Nanospace engineering of KOH activated carbon

Effect of activated carbon-based two-stage adsorption on biogenic amine reduction and quality of anchovy fish sauce at industrial scale

This study was aimed to investigate the effectiveness of activated carbon on reduction in biogenic amines (BAs) via two-stage adsorption process at industrial scale, and the consequent effect was evaluated by the taste and aroma of anchovy fish sauce. Through reaction surface methodology, the optimal working paratmeters were determined to adsorbent composition of 2% activated carbon and 0.9% diatomite under temperature of 27 °C for 97 min. Upon optimized settings at industrial scale, there were effective reductions in tryptamine (by 100%), cadaverine (by 10%), histamine (by 61%), and tyramine (by 96%), while the changes in taste-related amino nitrogen, total nitrogen, free amino acids, and color were minimum. In addition, off-flavor-causing compounds, such as alcohols and acids, were removed by the developed method. From the obtained results, the activated carbon-based two-stage adsorption approach can provide the framework for control of BAs contents in fish-based sauces or stocks at commercial and industrial scales.

Surface-Roughened Graphene Oxide Microfibers Enhance Electrochemical Reversibility

Here, we provide an optimized method for fabricating surface-roughened graphene oxide disk microelectrodes (GFMEs) with enhanced defect density to generate a more suitable electrode surface for dopamine detection with fast-scan cyclic voltammetry (FSCV). FSCV detection, which is often influenced by adsorption-based surface interactions, is commonly impacted by the chemical and geometric structure of the electrode's surface, and graphene oxide is a tunable carbon-based nanomaterial capable of enhancing these two key characteristics. Synthesized GFMEs possess exquisite electronic and mechanical properties. We have optimized an applied inert argon (Ar) plasma treatment to increase defect density, with minimal changes in chemical functionality, for enhanced surface crevices to momentarily trap dopamine during detection. Optimal Ar plasma treatment (100 sccm, 60 s, 100 W) generates crevice depths of 33.4 ± 2.3 nm with high edge plane character enhancing dopamine interfacial interactions. Increases in GFME surface roughness improve electron transfer rates and limit diffusional rates out of the crevices to create nearly reversible dopamine electrochemical redox interactions. The utility of surface-roughened disk GFMEs provides comparable detection sensitivities to traditional cylindrical carbon fiber microelectrodes while improving temporal resolution ten-fold with amplified oxidation current due to dopamine cyclization. Overall, surface-roughened GFMEs enable improved adsorption interactions, momentary trapping, and current amplification, expanding the utility of GO microelectrodes for FSCV detection.

Preparation of a hierarchical porous activated carbon derived from cantaloupe peel/fly ash/PEDOT:PSS composites as Pt-free counter electrodes of dye-sensitized solar cells

Hierarchical porous activated carbon/fly ash/PEDOT:PSS composites (AC:FA) for a counter electrode (CE) were created using a doctor blade technique and applied in dye sensitized solar cells. Hierarchical porous activated carbon (AC) was produced using a potassium hydroxide (KOH) activation process from cantaloupe peels (Cucumis melo L. var. cantaloupensis). AC was introduced into fly ash at various mass ratios to enhance several physical and electrochemical characteristics. Compared to bare FA, the AC:FA electrode displayed a high electrocatalytic activity for the iodide/triiodide redox (I - / I 3 - ) reaction. The test findings show that a higher proportion of AC has an impact on a CE's catalytic activity and charge transfer resistance. The power conversion efficiency (PCE) of the dye-sensitized solar cell (DSSC) attained 5.81 % using the AC:FA CE with AC in a mass ratio of FA in 3:1 (wt./wt.), which is very near the performance of manufactured DSSC's with a platinum (Pt)-based CE (5.91 %). The AC:FA CE stands out as a strong candidate to substitute for costly Pt CEs due to its enhanced electrochemical activity and charge transfer capabilities obtained with an inexpensive and simple production procedure.

Thermochemical Activation of Wood with NaOH, KOH and H3PO4 for the Synthesis of Nitrogen-Doped Nanoporous Carbon for Oxygen Reduction Reaction

Carbonization of biomass residues followed by activation has great potential to become a safe process for the production of various carbon materials for various applications. Demand for commercial use of biomass-based carbon materials is growing rapidly in advanced technologies, including in the energy sector, as catalysts, batteries and capacitor electrodes. In this study, carbon materials were synthesized from hardwood using two carbonization methods, followed by activation with H3PO4, KOH and NaOH and doping with nitrogen. Their chemical composition, porous structure, thermal stability and structural order of samples were studied. It was shown that, despite the differences, the synthesized carbon materials are active catalysts for oxygen reduction reactions. Among the investigated carbon materials, NaOH-activated samples exhibited the lowest Tafel slope values, of -90.6 and -88.0 mV dec-1, which are very close to the values of commercial Pt/C at -86.6 mV dec-1.

