Adsorption of CO2 on KOH activated carbon adsorbents: Effect of different mass ratios

Exploring the structural characteristics and adsorption capabilities of cost-effective N- doped activated carbon derived from waste biomass for CO2 adsorption

In this work, ACs were originated from two different bio-waste sources of Date and Jujube seeds (DS and JS). The influence of the precursor type as well as KOH chemical activator ratio on the structural properties and CO2 adsorption performances of synthesized ACs were assessed. Impact of pre-treatment of raw material via functionalization with urea on the performance of prepared adsorbents was also evaluated. Functionalized DS-based AC possessed the highest surface area and largest micropore volume equal to 864 m2/g and 0.33 cm3/g, respectively. CO2 adsorption behavior of ACs was experimentally evaluated via TGA at different adsorption temperatures of 25 and 50 °C and CO2 concentrations of 10 and 90 vol% under atmospheric pressure. Based on the TGA results, functionalized and non-functionalized DS-prepared ACs with KOH: biochar weight ratio of 2:1, demonstrated great CO2 capture capacity up to 1.3 and 1.2 mmol/g, respectively under realistic condition of 10 vol% CO2 and 25 °C. The urea-nitrogenation and KOH-activation as economical and simple approaches sensitively assisted preparation of a novel and promising N-doped porous AC from bio-waste resources which can be exploited for superior CO2 capture applications.

Competitive adsorption of acetaminophen and caffeine onto activated Tingui biochar: characterization, modeling, and mechanisms

Tingui biochar (TB) activated with potassium hydroxide (TB-KOH) was synthesized in the present study. The adsorption capacity of TB-KOH was evaluated for the removal of acetaminophen and caffeine in monocomponent and bicomponent solutions. As a result, the study of the TB-KOH characterization as well as the adsorption kinetics, isotherm, thermodynamics, and a suggestion of the global adsorption mechanism are presented. TB-KOH was characterized through physical-chemical analysis to understand its surface morphology and how it contributes to the adsorption of these drugs. Furthermore, modelling using advanced statistical physical models was performed to describe how acetaminophen and caffeine molecules are adsorbed in the active sites of TB-KOH. Through the characterizations, it was observed that the activation with KOH contributed to the development of porosity and functional groups (-OH, C-O, and C = O) on the surface of TB. The monocomponent adsorption equilibrium was reached in 90 min with a maximum adsorption capacity of 424.7 and 350.8 mg g-1 for acetaminophen and caffeine, respectively. For the bicomponent solution adsorption, the maximum adsorption capacity was 199.4 and 297.5 mg g-1 for acetaminophen and caffeine, respectively. The isotherm data was best fitted to the Sips model, and the thermodynamic study indicated that acetaminophen removal was endothermic, while caffeine removal was exothermic. The mechanism of adsorption of acetaminophen and caffeine by TB-KOH was described by the involvement of hydrogen bonds and π-π interactions between the surface of TB-KOH and the molecules of the contaminants.

Activated carbons-preparation, characterization and their application in CO2 capture: A review

In this paper, we provide a comprehensive review of the latest research trends in terms of the preparation, and characteristics of activated carbons regarding CO2 adsorption applications, with a special focus on future investigation paths. The reported current research trends are primarily closely related to the synthesis conditions (carbonization and physical or chemical activation process), to develop the microporosity and surface area, which are the most important factors affecting the effectiveness of adsorption. Furthermore, we emphasized the importance of regeneration techniques as a factor determining the actual technological and economic suitability of a given material for CO2 capture application. Consequently, this work provides a summary and potential directions for the development of activated carbons (AC). We attempt to create a thorough theoretical foundation for activated carbons while also focusing on identifying and specific statements of the most relevant ongoing research scope that might be advantageous to progress and pursue in the coming years.

