One-step KOH Activation Research Articles

Effective Adsorption of Chlorinated Polyfluoroalkyl Ether Sulfonates from Wastewater by Nano-Activated Carbon: Performance and Mechanisms

Chlorinated polyfluoroalkyl ether sulfonates (F-53B) were often used as mist suppressants in the chrome plating industry, resulting in the large discharge of F-53B-containing electroplating wastewater into the aquatic environment. Due to the high toxicity of F-53B, increasing attention has been paid to its efficient removal from wastewater. In this study, three nano-activated carbons were successfully prepared from coconut shell carbons by a simple one-step KOH activation method. The nitrogen adsorption/desorption experiments showed that the synthesized coconut shell activated carbons possessed a well-developed nano-pore structure, which was favorable for the adsorption of F-53B. The results suggested that the adsorption of F-53B on the coconut shell activated carbons followed pseudo-second-order kinetics and was better fitted in the Langmuir isotherm, indicating that the adsorption of F-53B was mainly controlled by chemical adsorption and was mainly monolayer adsorption. Theoretical calculation results revealed that the faster adsorption rate of F-53B on CSAC_800 than on CSAC_600 and CSAC_700 could be contributed to the lower adsorption energy of F-53B on CSAC_800 and the higher self-diffusion coefficients of F-53B in CSAC_800. The higher adsorption capacity of CSAC_800 (qm = 537.6 mg·g−1) for F-53B than that of CSAC_600 (qm = 396.83 mg·g−1) and CSAC_700 (qm = 476.19 mg·g−1) could be attributed to the higher specific surface area and larger number of adsorption sites of CSAC_800. The results of this study demonstrate that coconut shell activated carbons with a well-developed nano-pore structure are an effective adsorbent for F-53B removal and have a good application prospect.

Hierarchical Porous Activated Carbon Derived from Coconut Shell for Ultrahigh-Performance Supercapacitors.

In this research, we successfully produced hierarchical porous activated carbon from biowaste employing one-step KOH activation and applied as ultrahigh-performance supercapacitor electrode materials. The coconut shell-derived activated carbon (CSAC) features a hierarchical porous structure in a honeycomb-like morphology, leading to a high specific surface area (2228 m2 g-1) as well as a significant pore volume (1.07 cm3 g-1). The initial test with the CSAC electrode, conducted in a 6 M KOH loaded symmetric supercapacitor, demonstrated an ultrahigh capacitance of 367 F g-1 at a current density of 0.2 A g-1 together with 92.09% retention after 10,000 cycles at 10 A g-1. More impressively, the zinc-ion hybrid supercapacitor using CSAC as a cathode achieves a high-rate capability (153 mAh g-1 at 0.2 A g-1 and 75 mAh g-1 at 10 A g-1), high energy density (134.9 Wh kg-1 at 175 W kg-1), as well as exceptional cycling stability (93.81% capacity retention after 10,000 cycles at 10 A g-1). Such work thus illuminates a new pathway for converting biowaste-derived carbons into materials for ultrahigh-performance energy storge applications.

Production of hierarchical porous bio‑carbon based on deep eutectic solvent fractionated lignin nanoparticles for high-performance supercapacitor

