, D. R. Porous Nitrogen-Doped Carbon Microspheres Derived from Microporous Polymeric Organic Frameworks for High Performance Electric Double-Layer Capacitors. Chem. - Eur. J. 2015, 21, 2310-2314. (12) Zhang, P.; Qiao, Z. A.; Dai, S. Recent Advances in Carbon Nanospheres: Synthetic Routes and Applications. Chem. Commun. 2015, 51, 9246-9456. (13) Marzorati, S.; Vasconcelos, J. M.; Ding, J.; Longhi, M.; Colavita, P. E. Template-free Ultraspray Pyrolysis Synthesis of N/Fe-Doped Carbon Microspheres for Oxygen Reduction Electrocatalysis. J. Mater. Chem. A 2015, 3, 18920-18927. (14) Zhang, F.; Gu, D.; Yu, T. Mesoporous Carbon Single-Crystals from Organic-Organic Self-Assembly. J. Am. Chem. Soc. 2007, 129, 7746-7747. (15) Killops, K. L.; Rodriguez, C. G.; Lundberg, P.; Hawker, C. J.; Lynd, N. A. A Synthetic Strategy for the Preparation of Sub-100 nm Functional Polymer Particles of Uniform Diameter. Polym. Chem. 2015, 6, 1431-1435. (16) Roberts, A. D.; Li, X.; Zhang, H. Porous Carbon Spheres and Monoliths: Morphology Control, Pore Size Tuning and Their Applications as Li-ion Battery Anode Materials. Chem. Soc. Rev. 2014, 43, 4341-4356.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 34

(17) Dong, Y.; Nishiyama, N.; Egashira, Y.; Ueyama, K. Basic Amid Acid-Assisted Synthesis of Resorcinol-Formaldehyde Polymer and Carbon Nanospheres. Ind. Eng. Chem. Res. 2008, 47, 4712-4716. (18) Liu, J.; Qiao, S. Z.; Liu, H. Extension of the Stöber Method to the Preparation of Monodisperse Resorcinol-Formaldehyde Resin Polymer and Carbon Spheres. Angew. Chem. Int. Ed. 2011, 50, 5947-5951. (19) Wickramaratne, N. P.; Perera, V. S.; Ralph, J. M.; Huang, S. D.; Jaroniec, M. Cysteine-Assisted Tailoring of Adsorption Properties and Particle Size of Polymer and Carbon Spheres. Langmuir 2013, 29, 4032-4038. (20) Wickramaratne, N. P.; Xu, J.; Wang, M.; Zhu, L.; Dai, L.; Jaroniec, M. Nitrogen Enriched Porous Carbon Spheres: Attractive Materials for Supercapacitor Electrodes and CO2 Adsorption. Chem. Mater. 2014, 26, 2820-2828. (21) Zhou,

H.;

Xu,

S.;

Su,

H.

Facile

Preparation

and

Ultra-Microporous

Structure

of

Melamine-Resorcinol-Formaldehyde Polymeric Microspheres. Chem. Commun. 2013, 49, 3763-3765. (22) Wang, M.; Wang, J.; Qiao, W.; Ling, L.; Long, D. Scalable Preparation of Nitrogen-Enriched Carbon Microspheres for Efficient CO2 Capture. RSC Adv. 2014, 4, 61456-61464. (23) Zhao, J.; Niu, W.; Zhang, L. A Template-Free and Surfactant-Free Method for High-Yield Synthesis of

Highly

Monodisperse

3-Aminophenol-Formaldehyde

Resin

and

Carbon

Nano/Microspheres.

Macromolecules 2013, 46, 140-145. (24) Xu, Z.; Guo, Q. A simple Method to Prepare Monodisperse and Size-Tunable Carbon Nanospheres from Phenolic Resin. Carbon 2013, 52, 464-467. (25) Wickramaratne, N. P.; Jaroniec, M. Activated Carbon Spheres for CO2 Adsorption. ACS Appl. Mater. Interfaces 2013, 5, 1849-1855.


Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(26) Choma, J.; Jamioła, D.; Augustynek, K.; Marszewski, M.; Gao, M.; Jaroniec, M. New Opportunities in Stöber Synthesis: Preparation of Microporous and Mesoporous Carbon Spheres. J. Mater. Chem. A 2012, 22, 12636-12642. (27) Fuertes, A. B.; Valle-Vigón, P.; Sevilla, M. One-Step Synthesis of Silica@Resorcinol-Formaldehyde Spheres and their Application for the Fabrication of Polymer and Carbon Capsules. Chem. Commun. 2012, 48, 6124-6126. (28) Pol, V. G.; Shrestha, L. K.; Ariga, K. Tunable. Functional Carbon Spheres Derived from Rapid Synthesis of Resorcinol-Formaldehyde Resins. ACS Appl. Mater. Interfaces 2014, 6, 10649-10655. (29) Watts, J. F.; Wolstenholme, J. An Introduction to Surface Analysis by XPS and AES, 2nd ed. John, F. Watts.; John, Wolstenholme. John Wiley & Sons Inc: New Jersey 2003, pp 224. (30) Gaca, K. Z.; Sefcik, J. Mechanism and Kinetics of Nanostructure Evolution During Early Stages of Resorcinol-Formaldehyde Polymerisation. J. Colloid Interface Sci. 2013, 406, 51-59. (31) Nozawa, K.; Gailhanou, H.; Raison, L. Smart Control of Monodisperse Stöber Silica Particles: Effect of Reactant Addition Rate on Growth Process. Langmuir 2005, 21, 1516-1523. (32) Bhagat, P. N.; Patil, K. R.; Bodasa, D. S.; Paknikar, K. M. Hydrothermal Synthesis and Characterization of Carbon Nanospheres: A Mechanistic Insight. RSC Adv. 2015, 5, 59491-59494. (33) Keshmiri, M.; Kesler, O. Colloidal Formation of Monodisperse YSZ Spheres: Kinetics of Nucleation and Growth. Acta Mater. 2006, 54, 4149-4157. (34) Wickramaratne, N. P.; Jaroniec, M. Facile Synthesis of Polymer and Carbon Spheres Decorated with Highly Dispersed Metal Nanoparticles. Chem. Commun. 2014, 50, 12341-12343. (35) Su, F.; Poh, C. K.; Chen, J. S. Nitrogen-Containing Microporous Carbon Nanospheres with Improved Capacitive Properties. Energy Environ. Sci. 2011, 4, 717-724.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 34

(36) Liu, L.; Deng, Q.; Hou, X.; Yuan, Z. User-friendly Synthesis of Nitrogen-Containing Polymer and Microporous Carbon Spheres for Efficient CO2 Capture. J. Mater. Chem. 2012, 22, 15540-15548. (37) Sevilla, M.; Fuertes, A. B. Sustainable Porous Carbons with a Superior Performance for CO2 Capture. Energy Environ. Sci. 2011, 4, 1765-1771. (38) Sevilla, M.; Parra, J. B.; Fuertes, A. B. Assessment of the Role of Micropore Size and N-Doping in CO2 Capture by Porous Carbons. ACS Appl. Mater. Interfaces 2013, 5, 6360-6368. (39) Zhou, M.; Pu, F.; Wang, Z.; Guan, S. Nitrogen-Doped Porous Carbons through KOH Activation with Superior Performance in Supercapacitors. Carbon 2014, 68, 185-194. (40) Luiz, K. C. S.; Wickramaratne, N. P.; Ello, A. S.; Maria, J. F. C.; Carlos, E. F. C.; Mietek, J. Enhancement of CO2 Adsorption on Phenolic Resin-Based Mesoporous Carbons by KOH Activation. Carbon 2013, 65, 334-340. (41) Friedel, B.; Greulich-Weber, S. Preparation of Monodisperse, Submicrometer Carbon Spheres by Pyrolysis of Melamine–Formaldehyde Resin. Small 2006, 2, 859-863. (42) Ludwinowicz, J.; Jaroniec, M. Potassium Salt-Assisted Synthesis of Highly Microporous Carbon Spheres for CO2 Adsorption, Carbon 2015, 82, 297-303. (43) Liu, Z.; Du, Z.; Song, H. The Fabrication of Porous N-doped Carbon from Widely Available Urea Formaldehyde Resin for Carbon Dioxide Adsorption. J. Colloid Interface Sci. 2014, 416, 124-132. (44) Wang, Y.; Xia, Y. Recent Progress in Supercapacitors: From Materials Design to System Construction. Adv. Mater. 2013, 25, 5336-5342. (45) Han, J. P.; Xu, G. Y.; Ding, B.; Pan, J.; Dou, H.; MacFarlane, D. R. Porous Nitrogen-Doped Hollow Carbon Spheres Derived from Polyaniline for High Performance Supercapacitors. J. Mater. Chem. A 2014, 2, 5352–5357.


