Carbon microspheres with a uniform size of about 170 μm were prepared in a simple co-flow microfluidic device using solvent extraction method. An ethanol solution of colloidal silica and phenol formaldehyde (PF) resol was used as the dispersion phase, and a mixture of hexane and diisopropylamine was used as the continuous phase. The droplets of PF resol resin/silica were generated in the continuous phase.
Microporous and Mesoporous Materials 343 (2022) 112186 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso Preparation of hundred-micron carbon spheres using solvent extraction in a simple microchannel device Jie Li a, Zhenheng Xu a, Liang Yu b, *, Lixiong Zhang a, ** a b State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Tech University, Nanjing, 211816, China Chemical Technology, Luleå University of Technology, SE-971 87, Luleå, Sweden A R T I C L E I N F O A B S T R A C T Keywords: Hundred-micron carbon spheres Porous carbon microspheres Solvent extraction Microfluidics Phenol phenolic resin Carbon microspheres with a uniform size of about 170 μm were prepared in a simple co-flow microfluidic device using solvent extraction method An ethanol solution of colloidal silica and phenol formaldehyde (PF) resol was used as the dispersion phase, and a mixture of hexane and diisopropylamine was used as the continuous phase The droplets of PF resol resin/silica were generated in the continuous phase Colloidal silica assisted the for mation of the spherical structure and worked as a pore generator The continuous phase was also used as extractant and catalyst for PF resin/silica microspheres formation Curing, drying, carbonization and leaching were used for the post-treatment of the PF resin/silica microspheres to obtain porous carbon microspheres The carbon microspheres displayed a narrow size distribution and a high surface area of 679 m2/g coupled with adjustable mesopores and large mesopore volume Carbon microspheres prepared from the dispersion phase with different PF/silica ratios (denoted as carbon/silica (C/Si) ratios) were studied and the formation mechanism of the PF/silica microspheres was deeply explored Introduction Porous microspheres with size ranging from 100 to 1000 μm are widely used in various practical applications due to their suitable size for transportation and recovery [1] Because of the low density, high chemical stability and thermal conductivity, hundred-micron porous carbon spheres have been used in air and water purification, blood pu rification, CO2 adsorption, and electronic and energy storage devices [2–11] So far, polymerization is the most popular method for the prepara tion of hundred-micron carbon microspheres [11] and carbon spheres synthesized from polymers displayed higher mechanical strength [8] Divinylbenzene-based spherical activated carbon with size between 200 and 1200 μm were used for water purification, i.e removal of organic pollutants from water [6] The spherical activated carbon showed two times higher methylene blue adsorption capacity compared to the commercially available spherical activated carbon However, due to the low mesopore volume, the highest observed methylene blue adsorption capacity was only 32 mg/g Yang et al synthesized phenolic resin-based activated carbon spheres with different pore size distributions by using polyethylene glycol and polyvinyl butyral as pore-forming agents [7] The size of the mesopores was between and nm in the carbon spheres Therefore, they showed excellent adsorption capacity for large molecules e.g., creatinine and VB12 Activated carbon spheres with the diameter of 200–950 μm were prepared by carbonization of commer cially available polystyrene-based ion-exchange resin spheres [8] The polystyrene-based activated carbon spheres were times harder than the pitch-based activated carbons spheres Due to the large pore volume of 1.35 cm3/g, the spheres displayed high adsorption capacity of 153 mg/g for dibenzothiophene Polystyrene-based microporous activated carbon spheres with a narrower size distribution between 500 and 800 μm have been prepared by suspension polymerization of styrene monomer and followed by some post-treatment processes including sulfonation, oxidation, carbonization, and activation The obtained carbon spheres displayed a high surface area (1526 m2/g) and a large pore volume (0.73 