Owing to the low synthetic cost, low toxicity for most types and outstanding lignin solubility, deep eutectic solvents (DESs) have been recently exploited in fractionation of lignocellulosic biomass. Unfortunately, the DES-fractionated lignin, as another major product, was usually ignored and disposed improperly. Accordingly, the present study employed DES (choline chloride:lactic acid) to fractionate natural biomass for producing highly dispersed lignin nanoparticles. The obtained nano-lignin was utilized to prepare electrode materials for supercapacitors for the first time, and a higher specific capacitance than those prepared from conventional lignin was acquired. The results demonstrated that the lignin fractionation rate could be promoted via extending treatment time at low temperatures, whereas the DES to biomass mass ratio might be the lignin dissolution-limiting factor at high temperature. Uniform lignin nanoclusters could be obtained after DES fractionation, and increasing fractionation temperature was beneficial for preparing nano-lignin in DES. The cleavages of lignin-carbohydrate complexes and lignin subunits might account for the formation mechanism of lignin oligomers. Meanwhile, the aggregation of monolignols could contribute to the growth of lignin nanoparticles. The one-step KOH activation could induce hierarchical pores in lignin fractionated from moderate residence time, whereas two-step method was advisable for more aggregated DES-lignin. Based on the directly activated DES-lignin with a high surface area of 3577.3 m2 g−1, the prepared supercapacitor exhibited a superior specific capacitance of 248.8 F g−1. This study aimed to provide a novel method for producing high-performance energy storage carbon materials based on DES fractionated lignin from lignocellulose.

Tailored mesoporous structures of lignin-derived nano-carbons for multiple applications

This work uses a one-step KOH activation for lignin precursors to produce ultra-high mesoporous activated carbons (ACs) with an unprecedented combination of the surface area of 3207 m2 g−1 and mesopore ratio of 76%. The ACs are applied for supercapacitors (SCs) and methylene blue (MB) adsorption. The capacitance of the SCs in the three-electrode system reaches 812.3 F g−1 and demonstrates a remarkable maximum MB adsorption capacity of 1250 mg g−1. By modifying the process conditions, the mesopore ratio of ACs could be controlled from 10% to 80%. Compared with one-step activation, a two-step method produced microporous carbons with a lower surface area of 1227 m2 g−1 and a high micropore ratio of 73%. The capacitance of SCs with two-step ACs reached 228.1 F g−1 and the maximum adsorption capacity of 476.19 mg g−1 for MB adsorption. The two-step method limited the surface area but had a higher oxygen surface functionality, benefiting its electrochemical performance. A techno-economic analysis reveals that the one-step KOH activation-based process develops ACs with a minimum selling price of $7648/ton. This work demonstrates tuning the processing-structure-property-performance relationship of lignin-based ACs to make an economically viable domestic carbon source.

N, S, O Self-Doped Carbon Derived from Grapefruit Peel for High-Performance Supercapacitors.

The development of high-capacity carbon for supercapacitors is highly desirable but challenging. In this work, we design a N, S, O self-doped carbon electrode (NSOC-800) with high capacitance and good stability via the carbonization of grapefruit peel via a one-step KOH activation method without extra dopants. The existence of heteroatoms enables the NSOC-800 to have a high specific capacitance of 280 F/g and a great cycling performance, with 90.1% capacitance retention after 5000 cycles. Moreover, the symmetric supercapacitor with NSOC-800 electrodes delivers a maximum energy density of 5 Wh/kg with a power density of 473 W/kg. Such a promising method to achieve carbon materials with self-doping heteroatwoms is of great significance for developing highly efficient electrodes for energy storage devices.

Preparation of hierarchical porous carbon through one-step KOH activation of coconut shell biomass for high-performance supercapacitor

Here we report an effective and facile method for preparing porous carbons (CSCK-T-x) with highly developed hierarchical porosity for high-performance supercapacitor by one-step KOH activation of coconut shell carbon. The effects of carbonization temperature (T, °C) and KOH/C ratio (x) on the structure and electrochemical properties were studied systematically. As the KOH/C ratio and activation temperature increase, the SBET rapidly increases and then decreases and reaches a maximum (2143.6m2 g−1) at 800 °C with a KOH/C ratio of 2. Furthermore, CSCK-800-2 displayed abundant micropores and two concentrated mesopores at 4 nm and 14 nm. In a three-electrode test system, CSCK-800-2 exhibits a high specific capacitance of 317 F g−1 at a current density of 0.5 A g−1 and considerable rate retention of 68% at 20 A g−1. The symmetrical supercapacitor that was based on CSCK-800-2 showed a maximum energy density of 13.5 Wh kg−1 at 0.5 A g−1 with a superior cycling stability (99.7% of the capacitance retention after 10,000 cycles at 5 A g−1) in 6 M KOH electrolyte. The large specific surface area and unique hierarchical porosity of CSCK-800-2 enable it to have high ion-accessible surface and low-ion transport resistance. This one-step activation method provides an approach to convert biological waste into high-value hierarchical porous carbon material for electric double-layer capacitors.