Page 33 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(46) Chen, L.; Zhang, X.; Liang, H. Synthesis of Nitrogen-Doped Porous Carbon Nanofibers as an Efficient Electrode Material for Supercapacitors. ACS Nano 2012, 6, 7092-7102. (47) Ferrero, G. A.; Fuertes, A. B.; Sevilla, M. N-doped Microporous Carbon Microspheres for High Volumetric Performance Supercapacitors. Electrochim. Acta 2015, 168, 320-329.



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Table of Contents Graphic


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Strings of polymer microspheres stabilized by oxidized carbon nanotubes.

Carbon-Based Hybrid Aerogels: Preparation, Properties and Applications.

Bacteriagenic silver nanoparticles: synthesis, mechanism, and applications.

Preparation and Applications of 4-Methoxybenzyl Esters in Organic Synthesis.

Polymer synthesis: chaining up carbon dioxide.

Oligothiophene semiconductors: synthesis, characterization, and applications for organic devices.

Colloidal-sized metal-organic frameworks: synthesis and applications.

Easy synthesis of highly fluorescent carbon dots from albumin and their photoluminescent mechanism and biological imaging applications.

Framed carbon nanostructures: synthesis and applications in functional SPM tips.

Graphitic carbon nitride: synthesis, properties, and applications in catalysis.

Recent advances in carbon nanodots: synthesis, properties and biomedical applications.

Carbon Nanotube Membranes: Synthesis, Properties, and Future Filtration Applications.

Carbon nanotubes: properties, synthesis, purification, and medical applications.

Robust platforms for creating organic-inorganic nanocomposite microspheres: decorating polymer microspheres containing mussel-inspired adhesion layers with inorganic nanoparticles.

Biomimetic self-cleaning surfaces: synthesis, mechanism and applications.

Gel-limited synthesis of dumbbell-like Fe3O4-Ag composite microspheres and their SERS applications.

Conductive polymer nanocomposites with hierarchical multi-scale structures via self-assembly of carbon-nanotubes on graphene on polymer-microspheres.

Synthesis of porous upconverting luminescence α-NaYF4:Ln(3+) microspheres and their potential applications as carriers.

Novel hybrid organic thermoelectric materials:three-component hybrid films consisting of a nanoparticle polymer complex, carbon nanotubes, and vinyl polymer.

Synthesis and characterization of carbon cryogel microspheres from lignin-furfural mixtures for biodiesel production.

Urchin-like TiO₂@C core-shell microspheres: coupled synthesis and lithium-ion battery applications.

Recent applications of ring-rearrangement metathesis in organic synthesis.

Recent applications of the divinylcyclopropane-cycloheptadiene rearrangement in organic synthesis.

Carbon dioxide capture and use: organic synthesis using carbon dioxide from exhaust gas.