cm3/g) The adsorption capacity for CO2 was also high about 4.21 mmol/g at 25 ◦ C and ambient pressure [9] A so-called inverse-microemulsion-polymerization-phase-separation method has been developed for the preparation of carbon spheres using phenolic resin [10] The carbon spheres with the size of about 100 μm were * Corresponding author ** Corresponding author E-mail addresses: liang.yu@ltu.se (L Yu), lixiongzhang@yahoo.com (L Zhang) https://doi.org/10.1016/j.micromeso.2022.112186 Received April 2022; Received in revised form 29 July 2022; Accepted 12 August 2022 Available online 20 August 2022 1387-1811/© 2022 The Authors Published by Elsevier Inc This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/) J Li et al Microporous and Mesoporous Materials 343 (2022) 112186 composed of carbon nanoparticles with the size smaller than 100 nm Therefore, the carbon spheres displayed a hierarchical structure and high total pore volume of 2.78 cm3/g Due to the unique structure, the carbon spheres showed a rapid transport of electrolyte ions, and there fore displayed high potential in superior rate performance carbon-based supercapacitors Polymerization method is easy to scale up However, the wide size distribution of the spheres products is always a drawback of the method Phenolic resin is a decent carbon source for the synthesis of highquality carbon microspheres due to the high carbon content However, the polymerization of phenol and formaldehyde is a relatively slow process due to the high viscosity of the mixture of phenol and formal dehyde [12] Normally, a reaction time of h at 95 ◦ C is needed for the polymerization process [12] Singh et al., prepared macrosize phenolic beads (100–200 μm) by a suspension polymerization method with the reaction temperature of 96 ◦ C and reaction time of h [13] The phenolic beads can be used as precursors for the preparation of carbon sphere However, the beads showed a broad size distribution and poor structural properties, e.g., low porosity In some cases, additives are added to improve the formation process and reduce the polymerization time as well as improve the porosity of the obtained microspheres [14–16] However, the issue of the broad size distribution of micro spheres prepared from the conventional polymerization remains Therefore, a new method is necessary As it is well known, microchannel technique could reduce the reac tion time and temperature for time consuming and high temperature demanding systems [17] In addition, microchannel technique could prepare microspheres with more uniform size compared to the con ventional polymerization method [18–20] Steinbacher et al., summa rized the application of microchannel technique for the preparation of even size microdroplets and microspheres [17] Our group also has developed several microchannel devices for the preparation of nano particles, microspheres, and microcapsule materials in the last 15 years [18,21–23] Silica microspheres with the uniform size of 100 μm and various structures including solid, hollow, hollow with a hole and filbert-like solid structures were prepared in a simple T-type micro channel device [21] Monodisperse carbon hollow spheres were also prepared in such device [18] To improve the textural properties of the obtained carbon spheres, colloidal silica is often used as additive for the preparation of porous carbon Our previous report showed that the pore size of carbon spheres increased from 0.6 to 6.2 nm after removal of silica nanoparticles from poly (furfuryl alcohol)-silica composite mi crospheres [22] Therefore, the adsorption capacity for dye increased significantly Silica nanoparticles also have been employed to tailor ăber method [24] The porosity in carbon spheres using a modified Sto obtained carbon spheres showed both microporous and mesoporous structure with surface areas between 326 and 1500 m2/g and total pore volumes between 0.26 and 1.22 cm3/g Meanwhile, a high adsorption capacity of 7.8 mmol/g for CO2 were observed at ◦ C and bar [24] So far, large size (hundred-micron meters) mesoporous carbon spheres with an even size distribution have rarely been reported In the present work, hundred-micron carbon spheres with control lable porous structure were prepared using a simple microchannel de vice in combination with a solvent extraction method PF resin/silica