Adsorptive removal of CO2 on highly microporous activated carbons prepared from Eucalyptus camaldulensis wood: Effect of chemical activation

CO2 adsorption on carbonaceous materials obtained from forestry and urban waste materials: a comparative study

The increasing emissions of gaseous pollutants of anthropogenic origin, such as carbon dioxide (CO2), which causes global warming, have raised great interest in developing and improving processes that allow their mitigation. Among them, adsorption on porous materials has been proposed as a sustainable alternative. This work presents a study of CO2 equilibrium adsorption at low temperatures (0, 10, and 20 °C) over a wide range of low pressures, on activated carbon derived from Eucalyptus (ES) and Patula pine (PP) forest waste, and carbonaceous material derived from waste tires (WT). The precursors of these materials were previously prepared, and their physicochemical properties were characterized. ES and PP were thermochemically treated with phosphoric acid, and WT was oxidized with nitric acid. Additionally, these materials were used to obtain monoliths using uniaxial compaction techniques and different binding agents, with better results obtained with montmorillonite. A total of six adsorbent solids had their textural and chemical properties characterized and were tested for CO2 adsorption. The highest specific surface area (1405 m2 g-1), and micropore properties were found for activated carbon derived from Eucalyptus whose highest adsorption capacity ranged from 2.27 mmol g-1 (at 0 °C and 100 kPa) to 1.60 mmol g-1 (at 20 °C and 100 kPa). The activated carbon monoliths presented the lowest CO2 adsorption capacities; however, the studied materials showed high potential for CO2 capture and storage applications at high pressures. The isosteric heats of adsorption were also estimated for all the materials and ranged from 16 to 45 kJ mol-1 at very low coverage explained by the energetic heterogeneity and weak repulsive interactions among adsorbed CO2 molecules.

Remediation through the coordinated use of local rice husk residues for the selective adsorption of iron and nickel in real landfill leachate

Herein, we demonstrate the prospects of tackling several environmental problems by transforming a local rice husk residue into an effective adsorbent, which was then applied for the treatment of real landfill leachate (LL). The study focused on establishing (i) the effect of simple washing on morphological aspects, (ii) evaluating target adsorption capacity for total iron (Fe) and nickel (Ni), (iii) determining regeneration and reuse potential of the adsorbent and (iv) complying to the requirements of worldwide legislations for reuse of treated LL wastewater. The adsorbent was prepared by employing a simple yet effective purification process that can be performed in situ. The LL was collected post-membrane treatment, and the characterizations revealed high concentrations of Fe, Ni, and organic matter content. The simple washing affected the crystallinity, resulting in structural alterations of the adsorbents, also increasing the porosity and specific surface. The adsorption process for Ni occurred naturally at pH 6, but adjusting the pH to 3 significantly improved removal efficiency and adsorption capacity for total Fe. The kinetics were accurately described by the pseudo-second-order model, while the Langmuir model provided a better fit for the isotherms. The adsorbent was stable for 5 reuses, and the metals adsorbed were recovered through basic leaching. The removal capacities achieved underscore the remarkable effectiveness of the process, ensuring the treated LL wastewater meets rigorous global environmental legislations for safe use in irrigation. Thus, by employing the compelling methods herein optimized it is possible to refer to the of solving three environmental problems at once.

Impact of carbonization conditions and adsorbate nature on the performance of activated carbon in water treatment

The physical and chemical structure of activated carbon (AC) varies with the carbonization temperature, activation process and time. The texture and toughness of the starting raw material also determine the morphology of AC produced. The Brunauer-Emmet-Teller surface area (SBET) is small for AC produced at low temperatures but increases from 500 to 700 °C, and generally drops in activated carbons synthesized > 700 °C. Mild chemical activators and low activator concentrations tend to generate AC with high SBET compared to strong and concentrated oxidizing chemicals, acids and bases. Activated carbon from soft starting materials such as cereals and mushrooms have larger SBET approximately twice that of tough materials such as stem berks, shells and bones. The residual functional groups observed in AC vary widely with the starting material and tend to reduce under extreme carbonization temperatures and the use of highly concentrated chemical activators. Further, the adsorption capacity of AC shows dependency on the size of the adsorbate where large organic molecules such as methylene blue are highly adsorbed compared to relatively small adsorbates such as phenol and metal ions. Adsorption also varies with adsorbate concentration, temperature and other matrix parameters.