Household mixed plastic waste derived adsorbents for CO2 capture: A feasibility study

The feasibility of producing activated carbon (AC) from real Household Mixed Plastic Waste (HMPW) comprising of LDPE, HDPE, PP, PS, and PET for carbon capture via direct carbonisation followed by microwave-assisted or conventional thermally assisted chemical activation was investigated. A microwave-assisted activation procedure was adopted to assess the impact on the CO2 capture capacity of the resulting AC using both a lower temperature (400 °C vs. 700 °C) and a shorter duration (5 vs. 120 mins) than that required for conventional activation. The results obtained showed that the AC yield was 71 and 78% for the conventional and microwave-assisted samples, respectively. Microwave activation consumed five-fold less energy (0.19 kWh) than the conventional activation (0.98 kWh). Thermal stability results indicated total weight loss of 10.0 and 8.3 wt%, respectively, for conventional and microwave-activated samples over the temperature range of 25-1000 °C, with ACs from both activation routes displaying a type 1 nitrogen isotherm. The dynamic CO2 uptake capacity at 1 bar and 25 °C was 1.53 mmol/g, with maximum equilibrium uptake ranging between 1.32 and 2.39 mmol/g at temperatures (0-50 °C) and 1 bar for the conventionally activated AC. The analogous microwave-activated sample showed a higher dynamic CO2 uptake of 1.62 mmol/g and equilibrium uptake in the range 1.58-2.88 mmol/g under equivalent conditions. The results therefore indicate that microwave activation results in enhanced carbon capture potential. To the best of our knowledge, this is the first-time microwave heating has been employed to convert household mixed plastic wastes directly into ACs for carbon capture applications. This report therefore demonstrates that the management of mixed plastics could lead to the development of a circular economy through the conversion of waste into value-added materials.

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.

Production of MgFe2O4/activated carbons derived from a harmful grass Cynodon dactylon and their utilization for ciprofloxacin removal

Cynodon dactylon, an invasive species, exhibits its robust adaptability, reproduction and nutrient regime against the local species. Taking advantage of this harmful grass as a raw precursor to produce valuable materials for wastewater treatment has paid much attention. Herein, we report on the fabrication of Cynodom dactylon derived MgFe2O4@AC with a main goal of effective removal of ciprofloxacin antibiotic from water. Our findings showed that MgFe2O4@ACK1 composites attained mesoporous textures, high specific surface areas (884.3-991.6 m2 g-1), and MgFe2O4-20%@ACK1 was the most effective with a very high removal efficiency of 96.7%. The Elovich model was suitable for describing the kinetic of adsorption with (Radj)2 of 0.9988. Meanwhile, the isotherm data obeyed the Langmuir model corresponding to (Radj)2 of 0.9993. Qmax value of MgFe2O4-20%@ACK1 was determined at 211.67 mg g-1. The proposed adsorption mechanism primarily comprises five routes as follows, (i) pore-filling, (ii) π-π interaction, (iii) electrostatic interaction, (iv) hydrogen bonding, and (v) hydrophobic interaction. MgFe2O4-20%@ACK1 adsorbent could reuse with three cycles. We recommend that MgFe2O4/ACs derived from Cynodom dactylon could be high-efficiency adsorbents for the elimination of antibiotics.

Application of cellulose nanofiber as a promising air filter for adsorbing particulate matter and carbon dioxide

Pollution from particulate matter (PM) and toxic chemicals in the air cause some of the most critical health and environmental hazards in developed and developing countries. It can have a very destructive effect on human health and other living creatures. In particular, PM air pollution caused by rapid industrialization and population growth is a grave concern in developing countries. Oil and chemical-based synthetic polymers are non-environmentally friendly materials that lead to secondary environmental pollution. Thus, developing new and environmentally compatible renewable materials to construct air filters is essential. The goal of this review is to study the use of cellulose nanofibers (CNF) to adsorb PM in the air. Some of CNF's advantages include being the most abundant polymer in nature, biodegradable, and having a high specific surface area, low density, surface properties (broad possibility of chemical surface modification), high modulus and flexural stiffness, low energy consumption, which provide this new class of bio-based adsorbent with promising potential applications in environmental remediation. Such advantages have made CNF a competitive and highly in-demand material compared to other synthetic nanoparticles. Today, refining membranes and nanofiltration manufacturing are two important industries that could use CNF to provide a practical step in protecting the environment and saving energy. CNF nanofilters are capable of nearly eliminating most sources of air pollution, including carbon monoxide, sulfur oxides, nitrogen oxides, and PM_2.5-10 μm. They also have a high porosity and low resistance air (pressure drop) ratio compared to ordinary filters made from cellulose fiber. If utilized correctly, humans do not need to inhale harmful chemicals.