microspheres were first prepared in the simple microchannel device The microspheres were carbonized to obtained carbon/silica spheres Subsequently, porous carbon spheres were prepared after removal of silica The synthesized time was much shorter and the obtained carbon spheres were more even compared to the conventional polymerization method The conditions for the formation of PF resin/silica micro spheres in the microchannel device were optimized and the effect of carbon/silica ratio on the textural properties of the porous carbon spheres was investigated In addition, the mechanism of the formation of the microspheres in the microchannel was discussed Fig Experimental device diagram Experimental 2.1 Preparation of colloidal silica Colloidal silica with the concentration of about 10 wt% was prepared by mixing 2.6 g TEOS with 3.0 g ethanol and followed by slowly adding 1.35 g HCl (4 × 10− M) The mixture was stirred for h at room temperature 2.2 Preparation of phenol formaldehyde resol Phenol formaldehyde resol with a solids content of about 80 wt% was prepared using phenol and formaldehyde (37 wt%) as precursors and 20 wt% NaOH aqueous solution as catalyst as described in previous work [25] A mixture was first prepared by melting 12.2 g phenol at 42 ◦ C and subsequently adding 2.6 g 20 wt% NaOH under stirring Af terwards, formaldehyde solution (21 g) was added to the mixture The mixture was heated to 75 ◦ C and maintained for 60 until the mixture became red The mixture was then cooled down to room temperature and neutralized to pH of using × 10− M HCl The water in the mixture was removed by drying at 45 ◦ C for about days The obtained product was dissolved into ethanol to remove the NaCl precipitation Finally, the phenol formaldehyde resol resin was obtained after drying at 45 ◦ C to remove ethanol 2.3 Preparation of carbon microspheres Fig shows the microchannel device that used in the present work for the preparation of carbon microspheres precursors, i.e phenol formaldehyde resin microspheres The device has been described in our previous work [26] Briefly, two PTFE tubes (red pipes in Fig 1a) with the inner diameter of 0.56 mm were fixed in a T-type microchannel for continuous phase The length of the PTFE tube for the outlet of the T-type microchannel was 100 mm A needle with the inner diameter of 0.26 mm was inserted into the other inlet of the T-type microchannel The head of the needle should be placed at mm after the joint point of T as shown in Fig 1a The needle inlet will be used for dispersed phase The dispersed phase was a mixture of the colloidal silica, phenol formaldehyde resol, and ethanol The ethanol was used to control the solid concentration in the dispersed phase Continuous phase, i.e., the oil phase was a mixture of n-hexane, liquid paraffin, and diisopropylamine The dispersed phase and continuous phase were fed into the T-type microchannel at flowrates of 0.2 and 6.0 ml/h, respectively Liquid microdroplets were formed at the outlet of the needle due to the shearing force of the continuous phase A condenser column with the length of 750 mm and inner diameter of 20 mm connected to a flask was placed under the outlet of the T-type microchannel to collect the generated microspheres (Fig 1b) The composition of the liquid mixture in the column was the same as the continuous phase The microspheres were maintained in the oil phase for extraction PF resin/silica J Li et al Microporous and Mesoporous Materials 343 (2022) 112186 Fig Photographs of the obtained PF/silica microspheres with different m (C/Si), (a) ∞; (b) 17; (c) 15 Fig SEM images of (a) the overall morphology and (b) the surface of PF/ silica microspheres with m (C/Si) = 15 microspheres were obtained in the flask after ethanol and water were extracted The microspheres were cured at 100 ◦ C for 12 h and washed by n-hexane for three times to obtain the solid PF resin/silica micro spheres For comparison, solid phenol formaldehyde resin was prepared by mixing 1.0 g 80 wt% phenol formaldehyde resol with 0.1 g diiso propylamine, and subsequently curing at 100 ◦ C oven for 12 h The obtained solid phenol formaldehyde resin was washed by n-hexane for three times A tubular furnace was used to carbonize the PF resin/silica micro spheres under nitrogen atmosphere The temperature was first increased to 350 ◦ C and maintained