Highly efficient and selective CO2 capture of Li2CO3- and (Li-K)2CO3-based porous carbon composites

In this study, Li₂CO₃- and (Li-K)₂CO₃-based porous carbon composites were synthesized from terephthalic acid, lithium hydroxide and sodium hydroxide through calcination at different temperatures. These materials were fully characterized through X-ray diffraction, Raman spectroscopy, and nitrogen adsorption and desorption. Results showed that the excellent CO₂ capture capacities of LiC-700 °C and LiKC-600 °C were 140 and 82 mg CO₂ g^-1 at 0 °C and 25 °C, respectively. Additionally, it is calculated that the selectivity of LiC-600 °C and LiKC-700 °C with a CO₂/N₂ (15 : 85) mixture was about 27.41 and 15.04, respectively. Therefore, Li₂CO₃- and (Li-K)₂CO₃-based porous carbon materials could be used to effectively capture CO₂ with high capacity and high selectivity.

Valorization of Different Fractions from Butiá Pomace by Pyrolysis: H2 Generation and Use of the Biochars for CO2 Capture

This work valorizes butiá pomace (Butia capitata) using pyrolysis to prepare CO2 adsorbents. Different fractions of the pomace, like fibers, endocarps, almonds, and deoiled almonds, were characterized and later pyrolyzed at 700 °C. Gas, bio-oil, and biochar fractions were collected and characterized. The results revealed that biochar, bio-oil, and gas yields depended on the type of pomace fraction (fibers, endocarps, almonds, and deoiled almonds). The higher biochar yield was obtained by endocarps (31.9%wt.). Furthermore, the gas fraction generated at 700 °C presented an H2 content higher than 80%vol regardless of the butiá fraction used as raw material. The biochars presented specific surface areas reaching 220.4 m2 g-1. Additionally, the endocarp-derived biochar presented a CO2 adsorption capacity of 66.43 mg g-1 at 25 °C and 1 bar, showing that this material could be an effective adsorbent to capture this greenhouse gas. Moreover, this capacity was maintained for 5 cycles. Biochars produced from butiá precursors without activation resulted in a higher surface area and better performance than some activated carbons reported in the literature. The results highlighted that pyrolysis could provide a green solution for butiá agro-industrial wastes, generating H2 and an adsorbent for CO2.

Factors influencing the adsorption of antibiotics onto activated carbon in aqueous media

Widespread use of antibiotics for treating human and animal ailments has increased their discharge in the environment through excreta. Moreover, unscientific disposal of unused antibiotics has further increased their presence in the environmental matrices. Thus, occurrence of used and/or discarded antibiotics in water resources is becoming a growing concern across the globe. Antibiotics and their residues in the aquatic environment are emerging contaminants which pose a serious threat to the aquatic biota as well as human beings by enhancing antibiotic resistance. Various methods are being adopted for the removal of these contaminants. Adsorption over activated carbon is one such promising method which is environmentally friendly, cost-effective, and efficient. However, there are various factors which affect the overall process efficiency, such as, properties of activated carbon/antibiotics/reaction medium etc. In this article, emphasis has been laid down on evaluating these factors, so that the experimental procedures may be optimized to obtain the highest possible removal efficiency for antibiotics in the aqueous media.

Waste-based nanoarchitectonics with face masks as valuable starting material for high-performance supercapacitors

Surgical face masks waste is a source of microplastics (polymer fibres) and inorganic and organic compounds potentially hazardous for aquatic organisms during degradation in water. The monthly use of face masks in the world is about 129 billion for 7.8 billion people. Therefore, in this contribution the utilization of hazardous surgical face masks waste for fabrication of carbon-based electrode materials via KOH-activation and carbonization was investigated. The micro-mesoporous materials were obtained with specific surface areas in the range of 460 - 969 m²/g and a total pore volume of 0.311 - 0.635 cm³/g. The optimal sample showed superior electrochemical performance as an electrode material in supercapacitor in the three-electrode system, attaining 651.1F/g at 0.1 Ag^-1 and outstanding capacitance retention of 98 % after a test cycle involving 50'000 cycles. It should be emphasized that capacitance retention is one of the most crucial requirements for materials used as the electrodes in the supercapacitor devices. In this strategy, potentially contaminated face masks, common pandemic waste, is recycled into highly valuable carbon material which can serve in practical applications overcoming the global energy crisis. What is more, all microorganisms, including coronaviruses that may be on/in the masks, are completely inactivated during KOH-activation and carbonization.