Waste Coffee Ground-Derived Porous Carbon for Neurochemical Detection

We present an optimized synthetic method for repurposing coffee waste to create controllable, uniform porous carbon frameworks for biosensor applications to enhance neurotransmitter detection with fast-scan cyclic voltammetry. Harnessing porous carbon structures from biowastes is a common practice for low-cost energy storage applications; however, repurposing biowastes for biosensing applications has not been explored. Waste coffee ground-derived porous carbon was synthesized by chemical activation to form multivoid, hierarchical porous carbon, and this synthesis was specifically optimized for porous uniformity and electrochemical detection. These materials, when modified on carbon-fiber microelectrodes, exhibited high surface roughness and pore distribution, which contributed to significant improvements in electrochemical reversibility and oxidative current for dopamine (3.5 ± 0.4-fold) and other neurochemicals. Capacitive current increases were small, showing evidence of small increases in electroactive surface area. Local trapping of dopamine within the pores led to improved electrochemical reversibility and frequency-independent behavior. Overall, we demonstrate an optimized biowaste-derived porous carbon synthesis for neurotransmitter detection for the first time and show material utility for viable neurotransmitter detection within a tissue matrix. This work supports the notion that controlled surface nanogeometries play a key role in electrochemical detection.

A state-of-the-art review on biomass-derived carbon materials for supercapacitor applications: From precursor selection to design optimization

Biomass-derived carbon materials have the characteristics of a wide range of precursor sources, controllable carbon nano-dimension, large specific surface area and abundant heteroatoms doping. At present, biomass-derived carbon materials have been widely used in electrochemical energy storage devices, especially the research and development of biomass-derived carbon materials for supercapacitors has become mature and in-depth. Therefore, it is of importance to summarize the advanced technologies and strategies for optimizing biomass-derived carbon materials for supercapacitors, which will effectively promote the further development of high-performance supercapacitors. In this review, the recent research progress of biomass-derived carbon materials is provided in detail, including the selection of biomass precursors, the design of carbon nano-dimension and the theory of heteroatom doping. Besides, the preparation methods of biomass-derived carbon materials and the related processes of optimizing the electrochemical performance are also summarized. This review ends with the perspectives for future research directions and challenges in the field of biomass-derived carbon materials for electrochemical applications. This review aims to provide helpful reference information for the nano-dimensional design and electrochemical performance optimization of biomass-derived carbon materials for the practical application of supercapacitors.

Post-treatment strategies for pyrophoric KOH-activated carbon nanofibres

The effect of two atmospheric post-treatment conditions directly after the KOH activation of polyacrylonitrile-based nanofibres is studied in this work. As post-treatment different N2 : O2 flow conditions, namely high O2-flow and low O2-flow, are applied and their impact on occurring reactions and carbon nanofibres' properties is studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Raman spectroscopy, elemental analysis and CO2 and Ar gas adsorption. At high O2-flow conditions a pyrophoric effect was observed on the KOH-activated carbon nanofibers. Based on the obtained results from the TGA and DSC the pyrophoric effect is attributed to the oxidation reactions of metallic potassium formed during the KOH activation process and a consequent carbon combustion reaction. Suppression of this pyrophoric effect is achieved using the low O2-flow conditions due to a lower heat formation of the potassium oxidation and the absence of carbon combustion. Compared to the high O2-flow samples no partial destruction of the carbon nanofibers is observed in the SEM images. The determination of the adsorption isotherms, the surface area, the pore size distribution and the isosteric enthalpies of adsorption show the superior properties under low O2-flow conditions. The present micropore volume is increased from 0.424 cm3 g-1 at high O2-flow to 0.806 cm3 g-1 for low O2-flow samples, resulting in an increase of CO2 adsorption capacity of 38% up to 6.6 mmol g-1 at 1 bar. This significant improvement clearly points out the importance of considering highly exothermic potassium oxidation reactions and possible post-treatment strategies when applying KOH activation to electrospun carbon nanofiber materials.

Efficient dye removal from industrial wastewater using sustainable activated carbon and its polyamide nanocomposite derived from agricultural and industrial wastes in column systems

Sugar beet crown (SBC) waste was employed to produce sustainable activated carbon (AC) by a thermo-chemical activation procedure using a fixed ratio of H3PO4/SBC (1 : 1 w/w ratio) at 550 °C/2 h. An activated carbon/polyamide nano-composite (AC/PA) was also prepared through the polymerization of the fabricated AC (90%) with polyamide (PA, 10%) synthetic textile waste using a proper dissolving agent at a specified w/w ratio with the employed polymer (formic acid/PA = 82/18%). Both AC and its derivative AC/PA were employed in the remediation of dyes from industrial wastewater in column systems, and their efficiencies were compared at various applied experimental conditions. The adsorption of the industrial dye waste (IDW) was a pH-, flow rate-, and bed thickness-controlled process by the regarded adsorbents. Kinetic studies confirmed the suitability of the Thomas equation over the Yoon and Nelson model in predicting the dynamic adsorption process of IDW by AC and AC/PA as was assured by the close agreement among the calculated and experimental uptake capacities of both adsorbents at the same applied flow rates, suggesting the chemisorption nature of IDW adsorption. Additionally, electrostatic attraction was the leading mechanism of IDW adsorption by AC and AC/PA composite with some advantages of the former over the latter.