for h, followed by increasing to 700 ◦ C and maintained for h Porous carbon microspheres were eventually ob tained by immersing the carbon/silica spheres in 10 wt% HF for h to remove silica nanoparticles Solid phenol formaldehyde resin was carbonized at the same conditions to prepare carbon for comparison 2.4 Characterizations An optical microscope (Olympus CX31) and SEM instruments (Phi lips Quanta 200 and Hitachi− S4800) were used to observe the morphology of the obtained products N2 adsorption –desorption iso therms were determined at liquid nitrogen temperature using BEL SORPII instrument Prior the measurement, the samples were degassed at 120 ◦ C for h to remove any impurity The total pore volume was calculated at p/p0 of 0.99 and the BET method was used to estimate the surface area Pore size distributions were analyzed using the non-local density functional theory (NLDFT) A miniature double-frequency nu merical control ultrasonic cleaning machine (KQ-100VDV) was used to evaluate the mechanical strength of the carbon microspheres The mi crospheres were dispersed in water and treated in the ultrasonic clean ing machine under a frequency of 45 kHz for 30 The particles size distribution of the synthesized colloidal silica was measured using a Malvern Zetasizer (Nano-ZS) instrument Fig Optical micrograph of the process of extraction of microdroplets pre pared from m (C/Si) of 15 (a), 13 (b), 11 (c), 8.5 (d), and 6.5 (e) The size of the scale is 400 μm silica Spherical product could be obtained when m (C/Si) was 17, but the microspheres agglomerated slightly, see Fig 2b This resulted from the low colloidal silica concentrations Monodispersing microspheres were obtained when m (C/Si) decreased to 15, i.e., when the concen tration of colloidal silica increased The well dispersing microspheres formed in the column provided promising microspheres precursors for the late high temperature curing and carbonization Fig shows the SEM images of the PF/silica microspheres prepared from a mixture with m (C/Si) of 15 The microspheres have a uniform size of about 150 μm, which is much smaller than the liquid micro spheres generated from the microchannel due to the contraction during extraction To investigate the formation process of the PF/silica micro spheres, more experiments were carried out using dispersed phase with different m (C/Si) Different amounts of ethanol were used to maintain a constant solid concentration in the dispersed phase The size of the microdroplets at the outlet of the needle was 400 μm Fig shows the variations of the microdroplets in the extract as a function of extracting time, which prepared from the m (C/Si) of 15, 13, 11, 8.5, and 6.5, respectively Fig shows that the freshly generated microdroplets are trans parent, no matter with the ratio of m (C/Si), and the microdroplets became dark with the increase of the extracting time due to the gelation of colloidal silica and the polymerization of phenol formaldehyde resol The color of the microdroplets changed evenly when m (C/Si) ≥11 However, with the decrease of m (C/Si), i.e., increased the colloidal silica content, a transparent shell and a dark core were observed, which Results and discussion 3.1 Effect of silica contents Fig shows the photographs of the microspheres prepared using dispersed phases with different ratios of colloidal silica, phenol form aldehyde resol resin, and ethanol The mass ratios of carbon to silicon (m (C/Si)) in the dispersed phases were ∞, 17 and 15 However, the total content of solid in the dispersed phase was maintained constant at 35 wt % The continuous phase was comprised of n-hexane, liquid paraffin, and diisopropylamine with the volume ratio of 2:2:1 Fig shows that a large liquid droplet was generated from the small droplets prepared without colloidal silica, i.e., the droplets agglomer ated when the m (C/Si) was infinity This was due to the condensation polymerization of phenol formaldehyde resol is a slow process and an alkaline catalyst is needed, otherwise, the short residence time in the condensation column was not sufficient for the formation of stable phenol formaldehyde resin microspheres Therefore, a large liquid droplet was obtained in the flask However, stable PF/silica micro spheres could be formed in the column due to the gelation of colloidal J Li et al Microporous and