Ternary-doped hierarchical porous carbons derived from durian kernel as electrode materials for efficient energy storage devices

In this work, ternary-doped hierarchical porous carbons (HPCs) were prepared from the durian kernel (DK) via one-step KOH activation. Due to abundant heteroatoms in DK as well as KOH activation, the DK-derived activated carbons exhibit cheese-like morphology with hierarchical porous structure, large specific surface area and high N/O/S multi-doped content, triggering the excellent electrochemical performance as electrode materials in supercapacitor and lithium-ion battery. The novel N/O/S multi-doped HPC (DKAC-700) electrode, which is assembled in a symmetrical supercapacitor using 6 M KOH electrolyte, achieves a high specific capacitance of 330 F g−1 at 0.2 A g−1, as well as 96.7 % capacity retention after 10,000 cycles at 2 A g−1. Additionally, the lithium-ion battery using DKAC-700 as an anode exhibits an excellent rate capability (541 mAh g−1 at 0.5 A g−1 and 139 mAh g−1 at 20 A g−1) and cycling stability (capacity retention of 91.9 % after 250 cycles). This study significantly facilitates the application of biowaste-derived carbons in high-performance energy storage devices.

Insight into the Supercapacitive Behavior of Activated Hollow Porous Carbon Spheres in Different Electrolytes

Supercapacitive behaviors of the porous carbon electrode principally depend on the properties of electrolyte. In this paper, activated hollow porous carbon spheres (AHPCSs) with large specific areas were prepared by the hydrothermal method and subsequent one-step KOH activation treatment. The electrochemical performances and supercapacitive characteristics of the AHPCS supercapacitors were evaluated in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid electrolyte, 1 mol L–1 LiPF6 organic electrolyte, and 6 mol L–1 KOH aqueous electrolyte. It has been found that the supercapacitors with AHPCS electrode have definitely good supercapacitive behaviors in the three electrolytes. Especially, the AHPCS supercapacitor in the EMIMBF4 ionic liquid electrolyte that has a wide operating voltage of 0–3.0 V exhibits an excellent rate performance with capacitance retention of 72.3% from 0.5 to 10 A g–1 and a good cycle performance with a high capacitance retention of 94.2% after 4000 consecutive cycles. Moreover, it obtains a high energy density of 80.5 Wh kg–1 at 750 W kg–1, which transcends most of the currently reported carbon-based supercapacitors. Therefore, the supercapacitors with EMIMBF4 ionic liquid as electrolyte and AHPCSs as active electrode materials show tremendous potential in terms of boosting comprehensively electrochemical performance.

Preparation of activated carbon from unburned carbon in biomass fly ash and its supercapacitor performance

After the fuel undergoes pyrolysis and combustion in a biomass boiler, the fly ash contains some unburned carbon with abundant pores. However, their low porosities and specific surface areas cannot meet the requirements of the activated carbon for commercial supercapacitors, and the activation method to improve their pore structures is the key to enhance their applicability. After the one-step KOH activation treatment of the unburned carbon with the particle sizes > 0.2 mm, the results showed that the activated carbon has the largest specific area (1982 m2/g) at an impregnation ratio of 3.5:1, and the specific capacitance reached 207 F/g at the current density of 1 A/g. The above results indicate that unburned carbon-based activated carbon has a good double layer capacitance performance, providing a reference for the high value-added utilization of biomass fly ash.

