Activated Carbon from Rice Husk with One-Step KOH Mechanical Mixing Activation as Adsorbent for Treating Phenolic Wastewater

This study investigates how large-surface-area biocarbons with high phenolic adsorption capacities can be obtained from cheap and abundant rice husk(RH).The RH is directly mixed with potassium hydroxide(KOH)and activated in a flowing N_(2) atmosphere,and the effects of the pyrolysis temperature and KOH to RH ratio on the structure of the obtained activated carbon adsorbents and their adsorption of p-nitrophenol and phenol are studied.The results show that the optimum pyrolysis temperature of RH is 750℃,whereby the highest surface area of 2047 m^(2)/g and best adsorption performance are obtained with a KOH to RH ratio of 3:1.Moreover,the obtained biocarbons achieve a maximum adsorption capacity of 175 mg/g for phenol and 430 mg/g for p-nitrophenol,which are higher than most previously reported data.

Activated carbon prepared from waste tire pyrolysis carbon black via CO_(2)/KOH activation used as supercapacitor electrode

As the quantity of waste tires increases,more pyrolysis carbon black(CBp),a type of low value-added carbon black,is being produced.However,the application of CBp has been limited.Therefore,it is necessary to identify and expand applications of CBp.This work focuses on the preparation of activated carbon(AC)from CBp using the physicochemical activation of carbon dioxide(CO_(2))and potassium hydroxide(KOH).Thereafter,AC is applied to the electrode of the electrical double-layer capacitor(EDLC).The AC prepared by CO_(2)/KOH activation exhibited a hierarchical pore structure.The specific surface area increased from 415 to 733 m^(2)g^(−1),and in combination with low ash content of 1.51%,ensured abundant ion diffusion channels and active sites to store charge.The EDLC comprising the AC(AC-2)electrode prepared by excitation of CO_(2)(300 sccm)and KOH had a reasonable gravimetric specific capacitance of 192 F g^(−1)at 0.5 A g^(−1),and exhibited a good rate capability of 73%at 50 A g^(−1)in a three-electrode system.Moreover,the EDLC device comprising the AC-2 electrode delivered excellent cycling stability(capacitance retention of 106%after 10000 cycles at 2 A g^(−1)in a two-electrode system).Furthermore,a symmetric supercapacitor based on an AC electrode that exhibits a supreme energy density of 4.7 Wh kg^(−1)and a maximum power density of 6362.6 W kg^(−1)is demonstrated.

Two-Step Preparation of Hierarchical Porous Carbon Materials Derived from Tannin for Use as an Electrode Material for Supercapacitors

The development and utilization of biomass and agroforestry processing byproducts for high-value applications have been an important topic in the field of renewable materials research.Based on this,a two-step microwave hydrothermal pre-carbonization and KOH activation method was proposed to synthesize tannin-based activated carbons with a high specific surface area,hierarchical pore structure,and good electrochemical performance.The microstructure,texture properties,and physicochemical characteristics were investigated.The results show that the prepared tannin-based activated carbons presented a hierarchical pore structure(micro-and mesopores)with a specific surface area as high as 997.46 m^(3) g^(−1).The electrochemical analysis shows that the tannin-based activated carbons have good wettability and charge transfer rates.Under the three-electrode system with 6 M KOH as the electrolyte,the active material TAC_(600-4) had a maximum specific capacitance of 171 F g^(−1)at 0.5 A g^(−1).As the current density increases to 10 A g^(−1),the specific capacitance can still be maintained at 149 F g^(−1),indicating a good rate capability.Therefore,the specific surface area and pore size of tannin-based activated carbons can be effectively adjusted by the alkali/carbon ratio,making it a promising supercapacitor electrode material and providing a new method for the high-value development of tannins in the field of electrochemical energy storage.