Mesoporous Materials 343 (2022) 112186 Meanwhile, the particle size of the obtained PF/silica microspheres decreased with the increase of the m (C/Si) as shown in Fig 5, which showed that the content of colloidal silica has a significant effect on the microsphere size It is important to note that the total solids content in the dispersed phase was maintained constant at 35 wt% as mentioned above when m (C/Si) was changed More information about shell and core is explored as below Fig shows the PF/silica microspheres prepared from different ra tios of m (C/Si) Silica gel, i.e., a hydrogel with three-dimension struc ture will generate in the microdroplets when the content of colloidal silica was high Therefore, a more porous structure was obtained in the microspheres, see Fig 6b Microspheres with more compact structure was observed when the content of colloidal silica decreased, i.e., the content of phenol formaldehyde resol increased Since diisopropylamine in the extract catalysed the polymerization of phenol formaldehyde resol, the compact structures, mainly the compact shells were generated in the microsphere Therefore, the PF/silica microspheres with shells thickness of about μm, 15 μm and 18 μm were observed, when m (C/Si) increased from 6.5 to 15, see Fig We, therefore, can conclude that the core and the shell of PF/silica microspheres were mainly silica and phenol formaldehyde resin, respectively Fig Size of PF/silica microspheres as a function of m (C/Si) probably resulted from the phase separation during the gelation of colloidal silica (water phase) and the polymerization of phenol formal dehyde resol (oil phase) 3.2 Effect of diisopropylamine concentration Diisopropylamine was selected as catalyst for the polymerization of Fig SEM images of the whole, surface, cross-section and edge of the cross-section of the PF/silica microspheres prepared at m (C/Si) = 6.5 (˜ ad), m (C/Si) = 13 (e ~ h), and m (C/Si) = 15 (i ~ l) Fig SEM images of cross-section of PF/silica microsphere prepared at m (C/Si) = 15 and different diisopropylamine concentrations, (a) 10 wt%; (b) 40 wt%; (c) 60 wt%, and the cross-section edge of (d) 10 wt%, (e) 40 wt%, (f) 60 wt% J Li et al Microporous and Mesoporous Materials 343 (2022) 112186 separation In addition, silicate could be generated when the pH is high enough, i.e., at high diisopropylamine concentration, which could be easily rinsed away Therefore, the carbon content will be high and silica content will be much lower at the surface These explain the formation of shell on the surface of the microspheres (see Fig 7c, f) and the lower silicon in the shell when the concentration of diisopropylamine increased to 60 wt% Table summarizes the elements distribution in the microspheres The effect of diisopropylamine concentration on the formation pro cess of the microspheres were further explored by observing the change of the microdroplets in the extract with different compositions Fig shows the change of the colour of the microdroplets in the extract with low diisopropylamine concentration The microspheres became dark evenly However, the results in Fig 9, where the diisopropylamine concentration was higher, show a shell on the microsphere due to the fast polymerization of phenol formaldehyde on the surface and gelation of colloidal silica in the centre These images show clear phase separation Table Effect of diisopropylamine concentration on the distribution of elements in PF/ silica microspheres Diisopropylamine concentration (wt.%) 10 40 60 Distribution of elements in core/shell of the microsphere (wt.%) C 63.10/ 59.43 65.28/ 57.24 51.62/ 61.55 Si 6.65/ 2.82 8.68/ 4.61 14.05/ 3.19 N 0.06/ 2.41 1.49/ 3.88 0.09/ 4.03 O 30.20/ 35.34 24.55/ 34.26 34.24/ 31.23 3.3 Textural properties of the microspheres Fig 10 shows the SEM images of the microspheres after curing, carbonization and removal of silica Moreover, the microspheres were prepared from a dispersed phase with m (C/Si) = 11 and solid content of 35 wt% As it has been mentioned above, the microdroplets generated at the outlet of the needle were about 400 μm However, the size of the mi crospheres was contracted to about 260 μm after polymerization and extraction The size of the microsphere further decreased to about 170 μm after carbonization, and the sizes before and after removal of silica were almost the