Activated carbon prepared by co-pyrolysis of waste tobacco straw and waste LDPE mulch film: characterization and application for methylene blue removal

Efficient and inexpensive sorbents play a key role in removing organic pollutants from water bodies. In this study, a series of high surface area activated carbons (ACs) with excellent adsorption performance was prepared by co-pyrolysis of the waste tobacco straw and the waste low-density polyethylene (LDPE) mulch film. Using the maximum adsorption capacity of methylene blue (MB) as an indicator, the variables such as LDPE content, K₂CO₃ to raw material ratio, activation time, and activation temperature were optimized. The optimal synthesis conditions were as follows: LDPE content of 40%, K₂CO₃/raw material ratio of 1 : 2, activation temperature of 900 °C, and activation time of 100 min. The maximum adsorption capacity of MB was up to 849.91 mg g^-1. The results of scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and BET showed that the moderate addition of LDPE was beneficial to the pyrolysis of the waste tobacco straw, bringing about the enrichment of surface groups (-OH, -COOH) and increasing its specific surface area and pore volume (up to 1566.7 m² g^-1 and 0.996 cm³ g^-1, respectively). The equilibrium data of MB adsorption by the composite activated carbon (PAC) was consistent with the Langmuir isotherm, while the adsorption kinetics were better described by a pseudo-second-order kinetic model. This work reveals the feasibility of LDPE mulch film and waste tobacco straw as potential and inexpensive precursors for preparing high surface area AC adsorbents.

Adsorption of fulvic acid on mesopore-rich activated carbon with high surface area

The loss of dissolved organic matter (DOM), especially fulvic acid (FA), from soil by rainfall and runoff will reduce soil fertility and result in water pollution of DOM. Carbon materials including biochars (BCs) and activated carbons (ACs) are widely suggested for soil remediation and carbon immobilization. However, these suggested carbon materials are dominated by micropores, and largely limiting the adsorption capacity for FA. Therefore, a mesopore-rich activated carbon (KAC) with high surface area was prepared from bamboo chips to investigate the adsorption of FA. This KAC can adsorb FA more than ACs and BCs investigated in this study and reported in previous studies not only because of the high surface area (3108 m²/g), but also the higher mesopore volume proportion (57%). The negative pH effect on adsorption performance of KAC was weaker than that on AC and BC, because of the less polarity of KAC. Moreover, KAC was favorable to adsorb FA fractions with various molecular weights, higher aromaticity and higher polarity. This study indicated that KAC was a promising adsorbent for FA, and revealed the underlying adsorption mechanism of FA on KAC, which are helpful for the carbon immobilization and pollution control in soil.

Activated carbon derived from cherry flower biowaste with a self-doped heteroatom and large specific surface area for supercapacitor and sodium-ion battery applications

Herein, cherry flower waste-derived activated carbon (CFAC) with self-doped nitrogen is synthesized as a viable energy storage material for green and sustainable energy solutions. The activated carbon derived in this way is examined as an electric double-layer capacitance (EDLC)-type electrode material and sodium-ion battery (NIB) electrode material, and commendable performance is demonstrated for both of these energy storage applications. The specific surface area (SSA) and nitrogen content are observed to play a very delicate role in determining the charge storage ability of the CFAC, and the performance is optimized only by carefully balancing both of these properties. The optimized CFAC electrode supplied an excellent performance with a specific capacitance of 333.8 F g^-1 and capacity is maintained to more than 96% even after 38,000 charge-discharge cycles as an EDLC-type supercapacitor electrode material. Likewise, the CFAC/NIB also yielded remarkable performance with an average specific capacity of 150 mAh g^-1 and capacity retention of more than 84% after 200 charge-discharge cycles. Furthermore, an electrokinetic study was performed for both supercapacitor and NIB applications to identify the contribution from surface and diffusion type charge storage phenomena, consequently highlighting the role of the SSA and nitrogen content in the CFAC matrix.

Equisetum hyemale-derived unprecedented bioactive composite for hard and soft tissues engineering

Although Bioactive Glasses (BGs) have been progressively optimized, their preparation often still involves the use of toxic reagents and high calcination temperatures to remove organic solvents. In the present work, these synthesis related drawbacks were overcome by treating the ashes from the Equisetum hyemale plant in an ethanol/water solution to develop a bioactive composite [glass/carbon (BG-Carb)]. The BG-Carb was characterized by scanning electron microscopy, and transmission electron microscopy; and its chemical composition was assessed by inductively coupled plasma-optical emission spectroscopy. Brunauer-Emmett-Teller gas adsorption analysis showed a specific surface area of 121 m² g^-1. The formation of hydroxyapatite (HA) surface layer in vitro was confirmed by Fourier-transform infrared spectroscopy analysis before and after immersion in simulated body fluid (SBF) solution. The Rietveld refinement of the XRD patterns and selected area electron diffraction analyses confirmed HA in the sample even before immersing it in SBF solution. However, stronger evidences of the presence of HA were observed after immersion in SBF solution due to the surface mineralization. The BG-Carb samples showed no cytotoxicity on MC3T3-E1 cells and osteo-differentiation capacity similar to the positive control. Altogether, the BG-Carb material data reveals a promising plant waste-based candidate for hard and soft tissue engineering.