The Influence of Dry or Wet Activating Process to the Electrochemical Features of Biowaste Carbon

The utilization of biowaste to the activated carbon(AC)as electrode material is conducive to alleviating the energy crisis and promoting the high value-added.The popular KOH activation has been applied for years,but rare report clarified the difference of dry and wet activation,with which the batch producing technique could be different.Here nitrogen doped hierarchical AC was derived from wood chip by a wet or dry KOH activation.The surface area,framework structure and surface feature were characterized to reveal the effect of wet and dry activation.1.44 at%of nitrogen doped AC was made by dry KOH activation,which was higher than the AC derived from wet KOH activation with 1.36 at%of nitrogen.Their electrochemical properties were investigated in 6 mol L^(-1)of KOH,the capacitance of wAC was 401 F g^(-1)at 0.5 A g^(-1),but dAC possessed a capacitance of 215 F g^(-1).These indicated that AC obtained by using wet KOH activation displayed a potential application in energy field.

Synthesis,characterization and life cycle assessment of electrochemically exfoliated KOH-activated holey graphene

Graphene materials have drawn tremendous attention in recent years.The formation of holes and pores on graphene sheets can provide transfer channels and facilitate the ion/electron transport kinetics.In this study,graphene nanosheets were prepared electrochemically,and then,they were used as the starting material for the preparation of holey graphene(HG)through the KOH activation process.The weight ratio of initial electrochemically exfoliated graphene(EEG)to KOH was optimized according to the morphological features,BET surface area examination,graphene number of layers calculated from XRD patterns,and the ID/IG ratio obtained from Raman analysis.Results showed that increasing the KOH amount led to the achievement of higher values of ID/IG and surface area and less re-stacking of graphene sheets which occurs because of the heat treatment process.The environmental burdens of the production routes for the preparation of EEG and HG were investigated by cradle-to-gate life cycle assessment(LCA).The LCA results of EEG production indicated that electricity with the contributions of 94%,91%,82%,and 75%of the total impact in four environmental categories,including fossil fuel depletion,ozone depletion,global warming,and smog was the main environmental weakness.In the pore generation process,KOH was recognized as the biggest contributor(about 51%to 83%of the total impact)in six impact categories,including ozone depletion,non-carcinogenics,smog,global warming,carcinogenics,and eutrophication which could be attributed to its high consumption amount(21.9 kg).This work offers environmental considerations for the development of sustainable graphene materials.

Nitrogen-doped porous carbons from polyacrylonitrile fiber as effective CO_(2) adsorbents

In this report, nitrogen-doped porous carbons were synthesized from polyacrylonitrile fiber by a facile two-step synthesis process i.e. carbonization followed by KOH activation. Activation temperature and KOH/carbon ratio are two parameters to tune the porosity and surface chemical properties of sorbents. The as-obtained sorbents were carefully characterized.Special attention was paid concerning the change of sorbents’ morphology with respect to synthesis conditions. Under the activation temperatures of this study, the sorbents can still retain their fibrous structure when the KOH/carbon mass ratio is 1. Further increasing the KOH amount will destroy the original morphology of polyacrylonitrile fiber. CO_(2)adsorption performance tests show that a sorbent retaining the fibrous shape possesses the highest CO_(2)uptake of 3.95 mmol/g at 25℃and 1 bar. Comprehensive investigation found that the mutual effect of narrow microporosity and doped N content govern the CO_(2)adsorption capacity of these adsorbents. Furthermore, these polyacrylonitrile fiber-derived carbons present multiple outstanding CO_(2)capture properties such as excellent recyclability, high CO_(2)/N_(2)selectivity, fast adsorption kinetics, suitable heat of adsorption, and good dynamic adsorption capacity. Hence, nitrogen-doped porous carbons with fibrous structure are promising in CO_(2)capture.

Fabrication of coconut shell-derived porous carbons for CO_(2) adsorption application

Biomass-derived porous carbons have been considered as the most potential candidate for effective CO_(2) adsorbent thanks to being widely-available precursor and having highly porous structure and stable chemical/physical features.However,the biomass-derived porous carbons still suffer from the poor optimization process in terms of the synthesis conditions.Herein,we have successfully fabricated coconut shell-derived porous carbon by a simple one-step synthesis process.The as-prepared carbon exhibits advanced textual activity together with well-designed micropore morphology and possesses oxygen-containing functional groups(reached 18.81 wt%)within the carbon matrix.Depending on the different activating temperatures(from 700 to 800℃)and KOH/biomass mass ratios(from 0.3 to 1),the 750℃ and 0.5 mass ratio were found to be enabling the highest CO_(2) capture performance.The optimal adsorbent was achieved a high CO_(2) uptake capacity of 5.92 and 4.15 mmol·g^(−1) at 0 and 25℃(1 bar),respectively.More importantly,as-prepared carbon adsorbent exhibited moderate isosteric heat of adsorption and high CO_(2)/N_(2) selectivity.The results were revealed not only the textural feature but also the surface functional groups critically determine the CO_(2) capture performance,indicating coconut shell-derived porous carbon has a considerable potential as a solid-state adsorbent for the CO_(2) capture.