Waste furniture gasification using rice husk based char catalysts for enhanced hydrogen generation

Present study provides biohydrogen production methods from waste furniture via catalytic steam gasification with bio-char catalysts (raw char, KOH-activated char and steam-activated char). Total gas yield for the prepared chars was in the order of KOH-activated char > steam-activated char > raw char, whereas, H₂ selectivity was in the sequence of raw char > steam-activated char > KOH-activated char. Though KOH-activated char showed the highest gas yield, highest H₂ selectivity was obtained at the gasification experiment with raw char due to the large amount of Ca and K and its reasonable surface area (146.89 m²/g). Although the activation of raw biochar results in the increase of gas yield, it has the negative effect on H₂ generation due to the removal of alkali and alkaline earth metals for the KOH activated char and steam-activated char. This study shows that raw bio-char could be a potential solution for eco-friendly hydrogen production.

Evaluation of kinetics and mechanism properties of CO2 adsorption onto the palm kernel shell activated carbon

The volumetric adsorption kinetics of carbon dioxide (CO₂) onto the synthesized palm kernel shell activated carbon via single-stage CO₂ activation and commercial Norit® activated carbon were carried out at an initial pressure of approximately 1 bar at three different temperatures of 25, 50, and 100 °C. The experimental kinetics data were modelled by using the Lagergren's pseudo-first-order model and pseudo-second-order model. Comparing these two, the non-linear pseudo-second-order kinetics model presented a better fit towards CO₂ adsorption for both adsorbents, owing to its closer coefficient of determination (R²) to unity, irrespective of the adsorption temperature. In addition, kinetics analysis showed that the corresponding kinetics coefficient (rate of adsorption) of both activated carbons increased with respect to adsorption temperature, and thereby, it indicated higher mobility of CO₂ adsorbates at an elevated temperature. Nevertheless, CO₂ adsorption capacity of both activated carbons reduced at elevated temperatures, which signified exothermic and physical adsorption (physisorption) behaviour. Besides, process exothermicity of both carbonaceous adsorbents can be corroborated through activation energy (E_a) value, which was deduced from the Arrhenius plot. E_a values that were in range of 32-38 kJ/mol validated exothermic adsorption at low pressure and temperature range of 25-100 °C. To gain an insight into the CO₂ adsorption process, experimental data were fitted to intra-particle diffusion model and Boyd's diffusion model, and findings revealed an involvement of both film diffusion and intra-particle diffusion during CO₂ adsorption process onto the synthesized activated carbon and commercial activated carbon.

Pretreatment of lignocellulosic waste as a precursor for synthesis of high porous activated carbon and its application for Pb (II) and Cr (VI) adsorption from aqueous solutions

Effects of Elm tree sawdust pretreatments using alkali and alkaline earth metals (NaCl, KCl, CaCl₂, MgCl₂ and Elm tree ash) and deashing solutions (water, HCl, HNO₃ and aqua regia) before the carbonization process on the porosity of produced activated carbons and Pb (II) and Cr (VI) adsorption were studied. The activated carbons were characterized by pore size distribution, surface area, FTIR, and SEM-EDX analysies. Based on the results, HCl leaching pretreatment of the biomass increased the activated carbon adsorption capacity of Cr (VI) from 114 to 190 mg g^-1. The treatment of biomass with alkali and alkali earth metal salts, especially MgCl₂, remarkably increased the activated carbon adsorption capacity of Pb (II) from 233 to 1430 mg g^-1. The results indicated that Pb (II) adsorption was attributed to both the mesoporous structure of activated carbon and the abundance of Mg on the activated carbon's surface. On the other hand, the micropores played a major role in Cr (VI) adsorption capacity. The development of the micro- or mesoporous structure of activated carbons through pretreatment of lignocellulosic precursor could be an approach for providing high performance activated carbons for Pb (II) and Cr (VI) removal from aqueous solutions.