same Fig 11 shows the N2 adsorption-desorption isotherms of micro spheres prepared at different conditions The adsorption solely occurred at the initial pressure range for carbon/silica and carbon microspheres, which indicates only micropores generated in the microspheres The micropores similar with the activated carbon More micropores and mesopores were generated after removal of silica Fig 11 shows the pore size distributions of the obtained microsphere at different conditions The mesopores sizes of the carbon microspheres synthesized from C/Si = 6.5 was in the range of 5.7–8.3 nm Larger mesopores up to 12.3 nm were observed in the carbon microspheres prepared from C/Si = 11 Only micropores could be observed in C(PF) particles The micropo rosity in the carbon microspheres also increased after silica removal, and the size of the micropores is much smaller than the size of the silica particles in the colloidal silica (Fig 11d) This indicated that even smaller silica particles were generated in the carbon/silica micro spheres The smaller silica particles were probably developed from the dissolution of the TEOS-generated silica during the experiment [27,28] Table summarizes the textural properties of the prepared micro spheres at different conditions The surface area of pure carbon was only 126 m2/g, which was much smaller than the carbon/silica microspheres The surface area of carbon/silica microspheres increased significantly after removal of silica For instance, the surface area of carbon/silica microspheres prepared from a dispersed phase with m (C/Si) = 6.5 was 329 m2/g, and it increased to 679 m2/g after removal of silica, mean while, the total pore volume increased from 0.15 to 0.50 cm3/g These results indicated that colloidal silica was used not only as the assistant for the formation of the spherical structure, but also for the generation of porous structure, especially for the mesoporous structure, which makes the microsphere a wide application at macromolecules adsorption, drug delivery, supercapacitors, and catalysis It is important to note that the microspheres well preserved the spherical morphology (Fig 10) after the treatment in an ultrasonic bath (45 kHz) for 30 The results indicated a good mechanical strength of the carbon microspheres Porous carbon materials have been extensively studied in the last decades Macropore-rich activated carbon microspheres with size of Fig Optical micrographs of the extraction process of PF/silica microdroplets in the extraction phase The PF/silica were prepared with C/Si = 15 and solid content of 35 wt% The composition of extraction phase was liquid paraffin: nhexane: diisopropylamine = 8:9:3 The size of the scale is 400 μm Fig Optical micrographs of the extraction process of PF/silica microdroplets in the extraction phase The PF/silica were prepared with C/Si = 15 and solid content of 35 wt% The composition of extraction phase was liquid paraffin: nhexane: diisopropylamine = 8:3:9 The size of the scale is 300 μm phenol formaldehyde resol Meanwhile, it could enhance the gelation of colloidal silica The advantages of diisopropylamine catalyst are the lower reaction temperature, and high solubility in n-hexane and liquid paraffin Since the pH of the colloidal silica used in the present work was about 5, silica gel was formed when the microspheres interacted with diisopropylamine The concentration of diisopropylamine will affect the gelation rate of colloidal silica and the polymerization rate of phenol formaldehyde At low diisopropylamine concentration, the gelation and polymerization rate were low Diisopropylamine could diffuse into the microspheres before polymerization completed, therefore the elements distribution was quite even However, when the diisopropylamine concentration was high, phenol formaldehyde will be polymerized at the surface of the microspheres quickly, and more phenol formaldehyde resol will diffuse to the surface for polymerization Meanwhile, some diisopropylamine will diffuse into the microsphere and therefore silica gel formed inside the microspheres This process is similar to phase J Li et al Microporous and Mesoporous Materials 343 (2022) 112186 Fig 10 SEM images of microspheres after (a) aging; (b) carbonization; (c) removal of SiO2 by hydrofluoric acid The dispersed phase that used for the preparation of the