Activated Carbon Microspheres Research Articles

Boosted electrochemical performance of flower-like carbon microspheres derived from polyimides containing hydroxyl groups for supercapacitor electrodes

Herein, the flower-like microspheres derived from polyimides containing hydroxyl groups are firstly synthesized through a solvothermal technique. Then, the corresponding flower-like carbon microspheres are obtained after high-temperature carbonization. The influences of the poly(amic acid) concentration, solvothermal temperature, and treatment time on the electrochemical behaviors of carbon microspheres are investigated. The optimized carbon sample PC-2-180-10 demonstrates a distinct micro/mesopore characteristic, leading to a specific capacitance of 254.4 F g−1 at 0.5 A g−1. Subsequently, the sample is chemically activated with HNO3 for improving its electrochemical performance. When the HNO3 concentration is optimized as 6 M, the treatment temperature and time are 75 °C and 30 h respectively, the activated carbon microspheres APC-6-75-30 exhibit a maximum specific capacitance of 387.6 F g−1. Moreover, the APC-6-75-30 is symmetrically fabricated into a button-type supercapacitor (SC) device, and the SC shows a specific capacitance of 88.5 F g−1, with an energy density of 11.81 Wh kg−1 at a power density of 240.1 W kg−1. Six months later, the SC still demonstrates a better capacitive performance. Optimizing the solvothermal parameters and HNO3 treatment conditions, this work presents an effective strategy for boosting the electrochemical performance of flower-like carbon microspheres as a promising electrode for energy storage applications.

Low-temperature hydrothermal carbonization of activated carbon microsphere derived from microcrystalline cellulose as carbon dioxide (CO2) adsorbent

Activated carbon material produced by the low-temperature hydrothermal processes was needed to further decrease the production cost of CO2 adsorbent materials. In this study, we fabricated cellulose hydrochar microspheres (CHM) materials with a relatively low hydrothermal temperature (200 °C) with prolonged hydrothermal reaction time (48 h) using microcrystalline cellulose as a feedstock. The CHM is then further activated using a thermal and chemical agent. The activated carbon microsphere was then characterized using scanning electron microscopy (SEM), an X-ray diffractometer (XRD), and Fourier transforms infrared (FTIR) spectroscopy. The Brunauer–Emmett–Teller (BET) surface area (SBET) of the thermal activation (ACS) activated carbon was enhanced significantly with further chemical activation with KOH and NaOH, from 589 m2/g to 1334 m2/g and 2296 m2/g, respectively. Moreover, CHONS elemental analysis suggests that the chemical activation process enhances the surface functional group. Increasing textural properties and enrichment of the functional group of the ACS-NaOH and ACS-KOH samples gave a CO2 adsorption capacity up to 7.07 mmol/g after 300 min of contact. This finding enables the possibility of producing cellulose hydrochar microspheres using a low hydrothermal temperature that can be further activated to become CO2 adsorbent materials with great CO2 capture capabilities.

A novel micro-sphere activated carbon synthesized from waste cigarette butts for ammonia adsorption

Waste cigarette filters mainly contain hardly degradable cellulose acetate, toxic nicotine, and traces of heavy metals, and therefore cause environmental pollution hazards when discarded. In order to convert cigarette butt waste into a valuable product, this article investigates the preparation of activated carbon from cigarette butts via a two-step process of hydrothermal reaction and a subsequent chemical activation with phosphoric acid as an activator. During hydrothermal reaction, it was found that a process of decarboxylation and dehydration cleavage of acetate occurs, leading to micron fragments and subsequent agglomeration into carbonaceous micro-spheres. The cigarette-butts-derived activated carbon micro-spheres have a high BET surface area of ∼ 1406 m2/g and NH3 adsorption capacity of ∼ 35.9 mg/g. It was revealed that the ammonia adsorption capacity tends to be positively and linearly correlated with the acidic functional group content of the activated carbon surface while negatively with BET surface area.