Current State of Porous Carbon for Wastewater Treatment

Porous materials constitute an attractive research field due to their high specific surfaces; high chemical stabilities; abundant pores; special electrical, optical, thermal, and mechanical properties; and their often higher reactivities. These materials are currently generating a great deal of enthusiasm, and they have been used in large and diverse applications, such as those relating to sensors and biosensors, catalysis and biocatalysis, separation and purification techniques, acoustic and electrical insulation, transport gas or charged species, drug delivery, and electrochemistry. Porous carbons are an important class of porous materials that have grown rapidly in recent years. They have the advantages of a tunable pore structure, good physical and chemical stability, a variable specific surface, and the possibility of easy functionalization. This gives them new properties and allows them to improve their performance for a given application. This review paper intends to understand how porous carbons involve the removal of pollutants from water, e.g., heavy metal ions, dyes, and organic or inorganic molecules. First, a general overview description of the different precursors and the manufacturing methods of porous carbons is illustrated. The second part is devoted to reporting some applications such using porous carbon materials as an adsorbent. It appears that the use of porous materials at different scales for these applications is very promising for wastewater treatment industries.

Preparation, characterization, and efficient chromium (VI) adsorption of phosphoric acid activated carbon from furfural residue: an industrial waste

Furfural residue (FR) is an inevitable by-product of industrial furfural production. If FR is not managed properly, it will result in environmental problems. In this study, FR was used as a novel precursor for activated carbon (AC) production by H₃PO₄ activation under different conditions. Under optimum conditions, the prepared FRAC had high BET surface area (1,316.7 m²/g) and micro-mesoporous structures. The prepared FRAC was then used for the adsorption of Cr(VI). The effect of solution pH, contact time, initial Cr(VI) concentration, and temperature was systematically studied. Characterization of the adsorption process indicated that the experimental data were well-fitted by the Langmuir isotherm model and pseudo-second-order kinetics model. The maximum adsorption capacity of 454.6 mg/g was achieved at pH 2.0, which was highly comparable to the other ACs reported in the literatures. The preparation of FRAC using H₃PO₄ activation can make use of FR's characteristic acidity, which could make it preferable in practical industrial production.

Study on the effect of oxidation-ultrasound treatment on the electrochemical properties of activated carbon materials

Activated carbon (AC) has been widely used in water treatment because of its rich pore structure, large specific surface area, simple production process, low preparation cost and wide source of raw materials. In this paper, the regeneration efficiency of low-frequency ultrasonic pretreatment (40 kHz, 115Μw/cm³) on biological activated carbon (BAC) is investigated, and its principle is discussed. The results show that the micro-jet and micro-liquid flow with high temperature and pressure produced by micro-bubble rupture during ultrasonic cavitation play an important role in the regeneration of activated carbon. And optimum ultrasonic treatment time is determined (5 min). In addition, the preparation of cu-loaded activated carbon by ultrasound-microwave method is investigated to pretreat wastewater produced in paracetamol production. The results show that Cu and Cu oxides can be loaded on activated carbon surface by ultrasonic-microwave pretreatment. Finally, the pretreatments of activated carbon by physical, chemical and physical-chemical method are investigated. The effects of the above different pretreatment methods on the structure and adsorption properties of activated carbon are compared and evaluated.

Insight into activated carbon from different kinds of chemical activating agents: A review

Activated carbon (AC) is an important material in various fields owing to its low cost, well-developed porosity, and favorable chemical stability. Key factors for the optimal synthesis of AC are the carbon precursors, activation pathways, activating agents, and design of the procedure parameters. So far, no case studies have reviewed the activating agents used during the chemical activation process. Accordingly, the present review provides a summary of recent research, highlighting the development of activating agents during the process of AC. Detailed lists of pore-forming mechanisms by various activating agents, including alkaline, acidic, neutral, and self-activating agents, have been systematically summarized. Furthermore, the effects of activating agents on the experimental procedures have also been established. Finally, a comprehensive discussion about the influences of activating agents on the physical and chemical properties of the resultant AC is included. The objective of this study is to reveal and distinguish the individual roles of different activating agents during AC synthesis.