microspheres had a m (C/Si) = 11 and solid content of 35 wt% SEM images with different magnifications (d) and (e) of the microspheres after treatment in an ultrasonic bath (45 kHz) for 30 Fig 11 (a) N2 adsorption-desorption isotherms; (b) and (c) NLDFT pore size distributions of carbon/silica microspheres and carbon microspheres after removal of SiO2; (d) particle size distribution of the colloidal silica prepared in the present work about 100 μm have been prepared using inverse-microemulsionpolymerization-phase-separation coupling method The polymerization was performed at 120 ◦ C for 12 h Phenolic resin was used as carbon source, ethylene glycol was used as pore generator and hexamethy lenetetramine was used as the hardener for polymerization The carbon microspheres displayed a surface area as high as 1622 m2/g, but almost no mesoporous was observed [10] In addition, the microemulsion polymerization method is batch with complicated operation procedures, i.e., mixing and temperature control, and the prepared microsphere normally showed a wide particle size distribution The method using microchannel technology can produce microspheres continuously with narrow size distributions, and the temperature in microchannel is even due to the enhanced heat transfer In addition, the microspheres are formed in a much shorter time about 15 in the microchannel at room temperature Colloidal silica is more economical than the other organic pore generators, and the microchannel method is easy to scale up, which shows high potential for large applications Conclusions Carbon/silica microspheres and carbon microspheres with a size of hundred-micron have been successfully prepared using microchannel technique The process was quite economical due to the gentle reaction conditions, i.e., room temperature and short reaction time Colloidal silica can significantly reduce the time for the formation of microsphere due to the gelation The use of 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(μm) Surface area (m2/ g) Total pore volume (cm3/g) dp (nm) Ref C(PF) particles n/a 126 0.07 1.57 Carbon/silica microspheresa Carbon microspheresa Carbon/silica microspheresb Carbon microspheresb Activated carbon microspheres Macroporous carbon spheres Ordered mesoporous carbon sphere Phenolic resinbased carbon spheres 170 295 0.14 1.3 170 625 0.38 11.3 174 329 0.15 1.4 174 679 0.50 6.2 ~100 1622 2.78 >10 This work This work This work This work This work [10] 0.4 451 0.28 n/a [29] 0.3 601 1.70 10.4 [30] n/a 797 0.35 [7] a and b microspheres prepared from dispersed phases with m(C/Si) = 11 and 6.5, respectively stationary phase of chromatography, supercapacitor, and catalyst carrier Notes The authors declare no confliction of interest CRediT authorship contribution statement Jie Li: Writing – original draft, Investigation, Formal analysis Zhenheng Xu: Investigation, Formal analysis Liang Yu: Writing – re view & editing, Supervision, Formal analysis, Data curation Lixiong Zhang: Writing – review & editing, Funding acquisition, Conceptualization Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Data availability Data will be made available on request Acknowledgment The authors acknowledge the financial support from the Priority Academic Program Development of Jiangsu Higher Education Institutions References [1] J Zang, P Tian, G Yang, S Jia, S Zhou, H Xu, Y Wang, A facile preparation of pomegranate-like porous carbon by carbonization and activation of phenolic resin prepared via hydrothermal synthesis in KOH solution for high performance supercapacitor electrodes, Adv Powder Technol 30 (2019) 2900–2907 [2] N.P Wickramaratne, M Jaroniec, Activated carbon spheres for CO2 adsorption, ACS Appl Mater Interfaces (2013) 1849–1855 ... smaller than the carbon/ silica microspheres The surface area of carbon/ silica microspheres increased significantly after removal of silica For instance, the surface area of carbon/ silica microspheres... Education Institutions References [1] J Zang, P Tian, G Yang, S Jia, S Zhou, H Xu, Y Wang, A facile preparation of pomegranate-like porous carbon by carbonization and activation of phenolic resin... precipitation Finally, the phenol formaldehyde resol resin was obtained after drying at 45 ◦ C to remove ethanol 2.3 Preparation of carbon microspheres Fig shows the microchannel device that used in