High-porous activated carbon derived from Myristica fragrans shell using one-step KOH activation for methylene blue adsorption

This study aims to synthesise high-surface-area activated carbon (AC) from Myristica fragrans shell (MFS) waste via a one-step KOH activation process. Herein, the optimum conditions in AC production were achieved from the impregnation weight ratio of MFS to KOH 1:0.5 at 700 °C for 30 min of activation time, which resulted in 1462 m2/g and 0.873 cm3/g for the Brunauer-Emmet-Teller surface area and total pore volume, respectively. The optimised AC was used in the adsorption of methylene blue from synthetic solution in a continuous flow system. The maximum methylene blue adsorption capacity was high at 346.85 mg/g at 25 °C. The findings exhibited the feasibility of MFS waste to be employed as a promising and low-cost raw material for the production of high-surface-area AC for dye removal from water and augmentation of solid waste management.

3-D hierarchical porous carbon from oxidized lignin by one-step activation for high-performance supercapacitor

To convert lignin into high-valued carbon materials and understand the lignin structure function, oxidized lignin, a by-product from lignocellulose PHP-pretreatment (phosphoric acid plus hydrogen peroxide), was carbonized by one-step KOH-activation; the physico-chemical characteristics and electrochemical performances of the harvested carbons were also investigated. Results indicated the resultant carbons displayed 3-dimensional hierarchical porous morphology with maximum specific surface area of 3094 m2 g−1 and pore volume of 1.72 cm3 g−1 using 3:1 KOH/lignin ratio for carbonization. Three-electrode determination achieved a specific capacitance of 352.9 F g−1 at a current of 0.5 A g−1, suggesting a superior rate performance of this carbon. Two-electrode determination obtained an excellent energy density of 9.5 W h kg−1 at power density of 25.0 W kg−1. Moreover, 5000 cycles of charge/discharge reached 88.46% retention at 5 A g−1, implying an outstanding cycle stability. Basically, low molecular weight and abundant oxygen-containing functional groups of employed lignin mainly related to the excellent porous morphology and the outstanding electrochemical performances, suggesting the oxidized lignin was an ideal precursor to facilely prepare activated carbon for high-performance supercapacitor. Overall, this work provides a new path to valorize lignin by-product derived from oxidative pretreatment techniques, which can further promote the integrality of lignocellulose biorefinery.

Porous Carbons Derived from Sustainable Biomass via a Facile One-Step Synthesis Strategy as Efficient CO2 Adsorbents

In this work, porous carbons were achieved from sustainable biomass lotus stalk. Unlike the common carbonization-activation two-step method, a facile one-step KOH activation procedure was explored to make the carbonaceous sorbents. The as-made adsorbents have advanced porous structures and hold superior CO2 uptake, up to 3.68 and 5.11 mmol/g at 1 bar, 25 and 0 °C, respectively. After carefully checking the relationship of CO2 uptake with each porous characteristic, the volume of narrow micropores is found to be the leading factor that determines the CO2 adsorption abilities of the adsorbents under ambient conditions. Moreover, the narrower pore size distribution is also preferential to the adsorption of CO2. Apart from the high CO2 uptake, these lotus stalk-derived adsorbents also possess extra excellent CO2 capture properties such as good recyclability, fast adsorption kinetics, reasonable CO2/N2 selectivity, suitable heat of adsorption, and high dynamic adsorption capacity. These results demonstrate that these cost-effective carbonaceous adsorbents developed by the facile one-step method have potential in the application of actual CO2 capture.

CO2 adsorption of lignite chars after one-step KOH activation

The design and development of low-cost sorbents is vital for CO2 capture from flue gases.