Superior CO2 uptake on nitrogen doped carbonaceous adsorbents from commercial phenolic resin

In this study,N-doped porous carbons were produced with commercial phenolic resin as the raw material,urea as the nitrogen source and KOH as the activation agent.Different from conventional carbonization-nitriding-activation three-step method,a facile two-step process was explored to produce N-incorporated porous carbons.The as-obtained adsorbents hold superior CO2 uptake,i.e.5.01 and 7.47 mmol/g at 25℃and 0℃under 1 bar,respectively.The synergistic effects of N species on the surface and narrow micropores of the adsorbents decide their CO2 uptake under 25℃and atmospheric pressure.These phenolic resin-derived adsorbents also possess many extremely promising CO2 adsorption features like good recyclability,quick adsorption kinetics,modest heat of adsorption,great selectivity of CO2 over N2 and outstanding dynamic adsorption capacity.Cheap precursor,easy preparation strategy and excellent CO2 adsorption properties make these phenolic resin-derived N-doped carbonaceous adsorbents highly promising in CO2 capture.

Efficient nitrogen doped porous carbonaceous CO_(2) adsorbents based on lotus leaf

In this work, the waste biomass lotus leaf was converted into N-doped porous carbonaceous CO_(2) adsorbents. The synthesis process includes carbonization of lotus leaf, melamine post-treatment and KOH activation. For the resultant sorbents, high nitrogen content can be contained due to the melamine modification and advanced porous structure were formed by KOH etching. These samples were carefully characterized by different techniques and their CO_(2) adsorption properties were investigated in detail. These sorbents hold good CO_(2) adsorption abilities, up to 3.87 and 5.89 mmol/g at 25 and 0 °C under 1 bar, respectively. By thorough investigation, the combined interplay of N content and narrow microporous volume was found to be responsible for the CO_(2) uptake for this series of sorbents. Together with the high CO_(2) adsorption abilities, these carbons also display excellent reversibility, high CO_(2)/N 2 selectivity, applicable heat of adsorption, fast CO_(2) adsorption kinetics and good dynamic CO_(2) adsorption capacity. This study reveals a universal method of obtaining N-doped porous carbonaceous sorbents from leaves. The low cost of raw materials accompanied by easy synthesis procedure disclose the enormous potential of leaves-based carbons in CO_(2) capture as well as many other applications.

Hierarchical porous carbon derived from coal-based carbon foam for high-performance supercapacitors

Hierarchical porous carbon(HPC)from bituminous coal was designed and synthesized through pyrolysis foaming and KOH activation.The obtained HPC(NCF-KOH)were characterized by a high specific surface area(S_(BET))of 3472.41 m^(2)/g,appropriate mesopores with V_(mes)/V_(total)of 57%,and a proper amount of surface oxygen content(10.03%).This NCF-KOH exhibited a high specific capacitance of 487 F/g at 1.0 A/g and a rate capability of 400 F/g at 50 A/g based on the three-electrode configuration.As an electrode for a symmetric capacitor,a specific capacitance of 299 F/g at 0.5 A/g was exhibited,and the specific capacitance retained 96%of the initial capacity at 5 A/g after 10,000 cycles.Furthermore,under the power density of 249.6 W/kg in 6 mol/L KOH,a high energy density of 10.34 Wh/kg was obtained.The excellent charge storage capability benefited from its interconnected hierarchical pore structure with high accessible surface area and the suitable amount of oxygen-containing functional groups.Thus,an effective strategy to synthesize HPC for high-performance supercapacitors serves as a promising way of converting coal into advanced carbon materials.