Novel Bilayer-Shelled N, O-Doped Hollow Porous Carbon Microspheres as High Performance Anode for Potassium-Ion Hybrid Capacitors

HighlightsProposing a one-step pyrolysis strategy to fabricate a novel bilayer-shelled N, O-doped hollow porous carbon microspheres (NOHPC) anode.The optimized NOHPC anode displays a high K-storage capacity of 325.9 mAh g−1 at 0.1 A g−1 and excellent rate performance (201.1 mAh g−1 at 5 A g−1 after 6000 cycles).The assembled NOHPC//hollow porous activated carbon microspheres (HPAC) potassium ion hybrid capacitors deliver a high energy density of 90.1 Wh kg−1 at a power density of 939.6 W kg−1 even over 6000 cycles.

Activated carbon microspheres with high surface area for efficient organic contaminants removal

Modified carbon microspheres with large specific surface area (1334 m2 g−1) and abundant microporous structure are prepared using glucose as raw material via a simple hydrothermal and subsequent activation-carbonization process. The KHCO3 activation markedly increases the specific surface area (> 6 times) and pore volume (> 4 times) of obtained carbon microspheres, which endow it with excellent adsorption ability towards organic pollutants in aqueous solution. The KHCO3 activated carbon microspheres (KCMS) can efficiently remove 94 % methylene blue in 20 min (98 % in 60 min) at a low adsorbent dosage (10 mg adsorbent vs. 100 ml, 100 mg L−1 dye), and the saturation adsorption capacity reaches 1551.99 mg/g. The synergism of chemical interaction, pore filling effect, π-π interaction, hydrogen bond formation and electrostatic attraction gives KCMS excellent adsorption performance. The KCMS can be repeatedly used with high adsorption capacity. It also exhibits good adsorption ability towards rhodamine B (237.64 mg/g) and tetracycline (297.34 mg/g), indicating it is a wide range adsorbent. The results reveal that the activated carbon microspheres obtained by a simple process are efficient adsorbents for organic pollutants removal in wastewater. It suggests a new opportunity to develop novel low-cost adsorbent with excellent performance.

Performance and modeling of Ni(II) adsorption from low concentrated wastewater on carbon microspheres prepared from tangerine peels by FeCl3-assisted hydrothermal carbonization

The presence of heavy metals in the environment as a consequence of human activity is an issue that has caught the attention of researchers to find wastewater treatment solutions, such as adsorption. In this work, hydrochars and activated carbon microspheres are prepared from tangerine peels as carbon precursor and FeCl3 as activating and structure-directing agent in the hydrothermal carbonization, allowing to obtain hydrochar microspheres ranging from 50 to 3615 nm. In addition, a pyrochar was prepared by pyrolysis of the same precursor. The activated carbon shows the highest surface area (SBET up to 287 m2 g–1), but the basicity of the pyrochar (1.83 mmol g−1, SBET = 104 m2 g–1) was determinant in the adsorption of Ni, being considered the carbon-based material with the highest uptake capacity of Ni. Isotherm and kinetic adsorption of Ni on the most representative activated carbon microsphere, pyrochar and hydrochar microsphere are assessed by 10 and 7 models, respectively.

One-pot hydrothermal preparation of manganese-doped carbon microspheres for effective deep removal of hexavalent chromium from wastewater

Mn-doped activated carbon microspheres (MnOx/ACS) with super-high adsorption capacities and deep removal capability for hexavalent chromium (Cr(VI)) were successfully prepared via an ammonium persulfate-assisted hydrothermal method followed by potassium oxalate activation using KMnO4 and sucrose as raw materials. Their -physical and chemical properties, as well as those of Mn-doped non-activated carbon spheres (MnOx/CS), were characterized by XRD, SEM, TEM, EDS-mapping, XPS, N2 adsorption–desorption, ICP-AES, and elemental analysis. It was found that the manganese oxide (MnOx) particles were uniformly embedded within the carbon spheres via layer-by-layer capture, and the MnOx/ACS exhibited strong redox activity because of the multivalent nature of MnOx, resulting in excellent adsorption performance via reduction. In particular, MnOx/ACS-4 with a Mn content of 1.06 wt% and a specific surface area of 1405.7 m2 g−1 achieved a maximum adsorption capacity of 660.7 mg g−1; this can reduce Cr(VI) content to less than 0.05 mg L-1, which meets the corresponding Chinese drinking water quality standard when the initial concentration of Cr(VI) is less than 400 mg L-1. Furthermore, this highly efficient method can be extended to prepare V-, Mo-, or W-doped carbon microspheres with significantly enhanced adsorption performance for Cr(VI) compared to bare activated carbon sphere, indicating their good application prospect for the deep removal for heavy metal ions from wastewater.