Facile Synthesis of Nitrogen Self-Doped Porous Carbon Derived from Cicada Shell via KOH Activation for Simultaneous Detection and Removal of Cu2+

Sensitive detection and efficient removal of heavy metal ions with high toxicity and mobility are of great importance for environmental monitoring and control. Although several kinds of functional materials have been reported for this purpose, their preparation processes are complicated. Herein, nitrogen self-doped activated porous biochar (NAC) was synthesized in a facile process via an activation–carbonization strategy from cicada shell rich in chitin, and subsequently employed as an effective functional material for the simultaneous determination and removal of Cu²⁺ from aqueous media. With its unique porous structure and abundant oxygen-containing functional groups, along with the presence of heteroatoms, NAC exhibits high sensitivity for the electrochemical sensing of Cu²⁺ in concentrations ranging from 0.001 to 1000 μg·L⁻¹, with a low detection limit of 0.3 ng·L⁻¹. Additionally, NAC presents an excellent removal efficiency of over 78%. The maximum adsorption capacity is estimated at 110.4 mg/g. These excellent performances demonstrate that NAC could serve as an efficient platform for the detection and removal of Cu²⁺ in real environmental areas.

Activation-Induced Surface Modulation of Biowaste-Derived Hierarchical Porous Carbon for Supercapacitors

Wheat straw-derived carbon from the Wheatbelt region in Western Australia was subjected to chemical activation in an electrolyte containing either acid or base treatment. The findings showed an increase in electron/hole mobility towards the interfaces due to the presence of different surface functional groups such as C-SO_x -C and S=C in the carbon framework for acid activation. Likewise, the galvanostatic capacitance measured at a current density of 2 mA cm^-2 in a three-electrode configuration for acid-activated wheat straw exhibited 162 F g^-1 , while that for base-activated wheat straw exhibited 106 F g^-1 . An increase of 34.5 % more capacitance was achieved for acid-treated wheat straw. This improvement is attributed to the synergistic effects between surface functional groups and electrolyte ions, as well as the electronic structure of the porous electrode.

Controlled synthesis of graphene oxide/silica hybrid nanocomposites for removal of aromatic pollutants in water

The remarkable characteristics of graphene make it a model candidate for boosting the effectiveness of nano-adsorbents with high potential owing to its large surface area, π–π interaction, and accessible functional groups that interact with an adsorbate. However, the stacking of graphene reduces its influence adsorption characteristics and also its practical application. On the other hand, the widespread use of aromatic compounds in the industry has aggravated the contamination of the water environment, and how to effectively remove them has become a research hotspot. Herein, we develop the functionalization of silica nanoparticles on graphene oxide nanosheet (FGS) by a facile, cheap, and efficient synthesis protocol for adsorption of Trypan Blue (TB) and Bisphenol A (BPA). It was demonstrated that chemical activation with KOH at high autoclaving temperature successfully transformed rice husk ash (RHA) into FGS. The graphene oxide layered interlamination was kept open by using SiO₂ to expose the interlayers' strong adsorption sites. XRD, EDX, FTIR, Raman spectroscopy, SEM, HR-TEM, and BET surface area are used to investigate the chemical composition, structure, morphology, and textural nature of the as-produced FGS hybrid nanocomposite. The various oxygen-containing functional groups of the hybrid nanocomposites resulted in a significantly increased adsorption capacity, according to experimental findings. In addition, FGS2, the best composite, has a specific surface area of 1768 m²g⁻¹. Based on Langmuir isotherms, the maximal TB dye and BPA removal capacity attained after 30 min were 455 and 500 mg/g, respectively. The Langmuir isotherm model, a pseudo-second-order kinetic model, and an intraparticle diffusion model have all been used to provide mechanistic insights into the adsorption process. This suggests that BPA and TB adsorption on FGS2 is mostly chemically regulated monolayer adsorption. Due to its unique sp²-hybridized single-atom-layer structure, the exposed graphene oxide nanosheets' extremely hydrophobic effect, hydrogen bonding, and strong—electron donor–acceptor interaction contributed to their improved adsorption of BPA and TB. According to adsorption thermodynamics, FGS2 adsorption of TB and BPA is a spontaneous exothermic reaction that is aided by lowering the temperature. For adsorption-based wastewater cleanup, the produced nanocomposites with a regulated amount of carbon and silica in the form of graphene oxide and silica can be used. These findings suggest that functionalized GO/SiO₂ hybrid nanocomposites could be a viable sorbent for the efficient and cost-effective removal of aromatic chemicals from wastewater.

Successful Manufacturing Protocols of N-Rich Carbon Electrodes Ensuring High ORR Activity: A Review

The exploration and development of different carbon nanomaterials happening over the past years have established carbon electrodes as an important electrocatalyst for oxygen reduction reaction. Metal-free catalysts are especially promising potential alternatives for replacing Pt-based catalysts. This article describes recent advances and challenges in the three main synthesis manners (i.e., pyrolysis, hydrothermal method, and chemical vapor deposition) as effective methods for the production of metal-free carbon-based catalysts. To improve the catalytic activity, heteroatom doping the structure of graphene, carbon nanotubes, porous carbons, and carbon nanofibers is important and makes them a prospective candidate for commercial applications. Special attention is paid to providing an overview on the recent major works about nitrogen-doped carbon electrodes with various concentrations and chemical environments of the heteroatom active sites. A detailed discussion and summary of catalytic properties in aqueous electrolytes is given for graphene and porous carbon-based catalysts in particular, including recent studies performed in the authors’ research group. Finally, we discuss pathways and development opportunities approaching the practical use of mainly graphene-based catalysts for metal–air batteries and fuel cells.