On the use of plastic precursors for preparation of activated carbons and their evaluation in CO2 capture for biogas upgrading: a review

In circular economy, useful plastic materials are kept in circulation as opposed to being landfilled, incinerated, or leaked into the natural environment. Pyrolysis is a chemical recycling technique useful for unrecyclable plastic wastes that produce gas, liquid (oil), and solid (char) products. Although the pyrolysis technique has been extensively studied and there are several installations applying it on the industrial scale, no commercial applications for the solid product have been found yet. In this scenario, the use of plastic-based char for the biogas upgrading may be a sustainable way to transform the solid product of pyrolysis into a particularly beneficial material. This paper reviews the preparation and main parameters of the processes affecting the final textural properties of the plastic-based activated carbons. Moreover, the application of those materials for the CO₂ capture in the processes of biogas upgrading is largely discussed.

Yerba mate: From waste to activated carbon for supercapacitors

Developing technological solutions that use yerba mate waste as precursors is key to reducing the environmental impact caused by the lack of treatment and its accumulation in landfills. Due to their physicochemical properties, these residues can be used to develop activated carbons. Activated carbon is a versatile material with a high surface area that can be used for energy storage. In this work, yerba mate residues were valued by producing chemically activated carbon to be used as electrode material in supercapacitors. Activated carbons were developed through chemical activation in two steps with KOH. Variables such as impregnation ratio and activation temperature are studied. The developed carbons were characterized by physicochemical and electrochemical techniques. They were found to have high surface areas, up to 1800 m² g^-1, with a hierarchical porous distribution. A maximum specific capacitance of 644 F g^-1 at 0.1 A g^-1, and power values of ca 32,000 W kg^-1, at 33 A g^-1 were found. All the synthesized carbons have excellent electrochemical properties and are suitable for use as active material in supercapacitors.

The Influence of NH4NO3 and NH4ClO4 on Porous Structure Development of Activated Carbons Produced from Furfuryl Alcohol

The influence of NH₄NO₃ and NH₄ClO₄ on the porous texture and structure development of activated carbons produced from a non-porous polymeric precursor synthesized from furfuryl alcohol has been studied. The non-doped counterparts were prepared and studied for comparison purposes. NH₄NO₃ and NH₄ClO₄-doped polymers were carbonized under N₂ atmosphere at 600 °C, followed by CO₂ activation at 1000 °C and the obtained carbon materials and activated carbons were thoroughly characterized. The porosity characterization data have shown that NH₄NO₃-derived ACs present the highest specific surface area (up to 1523 m²/g in the experimental conditions studied), and the resulting porosity distributions are strongly dependent on the activation conditions. Thus, 1 h activation is optimum for the microporosity development, whereas larger activation times lead to micropores enlargement and conversion into mesopores. The type of doping salts used also has a substantial impact on the surface chemical composition, i.e., C=O groups. Moreover, NH₄NO₃ and NH₄ClO₄ constitute good sources of nitrogen. The type and contribution of nitrogen species are dependent on the preparation conditions. Quaternary nitrogen only appears in doped samples prepared by carbonization and pyrrolic, pyrydinic, and nitrogen oxide groups appear in the NH₄NO₃ -series. NH₄NO₃ incorporation has led to optimized materials towards CO₂ and C₂H₄ sorption with just 1 h activation time.