Preparation and electrochemical performance of activated carbon microspheres from recycled novolak phenol formaldehyde

In this study, an attempt is made to obtain porous activated carbon microspheres (ACMs) as supercapacitor electrodes by recycling waste novolak phenol formaldehyde (NPF) resins. These NPF-ACMs were prepared by a three-step procedure of hydrothermal synthesis, carbonization, and activation in turn. The effects of temperature, time, and sodium dodecyl sulfonate (SDS) addition on NPF-based microspheres were studied by the orthogonal method. The optimal preparation process of NPF-based microspheres was the following: 230 °C, 4 h, and a mass ratio of SDS: NPF of 24:1 by hydrothermal synthesis. Based on the above optimal conditions, NPF-ACMs were made, the yield of the microspheres after carbonization and chemical activation are 54% and 38%, and their electrochemical properties were analyzed. The NPF-ACMs had uniform size, a high surface area of 2528 m2 g−1, good dispersion, a low impedance of 0.46 Ω, highest specific capacitance of 118.6 F g−1 at 0.5 A g−1, good rate capability with 79% retention from 0.1 to 10 A g−1. Moreover, it showed high capacitance retention of 99.5% after 1000 cycles at a scan rate of 5 mV s−1. The results showed that waste NPF can be used as promising ACMs of the electrode material to increase its utilization value.

Activated carbon microspheres derived from hydrothermally treated mango seed shells for acetone vapor removal

Mango fruit seed shells were used as starting materials to produce activated carbons for the capture of acetone, a typical volatile organic compound (VOC), from gaseous streams. This fruit waste presents high volatiles and low ashes contents, as expected for the lignocelulosic materials commonly used for the preparation of activated carbons. The starting material was hydrothermally treated at 180 or 250 °C for 5 h and the obtained hydrochars were activated with KOH solutions. The carbon samples were characterized by SEM, EDX, TG/DTA, Raman spectroscopy and textural analysis by physisorption. The adsorption capacity and adsorption cycles were investigated by TG. The hydrochars presented spherical morphology and the activated carbons derived from them presented heterogeneous micropore structures allowing to high capacity of acetone vapor removal, namely 472 mg/g, at 30 °C and 363 mg/g, at 50 °C. The results indicate that the adsorption capacity of the activated carbons is directly related to their Dubinin-Astakhov micropore surface areas and microporous volumes determined by NLDFT. The adsorption of acetone vapor showed a pseudo-first order kinetics and both external and intra-particle transport contributed for the overall process. Highly efficient and stable acetone vapor removal was observed over the activated carbons after five cycles.

Geometrical effects on ionic diffusion in carbon‐carbon symmetric supercapacitors

There is a great need to understand the structural dependence of supercapacitors for the development of advanced electrode materials that can be used to improve the electrochemical performance and structural integrity. In this work, we investigate the effects of the size and pore width/size of activated carbon microspheres (ACMSs) with diameter in a range of 2.7 ± 0.54 to 9.45 ± 1.81 μm and average pore width in a range of 1.60 to 2.0 nm on the electrochemical impedance characteristics of carbon-carbon symmetrical supercapacitors. Both the size and pore width/size of the ACMSs have negligible effects on contact resistance. The activation energy for the migration/diffusion of electrolyte ions in the supercapacitors made from the ACMSs of nearly same porous structure increases nonlinearly with the increase of the average size of the ACMSs, which is likely associated with overscreening effect. The activation energy for the migration/diffusion of electrolyte ions in the supercapacitors made from the ACMSs of nearly same size increases first and then decreases as the pore width/size increases.