One-Step Activation Synthesized Hierarchical Porous Carbon Spheres from Resorcinol–Thiourea–Formaldehyde for Electrochemical Capacitors

In this work, a facile one-step KOH activation strategy has been developed toward synthesis of N/S-codoped hierarchical porous carbon spheres (NSHPCSs) from resorcinol–thiourea–formaldehyde sphere precursors. Quite different from the samples prepared by a traditional two-step activation that includes a successive KOH activation after carbonization, NSHPCSs possess a typical interconnected hierarchical porous structure comprised of macro-, meso-, and micropores with large pore volume and suitable pore size distribution, together with heteroatom doping of N and S. Originating from the above synergetic effect, the resultant NSHPCSs deliver a high specific capacitance of 295 F/g at 0.5 A/g, outstanding rate capability (78.6% retention at 20 A/g), and excellent cycling stability (95.2% retention over 5000 cycles). Furthermore, a symmetric supercapacitor achieves a high energy density of 7.36 Wh/kg at a power density of 100 W/kg. Thus, our study demonstrates an effective and simple approach of producing high-performance supercapacitor electrode materials for energy storage.

Alkali promoted the adsorption of toluene by adjusting the surface properties of lignin-derived carbon fibers.

The lignin-based carbon fibers were prepared by electrospinning followed by stabilization, carbonization, and activation (i.e., steam activation, one-step KOH activation, and metal activation). The effect of carbonization temperature on prepared carbon fibers (CFs) was investigated. As a result, 800°C is the most suitable carbonization temperature because the prepared carbon fibers possess greater specific surface area and pore volume. With the help of various characterization methods, the structural characteristics of the activated carbon fibers (ACFs) prepared by the three activation methods and the adsorption performance of toluene were compared. It was observed that the activated carbon fibers prepared by KOH one-step activation method (ACFK) exhibited higher specific surface area (1147.16m2/g) and greater toluene adsorption (463mg/g). Particularly, abundant microporous structures and surface functional groups play a vital role in the adsorption process. Further, the adsorption performance of toluene onto ACFK was further investigated in a gas-phase dynamic adsorption system and the results showed that ACFK has great potential application in adsorption of volatile organic compounds.

Oxygen-rich hierarchically porous carbons derived from pitch-based oxidized spheres for boosting the supercapacitive performance

Oxygen-rich hierarchically porous carbons are prepared by employing one-step KOH activation of pitch-based oxidized spheres (POS) as carbon precursors. The activation temperatures not only allow directed tailoring the porosity of carbon but also guarantee the preservation of moderate oxygen functional groups from POS, which are beneficial for efficiently integrating the electrical double layer capacitance and pseudocapacitance in one electrode. The as-prepared pitch-based activated carbons (PAC) possesses a high specific surface area of 2245 m2 g−1 with well-developed micropores, appropriate meso-macropores, and rich oxygen doping of 15.9 at%. Benefiting from the synergistic effect of hierarchical porosity and pseudocapacitive oxygen groups, PAC exhibit high specific capacitance of 427F g−1 and 302F g−1 at 0.5 A g−1 and 50 A g−1, respectively, as well as excellent capacitance retention of 71% in a three-electrode system with 6 M KOH electrolyte. Moreover, the as-assembled symmetrical supercapacitor displays a high energy of 5.79 Wh kg−1 at a power density of 9918 W kg−1 with excellent cycling stability with capacitance retention of 95% at 5 A g−1 after 10,000 cycles, which is higher than that of commercial Kuraray YP-50F. This finding demonstrates that one-step KOH activation coupled with oxygen-rich pitch may act as an optimal component to finely tailor the porosity and oxygen doping on activated carbons for energy storage applications.

Three-Dimensional Honeycomb-Like Porous Carbon with Both Interconnected Hierarchical Porosity and Nitrogen Self-Doping from Cotton Seed Husk for Supercapacitor Electrode.