Lignocellulose-based adsorbents: A spotlight review of the effective parameters on carbon dioxide capture process

The increasing demand for energy all around the world has led to a rise in greenhouse gases (GHGs), of which carbon dioxide (CO₂) is the most important. CO₂ is largely responsible for global warming and climate change. Processes such as carbon dioxide capture and storage (CCS), which have an effective role in climate mitigation, seem to be promising. In recent years, porous carbons, particularly activated carbons (ACs), have rapidly emerged as one of the most effective adsorbents of CO₂. However, the implementation of pristine ACs in the real world is still hindered due to their physical and weak adsorption, which makes these adsorbents sensitive to temperature and relatively poor in selectivity. Hence, the surface modification of ACs is essential in order to improve their surface area, pore structure and alkalinity. Numerous studies have reported lignocellulose-based ACs as very promising adsorbents of CO₂. In this review, the sources, health and environmental effects of CO₂, and the abatement methods of GHGs are described. In addition, the capture and separation of CO₂ from gas stream using various types of lignocellulose-based ACs are summarized. Furthermore, the key factors controlling the adsorption of CO₂ by ACs (characteristics of adsorbents, preparation conditions, as well as adsorption conditions) are comprehensively and critically discussed. Finally, future research needs and prospective research challenges are summarized.

Exploring a New Method to Study the Effects of Surface Functional Groups on Adsorption of CO2 and CH4 on Activated Carbons

The commercial coconut shell-activated carbon was modified to change the number of oxygen-containing functional groups. N₂ adsorption/desorption isotherms, Fourier transform infrared (FT-IR), and Boehm titration were adopted to describe the physical and chemical properties of the samples. The adsorption isotherms of CO₂ and CH₄ on both the unmodified and modified samples were measured. To better understand the effects of surface oxygen-containing functional groups on adsorption of CO₂ and CH₄, the overall adsorption could be considered as the result of adsorption within the pores and adsorption onto the oxygen-containing functional groups. Thus, a new way to understand different adsorption mechanisms by calculation was proposed. On the basis of the results, there is a significant correlation between the saturation adsorption capacity of CO₂ and the number of oxygen-containing functional groups, especially carboxyl and hydroxyl. According to the values of enthalpy (-12.2 to -20 kJ/mol), it can be known that the adsorption caused by oxygen-containing functional groups is exothermic and belongs to physisorption. A semiempirical relationship between the variation of the surface oxygen-functional groups and the variation of the adsorbed amount was established. The method proposed in this paper provides a new way to study the effects of surface functional groups on the adsorption of CO₂ and CH₄ and can be even promoted in studying the adsorption mechanism of other adsorbates.

Potential of adsorbents from agricultural wastes as alternative fillers in mixed matrix membrane for gas separation: A review

Mixed matrix membrane (MMM), formed by dispersing fillers in polymer matrix, has attracted researchers’ attention due to its outstanding performance compared to polymeric membrane. However, its widespread use is limited due to high cost of the commercial filler which leads to the studies on alternative low-cost fillers. Recent works have focused on utilizing agricultural wastes as potential fillers in fabricating MMM. A membrane with good permeability and selectivity was able to be prepared at low cost. The objective of this review article is to compile all the available information on the potential agricultural wastes as fillers in fabricating MMM for gas separation application. The gas permeation mechanisms through polymeric and MMM as well as the chemical and physical properties of the agricultural waste fillers were also reviewed. Additionally, the economic study and future direction of MMM development especially in gas separation field were discussed.

The production and application of carbon nanomaterials from high alkali silicate herbaceous biomass

Herein, value-added materials such as activated carbon and carbon nanotubes were synthesized from low-value Miscanthus × giganteus lignocellulosic biomass. A significant drawback of using Miscanthus in an energy application is the melting during the combustion due to its high alkali silicate content. An application of an alternative approach was proposed herein for synthesis of activated carbon from Miscanthus × giganteus, where the produced activated carbon possessed a high surface area and pore volume of 0.92 cm³.g⁻¹ after two activation steps using phosphoric acid and potassium hydroxide. The S_BET of the raw biomass, after first activation and second activation methods showed 17, 1142 and 1368 m².g⁻¹, respectively. Transforming this otherwise waste material into a useful product where its material properties can be utilized is an example of promoting the circular economy by valorising waste lignocellulosic biomass to widely sought-after high surface area activated carbon and subsequently, unconventional multi-walled carbon nanotubes. This was achieved when the activated carbon produced was mixed with nitrogen-based material and iron precursor, where it produced hydrophilic multi-wall carbon nanotubes with a contact angle of θ = 9.88°, compared to the raw biomass. synthesised materials were tested in heavy metal removal tests using a lead solution, where the maximum lead absorption was observed for sample AC-K, with a 90% removal capacity after the first hour of testing. The synthesis of these up-cycled materials can have potential opportunities in the areas of wastewater treatment or other activated carbon/carbon nanotube end uses with a rapid cycle time.