Tool for optimization of energy consumption of membrane-based carbon capture

The reduction of CO₂ emissions is a very challenging issue. The capture of CO₂ from combustion processes is associated with high energy consumption and decreases the efficiency of power-producing facilities. This can affect the economy and in specific cases, such as waste-to-energy plants, also their classification according to legislation. To allow the minimization of energy consumption, an optimization tool for membrane-based post-combustion capture was developed. The approach allows finding optimal membrane properties, membrane areas, and pressures for individual separation stages from the point of view of energy consumption. The core of the approach is represented by a mathematical model of the separation system that is based on a network flow problem. The model utilizes external simulation modules for non-linear problems to enable finding globally optimal results. These external modules approximate non-linear dependencies with any desired precision and allow using different mathematical descriptions of individual membrane stages without making changes to the model. Moreover, it allows easy substitution of the external module by experimental data and the model can be easily modified for specific purposes such as decision making, designing the separation process, as well as for regulation of process parameters in the case of dynamic operation. The ability of the model to optimize the process was verified on a case study and the results show that the optimization can significantly reduce the energy consumption of the process. For separation of 90% of CO₂ at the purity of 95% from initial flue gas with 13% CO₂ with state-of-the-art membranes based on the Robeson upper bound and three-stage process, the minimum power consumption was 1.74 GJ/t_CO2 including final CO₂ compression.

Versatile Strategy for the Preparation of Woody Biochar with Oxygen-Rich Groups and Enhanced Porosity for Highly Efficient Cr(VI) Removal

Biochar is widely used to remove hexavalent chromium [Cr(VI)] from wastewater through adsorption, which is recognized as a facile, cost-efficient, and high-selectivity approach. In this study, a versatile strategy that combines delignification with subsequent carbonization and KOH activation is proposed to prepare a novel woody biochar from waste poplar sawdust. By virtue of the unique multilayered and honeycomb porous structure induced by delignification and activation processes, the resultant activated carbonized delignified wood (ACDW) exhibits a high specific surface area of 970.52 m2 g-1 with increasing meso- and micropores and abundant oxygen-containing functional groups. As a benign adsorbent for the uptake of Cr(VI) in wastewater, ACDW delivers a remarkable adsorption capacity of 294.86 mg g-1 in maximum, which is significantly superior to that of unmodified counterparts and other reported biochars. Besides, the adsorption behaviors fit better with the Langmuir isotherm, the pseudo-second-order kinetic model, and the adsorption diffusion model in batch experiments. Based on the results, we put forward the conceivable adsorption mechanism that the synergistic contributions of the capillary force, electrostatic attraction, chemical complexation, and reduction action facilitate the Cr(VI) capture by ACDW.

Potassium hydroxide-modified algae-based biochar for the removal of sulfamethoxazole: Sorption performance and mechanisms

Biochar has been deemed one of the most promising sorbents for the removal of organic pollutants from aqueous solution. In this study, potassium hydroxide-modified Enteromorpha prolifera biochars (PEBCs) were prepared for the first time and applied for efficient sorption of a typical antibiotic, sulfamethoxazole (SMX). The characteristics of PEBCs, including morphology, pore structure, graphitization degree, surface functional groups, and surface element composition, were investigated. Moreover, sorption kinetic and isotherm experiments were carried out to explore the sorption process, performance, and mechanisms. The maximum sorption capacity for SMX can reach 744 mg g^-1, which is much higher than that reported for sorbents. The sorption of SMX onto PEBCs was controlled by both physical and chemical processes. Moreover, pore filling, hydrogen bonding, partitioning, π-π stacking, and electrostatic interactions were possible sorption mechanisms. This study indicated that the structure and properties of algal biochar can be further improved by potassium hydroxide modification at high temperature and applied as an excellent sorbent for the removal of antibiotics from aqueous solution.