Hierarchical porous structures with surface nitrogen-doped porous carbon are current research topics of interest for high performance supercapacitor electrode materials. Herein, a three-dimensional (3D) honeycomb-like porous carbon with interconnected hierarchical porosity and nitrogen self-doping was synthesized by simple and cost-efficient one-step KOH activation from waste cottonseed husk (a-CSHs). The obtained a-CSHs possessed hierarchical micro-, meso-, and macro-pores, a high specific surface area of 1694.1 m2/g, 3D architecture, and abundant self N-doping. Owing to these distinct features, a-CSHs delivered high specific capacitances of 238 F/g and 200 F/g at current densities of 0.5 A/g and 20 A/g, respectively, in a 6 mol/L KOH electrolyte, demonstrating good capacitance retention of 84%. The assembled a-CSHs-based symmetric supercapacitor also displayed high specific capacitance of 52 F/g at 0.5 A/g, with an energy density of 10.4 Wh/Kg at 300 W/Kg, and 91% capacitance retention after 5000 cycles at 10 A/g.

Biochar as a renewable source for high-performance CO2 sorbent

Natural gas wells evolve CO2 along with the hydrocarbon stream. Because of the wide use of natural gas as an energy source, the emission of CO2 from high pressure natural gas wells is of concern. While various sorbents have been developed to purify natural gas, studies are lacking on the use of renewable biosources, especially biochar, to prepare porous carbon sorbents for CO2 capture at high pressure. Here we report the use of low-cost biochar as the feedstock for a one-step KOH activation towards high surface area solid state CO2 sorbents. Under the optimal activation conditions, a surface area of 3167 m2 g−1 is reached with a CO2 uptake of 26.0 mmol g−1 (1.15 g g−1) at 30 bar and 25 °C. The cycling stability and CO2/CH4 selectivity of the synthesized biochar-derived porous carbon have been evaluated, and activity screenings show that wood wastes pyrolyzed at a mid-range temperature, 450 °C, are the preferred type of biochar for use as high performance CO2 sorbents in high pressure applications.

Efficient adsorption of PFOS and F53B from chrome plating wastewater and their subsequent degradation in the regeneration process

Wastewater from chrome plating industry contains high concentrations of perfluorooctane sulfonate (PFOS) and its alternative (chlorinated polyfluorinated ether sulfonate, namely F53B). It was the first time that simultaneous removal of PFOS and F53B from the actual wastewater was investigated using a granular reactivated carbon (R-CAC) prepared from commercial coconut-based activated carbon (CAC) through one-step KOH activation. The R-CAC removed much more PFOS and F53B than CAC, and even more than the best resin and chitosan reported. Both initial adsorption rate and adsorbed amount of F53B on R-CAC were much higher than PFOS, and adsorption isotherms of PFOS and F53B were described well by the Langmuir model. The coexisting organic matters in the wastewater were able to occupy the sorption sites for PFOS and F53B, significantly influencing their adsorption on R-CAC. The spent R-CAC was effectively regenerated by a novel method, hydrothermal-activated persulfate oxidation. The adsorbed PFOS and F53B as well as co-existing organic pollutants on R-CAC were degraded by persulfate free radicals, making sorption sites become available. The best regeneration efficiency of R-CAC was 93.3% and 97.6% for PFOS and F53B, respectively. This study accomplished the highly efficient adsorption and degradation of PFOS and F53B in actual wastewater.

Nitrogen-doped hierarchical porous carbon with high surface area derived from graphene oxide/pitch oxide composite for supercapacitors

A nitrogen-doped hierarchical porous carbon has been prepared through one-step KOH activation of pitch oxide/graphene oxide composite. At a low weight ratio of KOH/composite (1:1), the as-prepared carbon possesses high specific surface area, rich nitrogen and oxygen, appropriate mesopore/micropore ratio and considerable small-sized mesopores. The addition of graphene oxide plays a key role in forming 4nm mesopores. The sample PO–GO-16 presents the characteristics of large surface area (2196m2g−1), high mesoporosity (47.6%), as well as rich nitrogen (1.52at.%) and oxygen (6.9at.%). As a result, PO–GO-16 electrode shows an outstanding capacitive behavior: high capacitance (296Fg−1) and ultrahigh-rate performance (192Fg−1 at 10Ag−1) in 6M KOH aqueous electrolyte. The balanced structure characteristic, low-cost and high performance, make the porous carbon a promising electrode material for supercapacitors.