Preparation of activated carbon from Dipterocarpus alatus fruit and its application for methylene blue adsorption

Activated carbons were prepared from three parts of Dipterocarpus alatus fruit (wing, endocarp and pericarp), an abundant and renewable waste in Southeast Asia, by chemical activation using ZnCl₂, FeCl₃, H₃PO₄ and KOH and physical activation using CO₂ and steam. This study indicated that activated carbon prepared from Dipterocarpus alatus fruit could be employed as a promising adsorbent for the removal of methylene blue from aqueous solution. ZnCl₂ activation led to an activated carbon with a surface area of 843 m² g⁻¹ and was able to remove methylene blue from aqueous solution. Adsorption studies were performed and analysed using Langmuir and Freundlich isotherm equations. Adsorption data demonstrated an excellent fit with the Langmuir isotherm model, with the maximum adsorption capacity of 269.3 mg g⁻¹ at equilibrium. Pseudo-first order and pseudo-second order kinetic models were used in this study to describe the adsorption mechanism. The results show that methylene blue adsorption is pseudo-second order, indicating that liquid film diffusion, intra-particle diffusion and surface adsorption coexisted during methylene blue adsorption on the activated carbon. The activated carbon prepared from Dipterocarpus alatus fruit is a low cost and effective adsorbent with a fast rate for the removal of methylene blue from aqueous solutions when compared with a number of activated carbons studied in the literature.

Activated carbons were prepared from Dipterocarpus alatus fruit by chemical and physical activation and used for the removal of methylene blue from aqueous solution.

Production and characterisation of activated carbon and carbon nanotubes from potato peel waste and their application in heavy metal removal

Herein, activated carbon (AC) and carbon nanotubes (CNTs) were synthesised from potato peel waste (PPW). Different ACs were synthesised via two activation steps: firstly, with phosphoric acid (designated PP) and then using potassium hydroxide (designated PK). The AC produced after the two activation steps showed a surface area as high as 833 m2 g-1 with a pore volume of 0.44 cm3 g-1, where the raw material of PPW showed a surface area < 4 m2 g-1. This can help aid and facilitate the concept of the circular economy by effectively up-cycling and valorising waste lignocellulosic biomass such as potato peel waste to high surface area AC and subsequently, multi-walled carbon nanotubes (MWCNTs). Consequently, MWCNTs were prepared from the produced AC by mixing it with the nitrogen-based material melamine and iron precursor, iron (III) oxalate hexahydrate. This produced hydrophilic multi-wall carbon nanotubes (MWCNTs) with a water contact angle of θ = 14.97 °. Both AC and CNT materials were used in heavy metal removal (HMR) where the maximum lead absorption was observed for sample PK with a 84% removal capacity after the first hour of testing. This result signifies that the synthesis of these up-cycled materials can have applications in areas such as wastewater treatment or other conventional AC/CNT end uses with a rapid cycle time in a two-fold approach to improve the eco-friendly synthesis of such value-added products and the circular economy from a significant waste stream, i.e., PPW. Graphical abstract .

The feasibility of cost-effective manufacturing activated carbon derived from walnut shells for large-scale CO2 capture

The economic potential of activated carbon (AC) synthesis from walnut shell biomass for CO₂ capture was evaluated in the present study. For this purpose, the chemical activation was employed to manufacture ACs and the effect of different impregnation ratios of activation agents, comprising KOH (KH) and H₃PO₄ (HP), onto the properties of fabricated ACs was examined. The obtained results demonstrated that the synthesized AC by HP activation with an impregnation ratio of 1:2.5, which was identified as HP2.5, possesses the highest surface area (1512.6 m²/g), micropore volume percentage (74.65%), and CO₂ adsorption (3.55 mmol/g) at 1 bar and 30 °C. Moreover, the equilibrium CO₂ adsorption data for HP2.5 were better fitted with the Freundlich model, indicating the multilayer CO₂ adsorption onto the heterogeneous AC surface dominantly through a physisorption process. In addition, the economic estimations revealed a cost of about $1.83/kg for the ultimate production that was significantly lower than the most of available CACs in the market. Therefore, walnut shells can be considered as a cost-effective and promising biomass source from a scale-up point of view.