A study on activation mechanism in perspective of lignin structures and applicability of lignin-derived activated carbons for pollutant absorbent and supercapacitor electrode

In this study activated carbons were produced from the biorefinery waste lignin (Asian lignin (AL) USA & Inbicon lignin (IL) Denmark) to evaluate their potential in waste water treatment and as energy storage devices. These products were studied for their surface characteristics as a function of reaction temperature, time, and catalyst loading accordingly. Under the conditions with a temperature lower than 750 °C and within a reaction time of 1 h, the catalytic reaction of alkali-carbon bonding occurred from the external surface, and a turbostratic disorder structure with a large aromatic ring system was formed. More severe reaction conditions accelerated the volatile release of de-alkylated aromatics such as benzene and naphthalene, along with structure and surface collapse. The maximum BET surface area of 2782 m²/g was obtained at 750 °C, 2 h and catalyst ratio of 4. Lignin-derived activated carbon was more efficient for the removal of organic pollutants (<50% adsorption capacity) rather than heavy metals (adsorption capacity >90%) due to interaction of π-π bonding. Furthermore, the activated carbon has a potential to be used as a supercapacitor electrode with high specific capacitance (214.0 F/g AL lignin) and an excellent cyclic stability (95% of their initial capacity). The results of this study demonstrate that lignin is an attractive precursor to produce activated carbons with diverse applications both as biosorbent and as a carbon electrode material even so with acceptable performance.

Comparative Behavior of Viscose-Based Supercapacitor Electrodes Activated by KOH, H2O, and CO2

Activated carbons derived from viscose fibers were prepared using potassium hydroxide, carbon dioxide, or water vapor as activation agents. The produced activated carbon fibers were analyzed via scanning electron microscopy and energy dispersive X-ray spectroscopy, and their porosity (specific surface area, total pore volume, and pore size distribution) was calculated employing physisorption experiments. Activated carbon fibers with a specific surface area of more than 2500 m2 g−1 were obtained by each of the three methods. Afterwards, the suitability of these materials as electrodes for electrochemical double-layer capacitors (supercapacitors) was investigated using cyclic voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. By combining CO2 and H2O activation, activated carbon fibers of high purity and excellent electrochemical performance could be obtained. A specific capacitance per electrode of up to 180 F g−1 was found. In addition, an energy density per double-layer capacitor of 42 W h kg−1 was achieved. These results demonstrate the outstanding electrochemical properties of viscose-based activated carbon fibers for use as electrode materials in energy storage devices such as supercapacitors.

Zn-MOF decorated bio activated carbon for photocatalytic degradation, oxygen evolution and reduction catalysis

An emerging global necessity for alternative resources combined with maximum catalytic efficiency, low cost, and eco-friendly composite remains a hotspot in the scientific society. Hereby, a novel protocol is approached to design a heterostructure of Zinc MOF decorated on the surface of 2D activated carbon (AC) through a simplistic approach. To begin with, analytical, morphological and spectroscopical studies were performed to identify the functional moieties, cruciate-flower like morphology and oxidative state of atoms present in the composite Zn-MOF @AC. The photocatalytic material aids in degrading both cationic and anionic dye in a UV (254 nm) irradiated environment at a rate of 86.4% and 77.5% within 90 mins. Subsequently, the hybrid materials are coated on the carbon substrate to evaluate the catalytic activity using oxygen evolution and reduction reaction process. The mechanical insight for the catalytic activity relies on the electronic transitions of atoms on the edges of the sheets ascribing to d-d energy levels between the interfacial electron movement. Our composite exhibits an overpotential of 0.7 V and a Tafel slope of 70 mV/dec for the oxygen reduction reaction. This study proposes an alternate approach for developing MOF decorated carbon-based composites for photocatalytic degradability and energy necessity.

Pre-pyrolysis metal and base addition catalyzes pore development and improves organic micropollutant adsorption to pine biochar

Biochars were produced from pine feedstock pretreated with aqueous base, NaOH, at pH 9 and 11, and alkali and alkaline earth metals (AAEMs) Na, K, Ca, and Mg at 10^-3 and 1 M. The effects of base and AAEM feedstock pretreatment on biochar surface area, pore size distribution, and adsorption capacity of two organic micropollutants (OMPs), 2,4-dichlorophenoxyacetic acid and sulfamethoxazole, from surface water with background dissolved organic matter (DOM) were evaluated. Base pretreatment significantly increased surface area within micropores (<2 nm diameter). AAEM pretreatment caused pore widening, increasing surface area within pores >2 nm in diameter. The catalytic activity of AAEMs, assessed by generation of non-micropore surface area, decreased in the following order: Ca > K > Na > Mg. All pretreated biochars outperformed untreated biochar for OMP adsorption. Biochar pretreated by aqueous base at pH 11 showed over an order of magnitude increase in OMP adsorption, nearly matching the performance of commercial activated carbon. OMP adsorption from surface water was positively correlated with biochar micropore surface area and negatively correlated with non-micropore surface area, which was linked to higher levels of DOM competition. Base and AAEM pretreatment of biochar feedstocks can increase OMP adsorption for water treatment applications by tuning pore structure and surface area.