Self-assemblying behaviour of activated microporous carbon microspheres functionalized via water filtration process

Activated carbon spheres are truly innovative materials with their porous micro/nanostructure that gives them tunable and controllable surface properties (i.e. high surface area, size and orientation of pores etc.). They have great potential for applications as adsorbents for cleaning/purification of water, air and chemical substances, catalyst supports, energy storage and conversion, adsorption of chemical warfare agents, filtration and others. Magnetic functionalization of highly porous and high surface areas of activated carbons have received considerable attention for their more sophisticated and advanced utilization as “smart” and “self-assemblying” purposes. In this study, a novel fabrication technique was used to synthesize activated high compressive strength nanoporous carbon spheres. The functionalization via adsorption/impregnation of magnetic substances was occured during a well-known water treatment-filtering route to fill the pores with nano-sized magnetic particles. Unusually active and dynamic interactions of the magnetic phases were observed upon contacting into each other revealing self-assemblying behaviour of activated carbon microspheres. Dynamic magnetical interaction of self assemblying behaviour of these spheres may have further and advanced applications for variety of purposes.

Starch-based activated carbon micro-spheres for adsorption of methane with superior performance in ANG technology

In current research work, Nano porous carbon spheres were synthesized for efficient methane (CH4) adsorption. To this end, starch was employed as the starting carbon source which was carbonized at 800 °C. Therefore, in order to activate the carbonized samples, different ratios of KOH were used. The activation process was performed using Carbon: KOH ratios of 1:1, 1:2, and 1:4 at 800 °C. The prepared adsorbents were characterized by different techniques including FESEM, X-ray diffraction, FTIR, and BET. Furthermore, CH4 adsorption experiments were carried out on the prepared adsorbents which yielded very good performance. It was found that increasing the KOH content in the activation process increases both the specific surface area and total pore volume, which in turn enhanced the CH4 uptake. As a result of activation method, the best nano porous sample with Carbon:KOH ratio of 1:4 showed high specific surface area and pore volume up to 2222.3 m2/g and 1.72 cm3/g, respectively. The adsorbents had superior adsorption capacity of 12.81 mmole/g at 35 bar, which is much higher than those of literature. This adsorbent with excellent CH4 adsorption performance can be exploited in Adsorbed Natural Gas (ANG) technology to ensure energy storage and usage of high efficiencies.

Waste biomass valorization through production of xylose-based porous carbon microspheres for supercapacitor applications

Sequential potassium hydroxide (KOH)-phosphoric acid (H3PO4) activation was applied to biomass waste to fabricate activated carbon microspheres (mCMs) with a controllable porous structure. Carbon microspheres (CMs) were first synthesized from xylose using a bottom-up approach of hydrothermal carbonization. Sequential KOH and H3PO4 activation was applied to the CMs in a KOH-carbon solid reaction. This created pores, which were further enlarged by adsorption of H3PO4. The KOH:carbon (C) and H3PO4:C molar ratios, and the H3PO4 heating rate and activation time, were varied to investigate the effect on average pore size and pore distribution. A uniform porous structure was formed without destruction of the spherical shape, and an almost 700-fold increase in surface area was obtained over the non-activated CMs. Following activation with H3PO4, phosphorous groups were found to be present at the surface of the carbon microspheres. The mCM was tested as a supercapacitor electrode and was shown to have a maximum specific capacitance of up to 277F g−1. A Ragone plot showed the maximum power density to be 173.88 W Kg−1. This increased specific capacitance was attributed to the increase in surface area and the presence of phosphorous-containing acid sites on the material surface.

Activated Carbon Microsphere from Sodium Lignosulfonate for Cr(VI) Adsorption Evaluation in Wastewater Treatment.