Solid-Waste-Derived Carbon Dioxide-Capturing Materials

Solid sorbents are considered to be promising materials for carbon dioxide capture. In recent years, many studies have focused on the use of solid waste as carbon dioxide sorbents. The use of waste resources as carbon dioxide sorbents not only leads to the development of relatively low-cost materials, but also eliminates waste simultaneously. Different types of waste materials from biomass, industrial waste, household waste, and so forth were used as carbon dioxide sorbents with sufficient carbon dioxide capture capacities. Herein, progress on the development of carbon dioxide sorbents produced from waste materials is reviewed and covers key factors, such as the type of waste, preparation method, further modification method, carbon dioxide sorption performance, and kinetics studies. In addition, a new research direction for further study is proposed. It is hoped that this critical review will not merely sum up the major research directions in this field, but also provide significant suggestions for future work.

Mechanism of ultrasonic impregnation on porosity of activated carbons in non-cavitation and cavitation regimes

Ultrasonic impregnation has proven to be an effective method to improve surface area and pore volume during preparation of activated carbons. However, the mechanism by which the promotion effect of ultrasonic impregnation is still ambiguous. Fundamental wave pressure (FWP) and broadband integrated pressure (BIP) were used to estimate the non-cavitation (vibration) energy and cavitation energy, respectively. The effects of FWP and BIP on the pore volume, surface area, surface functional groups, and microcosmic morphology were investigated in non-cavitation and cavitation regimes. Ultrasonic vibration promoted the surface enlargement and pore development of activated carbons, and it mainly affected the development of mesopore volume (V_mes) in both the pore volume and the mesopore-size-distribution range. The V_mes was enhanced by 60%-100% in the non-cavitation regime. Ultrasonic cavitation also facilitated porosity development of activated carbons, and it mainly affected the development of specific surface area (S_BET) and micropore volume (V_mic). The excessive cavitation led to a decrease of the porosity of activated carbons, so the BIP should be optimized during impregnation. The highest S_BET, V_mic, and V_mes for activated carbons were obtained by in the presence of both FWP and BIP, which were enhanced by 29.05%, 30.23%, and 113.33%, respectively, compared with the corresponding value for the activated carbon prepared without using ultrasonic impregnation. This work provided new insight into the role of the acoustic energy present during impregnation in tuning properties of activated carbons.

Single-step synthesis of eucalyptus sawdust magnetic activated carbon and its adsorption behavior for methylene blue

Eucalyptus wood-based magnetic activated carbon (MAC) was prepared by single-step carbonization activation magnetization with FeCl₃ and utilized for the adsorption of methylene blue (MB).

Carbon Dioxide Adsorption Using High Surface Area Activated Carbons from Local Coals Modified by KOH, NaOH and ZnCl2 Agents

Activated carbons of various features were produced by the impregnation of local coal samples that were taken from Kilimli region of Zonguldak (Turkey) with chemical agents KOH, NaOH and ZnCl2 at different temperatures (600–800 °C) and concentrations (1:1–6:1 agent:coal), for their evaluation in CO2 adsorption studies. BET, DR, t-plot and DFT methods were used for the characterization of carbon samples based on N2 adsorption data obtained at 77 K. The pore sizes of activated carbons produced were generally observed to be in between 13–25 Å, containing highly micropores. Mesopore formations were higher in samples treated with ZnCl2. The highest value for the BET surface area was found as 2,599 m2 g−1 for the samples treated with KOH at 800 °C with a KOH to coal ratio of 4:1. It was observed that the CO2 adsorption capacities obtained at atmospheric pressure and 273 K were considerably affected by the micropore volume and surface area. The highest CO2 adsorption capacities were found as 9.09 mmol/g (28.57 % wt) and 8.25 mmol g−1 (26.65 % wt) for the samples obtained with KOH and NaOH treatments, respectively, at ratio of 4:1. The activated carbons produced were ordered as KOH>NaOH>ZnCl2, according to their surface areas, micropore volumes and CO2 adsorption capacities. The low-cost experimental methods developed by the utilization of local coals in this study enabled an effective capture of CO2 before its emission to atmosphere.