Upgrading of pine tannin biochars as electrochemical capacitor electrodes

Biochar derived from the pyrolysis of pine tannin is a green and available by-product of oil manufacturing that presents interesting features after having been activated by KOH at 650 °C. Different weight ratios of KOH to biochar were used and the resulting activated carbons (ACs) presented highly developed specific surface areas of up to 2190 m² g^-1, well-connected porosity and high oxygen content, leading to enhanced electrochemical performance when used as electrochemical capacitor electrodes in a 1 M H₂SO₄ aqueous electrolyte. Galvanostatic charge/discharge experiments evidenced that the best material achieved a maximum electrode capacitance of up to 232 F g^-1 (at 0.5 A g^-1) with a capacitance retention of 70% at 10 A g^-1 using commercial mass loadings (i.e., approx. 10 mg cm^-2). In addition, long cycling stability with a residual capacitance of 92 to 94% after 10,000 cycles at 5 A g^-1 was achieved. These results prove that ACs derived from pine tannin biochars have great potential for their commercial use as electrochemical energy storage devices.

A novel activation-hydrochar via hydrothermal carbonization and KOH activation of sewage sludge and coconut shell for biomass wastes: Preparation, characterization and adsorption properties

A two-stage method of hydrothermal carbonization and chemical activation technology was applied to prepare a novel, large surface area and rich-pore structure activation-hydrochar from sludge sewage and coconut shell due to its mild, low-cost, and well-developed merits. The pore-making mechanism of activation-hydrochar was discussed by FT-IR, XPS, SEM, TG, TG-MS, XRD, and BET characterization. These results illustrated that the first stage of hydrothermal carbonization achieved the rich-pore structure hydrochar via dehydration, decarboxylation, deamination, and rearrangement reactions. The subsequent KOH activation was conducive to the pore-forming process. Specifically, the pore structure of activation-hydrochar was ameliorated and abundant active adsorption sites were obtained by the modification. The adsorption properties of activation-hydrochar on Methylene Blue (MB) and Congo Red (CR) were systematically investigated, and the max adsorption capacities of those were obtained with 623.37 mg/g and 228.25 mg/g, respectively. The pseudo-second-order kinetics and Langmuir models were both fit to elucidate the adsorption process for both dyes. Thermodynamics revealed adsorption performance accompanied by the spontaneous and endothermic processes. In general, the research clearly indicated the synthesis route for activation-hydrochar, and its further adsorption performance, capacity, and mechanism on MB and CR. This research demonstrated that activation-hydrochar with the abundant surface area and rich-pore structure made it a candidate for the production of effective adsorption material. It is prospective to achieve the utilization of wastes and its further application in wastewater treatment.

Carbon material-immobilized ionic liquids were applied on absorption of Hg2+ from water phase

In this study, several immobilized ionic liquid adsorbents on carbon materials were synthesized with impregnation method. The carrier materials were activated carbon and three kinds of multi-walled carbon nanotubes. And the synthetic adsorbents immobilized different kinds of ionic liquids were characterized by Boehm titration, FT-IR, XPS, TG, and BET analysis, respectively. Finally, carbon materials after [C4mim]HSO₄ immobilization were selected as adsorbent to remove Hg²⁺ from water phase. The optimum conditions of adsorption test of ionic liquid immobilized by multi-walled carbon nanotubes were as follows: the initial concentration of Hg²⁺ was 400 mg/L, the adsorbent addition amount was 40 mg, the temperature was 20 °C, the reaction time was 200 min, the removal rate of Hg²⁺ peaked at 62.95%, the adsorption capacity was reached 79.00 mg/g. The optimum conditions of adsorption test of ionic liquid immobilized by activated carbon were as follows: the initial concentration of Hg²⁺ was 300 mg/L, the adsorbent addition amount was 0.2 g, the temperature was 20 °C, pH was 2.0, the reaction time was 100 min, the removal rate of Hg²⁺ was more than 99%, the adsorption capacity was 118.65 mg/g. The adsorption isotherm fitting study found that the adsorption of adsorbent on Hg²⁺ was more in line with the Langmuir model, and the adsorption kinetics study shows that the adsorption process is consistent with the pseudo-second-order kinetic equation. The results of kinetic analysis are further verified by thermodynamic analysis.