Preparation and evaluation of activated carbon from low-rank coal via alkali activation and its fundamental CO2 adsorption capacity at ambient temperature under pure pressurized CO2

The relationship between the CO2 adsorbed amount and specific surface area (a) or pore volumes (b) of the prepared activated carbon. The open plot is the prepared activated carbon. The solid plot is the activated carbon prepared from BN, TN, and SO.

Conversion of biomass to N, S co-doped porous graphene as an adsorbent for mercury vapor removal: optimization and DFT study

This study is devoted to optimization synthesis conditions of the N, S co-doped porous graphene via a single step thermal chemical activation process from agricultural wastes such as cabbage waste. To this end, the response surface method (RSM) was considered, and the synthesis parameters were varied in specific ranges. By doing so, the optimum conditions in terms of the best performance in mercury removal was determined which was characterized by TEM, SEM, BET, XRD, XPS, and FTIR techniques. The chosen key process parameters were Activation agent to carbon precursor ratio (A: KOH/C), Reaction time (B: Time), Activation temperature (C: Temperature), and (Dopant to carbon precursor ratio (D: Dopant/C). Each parameter was investigated in 3 levels with lower and upper bounds being A: 2-6; B:30-90 min.; C: 600-800 ˚C; D:2-10. The optimum conditions of the process were determined to be as: A: 2; B: 30 min.; C: 600 ˚C and D: 2. The optimized sample was prepared in repeated runs with reproducible results with Hg vapor adsorption capacity of 2100 µg/g at 40 ˚C and 2266 µg/g at 90 ˚C. In addition to the experiments, DFT calculations were also carried out which elucidated the positive role of N and S co-doping in improving the mercury adsorption intensity.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00712-y.

Evaluation of pyrochar and hydrochar derived activated carbons for biosorbent and supercapacitor materials

This study investigated effects of different thermal processes on characteristics of activated carbon to produce efficient biosorbents or supercapacitors using biomass resources. Pyrolysis char and hydrochar obtained from woody biomass were used as precursors for activated carbon under different atmospheric conditions (N₂ and air). In order to provide functional groups on the carbon surface, activated carbon under N₂ condition was subsequently acidified by HNO₃ and the other was simultaneously acidified under air condition. Additionally, potential for application as Pb²⁺ adsorbent and supercapacitor was evaluated. Thermochemical behaviors such as bonding cleavage and dehydration during activation processes were observed by TG and Py-GCMS analysis. Elemental analysis, FT-IR, Raman spectroscopy, and XPS analysis were carried out to confirm changes in structures of each carbon products. New plausible reaction mechanism for this observation was suggested with respect to the formation of a key intermediate in the presence of excess air. As for performance in applications, air activated carbon using hydrochar exhibited high versatility to function as both Pb²⁺ adsorbent (~41.1 mg/g) and energy storage material (~185.9 F/g) with high specific surface area, mesopore ratio, surface functional groups.

Synthesis of Porous Material from Coal Gasification Fine Slag Residual Carbon and Its Application in Removal of Methylene Blue

A large amount of coal gasification slag is produced every year in China. However, most of the current disposal is into landfills, which causes serious harm to the environment. In this research, coal gasification fine slag residual carbon porous material (GFSA) was prepared using gasification fine slag foam flotation obtained carbon residue (GFSF) as raw material and an adsorbent to carry out an adsorption test on waste liquid containing methylene blue (MB). The effects of activation parameters (GFSF/KOH ratio mass ratio, activation temperature, and activation time) on the cation exchange capacity (CEC) of GFSA were investigated. The total specific surface area and pore volume of GSFA with the highest CEC were 574.02 m2/g and 0.467 cm3/g, respectively. The degree of pore formation had an important effect on CEC. The maximum adsorption capacity of GFSA on MB was 19.18 mg/g in the MB adsorption test. The effects of pH, adsorption time, amount of adsorbent, and initial MB concentration on adsorption efficiency were studied. Langmuir isotherm and quasi second-order kinetic model have a good fitting effect on the adsorption isotherm and kinetic model of MB.

Hydrogen Storage in Pure and Boron-Substituted Nanoporous Carbons-Numerical and Experimental Perspective

Nanoporous carbons remain the most promising candidates for effective hydrogen storage by physisorption in currently foreseen hydrogen-based scenarios of the world’s energy future. An optimal sorbent meeting the current technological requirement has not been developed yet. Here we first review the storage limitations of currently available nanoporous carbons, then we discuss possible ways to improve their storage performance. We focus on two fundamental parameters determining the storage (the surface accessible for adsorption and hydrogen adsorption energy). We define numerically the values nanoporous carbons have to show to satisfy mobile application requirements at pressures lower than 120 bar. Possible necessary modifications of the topology and chemical compositions of carbon nanostructures are proposed and discussed. We indicate that pore wall fragmentation (nano-size graphene scaffolds) is a partial solution only, and chemical modifications of the carbon pore walls are required. The positive effects (and their limits) of the carbon substitutions by B and Be atoms are described. The experimental ‘proof of concept’ of the proposed strategies is also presented. We show that boron substituted nanoporous carbons prepared by a simple arc-discharge technique show a hydrogen adsorption energy twice as high as their pure carbon analogs. These preliminary results justify the continuation of the joint experimental and numerical research effort in this field.