Activated carbon from flash pyrolysis of eucalyptus residue

Forestry waste (eucalyptus sp) was converted into activated carbon by initial flash pyrolysis followed carbonization and CO₂ activation. These residues were obtained from a pilot plant in Spain that produces biofuel, the biochar represented 10–15% in weight. It was observed that the highest activation was achieved at a temperature of 800 °C, the specific surface increased with time but, on the contrary, high loss of matter was observed. At 600 °C, although there was an important increase of the specific surface and the volume of micropores, at this temperature it was observed that the activation time was not an influential parameter. Finally, at 400 °C it was observed that the activation process was not very significant. Assessing the average pore diameter it was found that the lowest value corresponded to the activation temperature of 600 °C, which indicated the development of microporosity. When the activation temperature increases up to 800 °C the pore diameter increased developing mesoporosity.

Carbon-Based Adsorbents for Postcombustion CO2 Capture: A Critical Review

The persistent increase in atmospheric CO2 from anthropogenic sources makes research directed toward carbon capture and storage imperative. Current liquid amine absorption technology has several drawbacks including hazardous byproducts and a high-energy requirement for regeneration; therefore, research is ongoing to develop more practical methods for capturing CO2 in postcombustion scenarios. The unique properties of carbon-based materials make them specifically promising for CO2 adsorption at low temperature and moderate to high partial pressure. This critical review aims to highlight the development of carbon-based solid sorbents for postcombustion CO2 capture. Specifically, it provides an overview of postcombustion CO2 capture processes with solid adsorbents and discusses a variety of carbon-based materials that could be used. This review focuses on low-cost pyrogenic carbon, activated carbon (AC), and metal-carbon composites for CO2 capture. Further, it touches upon the recent progress made to develop metal organic frameworks (MOFs) and carbon nanomaterials and their general CO2 sorption potential.

Capture of CO2 on γ-Al2O3 materials prepared by solution-combustion and ball-milling processes

A series of porous γ-Al2O3 materials was prepared by solution-combustion and ball-milling processes. The as-prepared powders were physicochemically characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 physisorption measurements and their performances in CO2 adsorption at different pressures (0.5 to 1.5 MPa) and temperatures (40 to 60ºC) were investigated. It was found that γ-Al2O3 synthesized by the solution-combustion process and ball milled at 10 hr exhibited the best CO2 adsorption performance at 60ºC and 1.5 MPa, achieving a maximum of 1.94 mmol/g compared to the four studied materials, as a result of their interesting microstructure and surface properties (i.e., nanocrystallinity, specific surface area, narrow pore size distribution, and large total pore volume). Our study shows that the γ-Al2O3 prepared by solution combustion followed by ball milling presents a fairly good potential adsorbent for efficient CO2 capture.

IMPLICATIONS

In this work, γ-Al2O3 materials were successfully obtained by solution combustion and modified via ball milling. These improved materials were systematically investigated as solid adsorbents of accessible surface areas, large pore volumes, and narrow pore size distribution for the CO2 capture. These studied solid adsorbents can provide an additional contribution and effort to develop an efficient CO2 capture method as means of alleviating the serious global warning problem.

Insights into properties of activated carbons prepared from different raw precursors by pyrophosphoric acid activation

Low-cost activated carbons (ACs) were prepared from four kinds of solid wastes: petroleum coke, Enteromorpha prolifera, lignin from papermaking black liquid and hair, by pyrophosphoric acid (H4P2O7) activation. Thermo-gravimetric analysis of the pyrolysis of H4P2O7-precursor mixtures implied that H4P2O7 had different influences on the pyrolysis behavior of the four raw materials. N2 adsorption/desorption isotherms, scanning electron microscopy, Fourier transform infrared spectroscopy and adsorption capacities for dyes were used to characterize the prepared activated carbons. AC derived from E. prolifera exhibited the highest surface area (1094m(2)/g) and maximum monolayer adsorption capacity for malachite green (1250mg/g). Kinetic studies showed that the experimental data were in agreement with the pseudo-second-order model. The adsorption isotherms were well described by the Langmuir isotherm model, indicating the adsorption of dye onto the ACs proceeded by monolayers.