In this study, activated carbon microsphere (SLACM) was prepared from powdered sodium lignosulfonate (SL) and polystyrene by the Mannich reaction and ZnCl2 activation, which can be used to remove Cr(VI) from the aqueous solution without adding any binder. The SLACM was characterized and the batch experiments were conducted under different initial pH values, initial concentrations, contact time durations and temperatures to investigate the adsorption performance of Cr(VI) onto SLACM. The results indicated that the SLACM surface area and average pore size were 769.37 m2/g and 2.46 nm (the mesoporous material), respectively. It was found that the reduced initial pH value, the increased temperature and initial Cr(VI) concentration were beneficial to Cr(VI) adsorption. The maximum adsorption capacity of Cr(VI) on SLACM was 227.7 mg/g at an initial pH value of 2 and the temperature of 40 °C. The adsorption of SLACM for Cr(VI) mainly occurred during the initial stages of the adsorption process. The adsorption kinetic and isotherm experimental data were thoroughly described by Elovich and Langmuir models, respectively. SL could be considered as a potential raw material for the production of activated carbon, which had a considerable potential for the Cr(VI) removal from wastewater.

Mesoporous NiMoO4 microspheres decorated by Ag quantum dots as cathode material for asymmetric supercapacitors: Enhanced interfacial conductivity and capacitive storage

Nickel molybdate (NiMoO4) as a ternary metal oxide has great potential as advanced electrode material for energy storage. However, the practical application of NiMoO4 electrode is hindered by its poor electrical conductivity. In this work, the surface of mesoporous NiMoO4 microspheres is decorated with silver quantum dots (Ag QDs/NiMoO4) by means of “dipping and drying”. It is interesting to find that an ohmic contact interface (electron anti-barrier layer) generates between the Ag QDs and NiMoO4 microsphere. Benefitting from the high specific surface area, abundant surface active sites, enhanced interfacial conductivity and porous structure of the Ag QDs/NiMoO4 microspheres, the composite electrode presents high specific capacitance of 3342.7 F g−1 at 1 mV s−1 and 2074 F g−1 at 1 A g−1 (nearly twice the value of the pristine mesoporous NiMoO4 microsphere electrode), good rate capability and improved cycling stability. Furthermore, an asymmetric supercapacitor assembled with the Ag QDs/NiMoO4 microspheres as cathode, spore-derived activated carbon microspheres as anode and 3 M KOH as aqueous electrolyte, reveals a relatively high energy density (48.5 Wh kg−1 at a power density of 212.5 kWh kg−1) and good cycling performance comparing with most of the reported NiMoO4-based asymmetric supercapacitors.

Large‐scale production of nitrogen‐ and oxygen‐containing activated carbon microspheres for supercapacitors

A main issue in the production of robust supercapacitors is the creation of efficient and cost‐effective electrodes. We present here the realization of a kind of nitrogen‐ and oxygen‐containing activated carbon microspheres made from divinylbenzene, diallyl phthalate, and acrylonitrile monomers, which can be produced on a large scale for use in supercapacitors. The supercapacitor's performance is optimized by adjusting the carbonization temperature of the microspheres. Our preliminary result shows that the supercapacitor displays a maximum capacitance of 300 F/g at the current density of 1.0 A/g and retains ~82% of the capacitance after 10,000 charge–discharge cycles.

Carbon microspheres prepared from the hemicelluloses-rich pre-hydrolysis liquor for contaminant removal

Pre-hydrolysis liquor (PHL) from the kraft-based dissolving pulp process contains large amounts of hemicelluloses, which is usually treated as an effluent and further efforts have to be involved to eliminate the pollution disposal. However, the hemicelluloses-rich PHL is a promising candidate for the production of carbon microspheres via hydrothermal carbonization. The yield of the carbon microspheres directly derived from the hydrothermal carbonization of the hemicelluloses-rich PHL (22.1%) was almost twice than that from xylose (13.1%). Furthermore, sulfuric acid and the lignin in the PHL could significantly improve the yield and change the size of the carbon microspheres obtained from the PHL. Additionally, the activated carbon microspheres functionalized with acrylic acid showed improved adsorption capacities for Pb(II) ion (273.4 mg/g) and methylene blue (701.3 mg/g). The hydrothermal carbonization of the PHL not only utilizes the hemicelluloses in the PHL, but also reduces the pollution load of the PHL significantly.