Facile synthesis and characterization of microporous-structured activated carbon from agro waste materials and its application for CO2 capture

Biomass-derived activated carbon was prepared from the agro waste materials, (wild sugarcane (WS) and saw dust (SD)) by chemical activation using phosphoric acid. The crystallinity, morphology, functional groups of the synthesized activated carbon were investigated. The effects of contact time (10-60 min), mass of adsorbent (0.05-0.2 g) and concentrations of CO2 (1 × 10-4 to 10 × 10-4 M) were analysed and the optimum adsorption conditions were found. Freundlich, Langmuir, Temkin, Dubinin-Radushkevich and Sips isotherm were used to analyse the adsorption data. The adsorption process was fitted with the Freundlich model. Adsorption capacity of agro waste-based sorbent was 5.225 × 10-3 mol/g. Thermodynamic parameters, such as ΔH0, ΔG0, ΔS0 , were calculated and it was found that the present system was a spontaneous process. From the kinetic studies, it was inferred that the Pseudo-second-order kinetics describes the kinetics of CO2 on AC-WSSD with an equilibrium point attained at 50 minutes with a high R2 value of 0.9602. The Brunauer Emmett Teller (BET) surface area of 1220 m2/g and an iodine value of 1360 m2/g were better indications for adsorption process. The interaction between CO2 and functional groups on the surface of the activated carbon was confirmed by FTIR. Desorption studies were carried out for three cycles with an efficiency of 93.2%.

Adsorption of Volatile Organic Compounds (VOCs) on Oxygen-rich Porous Carbon Materials Obtained from Glucose/Potassium Oxalate

To investigate the effects of oxygen-containing functional groups on the adsorption of volatile organic compounds (VOCs) with different polarity, oxygen-rich porous carbon materials (OPCs) were synthesized by heat treatment of glucose/potassium oxalate material. The carbon material had a large specific surface area (1697 m²  g^-1 ) and a high oxygen content (18.95 at.%). OPC exhibited high adsorption capacity of toluene (309 mg g^-1 ) and methanol (447 mg g^-1 ). The specific surface area and total pore volume determined the adsorption capacity of toluene and methanol at the high-pressure range, while the oxygen-containing groups became the main factor affecting the methanol adsorption at the low-pressure range due to the hydrogen bond interaction through the density functional theory (DFT) calculations. This study provides an important hint for developing a novel O-doped adsorbent for the VOCs adsorption applications and analyzing the role of oxygen-containing groups in the VOCs adsorption under the low-pressure range.

Acetic acid-mediated cellulose-based carbons: Influence of activation conditions on textural features and carbon dioxide uptakes

In this work, we developed a simple methodology for producing highly porous carbons. Herein, we combined the hydrothermal method with chemical activation to fabricate cellulose-based, melamine modified porous carbons, using acetic acid as an additive. The preparation conditions including activation temperature, activation time, and melamine ratio were varied to obtain an optimized adsorbent exhibiting efficient textural features and maximized carbon dioxide (CO₂) adsorption uptake. By varying the preparation conditions, high specific surface area (SSA) (1260-3019 m² g^-1), microporosity in the range of 0.21-1.13 cm³ g^-1, and a well-developed porous structure was obtained. The optimized adsorbent exhibits an excellent CO₂ adsorption uptake of 297.05 mg g^-1 (6.75 mmol g^-1) and 174.4 mg g^-1 (3.96 mmol g^-1) at 273 K and 298 K at 1 bar, respectively, due to the existence of ultra-micropores (<0.68 nm, < 0.81 nm), high SSA (3019 m² g^-1), and high nitrogen content (8%). Furthermore, the role of micropores in the CO₂ adsorption process suggests that micropores between 0.68 nm and 1 nm exhibit high CO₂ adsorption potential. Additionally, all synthesized carbons exhibited a high isosteric heat of adsorption (45 kJ mol^-1) and a greater affinity for adsorbed CO₂ species than nitrogen (N₂) molecules. Thus, as-fabricated porous carbon adsorbents are an effective competitor for CO₂ uptake applications to mitigate global warming.

Synergy between alkali activation and a salt template in superactive carbon production from lignin

Due to growing demand, the performance of traditional active carbon is insufficient. An innovative solution is superactive carbon with an ultra-high surface area as high as 3000 m² g^-1. However, this material is very costly due to the considerable amount of alkali used in its manufacturing. To obtain superactive carbon from lignin, KOH and KCl were used simultaneously. The method was thoroughly studied to describe the mechanism of pore origin and control the pore size. Because of synergy between KOH and KCl, superactive carbon with an ultra-high surface area (2938 ± 42 m² g^-1) was obtained at essentially diminished KOH consumption (1 g g^-1) in contrast to previously reported methods. The process was optimised using the response surface method. The pore size can be tuned by varying the amount of KOH and temperature. Observed synergy enabled reduced alkali consumption, overcoming the barrier to widespread implementation of superactive carbon.

Effect of KOH on the Energy Storage Performance of Molasses-Based Phosphorus and Nitrogen Co-Doped Carbon

In this study, we have evaluated the effect of potassium hydroxide (KOH) on the energy storage performance of metal-free carbon-based materials prepared from molasses. Molasses are a renewable-resource biomass and economical by-product of sugar refinement, used here as a carbon precursor. Two co-doped carbon materials using molasses were synthesized via a time and cost-efficient microwave carbonization process, with ammonium polyphosphate as a phosphorus and nitrogen doping agent. The phosphorus and nitrogen co-doped carbon (PNDC) samples were prepared in the presence and absence of a chemical activating agent (KOH), to study the role of chemical activation on PNDCs. Physical characterizations were performed to gain insight into the composition, pore size and topographical data of each material. Electrochemical characterization via cyclic voltammetry in 1 M sulfuric acid (H2SO4) as well as in 6 M KOH as electrolytes, revealed high current density and specific capacitance for the chemically activated material (PNDC2) compared to one without chemical activation (PNDC1). The capacitance value of 244 F/g in KOH electrolyte was obtained with PNDC2. It is concluded that addition of KOH prior to carbonization increases the surface functionality, which significantly enhances the electrochemical properties of the PNDC material such as current density, stability, and specific capacitance.

N-self-doped porous carbon derived from animal-heart as an electrocatalyst for efficient reduction of oxygen

Biomass-derived nitrogen-self-doped carbon was prepared by a simple and green approach based on the direct pyrolysis of pork heart using KOH as an activation reagent at controlled temperatures (700-900 °C). The obtained samples displayed a specific surface area up to 1718.84 m² g^-1, high content of nitrogen (3.03%) and interconnected porous structure, which is able to expose abundant active sites and promote mass transfer. Electrochemical measurements showed that our catalyst possessed a high electrocatalytic activity for oxygen reduction reaction in alkaline solution that is equivalent to that of commercial Pt/C. The sample carbonized at 700 °C (PC-APHs-700) with the onset potential of 0.92 V and half-wave potential of 0.80 V possessed the highest concentrations of graphite and pyridine nitrogen and exhibited the best performance among the PC-APHs-T samples. In addition, PC-APHs-700 had a higher long-term stability and stronger methanol tolerance than commercial Pt/C. This work demonstrates that it is a promising approach to develop and utilize carbon materials with added value as effective metal-free cathode catalysts for alkaline fuel cells based on economic and environmental friendly renewable biomass.

Comparison of acid exfoliators in carbon nanosheets synthesis from stinging nettle (Urtica dioica) for electrochemical applications

Carbon nanosheets (CNs) were successfully synthesized from nettle stem (NS) which is an inexpensive material with a high carbon content that is abundantly available in nature. CNs were produced using chemical (potassium hydroxide activation and acid exfoliation) and thermal treatments. Sulfuric (H2SO4), phosphoric (H3PO4) and nitric (HNO3) acid solutions were used for exfoliation. CNs exfoliated by H3PO4 have higher specific surface area (789 m2 g-1) compared to CNs exfoliated by H2SO4 (705 m2 g-1) and HNO3 (106 m2 g-1). In this work, NSCNs were found to be a potential candidate for electrode material in electrochemical capacitors. The maximum specific capacitance of the NSCNs exfoliated by H3PO4 is found to be 27.3 F g-1 at a current density of 0.05 A g-1, while the specific capacitance of NSCNs exfoliated by H2SO4 and HNO3 is 9.34 F g-1 and 1.71 F g-1, respectively. Energy density (0.06-0.95 Wh kg-1) and power density (20.9-26.7 W kg-1) of NSCNs are confirmed to be supercapacitor materials and can be applied in energy storage devices.

Magnetic bio-activated carbon production from lignin via a streamlined process and its use in phosphate removal from aqueous solutions

Lignin and ferrous salt were mechanically mixed, melted, carbonized and steam activated to produce magnetic bio-activated carbons (MBACs). Phosphate adsorption capacity measurement was conducted on representative MBAC, which has a high surface iron oxide proportion and mesoporous volume. The results indicate that iron species are embedded into the carbon matrix by lignin melting. Steam is not only an activation agent for pore generation and widening but is also effective for the oxidization of Hagg iron carbide produced via ferrous salt decomposition and subsequent reduction during the carbonization process to form magnetite. The porous and magnetic properties and surface iron oxide content of the produced MBACs can be modified by controlling the steam/magnetic biochar (MBC) ratio. The MBAC production process is streamlined and novel, compared with conventional coprecipitation or impregnation methods. The maximum phosphate adsorption onto the representative MBAC product using the best fitting model, i.e., the Langmuir-Freundlich model, is estimated to be 21.18 mg/g, suggesting that the representative MBAC product has a comparable phosphate adsorption capacity to most of the reported MBCs and MBACs.