Activated carbon spheres (ACS)@SnO2@NiO with a 3D nanospherical structure and its synergistic effect with AHP on improving the flame retardancy of epoxy resin

A novel activated carbon spheres (ACS)@SnO2@NiO hierarchical hybrid architecture was first synthesized and applied for enhancing the flame retardancy of epoxy (EP) resin via a cooperative effect. Herein, using activated carbon microspheres as the template, SnO2 and NiO nanospheres were successively anchored to it by a sedimentation‐calcination strategy. The well‐designed ACS@SnO2@NiO significantly enhanced the flame retardancy for consistency of EP composites, as demonstrated by thermogravimetric and cone calorimeter experiments. For instance, the incorporation of 2 wt% ACS@SnO2@NiO decreased by 15.5% maximum in the total smoke production, accompanying the higher graphitized char layer. In addition, the synergetic mechanism of flame retardancy between ACS@SnO2@NiO and aluminum hypophosphite (AHP) was investigated. The obtained sample satisfied the UL‐94 V‐0 rating with a 5.0 wt% addition of AHP and ACS@SnO2@NiO (the ratio of the mass fraction of AHP to ACS@SnO2@NiO is 4.5:0.5). Notably, the incorporation of AHP and ACS@SnO2@NiO resulted in a significant decrease in the fire hazard properties of EP resin; for instance, 4.5AHP‐0.5ACS@SnO2@NiO/EP resulted in a maximum decrease of 32.4% in the total smoke production as compared with that of pure EP resin. It should be noted that the improved flame‐retardant performance for the EP composites is primarily attributed to the synergistic effect of ACS@SnO2@NiO and AHP in promoting the formation of residual char in the condensed phase.

Preparation and Characterization of Wood-based Pre-oxidized Precursors and Activated Carbon Microspheres

Wood-based activated carbon microspheres (WACMs) were successfully prepared from Chinese fir. However, the weak thermal stability of the precursors resulted in melting at high activation temperatures, which led to a lower yield and poor adsorption properties. To promote the thermal stability of the precursors in the process without chemicals, this paper focused on the effects of the pre-oxidation before activation on the thermal stability and chemical structure of the precursors and the pore structure of the activated samples. The results showed that during the pre-oxidation process, the O/C ratio increased noticeably and the intensity of oxygen-containing functional groups, such as carbonyl, carboxyl, and ester groups, were enhanced, which contributed to the improvement of the thermal stability. Moreover, the etching effect of oxygen on the structure of the precursors was verified when the porous structure was enriched by activation. The activated sample pre-treated at pre-oxidation temperature 250 °C had the maximum micropore specific surface area and pore volume. As the temperature was raised to 280 °C, the mesopore specific surface area and pore volume increased, which indicated that the optimization of the pre-oxidation parameters contributed to the formation of the mesopore structure.

Effects of Chemical Curing on the Properties of Wood-based Precursors and Activated Carbon Microspheres

Wood-based precursors and activated carbon microspheres were prepared through chemical curing and activation. The effects of the hydrochloric acid concentration on the thermal stability of the precursors and pore structures of the wood-based activated carbon microspheres were studied by thermo-gravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and analysis of the specific surface area and pore structure. The results showed that the reaction between the carbocations and benzene rings contributed to an increase in the methylene bonds, which reinforced the cross-linking degree and thermal stability of the wood-based cured microspheres. After activation, a typical microporous structure and part of an irregular mesoporous structure were formed in the wood-based activated carbon microspheres. The specific surface area, micropore volume, and mesopore volume increased, reaching maximum values of 1551 m2/g, 0.506 cm3/g, and 0.246 cm3/g at 4 mol/L hydrochloric acid, respectively, and then decreased as the hydrochloric acid concentration increased. The pore size distributions of the micropore and mesopore areas were in the range of 0.5 nm to 1.4 nm and 2 nm to 10 nm, respectively.